3:00 PM on Friday, May 3, 2013
Location: Whittemore 457
Dr. Vinh Q. Nguyen from the physics department will be the speaker.
According to computer simulations, the slowest, largest-scale harmonic motions of solvated biomolecules and the relaxation times of water occur on the picosecond regime. Experimental methods for the characterization of these collective vibrational modes, however, have been severely lacking. In response, I have developed the world’s highest precision, highest sensitivity, and highest frequency dielectric spectrometer. Operating over the frequency range from 0.5 GHz up to 1.1 THz, this spectrometer provides an unparalleled ability to probe the dynamics of water and aqueous proteins over the 100 fs to 1 ns timescale. Using this spectrometer to characterize the collective dynamics of solvated lysozyme, I find that the collective vibrational modes of this protein are characterized by a hitherto unrecognized cutoff at 250 GHz (corresponding to 0.6 ps) arising due to the finite size of the molecule. Employing an effective medium approximation to describe the complex dielectric response of the protein in solution I find that each molecule is surrounded by a tightly held layer of 164 ± 5 water molecules that behave as if they are an integral part of the protein. Following studies of the spectra of water and of aqueous salt solutions I identify three Debye relaxations with the characteristic times of 8.56, 1.1 ps and 179 fs (at 25˚C). Of note, while the relative strengths of these relaxation modes depend in a systematic way on solute concentration, their relaxation times do not. The observation sheds new light on the femtosecond to picosecond collective dynamics of water and solvated biomolecules.
Dr. Vinh Nguyen is an Assistant Professor at the Department of Physics, Virginia Tech. Previously, he was a project scientist at the Department of Physics and the Institute for Terahertz Science and Technology, University of California at Santa Barbara. Before joining the University of California at Santa Barbara, he served as a senior research scientist at the Dutch Free Electron Laser facility - FELIX, Dutch Institute for Fundamental Energy Research, the Netherlands. Dr. Nguyen has received his Ph.D. degree from the University of Amsterdam, the Netherlands and his Master of Science in Physics at the Institute of Physics, Hanoi University of Science and Technology, Vietnam. His research focuses on the dynamics of electrons confined in very tiny semiconductor structures, photonic crystals, optical coherent control for quantum information science, organic solar cells, and dynamics of biomolecules in biologically-relevant aqueous environments through terahertz spectroscopy.