Thermal broadening of the Soret band in heme complexes and in heme-proteins: role of iron dynamics

✍ Scribed by Maurizio Leone; Antonio Cupane; Valeria Militello; Lorenzo Cordone

• Publisher: Springer
• Year: 1994
• Tongue: English
• Weight: 402 KB
• Volume: 23
• Category: Article
• ISSN: 1432-1017
• DOI: 10.1007/bf00188658

✦ Synopsis

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 heine-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.