Vibrational solvatochromism and electrochromism of cyanide, thiocyanate, and azide anions in water
Vibrational solvatochromism and electrochromism of cyanide, thiocyanate, and azide anions in water
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DOI：
10.1039/c0cp00214c
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发表时间：
2010-01-01
影响因子：
3.3
通讯作者：
Cho, Minhaeng
中科院分区：
文献类型：
--
作者：
Lee, Hochan;Choi, Jun-Ho;Cho, Minhaeng
小红外探针分子已被发现可用于测量凝聚态和蛋白质中的局部电场，也可通过监测它们的振动耦合和频移来研究核酸和蛋白质的结构和动力学。然而，由于探针周围的溶剂分子或蛋白质肽和侧基产生的局部电场在空间上不均匀且高度不均匀，因此精确描述这种红外探针的振动溶剂化频移仍然很困难。我们最近开发了一个分布式相互作用位点模型来描述溶液中腈、硫氰酸酯和叠氮衍生物化合物和氨基酸的振动溶剂致变色和电致变色。在这里，腈或叠氮拉伸是制造模式。研究发现，分布在红外探针分子上的这些相互作用位点共同起着感应红外探针周围局部电场分布的天线作用。一旦了解了给定红外探针的振动溶剂化变色，就有可能定量地描述它们的振动斯塔克效应。通过对水团簇中氰化物、硫氰酸盐和叠氮化物阴离子的量子化学计算，我们扩展了离子红外探针的分布位点模型，并计算了振动Stark调谐率，以便与实验结果进行直接比较。结果表明，阴离子溶质向周围水分子的电荷转移是显著的，但对假卤化物离子红外探针的振动溶剂变色和电变色的影响不大。我们期望本计算结果将用于建立离子红外探针的振动频率与凝聚相和蛋白质基质中的局部电场之间的关系。
Small IR probe molecules have been found to be useful to measure local electric fields in condensed phases and proteins and also to study nucleic acid and protein structure and dynamics by monitoring their vibrational couplings and frequency shifts. However, it is still difficult to accurately describe the vibrational solvatochromic frequency shifts of such IR probes, because the local electric fields produced by surrounding solvent molecules or by protein peptide and side groups are spatially non-uniform and highly inhomogeneous around a probe. We recently developed a distributed interaction site model to describe the vibrational solvatochromism and electrochromism of nitrile-, thiocyanato-, and azido-derivatized compounds and amino acids in solutions. Here, the nitrile or azido stretch is the maker mode. It was found that those interaction sites distributed over the IR probe molecule collectively act as an antenna sensing local electric field distributions around the IR probes. Once the vibrational solvatochromism of a given IR probe is understood, it becomes possible to quantitatively describe their vibrational Stark effects. Carrying out quantum chemistry calculations of cyanide, thiocyanate, and azide anions in water clusters, we extended the distributed site model for ionic IR probes and calculated the vibrational Stark tuning rates for direct comparisons with experimental results. It turns out that the charge transfers from an anionic solute to surrounding water molecules are significant, but their effects on vibrational solvatochromism and electrochromism of pseudohalide ionic IR probes are not. We anticipate that the present computational results will be of use to establish the relationship between vibrational frequency of an ionic IR probe and local electric field in condensed phases and protein matrices.