Change search
Refine search result
1234 101 - 150 of 161
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 101.
    Osella, Silvio
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Knippenberg, Stefan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Triggering On/Off States of Photoswitchable Probes in Biological Environments2017In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, no 12, p. 4418-4428Article in journal (Refereed)
    Abstract [en]

    The use of hybrid systems for which the change in properties of one component triggers the change in properties of the other is of outmost importance when "on/off' states are needed. For such a reason, azobenzene compounds are one of the most used probes due to their high photoswitching efficiency. In this study, we consider a new derivative of azobenzene interacting with different lipid membrane phases as a versatile fluorescent probe for phase recognition. By means of a multiscale approach, we found that the cis and trans conformers have different positions and orientations in the different lipid membranes (DOPC for the liquid disordered phase and DPPC for the gel phase), and these have a profound effect on the optical properties of the system, for both one and two photon absorption. In fact, we found that the cis state is the "on" state when the probe is inserted into the DOPC membrane, while it is in the "off' state in the DPPC membrane. This behavior enhances the selectivity of this probe for phase recognition, since the different environments will generate different responses on the same conformer of the probe. The same effect is found for the fluorescence anisotropy analysis, for which the trans (cis) isomer in DOPC (DPPC) presents a fast decay time. Due to the "on/off' effect it is possible to screen the different membrane phases via fluorescence decay time analysis, making this new probe versatile for phase detection.

  • 102. Pan, J.
    et al.
    Benko, G.
    Xu, Y. H.
    Pascher, T.
    Sun, Licheng C.
    Sundstrom, V.
    Polivka, T.
    Photoinduced electron transfer between a carotenoid and TiO2 nanoparticle2002In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 124, no 46, p. 13949-13957Article in journal (Refereed)
    Abstract [en]

    The dynamics of photoinduced electron injection and recombination between all-trans-8'-apo-beta-caroten-8'-oic acid (ACOA) and a TiO2 Colloidal nanoparticle have been studied by means of transient absorption spectroscopy. We observed an ultrafast (similar to360 fs) electron injection from the initially excited S-2 state of ACOA into the TiO2 conduction band with a quantum yield of similar to40%. As a result, the ACOA(.+) radical cation was formed, as demonstrated by its intense absorption band centered at 840 nm. Because of the competing S-2-S-1 internal conversion, similar to60% of the S-2-state population relaxes to the S-1 state. Although the S-1 state is thermodynamically favorable to donate electrons to the TiO2, no evidence was found for electron injection from the ACOA S, state, most likely as a result of a complicated electronic nature of the S, state, which decays with a similar to18 ps time constant to the ground state. The charge recombination between the injected electrons and the ACOA(.+) was found to be a highly nonexponential process extending from picoseconds to microseconds. Besides the usual pathway of charge recombination forming the ACOA ground state, about half of the ACOA(.+) recombines via the ACOA triplet state, which was monitored by its absorption band at 530 nm. This second channel of recombination proceeds on the nanosecond time scale, and the formed triplet state decays to the ground state with a lifetime of similar to7.3 mus. By examination of the process of photoinduced electron transfer in a carotenoid-semiconductor system, the results provide an insight into the photophysical properties of carotenoids, as well as evidence that the interfacial electron injection occurs from the initially populated excited state prior to electronic and nuclear relaxation of the carotenoid molecule.

  • 103. Pan, J. X.
    et al.
    Xu, Y. H.
    Sun, Licheng C.
    Sundstrom, V.
    Polivka, T.
    Carotenoid and pheophytin on semiconductor surface: Self-assembly and photoinduced electron transfer2004In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, no 10, p. 3066-3067Article in journal (Refereed)
  • 104. Percec, Virgil
    et al.
    Guliashvili, Tamaz
    Ladislaw, Janine S.
    Finne Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Stjerndahl, Anna
    Sienkowska, Monika J.
    Monteiro, Michael J.
    Sahoo, Sangrama
    Ultrafast synthesis of ultrahigh molar mass polymers by metal-catalyzed living radical polymerization of acrylates, methacrylates, and vinyl chloride mediated by SET at 25 degrees C2006In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 43, p. 14156-14165Article in journal (Refereed)
    Abstract [en]

    Conventional metal-catalyzed organic radical reactions and living radical polymerizations (LRP) performed in nonpolar solvents, including atom-transfer radical polymerization (ATRP), proceed by an innersphere electron-transfer mechanism. One catalytic system frequently used in these polymerizations is based on Cu(I)X species and N-containing ligands. Here, it is reported that polar solvents such as H2O, alcohols, dipolar aprotic solvents, ethylene and propylene carbonate, and ionic liquids instantaneously disproportionate Cu(I)X into Cu(0) and Cu(II)X-2 species in the presence of a diversity of N-containing ligands. This disproportionation facilitates an ultrafast LRP in which the free radicals are generated by the nascent and extremely reactive Cu(0) atomic species, while their deactivation is mediated by the nascent Cu(II)X-2 species. Both steps proceed by a low activation energy outer-sphere single-electron-transfer (SET) mechanism. The resulting SET-LRP process is activated by a catalytic amount of the electron-donor Cu(0), Cu2Se, Cu2Te, Cu2S, or Cu2O species, not by Cu(I) X. This process provides, at room temperature and below, an ultrafast synthesis of ultrahigh molecular weight polymers from functional monomers containing electronwithdrawing groups such as acrylates, methacrylates, and vinyl chloride, initiated with alkyl halides, sulfonyl halides, and N-halides.

  • 105. Polshin, Victor
    et al.
    Popescu, Delia-Laura
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Chanda, Arani
    Horner, David C.
    Beach, Evan S.
    Henry, Jennifer
    Qian, Yong-Li
    Horwitz, Colin P.
    Lente, Gabor
    Fabian, Istvan
    Munck, Eckard
    Bominaar, Emile L.
    Ryabov, Alexander D.
    Collins, Terrence J.
    Attaining control by design over the hydrolytic stability of Fe-TAML oxidation catalysts2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 13, p. 4497-4506Article in journal (Refereed)
    Abstract [en]

    The iron(III) complexes of tetra amidato macrocyclic ligands (TAMLs) ([Fe{1-X-1-2-X2C6H2-4,5-(NCOCMe2NCO)(2)CR2}(OH2)](-), 1: X-1 = X-2 = H, R-2 = Me-2 (a), R-2 = (CH2)(2) (b); X-1 = X-2 = Cl, R-2 = F-2, (c), etc.), which the proton is known to demetalate at pH < 3, are also subject to catalyzed demetalation by Bronsted acid buffer components at pH 4-9 such as H2PO4-, HSO3-, and CH3- CO2H, HO2CCH2CO2-. Buffers based on pyridine (py) and tris(hydroxymethyl)aminomethane (TRIS) are catalytically inactive. Where reactions proceed, the products are demetalated TAMLs and iron species of variable composition. Pseudo-first-order rate constants for the demetalation (k(obs)) are linear functions of the acid concentrations, and the effective second-order rate constants k(1),(eff) have a hyperbolic dependence on [H+] (k(1),eff = a(1)[H+]/(b(1)+[H+]). The rate of demetalation of 1a in H2PO4-/HPO42- buffer is appreciable, but the k(obs) values for 1b and 1c are immeasurably low, showing that the rates are strongly affected by the CR2 or "tail" fragments, which are known to potently affect the TAML basicity. The reactivities of 1 depend insignificantly on the aromatic ring or "head" group of 1. The proposed mechanism involves precoordination of the acidic buffer species followed by hydrolysis. The demetalating abilities of buffer species depend on their structures and acidities. Thus, although pyridine-2-carboxylic (picolinic) acid catalyzes the demetalation, its 3- and 4-isomers (nicotinic and isonicotininc acids) are inactive. The difference is rationalized to result from the ability that only coordinated picolinic acid has to deliver a proton to an amidato nitrogen in an intramolecular manner. The reaction order in picolinic acid equals one for la and two for 1a. For 1b, "inactive" pyridine and nicotinic acid speed up the demetalation in the presence of picolinic acid, suggesting that the second order arises from the axial binding of two pyridine molecules, one of which must be picolinic acid. The binding of pyridine- and imidazole-type ligands was confirmed by UV/vis equilibrium measurements and X-ray crystallography. The implications of these mechanistic findings for designing superior Fe-TAML oxidation catalysts and catalyst formulations are discussed using the results of DFT calculations.

  • 106.
    Privalov, Timofei
    et al.
    KTH, Superseded Departments, Chemistry.
    Macak, Peter
    KTH, Superseded Departments, Physics.
    Schimmelpfennig, B.
    Fromager, E.
    Grenthe, I.
    Wahlgren, Ulf
    KTH, Superseded Departments, Physics.
    Electron transfer in uranyl(VI)-uranyl(V) complexes in solution2004In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, no 31, p. 9801-9808Article in journal (Refereed)
    Abstract [en]

    The rates and mechanisms of the electron self-exchange between U(V) and U(VI) in solution have been studied with quantum chemical methods. Both outer-sphere and inner-sphere mechanisms have been investigated; the former for the aqua ions, the latter for binuclear complexes containing hydroxide, fluoride, and carbonate as bridging ligand. The calculated rate constant for the self-exchange reaction UO2+(aq) + UO22+(aq)UO22+(aq) + UO2+(aq), at 25 degreesC, is k = 26 M-1 s(-1). The lower limit of the rate of electron transfer in the inner-sphere complexes is estimated to be in the range 2 x 10(4) to 4 x 10(6) M-1 s(-1), indicating that the rate for the overall exchange reaction may be determined by the rate of formation and dissociation of the binuclear complex. The activation energy for the outer-sphere model calculated from the Marcus model is nearly the same as that obtained by a direct calculation of the precursor- and transition-state energy. A simple model with one water ligand is shown to recover 60% of the reorganization energy. This finding is important because it indicates the possibility to carry out theoretical studies of electron-transfer reactions involving M3+ and M4+ actinide species that have eight or nine water ligands in the first coordination sphere.

  • 107.
    Pronk, Sander
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Lindahl, Erik
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical & Computational Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Kasson, Peter M.
    Coupled Diffusion in Lipid Bilayers upon Close Approach2015In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 137, no 2, p. 708-714Article in journal (Refereed)
    Abstract [en]

    Biomembrane interfaces create regions of slowed water dynamics in their vicinity. When two lipid bilayers come together, this effect is further accentuated, and the associated slowdown can affect the dynamics of larger-scale processes such as membrane fusion. We have used molecular dynamics simulations to examine how lipid and water dynamics are affected as two lipid bilayers approach each other. These two interacting fluid systems, lipid and water, both slow and become coupled when the lipid membranes are separated by a thin water layer. We show in particular that the water dynamics become glassy, and diffusion of lipids in the apposed leaflets becomes coupled across the water layer, while the outer leaflets remain unaffected. This dynamic coupling between bilayers appears mediated by lipid-water-lipid hydrogen bonding, as it occurs at bilayer separations where water-lipid hydrogen bonds become more common than water-water hydrogen bonds. We further show that such coupling occurs in simulations of vesicle-vesicle fusion prior to the fusion event itself. Such altered dynamics at membrane-membrane interfaces may both stabilize the interfacial contact and slow fusion stalk formation within the interface region.

  • 108.
    Qin, Peng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Zhu, Hongjun
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630). KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Edvinsson, Tomas
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630).
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630). KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Design of an organic chromophore for p-type dye-sensitized solar cells2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 27, p. 8570-8571Article in journal (Refereed)
    Abstract [en]

    A successful model for the design of efficient dyes for p-type dye-sensitized solar cells (DSSCs) is presented. As an example, a novel and efficient organic dye containing a triphenylamine chromophore has been synthesized and successfully applied in a p-type DSSC. The highest incident photon-to-current conversion efficiency (IPCE) of 18% in the visible region has been obtained, which is the highest value so far in p-type DSSCs. This is remarkably high, considering that only 600 nm thin NiO mesoporous films were used as p-type DSSC electrodes.

  • 109. Real, Florent
    et al.
    Vallet, Valerie
    Wahlgren, Ulf
    Grenthe, Ingmar
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Ab initio study of the mechanism for photoinduced yl-oxygen exchange in uranyl(VI) in acidic aqueous solution2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 35, p. 11742-11751Article in journal (Refereed)
    Abstract [en]

    The mechanism for the photochemically induced isotope-exchange reaction (UO22+)-O-17/18(aq) + (H2O)-O-16 reversible arrow (UO22+)-O-16 (aq) + (H2O)-O-17/18 has been studied using quantum-chemical methods. There is a dense manifold of states between 22 000 and 54 000 cm(-1) that results from excitations from the sigma(u) and pi(u) bonding orbitals in the (1)Sigma(+)(g) ground state to the nonbonding f(delta) and f(phi) orbitals localized on uranium. On the basis of investigations of the reaction profile in the (1)Sigma(+)(g) ground state and the excited states (3)Delta(g) (the lowest triplet state) and (3)Gamma(g) (one of the several higher triplet states), the latter two of which have the electron configurations sigma(u)f(delta) and pi(u)f(phi) respectively, we suggest that the isotope exchange takes place in one of the higher triplet states, of which the (3)Gamma(g) state was used as a representative. The geometries of the luminescent (3)Delta(g) state, the lowest in the sigma(u)f(delta,phi) manifold (the "sigma" states), and the (1)Sigma(+)(g) ground state are very similar, except that the bond distances are slightly longer in the former. This is presumably a result of transfer of a bonding electron to a nonbonding f orbital, which makes the excited state in some respects similar to uranyl(V). As is the case for all of the states of the pi(u)f(delta,phi) manifold (the "pi" states), the geometry of the (3)Gamma(g) state is very different from that of the (3)Delta(g) "sigma" state and has nonequivalent U-O-yl distances of 1.982 and 1.763 angstrom; in the (3)Gamma(g) state, the yl-exchange takes place by transfer of a proton or hydrogen from water to the more distant yl-oxygen. The activation barriers for proton/hydrogen transfer in the ground state and the (3)Delta(g) and (3)Gamma(g) states are 186, 219, and 84 kJ/mol, respectively. The relaxation energy for the (3)Gamma(g) state in the solvent after photoexcitation is -86 kJ/mol, indicating that the energy barrier can be overcome; the "pi" states are therefore the most probable route for proton/hydrogen transfer. They can be populated after UV irradiation but are too high in energy (similar to 36000-40000 cm(-1)) to be reached by a single-photon absorption at 436 nm (22 900 cm(-1)), where experimental data have demonstrated that exchange can take place. Okuyama et al. [Bull. Res. Lab. Nucl. React. (Tokyo Inst. Technol.) 1978, 3, 39-50] have demonstrated that an intermediate is formed when an acidic solution of UO22+ (aq) is flash-photolyzed in the UV range. The absorption spectrum of this short-lived intermediate (which has a maximum at 560 nm) indicates that this species arises from 436 nm excitation of the luminescent (3)Delta(g) state (which has a lifetime of similar to 2 x 10(-6) s); this is sufficient to reach the reactive "pi" states. It has been speculated that the primary reaction in acidic solutions of UO22+(aq) is the formation of a uranyl(V) species; our resuls indicate that the structure in the luminescent state has some similarity to that of UO2+ but that the reactive species in the states is a cation radical with a distinctly different structure.

  • 110.
    Restorp, Per
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Somfai, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Stereoselective Synthesis of Functionalized Pyrrolidines via a [3 + 2]- Annulation of N-Ts-α-Amino Aldehydes and 1,3-Bis(silyl)propenes2006In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Journal of the American Chemical Society, Vol. 128, p. 12646-12647Article in journal (Refereed)
  • 111.
    Rios, Luz Amalia
    et al.
    Universidad del Valle, Colombia.
    Dolbier, William R. Jr
    University of Florida.
    Paredes, Rodrigo
    Universidad del Valle, Colombia.
    Lusztyk, Janusz
    NRC Canada.
    Ingold, K. U.
    NRC Canada.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Generation and Study of the Reactivity of alpha-Ammonium Distonic Radical Cations in Solution.1996In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 118, no 45, p. 11313-11314Article in journal (Refereed)
  • 112. Rochford, Jonathan
    et al.
    Chu, Dorothy
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Galoppini, Elena
    Tetrachelate porphyrin chromophores for metal oxide semiconductor sensitization: Effect of the spacer length and anchoring group position2007In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129, no 15, p. 4655-4665Article in journal (Refereed)
    Abstract [en]

    Four Zn(II)-tetra(carboxyphenyl)porphyrins in solution and bound to metal oxide (TiO2, ZnO, and ZrO2) nanoparticle films were studied to determine the effect of the spacer length and anchoring group position (para or meta) on their binding geometry and photoelectrochemical and photophysical properties. The properties of three types of anchoring groups (COOH and COONHEt3) for four Zn(II)-porphyrins (Zn(II)-5,10,15,20-tetra(4-carboxyphenyl)porphyrin (p-ZnTCPP), Zn(II)-5,10,15,20-tetra(3-carboxyphenyl)porphyrin (m-ZnTCPP), Zn(II)-5,10,15,20-tetra(3-(4-carboxyphenyl)phenyl)porphyrin (m-ZnTCP2P), and Zn(II)-5,10,15,20-tetra(3-ethynyl(4-carboxyphenyl)phenyl)porphyrin (m-ZnTC(PEP)P)) were compared. In m-ZnTCPP, m-ZnTCP2P, and m-ZnTC(PEP)P the four anchoring groups are in the meta position on the meso-phenyl rings of the porphyrin macrocycle, thus favoring a planar binding mode to the metal oxide surfaces. The three meta-substituted porphyrin salts have rigid spacer units of increasing length (phenyl (P), biphenyl (P-2), and diphenylethynyl (PEP)) between the porphyrin ring and the carboxy anchoring groups, thus raising the macrocycle from the metal oxide surface. All porphyrins studied here, when bound to TiO2 and ZnO, exhibited quenching of the fluorescence emission, consistent with electron injection into the conduction band of the semiconductor. Steady-state UV-vis and fluorescence studies of p-ZnTCPP on insulating ZrO2 showed evidence of aggregation and exciton coupling. This was not observed in any of the meta-substituted porphyrins. The photoelectrochemical properties (IPCE, V-oc, and I-sc) of the porphyrins bound to TiO2 films in solar cells have been measured and rationalized with respect to the sensitizer binding geometry and distance from the surface.

  • 113. Roizard, Sophie
    et al.
    Danelon, Christophe
    Hassaïne, Ghérici
    Piguet, Joachim
    Ecole Polytechnique Fédérale de Lausanne, Switzerland.
    Schulze, Katrin
    Hovius, Ruud
    Tampé, Robert
    Vogel, Horst
    Activation of G-protein-coupled receptors in cell-derived plasma membranes supported on porous beads2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 42Article in journal (Refereed)
    Abstract [en]

    G-protein-coupled receptors (GPCRs) are ubiquitous mediators of signal transduction across cell membranes and constitute a very important class of therapeutic targets. In order to study the complex biochemical signaling network coupling to the intracellular side of GPCRs, it is necessary to engineer and control the downstream signaling components, which is difficult to realize in living cells. We have developed a bioanalytical platform enabling the study of GPCRs in their native membrane transferred inside-out from live cells to lectin-coated beads, with both membrane sides of the receptor being accessible for molecular interactions. Using heterologously expressed adenosine A(2A) receptor carrying a yellow fluorescent protein, we showed that the tethered membranes comprised fully functional receptors in terms of ligand and G protein binding. The interactions between the different signaling partners during the formation and subsequent dissociation of the ternary signaling complex on single beads could be observed in real time using multicolor fluorescence microscopy. This approach of tethering inside-out native membranes accessible from both sides is straightforward and readily applied to other transmembrane proteins. It represents a generic platform suitable for ensemble as well as single-molecule measurements to investigate signaling processes at plasma membranes.

  • 114. Rundqvist, Jonas
    et al.
    Mendoza, Beatriz
    Werbin, Jeffrey L.
    Heinz, William F.
    Lemmon, Christopher
    Romer, Lewis H.
    Haviland, David B.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Hoh, Jan H.
    High fidelity functional patterns of an extracellular matrix protein by electron beam-based inactivation2007In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129, no 1, p. 59-67Article in journal (Refereed)
    Abstract [en]

    Controlling the organization of proteins on surfaces provides a powerful biochemical tool for determining how cells interpret the spatial distribution of local signaling molecules. Here, we describe a general high fidelity approach based on electron beam writing to pattern the functional properties of protein-coated surfaces at length scales ranging from tens of nanometers to millimeters. A silicon substrate is first coated with the extracellular matrix protein fibronectin, which is then locally inactivated by exposure to a highly focused electron beam. Biochemical inactivation of the protein is established by the loss of antibody binding to the fibronectin. Functional inactivation is determined by the inability of cells to spread or form focal adhesions on the inactivated substrate, resulting in cell shapes constrained to the pattern, while they do both (and are unconstrained) on the remaining fibronectin. These protein patterns have very high fidelity, and typical patterns agree with the input dimensions of the pattern to within 2%. Further, the feature edges are well defined and approach molecular dimensions in roughness. Inactivation is shown to be dose dependent with observable suppression of the specific binding at 2 mu C cm(-2) and complete removal of biochemical activity at similar to 50 mu C cm(-2) for 5 keV electrons. The critical dose for inactivation also depends on accelerating voltage, and complete loss of antibody binding was achieved at similar to 4-7 mu C cm(-2) for 1 keV electrons, which corresponds to similar to 50-90 electrons per cross-sectional area of a whole fibronectin dimer and similar to 2-4 electrons per type III fibronectin domain. AFM analysis of the pattern surfaces revealed that electron beam exposure does not remove appreciable amounts of material from the surface, suggesting that the patterning mechanism involves local inactivation rather than the ablation that has been observed in several organic thin film systems.

  • 115. Salazar-Alvarez, G.
    et al.
    Qin, Jian
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Sepelak, V
    Bergmann, I
    Vasilakaki, M
    Trohidou, N.
    Ardisson, D.
    Macedo, A.
    Mikhaylova, M.
    Muhammed, Mamoun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
    Baro, D
    Nogues, J.
    Cubic versus spherical magnetic nanoparticles: The role of surface anisotropy2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 40, p. 13234-13239Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of maghemite (gamma-Fe2O3) cubic and spherical nanoparticles of similar sizes have been experimentally and theoretically studied. The blocking temperature, TB, of the nanoparticles depends on their shape, with the spherical ones exhibiting larger TB. Other low temperature properties such as saturation magnetization, coercivity, loop shift or spin canting are rather similar. The experimental effective anisotropy and the Monte Carlo simulations indicate that the different random surface anisotropy of the two morphologies combined with the low magnetocrystalline anisotropy of gamma-Fe2O3 is the origin of these effects.

  • 116. Samec, Joseph S. M.
    et al.
    Ell, Alida H.
    Aberg, Jenny B.
    Privalov, Timofei
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Eriksson, Lars
    Backvall, Jan- E.
    Mechanistic study of hydrogen transfer to imines from a hydroxycyclopentadienyl ruthenium hydride. Experimental support for a mechanism involving coordination of imine to ruthenium prior to hydrogen transfer2006In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 44, p. 14293-14305Article in journal (Refereed)
    Abstract [en]

    Reaction of [2,3,4,5-Ph-4(eta(5)-C4COH) Ru(CO)(2)H] (2) with different imines afforded ruthenium amine complexes at low temperatures. At higher temperatures in the presence of 2, the complexes decomposed to give [Ru-2(CO)(4)(mu-H)(C4Ph4COHOCC4Ph4)] (1) and free amine. Electron-rich imines gave ruthenium amine complexes with 2 at a lower temperature than did electron-deficient imines. The negligible deuterium isotope effect (k(RuHOH)/k(RuDOD) = 1.05) observed in the reaction of 2 with N-phenyl[1-(4-methoxyphenyl) ethylidene]amine (12) shows that neither hydride (RuH) nor proton (OH) is transferred to the imine in the rate-determining step. In the dehydrogenation of N-phenyl-1-phenylethylamine (4) to the corresponding imine 8 by [2,3,4,5-Ph-4(eta(4)-C4CO) Ru(CO)(2)] (A), the kinetic isotope effects observed support a stepwise hydrogen transfer where the isotope effect for C-H cleavage (k(CHNH)/k(CDNH) = 3.24) is equal to the combined (C-H, N-H) isotope effect (k(CHNH)/k(CDND) = 3.26). Hydrogenation of N-methyl(1-phenylethylidene) amine (14) by 2 in the presence of the external amine trap N-methyl-1-(4-methoxyphenyl) ethylamine (16) afforded 90-100% of complex [2,3,4,5-Ph-4(eta(4)-C4CO)] Ru(CO)(2)NH(CH3)(CHPhCH3) (15), which is the complex between ruthenium and the amine newly generated from the imine. At -80 degrees C the reaction of hydride 2 with 4-BnNHsC(6)H(9)=NPh (18), with an internal amine trap, only afforded [2,3,4,5-Ph-4(eta(4)-C4CO)](CO)(2)RuNH(Ph)(C6H10-4-NHBn) (19), where the ruthenium binds to the amine originating from the imine, showing that neither complex A nor the diamine is formed. Above -8 degrees C complex 19 rearranged to the thermodynamically more stable [Ph-4(eta(4)-C4CO)](CO)(2)RuNH(Bn)(C6H10-4-NHPh) (20). These results are consistent with an inner sphere mechanism in which the substrate coordinates to ruthenium prior to hydrogen transfer and are difficult to explain with the outer sphere pathway previously proposed.

  • 117.
    Schaufelberger, Fredrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Ramström, Olof
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Kinetic Self-Sorting of Dynamic Covalent Catalysts with Systemic Feedback Regulation2016In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 138, no 25, p. 7836-7839Article in journal (Refereed)
    Abstract [en]

    Constructing small molecule systems that mimic the functionality exhibited in biological reaction networks is a key objective of systems chemistry. Herein, we report the development of a dynamic catalytic system where the catalyst activity is modulated through a dynamic covalent bond. By connecting a thermodynamically controlled rearrangement process to resolution under kinetic control, the catalyst system underwent kinetic self sorting, resulting in amplification of a more reactive catalyst while establishing a catalytic feedback mechanism. The dynamic catalyst system furthermore responded to catalytic events by self-perturbation to regulate its own activity, which in the case of upregulation gave rise to systemic autocatalytic behavior.

  • 118. Schultz, M. J.
    et al.
    Adler, R. S.
    Zierkiewicz, W.
    Privalov, Timofei
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Sigman, M. S.
    Using mechanistic and computational studies to explain ligand effects in the palladium-catalyzed aerobic oxidation of alcohols2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 23, p. 8499-8507Article in journal (Refereed)
    Abstract [en]

    The experimental and computational mechanistic details of the Pd(OAc)(2)/TEA-catalyzed aerobic alcohol oxidation system are disclosed. Measurement of various kinetic isotope effects and the activation parameters as well as rate law derivation support rate-limiting deprotonation of the palladium-coordinated alcohol. Rate-limiting deprotonation of the alcohol is contrary to the majority of related kinetic studies for Pd-catalyzed aerobic oxidation of alcohols, which propose rate-limiting beta-hydride elimination. This difference in the rate-limiting step is supported by the computational model, which predicts the activation energy for deprotonation is 3 kcal/mol higher than the activation energy for beta-hydride elimination. The computational features of the similar Pd(OAc)(2)/pyridine system were also elucidated. Details of the study illustrate that the use of TEA results in an active catalyst that has only one ligand bound to the Pd, resulting in a significant lowering of the activation energy for beta-hydride elimination and, therefore, a catalyst that is active at room temperature.

  • 119.
    Sebelius, Sara
    et al.
    Stockholms universitet.
    Olsson, Vilhelm J.
    Szabó, Kálmán J.
    Palladium Pincer Complex Catalyzed Substitution of Vinyl Cyclopropanes, Vinyl Aziridines, and Allyl Acetates with Tetrahydroxydiboron.: An Efficient Route to Functionalized Allylboronic Acids and Potassium Trifluoro(allyl)borates2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 30, p. 10478-10479Article in journal (Refereed)
  • 120. Sjodin, M.
    et al.
    Styring, S.
    Akermark, B.
    Sun, Licheng C.
    Hammarstrom, L.
    Proton-coupled electron transfer from tyrosine in a tyrosine-ruthenium-tris-bipyridine complex: Comparison with Tyrosine(z) oxidation in photosystem II2000In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 122, no 16, p. 3932-3936Article in journal (Refereed)
    Abstract [en]

    The pH- and the temperature dependence of the rate constant for electron transfer from tyrosine to ruthenium in Ru(II)(bpy)(2)(4-Me-4'CONH-L-tyrosine etyl ester-2,2'-bpy) 2PF(6) was investigated using flash photolysis. At a pH below the tyrosine pK(a) approximate to 10 the rate constant increased monotonically with pH. This increase was consistent with a concerted electron transfer/deprotonation mechanism. Also indicative of a concerted reaction was the unusually high reorganization energy, 2 eV, extracted from temperature-dependent measurements. Deprotonation of the tyrosine group, at pH > pK(a), resulted in a 100-fold increase in rate constant due to a decreased reorganization energy, lambda = 0.9 eV. Also, the rate constant became independent of pH, In Mn-depleted photosystem II a similar pH dependence has been found for electron transfer from tyrosine(Z) (Tyr(Z)) to the oxidized primary donor P680(+). On the basis of the kinetic similarities we propose that the mechanisms in the two systems are the same, that is, the electron transfer occurs as a concerted proton-coupled electron-transfer reaction, and at pH < 7 the Tyr(Z) proton is released directly to the bulk water.

  • 121. Sjodin, Martin
    et al.
    Irebo, Tania
    Utas, Josefin E.
    Lind, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Merenyi, Gabor
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Akermark, Bjorn
    Hammarstrom, Leif
    Kinetic effects of hydrogen bonds on proton-coupled electron transfer from phenols2006In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 40, p. 13076-13083Article in journal (Refereed)
    Abstract [en]

    The kinetics and mechanism of proton-coupled electron transfer (PCET) from a series of phenols to a laser flash generated [Ru(bpy)(3)](3+) oxidant in aqueous solution was investigated. The reaction followed a concerted electron-proton transfer mechanism (CEP), both for the substituted phenols with an intramolecular hydrogen bond to a carboxylate group and for those where the proton was directly transferred to water. Without internal hydrogen bonds the concerted mechanism gave a characteristic pH-dependent rate for the phenol form that followed a Marcus free energy dependence, first reported for an intramolecular PCET in Sjodin, M. et al. J. Am. Chem. Soc. 2000, 122, 3932-3962 and now demonstrated also for a bimolecular oxidation of unsubstituted phenol. With internal hydrogen bonds instead, the rate was no longer pH-dependent, because the proton was transferred to the carboxylate base. The results suggest that while a concerted reaction has a relatively high reorganization energy (lambda), this may be significantly reduced by the hydrogen bonds, allowing for a lower barrier reaction path. It is further suggested that this is a general mechanism by which proton-coupled electron transfer in radical enzymes and model complexes may be promoted by hydrogen bonding. This is different from, and possibly in addition to, the generally suggested effect of hydrogen bonds on PCET in enhancing the proton vibrational wave function overlap between the reactant and donor states. In addition we demonstrate how the mechanism for phenol oxidation changes from a stepwise electron transfer-proton transfer with a stronger oxidant to a CEP with a weaker oxidant, for the same series of phenols. The hydrogen bonded CEP reaction may thus allow for a low energy barrier path that can operate efficiently at low driving forces, which is ideal for PCET reactions in biological systems.

  • 122. Sjödin, M.
    et al.
    Styring, S.
    Wolpher, H.
    Xu, Y. H.
    Sun, Licheng C.
    Hammarström, L.
    Switching the redox mechanism: Models for proton-coupled electron transfer from tyrosine and tryptophan2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 11, p. 3855-3863Article in journal (Refereed)
    Abstract [en]

    The coupling of electron and proton transfer is an important controlling factor in radical proteins, such as photosystem II, ribinucleotide reductase, cytochrome oxidases, and DNA photolyase. This was investigated in model complexes in which a tyrosine or tryptophan residue was oxidized by a laser-flash generated trisbipyridine-Ru-III moiety in an intramolecular, proton-coupled electron transfer (PCET) reaction. The PCET was found to proceed in a competition between a stepwise reaction, in which electron transfer is followed by deprotonation of the amino acid radical (ETPT), and a concerted reaction, in which both the electron and proton are transferred in a single reaction step (CEP). Moreover, we found that we could analyze the kinetic data for PCET by Marcus' theory for electron transfer. By altering the solution pH, the strength of the Ru-III oxidant, or the identity of the amino acid, we could induce a switch between the two mechanisms and obtain quantitative data for the parameters that control which one will dominate. The characteristic pH-dependence of the CEP rate (M. Sjodin et al. J. Am. Chem. Soc. 2000, 122, 3932) reflects the pH-dependence of the driving force caused by proton release to the bulk. For the pH-independent ETPT on the other hand, the driving force of the rate-determining ET step is pH-independent and smaller. On the other hand, temperature-dependent data showed that the reorganization energy was higher for CEP, while the pre-exponential factors showed no significant difference between the mechanisms. Thus, the opposing effect of the differences in driving force and reorganization energy determines which of the mechanisms will dominate. Our results show that a concerted mechanism is in general quite likely and provides a low-barrier reaction pathway for weakly exoergonic reactions. In addition, the kinetic isotope effect was much higher for CEP (k(H)/k(D) > 10) than for ETPT (k(H)/k(D) = 2), consistent with significant changes along the proton reaction coordinate in the rate-determining step of CEP.

  • 123.
    Sonesson, Andreas W.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    A FRAP-based method to study protein surface diffusionIn: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126Article in journal (Other academic)
  • 124.
    Spadiut, Oliver
    et al.
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Ibatullin, Farid M.
    KTH, School of Biotechnology (BIO), Glycoscience.
    Peart, Jonelle
    KTH, School of Biotechnology (BIO), Glycoscience.
    Gullfot, Fredrika
    KTH, School of Biotechnology (BIO), Glycoscience.
    Martinez-Fleites, Carlos
    Ruda, Marcus
    Xu, Chunlin
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Sundqvist, Gustav
    KTH, School of Biotechnology (BIO), Glycoscience.
    Davies, Gideon J.
    Brumer, Harry
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Building Custom Polysaccharides in Vitro with an Efficient, Broad-Specificity Xyloglucan Glycosynthase and a Fucosyltransferase2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 28, p. 10892-10900Article in journal (Refereed)
    Abstract [en]

    The current drive for applications of biomass-derived compounds, for energy and advanced materials, has led to a resurgence of interest in the manipulation of plant polymers. The xyloglucans, a family of structurally complex plant polysaccharides, have attracted significant interest due to their intrinsic high affinity for cellulose, both in muro and in technical applications. Moreover, current cell wall models are limited by the lack of detailed structure-property relationships of xyloglucans, due to a lack of molecules with well-defined branching patterns. Here, we have developed a new, broad-specificity "xyloglucan glycosynthase", selected from active-site mutants of a bacterial endoxyloglucanase, which catalyzed the synthesis of high molar mass polysaccharides, with complex side-chain structures, from suitable glycosyl fluoride donor substrates. The product range was further extended by combination with an Arabidopsis thaliana alpha(1 -> 2)-fucosyltransferase to achieve the in vitro synthesis of fucosylated xyloglucans typical of dicot primary cell walls. These enzymes thus comprise a toolkit for the controlled enzymatic synthesis of xyloglucans that are otherwise impossible to obtain from native sources. Moreover, this study demonstrates the validity of a chemo-enzymatic approach to polysaccharide synthesis, in which the simplicity and economy of glycosynthase technology is harnessed together with the exquisite specificity of glycosyltransferases to control molecular complexity.

  • 125. Støchkel, K.
    et al.
    Hansen, C. N.
    Houmøller, J.
    Nielsen, L. M.
    Anggara, K.
    Linares, M.
    Norman, Patrick
    Linköping University, Sweden.
    Nogueira, F.
    Maltsev, O. V.
    Hintermann, L.
    Nielsen, S. B.
    Naumov, P.
    Milne, B. F.
    On the influence of water on the electronic structure of firefly oxyluciferin anions from absorption spectroscopy of bare and monohydrated ions in vacuo2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 17, p. 6485-6493Article in journal (Refereed)
    Abstract [en]

    A complete understanding of the physics underlying the varied colors of firefly bioluminescence remains elusive because it is difficult to disentangle different enzyme-lumophore interactions. Experiments on isolated ions are useful to establish a proper reference when there are no microenvironmental perturbations. Here, we use action spectroscopy to compare the absorption by the firefly oxyluciferin lumophore isolated in vacuo and complexed with a single water molecule. While the process relevant to bioluminescence within the luciferase cavity is light emission, the absorption data presented here provide a unique insight into how the electronic states of oxyluciferin are altered by microenvironmental perturbations. For the bare ion we observe broad absorption with a maximum at 548 ± 10 nm, and addition of a water molecule is found to blue-shift the absorption by approximately 50 nm (0.23 eV). Test calculations at various levels of theory uniformly predict a blue-shift in absorption caused by a single water molecule, but are only qualitatively in agreement with experiment highlighting limitations in what can be expected from methods commonly used in studies on oxyluciferin. Combined molecular dynamics simulations and time-dependent density functional theory calculations closely reproduce the broad experimental peaks and also indicate that the preferred binding site for the water molecule is the phenolate oxygen of the anion. Predicting the effects of microenvironmental interactions on the electronic structure of the oxyluciferin anion with high accuracy is a nontrivial task for theory, and our experimental results therefore serve as important benchmarks for future calculations.

  • 126.
    Svedendahl, Maria
    et al.
    KTH, School of Biotechnology (BIO), Biochemistry.
    Hult, Karl
    KTH, School of Biotechnology (BIO), Biochemistry.
    Berglund, Per
    KTH, School of Biotechnology (BIO), Biochemistry.
    Fast carbon-carbon bond formation by a promiscuous lipase2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 51, p. 17988-17989Article in journal (Refereed)
  • 127.
    Szabo, Zoltan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Csoregh, I.
    Combinatorial multinuclear NMR and X-ray diffraction studies of uranium(VI)-nucleotide complexes2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 43, p. 15236-15247Article in journal (Refereed)
    Abstract [en]

    The complex formation of uranium(VI) with four nucleoticles, adenosine- (AMP), guanosine(GMP), uridine- (UMP), and cyticline-monophosphate (CMP), has been studied in the alkaline pH range (8.5-12) by H-1, P-31, C-13, and O-17 NMR spectroscopy, providing spectral integral, chemical shift, homo and heteronuclear coupling, and diffusion coefficient data. We find that two and only two complexes are formed with all ligands in the investigated pH region independently of the total uranium(VI) and ligand concentrations. Although the coordination of the 5'-phosphate group and the 2'- and 3'-hydroxyl groups of the sugar unit to the uranyl ions is similar to that proposed earlier (Feldman complex), the number and the structures of the complexes are different. The uranium-to-nucleotide ratio is 6:4 in one of the complexes and 3:3 in the other one, as unambiguously determined by a combinatorial approach using a systematic variation of the ratio of two ligands in ternary uranium(VI)-nucleotide systems. The structure of the 3:3 complex has been determined by single-crystal diffraction as well, and the results confirm the structure proposed by NMR in aqueous solution. The results have important implications on the synthesis of oligonucleotides.

  • 128. Tang, Wen
    et al.
    Policastro, Gina M.
    Hua, Geng
    University of Akron, United States .
    Guo, Kai
    Zhou, Jinjun
    Wesdemiotis, Chrys
    Doll, Gary L.
    Becker, Matthew L.
    Bioactive Surface Modification of Metal Oxides via Catechol-Bearing Modular Peptides: Multivalent-Binding, Surface Retention, and Peptide Bioactivity2014In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 136, no 46, p. 16357-16367Article in journal (Refereed)
    Abstract [en]

    A series of multivalent dendrons containing a bioactive osteogenic growth peptide (OGP) domain and surface-binding catechol domains were obtained through solid phase synthesis, and their binding affinity to hydroxyapatite, TiO2, ZrO2, CeO2, Fe3O4 and gold was characterized using a quartz crystal microbalance with dissipation (QCM-d). Using the distinct difference in binding affinity of the bioconjugate to the metal oxides, TiO2-coated glass slides were selectively patterned with bioactive peptides. Cell culture studies demonstrated the bioavailability of the OGP and that OGP remained on the surface for at least 2 weeks under in vitro cell culture conditions. Bone sialoprotein (BSP) and osteocalcein (OCN) markers were upregulated 3-fold and 60-fold, respectively, relative to controls at 21 days. Similarly, 3-fold more calcium was deposited using the OGP tethered dendron compared to TiO2. These catechol-bearing dendrons provide a fast and efficient method to functionalize a wide range of inorganic materials with bioactive peptides and have the potential to be used in coating orthopaedic implants and fixation devices.

  • 129. Tenn, William J., III
    et al.
    Conley, Brian L.
    Hoevelmann, Claas H.
    Ahlquist, Mårten
    Division of Chemistry and Chemical Engineering, California Institute of Technology.
    Nielsen, Robert J.
    Ess, Daniel H.
    Oxgaard, Jonas
    Bischof, Steven M.
    Goddard, William A.
    Periana, Roy A.
    Oxy-Functionalization of Nucleophilic Rhenium(I) Metal Carbon Bonds Catalyzed by Selenium(IV)2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 7, p. 2466-2468Article in journal (Refereed)
    Abstract [en]

    We report that SeO(2) catalyzes the facile oxy-functionalization of (CO)(5)Re(I)-Me(delta-) with IO(4)(-) to generate methanol. Mechanistic studies and DFT calculations reveal that catalysis involves methyl group transfer from Re to the electrophilic Se center followed by oxidation and subsequent reductive functionalization of the resulting CH(3)Se(VI) species. Furthermore, (CO)(3)Re(I)(Bpy)-R (R = ethyl, n-propyl, and aryl) complexes show analogous transfer to SeO(2) to generate the primary alcohols. This represents a new strategy for the oxy-functionalization of M-R(delta-) polarized bonds.

  • 130.
    Tian, Haining
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Yu, Ze
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630).
    Hagfeldt, Anders
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630).
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Organic Redox Couples and Organic Counter Electrode for Efficient Organic Dye-Sensitized Solar Cells2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 24, p. 9413-9422Article in journal (Refereed)
    Abstract [en]

    A series of organic thiolate/disulfide redox couples have been synthesized and have been studied systematically in dye-sensitized solar cells (DSCs) on the basis of an organic dye (TH305). Photophysical, photoelectrochemical, and photovoltaic measurements were performed in order to get insights into the effects of different redox couples on the performance of DSCs. The polymeric, organic poly(3,4-ethylenedioxythiophene) (PEDOT) material has also been introduced as counter electrode in this kind of noniodine-containing DSCs showing a promising conversion efficiency of 6.0% under AM 1.5G, 100 mW.cm(-2) light illumination. Detailed studies using electrochemical impedance spectroscopy and linear-sweep voltammetry reveal that the reduction of disulfide species is more efficient on the PEDOT counter electrode surface than on the commonly used platinized conducting glass electrode. Both pure and solvated ionic-liquid electrolytes based on a thiolate anion have been studied in the DSCs. The pure and solvated ionic-liquid-based electrolytes containing an organic redox couple render efficiencies of 3.4% and 1.2% under 10 mW.cm(-2) light illumination, respectively.

  • 131. Torres, R. A.
    et al.
    Himo, Fahmi
    KTH, Superseded Departments, Biotechnology.
    Bruice, T. C.
    Noodleman, L.
    Lovell, T.
    Theoretical examination of Mg2+-mediated hydrolysis of a phosphodiester linkage as proposed for the hammerhead ribozyme2003In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 125, no 32, p. 9861-9867Article in journal (Refereed)
    Abstract [en]

    The hammerhead ribozyme is an RNA molecule capable of self-cleavage at a unique site within its sequence. Hydrolysis of this phosphodiester linkage has been proposed to occur via an in-line attack geometry for nucleophilic displacement by the 2'-hydroxyl on the adjoining phosphorus to generate a 2',3'cyclic phosphate ester with elimination of the 5'-hydroxyl group, requiring a divalent metal ion under physiological conditions. The proposed S(N)2(P) reaction mechanism was investigated using density functional theory calculations incorporating the hybrid functional B3LYP to study this metal ion-dependent reaction with a tetraaquo magnesium (II)-bound hydroxide ion. For the Mg2+-catalyzed reaction, the gas-phase geometry optimized calculations predict two transition states with a kinetically insignificant, yet clearly defined, pentacoordinate intermediate. The first transition state located for the reaction is characterized by internal nucleophilic attack coupled to proton transfer. The second transition state, the rate-determining step, involves breaking of the exocyclic P-O bond where a metal-ligated water molecule assists in the departure of the leaving group. These calculations demonstrate that the reaction mechanism incorporating a single metal ion, serving as a Lewis acid, functions as a general base and can afford the necessary stabilization to the leaving group by orienting a water molecule for catalysis.

  • 132. Triguero, L.
    et al.
    Fohlisch, A.
    Vaterlein, P.
    Hasselstrom, J.
    Weinelt, M.
    Pettersson, L. G. M.
    Luo, Yi
    KTH, Superseded Departments, Biotechnology.
    Ågren, Hans
    KTH, Superseded Departments, Biotechnology.
    Nilsson, A.
    Direct experimental measurement of donation/back-donation in unsaturated hydrocarbon bonding to metals2000In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 122, no 49, p. 12310-12316Article in journal (Refereed)
    Abstract [en]

    Using resonant and off-resonant X-ray emission spectroscopy, in combination with ground-state density functional calculations, we examine the electronic structure of chemisarbed ethylene and benzene on thr Cu(110) surface to investigate the suitability of the donation/back-donation bonding model given by Dewar(1) and Chart and Duncanson(2) (DCD) for the interaction of unsaturated hydrocarbons with metal surfaces. We give an experimental verification of the DCD model and find donation/back-donation to be twice as large for ethylene as for benzene. In particular, the degree of sigma-pi mixing (rehybridization) is found to correspond to the amount of donation/back-donation, which is put in relation to the aromatic and nonaromatic pi characters of benzene and ethylene, respectively.

  • 133.
    Tyrode, Eric
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Johnson, Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Corrosion Science.
    Kumpulainen, Atte
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Rutland, Mark
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Claesson, Per
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Hydration State of Non-ionic Surfactant Monolayers at the Liquid/Vapor Interface:  Structure Determination by Vibrational Sum Frequency Spectroscopy2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 48, p. 16848-16859Article in journal (Refereed)
    Abstract [en]

    The OH stretching region of water molecules in the vicinity of nonionic surfactant monolayers has been investigated using vibrational sum frequency spectroscopy (VSFS) under the polarization combinations ssp, ppp, and sps. The surface sensitivity of the VSFS technique has allowed targeting the few water molecules present at the surface with a net orientation and, in particular, the hydration shell around alcohol, sugar, and poly(ethylene oxide) headgroups. Dramatic differences in the hydration shell of the uncharged headgroups were observed, both in comparison to each another and in comparison to the pure water surface. The water molecules around the rigid glucoside and maltoside sugar rings were found to form strong hydrogen bonds, similar to those observed in tetrahedrally coordinated water in ice. In the case of the poly(ethylene oxide) surfactant monolayer a significant ordering of both strongly and weakly hydrogen bonded water was observed. Moreover, a band common to all the surfactants studied, clearly detected at relatively high frequencies in the polarization combinations ppp and sps, was assigned to water species located in proximity to the surfactant hydrocarbon tail phase, with both hydrogen atoms free from hydrogen bonds. An orientational analysis provided additional information on the water species responsible for this band.

  • 134.
    Tyrode, Eric
    et al.
    KTH, School of Chemical Science and Engineering (CHE).
    Rutland, Mark
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Bain, Colin D.
    Dep. of Chemistry, Durham University, UK.
    Adsorption of CTAB on Hydrophilic Silica Studied by Linear and Nonlinear Optical Spectroscopy2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 51, p. 17434-17445Article in journal (Refereed)
    Abstract [en]

    Vibrational sum-frequency spectroscopy (SFS) and total internal reflection Raman scattering (TIR Raman) have been used to study the adsorption of hexadecyltrimethylammonium bromide (CTAB) to hydrophilic silica. These two complementary techniques permit the determination of the adsorbed amount with a sensitivity of similar to 1% of the maximum surface coverage, changes in the average tilt of the adsorbed molecules, the presence of asymmetric aggregates in the adsorbed film, and the structure and orientation of the water molecules in the interfacial region. The TIR Raman spectra show a monotonic increase with CTAB concentration with no measurable changes in the relative intensities of the different polarization combinations probed, implying that no significant changes occur in the conformational order of the hydrocarbon chain. In the sum-frequency (SF) spectra, no detectable peaks from the surfactant headgroup and hydrophobic chain were observed at any surface coverage. Major changes are observed in the water bands of the SF spectra, as the originally negatively charged silica surface becomes positively charged with an increase in the adsorbed amount, inducing a change in the polar orientation of the water molecules near the surface. The detection limits for hydrocarbons chains in the SF spectra were estimated by comparison with the SF spectrum of a disordered octadecyltrichlorosilane monolayer. The simulations demonstrate that the asymmetry in the adsorbed CTAB layer at any concentration is less than 5% of a monolayer. The results obtained pose severe constraints on the possible structural models, in particular at concentrations below the critical micellar concentration where information is scarce. The formation of hemimicelles, monolayers and other asymmetric aggregates is ruled out, with centrosymmetric aggregates forming from early on in the adsorption process.

  • 135. Vallet, V.
    et al.
    Privalov, Timofei
    KTH, Superseded Departments, Chemistry.
    Wahlgren, U.
    Grenthe, Ingmar
    KTH, Superseded Departments, Chemistry.
    The mechanism of water exchange in AmO2(H2O)(5)(2+) and in the isoelectronic UO2(H2O)(5)(+) and NpO2(H2O)(5)(2+) complexes as studied by quantum chemical methods2004In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, no 25, p. 7766-7767Article in journal (Refereed)
  • 136. Vallet, V.
    et al.
    Wahlgren, U.
    Schimmelpfennig, B.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    Grenthe, I.
    The mechanism for water exchange in UO2(H2O)(5) (2+) and UO2(oxalate)(2)(H2O) (2-), as studied by quantum chemical methods2001In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 123, no 48, p. 11999-12008Article in journal (Refereed)
    Abstract [en]

    The mechanisms for the exchange of water between [UO2(H2O)(5)](2+), [UO2(oxalate)(2)(H2O)](2-), and water solvent along dissociative (D), associative (A) and interchange (1) pathways have been investigated with quantum chemical methods. The choice of exchange mechanism is based on the computed activation energy and the geometry of the identified transition states and intermediates. These quantities were calculated both in the gas phase and with a polarizable continuum model for the solvent. There is a significant and predictable difference between the activation energy of the gas phase and solvent models: the energy barrier for the D-mechanism increases in the solvent as compared to the gas phase, while it decreases for the A- and I-mechanisms. The calculated activation energy, AW, for the water exchange in [UO2(H2O)(5)](2+) is 74, 19, and 21 kJ/mol, respectively, for the D-, A-, and I-mechanisms in the solvent, as compared to the experimental value DeltaH(double dagger) = 26 +/- 1 kJ/mol. This indicates that the D-mechanism for this system can be ruled out. The energy barrier between the intermediates and the transition states is small, indicating a lifetime for the intermediate approximate to 10(-10) s, making it very difficult to distinguish between the A- and I-mechanisms experimentally. There is no direct experimental information on the rate and mechanism of water exchange in [UO2(oxalate)(2)(H2O)](2-)containing two bidentate oxalate ions. The activation energy and the geometry of transition states and intermediates along the D-, A-, and I-pathways were calculated both in the gas phase and in a water solvent model, using a single-point MP2 calculation with the gas phase geometry. The activation energy, AW, in the solvent for the D-, A-, and I-mechanisms is 56, 12, and 53 kJ/mol, respectively. This indicates that the water exchange follows an associative reaction mechanism. The geometry of the A- and I-transition states for both [UO2(H2O)(5)](2+) and [UO2(oxalate)(2)(H2O)](2-) indicates that the entering/leaving water molecules are located outside the plane formed by the spectator ligands.

  • 137.
    Vongvilai, Pornrapee
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Ramström, Olof
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Dynamic Asymmetric Multicomponent Resolution: Lipase-Mediated Amidation of a Double Dynamic Covalent System2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 40, p. 14419-14425Article in journal (Refereed)
    Abstract [en]

    The Strecker reaction is one of the most important multicomponent reactions developed, leading to alpha-aminonitriles that are versatile substrates for many synthetic applications. In the present study, this reaction type has been applied to a double dynamic covalent resolution protocol, leading to efficient C-C- and C-N-bond generation as well as chiral discrimination. The combination of transimination with iminecyanation enabled the dynamic exchange in more,than one direction around a single stereogenic center of restricted structure. This multiple exchange process could generate a vast range of compounds from a low number of starting materials in very short time. The resulting double dynamic covalent systems, created under thermodynamic control, were subsequently coupled in a one-pot process with kinetically controlled lipase-mediated transacylation. This resulted in complete resolution of the dynamic systems, yielding the optimal N-acyl-alpha-aminonitriles for the enzyme, where the individual chemoenzymatic reactions could produce enantiomerically pure acylated N-substituted alpha-aminonitriles in good yields.

  • 138.
    Wahlberg, Elisabet
    et al.
    KTH, School of Biotechnology (BIO).
    Härd, Torleif
    Conformational Stabilization of an Engineered Binding Protein2006In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 23, p. 7651-7660Article in journal (Refereed)
    Abstract [en]

    We analyzed the thermodynamic basis for improvement of a binding protein by disulfide engineering. The Z(SPA-1) affibody binds to its Z domain binding partner with a dissociation constant K-d = 1.6 mu M, and previous analyses suggested that the moderate \affinity is due to the conformational heterogeneity of free Z(SPA-1) rather than to a suboptimal binding interface. Studies of five stabilized Z(SPA-1) double cystein mutants show that it is possible to improve the affinity by an order of magnitude to K-d = 130 nM, which is close to the range (20 to 70 nM) observed with natural Z domain binders, without altering the protein-protein interface obtained by phage display. Analysis of the binding thermodynamics reveals a balance between conformational entropy and desolvation entropy: the expected and favorable reduction of conformational entropy in the best-binding Z(SPA-1) mutant is completely compensated by an unfavorable loss of desolvation entropy. This is consistent with a restriction of possible conformations in the disulfide-containing mutant and a reduction of average water-exposed nonpolar surface area in the free state, resulting in a smaller conformational entropy penalty, but also a smaller change in surface area, for binding of mutant compared to wild-type Z(SPA-1). Instead, higher Z domain binding affinity in a group of eight Z(SPA-1) variants correlates with more favorable binding enthalpy and enthalpy- entropy compensation. These results suggest that protein-protein binding affinity can be improved by stabilizing conformations in which enthalpic effects can be fully explored.

  • 139.
    Wang, Lei
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Stewart, Beverly
    Pu, Maoping
    Liu, Jianhui
    Privalov, Timofei
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Toward Controlling Water Oxidation Catalysis: Tunable Activity of Ruthenium Complexes with Axial Imidazole/DMSO Ligands2012In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 45, p. 18868-18880Article in journal (Refereed)
    Abstract [en]

    Using the combinations of imidazole and dimethyl :sulfoxide (DMSO) as axial ligands and 2,2'-bipyridine-6,6'-dicarboxylate (bda) as the equatorial ligand, we have synthesized six novel ruthenium complexes with noticeably different activity as water oxidation catalysts (WOCs). In four C-s symmetric Ru-II(kappa(3)-bda)(DMSO)L-2 complexes L = imidazole (1), N-methylimidazole (2), 5-methylimidazole (3), and 5-bromo-N-methylimidazole (4). Additionally, in two C-2v symmetric Ru-II(kappa(4)-bda)L-2 complexes L = 5-nitroimidazole (5) and 5-bromo-N-methylimidazole (6), that is, fully equivalent axial imidazoles. A detailed characterization of all complexes and the mechanistic investigation of the catalytic water oxidation have been carried out with a number of experimental techniques, that is, kinetics, electrochemistry and high resolution mass spectrometry (HR-MS), and density functional theory (DFT) calculations. We have observed the in situ formation: of a Ru-II-complex with the accessible seventh coordination position. The measured catalytic activities and kinetics of complex 1-6 revealed details about an important structure activity relation: the connection between the nature of axial ligands in the combination and either the increase or decrease of the catalytic activity. In particular, an axial DMSO group substantially increases the turnover frequency of WOCs reported in article, with the ruthenium-complex having one axial 5-bromo-N-methylimidazole and one axial DMSO: (4), we have obtained a high initial turnover frequency of similar to 180 s(-1). DFT modeling Of the binuclear reaction pathway of the O-O bond formation in catalytic Water oxidation further corroborated the concept of the mechanistic significance of the axial ligands and rationalized the experimentally observed difference in the activity of complexes with imidazole/DMSO and imidazole/imidazole combinations of axial ligands.

  • 140. Wang, N.
    et al.
    Wang, M.
    Wang, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zheng, D.
    Han, H.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Catalytic activation of H2 under mild conditions by an [FeFe]-hydrogenase model via an active μ-hydride species2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 37, p. 13688-13691Article in journal (Refereed)
    Abstract [en]

    A [FeFe]-hydrogenase model (1) containing a chelating diphosphine ligand with a pendant amine was readily oxidized by Fc+ (Fc = Cp 2Fe) to a FeIIFeI complex ([1]+), which was isolated at room temperature. The structure of [1]+ with a semibridging CO and a vacant apical site was determined by X-ray crystallography. Complex [1]+ catalytically activates H2 at 1 atm at 25 C in the presence of excess Fc+ and P(o-tol) 3. More interestingly, the catalytic activity of [1]+ for H2 oxidation remains unchanged in the presence of ca. 2% CO. A computational study of the reaction mechanism showed that the most favorable activation free energy involves a rotation of the bridging CO to an apical position followed by activation of H2 with the help of the internal amine to give a bridging hydride intermediate.

  • 141.
    Wennberg, Christian L.
    et al.
    Uppsala University, Sweden.
    van der Spoel, David
    Hub, Jochen S.
    Large Influence of Cholesterol on Solute Partitioning into Lipid Membranes2012In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 11, p. 5351-5361Article in journal (Refereed)
    Abstract [en]

    Cholesterol plays an important role in maintaining the correct fluidity and rigidity of the plasma membrane of all animal cells, and hence, it is present in concentrations ranging from 20 to 50 mol %. Whereas the effect of cholesterol on such mechanical properties has been studied exhaustively over the last decades, the structural basis for cholesterol effects on membrane permeability is still unclear. Here we apply systematic molecular dynamics simulations to study the partitioning of solutes between water and membranes. We derive potentials of mean force for six different solutes permeating across 20 different lipid membranes containing one out of four types of phospholipids plus a cholesterol content varying from 0 to 50 mol %. Surprisingly, cholesterol decreases solute partitioning into the lipid tail region of the membranes much more strongly than expected from experiments on macroscopic membranes, suggesting that a laterally inhomogeneous cholesterol concentration and permeability may be required to explain experimental findings. The simulations indicate that the cost of breaking van der Waals interactions between the lipid tails of cholesterol-containing membranes account for the reduced partitioning rather than the surface area per phospholipid, which has been frequently suggested as a determinant for solute partitioning. The simulations further show that the partitioning is more sensitive to cholesterol (i) for larger solutes, (ii) in membranes with saturated as compared to membranes with unsaturated lipid tails, and (iii) in membranes with smaller lipid head groups.

  • 142.
    Wennmalm, Stefan
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Widengren, Jerker
    KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
    Interferometry and fluorescence detection for simultaneous analysis of labeled and unlabeled nanoparticles in solution2012In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 48, p. 19516-19519Article in journal (Refereed)
    Abstract [en]

    A novel fluctuation spectroscopy technique based on interferometry is described. The technique, termed scattering interference correlation spectroscopy (SICS), autocorrelates the signals from the forward-scattered and transmitted laser light from nanoparticles (NPs) in solution. SICS has two important features: First, for unlabeled NPs with known refractive index, it analyzes not only the diffusion coefficient but also the effective cross section and concentration in a single measurement. Second, it can be combined with fluorescence correlation spectroscopy (FCS) for simultaneous analysis of labeled and unlabeled NPs. SICS is here demonstrated on unlabeled M13 phages and on unlabeled NPs with diameters of 210 nm down to 26 nm. It is also shown how the combination of SICS and FCS can be used to determine the fraction of fluorescent NPs in a mixture and estimate Kd from a single binding measurement.

  • 143. Wu, Bo
    et al.
    Hu, Jiahua
    Cui, Peng
    Jiang, Li
    Chen, Zongwei
    Zhang, Qun
    Wang, Chunru
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Visible-Light Photoexcited Electron Dynamics of Scandium Endohedral Metallofullerenes: The Cage Symmetry and Substituent Effects2015In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 137, no 27, p. 8769-8774Article in journal (Refereed)
    Abstract [en]

    Endohedral metallofullerenes (EMFs) have become an important class of molecular materials for optoelectronic applications. The performance of EMFs is known to be dependent on their symmetries and characters of the substituents, but the underlying electron dynamics remain unclear. Here we report a systematic study on several scandium EMFs and representative derivatives to examine the cage symmetry and substituent effects on their photoexcited electron dynamics using ultrafast transient absorption spectroscopy. Our attention is focused on the visible-light (530 nm as a demonstration) photoexcited electron dynamics, which is of broad interest to visible-light solar energy harvesting but is considered to be quite complicated as the visible-light photons would promote the system to a high-lying energy region where dense manifolds of electronic states locate. Our ultrafast spectroscopy study enables a full mapping of the photoinduced deactivation channels involved and reveals that the long-lived triplet exciton plays a decisive role in controlling the photoexcited electron dynamics under certain conditions. More importantly, it is found that the opening of the triplet channels is highly correlated to the fullerene cage symmetry as well as the electronic character of the substituents.

  • 144. Wu, H.
    et al.
    Zhou, Y.
    Yin, L.
    Hang, C.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Yi, T.
    Zhang, Q.
    Zhu, L.
    Helical self-assembly-induced singlet-triplet emissive switching in a mechanically sensitive system2017In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, no 2, p. 785-791Article in journal (Refereed)
    Abstract [en]

    In nanoscience, chirality has shown a significant ability to tune materials' electronic properties, whereas imposing macrochirality into the regulation of singlet-triplet features of organic optoelectronics remains a challenging research topic. Since the tuning for singlet and triplet excited-state properties in a single π-functional molecule connects to its multicolor luminescent application and potential improvement of internal quantum efficiency, we here report that supramolecular chirality can be employed to toggle the singlet and triplet emissions in a welldesigned asterisk-shaped molecule. Employing a hexathiobenzene-based single luminophore as a prototype and functionalizing it with chiral α-lipoiate side groups, we find that helical nanoarchitectures can accordingly form in mixed DMF/H20 solution. On this basis, switching between fluorescence and phosphorescence of the material can be realized upon helical self-assembly and dissociation. Such a behavior can be attributed to a helical-conformation-dependent manipulation of the intersystem crossing. Furthermore, reversible mechanoluminescence of the corresponding solid sample was also observed to rely on an analogous molecular self-assembly alternation. These results can probably provide new visions for the development of next-generation supramolecular chiral functional materials.

  • 145.
    Xie, Sheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. Univ Massachusetts Lowell, Dept Chem, Lowell, MA 01854 USA.
    Lopez, Steven A.
    Ramström, Olof
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Yan, Mingdi
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. Department of Chemistry, University of Massachusetts Lowell, Lowell, MA, United States .
    Houk, K. N.
    1,3-Dipolar Cycloaddition Reactivities of Perfluorinated Aryl Azides with Enamines and Strained Dipolarophiles2015In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 137, no 8, p. 2958-2966Article in journal (Refereed)
    Abstract [en]

    The reactivities of enamines and predistorted (strained) dipolarophiles toward perfluoroaryl azides (PFAAs) were explored experimentally and computationally. Kinetic analyses indicate that PFAAs undergo (3 + 2) cycloadditions with enamines up to 4 orders of magnitude faster than phenyl azide reacts with these dipolarophiles. DFT calculations were used to identify the origin of this rate acceleration. Orbital interactions between the cycloaddends are larger due to the relatively low-lying LUMO of PFAAs. The triazolines resulting from PFAAenamine cycloadditions rearrange to amidines at room temperature, while (3 + 2) cycloadditions of enamines and phenyl azide yield stable, isolable triazolines. The 1,3-dipolar cycloadditions of norbornene and DIBAC also show increased reactivity toward PFAAs over phenyl azide but are slower than enamineazide cycloadditions.

  • 146. Xie, Yongshu
    et al.
    Wei, Pingchun
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hong, Tao
    Zhang, Kai
    Furuta, Hiroyuki
    Macrocycle Contraction and Expansion of a Dihydrosapphyrin Isomer2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 51, p. 19119-19122Article in journal (Refereed)
    Abstract [en]

    Cyclization of a pentapyrrane with two terminal beta-linked pyrroles afforded a dihydrosapphyrin isomer (1) with the pyrroles linked in a unique beta,alpha-alpha,beta mode, which was rather reactive, and thus it readily underwent a ring-contracted rearrangement to a pyrrolyl norrole (2), and succeeding ring expansion to a terpyrrole-containing isosmaragdyrin analogue (4). 1, 2, and 4 contain the internal ring pathways with a minimum of 17, 15, and 16 atoms, respectively. 1, 2, and 4 are almost nonfluorescent, whereas the complex of 2 with Zn2+ shows a distinct NIR emission peak at 741 nm. The unprecedented pyrrole transformation chemistry by confusion approach is illustrated.

  • 147. Xu, Y.
    et al.
    Ruban, Andrei V.
    Mavrikakis, M.
    Adsorption and dissociation of O-2 on Pt-Co and Pt-Fe alloys2004In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, no 14, p. 4717-4725Article in journal (Refereed)
    Abstract [en]

    Self-consistent periodic density functional theory calculations (GGA-PW91) have been performed to study the adsorption of O and O-2 and the dissociation of O-2 on the (111) facets of ordered Pt3Co and Pt3Fe alloys and on monolayer Pt skins covering these two alloys. Results are compared with those obtained on two Pt(111) surfaces, one at the equilibrium lattice constant and the other laterally compressed by 2% to match the strain in the Pt alloys. The absolute magnitudes of the binding energies of O and O-2 follow the same order in the two alloy systems: Pt skin < compressed Pt(111) < Pt(111) < Pt3CO(111) or Pt-3-Fe(111). The reduced activity of the compressed Pt(111) and Pt skins for oxygen can be rationalized as being due to the shifting of the d-band center increasingly away from the Fermi level. We propose that an alleviation of poisoning by O and enhanced rates for reactions involving O may be some of the reasons why Pt skins are more active for the oxygen reduction reaction in low-temperature fuel cells. Finally, a linear correlation between the transition-state and final-state energies of O-2 dissociation on monometallic and bimetallic surfaces is revealed, pointing to a simple way to screen for improved cathode catalysts.

  • 148. Yang, Lei
    et al.
    Xu, Bo
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Bi, Dongqin
    Tian, Haining
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Boschloo, Gerrit
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Hagfeldt, Anders
    Johansson, Erik M. J.
    Initial Light Soaking Treatment Enables Hole Transport Material to Outperform Spiro-OMeTAD in Solid-State Dye-Sensitized Solar Cells2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 19, p. 7378-7385Article in journal (Refereed)
    Abstract [en]

    Efficient solid state dye-sensitized solar cells (sDSCs) were obtained using a small hole transport material, MeO-TPD (N,N,N',N'-tetrakis(4-methoxyphenyl)benzidine), after an initial light soaking treatment. It was discovered that the light soaking treatment for the MeO-TPD based solar cells is essential in order to achieve the high efficiency (4.9%), which outperforms spiro-OMeTAD based sDSCs using the same dye and device preparation parameters. A mechanism based on Li+ ion migration is suggested to explain the light soaking effect. It was observed that the electron lifetime for the MeO-TPD based sDSC strongly increases after the light soaking treatment, which explains the higher efficiency. After the initial light soaking treatment the device efficiency remains considerably stable with only 0.2% decrease after around 1 month (unsealed cells stored in dark).

  • 149. Yu, G.
    et al.
    Yin, S. W.
    Liu, Y. Q.
    Chen, J. S.
    Xu, X. J.
    Sun, X. B.
    Ma, D. G.
    Zhan, X. W.
    Peng, Q.
    Shuai, Z. G.
    Tang, B. Z.
    Zhu, D. B.
    Fang, W. H.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Structures, electronic states, photoluminescence, and carrier transport properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 17, p. 6335-6346Article, review/survey (Refereed)
    Abstract [en]

    The excellent electroluminescent (EL) properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles, 1-methyl-1,2,3,4,5-pentaphenylsilole (MPPS), and 1,1,2,3,4,5-hexaphenylsilole (HPS) have been found. Despite some studies devoted to these materials, very little is known about the real origin of their unique EL properties. Therefore, we investigated the structures, photoluminescence (PL), and charge carrier transport properties of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles as well as the effect of substituents on these characteristics. The single crystals of the three siloles involving 1,1-dimethyl-2,3,4,5-tetraphenylsilole (DMTPS), MPPS, and HIPS were grown and their crystal structures were determined by X-ray diffraction. Three siloles have nonplanar molecular structures. The substituents at 1,1-positions enhance the steric hindrance and have predominant influence on the twisted degree of phenyl groups at ring carbons. This nonplanar structure reduces the intermolecular interaction and the likelihood of excimer formation, and increases PL efficiency in the solid state. The silole films show high fluorescence quantum yields (75-85%), whereas their dilute solutions exhibit a faint emission. The electronic structures of the three siloles were investigated using quantum chemical calculations. The highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) are mainly localized on the silole ring and two phenyl groups at 2,5-positions in all cases, while the LUMOs have a significant orbital density at two exocyclic Si-C bonds. The extremely theoretical studies of luminescent properties were carried out. We calculated the nonradiative decay rate of the first excited state as well as the radiative one. It is found that the faint emission of DMTPS in solutions mainly results from the huge nonradiative decay rate. In solid states, molecular packing can remarkably restrict the intramolecular rotation of the peripheral side phenyl ring, which has a large contribution to the nonradiative transition process. This explains why the 1,1-disubstituted 2,3,4,5-tetraphenylsiloles in the thin films exhibit high fluorescence quantum yields. The charge carrier mobilities of the MPPS and HPS films were measured using a transient EL technique. We obtained a mobility of 2.1 x 10(-6) cm(2)/V(.)s in the MPPS film at an electric field of 1.2 x 10(6) V/cm. This mobility is comparable to that of Alq(3), which is one of the most extensively used electron transport materials in organic light-emitting diodes (LEDs), at the same electric field. The electron mobility of the HPS film is about similar to 1.5 times higher than that of the MPPS film. To the best of our knowledge, this kind of material is one of the most excellent emissive materials that possess both high charge carrier mobility and high PL efficiency in the solid states simultaneously. The excellent EL performances of MPPS and HPS are presumably ascribed to these characteristics.

  • 150.
    Zalubovskis, Raivis
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Bouet, Alexis
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Fjellander, Ester
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Constant, Samuel
    University of Geneva.
    Linder, David
    University of Geneva.
    Andreas, Fischer
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630).
    Lacour, Jérôme
    University of Geneva.
    Privalov, Timofei
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Moberg, Christina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Self-adaptable Catalysts: Substrate-Dependent Ligand Configuration2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 6, p. 1845-1855Article in journal (Refereed)
    Abstract [en]

    Pd(II) allyl and Pd(0) olefin complexes containing the configurationally labile ligand 1,2-bis-[4,5dihydro-3H-dibenzo[c-e]azepino]ethane were studied as models for intermediates in Pd-catalyzed allylic alkylations. According to NMR and DFT studies, the ligand prefers C-s conformation in both eta(3)-1,3-diphenylpropenyl and eta(3)-cyclohexenyl Pd(II) complexes, whereas in Pd(0) olefin complexes it adopts different conformations in complexes derived from the two types of allyl systems in both solution and, as verified by X-ray crystallography, in the solid state. These results demonstrate that the Pd complex is capable of adapting its structure to the reacting substrate. The different structural preferences also provide an explanation for the behavior of 1,3-diphenyl-2-propenyl acetate and 2-cyclohexenyl acetate in Pd-catalyzed allylic alkylations using pseudo-C-2 and pseudo-C-s symmetric ligands.

1234 101 - 150 of 161
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf