| Description |
Metal ions form with macrocyclic ligands more stable complexes than with analogous acyclic ligands from both thermodynamic and kinetic point of view. These complexes can be studied as suitable models in order to mimic the metaloenzyme activity. In this contribution, the catalytic activity of [M(cyclen)]2+ complexes (M = Zn, Cd, Cu, Ni, cyclen = 1,4,7,10-tetraazacyclodecane, [12]aneN4) which are mimicking enzymes was investigated for hydrolysis of acetic acid esters acting as substrate. The rate of ester hydrolysis was monitored by molecular absorption (for 4-nitrophenylacetate) or luminescence (for 4-methylumbelliferylacetate) spectroscopy and optimal experimental conditions (e.g. temperature, pH, buffer, etc.) were found. The catalytic activity of the most active Zn(II) and Cd(II) metal complexes is inhibited by some compounds due to formation of stable ternary complexes. The influence of various inhibiting agents (mostly base, e.g. Thymin, Uracil, Cytosin, Adenin, Guanin, and their simple nucleosides and nucleotides) on rate of ester hydrolysis was studied. The effect of minute structural changes of inhibitors is the highest for nucleotides and the smallest for bases. The inhibition constants were evaluated from experimental data and compared with analogous systems. Metal ions form with macrocyclic ligands more stable complexes than with analogous acyclic ligands from both thermodynamic and kinetic point of view. These complexes can be studied as suitable models in order to mimic the metaloenzyme activity. In this contribution, the catalytic activity of [M(cyclen)]2+ complexes (M = Zn, Cd, Cu, Ni, cyclen = 1,4,7,10-tetraazacyclodecane, [12]aneN4) which are mimicking enzymes was investigated for hydrolysis of acetic acid esters acting as substrate. The rate of ester hydrolysis was monitored by molecular absorption (for 4-nitrophenylacetate) or luminescence (for 4-methylumbelliferylacetate) spectroscopy and optimal experimental conditions (e.g. temperature, pH, buffer, etc.) were found. The catalytic activity of the most active Zn(II) and Cd(II) metal complexes is inhibited by some compounds due to formation of stable ternary complexes. The influence of various inhibiting agents (mostly base, e.g. Thymin, Uracil, Cytosin, Adenin, Guanin, and their simple nucleosides and nucleotides) on rate of ester hydrolysis was studied. The effect of minute structural changes of inhibitors is the highest for nucleotides and the smallest for bases. The inhibition constants were evaluated from experimental data and compared with analogous systems.
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