Effect of temperature perturbation on hydrogen bonding in aqueous solutions of different urea concentrations

Abstract

Water structure modification by urea and temperature has been studied in aqueous solution by analyses of changes in hydrogen bonding and extent of aggregation. ABSTRACT Water absorption peaks in near-infrared (NIR) and attenuated total reflectance (ATR)-Fourier transform infrared (FTIR), spectroscopy at different temperatures both in the absence and presence of urea have been analyzed to investigate hydrogen bonding in aqueous solution by perturbations of temperatures and concentration of urea. Concentration dependent basic spectra of aqueous urea solutions represent different clusters in the system originated from the difference of the extent of self-aggregation of urea molecules and water-urea interactions. Derivative and deconvoluted spectra confirm the presence of different structural components or clusters in pure water; but in presence of urea a new strong water cluster could be identified for the first time after certain concentration of urea. The degree of perturbation has been evaluated by 2D correlation and difference spectroscopy. Apparent molar volume, free energy change of activation (∆G), change in enthalpy of activation (∆H) and entropy of activation (∆S) for viscous flow of water in presence and absence of urea have been analyzed. The comprehensive analyses help to infer different extent of aggregation of urea molecules and formation of clusters by water-urea interactions in aqueous urea solutions.

Temperature Perturbation on Hydrogen Bonding in Aqueous Solutions at Different Amide Concentrations

“…The strengths of hydrogen bond of these clusters are not equal. In case of aqueous urea solution, two prominent shoulders appear at 5104 and 5164 cm −1 due to the presence of different clusters . This compares very well with the behavior of aqueous formamide system.…”

“…Hence, low energy is required to oscillate the bond. In analogous to aqueous formamide system, both bands of amide III (1466 cm −1 ) and overlapped band at 1635 cm −1 for aqueous urea system were shifted to lower wavenumbers with increasing concentration of urea …”

“…In a recent work, we extended the concept to aqueous urea system and could confirm that at all concentrations, urea disrupts water structure by forming direct hydrogen bond with water molecule . Interestingly, urea was reported to simultaneously act as a water structure maker additive where aggregated urea helps to form more organized water around itself …”

“…2D‐correlation spectroscopy was found to be useful for evaluation of the degree of perturbation, strength, and size of different clusters for aqueous system . Interestingly, urea was reported to simultaneously act as a water structure maker additive where aggregated urea helps to form more organized water around itself …”

“…A comparison of the experimental results with the results calculated by density functional theory (DFT) for different amide‐water complexes can be used to gain a deeper insight in to the mechanism of modification of the aqueous environment by amide molecules and help to have fundamental understanding of water structure modification. In this work, we further analyzed our results on water structure modification by the simplest and the most common amide, urea and compared the observations with those for a series of amides. The formation or disruption of different clusters was extensively studied in presence of formamide, NMF, and DMF in aqueous solutions at different temperatures and concentrations of amides by attenuated total reflectance‐Fourier transform IR (ATR‐ FTIR) and FT‐NIR spectroscopy.…”