Characterization of temperature-dependent iron-imidazole vibrational modes in far infrared.
The active site of several oxygen binding proteins can be mimicked with the ferric iron protoporphyrin IX derivative 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-frequency vibrational modes of the porphyrin-iron-imidazole bonding in infrared absorbance spectra. Assignment of the metal-ligand vibrations to signals at 396, 387, and 378 cm(-1) was performed by isotope labeling of the imidazole ligand. These modes were also found to be temperature-dependent and to display a linear increase of signal intensity between 25 and 150 K and, with a different slope, between 150 and 300 K. The modes at 396 and 399 cm(-1) show for 25 K an up-shift 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. Anharmonic couplings to doming modes are discussed, and the doming mode and hydrogen-bonding signature spectral range between 300 and 100 cm(-1) is presented.
Laboratoire de Spectroscopie Vibrationnelle et Electrochimie des Biomolécules, Institut de Chimie, UMR 7177, Université Louis Pasteur, 4 Rue Blaise Pascal, F-67000 Strasbourg, France.
Sabine
S
Dörr
Ulrich
U
Schade
Petra
P
Hellwig
Michele
M
Ortolani
D040761:Biomimetic Materials / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006860:Hydrogen Bonding; D007093:Imidazoles / Q000737:chemistry* / Q000378:metabolism; D007501:Iron / Q000737:chemistry* / Q000378:metabolism; D007553:Isotope Labeling; D008024:Ligands; D008667:Metalloproteins / Q000737:chemistry* / Q000378:metabolism; D008823:Micelles; D011524:Protoporphyrins / Q000737:chemistry / Q000378:metabolism; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013055:Spectrophotometry, Infrared / Q000379:methods; D013501:Surface-Active Agents / Q000737:chemistry; D013696:Temperature
D007093:Imidazoles; D008024:Ligands; D008667:Metalloproteins; D008823:Micelles; D011524:Protoporphyrins; D013501:Surface-Active Agents; D012967:Sodium Dodecyl Sulfate; D006418:Heme; C029899:imidazole; C028025:protoporphyrin IX; D007501:Iron