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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Calculation of Rate Constants for Proton Transfer between Tethered Oxygens
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Calculation of Rate Constants for Proton Transfer between Tethered Oxygens

机译：束缚氧之间质子转移的速率常数的计算

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摘要

To model proton transfer in biological systems, we consider a modified H_5O_2~+ system, in which each of the two outermost hydrogens (H~*) is assigned a large mass in order to represent a backbone. For the potential energy surface of our model, we add a harmonic function, called the "backbone term", to the potential energy function of Ojamae, Shavitt, and Singer for H_5O_2~+. This backbone term holds the H~* atoms apart and, thus, provides various oxygen-oxygen distances and barriers for proton transfer. Variational transition-state theory (CVT) rate constants converge for H~* masses greater than 1000 amu. These rate constants decrease exponentially as the backbone-backbone equilibrium distance increases. CVT rate constants also decrease as the backbone-term force constant increases and converge in the limit of a large backbone-term force constant. Tunneling effects are more important at low temperature and for larger values of backbone-term force constants or backbone-backbone equilibrium distances. The motion of the system along the minimum energy path from the saddle point to the product involves the motion of the proton between two relatively fixed oxygens followed by fragment motion and relaxation into the product well.
机译：为了模拟生物系统中的质子转移，我们考虑了一个经过改进的H_5O_2〜+系统，在该系统中，两个最外面的氢（H〜*）中的每一个都分配了较大的质量以表示骨架。对于我们模型的势能面，我们在Ojamae，Shavitt和Singer的H_5O_2〜+势能函数中添加了一个谐波函数，称为“主干项”。该主链术语将H〜*原子分开，从而为质子转移提供了各种氧-氧距离和势垒。当H〜*质量大于1000 amu时，变分过渡状态理论（CVT）速率常数收敛。随着骨干-骨干平衡距离的增加，这些速率常数呈指数下降。 CVT速率常数也随着骨架项力常数的增加而减小，并收敛于较大的骨架项力常数的极限。隧道效应在低温下以及对于较大的主干项力常数或主干-主干平衡距离值更重要。系统沿着从鞍点到产物的最小能量路径的运动涉及质子在两个相对固定的氧之间的运动，然后发生碎片运动并松弛到产物阱中。

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