Salamatova Evgeniia, Cunha Ana V, Shinokita Keisuke, Jansen Thomas L C, Pshenichnikov Maxim S
Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Phys Chem Chem Phys. 2017 Oct 25;19(41):27960-27967. doi: 10.1039/c7cp03222f.
Hydrogen-bonding plays a crucial role in many chemical and biochemical reactions. Alcohols, with their hydrophilic and hydrophobic groups, constitute an important class of hydrogen-bonding molecules with functional tuning possibilities through changes in the hydrophobic tails. Recent studies demonstrated that for solutions of alcohols changes in the hydrophobic tail significantly affect a broad range of dynamics properties of the liquid. Still, the understanding is lacking on the origin of such differences in terms of a solvent- versus a solute-dominated effect. Here we reveal this origin by studying hydrogen-bond dynamics in a number of alcohol molecules - from methanol to butanol - diluted in a hydrogen-bond accepting environment, acetonitrile. The dynamics were investigated by pump-probe and 2D infrared spectroscopy combined with molecular dynamics-spectral simulations, using the OH stretching mode as a reporter. For all the considered alcohols, the vibrational lifetime of the OH stretching mode was found to be ∼3 ps. The hydrogen-bond dynamics exhibit similar behavior with a fast (∼200 fs) initial relaxation dominated by librational motion and a slow (∼4 ps) relaxation due to hydrogen-bond exchange dynamics. The similar dynamics over such a broad range of alcohols led us to conclude that the previously observed differences in dynamics in bulk alcohols originate from the dependence of the solvent properties on the hydrophobic tail, while the solute properties as found herein are essentially independent of the hydrophobic tail.
氢键在许多化学和生物化学反应中起着至关重要的作用。醇类具有亲水和疏水基团，是一类重要的氢键分子，可通过改变疏水尾部来实现功能调控。最近的研究表明，对于醇溶液，疏水尾部的变化会显著影响液体的一系列动力学性质。然而，对于这种差异的起源，从溶剂主导效应还是溶质主导效应的角度来看，仍缺乏相关认识。在此，我们通过研究在氢键接受环境乙腈中稀释的从甲醇到丁醇的多种醇分子中的氢键动力学来揭示这一起源。使用OH伸缩振动模式作为报告基团，通过泵浦 - 探测和二维红外光谱结合分子动力学 - 光谱模拟来研究动力学。对于所有考虑的醇类，发现OH伸缩振动模式的振动寿命约为3皮秒。氢键动力学表现出相似的行为：快速（约200飞秒）的初始弛豫由摆动运动主导；慢速（约4皮秒）的弛豫则归因于氢键交换动力学。在如此广泛的醇类中观察到的相似动力学使我们得出结论：之前在本体醇类中观察到的动力学差异源于溶剂性质对疏水尾部的依赖性；而本文所发现的溶质性质基本上与疏水尾部无关。
