Cooperative hydrolysis of aryl esters on functionalized membrane surfaces and in micellar solutions

Abstract

Catalytic hydrolysis of peptides, proteins, phosphates or carboxylate esters in nature is catalysed by enzymes, which are efficient, fast and selective. Most of the hydrolytic chemical catalysts published so far mimic the active site of enzymes and contain metal complexes and amino acid residues. Their synthesis can be laborious, while the hydrolytic activity is still limited compared to enzymes. We present an approach that uses fluid membranes of vesicles and micelles as a support for amphiphilic additives, which cooperatively cleave aryl ester bonds. The membrane anchored bis-Zn(II)-complex 1 is hydrolytically active and hydrolyses fluorescein diacetate (FDA) with a second order rate constant (k₂) of 0.9 M⁻¹ s⁻¹. The hydrolytic activity is modulated by co-embedded membrane additives, bearing common amino acid side chain functional groups. With this approach, the hydrolytic activity of the system is enhanced up to 16 fold in comparison with cyclen 1 (k₂ = 14.7 M⁻¹ s⁻¹). DOPC and DSPC lipids form at room temperature fluid or gel phase membranes, respectively. Omitting the lipid, micellar solutions were obtained with hydrolytic activity reaching k₂ = 13.4 M⁻¹ s⁻¹. It is shown that cooperative hydrolysis is favoured in fluid membranes and micelles, allowing the active moieties to arrange freely. The embedding and dynamic self-assembly of membrane active components in fluid membranes and micelles provide facile access to hydrolytically active soft interfaces.