Investigation of the kinetics of exchange of water in Mn(Fe)-ethylenediamine-N,N′-disuccinic acid systems by nuclear magnetic relaxation

The number of water molecules in the complexes and the nature of their interaction with the central ions and with the active groups of the ligand were established by investigation of the kinetics of the exchange of water in Mn(Fe)-edds systems by nuclear magnetic relaxation. The Mn-edds·nH₂O complex contains three molecules of water, one of which is bound to the manganese ion while the other two are bound to the carboxyl groups of the edds. In the Fe-edds·nH₂O complex two water molecules are bound to the central ion and one to the carboxyl group of the edds. The mechanism of the exchange processes, which have intermolecular and intramolecular character, was established. The values of the kinetic parameters E_a, H and S indicate a preference for the S_N2 mechanism of exchange. The denticity and the structure of the complexes vary with variation of temperature.Institute of General and Inorganic Chemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 4, pp. 506–512, July–August, 1991. Original article submitted July 10, 1987.     

Characteristics of interfacial water affected by proteins adsorbed on activated carbon

The influence of proteins (bovine serum albumin, BSA, and mouse gamma-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.