| Popis: |
Some general regularities of the behaviour of high molecular weight synthetic catalysts, linear polyethyleneimines (PEI) containing alkyl radicals, from butyl to hexadecyl, and an enzyme, α-chymotrypsin, simulated by PEI, were established using the hydrolysis of a number of nitrophenyl esters. Similarly to α-chymotrypsin, the binding of the substrate molecules to the active centres, which include macromolecules surrounded by hydrocarbon radicals, is a kinetic step preceding hydrolysis. By the efficiency of binding, these high molecular catalysts approach α-chymotrypsin. Alkylated PEI demonstrate selectivity towards the structure of the radical in the substrate molecule both in the binding step and in the hydrolysis step, the difference in the hydrolysis rate constants for various substrates and catalysts reaching two orders of magnitude. The surroundings of the active centres in PEI macromolecules was found to affect their p K a . The shift of the p K a of aminogroups in the polymers into the acidic region, compared with the p K a of low molecular amines, amounts to three pH units with increased hydrophobicity of active centres. The difference in p K a between amino groups in alkylated PEI and low molecular amines of similar structure in a molecular solution, together with the efficient binding of substrates with polymeric catalysts, lead to the difference in activity between polymeric and low molecular catalysts, attaining 4 – 7 orders of magnitude in the pH range 7.5 – 8.5. |
