Coherent vibrational climbing in carboxyhemoglobin

Abstract

We demonstrate vibrational climbing in the CO stretch of carboxyhemoglobin pumped by midinfrared chirped ultrashort pulses. By use of spectrally resolved pump-probe measurements, we directly observed the induced absorption lines caused by excited vibrational populations up to v ‫؍‬ 6. In some cases, we also observed stimulated emission, providing direct evidence of vibrational population inversion. This study provides important spectroscopic parameters on the CO stretch in the strong-field regime, such as transition frequencies and dephasing times up to the v ‫؍‬ 6 to v ‫؍‬ 7 vibrational transition. We measured equally spaced vibrational transitions, in agreement with the energy levels of a Morse potential up to v ‫؍‬ 6. It is interesting that the integral of the differential absorption spectra was observed to deviate far from zero, in contrast to what one would expect from a simple onedimensional Morse model assuming a linear dependence of dipole moment with bond length.T he recent availability of ultrashort and intense midinfrared pulses in a compact setup (1) provides a convenient means for controlling the nuclear motion of molecules (2). With infrared pulses, only vibrational transitions are addressed while the molecule remains in its electronic ground state during the entire interaction. This makes such an approach particularly suited to complex systems such as proteins. Another fascinating possibility opened up by infrared vibrational control is the prospect of exploring the potential energy surface far from the harmonic region up to the transition state of intraprotein reactions.Coherent vibrational climbing consists of exciting a molecular vibration with an ultrashort midinfrared pulse, the broadband spectrum of which encompasses several vibrational transitions of the molecule. Indeed, these transition frequencies become smaller and smaller while climbing the ladder because of the molecular anharmonicity. Therefore, the climbing efficiency can be increased dramatically when using a negatively chirped pulse so that its high-frequency components, resonant with the lower transitions of the ladder, precede its low-frequency components, resonant with the upper transitions of the ladder. Coherent vibrational climbing can be viewed also as a rapid adiabatic passage leading to efficient excitation of the upper vibrational states, with an efficiency that in theory can be close to 100% because of the coherent nature of the interaction. Vibrational climbing has been demonstrated in small molecules, such as W(CO) 6 (3-5), NO (6), CO adsorbed on a Ru (001) surface (7), Cr(CO) 6 (8), Mo(CO) 6 (5), Fe(CO) 5 (5), and CH 2 N 2 (9). In this article, we report on the demonstration of coherent vibrational climbing in a biological system, carboxyhemoglobin (HbCO). This system was chosen rather than carboxymyoglobin, in which different CO-bound configurations result in an inhomogeneous broadening of the absorption line (10). Experimental MethodsThe 800-nm pulses produced by a titanium͞sapphire regenerative amplifier (Hurrican...

Multiply Excited Vibration of Carbon Monoxide in the Primary Docking Site of Hemoglobin Following Photolysis from the Heme

“…Our group further observed a progressive change of the absorption strength after CO photolysis 9 and demonstrated coherent MIR emission in MbCO 10 and coherent vibrational climbing in HbCO. 11 Although MIR pulses can have sufficiently broad spectra, the photobleach of Fe-bound CO and the absorption of docked CO have never been recorded simultaneously with a single probe pulse. Instead, they are measured individually, usually even with MIR probe beams that are spectrally shifted between the experiments.…”

“…(ii) the share of excess energy is not the prevalent aspect, but rather the reaction speed from bound to unbound CO molecules. Assuming that this transition proceeds faster for Soret band than that for Q-band excitation, the former might be regarded as "more impulsive" and hence may lead to a different vibrational distribution in the photolyzed CO. A further scenario, a significant contribution from vibrational climbing 11 in the docking site induced by the probe pulse itself is ruled out since no such effect is observed for Fe-bound CO, despite the much larger absorptivity compared to that of docked CO.…”

Direct observation of ligand transfer and bond formation in cytochrome c oxidase by using mid-infrared chirped-pulse upconversion

“…IR pump-probe spectroscopy approaches have relied either on timeconsuming frequency (3,9) or delay scanning (12) or, more recently, on expensive mercury cadmium teluride (HgCdTe) detector arrays (10,11,13,14) for detection of the IR probe. Here, we measure the transmitted mid-IR pulse using the recently demonstrated technique of upconversion into the visible range by sumfrequency generation with a chirped 800-nm pulse (15).…”

Carbonyl vibrational wave packet circulation in Mn2(CO)10 driven by ultrashort polarized laser pulses

“…Previous studies of metal-carbonyl compounds have been focused especially on laser-driven CO vibrational ladder climbing. [9][10][11] A particularly interesting example has been the experimental demonstration of ladder climbing up to the v CO = 6 state in carboxyhemoglobin by Joffre and coworkers. 11 For this example, Meier and Heitz have developed a non-reactive gas phase model to simulate the excitation dynamics by using local control theory.…”

“…[9][10][11] A particularly interesting example has been the experimental demonstration of ladder climbing up to the v CO = 6 state in carboxyhemoglobin by Joffre and coworkers. 11 For this example, Meier and Heitz have developed a non-reactive gas phase model to simulate the excitation dynamics by using local control theory. 12 It should be noted, however, that the main goal of the experiment had been to achieve cona) Electronic mail: oliver.kuehn@uni-rostock.de trolled metal-carbonyl bond breaking assisted by anharmonic couplings between the initially excited CO mode and the metal-CO bond.…”