Synthesis of New Cu(II)-Chelating Ligand Amphiphiles and Their Esterolytic Properties in Cationic Micelles

Abstract

Four new tetradentate 2,6-disubstituted pyridine and tridentate 2-substituted pyridine ligands were synthesized. Two of these compounds possessed a metal ion binding subunit in the form of a 2,6-disubstituted-4-N,N'-dimethylamine pyridine moiety. Cu(2+)-complexes of these ligands incorporated in cetyltrimethylammonium bromide (CTABr) micelles speeded the cleavage of p-nitrophenyldiphenyl phosphate and p-nitrophenyl hexanoate at pH 7.6. On the basis of a kinetic version of Job plot analysis, a 1:1 ligand/Cu(2+) stoichiometry was found to be the most active species. In CTABr micelles, the pK(a) values for the Cu(2+)-coordinated hydroxyl or pendant -CH(2)OH in these ligands were between 7.8 and 7.9. The metallomicellar systems displayed catalytic (turnover) behavior in the presence of excess substrates.

Crystal structure of diaqua-(μ-4,4′-bipyridine)-bis(N-salicylideneaspartato)- dicopper(II), Cu2(H2O)2(C11H9NO5)2(C10H8N2)

“…The use of Schiff bases as ligands in the formation of transitionmetal complexes has been extensively studied owing to their intrinsic properties, such as versatile spectroscopic and electrochemical responsive receptors for charged and neutral guests of these systems [1][2][3]. Interactions of biologically active metal ion such as copper(II) with L-amino-acid derivatives and peptide derivatives are of considerable interest as these often represent the behavior of metal ions in the enzymes [4][5][6][7].…”

Metallomicelles as potent catalysts for the ester hydrolysis reactions in water

“…Interestingly however, while 75 and 76 showed 'Burst' type kinetics in the presence of excess substrates, 77 manifested a fast turnover. These authors then developed tetradentate ligands, 78 and 79 and compared the catalytic activity against their analogous tridentate ligands, 80 and 81 [73]. In absence of a metal ion, ligand 79 alone in CTAB micelles showed moderate rate enhancements for the hydrolysis of PNPH or PNPDPP.…”

Metallomicellar Catalysis: Phosphodiester Hydrolysis Catalyzed by Cu(II), Zn(II), Ni(II), and Co(II) Complexes of Chelating Pyridyl Donor Ligands in CTAB Micellar Solution

“…In order to determine the chelating stoichiometry of the kinetically reactive metal complexes, the kinetic version of Job plots has been utilized, as shown in Figure 1, in which the apparent rate constants (k obsd ) are plotted as a function of the mole fraction (r) of ligand or metal ion, keeping their total concentration constant (Fejita et al 1988;Mancin et al 2000, Bhattacharya et al 2003. Figure 1 indicates that for ligands 1 and 2 in CTAB micellar solutions, r-values corresponding to the maximum k obsd are at about 0.67, suggesting that the 1:2 complexes (metal: ligand) should be the active species.…”