Molecular recognition of dipeptides. Catalysis of deuteration and hydrolysis of glycylglycine by dinuclear OBISDIEN Zn(II) complexes

Potentiometric equilibrium studies of the system: glycylglycine-Zn(II)-OBIS DIEN are described. Kinetic studies of hydrolysis and deuteration of glycyl glycine catalyzed by dinuclear Zn(II)-OBISDIEN complexes have been carried out. The hydroxyl groups coordinated to the metal ion in the complex play a n important role in the hydrolysis and deuteration reactions. The specific deuteration rate constants for individual species are k(LZn2HP4+) (P = glyc ylglycine) and k(LZn2P3+) = 0; k(LZn2(OH)P2+) = 7.0 x 10(-7) s-1; k(LZn2(OH )2P+) = 42.5 x 10(-7) s(-1) and k(LZn2(OH)3P+) = 42.5 x 10(-7) s(-1) also. the specific rate constants for the hydrolysis reaction are k(LZn2HP4+) and k(LZn2P3+) congruent to 1.0 x 10(-7) s(-1); k(LZn2(OH)P2+) = 4.6 x 10(-7) s(-1); k(LZn2(OH)2P+) = 4.8 x 10(-7) s(-1) and k(LZn2(OH)3P+) = 4.9 x 10(-7 ) s(-1). the results show that the most active species toward hydrolysis ar e the hydroxo species. The hydroxide groups are bound to the metal centers in the cavity of OBISDIEN, and glycylglycine probably has its carboxylate g roup coordinated to the Zn2+ on one side and the amide carbonyl coordinated to the other Zn2+ at the other side of the macrocycle. The role of the hyd roxide ion coordinated to the metal ion at the active center of hydrolytic enzymes seems to be important, and this model shows that the hydroxide ion coordinated to the metal center increases the rate constant of hydrolysis b y an average of 4.8 times, and the hydroxo complexes are the only active sp ecies for the deuteration reactions. (C) 1999 Elsevier Science S.A. All rig hts reserved.