AACP Seminar Series - Prof. David Nesbitt, JILA/NIST University of Colorado

In Search of Simplicity:
From Gas-Liquid Scattering to Single Molecule RNA Folding

One of the traditions of physical chemistry is trying to break down complicated problems into simpler ones that may be more readily tested at the fundamental level by comparison between experiment and theory. This talk will address examples from our group focusing on two extremely different chemical problems. The first involves what is taking place on the molecular and quantum state level for collision dynamics at the gasliquid interface, which we study by generating supersonic beams of molecules or highly reactive radicals, "bouncing" them onto freshly formed liquid surfaces in high vacuum, and probing the recoiling species with high resolution IR spectroscopy. Such data, for example, allow us to identify microscopic branching into two distinct channels: "trapping-desorption" events (where molecules "stick" long enough to lose their memory) and "impulsive scattering" events (where molecules leave within a few collisional interactions).

The second involves the folding kinetics and thermodynamics of small biomolecules such as RNA, which we study at the single molecule level by a sensitive combination of high numerical aperture microscopy, pulsed laser induced fluorescence and time correlated single photon counting methods. This approach permits one to "watch" the folding and unfolding of a single RNA construct in real time, from which one can determine rate constants as a function of cation concentration [Mg+2] and thereby learn about kinetics and thermodynamics of single molecules. One particular thrust is on the temperature dependence of single molecule kinetics, which gives insight into enthalpic and entropic contributions to barriers for molecular folding and unfolding.

For more information contact Prof. Christine Payne (404-385-3125).