NMR study of non-freezing water in protein-modified carbon adsorbents

Temperature dependences of 1H NMR spin–spin relaxation were studied for the non-freezing water at the surface of carbon matrices modified with proteins (human serum albumin (HSA) and mouse immunoglobulin (MIG)) in the presence of water-soluble carbodiimide. The entropy, DeltaS ne, and enthalpy, DeltaH ne, values characterizing molecular mobility in non-freezing water were estimated. The compensation effect was observed for all modified samples, which is well approximated by the linear dependence of the type DeltaH ne = T 0DeltaS ne + DeltaH ne 0. The compensation temperature T 0 = 231 ± 33 corresponds to such a state of non-freezing water, when the effect of modifying additives on the isobaric potential of molecular mobility activation in the non-freezing water, DeltaG ne, is minimal. The DeltaG ne has approximately constant value equal to DeltaH ne 0 = 24.2 ± 0.5 kJ/mol. Modification of the base carbon matrix with MIG protein results in higher structurization of the non-freezing water, whereas HSA reduces this structurization. The observed effects are explained in terms of the hydration of modifying agents and also by the peculiarities of their location on the surface of carbon adsorbent.