Time-resolved Raman spectroscopy with subpicosecond resolution: vibrational cooling and delocalization of strain energy in photodissociated (carbonmonoxy)hemoglobin

Abstract

A Raman spectrometer that provides both subpicosecond resolution and independent, tunable pump and probe pulses is described. The spectrometer is employed to obtain time-resolved spectra of (carbonmonoxy)hemoglobin (HbCO) at times from 0.2 to 95 ps subsequent to ligand photodissociation. The spectra are interpreted in terms of a vibrationally hot heme that cools substantially in 10 ps. Concomitant with the proposed vibrational cooling is a slower relaxation, which we suggest results from a protein response to heme doming induced by ligand detachment. Results and interpretations are discussed in the context of current models of the heme photophysics and of hemoglobin reactivity.

Direct observation of subpicosecond vibrational dynamics in photoexcited myoglobin

“…A further-redshifted tail disappears on a much faster timescale, ≈ 300 fs (Fig. 2c); as extensively discussed in the literature, these TA features are compatible with either the existence of intermediate electronic species 7,14,21,23,24 or with a hot ground state vibrational relaxation pathway 8,10 , as illustrated in Fig. 1b.…”

“…The corresponding energy relaxation processes have been extensively studied with a variety of ultrafast techniques, such as time-resolved infrared 7 and visible [8][9][10] absorption, as well as by Impulsive Raman 11 and Coherent Emission Interferometry 12 . Using Time-Resolved Resonance Raman (TR 3 ) and Transient Raman Resonance Spectroscopy (TRRS), heme cooling has been observed on the timescales of a few picoseconds by looking at either vibrational shift [13][14][15] or the Stokes/Antistokes ratio 2,16,17 of the totally symmetric in-plane breathing modes with large cross section (ν 4 and ν 7 )…”

“…In particular, owing to the difficulties to experimentally achieve simultaneous structural sensitivity and time resolution, contrasting hypotheses (schematically depicted in Fig. 1b) have been put forward for the dynamics at 50 fs < t < 5 ps with respect to the possible contributions of intermediate heme electronic states 7,8,10,14,17,19,[21][22][23][24][25] . To be able to address these issues we developed a novel Femtosecond Stimulated Resonance Raman setup (FSRRS) that uniquely combines high temporal precision and frequency resolution with fine tunability all over the heme proteins absorption spectrum.…”

Probing the electronic and geometric structure of ferric and ferrous myoglobins in physiological solutions by Fe K-edge absorption spectroscopy

“…[12][13][14] Important in the context of these studies is that hemoproteins are photosensitive, leading to a wide range of time-resolved optical and X-ray spectroscopic studies ranging from milliseconds to femtoseconds. [15][16][17][18][19][20][21][22][23][24][25][26][27] In these experiments, the biological function of ligand detachment from the heme is triggered by an optical (so-called pump) pulse, while the evolution of the system is probed by a second (typically optical or X-ray) pulse, with a tunable time delay with respect to the pump pulse. While optical tools can reach femtosecond resolution they do not provide direct structural information.…”

Transient and Time‐resolved Optical Studies of Photolyzed Carbonmonoxy Hemoglobin and Myoglobin

“…Rentzepis, Noe, and coworkers (Hutchinson and Noe, 1983;Noe eta/., 1978;Reynolds et a/., 1981) employed similar protocols, but interpreted their results in terms of mechanisms involving intermediate excited states. More recent studies (Martin et at., 1983;Petrich et a/., 1987;Petrich and Martin, 1989;Jongeward eta/., 1988) have utilized 5(}.. 70 fs pulses. They have established that bleaching of the ground state HbCO and MbCO Soret band is instantaneous on this timescale.…”