A Consistent Picture of the Proton Release Mechanism of oNBA in Water by Ultrafast Spectroscopy and Ab Initio Molecular Dynamics
A Consistent Picture of the Proton Release Mechanism of oNBA in Water by Ultrafast Spectroscopy and Ab Initio Molecular Dynamics
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DOI：
10.1021/jp109053r
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发表时间：
2011-02-10
影响因子：
3.3
通讯作者：
VandeVondele, Joost
中科院分区：
文献类型：
--
作者：
Donten, Mateusz L.;Hamm, Peter;VandeVondele, Joost
用瞬变泵浦探测红外光谱和从头算分子动力学相结合的方法，研究了水溶液中有争议的邻硝基苯甲醛(ONBA)光反应的皮秒和纳秒步骤。通过这种方式，测量的反应动力学得到了反应事件的原子图的补充，正如在显式溶剂中无偏模拟所获得的那样。我们的结果可以详细地描述oNBA质子光释放，这是一个基本重要的过程，并与在许多实验中使用oNBA作为质子笼有关。在第一步中，在亚皮秒时间尺度上形成稳定的烯酮中间体。该中间体以溶剂辅助的方式与羟基转移反应生成特征时间为7ps的亚硝基苯甲酸，最后在pH允许的条件下，该产物分子解离了一个时间常数为21 ns的羧基质子。这项工作中采用的理论和实验的特殊结合似乎足够普遍和强大，可以在超快反应系统的研究中找到广泛的应用。
With a combination of transient pump probe IR spectroscopy and ab initio molecular dynamics, the controversial pico- and nanosecond steps of the o-nitrobenzaldehyde (oNBA) photoreaction have been investigated in aqueous solution. In this way, the measured reaction kinetics have been complemented with an atomistic picture of the reactive events as obtained with unbiased simulations in explicit solvent. Our results allow for a detailed description of the oNBA proton photorelease, a process of fundamental importance and relevant to the use of oNBA as a proton cage in many experiments. In a first step, a stable ketene intermediate is formed on a subpicosecond time scale. This intermediate reacts in a solvent assisted way with an OH transfer to produce nitrosobenzoic acid with a characteristic time of 7 ps, Finally, in permitting pH conditions, this product molecule dissociates a carboxyl proton with a 21 ns time constant. The particular combination of theory and experiment employed in this work appears to be sufficiently general and powerful to find widespread application in the study of ultrafast reactive systems.