Chatterjee Srijan, Haldar Tapas, Ghosh Deborin, Bagchi Sayan
Physical and Materials Chemistry Division, CSIR-National Chemical Laboratory (CSIR-NCL), Dr. Homi Bhabha Road, Pune 411008, India.
Academy of Scientific and Innovative Research (AcSIR), Ghaziabad-201002, India.
J Phys Chem B. 2020 May 7;124(18):3709-3715. doi: 10.1021/acs.jpcb.9b11352. Epub 2020 Apr 28.
Deep eutectic solvents have emerged as inexpensive green alternatives to conventional solvents for diverse applications in chemistry and biology. Despite their importance as useful media in various applications, little is known about the microscopic solvation structures of deep eutectic solvents around solutes. Herein, we show that the electrostatic field, which can be estimated both from infrared experiments and theory, can act as a unified concept to report on the microscopic heterogeneous solvation of deep eutectic solvents. Using a fluorophore containing the carbonyl moiety as the solute and the electrostatic field as a descriptor of the solvation structure of the deep eutectic solvents, we report the residue-specific distribution, orientation, and hydrogen bonding in deep eutectic solvents constituting of choline chloride and alcohols of varying chain-lengths. We observe that an increase in alcohol chain-length not only affects the alcohol's propensity to form hydrogen bond to the solute but also alters the spatial arrangement of choline cations around the solute, thereby leading to a microheterogeneity in the solvation structure. Moreover, to extend our electrostatic field based strategy to other deep eutectic solvents, we report an emission spectroscopy based method. We show that this method can be applied, in general, to all deep eutectic solvents, irrespective of their constituents. Overall, this work integrates experiments with molecular dynamics simulations to provide insights into the heterogeneous DES solvation.
深共熔溶剂已成为传统溶剂廉价的绿色替代品，可用于化学和生物学的各种应用。尽管它们在各种应用中作为有用的介质很重要，但对于溶质周围深共熔溶剂的微观溶剂化结构却知之甚少。在此，我们表明，可通过红外实验和理论估算的静电场，能够作为一个统一的概念来描述深共熔溶剂的微观非均相溶剂化。使用含有羰基部分的荧光团作为溶质，并将静电场作为深共熔溶剂溶剂化结构的描述符，我们报道了由氯化胆碱和不同链长的醇组成的深共熔溶剂中残基特异性分布、取向和氢键。我们观察到醇链长度的增加不仅影响醇与溶质形成氢键的倾向，还改变了溶质周围胆碱阳离子的空间排列，从而导致溶剂化结构的微观非均相性。此外，为了将我们基于静电场的策略扩展到其他深共熔溶剂，我们报道了一种基于发射光谱的方法。我们表明，一般来说，这种方法可应用于所有深共熔溶剂，无论其成分如何。总的来说，这项工作将实验与分子动力学模拟相结合，以深入了解非均相深共熔溶剂的溶剂化作用。
