Hydrolysis of p-nitrophenyl esters of picolinic acid and N-protected amino acids by metalloenzyme models in vesicular assemblies

Mixed vesicles of N‐dodecyl‐N,N‐dimethyl‐1‐octadecanaminium bromide (C₁₈C₁₂) and functionalised 1,10‐phenanthroline ligands having two long alkyl chains and a nucleophilic hydroxymethyl (1), (S)‐2‐(hydroxymethyl)pyrrolidine (2) or ephedrine group (3, 4) at the α position, were investigated for their catalytic activities and enantioselectivities in the hydrolysis of 4‐nitrophenyl esters of picolinic acid (PNPP) and N‐protected leucine [D(L)‐Z‐Leu‐PNP and D(L)‐C₁₂‐Lcu‐PNP] in the presence of metal ions. The ZnII complex of the chiral ligand 2 in C₁₈C₁₂ vesicles exhibits the highest activity toward PNPP. The highest enantioselectivity in the stereoselective hydrolysis of D(L)‐C₁₂‐Lcu‐PNP (k^L_a,obs/k^D_a,obs = 3.6) was attained with the metallocatalyst 2‐Zn^II, whereas with 2‐Cu^II an inversion of stereoselectivity was observed (k^L_a,obs/k^D_a,obs = 0.68). The composition of the matrix in which catalyst and substrate are concentrated, affects the rate of hydrolysis but not the enantioselectivity. The rate of hydrolysis and the stereoselectivity are discussed in terms of the structure of the ligand, coordination geometry of the metal ion and the position of the metalloamphiphile in the surfactant aggregate.