Water Mobility in Aqueous Solutions of Macromolecular Pharmaceutical Excipients Measured by Oxygen-17 Nuclear Magnetic Resonance

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The dynamics of water molecules associated with water-soluble polymers were studied by ^<17>O-NMR. The observed spin-lattice relaxation time, T_<1(obs)>, of water in aqueous solutions of polyethylene glycol (PEG), poly(vinylpyrrolidone) (PVP) and gelatin at polymer concentrations below 0.12 g/g of water could be described by an isotropic two-state model with a fast exchange. The tendency for the polymers to reduce the T_<1(obs)> of water was on the oreder of PEG<gelatin<PVP. At higher concentrations, deviations from the model were observed for PVP and gelatin. The T_<1(obs)> of water in the PEG solution was not affected by the molecular weight of the polymer. This suggests that the microviscosity around the polymer molecules is governed by the interaction between the polymer unit and water molecules, and is not affected by the molecular weight of polymers in contrast to the "macroviscosity". The polymer-water interaction that reduced the T_<1(obs)> of water was found to decrease with increasing temperature for all the polymers studied. The T_<1(obs)> of water in the gelatin solution exhibited the largest temperature dependence, suggesting that changes might occur in the molecular structure of gelatin at higher temperatures.
社団法人日本薬学会の論文
1995-07-15