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Biomedical subjects

M C Symons

Publications and source records attributed to M C Symons.

At least 55 records · Page 3Linked to original sources
PubMed1988

Formation of radicals by mechanical processes.

The application of e.s.r. spectroscopy to the study of radicals formed by mechanical means (grinding, shearing, bending, cutting, etc.) is discussed. Two mechanisms are considered, one being the homolytic breaking of main-chain bonds in polymers, and the other being charge-transfer (tribo-electric effect). The former is thought to occur for high polymers whilst the latter may be important for certain inorganic materials especially ionic solids. Specific examples are given for the generation of radicals by cutting finger nails and by grinding bone. In both cases, well-defined e.s.r. spectra were obtained for which identifications are offered. Possible implications of the mechanical formation of radicals in bone are considered.

Bone and Bones↗
PubMed1987

'Water structure' versus 'radical scavenger' theories as explanations for the suppressive effects of DMSO and related compounds on radiation-induced transformation in vitro.

We report here that dimethylsulfoxide (DMSO): suppresses radiation-induced transformation in vitro, even when DMSO treatments begin as late as 10 days post-irradiation (when cells are in the confluent, stationary phase of growth); inhibits the 12-O-tetradecanoylphorbol-13-acetate (TPA) enhancement of radiation-induced transformation in vitro; does not affect the expression of transformed cells as foci (when surrounded by non-transformed cells); and may be affecting radiation-induced transformation through its solvent properties (i.e. the 'Water Structure' theory), while its effects on the TPA enhancement of radiation transformation may be mediated by its free radical scavenging abilities. DMSO, dimethylformamide (DMF) and dimethylacetamide (DMA) are similar solvents which are all very effective in their ability to suppress radiation-induced transformation in vitro (at concentrations in the cellular media down to 0.01%). As DMSO is known to be an extremely effective OH. free-radical scavenging agent, while DMF and DMA are not as efficient at scavenging free radicals, our results suggest that properties other than free-radical scavenging ability may be important in the suppressive effects of these compounds on radiation-induced transformation in vitro. It is known that low concentrations of such basic aprotic solvents modify water structure so as to suppress the protic (H-bond donor) reactivity of water and enhance its basic (H-bond receptor) reactivity. These reactivity changes may well be responsible for the effects noted above. DMSO, DMF and DMA are also capable of suppressing the TPA enhancement of radiation transformation (at concentrations of the compounds of 0.1% or higher). For this effect, the ability of these compounds to scavenge OH. shows a general correlation with their ability to suppress the TPA enhancement of transformation, suggesting that the 'Radical Scavenger' theory may explain the ability of DMSO to suppress promotion in vitro.

Acetamides↗
PubMed1985

Inorganic radicals of relevance to biological systems.

There is little doubt that the most important inorganic radicals involved in biological systems are those which are intermediates in the oxygen-water redox cycle, i.e. OH., O_2, and HO.2. Aspects of the structure and reactivities of these radicals are considered, together with methods of detection. In particular, the use of e.s.r. spectroscopy is outlined, including rapid-freeze and spin-trapping techniques. Attention is called to comparisons and contrasts between these radicals and corresponding sulphur-centered radicals, although these are not strictly "inorganic". The oxygen-centred radicals are usually generated in vivo by redox reactions, but they are also of importance in radiolytic processes because they are formed from water. Other radicals formed in this way whose structures and reactivities are considered include solvated electrons and hydrogen atoms.

Animals↗
PubMed1985

Electron spin resonance studies of intact mammalian skeletal muscle.

Samples of skeletal muscle from mice, rats and man have been examined by conventional electron spin resonance techniques. One major free-radical signal with g value 2.0036-2.004 was detected in all intact muscle samples and homogenates at 77 K whereas this signal was not seen at room temperature. Other less prominant signals were also detected. Thirty minutes of excessive contractile activity of rat hind limb muscles was found to result in a leakage of intracellular creatine kinase enzyme into the blood plasma and also produced an average 70% increase in the amplitude of the major electron spin resonance signal. These data support the hypothesis that increased free-radical activity may play some role in muscle damage caused by extensive muscular activity.

Animals↗
PubMed1984

Studies on human uterine cervix and rat uterus using S-, X- and Q-band electron-spin-resonance spectroscopy.

In previous studies we have reported on the detection of a strong e.s.r. signal in samples of normal human cervix; the signal is much reduced or absent in samples of invasive cancer of the cervix. In order to identify the species responsible for the strong signal, we have used X-, S- and Q-band e.s.r. spectroscopy. The major signal that is detectable in ground-up samples of cervix preserved at -196 degrees C has features consistent with the presence of a peroxy free radical. Good agreement with the experimental findings was obtained by computer simulation, using values for the g-tensor of gx = 2.002, gy = 2.005 and gz = 2.036. The peroxy radical is produced on grinding the normal cervix samples to a powder under liquid N2, and appears to be formed by modification of a pre-existing oxygen-containing complex. Control experiments eliminated the possibility that the strong signals seen in frozen powders prepared from normal cervix were artefacts only of the grinding procedure. Experiments with rats in vivo and with cervix samples in vitro are consistent with the conclusion that the peroxy radical is formed by disturbing the cyclo-oxygenase system that is involved in prostaglandin synthesis.

Animals↗
PubMed1983

Electron addition to the (FeO2) unit of oxyhaemoglobin Glycera.

Exposure of glassy solutions containing the monomeric fraction of the oxyhaemoglobin of the polychaete annelid Glycera dibranchiata to 60Co gamma-rays at 77 K resulted in electron addition to the (FeO2) moiety. The form of the g tensor components obtained from the ESR spectrum indicates that the spin-density on oxygen is much greater than that observed for similar paramagnetic centres formed in haemoglobin A or myoglobin. A major difference between these monomer haem units and normal haem units is that the distal histidine (E7 58) is replaced by leucine. We therefore postulate that the oxygen in the (FeO2)- units formed in haemoglobin A and myoglobin is hydrogen-bonded to the NH group of the distal histidine, whilst that of the (FeO2)- units in haemoglobin Glycera are not hydrogen-bonded. However, on annealing to approx. 160 K the spectrum changed irreversibly into one resembling those for (FeO2)- units in haemoglobin A and myoglobin. We postulate that this is caused by hydrogen-bonding to a water molecule in the haem pocket. Exposure of the polymeric fractions of haemoglobin Glycera to gamma-rays gave an (FeO2)- unit with an ESR spectrum remarkably similar to that obtained from oxymyoglobin. The X-ray structure of this protein is unknown but we suggest that our results could indicate the presence of a distal histidine in this material.

Animals↗
PubMed1982

Spin-trapping studies on the free-radical products formed by metabolic activation of carbon tetrachloride in rat liver microsomal fractions isolated hepatocytes and in vivo in the rat.

1. The metabolic activation of carbon tetrachloride to free-radical intermediates is an important step in the sequence of disturbances leading to the acute liver injury produced by this toxic agent. Electron-spin-resonance (e.s.r.) spin-trapping techniques were used to characterize the free-radical species involved. 2. Spin trapping was applied to the activation of carbon tetrachloride by liver microsomal fractions in the presence of NADPH, and by isolated intact rat hepatocytes. The results obtained with the spin trap N-benzylidene-2-methylpropylamine N-oxide ('phenyl t-butyl nitrone') (PBN) and [13C]carbon tetrachloride provide unequivocal evidence for the formation and trapping of the trichloromethyl free radical in these systems. 3. With the spin trap 2-methyl-2-nitrosopropane, however, the major free-radical species trapped are unsaturated lipid radicals produced by the initiating reaction of lipid peroxidation. 4. Although pulse radiolysis and other evidence support the very rapid formation of the trichloromethyl peroxy radical from the trichloromethyl radical and oxygen, no clear evidence for the trapping of the peroxy radical was obtainable. 5. The effects of a number of free-radical scavengers and metabolic inhibitors on the formation of the PBN-trichloromethyl radical adduct were studied, as were the influences of changing the concentration of PBN and incubation time. 6. High concentrations of the spin traps used were found to have significant effects on cytochrome P-450-mediated reactions; this requires caution in interpreting results of experiments done in the presence of PBN at concentrations greater than 50 mM.

Animals↗
PubMed1978

The relative electron affinities of the alpha and beta chains of oxyhaemoglobin as a function of pH and added inositol hexaphosphate. An electron spin resonance study.

Exposure of aqueous glasses of oxyhaemoglobin to 60Co gamma-rays at 77K results in electron addition to the FeO2 unit, the ESR spectrum for the alpha-chain electron adduct being well separated from that for the beta-chain. The relative yields of these two centres has been measured in the pH range 4.5 to 8.5, with or without added inositol hexaphosphate. We find that, in the absence of inositol hexaphosphate, the yield of beta-chain adduct is almost equal to that of the alpha-chains in the pH 4--5 region, but these rapidly diverge with increasing pH, the beta-yield increasing and the alpha-yield decreasing. After a plateau in the pH 6--8 region, the yield of beta-chain adduct decreases, but that of the alpha-chain adduct remains constant. In the presence of an excess of inositol hexaphosphate the pH change for the beta-adduct remains, but at low pH values the yield of the alpha-adduct is much greater than that of the beta-adduct. This constraint is removed with a pK of approx. 7.7 and at high pH values the yield of the beta-adduct is once again greater than that of the alpha-adduct. These results are significant in that they suggest that the electron affinities of the alpha and beta chains in oxyhaemoglobin are a function of pH, with that of the beta-chains being greater than that of the alpha-chains in the neutral region. Also inositol hexaphosphate clearly binds to one or both chains, and this has the effect of reversing the relative electron affinities of the two chains.

Electron Spin Resonance Spectroscopy↗
PubMed1978

Electron capture at the iron-oxygen centre in single crystals of oxymyoglobin studied by electron spin resonance spectroscopy.

Exposure of single crystals of oxy-myoglobin to 60Co gamma-rays at 77 K results in electron addition to the Fe-O2 units. The resulting ESR spectrum has been analysed to give the principal values and directions for the g-tensor of this unit. The results suggest that the dioxygen ligand is strongly tilted, the direction of tilt being close to one of the bisectors of the N-Fe-N bond angles. Possible reasons for this orientation are discussed.

Chemical Phenomena↗
PubMed1978

Electron addition to the active site of Cancer magister haemocyanins. An ESR study of cu(II) centres after gamma-radiolysis.

Exposure of aqueous glasses of Cancer magister haemocyanin to 60Co gamma-rays at 77 K results in a novel paramagnetic centre with ESR features showing hyperfine coupling to one strongly coupled 63/65 Cu nucleus and possibly one weakly interacting 63/65 Cu nucleus. Addition of electron scavengers showed that this centre is formed by electron addition. It is suggested that addition occurs at Cu2+-O2-Cu2+ units to give Cu2+-O2Cu+ centres. If this is correct, then electron-transfer between the two copper ions is slow or non-existent, possibly indicating that they are inequivalent. The centre is unstable, the signals being lost irreversibly on heating to approx. 270 K. The g parallel and A parallel (63/65Cu) data place this centre into the type I classification.

Animals↗
PubMed1975

Water structure and hydration.

Possible structures adopted by bulk water are discussed with special reference to the possible presence of monomeric water and the detection of 'free' -OH groups. The way in which water tends to accommodate small hydrophobic molecules is considered, with particular reference to the clathrate theory and the phenomenon of 'structure making'. Cage-pairing and cage-sharing processes are described. Consideration of the way water solvates cations and anions is followed by a discussion of the way these solvated ions interact with the bulk medium. Large symmetrical alkylammonium ions probably encourage clathrate cage formation, at least at low temperatures. Particular reference is made to the use of infrared, Raman, ultraviolet, n.m.r. and e.s.r. spectroscopic techniques to the study of water and aqueous solutions.

Chemical Phenomena↗