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  • 1.
    Gao, Li
    et al.
    Örebro University, School of Science and Technology.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Wegman [Palmebäck-Wegman], Pia
    Örebro University, School of Health and Medical Sciences.
    Wingren, Sten
    Örebro University, School of Health and Medical Sciences.
    Eriksson, Leif A.
    A mechanistic hypothesis for the cytochrome P450-catalyzed cis-trans isomerization of 4-hydroxytamoxifen: an unusual redox reaction2011In: Journal of Chemical Information and Modeling, ISSN 1549-9596, E-ISSN 1549-960X, Vol. 51, no 9, p. 2293-2301Article in journal (Refereed)
    Abstract [en]

    We provide a detailed description of the cis-trans isomerization of 4-hydroxytamoxifen/endoxifen catalyzed by several isoforms from the cytochrome P450 (CYP) superfamily, including CYP1B1, CYP2B6, and CYP2C19. We show that the reactions mainly involve redox processes catalyzed by CYP, DFT calculation results strongly suggest that the isomerization occurs via a cationic intermediate. The cationic cis-isomer is more than 3 kcal/mol more stable than the trans form, resulting in an easier conversion from trans-to-cis than cis-to-trans. The cis-trans isomerization is a rarely reported CYP reaction and is ascribed to the lack of a second abstractable proton on the ethenyl group of the triarylvinyl class of substrates. The cationic intermediates thus formed instead of the stable dehydrogenation products allow for isomerization to occur. As a comparison, the reactions for the tamoxifen derivatives are compared to those of other substrates, 4-hydroxyacetanilide and raloxifene, for which the stable dehydrogenation products are formed.

  • 2.
    Gao, Li
    et al.
    Örebro University, School of Science and Technology.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Wegman [Palmebäck-Wegman], Pia
    Örebro University, School of Science and Technology.
    Wingren, Sten
    Örebro University, School of Science and Technology.
    Eriksson, Leif A.
    Örebro University, School of Science and Technology.
    Conformational enantiomerization and estrogen receptor alpha binding of anti-cancer drug tamoxifen and its derivatives2011In: Journal of Chemical Information and Modeling, ISSN 1549-9596, E-ISSN 1549-960X, Vol. 51, no 2, p. 306-314Article in journal (Refereed)
    Abstract [en]

    The anticancer drug tamoxifen (TAM) displays two chiral vinyl propeller structures, which interconvert so rapidly that the process is undetectable on the NMR time scale. In the present work, the enantiomerization processes were investigated with molecular modeling techniques. The threshold mechanisms probed at the different rings were shown to be identical, i.e., involving a synchronous three-ring flip, with a correlated rotation of the rings. In order to reveal the pharmacological profiles of the two chiral forms, we performed structural studies on the ligand binding domain of estrogen receptor alpha. (ER alpha LBD) and associated ligands. The enantiomers, with opposite torsional twist, were found to be discriminated by ER alpha. For TAM and its main metabolites, the effects of the stereoselectivity of ER alpha are overcome by the low energy cost for helical inversion between the two torsional enantiomers, estimated to be similar to 3 kcal/mol.

  • 3.
    Kang, Yu
    et al.
    Sch Biotechnol, Dept Theoret Chem, Royal Inst Technol, Stockholm, Sweden; Dept Chem, Zhejiang Univ Hangzhou, Zhejiang, Peoples R China.
    Li, Xin
    Sch Biotechnol, Dept Theoret Chem, Royal Inst Technol, Stockholm, Sweden.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Wang, Qi
    Dept Chem, Zhejiang Univ Hangzhou, Zhejiang, Peoples R China.
    Ågren, Hans
    Sch Biotechnol, Dept Theoret Chem, Royal Inst Technol, Stockholm, Sweden.
    On the mechanism of protein adsorption onto hydroxylated and nonhydroxylated TiO2 surfaces2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 34, p. 14496-14502Article in journal (Refereed)
    Abstract [en]

    Protein adsorption onto implant surfaces is of great importance for the regulation of implant bioactivity. Surface modification of implants is a promising way in the molecular design of biocompatible materials against nonspecific adsorption of proteins. On the basis of these fundamental facts, we focus in this work on the different behavior of protein adsorption on hydroxylated and nonhydroxylated rutile TiO2 (110) surfaces through molecular dynamics simulations. Our investigation indicates that the distribution of the water molecules at the interface induced by the surface modification plays an important role in the protein adsorption. The surface with modified hydroxyl groups was observed to have much greater affinity to the protein, as reflected by the larger protein−surface electrostatic interaction and by the larger amount of adsorbed residues. The highly ordered structure of the modified hydroxyl groups on the hydroxylated surface diminishes the possibility of hydrogen bond formation between the surface and the water molecules above it, which in turn makes it easier for the protein to move closer to the surface with hydroxyl modification.

  • 4. Li, X.
    et al.
    Hede, T.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Leck, C.
    Ågren, H.
    Glycine in aerosol water droplets: a critical assessment of Kohler theory by predicting surface tension from molecular dynamics simulations2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 2, p. 519-527Article in journal (Refereed)
    Abstract [en]

    Aerosol particles in the atmosphere are important participants in the formation of cloud droplets and have significant impact on cloud albedo and global climate. According to the Kohler theory which describes the nucleation and the equilibrium growth of cloud droplets, the surface tension of an aerosol droplet is one of the most important factors that determine the critical supersaturation of droplet activation. In this paper, with specific interest to remote marine aerosol, we predict the surface tension of aerosol droplets by performing molecular dynamics simulations on two model systems, the pure water droplets and glycine in water droplets. The curvature dependence of the surface tension is interpolated by a quadratic polynomial over the nano-sized droplets and the limiting case of a planar interface, so that the so-called Aitken mode particles which are critical for droplet formation could be covered and the Kohler equation could be improved by incorporating surface tension corrections.

  • 5.
    Li, Xin
    et al.
    Sch Biotechnol, Dept Theoret Chem, Royal Inst Technol, Stockholm, Sweden; China Univ Sci & Technol, Shanghai 200237, Peoples R China.
    Hede, Thomas
    Dept Meteorol, Stockholm Univ, Stockholm, Sweden.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Leck, Caroline
    Dept Meteorol, Stockholm Univ, Stockholm, Sweden.
    Ågren, Hans
    Sch Biotechnol, Dept Theoret Chem, Royal Inst Technol, Stockholm, Sweden.
    Surface-active cis-pinonic acid in atmospheric droplets: A molecular dynamics study2010In: The Journal of Physical Chemistry Letters, ISSN 1948-7185, Vol. 1, no 4, p. 769-773Article in journal (Refereed)
    Abstract [en]

    Water vapor in the atmosphere can condensate and form cloud droplets when there is a certain amount of humidity and a presence of cloud condensation nuclei, and organic solutes called surfactants can significantly lower the surface tension of water — one of the parameters determining cloud droplet population. We here present a molecular dynamics study of the behavior of cis-pinonic acid, a commonly found organic compound in cloud condensation nuclei, and its effect on the surface tension of water clusters. Specifically, the decrease in surface tension is found to depend on not only the concentration of the organic compound but also the droplet size due to the spontaneous assembly of the surfactant molecules on the droplet surface. This leads to the conclusion that the partitioning of the surfactant between the bulk and surface plays an important role in the behavior of atmospheric aerosol particles and thus in their availability for cloud formation.

  • 6. Li, Xin
    et al.
    Rinkevicius, Zilvinas
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Tian, He
    Ågren, Hans
    Nuclear magnetic shielding of 113Cd(II) ion in aqua solution: a combined molecular dynamics/density functional theory study2008In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 112, no 36, p. 11347-11352Article in journal (Refereed)
    Abstract [en]

    We present a combined molecular dynamics simulation and density functional theory investigation of the nuclear magnetic shielding constant of the 113Cd(II) ion solvated in aqueous solution. Molecular dynamics simulations are carried out for the cadmium−water system in order to produce instantaneous geometries for subsequent determination of the nuclear magnetic shielding constant at the density functional theory level. The nuclear magnetic shielding constant is computed using a perturbation theory formalism, which includes nonrelativistic and leading order relativistic contributions to the nuclear magnetic shielding tensor. Although the NMR shielding constant varies significantly with respect to simulation time, the value averaged over increasing number of snapshots remains almost constant. The paramagnetic nonrelativistic contribution is found to be most sensitive to dynamical changes in the system and is mainly responsible for the thermal and solvent effects in solution. The relativistic correction features very little sensitivity to the chemical environment, and can be disregarded in theoretical calculations when a Cd complex is used as reference compound in 113Cd NMR experiments, due to the mutual cancelation between individual relativistic corrections.

  • 7. Li, Xin
    et al.
    Rinkevicius, Zilvinas
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Tian, He
    Ågren, Hans
    Paramagnetic Perturbation of the 19F NMR Chemical Shift in Fluorinated Cysteine by O2: A Theoretical Study2009In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 113, no 31, p. 10916-10922Article in journal (Refereed)
    Abstract [en]

    We present a combined molecular dynamics and density functional theory study of dioxygen-induced perturbation of the 19F NMR chemical shifts in an aqueous solution of fluorinated cysteine under 100 atm of O2 partial pressure. Molecular dynamics simulations are carried out to determine the dominant structures of O2 and the fluorinated cysteine complexes in water, and the collected structural information is exploited in computation of 19F chemical shifts using density functional theory. The obtained results indicate that the density redistribution of the O2 unpaired electrons between the dioxygen and fluorinated cysteine is responsible for the experimentally observed perturbation of the 19F NMR chemical shifts, where the Fermi contact interaction plays the key role. The O2-induced paramagnetic 19F chemical shift, averaged over the simulation trajectory, is comparable with the reported experimental values, proving the availability of the developed strategy for modeling 19F NMR chemical shifts in the presence of paramagnetic agents in an aqueous solution. The applicability of the combined molecular dynamics/density functional theory approach for dioxygen NMR perturbation to all resonating nuclei including 1H, 13C, 15N, and 19F is emphasized, and the ramification of this for investigations of membrane protein structures is discussed.

  • 8.
    Li, Xin
    et al.
    Sch Biotechnol, Dept Theoret Chem, Royal Inst Technol, Stockholm, Sweden; E China Univ Sci & Technol, Shanghai, People's R China.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Tian, He
    E China Univ Sci & Technol, Shanghai, People's R China.
    Ågren, Hans
    Sch Biotechnol, Dept Theoret Chem, Royal Inst Technol, Stockholm, Sweden.
    Computer simulations of aqua metal ions for accurate reproduction of hydration free energies and structures2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, no 10, article id 104505Article in journal (Refereed)
    Abstract [en]

    Metal ions play essential roles in biological processes and have attracted much attention in both experimental and theoretical fields. By using the molecular dynamics simulation technology, we here present a fitting-refining procedure for deriving Lennard-Jones parameters of aqua metal ions toward the ultimate goal of accurately reproducing the experimentally observed hydration free energies and structures. The polarizable SWM4-DP water model {proposed by Lamoureux et al. [J. Chem. Phys. 119, 5185 (2003)] } is used to properly describe the polarization effects of water molecules that interact with the ions. The Lennard-Jones parameters of the metal ions are first obtained by fitting the quantum mechanical potential energies of the hexahydrated complex and are subsequently refined through comparison between the calculated and experimentally measured hydration free energies and structures. In general, the derived Lennard-Jones parameters for the metal ions are found to reproduce hydration free energies accurately and to predict hydration structures that are in good agreement with experimental observations. Dynamical properties are also well reproduced by the derived Lennard-Jones parameters.

  • 9.
    Li, Xin
    et al.
    Dept Theoret Chem, Sch Biotechnol, Royal Inst Technol, Stockholm, Sweden; E China Univ Sci & Technol, Shanghai, Peoples R China.
    Zhang, Qiong
    Dept Theoret Chem, Sch Biotechnol, Royal Inst Technol, Stockholm, Sweden; E China Univ Sci & Technol, Shanghai, Peoples R China.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Ågren, Hans
    Dept Theoret Chem, Sch Biotechnol, Royal Inst Technol, Stockholm, Sweden.
    Tian, He
    E China Univ Sci & Technol, Shanghai, Peoples R China.
    Modulation of Iridium(III) phosphorescence via photochromic ligands: a density functional theory study2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 41, p. 13730-13736Article in journal (Refereed)
    Abstract [en]

    The photochromic iridium(iii) complex (Py-BTE)(2)Ir(acac) synthesized by Tan et al. [W. Tan et al., Org. Lett. 2009, 11, 161-164] has shown distinct photo-reactivity and photo-controllable phosphorescence. We here present a density functional theory study on the (Py-BTE)(2)Ir(acac) complex to explore the mechanism at the molecular level and to help further design of photochromic iridium(iii) complexes with the desirable properties. The hybrid functional PBE0, with 25% Hartree-Fock exchange, is found to give an optimal structure compared with X-ray crystallographic data. The absorption bands are well reproduced by using time-dependent density functional theory calculations, lending the possibility to assign the metal-to-ligand and intra-ligand charge transfer transitions. The radiative and nonradiative deactivation rate constants, k(r) and k(nr), are rationalized for both the open-ring and closed-ring forms of the complex. The very large k(nr) and small k(r) make the closed-ring form of the complex non-emissive. The triplet reactivity of the Py-BTE ligand is also studied by performing density functional theory calculations on the potential energy surfaces of the ground state and the lowest triplet state

  • 10.
    Lu, Hui
    et al.
    Dept Phys, E China Univ Sci & Technol, Shanghai, Peoples R China.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Lin, Xian
    Dept Phys, E China Univ Sci & Technol, Shanghai, Peoples R China.
    Fang, Bin
    Inst Nucl Phys, E China Univ Sci & Technol, Shanghai, Peoples R China.
    Luo, Duanbin
    Dept Phys, E China Univ Sci & Technol, Shanghai, Peoples R China.
    Laaksonen, Aatto
    Div Phys Chem, Dept Mat & Environm Chem, Stockholm Univ, Stockholm, Sweden.
    Effects of laser irradiation on the structure and optical properties of ZnO thin films2010In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 64, no 19, p. 2072-2075Article in journal (Refereed)
    Abstract [en]

    The effects of laser irradiation on the surface microstructure and optical properties of ZnO films deposited on glass substrates were investigated experimentally and compared with those of thermal annealing. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements showed that the irradiation treatment with an Ar+ laser of 514 nm for 5 min improves the crystalline quality of ZnO thin films through increasing the grain size and enhancing the c-axis orientation, with the effects similar to those of the thermal annealing at 500 °C for 1 h. Laser irradiation was found to be more effective both for the relaxation of the residual compressive stress in the as-grown films and for the modification of the surface morphology. A significant increase in the UV absorption and a widening in the optical band-gap of the films were also observed after laser irradiation.

  • 11. Lyubartsev, Alexander
    et al.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Laaksonen, Aatto
    Hierarchical multiscale modelling scheme from first principles to mesoscale2009In: Journal of Computational and Theoretical Nanoscience, ISSN 1546-1955, Vol. 6, no 5, p. 951-959Article in journal (Refereed)
    Abstract [en]

    We present a straight-forward implementation of a practical hierarchical multiscale modelling scheme which enables us to start from first-principles atomistic computer simulation and successively coarse-grain the model by leaving out uninteresting degrees of freedom. Using the Car-Parrinello method or our recently developed highly efficient tight-binding-like approximate density-functional quantum mechanical method,w e first perform first-principles simulations we obtain a set of atomistic pair-wise effective interaction potentials to be used as a force field with scaling up the system size 2–3 orders of magnitude. The atomistic simulations similarly provide a new set of effective potentials but at a chosen coarse-grain level suitable for large-scale mesoscopic or soft-matter simulations beyond the atomic resolution. Show several examples are shown of how this scheme is done based on effective interaction potentials to tie together the various scales of modelling.

  • 12.
    Tian, Boxue
    et al.
    Örebro University, School of Science and Technology.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Strid, Åke
    Örebro University, School of Science and Technology.
    Eriksson, Leif A.
    Örebro University, School of Science and Technology.
    Hydroxylation and ring-opening mechanism of an unusual flavoprotein monooxygenase, 2-Methyl-3-hydroxypyridine-5-carboxylic Acid Oxygenase: a theoretical study2010In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 16, no 8, p. 2557-2566Article in journal (Refereed)
    Abstract [en]

    Hybrid meta-GGA density functional theory MPWB1K functional is used to study the hydroxylation and ring-opening mechanism of 2-methyl-3-hydroxypyridine- 5-carboxylic acid oxygenase (MHPCO). This enzyme catalyzes the conversion of 2-methyl-3-hydroxypyridine-5-carboxylic acid (MHPC) to α-(N-acetylamino- methylene) succinic acid (AAMS), which is the essential ring-opening step in the bacterial degradation of Vitamin B6. MHPCO belongs to the flavin-containing aromatic hydroxylases. However, MHPCO is capable of catalyzing a subsequent aromatic ring cleavage reaction to yield acyclic products rather than hydroxylated aromatic ones. Our calculations show that the rearomatization of the hydroxylated intermediate occurs spontaneously in aqueous solution, implying that the ring-opening process occurs inside the enzyme active site with limited water around. The instability of the hydroxylated intermediate of MHPCO is the main reason that the acyclic products are formed. Previously proposed mechanisms for the ring-opening step are studied, and are shown to be less likely to occur (ΔΔG≠298 >35 kcal/mol). Two new pathways with reasonable barrier heights (ΔΔG≠298 <15 kcal/mol) are reported herein, which are in accordance with all experimental information present to date.

  • 13. Tu, Guangde
    et al.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Vahtras, Olav
    Ågren, Hans
    Core electron chemical shifts of hydrogen-bonded structures2009In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 468, no 4-6, p. 294-298Article in journal (Refereed)
    Abstract [en]

    We examine the possibility to study hydrogen-bonded structures through core ionization energies. We use a recently derived self-interaction corrected density functional theory method where the core ionization energies for all chemically shifted elements are obtained by a single calculation of the ground state of the structures. A direct dependency between the hydrogen atom to acceptor atom bond length and the chemical shift of the core ionization energy of the acceptor atom is found, something that has ramifications for the possibility of effective predictions of hydrogen bond lengths in hydrogen-bonded systems. This observation is verified by the conventional, much more time-consuming, self-consistent field calculations based on density functional theory.

  • 14.
    Tu, Yaoquan
    et al.
    Örebro University, School of Science and Technology.
    Laaksonen, Aatto
    Arrhenius Lab, Div Phys Chem, Stockholm Univ, Stockholm, Sweden.
    Implementing Quantum Mechanics into Molecular Mechanics: Combined QM/MM Modeling Methods2010In: Combining Quantum Mechanics and Molecular Mechanics:  Some Recent Progresses in QM/MM Methods / [ed] John R. Sabin and Erkki Brändas, San Diego, USA: Elsevier, 2010, p. 1-15Chapter in book (Other academic)
  • 15. Zhang, Qiong
    et al.
    Bulone, Vincent
    Ågren, Hans
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    A molecular dynamics study of the thermal response of crystalline cellulose I beta2011In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 18, no 2, p. 207-221Article in journal (Refereed)
    Abstract [en]

    Molecular dynamics simulations were performed to better understand the atomic details of thermal induced transitions in cellulose I beta. The latest version of the GLYCAM force field series (GLYCAM06) was used for the simulations. The unit cell parameters, density, torsion angles and hydrogen-bonding network of the crystalline polymer were carefully analyzed. The simulated data were validated against the experimental results obtained by X-ray diffraction for the crystal structure of cellulose I beta at room and high temperatures, as well as against the temperature-dependent IR measurements describing the variation of hydrogen bonding patterns. Distinct low and high temperature structures were identified, with a phase transition temperature of 475-500 K. In the high-temperature structure, all the origin chains rotated around the helix axis by about 30A degrees and the conformation of all hydroxymethyl groups changed from tg to either gt on origin chains or gg on center chains. The hydrogen-bonding network was reorganized along with the phase transition. Compared to the previously employed GROMOS 45a4 force field, GLYCAM06 yields data in much better agreement with experimental observations, which reflects that a cautious parameterization of the nonbonded interaction terms in a force field is critical for the correct prediction of the thermal response in cellulose crystals.

  • 16.
    Zhang, Qiong
    et al.
    AlbaNova Univ Ctr, Dept Theoret Chem, Royal Inst Technol, Stockholm, Sweden; Adv Mat Lab, E China Univ Sci & Technol, Shanghai, Peoples R China; Inst Fine Chem, E China Univ Sci & Technol, Shanghai, Peoples R China.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Tian, He
    Adv Mat Lab, E China Univ Sci & Technol, Shanghai, Peoples R China; Inst Fine Chem, E China Univ Sci & Technol, Shanghai, Peoples R China.
    Zhao, Yanli
    Dept Chem, Northwestern Univ, Evanston IL, USA.
    Stoddart, Fraser J.
    Dept Chem, Northwestern Univ, Evanston IL, USA.
    Ågren, Hans
    AlbaNova Univ Ctr, Dept Theoret Chem, Royal Inst Technol, Stockholm, Sweden; Adv Mat Lab, E China Univ Sci & Technol, Shanghai, Peoples R China; Inst Fine Chem, E China Univ Sci & Technol, Shanghai, Peoples R China.
    Working mechanism for a redox switchable molecular machine based on cyclodextrin: a free energy profiles approach2010In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 114, no 19, p. 6561-6566Article in journal (Refereed)
    Abstract [en]

    This paper reports the working mechanism for a redox-responsive bistable [2]rotaxane incorporating an alpha-cyclodextrin (alpha-CD) ring (J. Am. Chem. Soc. 2008, 130, 11294-11296), based on free energy profiles obtained from all-atom molecular dynamics simulations. Employing an umbrella sampling technique, the free energy profiles (potential of mean force, PMF) were calculated for the shuttling motion of the alpha-CD ring between a tetrathiafulvalene (TTF) recognition site and a triazole (TZ) unit on the dumbbell of the rotaxane for three oxidation states (0, +1, +2) of the TTF unit. These calculated free energy profiles verified the experimentally observed binding preference for each state. Analysis of the free energy components reveals that, for these alpha-CD-based rotaxanes with charged TTF units, the real driving force for the shuttling in the oxidized states is actually the interactions between water and the rotaxane components, which overwhelms the attractive interactions between the alpha-CD ring and the charged dumbbell. In this work, we put forward a feasible approach to correctly describe the complexation behavior of CD with charged species, that is, free energy profiles obtained from all-atom molecular dynamics simulation.

  • 17. Zhao, Ke
    et al.
    Tu, Yaoquan
    Örebro University, School of Science and Technology.
    Luo, Yi
    Molecular dynamics and quantum chemistry study on conformations and optical properties of hydrogen bonded dipolar merocyanine dyes2009In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 113, no 30, p. 10271-10276Article in journal (Refereed)
    Abstract [en]

    An earlier proposed strategy to orient two merocyanine dyes in the desirable head-to-tail parallel fashion through multiple hydrogen bonds has been examined by molecular dynamics simulations and quantum chemical calculations. Two different merocyanine dyes dissolved in chloroform solution under various conditions are simulated by molecular dynamics. It is found that two dipolar units can be well connected through various numbers of hydrogen bonds. Although the probability to form the desirable head-to-tail dimer is unfortunately small even under strong poling electric field and low temperature, the formation of unwanted antiparallel structure has been effectively reduced. Typical hydrogen bonded dimers obtained from molecular dynamics simulations have been studied by hybrid density functional calculations. It is found that only the most probable complex can lead to the optical absorption spectrum that is in close agreement with the corresponding experiments. Calculated results for dipole moments of ground and charge transfer states, as well as first hyperpolarizabilities, of three typical complexes have also been provided.

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