Water sorption by human cells

Abstract

Water sorption by powdered human callus was studied using a vacuum microbalance, X-ray powder diffraction and NMR relaxation. The sorption data were fitted to theoretical isotherms. At high relative vapour pressures an increase in the monolayer value was found which is probably related to the swelling of the material. Adsorption/desorption hysteresis is present below 0.75' relative vapour pressure (r.v.p.). Only a small increase in protein chain separation was observed on water uptake, indicating that the primary level of organization of the keratin is hardly affected. The effect of solvent extraction is to reduce the strength of water binding but to leave the monolayer values constant. Isosteric heats confirm the reduction in affinity for water on solvent extraction and show that totally extracted callus behaves as a mildly hydrophobic material. The results are consistent with a model in which the water binding properties of callus are determined by the presence of water soluble components which allow a monomolecular layer of water to be formed at low r.v.p. followed by physical multilayer formation. Adsorption of sodium dodecyl sulphate was found to increase the monolayer value while dodecyl trimethyl ammonium bromide left the monolayer value unchanged. The NMR relaxation behaviour of water in callus is very similar to that of water on human hair and wool fibres. An activation enthalpy of 48 kJ · mol −1 was found for the T 2 relaxation and a very broad T 1 minimum was observed at about −20°C at an operating frequency of 45 MHz corresponding to a correlation time of 2.2 ns.