EPR spectral investigation of radiation-induced radicals of gallic acid

In the present work, spectroscopic features of the radiation-induced radicals of gallic acid compounds were investigated using electron paramagnetic resonance (EPR) spectroscopy. While un-irradiated samples presented no EPR signal, irradiated samples exhibited an EPR spectrum consisting of an intense resonance line at the center and weak lines on both sides. Detailed microwave saturation investigations were carried out to determine the origin of the experimental EPR lines. It is concluded that the two side lines of the triplet satellite originate from forbidden “spin-flip” transitions. The spectroscopic and structural features of the radiation-induced radicals were determined using EPR spectrum fittings. The experimental EPR spectra of the two gallic acid compounds were consistent with the calculated EPR spectroscopic features of the proposed radicals. It is concluded that the most probable radicals are the cyclohexadienyl-type, \({\dot{\text{O}}}\left( {\text{OH}} \right)_{ 2} {\text{C}}_{ 6} {\text{H}}_{ 2} {\text{COOH}}\) radicals for both compounds.     

Additional criteria for EPR dosimetry using tooth enamel

Currently, EPR measurements are based on the assumption that odontogenesis (the series of events between the bud formation stage until the complete maturation of the tooth) is finished as soon as the tooth erupts. Consequently, it is also assumed that the hydroxyapatite concentration of the enamel (source of free radicals) does not depend on tooth age. However, the present work provides evidence that odontogenesis does not end after tooth eruption but continues for several years after eruption. Fifty-nine molars and pre-molars were analyzed by EPR spectroscopy. Tooth enamel samples were irradiated with different doses of gamma radiation from a 60Co source. The resulting EPR signals were evaluated in terms of posteruption tooth age and tooth position. It was found that, except for wisdom teeth, the concentration of the dosimetric EPR free radicals increased with tooth age after eruption and became constant after a certain period. A mathematical equation was developed to describe this effect as a function of tooth age, tooth position and applied dose. The results suggest that EPR measurements obtained on young teeth should be interpreted carefully unless data are available that would allow one to describe the effect of posteruptive enamel maturation on the EPR estimated dose quantitatively. Little or no correction is needed for older teeth. Since only a limited number of young teeth were available for the present study, further studies are needed to clarify the situation and quantify this effect.     

Q-band electron paramagnetic resonance dosimetry in tooth enamel: biopsy procedure and determination of dose detection limit

High-frequency Q-band (37 GHz) electron paramagnetic resonance (EPR) dosimetry allows to perform fast (i.e., measurement time <15 min) dose measurements using samples obtained from tooth enamel mini-biopsy procedures. We developed and tested a new procedure for taking tooth enamel biopsy for such dose measurements. Recent experience with EPR dose measurements in Q-band using mini-probes of tooth enamel has demonstrated that a small amount of tooth enamel (2–10 mg) can be quickly obtained from victims of a radiation accident. Accurate dose assessments can further be carried out in a very short time to provide important information for medical treatment. Here, the Q-band EPR dose detection limit for 5 and 10 mg samples is estimated to be 367 and 248 mGy, respectively. These values are comparable to the critical parameters determined for conventional X-band EPR in tooth enamel.     

Camel molar tooth enamel response to gamma rays using EPR spectroscopy

Tooth enamel samples from molar teeth of camel were prepared using a combined procedure of mechanical and chemical tooth treatment. Based on electron paramagnetic resonance (EPR) spectroscopy, the dose response of tooth enamel samples was examined and compared to that of human enamel. The EPR dose response of the tooth enamel samples was obtained through irradiation to gamma doses from 1 Gy up to 100 kGy. It was found that the radiation-induced EPR signal increased linearly with gamma dose for all studied tooth enamel samples, up to about 15 kGy. At higher doses, the dose response curve leveled off. The results revealed that the location of the native signal of camel tooth enamel was similar to that of enamel from human molars at 2.00644, but different from that of enamel from cows and goats. In addition, the peak-to-peak width (ΔH _pp) for human and camel molar teeth was similar. It was also found that the response of camel enamel to gamma radiation was 36% lower than that of human enamel. In conclusion, the results indicate the suitability of camel teeth for retrospective gamma dosimetry.     

Consistent simulation of X- and Q-band EPR spectra of an unsymmetric dinuclear Mn2(II,III) complex

Simulation of X- and Q-band electron paramagnetic resonance (EPR) spectra of an unsymmetric dinuclear [Mn(2)(II,III)L(mu-OAc)(2)]ClO(4) complex (1), (L is the dianion of 2-{[N,N-bis(2-pyridylmethyl)amino]methyl}-6-{[N-(3,5-di-tert-butyl-2-hydroxybenzyl)-N-(2-pyridylmethyl)amino]methyl}-4-methylphenol) was performed using one consistent set of simulation parameters. Rhombic g-tensors and hyperfine tensors were necessary to obtain satisfactory simulation of the EPR spectra. The anisotropy of the effective hyperfine tensors of each individual (55)Mn ion was further analyzed in terms of intrinsic hyperfine tensors. Detailed analysis shows that the hyperfine anisotropy of the Mn(III) ion is a result of the Jahn-Teller effect and thus an inherent character. In contrast, the anomalous hyperfine anisotropy of the Mn(II) ion is attributed as being transferred from the Mn(III) ion through the spin exchange interaction. The anisotropy parameter for the Mn(II) is deduced as D(II)=-1.26+/-0.2cm(-1). This is the first reported D(II) value for a Mn(II) ion in a weakly exchange coupled mixed-valence Mn(2)(II,III) complex with a bis-mu-acetato-bridge. The [see text] electronic configuration of the Mn(III) ion in 1 is revealed by the negative sign of its intrinsic hyperfine tensor anisotropy, Deltaa(III)=a(z)-a(x,y)=-46cm(-1). Lower spectral resolution of the Q-band EPR spectrum as compared to the X-band EPR spectrum is associated to large line width broadening of the x- and y-components in contrast to the z-component. The origins of the unequal distribution of line width between the z- and x-, y-components are discussed.     

Q-band EPR investigations of neuromelanin in control and Parkinson's disease patients

New insights into the understanding of the changes induced in the iron domain of neuromelanin (NM) upon development of Parkinson's disease (PD) have been gained by electron paramagnetic spectroscopy (EPR). The results of this study are compared with a previously reported variable temperature analysis of X-band EPR spectra of a NM specimen obtained from control brain tissues. The availability of high sensitivity instruments operating in the Q-band (34.4 GHz) allows us to deal with the low amounts of NM available from PD brains. The organization of iron in NM is in the form of polynuclear superparamagnetic/antiferromagnetic aggregates, but the lack of one or more signals in the EPR spectra of NM from PD suggests that the development of the pathology causes NM to decrease its ability to bind iron. Furthermore, the detection of the Mn(II) signal in the Q-band spectra is exploited as an additional internal probe to assess minor structural differences in iron domains of PD and control NM specimens.     

X- and Q-band electron paramagnetic resonance of CO2- in hydroxyapatite single crystals

Both X- and Q-band electron paramagnetic resonance (EPR) research has been conducted using slightly carbonated hydroxyapatite (HAp) single crystals after exposure to ionizing radiation. Below a temperature of 90 K, O(-) and CO(2-) radicals were detected, whereas at room temperature only CO(2-) spectra could be observed. The O(-) ion has previously been investigated in high-purity HAp single crystals, whereas EPR spectra of CO(2-) in HAp single crystals have not been reported. Both paramagnetic defects exhibit EPR angular variations in planes containing the c axis of the crystal from which spin Hamiltonian parameters were derived. Arguments are given for the presence of two CO(2-) defects in the irradiated HAp single crystals.     

EPR study of anion radicals of various N-quinonyl amino acids

Summary. Since peptide quinones possess great clinical potential in targeted chemotherapy, several series of novel N-quinonyl amino acids have been synthesized and their first products of reduction were studied by EPR spectroscopy. EPR spectra of the corresponding radical adducts were identified by computer simulation. The dependence between the splitting constants and the chemical structure of the N-quinonyl amino acids anion radicals was examined. Received January 4, 2000; Accepted March 14, 2000     

Mineral-organic-matrix relations in tooth enamel

X-ray and electron diffraction patterns show that β-pleated-sheet polypeptide chains are predominantly oriented approximately perpendicular to the c-axes of developing enamel apatite crystallites. This spatial relation suggests a specific role for enamelins in controlling crystal growth.     

A comparative study of the effect of cholesterol on bicelle model membranes using X-band and Q-band EPR spectroscopy

X-band and Q-band electron paramagnetic resonance (EPR) spectroscopic techniques were used to investigate the structure and dynamics of cholesterol containing phospholipid bicelles based upon molecular order parameters (S_mol), orientational dependent hyperfine splittings and line shape analysis of the corresponding EPR spectra. The nitroxide spin-label 3-β-doxyl-5-α-cholestane (cholestane) was incorporated into DMPC/DHPC bicelles to report the alignment of bicelles in the static magnetic field. The influence of cholesterol on aligned phospholipid bicelles in terms of ordering, the ease of alignment, phase transition temperature have been studied comparatively at X-band and Q-band. At a magnetic field of 1.25 T (Q-band), bicelles with 20 mol% cholesterol aligned at a much lower temperature (313 K), when compared to 318 K at a 0.35 T field strength for X-band, showed better hyperfine splitting values (18.29 G at X-band vs. 18.55 G at Q-band for perpendicular alignment and 8.25 G at X-band vs. 7.83 G at Q-band for the parallel alignment at 318 K) and have greater molecular order parameters (0.76 at X-band vs. 0.86 at Q-band at 318 K). Increasing cholesterol content increased the bicelle ordering, the bicelle-alignment temperature and the gel to liquid crystalline phase transition temperature. We observed that Q-band is more effective than X-band for studying aligned bicelles, because it yielded a higher ordered bicelle system for EPR spectroscopic studies.     

SEM analysis of tooth enamel

SEM analysis contains researches of tooth enamel surfaces of two populations. First group of samples is tooth enamel of prehistorically ancestor from Vucedol and the second group of samples is enamel of modern Croatian citizen. Even on small number of human teeth samples from cooperage site of Vucedol (3,000 BC) and today's Croatian people, we can conclude about chewing biometry of prehistorically ancestors and today's modern Croatian people, comparing interspecifically the morphology of enamel microdefects. With the interspecific comparison of morphology changes on tooth occlusal surfaces, we can connect the size and shape of abrasive particles and diet with microdefects of tooth enamel.     

EPR spin trapping of protein radicals

Electron paramagnetic resonance (EPR) spin trapping was originally developed to aid the detection of low-molecular-mass radicals formed in chemical systems. It has subsequently found widespread use in biology and medicine for the direct detection of radical species formed during oxidative stress and via enzymatic reactions. Over the last 15 years this technique has also found increasing use in detecting and identifying radicals formed on biological macromolecules as a result of either radical reactions or enzymatic processes. Though the EPR signals that result from the trapping of large, slowly tumbling radicals are often broad and relatively poor in distinctive features, a number of techniques have been developed that allow a wealth of information to be obtained about the nature, site, and reactions of such radicals. This article summarizes recent developments in this area and reviews selected examples of radical formation on proteins.     

Multifrequency EPR study of carbonate- and sulfate-derived radicals produced by radiation in shells and corallite

Shells of two sea mollusks (Venus sp.), pearl oyster (Meleagrina vulgaris) and corallite (white coral) were exposed to ionizing radiation (gamma and X rays) and then examined by EPR spectroscopy in X, Q and W band. The resulting spectra were analyzed and the g values of the EPR lines in the multicomponent spectra were determined. The increased resolution in Q- and W-band spectra allowed us to assign the observed lines to CO(2)(-) ion radicals (isotropic and orthorhombic), SO(2)(-) isotropic, SO(3)(-) (isotropic and axial), and Mn(2+) species. The assignments were confirmed by simulations of the spectra. Practical implications for the use of Q and/or W band in low-dose quantitative EPR measurements for dating and for accidental dose estimation are discussed.     

High-field EPR study of tyrosyl radicals in prostaglandin H(2) synthase-1

Various tyrosyl radicals generated by reaction of both native and indomethacin-inhibited ovine prostaglandin H synthase-1 with ethyl hydrogen peroxide were examined by using high-field/high-frequency EPR spectroscopy. The spectra for the initially formed tyrosyl radical commonly referred to as the "wide-doublet" species and the subsequent "wide-singlet" species as well as the indomethacin-inhibited "narrow-singlet" species were recorded at several frequencies and analyzed. For all three species, the g-values were distributed. In the case of the wide doublet, the high-field EPR spectra indicated that dominant hyperfine coupling was likely to be also distributed. The g(x)-values for all three radicals were found to be consistent with a hydrogen-bonded tyrosyl radical. In the case of the wide-doublet species, this finding is consistent with the known position of the radical and the crystallographic structure and is in contradiction with recent ENDOR measurements. The high-field EPR observations are consistent with the model in which the tyrosyl phenyl ring rotates with respect to both the protein backbone and the putative hydrogen bond donor during evolution from the wide-doublet to the wide-singlet species. The high-field spectra also indicated that the g-values of two types of narrow-singlet species, self-inactivated and indomethacin-inhibited, were likely to be different, raising the possibility that the site of the radical is different or that the binding of the inhibitor perturbs the electrostatic environment of the radical. The 130 GHz pulsed EPR experiments performed on the wide-doublet species indicated that the possible interaction between the radical and the oxoferryl heme species was very weak.     

Oxygen radicals produced by plant plasma membranes: an EPR spin-trap study

Plant plasma membranes are known to produce superoxide radicals, while the production of the hydroxyl radical, previously detected in complex plant tissues, is thought to occur in the cell wall. The mechanism of production of superoxide radicals by plant plasma membranes is, however, under dispute. It is shown, using electron paramagnetic resonance spectroscopy with a 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide spin-trap capable of differentiating between radical species, that isolated purified plasma membranes from maize roots produce hydroxyl radicals besides superoxide radicals. The results argue in favour of superoxide production through an oxygen and diphenylene iodonium-sensitive, NADH-dependent superoxide synthase mechanism, as well as through other unidentified mechanism(s). The hydroxyl radical is produced by an oxygen-insensitive, NADH-stimulated mechanism, which is enhanced in membranes in which the superoxide synthase is incapacitated by substrate removal or inhibition.