Session T35: Focus Session: Plyler Award Symposium

Earle K. Plyler Prize for Molecular Spectroscopy and Dynamics Lecture: 2D IR Spectroscopy of Peptide Conformation

Descriptions of protein and peptide conformation are colored by the methods we use to study them. Protein x-ray and NMR structures often lead to impressions of rigid or well-defined conformations, even though these are dynamic molecules. The conformational fluctuations and disorder of proteins and peptides is more difficult to quantify. This presentation will describe an approach toward characterizing and quantifying structural heterogeneity and disorder in peptides using 2D IR spectroscopy. Using amide I vibrational spectroscopy, isotope labeling strategies, and computational modeling based on molecular dynamics simulations and Markov state models allows us to characterize distinct peptide conformers and conformational variation. The examples illustrated include the beta-hairpin tripzip2 and elastin-like peptides.   

Vibrational spectroscopy of interacting water molecules

I will discuss a new simulation model for water that includes three-body interactions explicitly, and describe our theoretical approach for calculating OH-stretch spectroscopic observables. I will present illustrative examples, involving pump-probe energy-transfer-induced anisotropy decay in liquid water, IR and Raman line shapes in ice Ih, phase-sensitive SFG spectra of the liquid/vapor interface, and energetics and IR spectra for the different conformations of the water hexamer.   

Two-dimensional Fourier transform electronic spectroscopy

Sensitive interference detection of the electric field of femtosecond four-wave mixing signals (stimulated photon echoes) at their point of origin in the sample can be used to record two-dimensional (2D) Fourier transform electronic spectra. In direct analogy to 2D nuclear magnetic resonance, 2D Fourier transform spectra have nearly homogeneous linewidths in each frequency dimension and sort the signal spectrum according to the initial excitation frequency. The initial excitation frequency information is stored in a robust population grating, so 2D spectra can be used to study both coherent and incoherent processes, and have revealed coherent aspects of energy transfer processes. Femtosecond 2D spectra also have the advantage of ``freezing out'' vibrational motions as inhomogeneities, raising interesting questions about what kinds of broadening can be rephased in 2D spectra recorded with stimulated photon echo pulse sequences. This talk will focus on coherent aspects of non-adiabatic electronic curve crossing and their manifestation in 2D electronic spectra.