¹H NMR Investigation on Effect of Solute Concentration on the Hydrogen Bonding and Glass Transition of Three-Carbon Polyalcohol Aqueous Solutions

Abstract

We investigated the effects of solute concentration on the hydrogen bonding interactions of three-carbon polyalcohol aqueous solutions. In order to inspect the capacity of the solutions to form glass, proton nuclear magnetic resonance (1 H NMR) chemical shifts were determined in binary mixtures of water and 1-propanol (NPA), 2-propanol (IPA), 1,2-propanediol (PG), 1,3-propanediol (PD), and glycerol at room temperature and at atmospheric pressure using the external reference method. We found that the alkyl proton chemical shifts of PG with the CH3CH(OH)-group showed biphasic behavior, which was different from other molecules. Water molecules formed relatively strong O-H• • •O hydrogen bonds with the alcohol hydroxyls. The proton chemical shifts of H2O and the hydroxyl protons decrease with an increase in the number of alcohol hydroxyls at the same mole fraction. Moreover, the proton chemical shifts of H2O and hydroxyl protons with the same number of alcohol hydroxyls are different because of their different locations. The order of increased basicity agrees with the order of increased ice homogeneous nucleation suppression, that is, glycerol>PG>PD>IPA>NPA. This explains why glycerol and PG are more suitable as cryoprotective agents (CPAs) among the five polyalcohols.