Selective hydrolysis of phosphate esters, nitrophenyl phosphates and UpU, by dimeric zinc complexes depends on the spacer length

Article abstract of DOI:10.1021/ja00125a005

Zn(II) complexes of monomers and dimers derived from 1,4,7-triazacyclododecane and 1,5,9-triazacyclotetradecane were examined as catalysts for the hydrolyses of p-nitrophenyl phosphate and bis(p-nitrophenyl) phosphate and for the cyclizations of p-nitrophenyl 2-hydroxypropyl phosphate 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 dimer - with a 4,4′-biphenyl linker - in the hydrolysis of p-nitrophenyl phosphate, suggesting that two Zn(II) ions coordinate to the phosphate group, as in the enzyme alkaline phosphatase. However, for the hydrolysis or cyclization of the phosphate diesters, the longer biphenyl linker 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.