Nitrocefin hydrolysis

Scheme 26 Proposed mechanism for nitrocefin hydrolysis catalyzed by [Zn2(BPAN) ( i-0H)( a-02PPh2)](C104)2.

Proposed mechanism and rate law for pH-dependence of nitrocefin hydrolysis. 

Additional kinetic studies performed under conditions wherein less water was present (1 9 DMSO acetone containing 0.28 M H20) yielded =(8.9 0.3)x 103M-1. The difference between the equilibrium binding constant K for the nitrocefin hydrolysis reaction catalyzed by [Zn2(BPAN)( i-0H)( i-02PPh2)](C104)2 under... 

Variable temperature kinetic studies for the hydrolysis of nitrocefin catalyzed by [Zn2L3(p-0H)(N03)2] in acetone DMSO yielded AH% = 88.4 + 5.3 kJlVT1 and A= —45.3 + 16.0 JM 1K 1. These values are similar to those found for nitrocefin hydrolysis catalyzed by [Zn2(BPAN)(ii-0H)( i-02PPh2)](C104)2 in 1 9 DMSO ac-etone (Akfi = 96.1 5.2kJM 1 and AS = —22.4+12 JM 1K 1) and are consistent with intramolecular attack by the bridging hydroxide on the coordinated P-lactam substrate in the rate-determining step.140... 

An important conclusion from these comparative studies is that mononuclear Zn(II) complexes can be as efficient for nitrocefin hydrolysis as binuclear systems, thus providing evidence that the second zinc center (Zn2) in metallo- 3-lactamases is not required for nucleophile activation or catalytic activity. 

Fig. 4 Nitrocefin hydrolysis catalyzed by a dinuclear zinc(II) complex and its intermediate.

Fig. 5.22 Mechanism proposed for nitrocefin hydrolysis via the formation of the blue intermediate by Cd2(C02EtH2Ll)(CH3C00)2] and binding of nitrocefin to Cd2(C02EtL2) (CH3C00)2]+...

Fig. 6.39 Proposed mechanism of nitrocefin hydrolysis by [Co2(C02EtH2Ll)(CH3COO)2]" atpH 8...

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