The role of biopolymer structure in interactions between unlike biopolymers in aqueous medium

This paper elucidates the role of the structural factors (M(w), size, conformation) on the intensity of the interactions of biopolymer pairs which differ strongly in their molecular nature and structure, namely, 11S globulin-ovalbumin (pH 7.8, I = 0.1 mol/dm(3)); 11S globulin-dextran (pH 7.8, I = 0.1 mol/dm(3)), 11S globulin-pectinate (pH 7.8, I = 0.3 mol/dm3); fibrinogen-dextran (pH 7.4, I = 0.1 mol/dm(3)), fibrinogen-alginate (pH 7.4, I = 0.1 mol/dm(3)), alginate-dextran (pH 7.4, I = 0.1 mol/dm(3)) and alginate-carbohymethylcellulose (pH 7.4, I = 0.1 mol/dm(3)). For this purpose we have determined quantitatively the values of the cross second virial coefficients (A(23)) for the biopolymer pairs studied by light scattering and have carried out a comparison of the experimentally obtained values of the cross second virial coefficients with theoretical ones calculated on the basis of the size and conformational features of the interacting biopolymers (excluded volume contribution). Positive values of the An were observed for all the biopolymer pairs under investigation. This result testifies that there are thermodynamically unfavourable interactions between biopolymers in aqueous medium under experimental conditions. Thermodynamic incompatibility of the biopolymers in aqueous medium was observed turbidimetrically or by phase state analysis for all the biopolymer pairs studied. It was established that intensity of the thermodynamically unfavourable interactions between biopolymers correlates well with the contribution of the excluded volumes of the biopolymer molecules when uncharged. The electrostatic contribution to the intensity of the thermodynamically unfavourable interactions between biopolymers may be significant for interaction of the two similarly charged biopolymers. Correlation between the magnitudes of the forces due to the mutual exclusion of the biopolymers and phase equilibrium in the mixed aqueous solutions was observed. It was established that critical conditions of the phase separation and concentration area of the two-phase existence in the biopolymer systems are basically determined by the strength of the unfavourable interactions between different biopolymers and are independent of the nature of the main factors controlling interactions between biopolymers, namely, the excluded volume contribution or electrostatic interactions. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.