An ab initio study on the torsional surface of alkanes and its effect on molecular simulations of alkanes and a DPPC bilayer
An ab initio study on the torsional surface of alkanes and its effect on molecular simulations of alkanes and a DPPC bilayer
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DOI：
10.1021/jp0468096
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发表时间：
2005-03-24
影响因子：
3.3
通讯作者：
Pastor, RW
中科院分区：
文献类型：
--
作者：
Klauda, JB;Brooks, BR;Pastor, RW
从丁烷到庚烷的 119 种正构烷烃构象的能量大约在 CCSD(T)/cc-pVQZ 水平上计算。随着链长的增加，gauche (g) 构象异构体相对于反式 (t) 的能量降低。在所谓的“正戊烷效应”中，与不相邻的构象异构体相比，具有相同符号的相邻的高斯构象异构体是稳定的；例如，对于己烷，tgt、tgg 和 gtg 的能量分别为 0.600、0.930 和 1.18 kcal/mol。 CHARMM27 (C27) 力场中的扭转项适合计算出的 QM 能量，以产生修正后的势能 C27r。与 C27 相比，使用 C27r 对正烷烃（庚烷、癸烷、十三烷和十五烷）进行分子动力学模拟可产生更多的稀疏态、更高的转变率以及与实验的更高一致性。此外，水合 DPPC 脂质双层的 C27r 模拟与脂肪族链端的实验 NMR 氘序参数更加一致。
Energies of 119 conformations of normal alkanes from butane to heptane were calculated at approximately the CCSD(T)/cc-pVQZ level. Energies of gauche (g) conformers relative to trans (t) decrease as chain length increases. In what is termed the "positive pentane effect", adjacent gauche conformers of the same sign are stabilized compared to nonadjacent conformers; e.g., for hexane the energies of tgt, tgg, and gtg are 0.600, 0.930, and 1.18 kcal/mol, respectively. Torsional terms in the CHARMM27 (C27) force field were fit to the calculated QM energies to yield a revised potential, C27r. Molecular dynamics simulations of normal alkanes (heptane, decane, tridecane, and pentadecane) with C27r yield higher populations of gauche states, increased transition rates, and improved agreement with experiment as compared to C27. In addition, C27r simulations of a hydrated DPPC lipid bilayer yield improved agreement with the experimental NMR deuterium order parameters for the aliphatic chain ends.