Efforts toward Developing Probes of Protein Dynamics: Vibrational Dephasing and Relaxation of Carbon–Deuterium Stretching Modes in Deuterated Leucine

• Published in: The journal of physical chemistry. B 2009-06, Vol.113 (23), p.7991-7994
• Main Authors: Zimmermann, Jörg, Gundogdu, Kenan, Cremeens, Matthew E, Bandaria, Jigar N, Hwang, Gil Tae, Thielges, Megan C, Cheatum, Christopher M, Romesberg, Floyd E
• Format: Article
• Language: English
• Subjects: Carbon - chemistry; Deuterium - chemistry; Leucine - chemistry; Proteins - chemistry
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp900516c

The spectral position of C−D stretching absorptions in the so-called “transparent window” of protein absorption (1800−2300 cm−1) makes them well suited as probes of protein dynamics with high temporal and structural resolution. We have previously incorporated single deuterated amino acids into proteins to site-selectively follow protein folding and ligand binding by steady-state FT IR spectroscopy. Ultimately, our goal is to use C−D bonds as probes in time-resolved IR spectroscopy to study dynamics and intramolecular vibrational energy redistribution (IVR) in proteins. As a step toward this goal, we now present the first time-resolved experiments characterizing the population and dephasing dynamics of selectively excited C−D bonds in a deuterated amino acid. Three differently deuterated, Boc-protected leucines were selected to systematically alter the number of additional C−D bonds that may mediate IVR out of the initially populated bright C−D stretching mode. Three-pulse photon echo experiments show that the steady-state C−D absorption linewidths are broadened by both homogeneous and inhomogeneous effects, and transient grating experiments reveal that IVR occurs on a subpicosecond time scale and is nonstatistical. The results have important implications for the interpretation of steady-state C−D spectra and demonstrate the potential utility of C−D bonds as probes of dynamics and IVR within a protein.