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Silver J, al-Jaff G, Taies JA, Wilson MT, den Engelsen D, Fern GR, Ireland TG. Studies on the binding of CO to low-spin [Fe(II)(Por)L 2] complexes: an aid to understanding the binding of CO to haemoglobin and myoglobin. J Biol Inorg Chem 2023; 28:65-84. [PMID: 36478266 PMCID: PMC9938061 DOI: 10.1007/s00775-022-01969-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Accepted: 10/13/2022] [Indexed: 12/12/2022]
Abstract
The visible and Mössbauer spectra of [Fe(II)(Por)L2] and [Fe(II)(Por)L(CO)] complexes (where Por = protoporphyrin IX (PPIX) or tetra(p-sulfophenyl)porphyrin (TPPS) and L = an aliphatic or aromatic nitrogenous base) are reported and discussed. The results are compared to those of previously reported [Fe(II)(Por)L(CO)] complexes (where Por = PPIX, TPPS, PMXPP, TPP, OMTBP and OEP; L = a nitrogenous aromatic ligand) and HbCO (where Hb = haemoglobin) and MyCO (where My = myoglobin). A new approach, to extracting information from the Mössbauer parameters has been developed by plotting those of the [Fe(II)(Por)L2] complexes against those of [Fe(II)(Por)L(CO)] complexes for the same ligands, has yielded a series of trend lines that show a significant dependence on both the nature of the porphyrin and also of the nitrogenous ligand. Different trend lines were found for aromatic nitrogenous ligands to aliphatic nitrogenous ligands showing that the porphyrins could donate different amounts of charge to the Fe(II) cations as the L ligand changed, and hence, they display electron sink properties. From the plots, it was shown that haemoglobin and myoglobin both bind CO very strongly compared to the model complexes studied herein. Using the reported structural and Mössbauer data for the [Fe(II)(Por)L2] and [Fe(II)(Por)L(CO)] complexes, it proved possible and instructive to plot the Mössbauer parameters against a number of the bond lengths around the Fe(II) cations. The interpretation of the resulting trend lines both supported and facilitated the extension of our findings enabling further understanding of the geometry of the bonding in CO haemoglobin and CO myoglobin.
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Affiliation(s)
- Jack Silver
- grid.7728.a0000 0001 0724 6933College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH Middlesex UK
| | - Golzar al-Jaff
- grid.8356.80000 0001 0942 6946School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ Essex UK ,grid.444950.8Department of Chemistry, College of Education, Salahaddin University-Erbil, Erbil, Iraq
| | - Jehad A. Taies
- grid.8356.80000 0001 0942 6946School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ Essex UK ,Department of Chemistry, College of Education for Pure Science, University of Anwar, Ramadi, Iraq
| | - Michael T. Wilson
- grid.8356.80000 0001 0942 6946School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ Essex UK
| | - Daniel den Engelsen
- grid.7728.a0000 0001 0724 6933College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH Middlesex UK
| | - George R. Fern
- grid.7728.a0000 0001 0724 6933College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH Middlesex UK
| | - Terry G. Ireland
- grid.7728.a0000 0001 0724 6933College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH Middlesex UK
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Silver J, Al-Jaff G, Wilson MT, den Engelsen D, Fern GR, Ireland TG. Studies on the binding of nitrogenous bases to protoporphyrin IX iron(II) in aqueous solution at high pH values. J Biol Inorg Chem 2022; 27:297-313. [PMID: 35235042 PMCID: PMC8960585 DOI: 10.1007/s00775-022-01929-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Accepted: 01/14/2022] [Indexed: 10/28/2022]
Abstract
Studies are reported on the formation of low-spin six-coordinate [Fe(PPIX)L2] complexes from iron(II) protoporphyrin where L is one of a series of nitrogenous ligands (aliphatic, aromatic or heterocyclic). The bonding constants have been determined by titration of the metal complex with these ligands and are compared in relation to previous studies. The adduct formation was monitored utilising optical spectroscopy. In addition, Mӧssbauer spectroscopic experiments were conducted to monitor the electronic environment around the central iron atom in these complexes. The two complementary spectroscopic methods indicated that all nitrogen ligands formed low-spin octahedral complexes. The magnitude of the overall binding constants (β2 values) are discussed and related to (a) the pKa values of the free ligands and (b) the Mössbauer parameter ΔEQ, which represents the quadrupole splitting of the haem iron. The β2 and ΔEQ values are also discussed in terms of the structure of the ligand. Cooperative binding was observed for nearly all the ligands with Hill coefficients close to 2 for iron(II) protoporphyrin; one of these ligands displayed a much greater affinity than any we previously studied, and this was a direct consequence of the structure of the ligand. Overall conclusions on these and previous studies are drawn in terms of aliphatic ligands versus aromatic ring structures and the absence or presence of sterically hindered nitrogen atoms. The implications of the work for the greater understanding of haem proteins in general and in particular how the nitrogenous ligand binding results are relevant to and aid the understanding of the binding of inhibitor molecules to the cytochrome P450 mono-oxygenases (for therapeutic purposes) are also discussed. Changes in the electronic absorption spectra of five-coordinate [Fe(II)(PPIX)(2-MeIm)] that occurred as the temperature was lowered from room temperature to 78° K.
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Affiliation(s)
- Jack Silver
- College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, Middlesex, UK
| | - Golzar Al-Jaff
- School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, Essex, UK.,Department of Chemistry, College of Education, Salahaddin University-Erbil, Erbil, Iraq
| | - Michael T Wilson
- School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, Essex, UK
| | - Daniel den Engelsen
- College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, Middlesex, UK
| | - George R Fern
- College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, Middlesex, UK
| | - Terry G Ireland
- College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, Middlesex, UK.
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A Mössbauer study on the (protoporphyrinato IX)iron(II) complexes of imidazole and substituted imidazoles as axial ligands in frozen aqueous solutions. Inorganica Chim Acta 1989. [DOI: 10.1016/s0020-1693(00)80797-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Medhi OK, Silver J. Mössbauer spectroscopic evidence for molecular complex formation between histidine and μ-oxo-bis(protoporphyrinato IX)iron(III). Inorganica Chim Acta 1989. [DOI: 10.1016/s0020-1693(00)83227-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Towards an understanding of the quadrupole splittings found in the Mössbauer spectroscopic data of a number of substituted tetraphenylporphyriniron(III) halides. Inorganica Chim Acta 1988. [DOI: 10.1016/s0020-1693(00)86305-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Silver J, Jassim QA. Reactions that involve collapse of the ‘superphthalocyanine’ dioxocyclopentakis(1-iminoisoindolinato)uranium(VI) to either phthalocyanine or metal phthalocyanine. Inorganica Chim Acta 1988. [DOI: 10.1016/s0020-1693(00)86301-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Silver J, Lukas B, Al Taies J. Mössbauer studies on tetra(p-sulphophenyl)porphyrin iron(II) solutions. Inorganica Chim Acta 1987. [DOI: 10.1016/s0020-1693(00)87102-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Silver J, Al-Jaff G, Al-Taies J. Mössbauer spectroscopic studies on concentrated protoporphyrin IX iron(II) solutions. Inorganica Chim Acta 1987. [DOI: 10.1016/s0020-1693(00)83280-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Studies on the reactions of ferric iron with glutathione and some related thiols. Part IV. A study of the reaction of glutathione with protoporphyrin IX iron(III). Inorganica Chim Acta 1985. [DOI: 10.1016/s0020-1693(00)84348-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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