SELECTIVE HYDROLYSIS OF PHOSPHATE-ESTERS, NITROPHENYL PHOSPHATES AND UPU, BY DIMERIC ZINC-COMPLEXES DEPENDS ON THE SPACER LENGTH

Zn(II) complexes of monomers and dimers derived from 1,4,7-triazacyclo dodecane and 1,5,9-triazacyclotetradecane were examined as catalysts f or the hydrolyses of p-nitrophenyl phosphate and bis(p-nitrophenyl) ph osphate and for the cyclizations of p-nitrophenyl 2-hydroxypropyl phos phate and 3',5'-uridyluridine (UpU). The dimers with 1,4-phenyl and 1, 3-phenyl linkers were more effective than were monomers or a longer di mer-with a 4,4'-biphenyl linker-in the hydrolysis of p-nitrophenyl pho sphate, suggesting that two Zn(II)) ions coordinate to the phosphate g roup, as in the enzyme alkaline phosphatase. However, for the hydrolys is or cyclization of the phosphate diesters, the longer biphenyl linke r was preferred. In this case one Zn(II) coordinates to the phosphate group while the other delivers a nucleophilic oxide anion. Bell-shaped pH vs rate profiles were seen in both cases, but with different pK's related to the specific mechanisms in the two cases.