Effect of intermolecular orientation upon proton transfer within a polarizable medium.
Effect of intermolecular orientation upon proton transfer within a polarizable medium.
复制标题
分子间取向对可极化介质内质子转移的影响。
DOI：
10.1016/s0006-3495(91)82121-x
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发表时间：
1991
影响因子：
3.4
通讯作者：
Duan,X
中科院分区：
文献类型：
--
作者：
Scheiner,S;Duan,X
采用从头计算方法研究了细菌视紫红质中质子转移过程。HN= CH 2作为Schiff碱的小原型，而HCOO-模拟其含羧酸根的抗衡离子，HO-模拟酪氨酸的水的羟基，导致HCOO-·H+·NHCH 2和HO-·H+·NHCH 2络合物。在隔离中，两种复合物都倾向于中性对构型，其中中心质子与阴离子缔合。然而，Schiff碱可能在前一个络合物中质子化，产生HCOO-.+ HNHCH 2离子对，当存在与外部可极化介质的高度介电耦合时。在中间水平耦合的范围内，质子的平衡位置（在羧酸盐或席夫碱上）可以通过适当改变分子间角度来切换。在质子转移可能的耦合范围内，由60度重取向引起的pK位移计算为约5-12 pK U。质子转移的能垒增强了角度和介电耦合的变化引起质子转移的能力。
Ab initio calculations are used to investigate the proton transfer process in bacteriorhodopsin. HN=CH2 serves as a small prototype of the Schiff base while HCOO- models its carboxylate-containing counterion and HO- the hydroxyl group of water of tyrosine, leading to the HCOO-.H+.NHCH2 and HO-.H+.NHCH2 complexes. In isolation, both complexes prefer a neutral pair configuration wherein the central proton is associated with the anion. However, the Schiff base may be protonated in the former complex, producing the HCOO-.+HNHCH2 ion pair, when there is a high degree of dielectric coupling with an external polarizable medium. Within a range of intermediate level coupling, the equilibrium position of the proton (on either the carboxylate or Schiff base) can be switched by suitable changes in the intermolecular angle. pK shift resulting from a 60 degrees reorientation are calculated to be some 5–12 pK U within the coupling range where proton transfers are possible. The energy barrier to proton transfer reinforces the ability of changes in angle and dielectric coupling to induce a proton transfer.