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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Classical trajectory simulations of photoionization dynamics of tryptophan: Intramolecular energy flow, hydrogen-transfer processes and conformational transitions
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Classical trajectory simulations of photoionization dynamics of tryptophan: Intramolecular energy flow, hydrogen-transfer processes and conformational transitions

机译：色氨酸光电离动力学的经典轨迹模拟：分子内能流，氢转移过程和构象转变

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摘要

One-photon and two-photon ionization dynamics of tryptophan is studied by classical trajectory simulations using the semiempirical parametric method number 3 (PM3) potential surface in "on the fly" calculations. The tryptophan conformer is assumed to be in the vibrational ground state prior to ionization. Initial conditions for the trajectories are weighted according to the Wigner distribution function computed for that state. Vertical ionization in the spirit of the classical Franck-Condon principle is assumed. For the two-photon ionization process the ionization is assumed to go resonantively through the first excited state. Most trajectories are computed, and the analysis is carried out for the first 10 ps. A range of interesting effects are observed. The main findings are as follows: (1) Multiple conformational transitions are observed in most of the trajectories within the ultrafast duration of 10 ps. (2) Hydrogen transfer from the carboxyl group to the amino group and back has been observed. A zwitterion is formed as a transient state. (3) Two new isomers are formed during the dynamics, which have apparently not been previously observed. (4) Fast energy flow between the ring modes and the amino acid backbone is observed for both one- and two-photon ionization. However, the effective vibrational temperatures only approach the same value after 90 ps. The conformation transition dynamics, the proton-transfer processes and the vibrational energy flow are discussed and analyzed.
机译：色氨酸的一光子和二光子电离动力学是通过经典的轨迹模拟方法研究的，该方法使用半经验参数方法3号（PM3）势能面进行“动态”计算。色氨酸构象体假定为在电离之前处于振动基态。根据为该状态计算的维格纳分布函数，对轨迹的初始条件进行加权。假定按照经典弗兰克-康登原理的精神进行垂直电离。对于双光子电离过程，假定电离共振地通过第一激发态。计算了大多数轨迹，并在前10 ps进行了分析。观察到一系列有趣的效果。主要发现如下：（1）在10 ps的超快时间内，大多数轨迹中都观察到了多个构象转变。 （2）已经观察到氢从羧基转移到氨基并再转移回来。两性离子形成为瞬态。 （3）在动力学过程中形成了两个新的异构体，显然以前没有观察到。 （4）对于单光子和双光子电离，在环模和氨基酸主链之间观察到快速能量流。但是，有效振动温度仅在90 ps后才接近相同值。讨论并分析了构象转变动力学，质子传递过程和振动能流。

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