Donald B. McPhail

Electron spin resonance spectroscopic assessment of the antioxidant potential of teas in aqueous and organic media

Electron spin resonance methodology has been used to assess the hydrogen-donating (antioxidant) ability of catechins and extracts of green and black tea to Fremys radical and galvinoxyl radical in aqueous and organic solutions, respectively. Catechin flavanols accounted for 77-82% of the total antioxidant activity of green tea but only 47-58% of that of black tea. The radical quenching ability of the green tea was 21-24% more effective than that of the black tea in both aqueous and lipophilic systems. Epigallocatechin gallate was the most effective at reducing the two radical species, whereas epigallocatechin was least effective in the galvinoxyl/ethanol system, and catechin least effective in the Fremys radical/water system. In a model system comprising a mixture of the flavanols in ethanolic or aqueous solution, in the same concentrations as they were present in the tea extracts, the antioxidant potential was a simple summation of the activity of the individual components indicating no synergistic or antagonistic side reactions. Results demonstrate that flavanol components of teas exhibit potent antioxidant activity in both aqueous and organic media. This will be of physiological relevance if such compounds partition into both the aqueous and lipid compartment of cells.

Electron spin resonance study of copper(II)–amino-acid complexes: evidence for cis and trans isomers and the structures of copper(II)–histidinate complexes in aqueous solution

Electron spin resonance spectra are reported for copper(II)–amino-acid complexes [CuL]n+ and [CuL2]m+(for 12 α-amino-acids) and [Cu(HL)L]+(HL = L-histidine). Buffer solutions of aqueous copper(II) and ligand were prepared to give optimum concentrations of these complexes. Isotropic g and A values are in the ranges 2.144–2.157 and 5.5–6.5 mT respectively for [CuL]n+ and 2.118–2.127 and 6.4–7.1 mT respectively for [CuL2]m+. The high-field absorption for [CuL2]m+ complexes showed nitrogen hyperfine structure, which for 63Cu and solvent D2O could be resolved in the second derivative into two overlapping quintet components characteristic of cis(N, N, O–, O–) and trans(N, O–, N, O–) isomers respectively. Spectra have been fitted to this model by computer simulation. From observed nitrogen hyperfine structure, and by comparison with spectra of other amino-acid complexes and that of bis(histamine)copper(II), it is deduced that the histidinate complex [Cu(HL)L]+ has three nitrogen atoms co-ordinated to copper in the planar co-ordination sites, whereas [CuL2] appears to consist of a mixture of structures having three and four nitrogen atoms bound to the copper.

Electron spin resonance (ESR) spectroscopic assessment of the contribution of quercetin and other flavonols to the antioxidant capacity of red wines

Health benefits of red wine have been ascribed in part to the antioxidant properties of quercetin and other flavonols. Red wines, however, contain many other polyphenolic compounds with antioxidant potential. The present study has assessed the antioxidant capacity of seven red wines using electron spin resonance spectrometry to measure their ability to donate hydrogen atoms to a stable Fremys radical. Antioxidant capacity of the wines was strongly related to the total phenol content (r = 0.872, P < 0.01) but less so to total flavonol content (r = 0.651, P < 0.10). The only flavonols detected in the wines by HPLC with post-column derivatisation were the aglycones and conjugated forms of quercetin and myricetin. These accounted for less than 2% of total phenolic content when expressed as gallic acid equivalents. Although these flavonols showed marked ability to quench Fremys radical, they contributed less than 1.5% to the total antioxidant capacity of the wines. Consequently, quercetin is not a major antioxidant in red wine. The antioxidant activity of other polyphenols may be of greater importance in contributing to the reputed health benefits of moderate wine consumption.

Novel flavonoids as anti-cancer agents: mechanisms of action and promise for their potential application in breast cancer.

Flavonoids are a large group of ubiquitous polyphenolic secondary metabolites in plants with a wide range of properties, including a widely reported anti-cancer effect. The present review focuses on the different known mechanisms partaking in said anti-tumour effects, with particular emphasis on breast cancer. Their structure and reactivity allows flavonoids to work as antioxidant agents and phyto-oestrogens, modulating oestrogen signalling and metabolism to induce an overall anti-proliferative response. Other effects include the ability of flavonoids to modulate the CYP1 (cytochrome P450 1) and ABC (ATP-binding cassette) protein families, involved in carcinogenesis and drug delivery respectively. They can also induce apoptosis and cell cycle arrest and regulate other signalling pathways involved in the development and progression of cancer. In conclusion, there is accumulating evidence on the versatility of flavonoids and the numerous activities contributing to their anti-tumour effect. The complex, yet effective, mechanism of action of flavonoids, together with their interesting pharmacological properties, is the basis for their potential application in breast and other cancers. This rationale has led to the current interest in the application of flavonoids, including clinical trials currently underway and the development of novel flavonoids with improved properties, which hold great promise for tackling breast cancer.

Oxygen-Induced Free Radical in Wheat Roots

ESR experiments have shown that free radicals are formed in wheat plant roots as a result of exposure to O2. Although the radical(s) has not been positively identified, the nature of the spectra allows simple oxygen-derived radicals, such as O2-, HO2. and OH., to be excluded as possibilities. Adsorption of Cu(II), but not Zn(II) or Cd(II) by the root results in a rapid decay of the radical signal to reach a level of 10% of its original intensity after a few minutes.

The occurrence of copper, iron, zinc and other elements and the nature of some copper and iron complexes in humic substances from municipal refuse disposed of in a landfill

Municipal refuse was allowed to decompose in a simulated landfill for 20 months. Three different models were studied in which the refuse, in 40 m3 lots, was either compacted or mixed 2:1 with sewage sludge, the latter being studied in both uncompacted and compacted states. At 2, 6, 12 and 20 months, humic substances were extracted from samples with 0.1 M Na2P4O7 and 0.1 M NaOH, and humic acids isolated by precipitation after acidification with HCl. The humic substances were examined by electron paramagnetic resonance (EPR) to determine the free radical content and the nature of some of the metal complexes present. The principal form of copper was present in either a square planar or a tetragonally-distorted octahedral environment, probably coordinated to two nitrogen and two oxygen atoms. Fe3+ was present in at least three different environments. In one, it was probably in a complex with rhombic symmetry; another showed Fe3+ in an axially-symmetric environment, most likely as a ferric porphyrin. No distinctions could be made between the concentrations or forms of metals present in the refuse humic substances as a result of adding sewage sludge, but the additions increased the yield of humic substances, particularly in the uncompacted landfill. Humic substances in the refuse retain metal elements in complexed forms which will restrict their release from the landfill.

Spin trapping of free radicals and lipid peroxidation in microsomal preparations from malignant hyperthermia susceptible pigs

Microsomes were prepared from livers of malignant hyperthermia susceptible (MHS) or resistant (MHR) pigs. On incubation with the spin trap alpha-(4-pyridyl-l-oxide)-N-tert-butylnitrone (4-POBN), the microsomes from MHS pigs produced a characteristic electron spin resonance (ESR) signal at a greater rate than those from MHR pigs. Increased formation in the incubations of thiobarbituric acid reactive substances (TBARS) by the microsomes of the MHS pigs indicated an enhanced susceptibility to free radical-mediated lipid peroxidation. These results provide further evidence that MHS pigs have an antioxidant abnormality which may contribute to the fatal MH response. However the nature of the abnormality is unclear. The enhanced formation of unstable free radicals and indices of lipid peroxidation was not due to decreased vitamin E concentration or glutathione peroxidase activity in the microsomes. Furthermore, fatty acid profiles were similar in microsomes from MHS and MHR pigs indicating similar amounts of potential substrate for TBARS formation.

AN ELECTRON SPIN RESONANCE INVESTIGATION OF INTERNAL RUST SPOT, A PHYSIOLOGICAL DISORDER OF THE POTATO TUBER

ESR spectroscopy has been used to investigate the formation of paramagnetic species during the development of internal rust spot (IRS) in the potato tuber. Production of free radicals and oxidation of metal ions such as Fe(II) and Mn(II) occur when necrotic tissue is formed. However, since IRS develops in periods of calcium stress (low calcium supply), it is suggested that the principal cause of the disorder is a loss of cell membrane integrity which is brought about by a lack of calcium. Cell senescence and the formation of necrotic tissue may then result either from increased oxygen radical production within the cell or from oxidation of metal complexes in the extracellular regions of the tissue.

Spin trapping of free radicals in homogenates of heart from selenium and vitamin E deficient rats.

The formation of unstable free radical species in homogenates of heart from selenium and/or vitamin E deficient rats has been investigated by electron spin resonance spectroscopy using the spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone. There was only a small amount of free radical formation by heart from control or selenium deficient animals. However, the amounts and rates of formation of free radicals were significantly higher in animals with vitamin E deficiency and higher still in those with combined selenium and vitamin E deficiency.

Elucidation of phenol-Cu interaction mechanisms by potentiometry, ESR, UV absorption spectroscopy and molecular simulations

Abstract In order to determine the dominant properties, which control the interactions of monomeric hydrosoluble phenols with Cu2+ in soil solutions, four different techniques were used. CuSO4 was added to ortho-dihydroxy-phenol (ODP) solutions under controlled temperature, pH, and ionic strength conditions and Cu2+-ODP interactions were studied by alkaline potentiometric titrations, electron spin resonance and UV absorption. Molecular dynamic simulations were also performed for conformational studies. From the titration curves, the shifts in isotropic A and g values, the evolution of the UV absorption band at 400 nm and the calculation of the potential energy of the different complexes, a three-step interaction mechanism was proposed. In the process an inner-sphere complex was formed, Cu(II) is being reduced and an oxydative polymerisation chain reaction initiated. The driving force of the reaction was the energetic stability obtained upon interaction of Cu2+ with the substrate. The ideal conformation was reached at the catechol site and not at carboxylic or hydroxy–methoxy sites. The pKa values of the phenols had little influence on the interaction process but the type and number of interacting sites on the benzene ring influenced the proceeding of progress of the reaction. Increasing the pH of the solution increased the amount of complexed species, but also the number of ligands around the Cu2+ion.