Williams Group Research

The Williams Group

University Park, PA

Research

Our group uses chemical synthesis, bottom-up fabrication, and self-assembly to create complex inorganic nanostructures. The functional reactivities of magnetic and semiconductor nanoparticles are used as biomolecular probes, specific targeting, and to exert external forces on these systems. Our inorganic nucleic acid mimics are models for multi-electron and energy transfer, which we apply to complex problems in chemical sensors, molecular electronics, and artificial photosynthesis.

1. Inorganic DNA: Metal-Linked Pseudopeptides.

We have built and studied a new class of biomimetic macromolecules (inorganic DNA, iDNA), which consist of metal-linked peptide chains. These foundational investigations demonstrate the creation of artificial peptidic scaffolds that self-assemble into functional architectures upon metal coordination. As an alternative to nucleic acid base pairing, our metal chelation binding motif provides a new strategy for molecular recognition and self-assembly of nanoscale structures. Modularity of the pseudopeptides allows us to make simple changes in structure. Our ultimate goal is to build, expand and increase their complexity for creation of molecular electronic components (diodes, switches, gain elements), catalytic antennas (multichromophores and catalysts), and sensors with highly interfaced recognition-dependent electronic and photonic properties.

The most interesting property of iDNA structures is that they function as redox systems to experimentally study and control multi-electron transport. Our structures are distinctive because the lack of bridging ligands between redox sites means that multi-electron transfers between weakly coupled metal complexes will predominantly occur by electron hopping. The arrangement conferred by the peptide duplexes results in one-dimensional electron hopping frameworks. We are strategically placed to probe, understand and apply these supramolecular structures to complex questions of electron transport in multifunctional arrays.

2. Selective Transport and Placement of Inorganic Nanoparticles.

Our demonstrated leadership is the product of a multi-faceted approach that encompasses materials synthesis and analytical methods development, and application of these to biological systems. Using magnetotactic bacteria for inspiration, we assemble chemically functional and magnetic nanoparticles whose solution transport and placement on surfaces is manipulated with applied magnetic fields or with attached motor proteins. We were the first group to apply click chemistry to functionalize nanoparticles; the first to apply field flow fractionation to the separation of magnetic nanoparticles; and the first to demonstrate control over motor protein patterning and function with conjugated magnetic nanoparticles. We are uniquely positioned to make continued advancements at the interface of magnetic nanoscale materials and biology, where the broader interests include site-specific drug delivery, magnetic resonance imaging contrast agents, and separation of complex mixtures.