Vibrational relaxation in carotenoids in vivo and in vitro: picosecond time-resolved anti-Stokes resonance Raman spectroscopy

Probing Structure and Reaction Dynamics of Proteins Using Time-Resolved Resonance Raman Spectroscopy

The mechanistic understanding of protein functions requires insight into the structural and reaction dynamics. To elucidate these processes, a variety of experimental approaches are employed. Among them, time-resolved (TR) resonance Raman (RR) is a particularly versatile tool to probe processes of proteins harboring cofactors with electronic transitions in the visible range, such as retinal or heme proteins. TR RR spectroscopy offers the advantage of simultaneously providing molecular structure and kinetic information. The various TR RR spectroscopic methods can cover a wide dynamic range down to the femtosecond time regime and have been employed in monitoring photoinduced reaction cascades, ligand binding and dissociation, electron transfer, enzymatic reactions, and protein un- and refolding. In this account, we review the achievements of TR RR spectroscopy of nearly 50 years of research in this field, which also illustrates how the role of TR RR spectroscopy in molecular life science has changed from the beginning until now. We outline the various methodological approaches and developments and point out current limitations and potential perspectives.

Vibrational relaxation dynamics of β-carotene and its derivatives with substituents on terminal rings in electronically excited states as studied by femtosecond time-resolved stimulated Raman spectroscopy in the near-IR region

Time-resolved near-IR stimulated Raman spectroscopy indicates acceleration of vibrational relaxation in carotenoids by carbonyl substitution on their peripheral rings.

Vibrational Relaxation in beta-Carotene Probed by Picosecond Stokes and Anti-Stokes Resonance Raman Spectroscopy

Picosecond time-resolved Stokes and anti-Stokes resonance Raman spectra of all-trans-beta-carotene are obtained and analyzed to reveal the dynamics of excited-state (S(1)) population and decay, as well as ground-state vibrational relaxation. Time-resolved Stokes spectra show that the ground state recovers with a 12.6 ps time constant, in agreement with the observed decay of the unique S(1) Stokes bands. The anti-Stokes spectra exhibit no peaks attributable to the S(1) (2A(g) (-)) state, indicating that vibrational relaxation in S(1) must be nearly complete within 2 ps. After photoexcitation there is a large increase in anti-Stokes scattering from ground-state modes that are vibrationally excited through internal conversion. The anti-Stokes data are fit to a kinetic scheme in which the C=C mode relaxes in 0.7 ps, the C-C mode relaxes in 5.4 ps and the C-CH(3) mode relaxes in 12.1 ps. These results are consistent with a model for S(1)-S(0) internal conversion in which the C=C mode is the primary acceptor, the C-C mode is a minor acceptor, and the C-CH(3) mode is excited via intramolecular vibrational energy redistribution.