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

Abstract

We have implemented the recently demonstrated technique of chirped-pulse upconversion of midinfrared femtosecond pulses into the visible in a visible pump-midinfrared probe experiment for high-resolution, high-sensitivity measurements over a broad spectral range. We have succeeded in time-resolving the CO ligand transfer process from the heme Fe to the neighboring CuB atom in the bimetallic active site of mammalian cytochrome c oxidase, which was known to proceed in <1 ps, using the full CO vibrational signature of Fe-CO bond breaking and CuB-CO bond formation. Our differential transmission results show a delayed onset of the appearance of the CuB-bound species (200 fs), followed by a 450-fs exponential rise. Trajectories calculated by using moleculardynamics simulations with a Morse potential for the CuB-C interaction display a similar behavior. Both experimental and calculated data strongly suggest a ballistic contribution to the transfer process.

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

“…The pump pulse energy is set to 250 nJ (280 nJ), the angle between pump and probe polarization is set to 0°(90°), and every second (third) pulse is chopped for the experiments s h o w ni nF i g u r e s1 -3 (Figure 4), respectively. We then use CPU, 12 as recently introduced to transient absorption 30,29 and multidimensional [31][32][33][34] spectroscopy, where the MIR probe pulses are upconverted to the visible with the chirped 800 nm pulses in a MgO:LiNbO 3 crystal. The chirp is subsequently corrected, 13 and a straightforward frequency calibration by comparison to atmospheric absorption lines is performed.…”

Lower frequency region mid-infrared spectroscopy by chirped pulse upconversion

“…We conclude that also in the 1000cm −1 to 2000cm −1 region midIR unpconversion is an attractive alternative to direct midIR detection, enabling the use of cheaper CCD detectors and affording a sampling of 2048 channels instead of the standard 32, 64 or 128 in MCT arrays [1][2][3]. The baseline fluctuation is a severe problem when weak signals are measured, but this can be resolved by introducing an additional beam as reference.…”

“…The chirped pulse upconversion method has been applied to 2D spectroscopy and pump probe measurements in the frequency region above 1800cm −1 [1][2][3][4], limiting the application mainly to CO coordination compounds. We report the upconversion of pump probe transient signals in the frequency region below 1800cm −1 , using the nonlinear optical crystal AgGaGeS 4 , realizing an important expansion of the application range of this method.…”

Characterization of mid-infrared femtosecond pulses [Invited]

“…3(c)], because the mid-IR part of the setup simply consists of focusing the mid-IR beam onto the nonlinear crystal. Furthermore, this method can be efficiently integrated into multidimensional [60] or pump-probe [61] experiments. After characterizing the local-oscillator or probe pulse in situ, the experiment can proceed by blocking one of the chirped 800 nm pulses, which turns the setup into an upconversion mid-IR spectrometer [17,62,63].…”