“Protein-Like” Copolymers: Effect of Polymer Architecture on the Performance in Bioseparation Process

Abstract

Recently, a new class of copolymers, so-called protein-like copolymers has been predicted theoretically by computer simulation. In these copolymers. the conformation of the copolymer determines the exposure of certain comonomer units to the outer solution. Depending on the conformation, copolymer molecules with essentially the same comonomer composition could have pronouncedly different properties. The authors demonstrated experimentally such behavior in case of poly[(N- vinylcaprolactam)-co-(N-vinylimidazole)] (Dokl. Chem. 2001,375, 637). One more group of copolymers with protein-like behavior is copolymers of N-isopropylacryl-amide with N-vinylimidazole. Poly[(N-isopropylacryl-amide)-co-(N-vinylimidazole)] was synthesized by radical polymerization and separated into two fractions using immobilized metal affinity chromatography on Cu2+-loaded iminodiacetic acid Sepbarose CL 6B (Cu2+-IDA-sepharose). The unbound fraction which passed through the column and bound fraction eluted with ethylenediaminetetraacetic acid, disodium salt (EDTA) solution differed significantly in molecular weight, 1.4 x 10(6) and 1.35 x 10(5), respectively but were very close in comonomer composition, 7.8 and 9.1 mol-% of imidazole, respectively. The composition of bound fraction was confirmed by titration of imidazole groups. Despite close chemical composition, the bound and unbound fraction behaved differently with respect to temperature-induced phase separation at different pH values, the dependence of hydrodynamic diameter on pH and concentration of Cu2+- ions, and the coprecipitation of soybean trypsin inhibitor with the copolymer in the presence of Cu2+-ions. The differences in the behavior of copolymer fractions are rationalized assuming that the bound fraction presents a protein-like copolymer. The dependence of hydrodynamic diameter of bound (closed symbols) and unbound (open symbols) poly(NI-PAAM-VI) at different Cu2+/vinylimidazole ratios (n(Ca)/n(VI)), The polymer concentration was 4.5 mg (.) ml(-1) and pH 7.5 was obtained in all systems by using 0.010 m HEPES as a buffer. Mean values from five correlation functions are given. (Less)