SOURCE OF CATALYSIS OF DEPHOSPHORYLATION OF P-NITROPHENYLDIPHENYLPHOSPHATE BY METALLOMICELLES

A series of dimethylaminomethyl)-6-(alkylaminomethyl)pyridines of vari ous lipophilicities have been synthesized: their complexes with Cu-II ions (2a-c: R = CH3, C12H25, C16H33) catalyse cleavage of p-nitropheny ldiphenylphosphate (PNPDPP). The rate constants were compared with tho se obtained with C-II complexes made of ligands N-alkyl-N,N',N'-trimet hyl-1,2-diaminoethane (1a-c: R = CH3,C14H29, C16H33). When the alkyl g roup is a C-12 (or longer) chain complexes 1b,c and 2b,c form metallom icelles. The apparent pK, of Cu-II-coordinated water is ca. 8 for 2a,b , and ca. 6 and ca. 7 for 1a and b, respectively, The aim of the work was to establish the source of rate acceleration in metallomicelles. B ecause the pyridine-based complexes 2a-c have only one free position f or strong coordination to water, while complexes la-c have two such po sitions, complexes la-c can potentially activate both the nucleophile and the substrate, The results indicate that: (a) the nucleophilicity of the L-Cu-II-OH species is similar in metallomicelles and monomeric complexes; (b) free OH- is a slightly better nucleophile than Cu-II-bo und OH- in all complexes but 1a; (c) electrophilic assistance is only present in the monomeric; complex 1a and vanishes in metallomicelles.