54967-69-0Relevant articles and documents
Axial thiophenolate coordination on diiron(III)bisporphyrin: Influence of heme-heme interactions on structure, function and electrochemical properties of the individual heme center
Sil, Debangsu,Tuglak Khan, Firoz Shah,Rath, Sankar Prasad
, p. 11925 - 11936 (2015/02/02)
The binding of a series of substituted thiophenols as axial ligands on a highly flexible ethane-bridged diiron(III)bisporphyrin framework has been investigated as a model of diheme proteins. Spectroscopic characterization reveals a high-spin (S = 5/2) state of iron for all of the pentacoordinate thiophenolato complexes. In the UV-visible spectra of the complexes, the positions of the Soret and band I have been found to be dependent on the pKa of thiophenols. The alternating shift pattern, which has opposite sign of the chemical shifts for meta- vs. ortho- and para- protons in the 1H NMR spectra, is attributed to negative and positive spin densities, respectively, on thiophenolate carbon atoms and is indicative of π-spin delocalization to the bound thiophenolate ligand. The Fe(III)/Fe(II) redox couple of the complexes bears a linear relationship with the pKa of thiophenol and is found to be positively shifted with decreasing pKa. The effect of the electronic nature of the substituent on the thiophenolate ring has also been demonstrated in which a large potential range of 540 mV was observed (in contrast to the value of only 270 mV in case of monoheme analogues) for the Fe(III)/Fe(II) redox couple on going from monoheme to diheme and is attributed to the interheme interaction. Also, the Fe(III)/Fe(II) redox potential of the thiophenolato complexes has been found to be more positively shifted compared to their phenolato analogues, which was further supported by DFT calculation. The addition of another thiophenol at the sixth axial position of the five-coordinate thiophenolato complex causes a change in iron spin from high (S = 5/2) to low (S = 1/2) along with a large positive shift of 490 mV for the Fe(III)/Fe(II) redox couple.
Spectrophotometric and resonance Raman studies on the formation of phenolate and thiolate complexes of (octaethylporphinato)iron(III)
Uno, Tadayuki,Hatano, Keiichiro,Nishimura, Yoshifumi,Arata, Yoji
, p. 2803 - 2807 (2008/10/08)
Reactions of (octaethylporphinato)iron(III) methoxide, Fe(OEP)(OMe), with a series of phenols, carboxylic acids (ROH), and thiols (RSH) were monitored by spectrophotometric techniques. The equilibrium constants for addition of ROH to Fe(OEP)(OMe) were measured, and it was found that increased acidity of the ROH moiety caused the equilibrium constant to increase. The reaction of Fe(OEP)(OMe) with RSH proceeded significantly slowly at 20°C. The second-order rate constants were obtained and were found to increase with the increase of RSH acidity. These indicate that dissociation of a proton from an ROH or RSH moiety will promote the formation of the product species Fe(OEP)(OR) or Fe(OEP)(SR). By the use of resonance Raman spectroscopy, both product species were found to be five-coordinate ferric high-spin complexes. The Fe(OEP)(OPh) complex showed the ν(Fe-OPh) stretching Raman line at 607 cm-1. The visible absorption maxima of the porphyrin π to iron dπ transitions (CT band) of Fe(OEP)(OR) and Fe(OEP)(SR) were a linear function of the pKa of ROH and RSH, and the hypsochromic shift with the increasing pKa was explained in terms of the electron-donating ability of the OR and SR ligands. The absorption maxima of Fe(OEP)(SR) were generally shifted to longer wavelength than those of Fe(OEP)(OR).
Iron(II, III)-Chlorin and Isobacteriochlorin Complexes. Models of the Heme Prosthetic Groups in Nitrite and Sulfite Reductases: Means of Formation and Spectroscopoic and Redox Properties
Stolzenberg, Alan M.,Strauss, Steven H.,Holm, R. H.
, p. 4763 - 4778 (2007/10/02)
Extensive series of iron(II, III)-hydroporphyrin complexes of the types Fe(P)L, 0,+, 2O, and Fe(P), with P = octaethylchlorin (OEC) and octaethylisobacteriochlorin (OEiBC) and L, L' = neutral or uninegative axial ligands, have been synthesized and isolated or generated in solution.Means of synthesis and reactivity properties of OEC and OEiBC complexes parallel those of octaethylporphyrin (OEP) complexes.This behavior, together with a detailed body of physicochemical properties (absorption, MCD, 1H NMR, EPR, and infrared spectra and voltammetry), serves to identity all new complexes.Certain of the OEiBC species are pertinent as possible analogues of the siroheme prosthetic group of nitrite and sulfite reductases.Physicochemical properties of OEP, OEC, and OEiBC complexes at parity of axial ligation are compared in an attempt to identify any intrinsic features of isobacteriochlorin species that might render them particularly suitable for mediation of multielectron reductions of substrates as executed by siroheme enzymes.Properties such as Fe(III)/Fe(II) potentials and νCO of Fe(P)L(CO) and Fe(P)(CO)1,2 were found to be nearly invariant to P, indicating little cis effect of these macrocycles, which are in different reduction levels.That property most dependent on macrocycle structure was found to be the potential for ring-based oxidation which increases in the order OEiBC OEC OEP.Comparative properties are discussed in some detail and are related to available information on sirohemes, including the question of axial ligation in the native enzyme.This research affords the first comprehensive examination of the preparation and chemical, spectroscopic, and redox properties of iron(II, III)-hydroporphyrin complexes.
