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Restricted rotational motion of CO in a protein internal cavity: Evidence for nonseparating correlation functions from IR pump-probe spectroscopy
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View: Figures


Image of FIG. 1.
FIG. 1.

Active site structure of Mb mutant L29W. The CO ligand is included at sites (heme bound), at the initial docking site and in the Xe4 cavity (site ).

Image of FIG. 2.
FIG. 2.

(a) Model potential (inset) and normalized FTIR absorption spectra of in the Xe4 pocket of Mb double mutant L29W-S108L at 20, 50, and . The maximum absorbance in the laser experiments was at . (b) Transient absorption spectrum after broad band excitation at a pump-probe delay of and for a sample initially at . The large bleaching signal at the long delay is due to an increase in sample temperature. (c) Transient absorption spectra after narrow band excitation at at pump-probe delays of 50 (open triangles) and (solid squares).

Image of FIG. 3.
FIG. 3.

(a) Anisotropy signal as a function of delay between pump and probe pulses at sample temperatures of 20 and . The solid/dotted line shows the anisotropy signal of an ensemble of freely rotating CO molecules at , horizontal lines are averages over the long delays. (b) Long delay averages of the anisotropy signal as a function of temperature. Solid circles and triangles correspond to two different sets of data, error bars represent the scatter over the interval between 50 and . The lower dashed-dotted line shows the expected anisotropy for factorizing correlation functions [Eq. (7)], the solid line is the result of a Monte Carlo evaluation of the full correlation functions .

Image of FIG. 4.
FIG. 4.

(a) Schematic view of the pump-probe experiment. The molecules reorient during emission of the third-order polarization, created by two-field interactions with the pump pulse at time 0 and one-field interaction with the probe pulse at time . (b, c) Logarithmic plot of cuts through the simulated four-point correlation functions (upper lines) and (lower lines) for parallel and perpendicular polarizations of pump and probe pulses, respectively. In (b) , in (c) is larger than the initial fast decay. (d) Normalized -Fourier transform of the four-point correlation functions for parallel and perpendicular polarization, showing the different spectral shapes. The vertical axis is scaled logarithmically.

Image of FIG. 5.
FIG. 5.

Left: Simulated decay of the correlation functions and for a sample with all internal cavity axes aligned in the direction (at ). The components of the transition dipole moments perpendicular to reorient without restrictions. As a result, the linear absorption spectrum measured with -polarized light is much broader than the one measured with -polarized light (right).

Image of FIG. 6.
FIG. 6.

(a) Simulated correlation functions (solid black), (dashed-dotted gray), and (dotted) at . The same curves for a sample of fully oriented proteins are shown in (b) for the light field parallel and (c) perpendicular to the preferred direction.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Restricted rotational motion of CO in a protein internal cavity: Evidence for nonseparating correlation functions from IR pump-probe spectroscopy