53470-09-0Relevant articles and documents
Tuning the Vibrational Relaxation of CO Bound to Heme and Metalloporphyrin Complexes
Hill, Jeffrey R.,Ziegler, Christopher J.,Suslick, Kenneth S.,Dlott, Dana D.,Rella, C. W.,Fayer, M. D.
, p. 18023 - 18032 (2007/10/03)
Picosecond mid-infrared pump-probe experiments were used to investigate vibrational relaxation (VR, which here denotes loss of excess vibrational energy) of CO bound to synthetic heme and porphyrin complexes with different metal atoms (M = Fe, Ru, Os) and different proximal ligands (imidazoles and pyridines).Isotope effects of 13CO vs 12CO and solvent effects were also studied.A remarkable correlation between the carbonyl vibrational lifetime and the carbonyl vibrational frequency νCO is observed.The vibrational lifetime decreases as νCO decreases.The lifetime-frequency correlation is consistent with a linear reaction between carbonyl vibrational relaxation rate and νCO.Hemes and porphyrins show similar lifetime-frequency correlations, but the absolute value of the VR rate in meso-tetraphenylporphyrin complexes is slightly faster than in protoporphyrin IX dimethyl ester heme complexes.The predominant VR process is shown to be intramolecular transfer from CO to heme vibrations, rather than intermolecular transfer from CO to solvent vibrations.The intramolecular process occurs by anharmonic coupling via ?-bonding between CO and the metalloporphyrin and heme.In metalloporphyrin and heme complexes, changes in back-bonding to CO simultaneously affect both CO frequency and the strength of anharmonic coupling, accounting for the observed lifetime-frequency correlation.Increasing back-bonding lowers the CO frequency and increases the anharmonic coupling, shortening the vibrational lifetime.Similar lifetime-frequency correlations are observed in wild-type and mutant heme proteins.It is possible to continuously tume the vibrational relaxation rate of CO over a range spanning about a factor of 4, by systematic modification of the chemical structure of the heme or porphyrin complex to which it is bound.
13C and 17O NMR and IR spectroscopic study of a series of carbonyl(4-substituted pyridine)(meso-tetraphenylporphinato)iron(II) complexes. Correlations between NMR chemical shifts and IR stretching frequencies of the carbonyl ligand and taft parameters of the pyridine substituent
Box, James W.,Gray, Gary M.
, p. 2774 - 2778 (2008/10/08)
The results of a 13C and 17O NMR and IR spectroscopic study of a series of carbonyl(4-substituted pyridine) (meso-tetraphenylporphinato)iron(II) (Fe(TPP)(CO)(py-4-X)) complexes are presented. Good to excellent linear correlations between the 13C and 17O NMR chemical shifts and the IR stretching frequencies of the carbonyl ligand are observed as the pyridine substituent is varied. Good to excellent linear correlations are also observed between these NMR chemical shifts and IR stretching frequencies and the NMR chemical shifts and IR stretching force constants for the trans carbonyls of a series of cis-Mo(CO)4(py-4-X)2 complexes as the pyridine substituent is varied. The relationship between the donor ability of the pyridine ligands and the 13C and 17O NMR chemical shifts and IR stretching frequencies of the carbonyl ligands in the Fe(TPP)(CO)(py-4-X) complexes has been quantitated by fitting the spectroscopic data to the single and the dual Taft substituent parameters of the pyridine substituent. Good to excellent correlations are observed. The upfield shift in the 13C NMR resonance of the carbonyl ligand as the electron-donor ability of the pyridine increases is unique. This has been rationalized by using the Buchner and Schenk description of metal carbonyl 13C NMR chemical shifts.
Electronic Control of Ferroporphyrin Ligand-Binding Kinetics
Stanford, Marlene A.,Swartz, James C.,Phillips, Terry E.,Hoffman, Brian M.
, p. 4492 - 4499 (2007/10/02)
Measurements of the rates of CO binding to ferrous porphyrins have been used to examine two different mechanisms which have been proposed to explain protein control of heme reactivity.The results indicate that electronic control through ?-donor/acceptor interactions with the macrocyclic porphyrin rings is not important in controlling the heme reactivity of hemoglobin or of other hemoproteins.However, hydrogen bonding to the metal-bound imidazole can have a powerful influence on heme reactivity.
