An insight into hydration structure of sodium glycinate from ab initio quantum chemical study

Ab initio study of hydrated cesium iodide dimer (CsI)2-/0(H2O)0-6 and the cation size effect on (MI)2-/0(H2O)0-6 (M = Li, Na, K, Cs)

The structures of microsolvated (CsI)₂^-/0(H₂O)_0-6 clusters were determined using ab initio calculations. Our studies show that one Cs atom at the apex was firstly separated from the pyramid-shaped (CsI)₂^- unit when the water number reaches 3, whereas CsI distances did not increase significantly from n = 0 to 6 for neutrals. Additionally, the atomic charge and reduced density gradient analyses were carried out; the results reveal that the extra electrons are almost entirely localized on terminal Cs atom and the Cs⁺-water interactions dominate in (CsI)₂^-(H₂O)_0-6. The water-water interactions show up at n = 5. The comparison of (CsI)₂^-/0(H₂O)_n with (MI)₂^-/0(H₂O)_n (M = Li, Na, K) shows that neutral (CsI)₂ is the most difficult to be separated, which matches the law of matching water affinity. As for anions, the most difficult separation occurs in the case of small size (LiI)₂^- due to the effect of extra electrons, and (MI)₂^- with larger size cation is more likely to interact with water to form a pyramid structure.

Tracing Local Nanostructure of the Aqueous Solutions of the Biocompatible [Cho][Gly] Ionic Liquid: Importance of Hydrogen Bond Attraction between Like-Charged Ions

The neat and aqueous solutions of the cholinium glycinate ionic liquid (IL), [Cho][Gly], at different water mole fractions, x_ws, are studied by molecular dynamics simulations. The changes in the local nanostructure of systems with composition have been determined by calculation of various structural distribution functions. Hydrogen bond (H-bond) attractions determine the major relative orientations of the oppositely and like charged nearest neighbors. The cation-anion H-bonds mainly form between the hydrogen of the hydroxyl or methyl groups of the cation and the carboxylate oxygen of the anion. A preferred (antiparallel) arrangement between adjacent [Cho]⁺ cations is due to the effective H-bond between the hydroxyl oxygen and the methyl hydrogen sites that promotes the like-charge cluster formation. Adding water decreases the occurrence probability of the [Cho]⁺···[Gly]^-···[Cho]⁺ bridge structure in the aqueous solutions due to the formation of the [Gly]^-···HOH···[Gly]^- structure via H-bonding. Observed density trend versus x_w is interpreted based on an interstice model and investigating the water cluster size distribution. Finally, the effect of x_w on the infrared (IR) vibrational spectra were studied and blue and red shifts were observed for the stretching and bending vibrational modes of the hydroxyl group of [Cho]⁺, respectively. Current findings will improve the efficient engineering design and task-specific applications of aqueous solutions of bio-ILs consist of [Cho]⁺ and amino acid anions.