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.

Dating of palaeoanthropological nuragic skeletal tissues using electron paramagnetic resonance (EPR) spectrometry.

Dating of skeletons of Nuragic population living in Sardinia island centuries BP, based on the quantitative evaluation of the concentration of stable paramagnetic species produced by ionising radiation in tooth enamel was performed by using EPR spectrometry. Applying the additive dose method (60Co gamma rays) and comparative calculations based on analogous measurements done with Roman skeleton of the known age as discovered close to Nuragic tomb (Tombs of Giants, La Testa S. Teresa di Gallura, Sardinia) the age of Nuragic skeleton was evaluated as equal to about 3,200 years (1,200 years BC). The total error of EPR measurements and dose extrapolation was estimated for 10-12%. Crystallinity of bone mineral in Nuragic skeleton evaluated by the EPR technique, adapted earlier by some of the authors of the present paper for biomedical studies on mineralised tissues, is only little changed after the centuries of its deposition in the tomb when compared with contemporary bone tissue. Comparison of chemical composition of Nuragic skeleton contaminated through slow percolation by rain of floods with that of contemporary bone sample shows the increase of the concentration of Fe, PO4, SiO2, Al and Mg, Fe, SiO2, AP are not present in contemporary bones. As expected, the contamination was minimal in tooth enamel.

Reduction of selected oligopeptides containing methionine induced by hydrated electrons.

Bimolecular rate constants for the reaction of the hydrated electron with zwitterionic forms of several linear oligopeptides containing methionine were determined using the pulse radiolysis technique. The rate constants were found to vary in the range of (0.2-1.2) x 10(9) M(-1) s(-1). The reactivity of the peptides toward e(aq)- is governed by the pKa of the N-terminal amino group and the number of peptide bonds. At a fixed number of peptide bonds, the reactivity increases with the pKa, and for a given N-terminal amino acid residue, it increases with the number of peptide bonds. For the linear peptides the observed transient spectra are assigned to deaminated oligopeptide radicals, *CHRCONH approximately, obtained due to rapid deamination of the corresponding electron adducts formed initially. The radicals derived from oligopeptides containing methionine at the N-terminus absorb at approximately 400 nm with extinction coefficients of approximately 1300+/-150 M(-1) cm(-1). Their absorption maxima are shifted hypsochromically by approximately 30 nm with respect to those derived from oligopeptides with glycine at the N-terminus. The e(aq)- reacts with cyclic Met-Met, k = 2.0 x 10(9) M(-1) s(-1), probably by addition to the carbonyl bond, forming an adduct absorbing below 250 nm with epsilon250 = 2300+/-250 M(-1) cm(-1).