Fig. 3: Representative time-resolved vibrational spectra obtained on the picosecond timescale for CO photolyzed from the isolated carbonmonoxy chains of human HbCO.
From: Direct observation of two-channel photodissociation of carbon monoxide from the hemoglobin subunits
The transient spectra obtained for the isolated carbonmonoxy α chains (a) and carbonmonoxy β chains (b) at selected time delays (indicated in the key). For clarity, the background has been subtracted from the measured spectra. The arrows indicate the time evolution of the signal. The spectra shown correspond to the magic angle relative polarization between the pump and the probe beams. Similar spectra were obtained for the other two (parallel and perpendicular) polarization conditions. Time dependence of the normalized total integrated area of the vibrational spectra of CO photolyzed from the isolated carbonmonoxy α chains (c) and carbonmonoxy β chains (d). To calculate the total integrated area, the transient bands corresponding to the CO molecules, produced in both the ground vibrational state (ν = 0) and the first excited vibrational state (ν = 1), were taken into account. The total integrated area was calculated for the spectral region of 2090 to 2160 cm–1 after the baseline subtraction. The normalized areas at selected time delays after the photoexcitation are shown as open circles. The time delays, t, range from 3 to 1000 ps (c) and from 3 to 500 ps (d). The solid line is a fit to the equation: A(t) = Amax·(1 – Ainc·exp(–t/τinc)), where Amax is the maximum area value, Ainc is the increase in the normalized area, τinc is the time constant for the increase in the normalized area. The time constant τinc was found to be ~20 ps, the increase in the normalized area being no more than 0.2. The time-resolved mid-IR measurements were repeated 4 times for each sample. In a single measurement, typically 75 time delay points were used. Each time-resolved mid-IR spectrum shown on (a, b) or each time delay point shown on (c, d) corresponds to 150,000 averaged laser shots. Conditions: 50 mM Tris buffer, pD 8.2, at 19 °C. Concentrations of the carbonmonoxy α and β chains were 3.0 and 4.0 mM in heme, respectively. Excitation wavelength, λexc = 543 nm. Source data are provided as a Source Data file.
