Molecular recognition : conformational memory and the macroscopic functional character of heteropolymer gels

Abstract

Molecular Recognition is an implicit and necessary step for proteins to realize their function. The late Professor Toyoichi Tanaka of M.I.T. proposed that polymer gels be used as protein 'mimics'. Multi-contact adsorption is engineered as a measure of gel function. Adsorbers within the gel's polymer network cluster to form an active site for molecular capture. A gel's conformation impacts both protein folding, and the testing of the polymer freezing transition. Multi-contact adsorption has been observed in gels, and is affected by the gel's volume phase transition. In our study, gels were synthesized to contain carboxyl groups that are incorporated either randomly, or by chemical imprinting using the template, Pb(MAAc)2 . After removing the guest molecule, we test adsorption of divalent molecules, lead (Pb+2), the original guest molecule, or calcium (Ca+2). We evaluate the gel's ability to recognize target molecules by analyzing the affinity and saturation values obtained using the Langmuir adsorption isotherm. Two methods are used to obtain adsorption data: 1) complexation of 4-(2-Pyridylazo)-resorcinol with lead (Pb+2) for spectrometric determination of lead equilibrium concentrations, and 2) an ion sensitive electrode was used for calcium concentrations. We show that method 1) involves less error than method 2). Imprinting improves multi-contact adsorption by gels. Collapsing the gel via the phase transition positively affects adsorption of both Pb+ and Ca+2. Our gels adsorb lead better than calcium, indicating a favoring of the original guest molecule. However, the gel cannot recover all active sites that were intended during synthesis. We discover, more in imprinted gels, that positive changes in affinity result as a function of increased cross-linking density.

(cont.) We discuss the preparation and topological aspects that impact conformation and the potential impact on testing conformational memory and creating successful protein mimics.