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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 30, Number 1
BKCSDE 30(1)
January 20, 2009 

Dynamics of CO Rebinding to Protoheme in Viscous Solutions
Taegon Lee, Jaeheung Park, Jooyoung Kim, Sangwoo Joo, Manho Lim*
CO Rebinding, Protoheme, Fs vibrational spectroscopy, Viscous solution
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.
177 - 182
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