Solvent-Independent Anharmonicity for Carbonyl Oscillators.
Solvent-Independent Anharmonicity for Carbonyl Oscillators.
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DOI：
10.1021/acs.jpcb.7b00537
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发表时间：
2017-03-16
期刊：
影响因子：
--
通讯作者：
Boxer SG
中科院分区：
文献类型：
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作者：
Schneider SH;Kratochvil HT;Zanni MT;Boxer SG
为了理解凝聚相中分子间的非共价相互作用，振动频移的物理起源已经被广泛研究。以羰基为例，振动溶剂变色、分子动力学模拟和振动斯塔克光谱表明，在简单溶剂中观察到的频移主要是由振动斯塔克效应引起的环境电场引起的。这与许多以前引用的振动频率移动的描述相反，例如键的极化，即键的力常数和/或部分核电荷因环境而改变，通常以有利的共振结构来说明。在这里，我们通过使用2D IR测量的振动溶剂变色性来检验这些假设，以评估键的非谐性与溶剂的关系。这些结果表明，用正己烷、DMSO和D2O进行测试时，羰基键的非谐性与溶剂无关，并得到了模拟2D光谱的支持。为了支持线性振动Stark效应，这些2D IR测量结果与Stark调谐率不受氢键和非氢键环境产生的电场扰动的断言一致，进一步扩大了羰基探针在研究分子间相互作用方面的普遍适用性。
The physical origins of vibrational frequency shifts have been extensively studied in order to understand noncovalent intermolecular interactions in the condensed phase. In the case of carbonyls, vibrational solvatochromism, MD simulations, and vibrational Stark spectroscopy suggest that the frequency shifts observed in simple solvents arise predominately from the environment’s electric field due to the vibrational Stark effect. This is contrary to many previously invoked descriptions of vibrational frequency shifts, such as bond polarization, whereby the bond’s force constant and/or partial nuclear charges are altered due to the environment, often illustrated in terms of favored resonance structures. Here we test these hypotheses using vibrational solvatochromism as measured using 2D IR to assess the solvent dependence of the bond anharmonicity. These results indicate that the carbonyl bond’s anharmonicity is independent of solvent as tested using hexanes, DMSO, and D2O and is supported by simulated 2D spectra. In support of the linear vibrational Stark effect, these 2D IR measurements are consistent with the assertion that the Stark tuning rate is unperturbed by the electric field generated by both hydrogen and non-hydrogen bonding environments and further extends the general applicability of carbonyl probes for studying intermolecular interactions.