Characterization of Temperature-Dependent Iron-Imidazole Vibrational Modes in Far Infrared

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• 作者：Sabine Dö ; rr ; Ulrich Schade ; Petra Hellwig ; Michele Ortolani
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：December 27, 2007
• 年：2007
• 卷：111
• 期：51
• 页码：14418 - 14422
• 全文大小：205K
• 年卷期：v.111,no.51(December 27, 2007)
• ISSN：1520-5207

文摘

The active site of several oxygen binding proteins can be mimicked with the ferric iron protoporphyrin IXderivative hemin, coordinating two imidazole molecules and embedded in sodium dodecyl sulfate (SDS)micelles; the detergent simulates the hydrophobic cavity of heme proteins. We studied the low-frequencyvibrational modes of the porphyrin-iron-imidazole bonding in infrared absorbance spectra. Assignment ofthe metal-ligand vibrations to signals at 396, 387, and 378 cm^-1 was performed by isotope labeling of theimidazole ligand. These modes were also found to be temperature-dependent and to display a linear increaseof signal intensity between 25 and 150 K and, with a different slope, between 150 and 300 K. The modes at396 and 399 cm^-1 show for 25 K an upshift about 4 cm^-1 and the signal at 378 cm^-1 a small downshift,indicating the involvement of antisymmetric stretching modes and, in the latter, of bending motions. Anharmoniccouplings to doming modes are discussed, and the doming mode and hydrogen-bonding signature spectralrange between 300 and 100 cm^-1 is presented.