Concentration and isotope effects in the stability of agarose gelsa)

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Abstract
Agarose–water gelling systems are of interest as models for extended supramolecular and molecular structures of wide biological significance. Precise photometric recording techniques as recently revived are here used for a study of the influence of polymer concentration and deuterium isotope substitution on molecular and supramolecular order. These techniques are suitable for studying both types of order in one and the same sample. Experiments at different polysaccharide concentrations allowed evaluation, under limiting assumptions, of the heat of reaction of the polymer cross-linking processes. Substitution of H2O with D2O improved the stability of molecular structures as well as recognition and adhesion among ordered molecules, responsible for the growth of supramolecular order. The potential factors governing stabilization of both types of order are discussed. A sole role of a greater strength of deuterium bonding is not inferred from our data. A role of isotopic alterations of the entropy term due to interactions between solvent and the polymer nonpolar groups appears probable. Closely similar conclusions were reached in a recent study of polynucleotide systems.