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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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Moosavi-Movahedi A, Semsarha F, Heli H, Nazari K, Ghourchian H, Hong J, Hakimelahi G, Saboury A, Sefidbakht Y. Micellar histidinate hematin complex as an artificial peroxidase enzyme model: Voltammetric and spectroscopic investigations. Colloids Surf A Physicochem Eng Asp 2008. [DOI: 10.1016/j.colsurfa.2008.01.047] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Das DK, Medhi OK. The role of heme propionate in controlling the redox potential of heme: square wave voltammetry of protoporphyrinato IX iron (III) in aqueous surfactant micelles. J Inorg Biochem 1998; 70:83-90. [PMID: 9666570 DOI: 10.1016/s0162-0134(98)10002-8] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The proton equilibrium in aqueous surfactant solutions of hemin, (PPIX)Fe(H2O)+2, involving the propionic acid groups is reported (PPIX = protoporphyrinato IX). The surfactant used are sodium dodecyl sulphate (SDS), triton X-100 (TX-100) and hexadecyl trimethylammonium bromide (CTAB). The pKa values, determined spectroscopically from the pH variations of the Soret absorption, are found at ca. 3.5 in SDS and TX-100 micelles. In the cationic surfactant (CTAB) the absorbance of hemin is independent of the hydrogen ion concentration in solution and this surfactant form a salt-link with the heme propionate group. The dependence of mid-point potential on pH indicates that the heme propionate undergoes a redox-linked changed in pKa from 3.2-3.5 in the ferric form to 4.4-4.5 in the ferrous form (27 degrees C, mu = 0.2 M). The change in the mid-point potential per unit change in pH. delta E/delta pH, is ca. -59 mV. Replacement of the water molecules in hemin by tetrahydrofuran, (PPIX)Fe(thf)+2, induces a considerable shift of pKa of the heme propionate: 6.2-6.8 in the ferric form and 7.5-7.8 in the ferrous form. The lower value of pKa in diaquo hemin is attributed to stabilisation of the propionate by a hydrogen bond with coordinated water molecules. All these results may be interpreted in terms of the involvement of a heme propionate group in redox linked uptake of protons and the influence of hydrogen bonding and salt-link formation on the pKa of the proton equilibrium.
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Affiliation(s)
- D K Das
- Department of Chemistry, Gauhati University, Assam, India
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Hassan MK, Hassan RM, Abd-Alla MA. Synthesis and characterization of high-spin iron(III)-sulpha drug complexes and their biological activity. MONATSHEFTE FUR CHEMIE 1991. [DOI: 10.1007/bf00815921] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Medhi OK. Models of the cytochromes-b and related heme proteins. J CHEM SCI 1990. [DOI: 10.1007/bf02841948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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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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