Characteristics of interfacial water affected by proteins adsorbed on activated carbon

Abstract

The influence of proteins (bovine serum albumin, BSA, and mouse γ-globulin, IgG) physically adsorbed or covalently attached via coupling with N-cyclohexyl-N′-(2-morpholinoethyl) carbodiimide methyl-p-toluenesulfonate, CMC, to the surface of activated carbon SCN (spherical carbon with nitrogen) on the mobility of interfacial water molecules was studied by means of 1H NMR spectroscopy with freezing-out of bulk water at 180<T<273 K. Relaxation processes in the interfacial non-freezing water were investigated measuring transverse time t2 of proton relaxation dependence on the presence of proteins and CMC. The distribution function of activation free energy of relaxation (with a maximum at 20–22 kJ/mol) was calculated for the protein–water–carbon systems using a regularization procedure and the relationships between t2 and the amounts of the interfacial water unfrozen at T<250 K assuming the Arrhenius-type dependence for t2−1 on temperature. The state of unfrozen water in pores of SCN shows that the low temperature relaxation processes occur in narrow pores with half-width X<1.5 nm.