Bernard A. Goodman

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.

COMPARISON OF SALT MARSH HUMIC ACID WITH HUMIC-LIKE SUBSTANCES FROM THE INDIGENOUS PLANT SPECIES SPARTINA ALTERNIFLORA (LOISEL)

Substances resembling humic acids were extracted from fresh plant material (Spartina alterniflora) and from dead plant debris. Their elemental composition, spectral characteristics in the UV, visible and IR regions, and electron spin resonance were compared with those of humic acid from mud in which the plants were growing. The results show the plant humic substances to consist of a higher portion of aliphatic compounds in their complex structures than that from mud. However, the overall similarities between the extracted material from the different sources indicate that S. alterniflora makes a direct contribution to the humic substances in the salt marsh ecosystems.

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.

Characterization of iron-fulvic acid complexes using Mossbauer and EPR spectroscopy

Abstract The usefulness of Mossbauer and electron paramagnetic resonance (EPR) spectroscopy in characterizing the products of the reaction of iron with humic substances is discussed and illustrated with results obtained from soil fulvic acids. These results show that the nature of the products varies with pH and with the iron:fulvic acid ratio. Reduction of iron(III) to iron(II) increases with decreasing pH, and complexation, in the form of mononuclear Fe(III) species, increases with decreasing Fe:fulvic acid ratios, but shows little pH dependence. Evidence is also seen for the presence of polynuclear species even when large excesses of fulvic acid are present.

Notes. Electron spin resonance parameters for some copper(II)–bis(amino-acid) complexes

The presence of two components, presumably cis and trans isomers, was previously indicated by the 14N superhyperfine structure pattern in the e.s.r. spectra of a number of copper(II)–bis(amino-acid) complexes in aqueous solution. In the present work the g and hyperfine values of the individual species have been obtained from spectra of the 63Cu and 65Cu isotopes. Significantly different values have been observed for the two components and these differences are discussed in terms of possible deviations from the ideal square-planar structure in the cis and trans isomers.

An electron spin resonance investigation of the nature of the complexes formed between copper(II) and glycylhistidine

The pH dependence of the formation of complexes between copper(II) and the peptide glycylhistidine has been investigated for metal : ligand ratios of 1 : 1 and 1 : 2 by e.s.r. spectroscopy. Five complex species are seen with the 1 : 2 ratio solutions, 4 of which are also observed with the 1 : 1 ratio solutions. In each case 14N superhyperfine structure is resolved in fluid solution by working with the 63Cu isotope and recording second-derivative spectra, thus producing a direct measurement of the number of nitrogen atoms bound to copper. Superhyperfine structure was also resolved in the frozen-solution spectra of several of the complexes, although this was not always consistent with the conclusions drawn from the fluid-solution spectra. The likely composition and coordination of the various species are discussed with reference to published results from electrochemical and u.v.-visible spectroscopic methods.