L-alanine in a droplet of water: A density-functional molecular dynamics study

被引:75
作者
Degtyarenko, Ivan M.
Jalkanen, Karl J.
Gurtovenko, Andrey A.
Nieminen, Risto M.
机构
[1] Aalto Univ, Phys Lab, FIN-02015 Helsinki, Finland
[2] Curtin Univ Technol, Dept Appl Chem, Nanochem Res Inst, Perth, WA 6845, Australia
[3] Univ Bradford, Inst Pharmaceut Innovat, Computat Lab, Bradford BD7 1DP, W Yorkshire, England
关键词
D O I
10.1021/jp0676991
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
We report the results of a Born-Oppenheimer molecular dynamics study on an L-alanine amino acid in neutral aqueous solution. The whole system, the L-alanine zwitterion and 50 water molecules, was treated quantum mechanically. We found that the hydrophobic side chain (R = CH3) defines the trajectory path of the molecule. Initially fully hydrated in an isolated droplet of water, the amino acid moves to the droplet's surface, exposing its hydrophobic methyl group and alpha-hydrogen out of the water. The structure of an L-alanine with the methyl group exposed to the water surface was found to be energetically favorable compared to a fully hydrated molecule. The dynamic behavior of the system suggests that the first hydration shell of the amino acid is localized around carboxylate (CO2-) and ammonium (NH3+) functional groups; it is highly ordered and quite rigid. In contrast, the hydration shell around the side chain is much less structured, suggesting a modest influence of the methyl group on the structure of water. The number of water molecules in the first hydration shell of an alanine molecule is constantly changing; the average number was found to equal 7. The molecular dynamics results show that L-alanine in water does not have a preferred conformation, as all three of the molecule's functional sites (i.e., CH3, NH3+, CO2-) perform rotational movements around the C-alpha-site bond.
引用
收藏
页码:4227 / 4234
页数:8
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