Reversible molecular adsorption as a tool to observe freezing and to perform design of heteropolymer gels

Protein folding is one of the most challenging problems in science. How can polymers memorize and fold into unique conformations? How can they recogni ze molecules, catalyze chemical reactions, transfer molecular information, and create motions? The principle behind these mechanisms lies in the conce pt of thermodynamically stable phases of heteropolymers. Recent theories pr edict that the collapsed phase should be further classified into three phas es: freely fluctuating like liquid, frozen in degenerate conformations, and frozen in a unique conformation. This yields a clue on how one can attempt creation artificial polymers capable to mimic some of the protein properti es and functions. The reversible adsorption of target molecules is suggeste d as a primary means to achieve this goal. Target molecules with multiple a dsorption sites play a twofold role. First, they mediate specific interacti ons between monomers and thus serve as "gluons". Second, monitoring the ads orption provides the experimental possibility to test directly on monomer c ontacts, which is directly related to observation of the order parameter as sociated with heteropolymer freezing transition. A slight change in the bac kbone conformation alters the spacial arrangement of the group, allowing fo r reversible adsorption and release. Polymer gels are developed that can re versibly change their affinity to target molecules by orders of magnitude. The gels are made of copolymers of backbone monomers that can reorganize th emselves through thermal volume phase transition and of monomers that can a ttract the target at multiple contact points. Further the gels "imprinted" with the target showed a marked increase in the affinity, thus mimicing a p rotein-like ability to memorize and recognize certain target.