The V amylose–water system: Enthalpy of hydration on the helix exterior

The reaction, V amylose hydrate ⇄ H2O + V amylose dehydrate, where the amylose hydrate and dehydrate are pseudohexagonal, helical species with packing diameters of 13.7 and 13.0 A., respectively, has been studied. The V amyloses were exposed to water vapor pressures at various temperatures, with phase determination obtained by identifying solid reactant and product from their x‐ray patterns. Reversibility of reaction was found to occur over a 50–96°C. range. A Clausius‐Clapeyron plot yields a ΔH of reaction of 10.4 kcal./mole of water released, which value is close to analogous heats of reaction of many common hydrate systems.