Dr. Plusquellic’s research interests in the Molecular Applications Project center on fully-state resolved studies of biomolecules and bichromophores in the microwave (MW), terahertz (THz), and ultraviolet (UV) spectral regions. The THz spectral region provides access to the lowest frequency collective motions of biomolecular systems that are responsible for the large scale conformational changes associated with folding and activation of protein, polynucleotide and polysaccharide backbones. We have pioneered the use of high-resolution THz laser sources to investigate the fully state-resolved vibrational spectra of polypeptides and to characterize the spectral response to hydration of hydrophobic and hydrophilic sites in a wide variety of crystalline structures. We are also developing new instrumentation to enhance the spectral and spatial resolution and sensitivity in this region using waveguides, dual beam and adaptive near-field imaging approaches. Currently, THz investigations of β-turn and β-hairpin conformations of β-amyloid peptides are being performed to understand aggregation pathways associated with protein misfolding diseases such as Alzheimer’s disease, Parkinson’s, Huntington’s and islet amyloidosis in type 2 diabetes. Support for this program benefits from the joint NIH/NIST NRC postdoctoral program with Dr. Gerhard Hummer of the NIDDK at NIH.
In the UV, high resolution laser and cavity ringdown techniques are used to determine the 3D molecular structures of methyl terminated peptide mimetics in the gas phase and of chirally pure transmembrane mimetics in lipid bilayers supported at fused silica/water interfaces. Circular dichroism studies of the chirally pure forms assembled in lipid bilayer membranes are sensitive to the local molecular conformation of the attached peptide backbone. When coupled with gas phase results, these studies provide insight into the influence of the solvent and interfacial structure on the chiral selectivity important in bioactivity. In a different area, a series of aromatic bichromophores have been investigated to fully understand the coupling mechanisms and electronic energy transport dynamics arising from excitonic interactions between chromophores in close proximity. This work is done in collaboration with Prof. Timothy S. Zwier’s group at Purdue University. Completed studies have revealed that the transition dipole coupling and deactiviation mechanisms (through internal conversion) depend strongly on the 3D structure, symmetry and conformational flexibility of the attached chromophores, properties that define the energy landscapes of the coupled electronic states. Together with detailed theoretical investigations, there results may serve to optimize designs of charge transfer systems for more efficient solar energy conversion.
Dr. Plusquellic is fellow of the American Physical Society (since 2009). Other professional associations include membership in American Chemical Society (since 1992) and American Association for the Advancement of Science (since 2001). He has served as co-organizer of “Sub-millimeter and THz Spectroscopy in the Gas and Condensed Phases” at Ohio State University Molecular Spectroscopy Symposium in June, 2008 and has co-authored 65 technical peer-reviewed papers, delivered 28 invited talks and holds one U.S. Patent.
Quantum Electronics and Photonics Division
Sources and Detectors Group
1995-present, NIST, Gaithersburg, MD
1992-1995, JILA/NIST, Boulder, CO
Ph.D. Physical Chemistry, University of Pittsburgh, PA
B.A. Chemistry with minor in Mathematics, Indiana University of Pennsylvania, Indiana, PA