Structure, conformation and molecular mobility of modified polyethyleneimine—functional and structural analogues of α-chymotrypsin

Abstract

The alkylated polyethyleneimine (PEI-C n) is a homogeneous catalyst for hydrolysis of p-nitrophenyl esters. Its activity increases about 10 3 times with the length of the side groups in polymer chains that furnish configuration of active centres in macromolecules in water solution. The values of the sedimentation coefficients and of the intrinsic viscosity of PEI-C n in water solution indicate formation of compact globules with C 13 and C 16 alkyl groups, similar to the conformation of globular proteins. The spin echo in the PMR method showed reduction of intermolecular motion in these polymers, also indicating the formation of the compact structure in solution as a result of the hydrophobic interactions of the alkyl side groups. X-ray investigation showed that alkyl groups in PEI-C 16 are arranged in a hexagonal crystalline lattice with d = 4.2 A ̊ , which melts in the range 36–39°, depending on the degree of alkylation. All these data are in agreement with the idea that high catalytic activity is due to the globular structure of macromolecules in solution.