H‐Bonding in Water of Hydration: NIR Spectral Studies of Hydration Behavior of 1‐n‐Alkyl‐3‐metylimidazolium‐Based Bromide and Amino Acid Ionic Liquids at 298.15 K

Abstract

H‐bonding in ionic hydration is crucial for understanding various phenomena such as osmolyte effects, ion transport, electrochemical processes, etc. Ionic liquids (ILs) from the biomaterials have great affinity for protein solubility and stabilization due to hydrophobicity and hydrogen bonding ability. To explore potential use of ionic liquids, it is essential to understand hydration of ionic liquids with detailed information on H‐bonding within the water of hydration. In this context, near‐infrared spectral investigation of H‐bonding in water of hydration of 1‐n‐alkyl‐3‐methylimidazolium bromides and 1‐ethyl‐3‐methylimidazolium based amino acid ionic liquids were made through simultaneous estimation of hydration number and hydration spectra of ILs in the spectral range of 7800‐5800 cm−1. Weak H‐bonding extist in the water of hydration for 1‐n‐alkyl‐3‐methylimidazolium bromides while strong cooperative H‐bonding exists in case of amino acid ionic liquids leading to higher hydration numbers. The results further demonstrate that the individual resolved spectral components can be used to analyse (qualitatively and quantitatively) different types of H‐bonded species at ionic surfaces. Along with all these, the effect of hydrophobicity on hydration behavior as well as on the nature and strength of H‐bonding within the hydration shell of ions are also probed and discussed.

Density and Speed-of-Sound Measurements for Dilute Binary Mixtures of Diethylammonium-Based Protic Ionic Liquids with Water

“…19 Near-infrared (NIR) investigations for aqueous solutions of amino acid ionic liquids (AAILs) showed that water in the hydration shell of amino acid anions makes a major contribution to the icelike structure, i.e., the hydration shell of amino acid anions is highly structured. 59 Seen in this light, the observed large hydration numbers for studied PILs are due to the cooperative H-bonding of the carboxylate functional group of anions with the surrounding water. The hydration numbers of PILs at infinite dilution (Table 9) reveal that the hydration numbers increase with an increase in the hydrophobicity of the anions of PILs, and this trend exists even at the finite concentrations studied, indicating that the hydrophobic hydration existing at infinite dilution persists even at a higher concentration although ion association occurs at the highest concentration studied (Figure 11).…”

“…Recently, we observed large hydration numbers for amino acid ionic liquids and further showed that the observed hydration numbers are solely due to the amino acid anions, as the associated cations are only slightly hydrated. 19,59 The analysis of partial molar entropy data and enthalpy−entropy compensation effects revealed that the observed large hydration numbers for amino acid ionic liquids are due to cooperative H-bonding with and around the carboxylate functionality of amino acid anions. 19 Near-infrared (NIR) investigations for aqueous solutions of amino acid ionic liquids (AAILs) showed that water in the hydration shell of amino acid anions makes a major contribution to the icelike structure, i.e., the hydration shell of amino acid anions is highly structured.…”

In situ insight into the self-assembly evolution of ABA-type block copolymers in water during the gelation process using infrared spectroscopy and near-infrared spectroscopy

“…5a1 and b1, respectively, corresponding to the absorption of 2 v 3 and v 2 + v 3 of CH groups. 58,59 For a clear comparison, the transformed spectra of homopolymer PDAAM (yellow curve) and PDAAM powder (purple curve) were also plotted in the two figures, respectively. PC1 is compared with the transformed spectra of homopolymer PDAAM, and similarities were found between them.…”

“…5a1 and b1, respectively, corresponding to the absorption of 2v 3 and v 2 + v 3 of CH groups. 58,59 For a clear Fig. 5 The first two PCs (a and b) in the region from 6200 to 5600 cm À1 , and the third (c) and sixth (d) PCs in the region from 7200 to 6400 cm À1 obtained by NPCA from the spectra: the loading (a1-d1), time scores (a2-d2), temperature scores (a3-d3) and concentration scores (a4-d4); the lines in (b3-d3) were obtained by linear fitting in two or three stages.…”

Dielectric Relaxation and Hydration Interactions for Protic and Aprotic Ionic Liquids using Time Domain Reflectometry

“…Microscopic scenarios in terms of interactions proposed from these techniques highlights ion–solvent interaction, but complete and coherent understanding in terms of weakening or strengthening of interactions between ions and water is not clear. In our laboratory the ion–ion, ion–solvent, and ion–pair interactions and hydrophobic effects have been studied using near-infrared (NIR) spectroscopy and with the help of thermodynamic properties obtained using vapor pressure, density, and speed of sound measurements. − The obtained thermodynamic parameters such as osmotic coefficient, partial molar volumes, and isentropic and isothermal compressibilities infer a combination of numerous interactions, so it is complex to validate the strengthening and weakening of specific interactions responsible for their kosmotropic or chaotropic behavior of ionic liquids in aqueous medium. The observed interactions of ILs with water studied using different techniques discussed above are strongly related to H-bonding and non-H-bonding nature of ILs.…”