Thermal broadening of the Soret band in heme complexes and in heme-proteins: role of iron dynamics |
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Authors: | Maurizio Leone Antonio Cupane Valeria Militello Lorenzo Cordone |
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Institution: | (1) Consorzio INFM, and GNSM (CNR), Istituto di Fisica dell'Università di Palermo, Via Archirafi 36, 1-90123 Palermo, Italy |
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Abstract: | We report the thermal broadening of the Soret band in heme-CO, heme-OH and protoporphyrin IX in the temperature range 300–20 K. For protoporphyrin IX the temperature dependent Gaussian line broadening follows the behavior predicted by the harmonic approximation in the entire temperature range investigated. In contrast, for heme-CO and heme-OH the harmonic behavior is obeyed only up to about 180 K and an anomalous line broadening increase is observed at higher temperatures. This effect is attributed to the onset of anharmonic motions of the iron atom with respect to the porphyrin plane. Comparison with previously reported analogous data for heme proteins enables us to suggest that the onset of substate interconversions in these latter systems can be reflected in motions of the iron atom with respect to the porphyrin plane.
Correspondence to: L. Cordone |
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Keywords: | Protein dynamics Optical spectroscopy Protoporphyrin IX |
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