Special structural and dynamical interplay of cyano-based novel deep eutectic solvents

Abstract

Research studies on novel deep eutectic solvent (DES) systems, their features, and potential utilization are becoming highly attractive. Novel eutectic mixtures composed of cyano-based derivatives (bromophenylacetonitrile and bromobenzonitrile) and levulinic acid are described herein. These systems were characterized by Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and differential scanning calorimetry (DSC). Quantum mechanical calculations, including electrostatic potential surfaces and visual analysis of non-bonded interactions, were applied to study hydrogen bonding in minimal molecular clusters. Other microscopic features were evaluated by classical molecular dynamics simulations, including contact probability, radial distribution functions, pair dynamic analysis, and void distribution. It is interesting to find the occurrence of a proton transfer process in the system based on 3-bromobenzonitrile, which in turn may affect the chemical shifts of corresponding protons in NMR characterization. The structures of these systems were determined by the formation of heteroassociations through hydrogen bonds between the cyano site in bromophenylacetonitrile/bromobenzonitrile and the hydroxyl hydrogen bond donor site in levulinic acid. Nevertheless, the homoassociations of starting materials with a longer dimer lifetime cannot be ignored since they contributed to the formation of heterogeneous nanostructures in DESs. These simultaneous and competing nanostructures can be considered as the driving forces for the eutectic solvent formation. The developed solvents can be further utilized in a variety of chemical and biochemical applications.