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RISS 인기검색어
- 검색키워드
- 저자 : Schermann, Jean-Pierre (검색결과 4 건)
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Kim, Ju-Young,Schermann, Jean Pierre,Lee, Sung-Yul Korean Chemical Society 2010 Bulletin of the Korean Chemical Society Vol.31 No.1
Calculations are presented for the $\gamma$-aminobutyric acid-$(H_2O)_n$ (n = 0-5) clusters in both canonical and zwitterionic forms. We examine the effects of microsolvation on the structures and transformation between the canonical and zwitterionic forms. The canonical forms are predicted to be more stable for n = 0-4. With five microsolvating water molecules, the two forms of $\gamma$-aminobutyric acid become quasidegenerate, with the energies of zwitterionic forms slightly (by 1 - 3 kcal/mol) higher. The lowest energy zwitterionic conformer of $\gamma$-aminobutyric acid-$(H_2O)_5$ cluster is calculated to isomerize to canonical form through a barrier-less proton transfer process and is thus predicted to be kinetically unstable. Therefore, we predict that the canonical conformers of $\gamma$-aminobutyric acid should be observed predominantly in the gas phase at low temperature in presence of up to five water molecules.
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Keun Woo Lee,Jean Pierre Schermann,Sungyul Lee 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.1
Calculations are presented for the γ-aminobutyric acid-(H2O)n (n = 0-5) clusters in both canonical and zwitterionic forms. We examine the effects of microsolvation on the structures and transformation between the canonical and zwitterionic forms. The canonical forms are predicted to be more stable for n = 0-4. With five microsolvating water molecules, the two forms of γ-aminobutyric acid become quasidegenerate, with the energies of zwitterionic forms slightly (by 1 - 3 kcal/mol) higher. The lowest energy zwitterionic conformer of γ-aminobutyric acid-(H2O)5 cluster is calculated to isomerize to canonical form through a barrier-less proton transfer process and is thus predicted to be kinetically unstable. Therefore, we predict that the canonical conformers of γ-aminobutyric acid should be observed predominantly in the gas phase at low temperature in presence of up to five water molecules.
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Gaigeot, Marie-Pierre,Cimas, Alvaro,Seydou, Mahamadou,Kim, Ju-Young,Lee, Sungyul,Schermann, Jean-Pierre American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.51
<P>The role of water in the structural change of nicotine from its inactive form in the gas phase to its bioactive form in aqueous solution has been investigated by two complementary theoretical approaches, i.e., geometry optimizations and molecular dynamics. Structures of the lowest-energy nicotineH(+)-(H(2)O)(n) complexes protonated either on the pyridine (inactive form) or pyrrolidine (active form) ring have been calculated, as well as the free-energy barriers for the proton-transfer tautomerization between the two cycles. These structures show chains of 2-4 water molecules bridging the two protonation sites. The room-temperature free-energy barrier to tautomerization along the minimum-energy path from the pyridine to the pyrrolidine cycle drops rapidly when the number of water molecules increases from 0 to 4, but still remains rather high (16 kJ/mol with four water molecules), indicating that the proton transfer is a rather difficult and rare event. We compare results obtained through this explicit water molecule approach to those obtained by means of continuum methods. Car-Parrinello molecular dynamics (CPMD) simulations of the proton-transfer process in bulk with explicit water molecules have been conducted at room temperature. No spontaneous proton transfers have been observed during the dynamics, and biased CPMD simulations have therefore been performed in order to measure the free-energy profile of the proton transfer in the aqueous phase and to reveal the proton-transfer mechanism through water bridges. The MD bias involves pulling the proton from the pyridine ring to the surrounding bulk. Dynamics show that this triggers the tautomerization toward the pyrrolidine ring, proceeding without energy barrier. The proton transfer is extremely fast, and protonation of the pyrrolidine ring was achieved within 0.5 ps. CPMD simulations confirmed the pivotal role played by the water molecules that bridge the two protonation sites of nicotine within the bulk of the surrounding water.</P>
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Kim, Jiah,Kim, Seong Keun,Gré,goire, Gilles,Manil, Bruno,Schermann, Jean Pierre American Chemical Society 2011 The Journal of physical chemistry A Vol.115 No.33
<P>The <I>N</I>-hexanoyl-homoserine lactone (C6-HSL) molecule has been investigated by means of infrared multiphoton dissociation (IRMPD) and Fourier-transform infrared spectroscopy (FT-IR) under different conditions in an attempt to mimic biological situations encountered in communication between bacteria for quorum sensing. The protonated molecular ion was studied in the gas-phase that corresponds to a solvent-free situation somewhat analogous to that encountered in the receptor. The simulation of the IRMPD spectrum of the isolated ion was then conducted by means of quantum chemistry calculations in vacuum. In the case of the neutral species, the FT-IR spectra were recorded in D<SUB>2</SUB>O, mimicking the cytosolic and extracellular media as well as in 1-octanol that is often used for simulation of cell membranes. The interpretation was conducted by considering a C6-HSL molecule in its <I>endo</I> or <I>exo</I> conformation hydrogen-bonded to, respectively, six D<SUB>2</SUB>O and four 1-octanol molecules. A satisfying agreement with the experimental FT-IR studies conducted in solution at room temperature was obtained as long as a continuum IEFPCM model was added to the explicit solvent environment.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcafh/2011/jpcafh.2011.115.issue-33/jp205025p/production/images/medium/jp-2011-05025p_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp205025p'>ACS Electronic Supporting Info</A></P>
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