Exploring the Conformational Variability in the Heme b Propionic Acid Side Chains through the Effect of a Biological Probe: A Study of the Isolated Ions
详细信息 查看全文
- 作者：Alberto De Petris ; Barbara Chiavarino ; Maria Elisa Crestoni ; Cecilia Coletti ; Nazzareno Re ; Simonetta Fornarini
- 刊名：Journal of Physical Chemistry B
- 出版年：2015
- 出版时间：February 5, 2015
- 年：2015
- 卷：119
- 期：5
- 页码：1919-1929
- 全文大小：408K
- ISSN：1520-5207
文摘
The iron(III) protoporphyrin IX complex with imidazole, a biologically relevant ligand, occupying an axial position, has been studied by infrared multiple photon dissociation (IRMPD) spectroscopy. The complex has been delivered in gas-phase by electrospray ionization (ESI), mass selected in an ion trap, and assayed by IRMPD spectroscopy in two complementary frequency regions. The fingerprint range (900鈥?900 cm鈥?) has been scanned using the Orsay free-electron laser beamline (CLIO), while the X鈥揌 (X = C,N,O) stretching region (3000鈥?600 cm鈥?) has been inspected using a tabletop IR optical parametric oscillator/amplifier (OPO/OPA) laser source. DFT calculations have been performed to obtain a comprehensive pattern of the various potential conformers yielding optimized geometries, relative thermodynamic parameters, and respective IR spectra. The comparison between the IR spectra for representative conformers and the experimental IRMPD features suggests the coexistence of two families of conformers involving different degrees of folding and hydrogen bonding between the two propionic acid functionalities on the periphery of the protoporphyrin IX macrocycle in a ratio depending on environmental conditions such as ESI solvent and temperature. The observed conformational variability of the porphyrin substituents in the naked heme鈥搃midazole complex is consistent with the fine-tuning of the reactivity properties of this important prosthetic group by the specific surroundings in the protein core.