title: The characterisation of structural and antioxidant properties of isoflavone metal chelates.
abstract: Isoflavone metal chelates are of interest as isoflavones act as oestrogen mimics. Metal interactions may enhance isoflavones biological properties so understanding isoflavone metal chelation is important for the commercial application of isoflavones. This work aimed to determine if isoflavones, daidzein (4',7-dihydroxyisoflavone) and genistein (4',5,7-trihydroxyisoflavone) could chelate with metals as isoflavone chelates. Biochanin A (4'-methoxy-5,7-dihydroxyisoflavone) was also examined for it's ability to chelate with Cu(II) and Fe(III). This study found daidzein does not chelate with Cu(II) and Fe(III) but genistein and biochanin A chelate with a 1:2 M/L stoichiometry. The copper and iron chelates were synthesised and characterised by elemental analysis, FTIR, thermogravimetric analysis (TGA) and electrospray ionisation mass spectrometry (ESI-MS). These studies indicated a 1:2 M/L stoichiometry and suggested the isoflavones bind with the metals at the 4-keto and the 5-OH site. 2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition assays showed that copper isoflavone chelates have higher antioxidant activity than free isoflavones while the iron isoflavone chelates showed pro-oxidant activity compared to the free isoflavone. Synergistic DPPH studies with 0.02 mM ascorbic acid revealed copper chelates exhibit reduced antioxidant activity versus free isoflavones whereas the iron chelates showed lower pro-oxidant activity except at 1.0 mM.
authors.affiliation: Department of Chemical & Life Sciences, School of Science, Waterford Institute of Technology, Waterford, Ireland. sdowling@wit.ie
authors.forename: Stephen
authors.initials: S
authors.lastname: Dowling
authors.forename: Fiona
authors.initials: F
authors.lastname: Regan
authors.forename: Helen
authors.initials: H
authors.lastname: Hughes
mesh_terms: D000975:Antioxidants / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D001713:Biphenyl Compounds / Q000737:chemistry; D002614:Chelating Agents / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D019833:Genistein / Q000737:chemistry / Q000494:pharmacology; D007529:Isoflavones / Q000737:chemistry* / Q000494:pharmacology; D008670:Metals / Q000037:antagonists & inhibitors / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction / Q000187:drug effects; D010851:Picrates / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D017550:Spectroscopy, Fourier Transform Infrared; D013818:Thermogravimetry
chemical_list: D000975:Antioxidants; D001713:Biphenyl Compounds; D002614:Chelating Agents; D007529:Isoflavones; D008670:Metals; D010851:Picrates; C004742:daidzein; C004931:1,1-diphenyl-2-picrylhydrazyl; D019833:Genistein; C004541:biochanin A