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  • 51.
    Halldin Stenlid, Joakim
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Johansson, Adam Johannes
    Leygraf, Christopher
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Computational Analysis of the Early Stage of Cuprous Oxide Sulphidation: A Top-Down Process2017Inngår i: Corrosion Engineering, Science and Technology, ISSN 1478-422X, E-ISSN 1743-2782, Vol. 52, nr S1, s. 50-53Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The initial steps of Cu2O sulphidation to Cu2S have been studied using plane-wave density functional theory at the PBE-D3+U level of sophistication. Surface adsorption and dissociation of H2S and H2O, as well as the replacement reaction of lattice oxygen with sulphur, have been investigated for the most stable (111) and (100) surface facets under oxygen-lean conditions. We find that the (100) surface is more susceptible to sulphidation than the (111) surface, promoting both H2S adsorption, dissociation and the continued oxygen–sulphur replacement. The results presented in this proceeding bridge previous results from high-vacuum experiments on ideal surface to more realistic corrosion conditions and set the grounds for future mechanistic studies. Potential implications on the long-term final disposal of spent nuclear fuel are discussed.

  • 52.
    Halldin Stenlid, Joakim
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Soldemo, Markus
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Johansson, A. J.
    Leygraf, Christofer
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
    Götelid, Mats
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Weissenrieder, Jonas
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Reactivity at the Cu2O(100):Cu-H2O interface: a combined DFT and PES study2016Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, nr 44, s. 30570-30584Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The water-cuprite interface plays an important role in dictating surface related properties. This not only applies to the oxide, but also to metallic copper, which is covered by an oxide film under typical operational conditions. In order to extend the currently scarce knowledge of the details of the water-oxide interplay, water interactions and reactions on a common Cu2O(100):Cu surface have been studied using high-resolution photoelectron spectroscopy (PES) as well as Hubbard U and dispersion corrected density functional theory (PBE-D3+U) calculations up to a bilayer water coverage. The PBE-D3+U results are compared with PBE, PBE-D3 and hybrid HSE06-D3 calculation results. Both computational and experimental results support a thermodynamically favored, and H2O coverage independent, surface OH coverage of 0.25-0.5 ML, which is larger than the previously reported value. The computations indicate that the results are consistent also for ambient temperatures under wet/humid and oxygen lean conditions. In addition, both DFT and PES results indicate that the initial (3,0; 1,1) surface reconstruction is lifted upon water adsorption to form an unreconstructed (1 x 1) Cu2O(100) structure.

  • 53. Holm, A. H.
    et al.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi (stängd 20110630).
    Daasbjerg, K.
    Elucidation of the thermochemical properties of triphenyl- or tributyl-substituted Si-, Ge-, and Sn-centered radicals by means of electrochemical approaches and computations2005Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 127, nr 8, s. 2677-2685Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Redox potentials of a number of triphenyl- or tributyl-substituted Si-, Ge-, or Sn-centered radicals, R3M., have been measured in acetonitrile, tetrahydrofuran, or dimethyl sulfoxide by photomodulated voltammetry or through a study of the oxidation process of the corresponding anions in linear sweep voltammetry. For the results pertaining to the Ph3M. series (including literature data for M = C), the order of reduction potentials follows Sn > Ge > C > Si, while for the two oxidation potentials, it is C > Si. The effect of the R group on the redox properties of R3Sn. is pronounced in that the reduction potential is more negative by 490 mV in tetrahydrofuran (390 mV in dimethyl sulfoxide) when R is a butyl rather than a phenyl group. The experimental trends have been substantiated through quantum chemical calculations, and they can be explained qualitatively by considering a combination of effects, such as charge capacity being most pronounced for the heavier elements, resonance stabilization present for the planar Ph3C. and all R3M+, and finally a contribution from solvation. The solvation of R3M- is observed to be relatively strong because of a rather localized negative charge in the pyramidal geometry. However, there is no evidence in the calculations to support the existence of covalent interactions between solvent and anions. The solvation of R3M+ is relatively weak, which may be attributed to the planar geometry around the center atom, leading to more spread out charge than that for a pyramidal geometry. Although the calculated solvation energies based on the polarizable continuum model approach exhibit the expected trends, they are not able to reproduce the experimentally derived values on a detailed level for these types of ions. An evaluation of the general performance of the continuum model is provided on the basis of present and previous studies.

  • 54. Holm, A. H.
    et al.
    Yusta, L.
    Carlqvist, P.
    Brinck, Tore
    KTH, Tidigare Institutioner                               , Kemi.
    Daasbjerg, K.
    Thermochemistry of arylselanyl radicals and the pertinent ions in acetonitrile2003Inngår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 125, nr 8, s. 2148-2157Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reduction and oxidation potentials of a series of parasubstituted phenylselanyl radicals, XC6H4Se*, have been measured using photomodulated voltammetry in acetonitrile. The thermodynamic significance of these data was substantiated through a study of the oxidation process of the pertinent selenolates in linear sweep voltammetry. Both the reduction and the oxidation potentials correlate linearly with the Hammett substituent coefficients sigma and sigma(+) leading in the latter case to slopes, rho(+), of 2.5 and 3.8, respectively. Through comparison of these slopes with those published previously for the O- and S-centered analogues, it is revealed that the pi-interaction becomes progressively smaller as the size of the radical center increases in the order O, S, and Se. Solvation energies of the pertinent selenolates and selanylium ions have been extracted from thermochemical cycles incorporating the measured electrode potentials for XC6H4Se* as well as electron affinities and ionization potentials obtained from theoretical calculations at the B3LYP/6-31+G(d) level. The extracted data show the expected overall substituent dependency for both kinds of ions; that is, the absolute value of the solvation energy decreases as the charge becomes more delocalized. The data have also been compared with solvation energies computed using the polarizable continuum model (PCM). Interestingly, we find that, while the model seems to work well for selenolates, it underestimates the solvation of selanylium ions in acetonitrile by as much as 25 kcal mol(-1). These large deviations are ascribed to the fact that the PCM method does not take specific solvent effects into account as it treats the solvent as a continuum described solely by its dielectric constant. Gas-phase calculations show that the arylselanylium ions can coordinate covalently to one or two molecules of acetonitrile in strong Ritter-type adducts. When this strong interaction is included in the solvation energy calculations by means of a combined supermolecule and PCM approach, the experimental data are reproduced within a few kcal mol-1. Although the energy difference of the singlet and triplet spin states of the arylselanylium ions is small for the gas-phase structures, the singlet cation is undoubtedly the dominating species in solution because the triplet cation lacks the ability to form covalent bonds.

  • 55.
    Ito, Mika
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Novel Approach for Identifying Key Residues in Enzymatic Reactions: Proton Abstraction in Ketosterbid Isomerase2014Inngår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, nr 46, s. 13050-13058Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose a computationally efficient approach for evaluating the individual contributions of many different residues to the catalytic efficiency of an enzymatic reaction. This approach is based on the fragment molecular orbital (FMO) method, and it defines the energy of a deletion form, i.e., the energy of the system when a particular residue is deleted. Using this approach, we found that, among 10 investigated residues, three, Tyr14, Asp99, and Tyr55, in this order, significantly reduce the activation energy of the proton abstraction from a substrate, cyclopent-2-enone, catalyzed by ketosteroid isomerase (KSI). The relative activation energies estimated in this study are in good agreement with available previous experimental and theoretical data obtained for the similar proton abstraction with a native substrate and substitution mutants of KSI. It was thus indicated that the new approach is efficient for rationally evaluating the catalytic effects of multiple residues on an enzymatic reaction.

  • 56. Jin, P.
    et al.
    Brinck, Tore
    KTH, Tidigare Institutioner                               , Kemi.
    Murray, J. S.
    Politzer, P.
    Computational prediction of relative group polarizabilities2003Inngår i: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 95, nr 05-apr, s. 632-637Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Earlier work has shown that molecular polarizabilities correlate well with the quantity V/(I) over bar (S,ave), where V is the volume of the molecule and (I) over bar (S,ave) is the average value of the local ionization energy on its surface. We now extend this to group polarizabilities; we computed V/(I) over bar (S,ave) for four common chemical groups (NO2, CH3, NH2, and OH) in a variety of molecules. The transferabilities of (I) over bar (S,ave), V, and V/(I) over bar (S,ave) are examined, as well as the correlation between V/(I) over bar (S,ave) and literature polarizabilities of CH3, NH2, and OH. This permits the value for NO2 to be predicted (alpha = 2.77 Angstrom(3)). The dependence of (I) over bar (S,ave), and therefore V/(I) over bar (S,ave), upon the remainder of the molecule is discussed.

  • 57.
    Johansson, Adam Johannes
    et al.
    Royal Inst Technol KTH, S-10044 Stockholm, Sweden..
    Lilja, Christina
    Swedish Nucl Fuel & Waste Management Co, SE-10124 Stockholm, Sweden..
    Brinck, Tore
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi. Royal Inst Technol KTH, S-10044 Stockholm, Sweden..
    Erratum to: On the formation of hydrogen gas on copper in anoxic water2012Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, nr 8Artikkel i tidsskrift (Fagfellevurdert)
  • 58.
    Johansson, Adam Johannes
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Lilja, Christina
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    On the formation of hydrogen gas on copper in anoxic water2011Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 135, nr 8, s. 084709-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrogen gas has been detected in a closed system containing copper and pure anoxic water [P. Szakalos, G. Hultquist, and G. Wikmark, Electrochem. Solid-State Lett. 10, C63 (2007) and G. Hultquist, P. Szakalos, M. Graham, A. Belonoshko, G. Sproule, L. Grasjo, P. Dorogokupets, B. Danilov, T. Aastrup, G. Wikmark, G. Chuah, J. Eriksson, and A. Rosengren, Catal. Lett. 132, 311 (2009)]. Although bulk corrosion into any of the known phases of copper is thermodynamically forbidden, the present paper shows how surface reactions lead to the formation of hydrogen gas in limited amounts. While water cleavage on copper has been reported and investigated before, formation of molecular hydrogen at a single-crystal Cu[100] surface is here explored using density functional theory and transition state theory. It is found that although solvent catalysis seems possible, the fastest route to the formation of molecular hydrogen is the direct combination of hydrogen atoms on the copper surface. The activation free energy (Delta G(s)double dagger(f)) of hydrogen formation in condensed phase is 0.70 eV, which corresponds to a rate constant of 10 s(-1) at 298.15 K, i.e., a relatively rapid process. It is estimated that at least 2.4 ng hydrogen gas could form per cm(2) on a perfect copper surface.

  • 59.
    Kleimark, Jonatan
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Delanoe, Romain
    Demaire, Alain
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Ionization of ammonium dinitramide: decomposition pathways and ionization products2013Inngår i: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 132, nr 12, s. UNSP 1412-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The decomposition pathways of ionized ammonium dinitramide (ADN) have been analyzed using the B3LYP and the M06-2X density functional theory methods, coupled cluster theory and the composite CBS-QB3 method. Ionization and subsequent decomposition of the major decomposition products have also been studied. The ADN(+) ion dissociates into the stable DN radical and NH4+ with a dissociation enthalpy of 50 kJ/mol. The subsequently formed DN+ ion has an activation enthalpy of 102 kJ/mol for decomposition into N2O, O-2 and NO+. A competing pathway for ionization and decomposition of ADN involves the HDN+ ion, which dissociates into NO2+ and HNNO2 with a barrier of only 17 kJ/mol. The ionization product HNNO2+ is stable toward further decomposition, and the barrier for isomerization to HONNO+ is 167 kJ/mol. The computed adibatic ionization potentials of ADN, HDN, DN and HNNO2 are 9.4, 11.5, 10.2 and 10.9 eV, respectively. The results of the study have implications for the future use of ADN in propellants for electromagnetic space propulsion.

  • 60. Koefoed, Line
    et al.
    Vase, Karina H.
    Halldin Stenlid, Joakim
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Yoshimura, Yuichi
    Lund, Henning
    Pedersen, Steen U.
    Daasbjerg, Kim
    On the Kinetic and Thermodynamic Properties of Aryl Radicals Using Electrochemical and Theoretical Approaches2017Inngår i: CHEMELECTROCHEM, ISSN 2196-0216, Vol. 4, nr 12, s. 3212-3221Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, sampled-current voltammetry performed on a series of aryldiazonium, diaryliodonium, and triarylsulfonium salts allows the determination of the reduction potential of aryl radicals in acetonitrile. Specifically, this is accomplished by measuring the number of electrons consumed in the reduction process as a function of the applied potential. For the phenyl, 4-bromophenyl, and 4-nitrophenyl radicals, the reduction potential is found to be -0.91 +/- 0.06, -0.90 +/- 0.10, and -0.98 +/- 0.06 V vs. SCE, respectively. Furthermore, from measurements on an extended series of substituted compounds, it is concluded that the substituent effect on the reduction potential is small, which can be explained by the sigma nature of the aryl radical as evidenced from theoretical calculations. At the same time this yields a mean value for the reduction potential of the aryl radical of -0.87 V +/- 0.03 V vs. SCE. Determination of the intrinsic barrier and the standard potential from the data obtained are more uncertain since it is unknown to which extent the competing reference reaction, the electrochemical grafting reaction, is affected by the applied potential. From calculations using density functional theory, the intrinsic barrier for the reduction of the phenyl radical is determined to be 0.32 eV.

  • 61. Kona, Juraj
    et al.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    A combined molecular dynamics simulation and quantum chemical study on the mechanism for activation of the OxyR transcription factor by hydrogen peroxide2006Inngår i: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 4, nr 18, s. 3468-3478Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Molecular dynamics (MD) simulations have been performed on the regulatory domain of the Escherichia coli OxyR transcription factor for the different chemical states along the mechanistic cycle for its activation by hydrogen peroxide. Conformational analysis indicates that His198 and Arg220 catalytic residues can be involved in the biochemical process of activation of OxyR. On the basis of the simulation data, a detailed mechanism for the oxidation process is suggested in which His198, in the presence of an arginine residue, functions as a unique acid - base catalyst in the successive oxidations of Cys199 and Cys208 by hydrogen peroxide. This mechanistic proposal has been tested by density functional theory (DFT-B3LYP) and ab initio (MP2) calculations on model systems. The two oxidations are both identified as nucleophilic substitution reactions of S(N)2 type with deprotonated cysteines functioning as nucleophiles. Both reactions have a calculated free energy of activation close to 15 kcal mol(-1), which is consistent with the available experimental data on the kinetics of the activation process.

  • 62.
    Laurell Nash, Anna
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Hertzberg, Robin
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Wen, Ye-Qian
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Dahlgren, Björn
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Moberg, Christina
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Dual Lewis Acid/Lewis Base Catalyzed Acylcyanation of Aldehydes: A Mechanistic Study2016Inngår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 22, nr 11, s. 3821-3829Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A mechanistic investigation, which included a Hammett correlation analysis, evaluation of the effect of variation of catalyst composition, and low-temperature NMR spectroscopy studies, of the Lewis acid-Lewis base catalyzed addition of acetyl cyanide to prochiral aldehydes provides support for a reaction route that involves Lewis base activation of the acyl cyanide with formation of a potent acylating agent and cyanide ion. The cyanide ion adds to the carbonyl group of the Lewis acid activated aldehyde. O-Acylation by the acylated Lewis base to form the final cyanohydrin ester occurs prior to decomplexation from titanium. For less reactive aldehydes, the addition of cyanide is the rate-determining step, whereas, for more reactive, electron-deficient aldehydes, cyanide addition is rapid and reversible and is followed by rate-limiting acylation. The resting state of the catalyst lies outside the catalytic cycle and is believed to be a monomeric titanium complex with two alcoholate ligands, which only slowly converts into the product.

  • 63. Liljenberg, Magnus
    et al.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi (stängd 20110630).
    Herschend, Björn
    Rein, Tobias
    Rockwell, Glen
    Svensson, Mats
    A pragmatic procedure for predicting regioselectivity in nucleophilic substitution of aromatic fluorides2011Inngår i: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 52, s. 3150-3153Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The scope and limitations of a method for predicting the regioisomer distribution in kinetically controlled nucleophilic substitution reactions of aromatic fluorides have been investigated. This method is based on calculating the relative stabilities of the isomeric σ-complex intermediates using DFT. A wide set of substrates and anionic nucleophiles have been investigated. Predictions from this method can be used quantitatively—these agree to an average accuracy of ±0.5 kcal/mol with experimental observations in eleven of the twelve investigated reactions.

  • 64. Liljenberg, Magnus
    et al.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi (stängd 20110630).
    Herschend, Björn
    Rein, Tobias
    Rockwell, Glen
    Svensson, Mats
    Validation of a Computational Model for Predicting the Site for Electrophilic Substitution in Aromatic Systems2010Inngår i: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 75, nr 14, s. 4696-4705Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated the scope and limitations of a method for predicting the regioisomer distribution in electrophilic aromatic substitution reactions that are under kinetic control. This method is based on calculation of the relative stabilities of the sigma-complex intermediates using density functional theory. Predictions from this method can be used quantitatively for halogenations; it agreed to an accuracy of about 1 kcal/mol with experimental observations in 10 of the 11 investigated halogenation reactions. For nitrations, the method gave useful predictions for heterocyclic substrates. The method failed for nitration of monosubstituted benzenes, and we expect that more elaborate model systems, including explicit solvent molecules, will be necessary to obtain quantitatively useful predictions for such cases. For Lewis acid promoted Friedel Crafts acylations, the method can be expected to give qualitatively correct predictions, that is, to point out the dominating isomer. For substrates where the regioisomeric outcome is highly dependent on the reaction conditions, the method can only be of qualitative use if the concentration of the free Lewis acid is high during the reaction. We have also compared the predictive capacity of the method to that of a modern reactivity index, the average local ionization energy, I(r). The latter method is found to predict the regisolectivity in halogenations and nitrations qualitatively correctly if the positions for the I(r) minima (I-S,I-min) are not too sterically hindered but fails for qualitative predictions of F C reactions. The downscaled I-S,I-min values also perform well for the quantitative prediction of regioisomer distributions of halogenations. The accuracy is slightly lower than that for the new method.

  • 65. Liljenberg, Magnus
    et al.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi (stängd 20110630).
    Herschend, Björn
    Rein, Tobias
    Tomasi, Simone
    Svensson, Mats
    Predicting Regioselectivity in Nucleophilic Aromatic Substitution2012Inngår i: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 77, nr 7, s. 3262-3269Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have investigated practical and computationally efficient methods for the quantitative prediction of regioisomer distribution in kinetically controlled nucleophilic aromatic substitution reactions. One of the methods is based on calculating the relative stabilities of the isomeric sigma-complex intermediates using DFT. We show that predictions from this method can be used quantitatively both for anionic nucleophiles with F- as leaving group, as well as for neutral nucleophiles with HF as leaving group. The sigma-complex approach failed when the leaving group was Cl/HCl or Br/HBr, both for anionic and neutral nucleophiles, because of difficulties in finding relevant sigma-complex structures. An approach where we assumed a concerted substitution step and used such transition state structures gave quantitatively useful results. Our results are consistent with other theoretical works, where a stable sigma-complex has been identified in some cases, whereas others have been indicated to proceed via a concerted substitution step.

  • 66.
    Liljenberg, Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Rein, Tobias
    Svensson, Mats
    Utilizing the sigma-complex stability for quantifying reactivity in nucleophilic substitution of aromatic fluorides2013Inngår i: Beilstein Journal of Organic Chemistry, ISSN 2195-951X, E-ISSN 1860-5397, Vol. 9, s. 791-799Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A computational approach using density functional theory to compute the energies of the possible sigma-complex reaction intermediates, the "sigma-complex approach", has been shown to be very useful in predicting regioselectivity, in electrophilic as well as nucleophilic aromatic substitution. In this article we give a short overview of the background for these investigations and the general requirements for predictive reactivity models for the pharmaceutical industry. We also present new results regarding the reaction rates and regioselectivities in nucleophilic substitution of fluorinated aromatics. They were rationalized by investigating linear correlations between experimental rate constants (k) from the literature with a theoretical quantity, which we call the sigma stability (SS). The SS is the energy change associated with formation of the intermediate sigma-complex by attachment of the nucleophile to the aromatic ring. The correlations, which include both neutral (NH3) and anionic (MeO-) nucleophiles are quite satisfactory (r = 0.93 to r = 0.99), and SS is thus useful for quantifying both global (substrate) and local (positional) reactivity in SNAr reactions of fluorinated aromatic substrates. A mechanistic analysis shows that the geometric structure of the sigma-complex resembles the rate-limiting transition state and that this provides a rationale for the observed correlations between the SS and the reaction rate.

  • 67.
    Liljenberg, Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Halldin Stenlid, Joakim
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    An investigation into rate-determining factors in electrophilic aromatic halogenationManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We have studied the halogenations of monosubstituted benzenes in polar, protic solvents at the PCMM06-2X/6-311G(d,p) level. We verify that the reaction with Cl2 proceeds through a C-atom coordinated π-complex and a rate-determining transition state for the formation of the σ-complex.

    The last step of this reaction proceeds in two steps – first the dissociation of Cl- and then the abstraction of the proton with a weak base. The use of the σ-complex as a model for the ratedetermining transition state is more accurate the later this transition state comes along the reaction coordinate, and thus, it is in general more accurate for halogenations than for nitrations, and for halogenations the more deactivated the substrate. The bromination of anisole with Br2 is shown to have a much later rate-determining transition state than the corresponding reaction with Cl2. The energy barrier for the abstraction of the proton in the iodination of anisole and phenol was several times higher than the corresponding step in chlorination and nitration, and the transition state structure obtained with ICl as electrophile is for both substrates consistent with a concerted reaction without the formation of a stable σ-complex. The computed hydrogen kinetic isotope effects are in good agreement with experiment.

  • 68.
    Liljenberg, Magnus
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Tillämpad fysikalisk kemi.
    Halldin Stenlid, Joakim
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Mechanism and regioselectivity of electrophilic aromatic nitration in solution: the validity of the transition state approach2018Inngår i: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 24, nr 1, artikkel-id 15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The potential energy surfaces in gas phase and in aqueous solution for the nitration of benzene, chlorobenzene, and phenol have been elucidated with density functional theory at theM06-2X/6-311G(d,p) level combined with the polarizable continuum solvent model (PCM). Three reaction intermediates have been identified along both surfaces: the unoriented pi-complex (I), the oriented reaction complex (II), and the sigma-complex (III). In order to obtain quantitatively reliable results for positional selectivity and for modeling the expulsion of the proton, it is crucial to take solvent effects into consideration. The results are in agreement with Olah's conclusion from over 40 years ago that the transition state leading to (II) is the rate-determining step in activated cases, while it is the one leading to (III) for deactivated cases. The simplified reactivity approach of using the free energy for the formation of (III) as a model of the rate-determining transition state has previously been shown to be very successful for halogenations, but problematic for nitrations. These observations are rationalized with the geometric and energetic resemblance, and lack of resemblance respectively, between (III) and the corresponding rate determining transition state. At this level of theory, neither the sigma-complex (III) nor the reaction complex (II) can be used to accurately model the rate-determining transition state for nitrations.

  • 69.
    Liljenberg, Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Halldin Stenlid, Joakim
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Theoretical Investigation into Rate-Determining Factors in Electrophilic Aromatic Halogenation2018Inngår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, nr 12, s. 3270-3279Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The halogenation of monosubstituted benzenes in aqueous solvent was studied using density functional theory at the PCM-M06-2X/6-311G(d,p) level. The reaction with Cl-2 begins with the formation of C atom coordinated pi-complex and is followed by the formation of the sigma-complex, which is rate-determining. The final part proceeds via the abstraction of the proton by a water molecule or a weak base. We evaluated the use of the sigma-complex as a model for the rate-determining transition state (TS) and found that this model is more accurate the later the TS comes along the reaction coordinate. This explains the higher accuracy of the model for halogenations (late TS) compared to nitrations (early TS); that is, the more deactivated the substrate the later the TS. The halogenation with Br-2 proceeds with a similar mechanism as the corresponding chlorination, but the bromination has a very late rate-determining TS that is similar to the sigma-complex in energy. The iodination with ICl follows a different mechanism than chlorination and bromination. After the formation of the pi-complex, the reaction proceeds in a concerted manner without a sigma-complex. This reaction has a large primary hydrogen kinetic isotope effect in agreement with experimental observations.

  • 70.
    Liljenberg, Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Halldin Stenlid, Joakim
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Theoretical investigation of regioselectivity in electrophilic aromatic nitrationManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The potential energy surfaces in gas phase and in aqueous solution for the nitration of benzene, chlorobenzene and phenol have been elucidated with density functional theory at the M06-2X/6-311G(d,p) level combined with the polarizable continuum solvent model (PCM). Three reaction intermediates have been identified along both surfaces: the unoriented π-complex (I), the oriented reaction complex (II) and the σ-complex (III). In order to obtain quantitatively reliable results for positional selectivity and for modeling the expulsion of the proton, it is crucial to take solvent effects into consideration. The results are in agreement with Olah´s conclusion from over 40 years ago that the transition state leading to (II) is the rate-determining step in activated cases, while it is the one leading to (III) for deactivated cases. The simplified reactivity approach of using the free energy for the formation of (III) as a model of the ratedetermining transition state, has previously been shown to be very successful for halogenations, but problematic for nitrations. These observations are rationalized with the geometric and energetic resemblance, and lack of resemblance respectively, between (III) and the corresponding rate determining transition state. At this level of theory, neither the σ-complex (III) nor the reaction complex (II) can be used to accurately model the rate-determining transition state for nitrations.

  • 71.
    Lind, Johan
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Merenyi, Gabor
    KTH, Tidigare Institutioner                               , Kemi.
    Johannson, E.
    Brinck, Tore
    KTH, Tidigare Institutioner                               , Kemi.
    Reaction of peroxyl radicals with ozone in water2003Inngår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 107, nr 5, s. 676-681Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The reactivity of alkylperoxyl radicals and -O3SOO* toward ozone was investigated. The peroxyl radicals were produced by steady-state gamma-radiolysis in the presence Of O-3. The rate constants were extracted from the decay rate of ozone measured during the irradiation. The rate constants vary between 7 x 10(3) and 2 x 10(5) M-1 s(-1) and there is a trend of increasing rate constant with electron-withdrawing substituent. Quantum chemical computations support a mechanism, according to which formation of an alkyl trioxide radical is the rate-determining step. This is followed by rapid expulsion Of O-2 to yield the alkoxyl radical. Conceivably, the alkyl trioxide radical is preceded by an extremely unstable alkyl pentoxide radical in equilibrium with the reactants.

  • 72.
    Linder, Mats
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    On the Method-Dependence of Transition State Asynchronicity in Diels-Alder ReactionsManuskript (preprint) (Annet vitenskapelig)
  • 73.
    Linder, Mats
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    On the method-dependence of transition state asynchronicity in Diels-Alder reactions2013Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 14, s. 5108-5114Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work discusses the dependence of transition state geometries on the choice of quantum chemical optimization method for the extensively studied Diels-Alder reaction. Rather significant differences are observed between post-Hartree-Fock methods and (hybrid) density functional theory, where the latter predicts larger asynchronicities. The results show that the low MP2 asynchronicity observed is likely artificial. Still, there are significant discrepancies between hybrid and pure density functionals. The role of the exchange functional seems to be most prominent in less activated reacting systems, while the importance of the correlation functional seems to increase as they become more activated by, e. g., an electron-donating group on the diene. To correct the dubious MP2 geometries, we employed the SCS-MP2 protocol for transition state optimization, which leads to significantly better results with respect to CCSD/6-31+G(d) level calculations. We conclude that in order for hybrid functionals to give descriptions consistent with the sample post-Hartree-Fock methods, a balanced combination of both Hartree-Fock exchange (with a couple of exceptions) and a well-behaved correlation functional is required. Given that the benchmark CCSD/6-31+ G(d) geometries are sufficient representations, the best geometries were obtained using omega B97X(D), B2PLYP(D) and M06-2X.

  • 74.
    Linder, Mats
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Stepwise Diels-Alder: More than Just an Oddity? A Computational Mechanistic Study2012Inngår i: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 77, nr 15, s. 6563-6573Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have employed hybrid DFT and SCS-MP2 calculations at the SMD-PCM–6-311++G(2d,2p)//6-31+G(d) level to investigate the relationship between three possible channels for forming a Diels–Alder adduct from a highly nucleophilic diene and moderately to highly electrophilic dienophiles. We discuss geometries optimized using the B3LYP and M06-2X functionals with the 6-31+(d) basis set. The transition states and intermediates are characterized on the basis of geometric and electronic properties, and we also address the possibility of predicting detectability of a zwitterionic intermediate based on its relative stability. Our results show that a conventional Diels–Alder transition state conformation yields intermediates in all four investigated cases, but that these are too short-lived to be detected experimentally for the less activated reactants. The stepwise trans pathway, beginning with a conjugate addition-like transition state, becomes increasingly competitive with more activated reactants and is indeed favored for the most electrophilic dienophiles. Addition of a trans diene leads to a dead-end as the trans intermediates have insurmountable rotation barriers that prohibit formation of the second bond, unless another, heterocyclic intermediate is formed. We also show that introduction of a hydrogen bond donating catalyst favors a stepwise pathway even for less activated dienophiles.

  • 75.
    Linder, Mats
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Synergistic activation of the Diels-Alder reaction by an organic catalyst and substituents: a computational study2009Inngår i: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 7, nr 7, s. 1304-1311Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory (DFT), using the hybrid functionals B3LYP and B2PLYP, has been employed to investigate the activation of the acrolein-butadiene Diels-Alder reaction, mediated by a thiourea catalyst. Effects due to electron-donating groups (EDGs) on the diene, as well as electron-withdrawing groups (EWGs) on the dienophile, have also been studied. Organic catalysts such as thioureas are known to lower the activation energy through hydrogen-bonding to the carbonyl oxygen, in a way that mimics the oxyanion holes of hydrolytic enzymes. EDGs and EWGs were found to further activate the reaction, and the catalyst showed a synergistic behavior towards the EDGs. Polar solvents were found to reduce the overall activation energy, but also the relative catalytic effect of the thiourea, in accordance with experimental studies. The substituent-mediated reactions displayed more asynchronous transition structures with lower activation energy, which led us to investigate the possibility of an alternative two-step, Michael-type route, similar to what has been found in macrophomate synthase. Although the concerted Diels-Alder route was found to be favored over the Michael route, the calculated activation energy difference is less than 1 kcal mol(-1), which suggests that the two mechanisms compete, and could be responsible for the particular stereochemical outcome of an experiment.

  • 76.
    Linder, Mats
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Hermansson, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Liebeschuetz, John
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Computational design of a lipase for catalysis of the Diels-Alder reaction2011Inngår i: Journal of Molecular Modeling, ISSN 1610-2940, E-ISSN 0948-5023, Vol. 17, nr 4, s. 833-849Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Combined molecular docking, molecular dynamics (MD) and density functional theory (DFT) studies have been employed to study catalysis of the Diels-Alder reaction by a modified lipase. Six variants of the versatile enzyme Candida Antarctica lipase B (CALB) have been rationally engineered in silico based on the specific characteristics of the pericyclic addition. A kinetic analysis reveals that hydrogen bond stabilization of the transition state and substrate binding are key components of the catalytic process. In the case of substrate binding, which has the greater potential for optimization, both binding strength and positioning of the substrates are important for catalytic efficiency. The binding strength is determined by hydrophobic interactions and can be tuned by careful selection of solvent and substrates. The MD simulations show that substrate positioning is sensitive to cavity shape and size, and can be controlled by a few rational mutations. The well-documented S105A mutation is essential to enable sufficient space in the vicinity of the oxyanion hole. Moreover, bulky residues on the edge of the active site hinders the formation of a sandwich-like nearattack conformer (NAC), and the I189A mutation is needed to obtain enough space above the face of the alpha,beta-double bond on the dienophile. The double mutant S105A/I189A performs quite well for two of three dienophiles. Based on binding constants and NAC energies obtained from MD simulations combined with activation energies from DFT computations, relative catalytic rates (v (cat) /v (uncat) ) of up to 103 are predicted.

  • 77.
    Linder, Mats
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Johansson, Adam Johannes
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Mechanistic Insights into the Stepwise Diels-Alder Reaction of 4,6-Dinitrobenzofuroxan2012Inngår i: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 14, nr 1, s. 118-121Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stepwise Diels-Alder reaction between 1-trimethylsiloxy-1,3-butadiene and 4,6-dinitrobenzofuroxan is explored using state-of-the-art computational methods. The results support a stepwise mechanism via a persistent Intermediate, however, not the one previously reported (Lakhdar et al., Chem. Eur. J. 2007, 16,5681) but a heterocyclic adduct. The novel OFT functional M062X and the SCS-MP2 method were essential to reproduce a reasonable potential energy surface for this challenging system.

  • 78.
    Linder, Mats
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Johansson, Adam Johannes
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Manta, Bianca
    KTH, Skolan för kemivetenskap (CHE).
    Olsson, Philip
    KTH, Skolan för kemivetenskap (CHE).
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Envisioning an enzymatic Diels-Alder reaction by in situ acid-base catalyzed diene generation2012Inngår i: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 48, nr 45, s. 5665-5667Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present and evaluate a new and potentially efficient route for enzyme-mediated Diels-Alder reactions, utilizing general acid-base catalysis. The viability of employing the active site of ketosteroid isomerase is demonstrated.

  • 79.
    Linder, Mats
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi (stängd 20110630).
    Johansson, Adam Johannes
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi (stängd 20110630).
    Olsson, Tjelvar S. G.
    Liebeschuetz, John
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi (stängd 20110630).
    Designing a New Diels-Alderase: A Combinatorial, Semirational Approach Including Dynamic Optimization2011Inngår i: JOURNAL OF CHEMICAL INFORMATION AND MODELING, ISSN 1549-9596, Vol. 51, nr 8, s. 1906-1917Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A computationally inexpensive design strategy involving 'semirational' screening for enzymatic catalysis is presented. The protocol is based on well-established computational methods and represents a holistic approach to the catalytic process. The model reaction studied here is the Diels-Alder, for which a successful computational design has recently been published (Siegel, J. B. et al. Science 2010, 329, 309-313). While it is a leap forward in the field of computational design, the focus on designing only a small fraction of the active site gives little control over dynamics. Our approach explicitly incorporates mutagenesis and the analysis of binding events and transition states, and a promising enzyme substrate candidate is generated with relatively little effort. We estimate catalytic rate accelerations of up to 10(5).

  • 80.
    Linder, Mats
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Johansson, Adam Johannes
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Olsson, Tjelvar S.G.
    Cambridge Crystallographic Data Centre.
    Liebeschuetz, John
    Cambridge Crystallographic Data Centre.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Computational design of a Diels-Alderase from a thermophilic esterase: the importance of dynamics2012Inngår i: Journal of Computer-Aided Molecular Design, ISSN 0920-654X, E-ISSN 1573-4951, Vol. 26, nr 9, s. 1079-1095Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A novel computational Diels-Alderase design, based on a relatively rare form of carboxylesterase from Geobacillus stearothermophilus, is presented and theoretically evaluated. The structure was found by mining the PDB for a suitable oxyanion hole-containing structure, followed by a combinatorial approach to find suitable substrates and rational mutations. Four lead designs were selected and thoroughly modeled to obtain realistic estimates of substrate binding and prearrangement. Molecular dynamics simulations and DFT calculations were used to optimize and estimate binding affinity and activation energies. A large quantum chemical model was used to capture the salient interactions in the crucial transition state (TS). Our quantitative estimation of kinetic parameters was validated against four experimentally characterized Diels-Alderases with good results. The final designs in this work are predicted to have rate enhancements of a parts per thousand 10(3)-10(6) and high predicted proficiencies. This work emphasizes the importance of considering protein dynamics in the design approach, and provides a quantitative estimate of the how the TS stabilization observed in most de novo and redesigned enzymes is decreased compared to a minimal, 'ideal' model. The presented design is highly interesting for further optimization and applications since it is based on a thermophilic enzyme (T (opt) = 70 A degrees C).

  • 81.
    Linder, Mats
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Ranganathan, Anirudh
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    "Adapted Linear Interaction Energy": A Structure-Based LIE Parametrization for Fast Prediction of Protein-Ligand Affinities2013Inngår i: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 9, nr 2, s. 1230-1239Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a structure-based parametrization of the Linear Interaction Energy (LIE) method and show that it allows for the prediction of absolute protein-ligand binding energies. We call the new model "Adapted" LIE (ALIE) because the a and beta coefficients are defined by system-dependent descriptors and do therefore not require any empirical gamma term. The best formulation attains a mean average deviation of 1.8 kcal/mol for a diverse test set and depends on only one fitted parameter. It is robust with respect to additional fitting and cross-validation. We compare this new approach with standard LIE by Aqvist and co-workers and the LIE + gamma SASA model (initially suggested by Jorgensen and co-workers) against in-house and external data sets and discuss their applicabilities.

  • 82.
    Lousada, Claudio M.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Application of reactivity descriptors to the catalytic decomposition of hydrogen peroxide at oxide surfaces2015Inngår i: Computational and Theoretical Chemistry, ISSN 2210-271X, E-ISSN 2210-2728, Vol. 1070, s. 108-116Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have employed density functional theory (DFT) calculations using the PBE0 functional to study the reaction of decomposition of H2O2 on clusters of: ZrO2, TiO2, Y2O3, Fe2O3, CeO2, CuO, Al2O3, NiO2, PdO2 and Gd2O3. The formation of the products of decomposition of H2O2 and their binding onto these oxides are discussed. The obtained energy barriers for H2O2 decomposition deviate from experimental data in absolute average by 4 kJ mol(-1). The only exceptions are CeO2 and Fe2O3 for which the deviations are very large. The adsorption of HO radicals onto the clusters was also studied. Reactivity descriptors obtained with DFT calculations are correlated with experimental data from literature. We found a direct correlation between the adsorption energy of HO radicals and the change in Mulliken charge of the cation present in the oxide, upon adsorption of these radicals. Other DFT and experimentally obtained reactivity descriptors based on properties of the cations present in the oxides, such as the ionization potential and electronegativity are plotted against experimental and DFT computed properties, respectively. Following the Bronsted-Evans Polanyi principle, there is a correlation between the adsorption energy of the product HO radical and the energy barrier for decomposition of H2O2. The good correlations between experimental data and the data obtained with DFF using minimalistic cluster models of the oxides surfaces indicates that on the real systems the processes that determine the reactivity of H2O2 are very dependent on localized properties of the surfaces.

  • 83.
    Lousada, Claudio M.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Johansson, Adam Johannes
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Mechanism of H2O2 Decomposition on Transition Metal Oxide Surfaces2012Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 17, s. 9533-9543Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We performed an experimental and density functional theory (DFT) investigation of the reactions of H2O2 with ZrO2, TiO2, and Y2O3. In the experimental study we determined the reaction rate constants, the Arrhenius activation energies, and the activation enthalpies for the processes of adsorption and decomposition of H2O2 on the surfaces of nano- and micrometersized particles of the oxides. The experimentally obtained enthalpies of activation for the decomposition of H2O2 catalyzed by these materials are 30 +/- 1 kJ.mol(-1) for ZrO2, 34 +/- 1 kJ.mol(-1) for TiO2, and 44 +/- 5 kJ.mol(-1) for Y2O3. In the DFT study, cluster models of the metal oxides were used to investigate the mechanisms involved in the surface process governing the decomposition of H2O2. We compared the performance of the B3LYP and M06 functionals for describing the adsorption energies of H2O2 and HO center dot onto the oxide surfaces as well as the energy barriers for the decomposition of H2O2. The DFT models implemented can describe the experimental reaction barriers with good accuracy, and we found that the decomposition of H2O2 follows a similar mechanism for all the materials studied. The average absolute deviation from the experimental barriers obtained with the B3LYP functional is 6 kJ.mol(-1), while with the M06 functional it is 3 kJ.mol(-1). The differences in the affinity of the different surfaces for the primary product of H2O2 decomposition, the HO radical, were also addressed both experimentally and with DFT. With the experiments we found a trend in the affinity of HO center dot toward the surfaces of the oxides, depending on the type of oxide. This trend is successfully reproduced with the DFT calculations. We found that the adsorption energy of HO center dot varies inversely with the ionization energy of the metal cation present in the oxide.

  • 84.
    Lousada Patricio, Cláudio Miguel
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Johansson, Adam Johannes
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Reactivity of metal oxide clusters with hydrogen peroxide and water: a DFT study evaluating the performance of different exchange-correlation functionals2013Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 15, s. 5539-5552Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have performed a density functional theory (DFT) investigation of the interactions of H2O2, H2O and HO radicals with clusters of ZrO2, TiO2 and Y2O3. Different modes of H2O adsorption onto the clusters were studied. In almost all the cases the dissociative adsorption is more exothermic than molecular adsorption. At the surfaces where H2O has undergone dissociative adsorption, the adsorption of H2O2 and the transition state for its decomposition are mediated by hydrogen bonding with the surface HO groups. Using the functionals B3LYP, B3LYP-D and M06 with clusters of 26 and 8 units of ZrO2, the M06 functional performed better than B3LYP in describing the reaction of decomposition of H2O2 and the adsorption of H2O. Additionally, we investigated clusters of the type (ZrO2)2, (TiO2)2 and (Y2O3) and the performance of the functionals B3LYP, B3LYP-D, B3LYP*, M06, M06-L, PBE0, PBE and PWPW91 in describing H2O2, H2O and HO˙ adsorption and the energy barrier for decomposition of H2O2. The trends obtained for HO˙ adsorption onto the clusters are discussed in terms of the ionization energy of the metal cation present in the oxide. In order to correctly account for the existence of an energy barrier for the decomposition of H2O2, the functional used must include Hartree-Fock exchange. Using minimal cluster models, the best performance in describing the energy barrier for H2O2 decomposition was obtained with the M06 and PBE0 functionals - the average absolute deviations from experiments are 6 kJ mol(-1) and 5 kJ mol(-1) respectively. With the M06 functional and a larger monoclinic (ZrO2)8 cluster model, the performance is in excellent agreement with experimental data. For the different oxides, PBE0 was found to be the most effective functional in terms of performance and computational time cost.

  • 85.
    Marinado, Tannia
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Hagberg, Daniel P.
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    Edvinsson, Tomas
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Boschloo, Gerrit
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Tian, Haining
    Yang, Xixhuan
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Energy level tuning of organic dyes for fundamental studies of the oxide/dye/electrolyte interface in solar cellsManuskript (Annet vitenskapelig)
  • 86.
    Qin, Peng
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Gibson, Elizabeth A.
    Linder, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Sun, Licheng
    Structural Modifications to Triphenylamine Based Chromophores for Control of Charge Recombination in p-Type Dye-Sensitized Solar CellsManuskript (preprint) (Annet vitenskapelig)
  • 87.
    Qin, Peng
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Linder, Mats
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Boschloo, Gerrit
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    High Incident Photon-to-Current Conversion Efficiency of p-Type Dye-Sensitized Solar Cells Based on NiO and Organic Chromophores2009Inngår i: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 21, nr 29, s. 2993-2996Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The synthesis and characterization of an organic dye, P4, together with its performance in p-type dye-sensitized solar cells (DSSCs) is presented. A solar-cell device based on P4 and an electrolyte that contains the I-/I-3(-) couple in acetonitrile yielded an IPCE value of 44% on a transparent NiO film only 1-1.4 mu m thick, the highest value obtained so far.

  • 88.
    Qin, Peng
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Wiberg, Joanna
    Gibson, Elizabeth A.
    Linder, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Li, Lin
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Hagfeldt, Anders
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Albinsson, Bo
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi. KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Synthesis and Mechanistic Studies of Organic Chromophores with Different Energy Levels for p-Type Dye-Sensitized Solar Cells2010Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 10, s. 4738-4748Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A series of donor-pi-acceptor dyes with different electron-withdrawing groups were designed and synthesized for p-type dye-sensitized Solar cells. The modification of dye structures shows significant influence on the photophysical, electrochemical, and photovoltaic performance of the dyes. DSSCs based on these dyes show maximum 63% and minimum 6% of incident monochromatic photon-to-current conversion efficiencies. The two dyes with the highest (P1) and lowest (P3) efficiencies were Studied by femtosecond transient absorption spectroscopy, which shows a fast injection rate of more than (250 fs)(-1) for both dyes. Such fast injection corresponds to more than 90% injection efficiency. The photoinduced absorption Spectroscopy Study of sensitized NiO films in the presence of electrolyte showed poor regeneration of 113 due to all insufficient driving force. This, together with aggregation of the dye on the NiO film, explained the poor solar cell performance.

  • 89. Rahm, M.
    et al.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Green Propellants Based on Dinitramide Salts: Mastering Stability and Chemical Compatibility Issues2014Inngår i: Green Energetic Materials, Wiley-Blackwell, 2014, s. 179-204Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Mastery of dinitramide salts requires the intertwined use of compatibility testing, surface sensitive spectroscopy, and quantum chemical calculations. This chapter shows these combined approaches providing atomistic and fundamental understanding of the complex processes that govern the decomposition, reactivity, and in the end, usefulness of dinitramide-based materials. Polarized dinitramide anions residing on the surface of dinitramide salts are theoretically predicted to exist and to dramatically accelerate decomposition. Such structures have been observed on the outmost monolayers of ammonium dinitramide (ADN) crystals using surface sensitive vibrational spectroscopy. Stabilization of ADN is realized by hindering the polarization of such structures with surface-active stabilizing agents. The full mechanisms for the self-decomposition of solid-state ADN and potassium dinitramide (KDN) are presented. Radical decomposition intermediates stress the necessity of using anti-oxidants as stabilizers. The anomalous solid-state behavior that has been observed in several dinitramide salts is also discussed and explained. Finally, the use of the dinitramide moiety in synthesis is briefly reviewed, and several mechanisms for its reactions with various olefinic double bonds are discussed.

  • 90.
    Rahm, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Dinitraminic acid (HDN) isomerization and self-decomposition revisited2008Inngår i: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 348, nr 1-3, s. 53-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory (DFT) and the ab initio based CBS-QB3 method have been used to study possible decomposition pathways of dinitraminic acid HN(NO2)(2) (HDN) in gas-phase. The proton transfer isomer of HDN, O2NNN(O)OH, and its conformers can be formed and converted into each other through intra- and intermolecular proton transfer. The latter has been shown to proceed substantially faster via double proton transfer. The main mechanism for HDN decomposition is found to be initiated by a dissociation reaction, splitting of nitrogen dioxide from either HDN or the HDN isomer. This reaction has an activation enthalpy of 36.5 kcal/mol at the CBS-QB3 level, which is in good agreement with experimental estimates of the decomposition barrier.

  • 91.
    Rahm, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Kinetic Stability and Propellant Performance of Green Energetic Materials2010Inngår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 16, s. 6590-6600Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A thorough theoretical investigation of four promising green energetic materials is presented. The kinetic stability of the dinitramide, trinitrogen dioxide, pentazole, and oxopentazole anions has been evaluated in the gas phase and in solution by using high-level ab initio and DFT calculations. Theoretical UV spectra, solid-state heats of formation, density, as well as propellant performance for the corresponding ammonium salts are reported. All calculated properties for dinitramide are in excellent agreement with experimental data. The stability of the trinitrogen dioxide anion is deemed sufficient to enable synthesis at low temperature, with a barrier for decomposition of approximately 27.5 kcal mol(-1) in solution. Oxopentazolate is expected to be approximately 1200 times more stable than pentazolate in solution, with a barrier exceeding 30 kcal mol(-1), which should enable handling at room temperature. All compounds are predicted to provide high specific impulses when combined with aluminum fuel and a polymeric binder, and rival or surpass the performance of a corresponding ammonium perchlorate based propellant. The investigated substances are also excellent monopropellant candidates. Further study and attempted synthesis of these materials is merited.

  • 92.
    Rahm, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Novel 1,3-dipolar cycloadditions of dinitraminic acid: Implications for the chemical stability of ammonium dinitramide2008Inngår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 112, nr 11, s. 2456-2463Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory at the B3LYP/6-31+G(d,p) level and ab initio calculations at the CBS-QB3 level have been used to analyze 1,3 dipolar cycloaddition reactions of dinitraminic acid (HDN) and its proton transfer isomer (HO(O)NNNO2). It is shown that the nitro group of HDN and the -N-N = O functionality of the isomer react readily with carbon-carbon double bonds. Cycloadditions of HDN are compared with the corresponding reactions with azides and nitrile oxides as 1,3 dipoles. It is shown that the reactivities of HDN and its proton transfer isomer decrease with increasing electron withdrawing power of the substituents adjacent to the carbon-carbon double bond. In contrast, for azides and nitrile oxides, the highest reactivity is obtained with dipolarophiles with strongly electron withdrawing substituents. The observed reactivity trends allow for the design of unsaturated compounds that are highly reactive toward azides and chemically inert toward dinitramides. This may be of relevance for the development of binder materials for ammonium dinitramide based propellants.

  • 93.
    Rahm, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    On the Anomalous Decomposition and Reactivity of Ammonium and Potassium Dinitramide2010Inngår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 114, nr 8, s. 2845-2854Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mechanistic pathways for the thermal decomposition of the solid-state energetic oxidizers ammonium dinitramide (ADN) and potassium dinitramide (KDN) have been deciphered by carefully considering previously performed experimental studies and using state of the art quantum chemical modeling of molecular clusters. Decomposition is governed by surface chemical processes, involving polarized (twisted) dinitramide anions of reduced stability. Under atmospheric and low-pressure conditions, the rate-determining step for the decomposition of these dinitramide salts is the dissociation into NO, and NNO2- radicals. The activation barriers for these steps are estimated to be 30 and 36 kcal/mol for ADN and KDN, respectively. The known stabilizing effect of water is explained by its hydrogen bonding ability, which counteracts polarization of surface dinitramides. The reactivity of ADN toward Various chemical environments is likely explained through metastable decomposition radical intermediates. Donation of hydrogen bonds, antioxidant character, and basicity are properties believed to correlate with a compound's ability to act as a stabilizer for dinitramide salts.

  • 94.
    Rahm, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE).
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Centra, Molekylär elektronik, CMD.
    Solid-state modeling of dinitramide decomposition2009Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 238Artikkel i tidsskrift (Annet vitenskapelig)
  • 95.
    Rahm, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    The anomalous solid state decomposition of ammonium dinitramide: a matter of surface polarization2009Inngår i: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, nr 20, s. 2896-2898Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polarized dinitramide anions on the surface of solid ammonium dinitramide (ADN) have a decomposition barrier that is reduced by 16 kcal mol(-1) and explain the anomalous solid state decomposition of ADN.

  • 96.
    Rahm, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Dvinskikh, Sergey V.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Furo, Istvan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Experimental Detection of Trinitramide, N(NO2)(3)2011Inngår i: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 50, nr 5, s. 1145-1148Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Propeller propellant: The largest nitrogen oxide to date, trinitramide (TNA), has been prepared following extensive quantum chemical studies in which its kinetic stability and several physical properties were estimated. TNA was detected using IR and NMR spectroscopy. The compound is highly energetic and shows promise for cryogenic propulsion and as a reagent in high-energy-density material research.

  • 97.
    Rahm, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Trinchero, Adriana
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Envisioning New High Energy Density Materials: Stability, Detection and Performance2010Inngår i: 41st International  Annual Conference of  ICT (Energetic Materials) : , 2010, s. 9/1-9/11Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    There is great need for new environmentally friendly energetic materials. One promising oxidizer currently under investigation for numerous applications is ammonium dinitramide (ADN, NH4N(NO2)2). After deciphering the thermal decomposition behavior of this salt theoretically, we have sought to find other all-nitrogen-oxygen compounds with similar advantageous properties. By considering electronic and structural characteristics related to the dinitramide, we have investigated a number of promising energetic anions using high-level density functional theory and ab initio methods.   Theoretical kinetic stabilities, UV-spectra, solid-state heats of formation, densities, as well as propellant performances of the corresponding ammonium salts with aluminum fuel are reported. The potential for significant performance gains is seen by comparison to standard ammonium perchlorate (AP) and ADN-formulations. Reasonable stabilities and straightforward detection at room temperature should encourage attempted synthesis of several of the investigated materials.

  • 98.
    Rahm, Martin
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Tyrode, Eric
    KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Johnson, Magnus
    KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära.
    The Molecular Surface Structure of Ammonium and Potassium Dinitramide: A Vibrational Sum Frequency Spectroscopy and Quantum Chemical Study2011Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, nr 21, s. 10588-10596Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Vibrational sum frequency spectroscopy (VSFS) and quantum chemical modeling have been employed to investigate the molecular surface structure of ammonium and potassium dinitramide (ADN and KDN) crystals. Identification of key vibrational modes was made possible by performing density functional theory calculations of molecular clusters. The surface of KDN was found to be partly covered with a thin layer of the decomposition product KNO3, which due to its low thickness was not detectable by infrared and Raman spectroscopy. In contrast, ADN exhibited an extremely inhomogeneous surface, on which polarized dinitramide anions were present, possibly together with a thin layer of NH4NO3. The intertwined use of theoretical and experimental tools proved indispensable in the analysis of these complex surfaces. The experimental verification of polarized and destabilized dinitramide anions stresses the importance of designing surface-active polymer support, stabilizers, and/or coating agents, in order to enable environmentally friendly ADN-based solid-rocket propulsion.

  • 99. Robbins, Adele M.
    et al.
    Jin, Ping
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi (stängd 20110630).
    Murray, Jane S.
    Politzer, Peter
    Electrostatic potential as a measure of gas phase carbocation stability2006Inngår i: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 106, nr 14, s. 2904-2909Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Assessment of the relative stabilities of carbocations is important for interpreting reaction mechanisms as well as in organic synthesis. A common approach is in terms of hydride affinities; however these depend on a second system, a neutral molecule, as well as the ion. In the present work, we propose a measure of gas phase carbocation stability that is dependent solely on the properties of the ion: the magnitude of the most positive surface electrostatic potential associated with the carbon framework. This quantity, labeled V-S,V-max, reflects a key factor, the extent to which the positive charge has been delocalized. We have computed V-S,V-max for 28 carbocations, and we show that the overall trends predicted are physically meaningful in terms of experimental observations. Mulliken atomic charges are not satisfactory for this purpose.

  • 100.
    Rudberg, Elias
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Brinck, Tore
    KTH, Skolan för kemivetenskap (CHE), Kemi, Fysikalisk kemi.
    Computation of Franck-Condon factors for many-atom systems: simulated photoelectron spectra of formic acid isotopologues2004Inngår i: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 302, nr 1-3, s. 217-228Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Simulated photoelectron spectra of the four formic acid isotopologues HCOOH, HCOOD, DCOOH and DCOOD are reported. The simulations are based on computed multidimensional harmonic Franck-Condon factors (FCFs) for transitions from the ground state of the neutral molecule to the two lowest electronic states of the cation. The geometrical parameters and force constants used in the Franck-Condon analysis have been obtained at the B3LYP/6-311 +G(3df,2p) level of theory. The results are compared with well-resolved experimental spectra, and good agreement between simulated and experimental spectra is found, in particular for the first PES band. Using the computed FCFs, the vibrational fine structure of the first two bands of the experimental spectra is analyzed, and vibrational frequencies for the two cationic states are extracted from the experimental data.

123 51 - 100 of 118
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