Mobility of water in NaCl and brain heart infusion (BHI) solutions as studied by 17O NMR

Abstract

The molecular dynamic behaviour of water molecules in aqueous solution has been determined by oxygen-17 NMR according to the anisotropic reorientation, two-correlation-time model for bound water. Solutions of brain heart infusion (BHI), NaCl and their 1:1 mixture have been analysed. The anisotropic water population was distinguished into a slow (τs bw) and a fast (τf bw) relaxing component. The slow relaxing component was affected by the nature of the solute, while the fast relaxing component was not. NaCl was found to bind water molecules more strongly (higher τs bw) than BHI. Water was more bound in the 1:1 mixture than in the solution containing only BHI. The population of bound water (P bw) was concentration dependent and increased with increasing solids content. BHI, at the suspension point, bound ∼50% of the total water, while NaCl at saturation bound only ∼10%. The 1:1 mixture bound water in a synergistic manner that resulted in a slightly higher Pbw, than in BHI at each solid concentration. The Pbw correlated well with the amount of unfreezable water (as measured by DSC) present in the BHI samples.