DOI: 10.1007/s10967-007-0919-1 Journal of Radioanalytical and Nuclear Chemistry, Vol. 273, No.3 (2007) 609–614 0236–5731/USD 20.00 Akadémiai Kiadó, Budapest © 2007 Akadémiai Kiadó, Budapest Springer, Dordrecht ESR study of ascorbic acid irradiated with gamma-rays H. Tuner,* M. Korkmaz Hacettepe University, Department of Physics Engineering, Beytepe, 06800 Ankara, Turkey (Received June 27, 2006) The interest in application of high-energy ionizing radiation for sterilization of pharmaceutical products and foodstuffs has led a number of workers to investigate the radiation sensitivity of vitamins. Aside from its use as a vitamin, ascorbic acid (AA) or some derivatives are employed as antioxidants in foodstuffs. The effects of ionizing radiation on AA in simple solutions and in mixture of naturally occurring compounds have been extensively reported in the literature. However, the effects of ionizing radiation on solid AA were reported in few works which described rather dosimetric features of AA. No reports, except one, are available describing the characteristic features of the radiolytic intermediates produced after irradiation of polycrystalline AA. Irradiation studies performed on single crystal of AA has led us to reinvestigate our previous work on the radiolytic intermediates produced in irradiated polycrystalline AA. Three radical species, rather than two, having different characteristics were decided contributing to the formation of experimental electron spin resonance (ESR) spectrum of γ-irradiated polycrystalline AA. Spectral parameters of these species were calculated after exhaustive spectrum simulation calculations based on data derived from experimental microwave saturation and dose-response studies. Introduction Ascorbic acid (AA) is a water-soluble vitamin and most important free oxygen scavenger. AA is stable when dry, but in solution it is readily oxidized to dehydroascorbic acid (DHAA), 1 especially in the presence of trace amounts of copper, iron and alkali. Its molecular structure is given in Fig. 1. AA or some derivatives are employed as antioxidants and radiation protector in foodstuffs, to prevent rancidity, browning of cut apples and other fruits and in meat curing. 2 AA is noted for its complex multi-functional effects. Depending on medium conditions, AA can act as an antioxidant, pro-oxidant, metal cheaters, a reducing agent or an oxygen scavenger. Radiosensitivity and stability of AA in different in vitro systems and in different matrices were the subject of different research works using ESR spectroscopy and other methods. 3–9 Radiation damage produced in irradiated solid AA were also reported in the literature using ESR spectroscopy, but those investigations which considered only the variations of the intensities of the resonance line of doublet appearance, were rather oriented toward the determination of AA dosimetric properties. 10,11 Spectroscopic parameters of the radicalic species produced upon irradiation were not reported in none of these works except the ESR work carried out in our laboratory. Spectrum simulation calculations based on the presence of two different radical species and on signal intensity data derived from a room temperature spectrum were performed in this work. However, our later studies on irradiated single crystals of AA revealed that ESR spectra of crystalline samples consist, in general, more than nine resonance lines of different * E-mail: htuner@hacettepe.edu.tr intensities except some specific orientations. Hence, it was concluded that such a spectrum cannot be explain along with radical species with unpaired electrons localized on carbon and oxygen atoms of five member rings as advised in Reference 10. Therefore, it was decided that species produced after the damage of the – CHOHCH 2 OH molecular part of AA should also take part in the formation of experimental ESR spectra of irradiated solid AA. Consequently, in the present work, simulation calculations performed in our previous work were repeated adopting a model consisting of the presence of three different radical species using, as input, the data derived from experimental microwave and dose-response studies carried out for irradiated polycrystalline AA. Experimental AA fine powder was supplied by Vankim Ltd. (Istanbul, Turkey). The AA samples, in polycarbonate vials, were irradiated in the dose range 0.5–25 kGy. All irradiations were performed at room temperature using a 60 Co ionizing radiation source at the Sarayköy Establishment of the Turkish Atomic Energy Agency in Ankara. The dose rate (1.6 kGy/h) was previously calibrated using Fricke dosimetry. The ESR spectra were recorded at room temperature using a Bruker EMX 131 X-band spectrometer equipped with a cylindrical cavity. Numbers were assigned to the observed resonance peaks and intensity measurements were performed with respect to the spectrum base line. An unirradiated sample was kept as a reference.