Histidine esters, nickel complexes

More detailed studies of reactions of this type have been reported.96,97 Nickel(II) complexes of histidine and tryptophan provide stereoselectivity in the hydrolysis of histidine methyl ester, but stereoselectivity is not observed with nickel(Il) complexes of aspartic acid or methionine. Only tridentate ligands with a minimum steric bulk appear to be capable of exhibiting stereoselectivity in reactions of this type. 

Solvolysis of Organic Ligands.— The catalysis of hydrolysis of organic esters by metal ions or complexes has been much studied for many years. Recent examples of kinetic studies include hydrolysis of oxalate esters catalysed by a variety of ions, and of the bis[-L-(-J-)-histidine methyl ester] complexes of copper(n) and of nickel(n). The relative catalytic effects of several copper(n) complexes, including Cu(imda), Cu(nta), and Cu(dien) +, on the hydrolysis of methyl glycinate have been determined. Rate constants for base hydrolysis of this ester correlate with stability constants for mixed complexes of this ester with the above-named copper(n) complexes. ... 

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