Nuclear magnetic resonance and thermochemical studies on the influence of urea on water structure

Hydrogen bonding dominated self-assembly mechanism of amphiphilic molecules in Chinese Baijiu

Molecular mechanisms underlying the aging of Chinese Baijiu remained elusive. This study proposed the self-assembly behavior of amphiphilic molecules dominated by hydrogen bonds in Chinese Baijiu for the first time. The self-assembly degree of amphiphilic clusters gradually intensifies with the prolonged storage time of Baijiu, comprehensively characterized at both micro and macro levels. The results indicated that the blue-shift of the Raman hydrogen bond vibrational peak (about 11 cm-1 and 7 cm-1, respectively), the increase in viscosity (5.71% and 2.22%, respectively), and the rise in dielectric constant (95.63% and 94.99%, respectively) during the 17-year cellaring process of Strong-flavor Baijiu and Jiang-flavor Baijiu were consistent with the evolutionary trends observed in molecular dynamics simulations. The essential driving factors of cluster structure alteration of amphiphilic aroma substances in Chinese Baijiu during cellaring were demonstrated from molecular level. This study provided a research approach to comprehending the aging mechanism of Chinese Baijiu from the micro level.

Fluorescence spectroscopic and viscosity studies of hydrogen bonding in Chinese Fenjiu

The associative behavior of ethanol with water and total hydrogen bonding property in Chinese Fenjiu were examined on the basis of fluorescence and viscosity measurements, respectively. Ethyl esters and acetic acid initially strengthened and then weakened ethanol-water hydrogen-bonding structure, while sodium chloride exhibited its enhanced effect. The fluorescence intensities and viscosities were measured for 12 Fenjiu samples of a distillery, aged for 0-20 years in two different types of containers. The ethanol-water fluorescence intensities and viscosities of Fenjiu samples are proportional to their contents of sodium ion and opposite to their contents of total esters. It can be concluded that the strength of the ethanol-water hydrogen bonding as well as the total hydrogen bonding in aged Fenjiu are directly predominated by total esters lost and sodium ion gained in ceramic containers and not dependent on just the aging time.

Molecular structure and dynamics of liquids: aqueous urea solutions

In this review a multi-technical approach to the analysis of the structure and dynamics of the urea/water system is described. The reorientational movement of the solute molecule is investigated by the analysis of spectral band-shapes, as well as with the use of the optical Kerr effect (OKE) and molecular dynamics simulation (MDS). The effect of solute concentration on the structure and dynamics of the aqueous solutions (aggregation, orientational distribution, solvation...) is studied by molecular dynamics simulation and neutron scattering. The results obtained by other techniques are included to provide a critical analysis. Finally, the low-frequency Raman spectra of the system are interpreted on the basis of the semi-quantitative information obtained by molecular dynamics simulation.

Gibbs Energy of Transfer of H+ Ion from Water to Urea-Water Mixtures

The thermodynamic dissociation constants for the isoelectronic reaction LH