Comprehensive study on the structure and dynamics of ammonium-based biocompatible ionic liquids

Ammonium-based biocompatible ionic liquids (bio-ILs) are low-cost, non-toxic, widely available, biodegradable, and thermally stable compared to conventional ILs. This study highlights the structural and dynamic properties of (2-hydroxyethyl)trimethylammonium glycinate, known as choline glycinate ([CHO][GLY]), and ethyltrimethylammonium glycinate ([AMO][GLY]) examined using quantum mechanical computation and molecular dynamics (MD) simulations. The density functional theory (DFT) results reveal a stronger orbital interaction and increased stability in [CHO][GLY] due to the greater energy gap compared to that of [AMO][GLY]. This suggests that electron transfer is more likely in [AMO][GLY] during chemical reactions, indicating lower kinetic stability and higher chemical reactivity compared to [CHO][GLY]. Moreover, the study identifies the most important chemical reactivity species based on electronegativity (χ) and chemical hardness (η). Both values are lower for [AMO][GLY], reflecting its less pronounced nucleophilic sites compared with the [CHO][GLY] bio-IL.The hydrogen bond (HB) energy and cation-anion interaction energy (E_int) are found to be more significant in the [CHO][GLY] bio-IL, aligning with its higher anodic limit. These results suggest that the [CHO][GLY] bio-IL can be a more stable medium for separation, due to its ability to form stronger interactions, while the [AMO][GLY] bio-IL offers superior mass transport properties, making the two systems complementary for different green chemistry applications.