• Bulletin of the Korean Chemical Society
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• 제31권12호
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• pp.3771-3776
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• 2010

The dynamics of the $CN^-$-ligated ferric cytochrome c (CytcCN) in $D_2O$ at 283 K following Q-band photoexcitation at 575 nm was observed using femtosecond time-resolved vibrational spectroscopy. The equilibrium vibrational spectrum of the CN stretching mode of CytcCN shows two overlapping bands: one main band (82%) at $2122\;cm^{-1}$ with $23\;cm^{-1}$ full width at half maximum (fwhm) and the other band (18%) at $2116\;cm^{-1}$ with $7\;cm^{-1}$ fwhm. The time-resolved spectra show bleaching of the CN fundamental mode of CytcCN and two absorption features at lower energies. The bleach signal and both absorption features are all formed within the time resolution of the experiment (< 200 fs) and decay with a life time of 1.9 ps. One transient absorption feature, appearing immediately red to the bleach signal, results from the thermal excitation of low-frequency modes of the heme that anharmonically couple to the CN fundamental mode, thereby shifting the CN mode to lower energies. The shift of the CN mode decays with a lifetime of 2 ps, equivalent to the time scale for vibrational cooling of the low-frequency heme modes. The other transient absorption feature, which is 3.3 times weaker than the bleach signal and shifted $27\;cm^{-1}$ toward lower energies, is attributed to the CN mode in an electronically excited state where the CN bond is weakened with a lowered extinction coefficient. These observations suggest that photoexcited CytcCN mainly undergoes ultrafast radiationless relaxation, causing photo-deligation of $CN^-$ from CytcCN highly inefficient. As also observed in $CN^-$-ligated myoglobin, inefficient ligand photodissociation might be a general property of $CN^-$-ligated ferric hemes.

• Bulletin of the Korean Chemical Society
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• 제30권1호
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• pp.177-182
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• 2009

We present the geminate rebinding kinetics measurements of CO to 2-methylimidazole (2-MeIm) bound ferrous protoporphyrin- IX (FePPIX) in alkaline glycerol/water mixtures at 293 K after photolysis. The kinetics was probed by monitoring the CO stretching mode using femtosecond vibrational spectroscopy. When 2-MeIm is used in excess, heme dimers that typically form in low viscosity solutions disappear as the viscosity of the solvent increases. Heme aggregates formed in low viscosity solutions turn monomeric as more 2-MeIm is added, suggesting that 6-coordinated heme, including a strong proximal histidine tends to be in the monomeric form. The vibrational band of CO in the 2-MeIM-FePPIX-CO is well described by a single Gaussian function centered at 1958 $cm^-1$ and 28 $cm^-1$ full width at half maximum. The efficiency and rate of the geminate rebinding of CO to the heme increase with viscosity of the solvent, suggesting that retention of the dissociated CO near the heme, for a longer period by the viscous solvent media, accelerates rebinding.

• Bulletin of the Korean Chemical Society
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• 제24권11호
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• pp.1675-1679
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• 2003

The photodynamics of excited-state intramolecular proton transfer reaction of 1-hydroxyanthraquinone (1-HAQ) and 1-deuterioanthraquinone was investigated in toluene with time-resolved emission and femtosecond transient transmittance techniques at room temperature. The temporal profiles of transient transmittance of 1-HAQ could be well described with multi-decaying time constants. The ultrafast time constant within ca. 260 fs reflects the dynamics of proton transfer. The decay component of 2 ps is assigned to an additional proton translocation process induced by the intramolecular vibrational relaxation, whereas the decay component of 18 ps is assigned to the vibrational cooling process, while the long component (200 ps) can be explained in terms of the relaxation from excited-state keto-tautomer to its ground state. Time-resolved anisotropy decay dynamics and isotope effects on the photodynamics reveals that the ESIPT from enol-tautomer to keto-one of 1-HAQ is barrierless reaction and coupled to a vibrational relaxation process.