Gemini metallomicellar catalysis: Hydrolysis of p-nitrophenyl picolinate catalyzed by Cu(II) and Ni(II) complexes of macrocyclic ligands in gemini surfactant micelles

Abstract

Cu(II) and Ni(II) complexes of two hexaaza macrocyclic ligands with and without pendant hydroxyl groups, 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane ( 1) and 3,10-bis(2-ethyl)-1,3,5,8,10,12-hexaazacyclotetradecane ( 2), were synthesized. Effects of these complexes on the hydrolysis of p-nitrophenyl picolinate (PNPP) in micelles of cationic gemini surfactants with different spacer lengths, alkanediyl-α,ω-bis(dimethyl dodecylammonium bromide) (designated as 12- s-12, s = 2, 3 and 6), have been investigated at 25 °C. The results showed that metallomicelle systems containing gemini surfactants exhibited more efficient activities for hydrolysis of PNPP than those containing the corresponding single-chained conventional surfactant dodecyltrimethyl-ammonium bromide (DTAB). For gemini surfactants, it was found that catalytic activity of the metallomicellar systems containing the surfactant 12-2-12 was lower than those of surfactants 12-3-12 and 12-6-12. In addition, metal complexes of microcyclic ligand 1 bearing pendant hydroxyl groups showed higher catalytic activities than corresponding metal complexes of 2 without hydroxyl group, indicating that ligand hydroxyl groups play an important role for catalyzed hydrolysis of PNPP in metallomicellar systems.