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  • 1.
    Ahlquist, Mårten
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fabrizi, Giancarlo
    Cacchi, Sandro
    Norrby, Per-Ola
    Technical Univeristy of Denmark.
    The mechanism of the phosphine-free palladium-catalyzed hydroarylation of alkynes2006In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 39, p. 12785-12793Article in journal (Refereed)
    Abstract [en]

    The mechanism of the Pd-catalyzed hydroarylation and hydrovinylation reaction of alkynes has been studied by a combination of experimental and theoretical methods (B3LYP), with an emphasis on the phosphine-free version. The regioselectivity of the hydroarylation and hydrovinylation shows unexpected differences, which could be attributed mainly to the higher steric demand of the cyclohexenyl group as compared to the phenyl group. Hydroarylation of alpha,beta-acetylenic carbonyl substrates yields a very unusual anti-Michael selectivity, which is shown to result from reaction of the nonconjugated double bond, leaving the conjugation intact. In all cases were the regioselectivities reproduced by the calculations.

  • 2.
    Ahlquist, Mårten
    et al.
    Technical University of Denmark.
    Nielsen, Robert J.
    Periana, Roy A.
    Goddard, William A., III
    Product Protection, the Key to Developing High Performance Methane Selective Oxidation Catalysts2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 47, p. 17110-17115Article in journal (Refereed)
    Abstract [en]

    Selective, direct conversion of methane to methanol might seem an impossible task since the C-H bond energy of methane is 105 kcal mol(-1) compared to the C-H bond energy for methanol of 94. We show here that the Catalytica catalyst is successful because the methanol is protected as methyl bisulfate, which is substantially less reactive than methanol toward the catalyst. This analysis suggests a limiting performance for systems that operate by this type of protection that is well above the Catalytica system.

  • 3.
    Andrén, Oliver C. J.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Fernandes, Aristi P.
    Malkoch, Michael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Heterogeneous Rupturing Dendrimers2017In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126Article in journal (Refereed)
    Abstract [en]

    Utilizing macromolecular scaffolds as templates for the production of small molecules that are distinctively different from the original monomer feedstock has many potential applications. Herein, as a proof-of-concept, a family of dendrimers displaying internally queued disulfide bridges were synthesized and exploited as flawless macromolecular templates that selectively rupture into a set of monomeric mercaptans. Disassembly was accomplished in a reducing environment, using DTT as an external stimulus, and the thiol constituents were successfully isolated. Their composition was dictated by three dendritic regions, i.e., (i) the symmetrical trithiol of the core (C3), (ii) the interior-asymmetric trithiols (CD2), and (iii) the periphery-asymmetric monothiols (DB2), in which B functionality is of an orthogonal nature. Taking into account the steady state between disulfides and thiols in all living cells, the collapse of the dendrimers to a multitude of smaller thiols was intracellularly assessed as a means to disrupt the balance of reactive oxygen species (ROS) often elevated in cancer cells. Indeed, the fragmentation induced a significant increase of ROS in human lung carcinoma A549 cells. These findings can potentially alter the perception of dendrimers being limited to carriers to being prodrugs for intracellular delivery of ROS with the potential to fight cancer.

  • 4. Baber, Ashleigh E.
    et al.
    Xu, Fang
    Dvorak, Filip
    Mudiyanselage, Kumudu
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Senanayake, Sanjaya D.
    Sadowski, Jerzy T.
    Rodriguez, José A.
    Matolín, Vladimír
    White, Michael G.
    Stacchiola, Darío J.
    In Situ Imaging of Cu2O under Reducing Conditions: Formation of Metallic Fronts by Mass Transfer2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 45, p. 16781-16784Article in journal (Refereed)
    Abstract [en]

    Active catalytic sites have traditionally been analyzed based on static representations of surface structures and characterization of materials before or after reactions. We show here by a combination of in situ microscopy and spectroscopy techniques that, in the presence of reactants, an oxide catalyst's chemical state and morphology are dynamically modified. The reduction of Cu2O films is studied under ambient pressures (AP) of CO. The use of complementary techniques allows us to identify intermediate surface oxide phases and determine how reaction fronts propagate across the surface by massive mass transfer of Cu atoms released during the reduction of the oxide phase in the presence of CO. High resolution in situ imaging by AP scanning tunneling microscopy (AP-STM) shows that the reduction of the oxide films is initiated at defects both on step edges and the center of oxide terraces.

  • 5. Baias, Maria
    et al.
    Dumez, Jean-Nicolas
    Svensson, Per Henrik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Schantz, Staffan
    Day, Graeme M.
    Emsley, Lyndon
    De Novo Determination of the Crystal Structure of a Large Drug Molecule by Crystal Structure Prediction-Based Powder NMR Crystallography2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 46, p. 17501-17507Article in journal (Refereed)
    Abstract [en]

    The crystal structure of form 4 of the drug 4-[4-(2-adamantylcarbamoyl)-5-tert-butyl-pyrazol-1-yl]benzoic acid is determined using a protocol for NMR powder crystallography at natural isotopic abundance combining solid-state H-1 NMR spectroscopy, crystal structure prediction, and density functional theory chemical shift calculations. This is the first example of NMR crystal structure determination for a molecular compound of previously unknown structure, and at 422 g/mol this is the largest compound to which this method has been applied so far.

  • 6. Baranov, A. I.
    et al.
    Kloo, Lars A.
    KTH, Superseded Departments, Chemistry.
    Olenev, A. V.
    Popovkin, B. A.
    Romanenko, A. I.
    Shevelkov, A. V.
    Unique (infinity Ni8Bi8S)-Ni-1 metallic wires in a novel quasi-1D compound. Synthesis, crystal and electronic structure, and properties of Ni8Bi8SI2001In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 123, no 49, p. 12375-12379Article in journal (Refereed)
    Abstract [en]

    A new quasi-one-dimensional compound Ni8Bi8SI has been synthesized and its crystal structure determined from single-crystal X-ray diffraction data. The structure of Ni8Bi8SI consists of [(infinityNi8Bi8S)-Ni-1] columns separated by iodine atoms. Conductivity and magnetic susceptibility measurements (down to 4.2 K) show that Ni8Bi8SI is a one-dimensional metal and exhibits Pauli paramagnetic properties. These observations are in good agreement with the results from electronic structure calculations. An analysis of the chemical bonding employing difference electron charge density maps reveals strong multicenter Ni-Bi bonds and pair Ni-S interactions within the [(infinityNi8Bi8S)-Ni-1] columns. Only electrostatic interactions are inferred between the columns and iodine atoms.

  • 7.
    Berglund, Per
    et al.
    University of Toronto, Canada.
    DeSantis, Grace
    Stabile, Michele R.
    Shang, Xiao
    Gold, Marvin
    Bott, Richard R.
    Graycar, Thomas P.
    Lau, Tony Hing
    Mitchinson, Colin
    Jones, J. Bryan
    Chemical Modification of Cysteine Mutants of Subtilisin Bacillus lentus Can Create Better Catalysts Than the Wild-Type Enzyme1997In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 119, no 22, p. 5265-5266Article in journal (Refereed)
  • 8. Bertelsen, Søren
    et al.
    Dinér, Peter
    Johansen, Rasmus Lyng
    Jørgensen, Karl Anker
    Asymmetric organocatalytic beta-hydroxylation of alpha, beta-unsaturated aldehydes2007In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129 1536-1537, no 6, p. 1536-1537Article in journal (Refereed)
    Abstract [en]

    The first catalytic enantioselective β-hydroxylation of α,β-unsaturated aldehydes is presented. Using commercially available (E)-benzaldehyde oxime in the presence of 2-[bis(3,5-bis-trifluoromethyl-phenyl)trimethyl-silanyloxymethyl]pyrrolidine as organocatalyst, the corresponding chiral carbonyl β-oxime ethers are obtained in high yields and with excellent enantioselectivities. These optically active carbonyl and hydroxy β-oxime ethers are highly interesting biological compounds in, e.g., sex pheromone analogues, highly potent antiinflammatory agents, and penicillin and cephalosporin analogues. The chiral carbonyl β-oxime ethers can be reduced to the corresponding 1,3-diols in high yields. Furthermore, the organocatalytic enantioselective β-hydroxylation of α,β-unsaturated aldehydes could be performed on gram scale without loss of enantioselectivity.

  • 9. Bertelsen, Søren
    et al.
    Marigo, Mauro
    Brandes, Sebastian
    Dinér, Peter
    Jørgensen, Karl Anker
    Dienamine catalysis: organocatalytic asymmetric gamma-amination of alpha,beta-unsaturated aldehydes2006In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 39, p. 12973-12980Article in journal (Refereed)
  • 10.
    Blid, Jan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Panknin, Olaf
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Somfai, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Asymmetric [2,3]-sigmatropic rearrangement of allylic ammonium ylides2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 26, p. 9352-9353Article in journal (Refereed)
    Abstract [en]

    An asymmetric Lewis acid-mediated [2,3]-sigmatropic rearrangement of allylic amines has been developed, affording the corresponding homoallylic amines in good yield and excellent enantioselectivities. The rearrangement proceeds by complexation of the chiral Lewis acid to the amine followed by deprotonation and rearrangement.

  • 11.
    Branneby, Cecilia
    et al.
    KTH, Superseded Departments, Biotechnology.
    Carlqvist, Peter
    KTH, Superseded Departments, Chemistry.
    Magnusson, Anders
    KTH, Superseded Departments, Biotechnology.
    Hult, Karl
    KTH, Superseded Departments, Biotechnology.
    Brinck, Tore
    KTH, Superseded Departments, Chemistry.
    Berglund, Per
    KTH, Superseded Departments, Biotechnology.
    Carbon-Carbon Bonds by Hydrolytic Enzymes2003In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 125, no 4, p. 874-875Article in journal (Refereed)
    Abstract [en]

    Enzymes are efficient catalysts in synthetic chemistry, and their catalytic activity with unnatural substrates in organic reaction media is an area attracting much attention. Protein engineering has opened the possibility to change the reaction specificity of enzymes and allow for new reactions to take place in their active sites. We have used this strategy on the well-studied active-site scaffold offered by the serine hydrolase Candida antarctica lipase B (CALB, EC 3.1.1.3) to achieve catalytic activity for aldol reactions. The catalytic reaction was studied in detail by means of quantum chemical calculations in model systems. The predictions from the quantum chemical calculations were then challenged by experiments. Consequently, Ser105 in CALB was targeted by site-directed mutagenesis to create enzyme variants lacking the nucleophilic feature of the active site. The experiments clearly showed an increased reaction rate when the aldol reaction was catalyzed by the mutant enzymes as compared to the wild-type lipase. We expect that the new catalytic activity, harbored in the stable protein scaffold of the lipase, will allow aldol additions of substrates, which cannot be reached by traditional aldolases

  • 12. Brena, Barbara
    et al.
    Siegbahn, Per E. M.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Modeling Near-Edge Fine Structure X-ray Spectra of the Manganese Catalytic Site for Water Oxidation in Photosystem II2012In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 41, p. 17157-17167Article in journal (Refereed)
    Abstract [en]

    The Mn Is near-edge absorption fine structure (NEXAFS) has been computed by means of transition-state gradient-corrected density functional theory (DFT) on four Mn4Ca clusters modeling the successive S-0 to S-3 steps of the oxygen-evolving complex (OEC) in photosystem II (PSII). The model clusters were obtained from a previous theoretical study where they were determined by energy minimization. They are composed of Mn(III) and Mn(IV) atoms, progressing from Mn(III)(3)Mn(IV) for S-0 to Mn(III)(2)Mn(IV)(2) for S-1 to Mn(III)Mn(IV)(3) for S-2 to Mn(IV)(4) for S-3, implying an Mn-centered oxidation during each step of the photosynthetic oxygen evolution. The DFT simulations of the Mn Is absorption edge reproduce the experimentally measured curves quite well. By the half-height method, the theoretical IPEs are shifted by 0.93 eV for the S-0 -> S-1 transition, by 1.43 eV for the S-1 -> S-2 transition, and by 0.63 eV for the S-2 -> S-3 transition. The inflection point energy (IPE) shifts depend strongly on the method used to determine them, and the most interesting result is that the present clusters reproduce the shift in the S-2 -> S-3 transition obtained by both the half-height and second-derivative methods, thus giving strong support to the previously suggested structures and assignments.

  • 13.
    Brinck, Tore
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Haeberlein, Markus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    A Computational Analysis of Substituent Effects on the O-H Bond Dissociation Energy in Phenols: Polar Versus Radical Effects1997In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 119, no 18, p. 4239-4244Article in journal (Refereed)
  • 14.
    Brumer, Harry
    et al.
    KTH, Superseded Departments, Biotechnology.
    Zhou, Qi
    KTH, Superseded Departments, Biotechnology.
    Baumann, Martin J.
    KTH, Superseded Departments, Biotechnology.
    Carlsson, Kjell
    KTH, Superseded Departments, Biotechnology.
    Teeri, Tuula
    KTH, Superseded Departments, Biotechnology.
    Activation of crystalline cellulose surfaces though the chemoenzymatic modification of xyloglucan2004In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, no 18, p. 5715-1721Article in journal (Refereed)
    Abstract [en]

    Cellulose constitutes an important raw material for many industries. However, the superb load-bearing properties of cellulose are accompanied by poor chemical reactivity. The hydroxyl groups on cellulose surfaces can be reacted but usually not without loss of fiber integrity and strength. Here, we describe a novel chemoenzymatic approach for the efficient incorporation of chemical functionality onto cellulose surfaces. The modification is brought about by using a transglycosylating enzyme, xyloglucan endotranglycosylase, to join chemically modified xyloglucan oligosaccharides to xyloglucan, which has a naturally high affinity to cellulose. Binding of the chemically modified hemicellulose molecules can thus be used to attach a wide variety of chemical moieties without disruption of the individual fiber or fiber matrix.

  • 15. Brun, Matthias A
    et al.
    Griss, Rudolf
    Reymond, Luc
    Tan, Kui-Thong
    Piguet, Joachim
    National Centre of Competence in Research Chemical Biology, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
    Peters, Ruud J R W
    Vogel, Horst
    Johnsson, Kai
    Semisynthesis of fluorescent metabolite sensors on cell surfaces.2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 40Article in journal (Refereed)
    Abstract [en]

    Progress in understanding signal transduction and metabolic pathways is hampered by a shortage of suitable sensors for tracking metabolites, second messengers, and neurotransmitters in living cells. Here we introduce a class of rationally designed semisynthetic fluorescent sensor proteins, called Snifits, for measuring metabolite concentrations on the cell surface of mammalian cells. Functional Snifits are assembled on living cells through two selective chemical labeling reactions of a genetically encoded protein scaffold. Our best Snifit displayed fluorescence intensity ratio changes on living cells significantly higher than any previously reported cell-surface-targeted fluorescent sensor protein. This work establishes a generally applicable and rational strategy for the generation of cell-surface-targeted fluorescent sensor proteins for metabolites of interest.

  • 16.
    Cao, Hui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Jiang, Jun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ma, Jing
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Temperature-dependent statistical behavior of single molecular conductance in aqueous solution2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 21, p. 6674-+Article in journal (Refereed)
    Abstract [en]

    We have combined molecular dynamics simulations with first principles calculations to study electron 4 transport in a single molecule of perylene tetracarboxylic diimide (PTCDI) sandwiched between two gold electrodes with an aqueous electrolyte. This combination has for the first time allowed one to reveal statistical behavior of molecular conductance in solution at different temperatures and to produce conductance histograms that can be directly compared with experiments. Our calculations show that experimentally observed temperature-dependent conductance ran be attributed to the thermal effect on the hydrogen bonding network around the molecule and can be described by the radial distribution of water molecules surrounding the oxygen atom in the PTCDI molecule.

  • 17.
    Cao, Hui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Ma, Jing
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Statistical Behavior of Electrochemical Single Molecular Field Effect Transistor2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126Article in journal (Refereed)
  • 18. Cappel, Ute B
    et al.
    Feldt, Sandra M
    Schöneboom, Jan
    Hagfeldt, Anders
    Boschloo, Gerrit
    The influence of local electric fields on photoinduced absorption in dye-sensitized solar cells.2010In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 26, p. 9096-101Article in journal (Refereed)
    Abstract [en]

    The dye-sensitized solar cell (DSC) challenges conventional photovoltaics with its potential for low-cost production and its flexibility in terms of color and design. Transient absorption spectroscopy is widely used to unravel the working mechanism of DSCs. A surprising, unexplained feature observed in these studies is an apparent bleach of the ground-state absorption of the dye, under conditions where the dye is in the ground state. Here, we demonstrate that this feature can be attributed to a change of the local electric field affecting the absorption spectrum of the dye, an effect related to the Stark effect first reported in 1913. We present a method for measuring the effect of an externally applied electric field on the absorption of dye monolayers adsorbed on flat TiO(2) substrates. The measured signal has the shape of the first derivative of the absorption spectra of the dyes and reverses sign along with the reversion of the direction of the change in dipole moment upon excitation relative to the TiO(2) surface. A very similar signal is observed in photoinduced absorption spectra of dye-sensitized TiO(2) electrodes under solar cell conditions, demonstrating that the electric field across the dye molecules changes upon illumination. This result has important implications for the analysis of transient absorption spectra of DSCs and other molecular optoelectronic devices and challenges the interpretation of many previously published results.

  • 19.
    Carlmark, Anna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Malmström, Eva
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Atom transfer radical polymerization from cellulose fibers at ambient temperature2002In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 124, no 6, p. 900-901Article in journal (Refereed)
    Abstract [en]

    Cellulose fibers have been successfully grafted with poly(methyl acrylate) using atom transfer radical polymerization, mediated by Me6-TREN and Cu(I)Br at ambient temperature. The initially hydrophilic cellulose was first modified by reacting the hydrozyl groups with 2-bromoisobutyryl bromide whereupon methyl acrylate was grafted from the surface. The resulting polymer-grafted papers were extremely hydrophobic, θa = 133°. FT-IR analysis indicates that the amount of grafted polymer can be controlled by adding sacrificial initiator to the polymerizing system. Size exclusion chromatography of the bulk polymer revealed narrow polydispersities and a molecular weight corresponding to the ratio [M]:[I].

  • 20. Crespo, Gaston A.
    et al.
    Mistlberger, Guenter
    Bakker, Eric
    Electrogenerated Chemiluminescence for Potentiometric Sensors2012In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 1, p. 205-207Article in journal (Refereed)
  • 21. Danila, Ion
    et al.
    Riobe, Francois
    Piron, Flavia
    Puigmarti-Luis, Josep
    Wallis, John D.
    Linares, Mathieu
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Beljonne, David
    Amabilino, David B.
    Avarvari, Narcis
    Hierarchical Chiral Expression from the Nano- to Mesoscale in Synthetic Supramolecular Helical Fibers of a Nonamphiphilic C(3)-Symmetrical pi-Functional Molecule2011In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 21, p. 8344-8353Article in journal (Refereed)
    Abstract [en]

    The controlled preparation of chiral structures is a contemporary challenge for supramolecular science because of the interesting properties that can arise from the resulting materials, and here we show that a synthetic nonamphiphilic C(3) compound containing pi-functional tetrathiafulvalene units can form this kind of object. We describe the synthesis, characterization, and self-assembly properties in solution and in the solid state of the enantiopure materials. Circular dichroism (CD) measurements show optical activity resulting from the presence of twisted stacks of preferential helicity and also reveal the critical importance of fiber nucleation in their formation. Molecular mechanics (MM) and molecular dynamics (MD) simulations combined with CD theoretical calculations demonstrate that the (5) enantiomer provides the (M) helix, which is more stable than the (P) helix for this enantiomer. This relationship is for the first time established in this family of C(3) symmetric compounds. In addition, we show that introduction of the "wrong" enantiomer in a stack decreases the helical reversal barrier in a nonlinear manner, which very probably accounts for the absence of a "majority rules" effect. Mesoscopic chiral fibers, which show inverted helicity, i.e. (P) for the (S) enantiomer and (M) for the (R) one, have been obtained upon reprecipitation from dioxane and analyzed by optical and electronic microscopy. The fibers obtained with the racemic mixture present, as a remarkable feature, opposite homochiral domains within the same fiber, separated by points of helical reversal. Their formation can be explained through an "oscillating" crystallization mechanism. Although C(3) symmetric disk-shaped molecules containing a central benzene core substituted in the 1,3,5 positions with 3,3'-diamido-2,2'-bipyridine based wedges have shown peculiar self-assembly properties for amphiphilic derivatives, the present result shows the benefits of reducing the nonfunctional part of the molecule, in our case with short chiral isopentyl chains. The research reported herein represents an important step toward the preparation of functional mesostructures with controlled helical architectures.

  • 22.
    Dincbas-Renqvist, Vildan
    et al.
    KTH, Superseded Departments, Biotechnology.
    Lendel, Christofer
    KTH, School of Biotechnology (BIO).
    Dogan, Jakob
    KTH, Superseded Departments, Biotechnology.
    Wahlberg, Elisabet
    KTH, Superseded Departments, Biotechnology.
    Härd, Torleif
    Göteborgs Universitet.
    Thermodynamics of folding, stabilization, and binding in an engineered protein-protein complex2004In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, no 36, p. 11220-11230Article in journal (Refereed)
    Abstract [en]

    We analyzed the thermodynamics of a complex protein-protein binding interaction using the (engineered) Z(SPA-1) affibody and it's Z domain binding partner as a model. Free Z(SPA-1) exists in an equilibrium between a molten-globule-like (MG) state and a completely unfolded state, wheras a well-ordered structure is observed in the Z:Z(SPA-1) complex. The thermodynamics of the MG state unfolding equilibrium can be separated from the thermodynamics of binding and stabilization by combined analysis of isothermal titration calorimetry data and a separate van't Hoff analysis of thermal unfolding. We find that (i) the unfolding equilibrium of free Z(SPA-1) has only a small influence on effective binding affinity, that (ii) the Z:Z(SPA-1) interface is inconspicuous and structure-based energetics calculations suggest that it should be capable of supporting strong binding, but that (iii) the conformational stabilization of the MG state to a well-ordered structure in the Z:Z(SPA-1) complex is associated with a large change in conformational entropy that opposes binding.

  • 23.
    Dong, Hai
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Rahm, Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Ramström, Olof
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Supramolecular Control in Carbohydrate Epimerization: Discovery of a New Anion Host−Guest System2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, p. 15270-15271Article in journal (Refereed)
    Abstract [en]

    A new anion-carbohydrate recognition system is described. Pyranosides with axial protons in 1-, 3-, and 5-position proved efficient, forming relatively strong complexes between the anion and the B-face of the carbohydrate. This system could furthermore be used in supramolecular control in Lattrell-Dax epimerization reactions, leading to either activation or deactivation effects.

  • 24.
    Duan, Lele
    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.
    Xu, Yunhua
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Isolated Seven-Coordinate Ru(IV) Dimer Complex with HOHOH (-) Bridging Ligand as an Intermediate for Catalytic Water Oxidation2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 30, p. 10397-+Article in journal (Refereed)
    Abstract [en]

    With the inspiration from an oxygen evolving complex (OEC) in Photosystern II (PSII), a mononuclear Ru(II) complex with a tetradentate ligand containing two carboxylate groups has been synthesized and structurally characterized. This Ru(II) complex showed efficient catalytic properties toward water oxidation by the chemical oxidant cerium(IV) ammonium nitrate. During the process of catalytic water oxidation, Ru(III) and Ru(IV) species have been successfully isolated as intermediates. To our surprise, X-ray crystallography together with HR-MS revealed that the Ru(IV) species is a seven-coordinate Ru(IV) dimer complex containing a [HOHOH](-) bridging ligand. This bridging ligand has a short O center dot center dot center dot O distance and is hydrogen bonded to two water molecules. The discovery of this very uncommon seven-coordinate Ru(IV) dimer together with a hydrogen bonding network may contribute to a deeper understanding of the mechanism for catalytic water oxidation. It will also provide new possibilities for the design of more efficient catalysts for water oxidation, which is the key step for solar energy conversion into hydrogen by tight-driven water splitting, the ultimate challenge in artificial photosynthesis.

  • 25.
    Duan, Sai
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Tian, Guangjun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Shao, Jiushu
    Dong, Zhenchao
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Theoretical Modeling of Plasmon-Enhanced Raman Images of a Single Molecule with Subnanometer Resolution2015In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 137, no 30, p. 9515-9518Article in journal (Refereed)
    Abstract [en]

    Under local plasmonic excitation, Raman images of single molecules can now surprisingly reach subnanometer resolution. However, its physical origin has not been fully understood. Here we report a quantum-mechanical description of the interaction between a molecule and a highly confined plasmonic field. We show that When the spatial distribution of the plasmonic field is comparable to the size of the molecule, the optical transition matrix of the molecule becomes dependent on the position and distribution of the plasmonic field, resulting in a spatially resolved high-resolution Raman image of the molecule. The resonant Raman image reflects the electronic transition density of the molecule. In combination with first-principles calculations, the simulated Raman linage of a porphyrin derivative adsorbed on a silver surface nicely reproduces its experimental counterpart. The present theory provides the basic framework for describing linear and nonlinear responses of molecules under highly confined plasmonic fields.

  • 26. Dvinskikh, Sergey V.
    et al.
    Durr, U.
    Yamamoto, K.
    Ramamoorthy, A.
    A high-resolution solid-state NMR approach for the structural studies of bicelles2006In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 19, p. 6326-6327Article in journal (Refereed)
  • 27. Dvinskikh, Sergey V.
    et al.
    Durr, Ulrich H. N.
    Yamamoto, Kazutoshi
    Ramamoorthy, Ayyalusamy
    High-resolution 2D NMR spectroscopy of bicelles to measure the membrane interaction of ligands2007In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129, no 4, p. 794-802Article in journal (Refereed)
    Abstract [en]

    Magnetically aligned bicelles are increasingly being used as model membranes in solution- and solid-state NMR studies of the structure, dynamics, topology, and interaction of membrane-associated peptides and proteins. These studies commonly utilize the PISEMA pulse sequence to measure dipolar coupling and chemical shift, the two key parameters used in subsequent structural analysis. In the present study, we demonstrate that the PISEMA and other rotating-frame pulse sequences are not suitable for the measurement of long-range heteronuclear dipolar couplings, and that they provide inaccurate values when multiple protons are coupled to a C-13 nucleus. Furthermore, we demonstrate that a laboratory-frame separated-local-field experiment is capable of overcoming these difficulties in magnetically aligned bicelles. An extension of this approach to accurately measure C-13-P-31 and H-1-P-31 couplings from phospholipids, which are useful to understand the interaction of molecules with the membrane, is also described. In these 2D experiments, natural abundance C-13 was observed from bicelles containing DMPC and DHPC lipid molecules. As a first application, these solid-state NMR approaches were utilized to probe the membrane interaction of an antidepressant molecule, desipramine, and its location in the membrane.

  • 28.
    Edlund, Ulrica
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Källrot, Martina
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Single-Step Covalent Functionalization of Polylactide Surfaces2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 24, p. 8865-8871Article in journal (Refereed)
    Abstract [en]

    A single-step, nondestructive, and versatile technique for the grafting and chemical surface modification of biodegradable polymers such as polylacticle is described. The substrates are subjected to the vapor phase of any of three investigated vinyl monomers: acrylamide, maleic anhydride, and N-vinylpyrrolidone, and grafting is induced by photoinitiation of benzophenone under solvent free conditions. The modified surfaces exhibit higher wettability, and the grafting is verified by X-ray photoelectron spectroscopy, attenuated total reflection Fourier-transform IR, contact-angle measurements, and scanning electron microscopy. The graft-chain pendant groups remain functional and can subsequently be modified so that a tailor-made surface with desired properties may be achieved.

  • 29. Ellis, W. Chadwick
    et al.
    Tran, Camly T.
    Denardo, Matthew A.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Ryabov, Alexander D.
    Collins, Terrence J.
    Design of More Powerful Iron-TAML Peroxidase Enzyme Mimics2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 50, p. 18052-+Article in journal (Refereed)
    Abstract [en]

    Environmentally useful, small molecule mimics of the peroxidase enzymes must exhibit very high reactivity in water near neutral pH. Here we describe the design and structural and kinetic characterization of a second generation of iron(III)-TAML activators with unprecedented peroxidase-mimicking abilities. Iterative design has been used to remove the fluorine that led to the best performers in first-generation iron-TAMLs. The result is a superior catalyst that meets a green chemistry objective by being comprised exclusively of biochemically common elements. The rate constants for bleaching at pH 7, 9, and 11 of the model substrate, Orange 11, shows that the new Fe-III-TAML has the fastest reactivity at pH's closer to neutral of any TAML activator to date. Under appropriate conditions, the new catalyst can decolorize Orange 11 without loss of activity for at least 10 half-lives, attesting to its exceptional properties as an oxidizing enzyme mimic.

  • 30. Ellis, W. Chadwick
    et al.
    Tran, Camly T.
    Roy, Riddhi
    Rusten, Marte
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Ryabov, Alexander D.
    Blumberg, Bruce
    Collins, Terrence J.
    Designing Green Oxidation Catalysts for Purifying Environmental Waters2010In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 28, p. 9774-9781Article in journal (Refereed)
    Abstract [en]

    We describe the synthesis, characterization, aqueous behavior, and catalytic activity of a new generation of Fe-III-TAML (tetraamido macrocycle ligand) activators of peroxides (2), variants of [Fe{(OC)(2)(o,o'-NC6H4NCO)(2)CMe2}(OH2)(-)] (2d), which have been designed to be especially suitable for purifying water of recalcitrant oxidizable pollutants. Activation of H2O2 by 2 (k(I)) as a function of pH was analyzed via kinetic studies of Orange II bleaching. This was compared with the known behavior of the first generation of Fe-III-TAMLs (1). Novel reactivity features impact the potential for oxidant activation for water purification by 2d and its aromatic ring-substituted dinitro (2e) and tetrachloro (2f) derivatives. Thus, the maximum activity for 2e occurs at pH 9, the closest yet to the EPA guidelines for drinking water (6.5-8.5), allowing 2e to rapidly activate H2O2 at pH 7.7. In water, 2e has two axial water ligands with pK(a)'s of 8.4 and 10.0 (25 degrees C). The former is the lowest for all Fe-III-TAMLs developed to date and is key to 2e's exceptional catalytic activity in neutral and slightly basic solutions. Below pH 7, 2d was found to be quite sensitive to demetalation in phosphate buffers. This was overcome by iterative design to give 2e (hydrolysis rate 2d > 100 x 2e). Mechanistic studies highlight 2e's increased stability by establishing that to demetalate 2e at a comparable rate to which H2PO4- demetalates 2d, H3PO4 is required. A critical criterion for green catalysts for water purification is the avoidance of endocrine disruptors, which can impair aquatic life. Fe-III-TAMLs do not alter transcription mediated by mammalian thyroid, androgen, or estrogen hormone receptors, suggesting that 2 do not bind to the receptors and reducing concerns that the catalysts might have endocrine disrupting activity.

  • 31. Feldt, Sandra M.
    et al.
    Gibson, Elizabeth A.
    Gabrielsson, Erik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Design of Organic Dyes and Cobalt Polypyridine Redox Mediators for High-Efficiency Dye-Sensitized Solar Cells2010In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 46, p. 16714-16724Article in journal (Refereed)
    Abstract [en]

    Dye-sensitized solar cells (DSCs) with cobalt-based mediators with efficiencies surpassing the record for DSCs with iodide-free electrolytes were developed by selecting a suitable combination of a cobalt polypyridine complex and an organic sensitizer. The effect of the steric properties of two triphenylamine-based organic sensitizers and a series of cobalt polypyridine redox mediators on the overall device performance in DSCs as well as on transport and recombination processes in these devices was compared. The recombination and mass-transport limitations that, previously, have been found to limit the performance of these mediators were avoided by matching the properties of the dye and the cobalt redox mediator. Organic dyes with higher extinction coefficients than the standard ruthenium sensitizers were employed in DSCs in combination with outer-sphere redox mediators, enabling thinner TiO2 films to be used. Recombination was reduced further by introducing insulating butoxyl chains on the dye rather than on the cobalt redox mediator, enabling redox couples with higher diffusion coefficients and more suitable redox potential to be used, simultaneously improving the photocurrent and photovoltage of the device. Optimization of DSCs sensitized with a triphenylamine-based organic dye in combination with tris(2,2'-bipyridyl)cobalt(II/III) yielded solar cells with overall conversion efficiencies of 6.7% and open-circuit potentials of more than 0.9 V under 1000 W m(-2) AM1.5 G illumination. Excellent performance was also found under low light intensity indoor conditions.

  • 32. Franzen, Johan.
    et al.
    Marigo, M.
    Fielenbach, D.
    Wabnitz, T. C.
    Kjaersgaard, A.
    Jorgensen, K. A.
    A general organocatalyst for direct alpha-functionalization of aldehydes: Stereoselective C-C, C-N, C-F, C-BR, and C-S bond-forming reactions. Scope and mechanistic insights2005In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, no 51, p. 18296-18304Article in journal (Refereed)
    Abstract [en]

    The development of a general organocatalyst for the alpha-functionalization of aldehydes, via an enamine intermediate, is presented. Based on optically active alpha,alpha-diarylprolinol silyl ethers, the scope and applications of this catalyst for the stereogenic formation of C-C, C-N, C-F, C-Br, and C-S bonds are outlined. The reactions all proceed in good to high yields and with excellent enantioselectivities. Furthermore, we will present mechanistic insight into the reaction course applying nonlinear effect studies, kinetic resolution, and computational investigations leading to an understanding of the properties of the alpha,alpha-diarylprolinol silyl ether catalysts.

  • 33. Franzén, Johan
    et al.
    Bäckvall, Jan-Erik
    Carbon-carbon bond formation in palladium(II)-catalyzed allylic oxidation: A novel oxidative carbocyclization of allene-substituted olefins2003In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 125, no 20, p. 6056-6057Article in journal (Refereed)
    Abstract [en]

    A new efficient palladium(II)-catalyzed oxidative carbocyclization has been developed. It was found that allene-substituted olefins 1 cyclized in the presence of 1 mol % Pd(O2CCF3)2 and p-benzoquinone (2 equiv) to give bicyclic ring systems 2 in good to excellent yields. The cyclization constitutes a new type of carbon−carbon bond forming reaction between an allene and an olefin under oxidative conditions.

  • 34. Franzén, Johan
    et al.
    Löfstedt, Joakim
    Dorange, Ismet
    Bäckvall, Jan-E
    Allenes as carbon nucleophiles in palladium-catalyzed reactions: Observation of anti attack of allenes on (pi-allyl)palladium complexes2002In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 124, no 38, p. 11246-11247Article in journal (Refereed)
    Abstract [en]

    In the palladium-catalyzed cyclization of allenic allylic esters using Pd(dba)2 as catalyst, it was shown that the allene acts as a carbon nucleophile. Intermediates were isolated and stereochemical studies established that the double bond of the allene has attacked the (π-allyl)palladium intermediate on the face opposite to that of palladium.

  • 35. Franzén, Johan
    et al.
    Löfstedt, Joakim
    Falk, Jennica
    Bäckvall, Jan Erling
    Stereoselective palladium-catalyzed carbocyclization of allenic allylic carboxylates2003In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 125, no 46, p. 14140-14148Article in journal (Refereed)
    Abstract [en]

    Palladium(0)-catalyzed reaction of allene-substituted allylic carboxylates 3-8 employing 2-5 mol % of Pd(dba)(2) in refluxing toluene leads to the carbocyclization and elimination of carboxylic acid to give bicyclo[4.3.0]nonadiene and bicyclo[5.3.0]decadiene derivatives (12-17). The carbon-carbon bond formation is stereospecific, occurring syn with respect to the leaving group. Addition of maleic anhydride as a ligand to the above-mentioned procedures changed the outcome of the reaction, and under these conditions 3-5 afforded cycloisomerized products 21-23. The experimental results are consistent with a mechanism involving oxidative addition of the allylic carboxylate to Pd(0) to give an electron-deficient (pi-allyl)palladium intermediate, followed by nucleophilic attack by the allene on the face of the pi-allyl opposite to that of the palladium atom. Furthermore, it was found that the Pd(dba)(2)-catalyzed cyclization of the trans-cycloheptene derivative (trans-8) can be directed to give either the trans-fused (trans-17) or the cis-fused (cis-17) ring system by altering the solvent. The former reaction proceeds via a nucleophilic trans-allene attack on the (pi-allyl)palladium intermediate, whereas the latter involves a syn-allene insertion into the allyl-Pd bond of the same intermediate. The products from the carbocylization undergo stereoselective Diels-Alder reactions to give stereodefined polycyclic systems in high yields.

  • 36. Gao, Yan
    et al.
    Ding, Xin
    Liu, Jianhui
    Wang, Lei
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Lu, Zhongkai
    Li, Lin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Visible Light Driven Water Splitting in a Molecular Device with Unprecedentedly High Photocurrent Density2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 11, p. 4219-4222Article in journal (Refereed)
    Abstract [en]

    A molecular water oxidation catalyst (2) has been synthesized and immobilized together with a molecular photosensitizer (1) on nanostructured TiO2 particles on FTO conducting glass, forming a photoactive anode (TiO2(1+2)). By using the TiO2(1+2) as working electrode in a three-electrode photoelectrochemical cell (PEC), visible light driven water splitting has been successfully demonstrated in a phosphate buffer solution (pH 6.8), with oxygen and hydrogen bubbles evolved respectively from the working electrode and counter electrode. By applying 0.2 V external bias vs NHE, a high photocurrent density of more than 1.7 rnA.cm(-2) has been achieved. This value is higher than any PEC devices with molecular components reported in literature.

  • 37. Gao, Yan
    et al.
    Åkermark, Torbjörn
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Liu, Jianhui
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Åkermark, Björn
    Nucleophilic Attack of Hydroxide on a Mn-V Oxo Complex: A Model of the O-O Bond Formation in the Oxygen Evolving Complex of Photosystem II2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 25, p. 8726-+Article in journal (Refereed)
    Abstract [en]

    A manganese(III) corrole complex, 1, has been synthesized and used to study a potential mechanism for oxidation of water to molecular oxygen. Oxidation by t-BuOOH gave the Mn-V=O complex 2. Addition of hydroxide Led to release of oxygen via the Mn-IV complex 4 and regeneration of complex 1. It could be shown that the oxygen from O-18-labeted water was incorporated in both the formed molecular oxygen and the peroxy intermediate 4.

  • 38.
    Gardner, James M.
    et al.
    Johns Hopkins University.
    Abrahamsson, Maria
    Johns Hopkins University.
    Farnum, Byron H.
    Johns Hopkins University.
    Meyer, Gerald J.
    Johns Hopkins University.
    Visible Light Generation of Iodine Atoms and I-ˆ’I Bonds: Sensitized I-ˆ’ Oxidation and I3-ˆ’ Photodissociation2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 44, p. 16206-16214Article in journal (Refereed)
    Abstract [en]

    Direct 355 or 532 nm light excitation of TBAI3, where TBA is tetrabutyl ammonium, in CH3CN at room temperature yields an iodine atom, I?, and an iodine radical anion, I2??. In the presence of excess iodide, the iodine atom reacts quantitatively to yield a second equivalent of I2?? with a rate constant of k = 2.5 ± 0.4 ? 1010 M?1 s?1. The I2?? intermediates are unstable with respect to disproportionation and yield initial reactants, k = 3.3 ± 0.1 ? 109 M?1 s?1. The coordination compound Ru(bpz)2(deeb)(PF6)2, where bpz is 2,2?-bipyrazine and deeb is 4,4?-(C2H5CO2)2-2,2?-bipyridine, was prepared and characterized for mechanistic studies of iodide photo-oxidation in acetonitrile at room temperature. Ru(bpz)2(deeb)2+ displayed a broad metal-to-ligand charge transfer (MLCT) absorption band at 450 nm with ε = 1.7 ? 104 M?1 cm?1. Visible light excitation resulted in photoluminescence with a corrected maximum at 620 nm, a quantum yield ? = 0.14, and an excited state lifetime τ = 1.75 ?s from which kr = 8.36 ? 104 s?1 and knr = 5.01 ? 105 s?1 were abstracted. Arrhenius analysis of the temperature dependent excited state lifetime revealed an activation energy of ?2500 cm?1 and a pre-exponential factor of 1010 s?1, assigned to activated surface crossing to a ligand field or MLCT excited state. Steady state light excitation of Ru(bpz)2(deeb)2+ in a 20 mM TBAI acetonitrile solution resulted in ligand loss photochemistry with a quantum yield of 5 ? 10?5. The MLCT excited state was dynamically quenched by iodide with Ksv = 1.1 ? 105 M?1 and kq = 6.6 ± 0.3 ? 1010 M?1 s?1, a value consistent with diffusion-limited electron transfer. Excited state hole transfer to iodide was quantitative but the product yield was low due to poor cage escape yields, ?CE = 0.042 ± 0.001. Nanosecond transient absorption was used to quantify the appearance of two photoproducts [Ru(bpz?)(bpz)(deeb)]+ and I2??. The coincidence of the rate constants for [Ru(bpz?)(bpz)(deeb)]+ formation and for excited state decay indicated reductive quenching by iodide. The rate constant for the appearance of I2?? was about a factor of 3 slower than excited state decay, k = 2.4 ± 0.2 ? 1010 M?1 s?1, indicating that I2?? was not a primary photoproduct of excited state electron transfer. A mechanism was proposed where an iodine atom was the primary photoproduct that subsequently reacted with iodide, I? + I? ? I2??. Charge recombination Ru(bpz?)(bpz)(deeb)+ + I2?? ? Ru(bpz)2(deeb)2+ + 2I? was highly favored, ?Go = ?1.64 eV, and well described by a second-order equal concentration kinetic model, kcr = 2.1 ± 0.3 ? 1010 M?1 s?1.

  • 39.
    Gardner, James M
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Beyler, Maryline
    Uppsala University.
    Karnahl, Michael
    Uppsala University.
    Tschierlei, Stefanie
    Uppsala University.
    Ott, Sascha
    Uppsala University.
    Hammarström, Leif
    Uppsala University.
    Light-Driven Electron Transfer between a Photosensitizer and a Proton-Reducing Catalyst Co-adsorbed to NiO2012In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 47, p. 19322-19325Article in journal (Refereed)
    Abstract [en]

    While intermolecular hole-hopping along the surface of semiconductors is known, there are no previous examples of electron-hopping between molecules on a surface. Herein, we present the first evidence of electron transfer from the photoreduced sensitizer Coumarin-343 (C343) to complex 1, both bound on the surface of NiO. In solution, 1 has been shown to be a mononuclear Fe-based proton-reducing catalyst. The reduction of 1 is reversible and occurs within 50 ns after excitation of C343. Interfacial recombination between the reduced 1(-) and NiO hole occurs on a 100 µs time scale by non-exponential kinetics. The observed process is the first essential step in the photosensitized generation of H2 from a molecular catalyst in the absence of a sacrificial donor reagent.

  • 40.
    Gardner, James M.
    et al.
    Johns Hopkins University.
    Giaimuccio, Jovan M.
    Johns Hopkins University.
    Meyer, Gerald J.
    Johns Hopkins University.
    Evidence for Iodine Atoms as Intermediates in the Dye Sensitized Formation of I-ˆ’I Bonds2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 51, p. 17252-17253Article in journal (Refereed)
    Abstract [en]

    Visible light excitation of [Ru(bpz)2(deeb)](PF6)2, where bpz is 2,2?-bipyrazine and deeb is 4,4?-(CO2Et)2-2,2?-bipyridine, in acetonitrile solutions with iodide is shown to initiate excited-state electron transfer reactions that yield iodine atoms. The iodine atoms subsequently react with iodide to form the I?I bond in I2??. The resultant Ru(bpz?)(bpz)(deeb)+, I2?? stores ?1.64 eV of free energy and returns cleanly to ground-state products with kcr = (2.1 ± 0.3) ? 1010 M?1 s?1.

  • 41.
    Ghiringhelli, Luca M
    et al.
    Max-Planck-Institute for Polymer Research, Mainz, Germany.
    Hess, Berk
    Max-Planck-Institute for Polymer Research, Mainz, Germany.
    van der Vegt, Nico F A
    Max-Planck-Institute for Polymer Research, Mainz, Germany.
    Delle Site, Luigi
    Max-Planck-Institute for Polymer Research, Mainz, Germany.
    Competing adsorption between hydrated peptides and water onto metal surfaces: from electronic to conformational properties2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 40, p. 13460-13464Article in journal (Refereed)
    Abstract [en]

    Inorganic-(bio)organic interfaces are of central importance in many fields of current research. Theoretical and computational tools face the difficult problem of the different time and length scales that are involved and linked in a nontrivial way. In this work, a recently proposed hierarchical quantum-classical scale-bridging approach is further developed to study large flexible molecules. The approach is then applied to study the adsorption of oligopeptides on a hydrophilic Pt(111) surface under complete wetting conditions. We examine histidine sequences, which are well known for their binding affinity to metal surfaces. Based on a comparison with phenylalanine, which binds as strong as histidine under high vacuum conditions but, as we show, has no surface affinity under wet conditions, we illustrate the mediating effects of near-surface water molecules. These contribute significantly to the mechanism and strength of peptide binding. In addition to providing physical-chemical insights in the mechanism of surface binding, our computational approach provides future opportunities for surface-specific sequence design.

  • 42.
    Gioia, Claudio
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Lo Re, Giada
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Lawoko, Martin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Berglund, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Tunable thermosetting epoxies based on fractionated and well-characterized lignins2018In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126Article in journal (Refereed)
  • 43. Goldstein, S.
    et al.
    Merenyi, Gabor
    KTH, Superseded Departments, Chemistry.
    Russo, A.
    Samuni, A.
    The role of oxoammonium cation in the SOD-Mimic activity of cyclic nitroxides2003In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 125, no 3, p. 789-795Article in journal (Refereed)
    Abstract [en]

    Cyclic nitroxides (RNO.) mimic the activity of superoxide dismutase (SOD) and demonstrate antioxidant properties in numerous in vitro and in vivo models. Their broad antioxidant activity may involve the participation of their reduced and oxidized forms, that is, hydroxylamine (RNO-H) and oxoammonium cation (RNO+). To examine this possibility we studied the reactions of RNO+ and RNO+ with HO2./O-2(.-) and with several reductants by pulse radiolysis and rapid-mixing stopped-flow techniques. The oxoammonium cations were generated by electrochemical and radiolytic oxidation of 2,2,6,6-tetramethylpiperidinoxyl (TPO) and 3-carbamoyl-2,2,5,5-tetramethylpyrrolidinoxyl (3-CP). The rate constant for the reaction of RNO. with HO2. to form RNO+ was determined to be (1.2 +/- 0.1) x 10(8) for TPO and (1.3 +/- 0.1) x 10(6) M-1 s(-1) for 3-CP. The kinetics results demonstrate that the reaction of RNO. with HO2. proceeds via an inner-sphere electron-transfer mechanism. The rate constant for the reaction of RNO. with O-2(.-) is lower than 1 x 10(3) M-1 s(-1). The rate constant for the reaction of RNO+ with O-2(.-) was determined to be (3.4 +/- 0.2) x 10(9) for TPO+ and (5.0 +/- 0.2) x 10(9) M-1 s(-1) for 3-CP+. Hence, both nitroxides catalyze the dismutation of superoxide through the RNO./RNO+ redox couple, and the dependence of the catalytic rate constant, k(cat), on pH displayed a bell-shaped curve having a maximum around pH 4. The oxoammonium cation oxidized ferrocyanide and HO2- by a one-electron transfer, whereas the oxidation of methanol, formate, and NADH proceeded through a two-electron-transfer reaction. The redox potential of RNO./RNO+ couple was calculated to be 0.75 and 0.89 V for 3-CP and TPO, respectively. The elucidated mechanism provides a clearer insight into the biological antioxidant properties of cyclic nitroxides that should permit design of even more effective antioxidants.

  • 44. Goldstein, S.
    et al.
    Merenyi, Gabor
    KTH, Superseded Departments, Chemistry.
    Samuni, A.
    Kinetics and mechanism of (NO2)-N-. reacting with various oxidation states of myoglobin2004In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, no 48, p. 15694-15701Article in journal (Refereed)
    Abstract [en]

    Nitrogen dioxide ((NO2)-N-.) participates in a variety of biological reactions. Of great interest are the reactions of (NO2)-N-. with oxymyoglobin and oxyhemoglobin, which are the predominant hemeproteins in biological systems. Although these reactions occur rapidly during the nitrite-catalyzed autoxidation of hemeproteins, their roles in systems producing (NO2)-N-. in the presence of these hemeproteins have been greatly underestimated. In the present study, we employed pulse radiolysis to study directly the kinetics and mechanism of the reaction of oxymyoglobin (MbFe(II)O(2)) with (NO2)-N-.. The rate constant of this reaction was determined to be (4.5 +/- 0.3) x 10(7) M(-1)s(-1), and is among the highest rate constants measured for (NO2)-N-. with any biomolecule at pH 7.4. The interconversion among the various oxidation states of myoglobin that is prompted by nitrogen oxide species is remarkable. The reaction of MbFeIIO(2) with (NO2)-N-. forms MbFeIIIOONO(2), which undergoes rapid heterolysis along the O-O bond to yield MbFe(V)=O and NO3-. The perferryl-myoglobin (MbFe(V=)O) transforms rapidly into the ferryl species that has a radical site on the globin ((.)MbFe(IV)=O). The latter oxidizes another oxymyoglobin (10(4) M(-1)s(-1) < k(17) < 10(7) M(-1)s(-1)) and generates equal amounts of ferrylmyoglobin and metmyoglobin. At much longer times, the ferrylmyoglobin disappears through a relatively slow comproportionation with oxymyoglobin (k(18) = 21.3 +/- 5.3 M(-1)s(-1)). Eventually, each (NO2)-N-. radical converts three oxymyoglobin molecules into metmyoglobin. The same intermediate, namely MbFe(III)OONO(2), is also formed via the reaction peroxynitrate (O2NOO-/O2NOOH) with metmyoglobin (k(19) = (4.6 +/- 0.3) x 10(4) M(-1)s(-1)). The reaction of (NO2)-N-. With ferrylmyoglobin (k(20) = (1.2 +/- 0.2) x 10(7) M(-1)s(-1)) yields MbFe(III)ONO(2), which in turn dissociates (k(21) = 190 +/- 20 s(-1)) into metmyoglobin and NO3-. This rate constant was found to be the same as that measured for the decay of the intermediate formed in the reaction of MbFe(II)O(2) with (NO2)-N-. which suggests that MbFe(III)ONO(2) is the intermediate observed in both processes. This conclusion is supported by thermokinetic arguments. The present results suggest that hemeproteins may detoxify (NO2)-N-. and thus preempt deleterious processes, such as nitration of proteins. Such a possibility is substantiated by the observation that the reactions of NO2 with the various oxidation states of myoglobin lead to the formation of metmyoglobin, which, though not functional in the gas transport, is nevertheless nontoxic at physiological pH.

  • 45. Groenhof, Gerrit
    et al.
    Bouxin-Cademartory, Mathieu
    Hess, Berk
    De Visser, Sam P
    Berendsen, Herman J C
    Olivucci, Massimo
    Mark, Alan E
    Robb, Michael A
    Photoactivation of the photoactive yellow protein: why photon absorption triggers a trans-to-cis Isomerization of the chromophore in the protein.2004In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, no 13, p. 4228-4233Article in journal (Refereed)
    Abstract [en]

    Atomistic QM/MM simulations have been carried out on the complete photocycle of Photoactive Yellow Protein, a bacterial photoreceptor, in which blue light triggers isomerization of a covalently bound chromophore. The "chemical role" of the protein cavity in the control of the photoisomerization step has been elucidated. Isomerization is facilitated due to preferential electrostatic stabilization of the chromophore's excited state by the guanidium group of Arg52, located just above the negatively charged chromophore ring. In vacuo isomerization does not occur. Isomerization of the double bond is enhanced relative to isomerization of a single bond due to the steric interactions between the phenyl ring of the chromophore and the side chains of Arg52 and Phe62. In the isomerized configuration (ground-state cis), a proton transfer from Glu46 to the chromophore is far more probable than in the initial configuration (ground-state trans). It is this proton transfer that initiates the conformational changes within the protein, which are believed to lead to signaling.

  • 46.
    Hagberg, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Marinado, Tannia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Karlsson, Karl Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Molecular Engineering of Organic Chromophores for Dye Sensitized Solar Cell Applications2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, p. 6259-6266Article in journal (Refereed)
    Abstract [en]

    Novel unsymmetrical organic sensitizers comprising donor, electron-conducting, and anchoring groups were engineered at a molecular level and synthesized for sensitization of mesoscopic titanium dioxide injection solar cells. The unsymmetrical organic sensitizers 3-(5-(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D5), 3-(5-bis(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D7), 5-(4-(bis(4-methoxyphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D9), and 3-(5-bis(4,4'-dimethoxydiphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D11) anchored onto TiO2 and were tested in dye-sensitized solar cell with a volatile electrolyte. The monochromatic incident photon-to-current conversion efficiency of these sensitizers is above 80%, and D11-sensitized solar cells yield a short-circuit photocurrent density of 13.90 +/- 0.2 mA/cm(2), an open-circuit voltage of 740 +/- 10 mV, and a fill factor of 0.70 +/- 0.02, corresponding to an overall conversion efficiency of 7.20% under standard AM 1.5 sun light. Detailed investigations of these sensitizers reveal that the long electron lifetime is responsible for differences in observed open-circuit potential of the cell. As an alternative to liquid electrolyte cells, a solid-state organic hole transporter is used in combination with the D9 sensitizer, which exhibited an efficiency of 3.25%. Density functional theory/time-dependent density functional theory calculations have been employed to gain insight into the electronic structure and excited states of the investigated species.

  • 47.
    Hakkarainen, Minna
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Höglund, Anders
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Albertsson, Ann-Christine
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Tuning the release rate of acidic degradation products through macromolecular design of caprolactone-based copolymers2007In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129, no 19, p. 6308-6312Article in journal (Refereed)
    Abstract [en]

    Macromolecular engineering is presented as a tool to control the degradation rate and release rate of acidic degradation products from biomedical polyester ethers. Three different caprolactone/1,5-dioxepan-2-one (CL/DXO) copolymers were synthesized: DXO/CL/DXO triblock, CL/DXO multiblock, and random cross-linked CL/DXO copolymer. The relation of CL and DXO units in all three copolymers was 60/40 mol %. The polymer discs were immersed in phosphate buffer solution at pH 7.4 and 37 degrees C for up to 364 days. After different time periods degradation products were extracted from the buffer solution and analyzed. In addition mass loss, water absorption, molecular weight changes, and changes in thermal properties were determined. The results show that the release rate of acidic degradation products, a possible cause of acidic microclimates and inflammatory responses, is controllable through macromolecular design, i.e., different distribution of the weak linkages in the copolymers.

  • 48.
    Hallberg, Fredrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Stilbs, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Ion Pairing in Ethanol/Water Solution Probed by Electrophoretic and Diffusion NMR2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 39, p. 13900-Article in journal (Refereed)
    Abstract [en]

    We demonstrate that a combination of electrophoretic NMR and diffusion NMR experiments can measure the average charge carried by ions in solution. This average charge is used as a quantitative indicator of ion pairing. Our results show that there is a Hofmeister relation in the ion pairing between monovalent anions and the tetramethylammonium cation in 95% ethanol/water solution. The ion pairing of the divalent sulfate ion was larger than that shown by any of the monovalent anions.

  • 49.
    Hallberg, Fredrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Weise, Christoph F.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Yushmanov, Pavel V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Thyboll Pettersson, Erik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Stilbs, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Molecular complexation and binding studied by electrophoretic NMR spectroscopy2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 24, p. 7550-+Article in journal (Refereed)
    Abstract [en]

    Electrophoretic mobilities obtained on a molecularly selective manner by electrophoretic NMR can be used to proved a quantitative characterization of the composition and stoichiometry of molecular complexes. This is demonstrated in complexes formed by uncharge cyclodextrins which attain an electrophoretic mobility upon inclusion of charged surfactants.

  • 50.
    Halldin Stenlid, Joakim
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Extending the σ-Hole Concept to Metals: An Electrostatic Interpretation of the Nanostructural Effects in Gold and Platinum Catalysis2017In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126Article in journal (Refereed)
    Abstract [en]

    Crystalline surfaces of gold are chemically inert, whereas nanoparticles of gold are excellent catalysts for many reactions. The catalytic properties of nanostructured gold have been connected to increased binding affinities of reactant molecules to low-coordinated Au atoms. Here we show that the high reactivity at these sites is a consequence of the formation of σ-holes, i.e. maxima in the surface electrostatic potential (Vs,max) due to the overlap of mainly the valence s-orbitals when forming the bonding σ-orbitals. The σ-holes are binding sites for Lewis bases, and binding energies correlate with magnitudes of the Vs,max. For symmetrical Au clusters, of varying size, the most positive Vs,max are found at corners, edges, and surfaces (facets) and decreasing in that order. This is in agreement with the experimentally and theoretically observed dependence of catalytic activity on local structure. The density of σ-holes can explain the increasing catalytic activity with decreasing particle size also for other transition metal catalysts, such as platinum.

1234 1 - 50 of 167
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