Templated Molecular Recognition Materials: Theory and Simulation

Yale University, New Haven CT

Investigators

Abstract

Paul R. Van Tassel Wayne State University "Templated Molecular Recognition Materials: Theory and Simulation" Molecular recognition (MR) is a term used to describe the strong and highly specific binding between complementary patterns of weakly interacting sites. In living systems, MR is at the origin of many biological functions, including signal transduction and assembly guidance. Fully synthetic materials capable of MR are potentially useful as bio-mimics, sensors, tissue engineering substrates, and separation/purification agents and offer clear advantages in terms of cost and robustness compared to conventional materials into which true biological structures (proteins, peptides, nucleic acids) are incorporated. A universal strategy for preparing synthetic MR materials is through the nanoscale assembly of functionalized, polymerizable monomers in the presence of molecular or supramolecular templates. Following polymerization and template removal, the material will (ideally) possess a shape and pattern, on a nanometer length scale, that complements those of the template. The idea behind templated molecular recognition (TMR) is straightforward and some applications have appeared (most notably, the molecularly imprinted polymers). However, progress is limited by the current poor quantitative understanding of elemental issues like the influence of template morphology on the material's structure and recognition ability. In particular, no theoretical description is currently available to predict recognition from template and monomer structures and synthesis variables (e.g. precursor composition, temperature, etc.). It is the overall goal of this work to develop such a description. A molecular-based model inspired by the TMR formation process is proposed whose starting point is a functional monomer / template / solvent mixture in equilibrium with respect to a molecular force field. Polymerization of the monomers is accounted for by an instantaneous quench, or freezing, of the molecular positions. The template and solvent are then removed, and the remaining (quenched) monomers serve as the initial model material into which is immersed a new solution containing molecules identical or structurally related to the original template. Post-polymerization structural alterations are also possible through expansion/contraction or de-densification. Of particular significance is our proposed equilibrium based theoretical approach, exploiting the replica method originally developed to study spin glasses, to determine the binding thermodynamics of the model system. Complementary molecular computer simulations are also proposed. The first objective is to establish this theoretical description for simple model systems capable of TMR. An integral equation theory will be developed to calculate the thermodynamics of chain molecule and cluster adsorption in this model material. The significance will be the first theoretical description of TMR. The second objective is to apply the theoretical description to carefully chosen model monomer, template, and adsorbate structures in order to answer to important fundamental questions on TMR. The significance will be the first fundamental, molecular-level understanding of TMR. The third objective is to use the theoretical description to predict TMR in a system reported in the literature. The significance will be the first predictive model of TMR. Industrial and Societal Impact: The proposed theoretical description of TMR will be a valuable tool in the development of nanostructured materials capable of high affinity binding. Examples of materials whose rational design will be enabled include molecularly imprinted polymers (MIPs), directed surface assembled monolayers, template functionalized inorganics, and protein templated biomimics - these may find important application as sensors, selective adsorbents, and tissue engineering substrates and offer significant advantages in cost, robustness, and biocompatibility over conventional materials into which true biological structures (proteins, peptides, nucleic acids) are incorporated. Using this description, current practical problems such as low density, poor accessibility, and heterogeneous binding strength of the recognition sites may be overcome. Additionally, the ability of these organically formed materials to function in an aqueous environment will be enhanced. One can envision a future where nanostructural modification by templating is routinely used to tailor materials for specific binding applications. Also, minorities and women will be encouraged to participate at this large, urban university. Finally, a seminar series is planned in which the students will be required to make presentations relating to their part of the research.