ESR study of ascorbic acid irradiated with gamma-rays

The interest in application of high-energy ionizing radiation for stenlization 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.     

Kinetic investigation of the reaction of pertechnetate with thiourea in a hydrochloric acid solution

Reactions of pertechnetate ion with thiourea (tu) in a hydrochloric acid solution have been investigated by spectrophotometry. Two consecutive reactions were observed for the formation of a technetium-thiourea complex. The intermediate is considered to be a Tc(V)-tu complex ([TcO(tu)₄]³⁺). The observed reaction rates of these two reactions were found to be second order with respect to the concentration of thiourea. The rate-determining step in the 1st step was concluded tobe the reduction of Tc(VII) to Tc(V) and that in the 2nd step to be the reduction of Tc(V) to Tc(III).     

Solute species and equilibria in concentrated zinc chloride/hydrochloric acid solutions

Examination of a series of concentrated ZnCl₂HClH₂O solutions with chloride/zinc stoichiometries ranging from 2:1 to 6:1 and with the mole fraction of Zn²⁺ being 0·015 in each solution have been examined by X-ray diffraction. The mean coordination of Zn²⁺ in each solution is pseudotetrahedral with the ZnCl and ZnO contact distances being 2·30 and 2·05 Å, respectively. The average number of chlorides tightly bonded to Zn²⁺ is, as expected, significantly related to the chloride/zinc and/or the chloride/water stoichiometries. The formation constant for tetrachlorozincate (II) in these solutions is ca. 80 M⁻² if it is assumed that tetrachlorozincate(II) and/or dichlorodiaquozinc(II) are the principal species in each of these solutions.     

The reduction kinetics of pertechnetate by thiocyanate in perchloric acid medium

The reduction kinetics of pertechnetate by thiocyanate in perchloric acid is studied by spectrophotometric method. The effect of the concentrations of pertechnetate, hydrogen ion and thiocyanate on the reaction rate is investigated. The kinetic expression at 25°C is: −dC _VII/dt=(2.2±0.4)·10⁻³ [TcO₄ ⁻]^1.1 [H⁺]^3.2 [SCN⁻]^3.3 The effect of temperature on the reaction rate is studied. The activation energy is 91 kJ/mol. The possible mechanism of the reaction is discussed.     

Preparation of (99m)Tc labeled vitamin C (ascorbic acid) and biodistribution in rats

The aim of this study was to label ascorbic acid with (99m)Tc and to investigate its radiopharmaceutical potential in rats. Ascorbic acid was labeled with (99m)Tc using the stannous chloride method. The radiochemical purity of [(99m)Tc]ascorbic acid ((99m)Tc-AA) was determined by RTLC, paper electrophoresis, and RHPLC methods. The labeling yield was found to be 93+/-5.0%. The maximum labeling yield of (99m)Tc-AA was determined at pH 5 and 25 degrees C. The biodistribution studies related to (99m)Tc-AA were done in male albino Wistar rats. (99m)Tc-AA, which has a specific activity of 13.02 GBq/mmol, was administered into the tail vein of the rats. The rats were sacrificed at 15, 30, 60, and 120 min after the injection by heart puncture under ether anaesthesia. The organs were weighed after removal. Their activities were counted using a Cd(Te) detector equipped with a RAD 501 count system. The %ID/g (% of injected dose per gram of tissue weight) in each organ and in blood was calculated. Maximum uptake of (99m)Tc-AA was observed in prostate and kidneys at the 60th min. (99m)Tc-AA may be a promising radiopharmaceutical for the imaging of prostate and kidneys.     

Oxidaiton of tin/II/ in air-kept hydrochloric acid solutions

An air-storage stability of tin/II/ chloride solution was studied by voltammetric and spectrophotometric methods. The chosen concentration range was due to the problems of the kits preparation for a^99mTc generator. The rate of oxidation of tin/II/ in the range of 0.04–12.5 mg.ml^–1 was shown to decrease with an increase in tin concentration. According to the obtained results one can determine maximal storage time for the correct practical use.     

Kinetic-spectrophotometric determination of ascorbic acid by inhibition of the hydrochloric acid-bromate reaction

A new analytical method was developed for the determination of ascorbic acid in fruit juice and pharmaceuticals. The method is based on its inhibition effect on the reaction between hydrochloric acid and bromate. The decolourisation of Methyl Orange by the reaction products was used to monitor the reaction spectrophotometrically at 510 nm. The linearity range of the calibration graph depends on bromate concentration. The variable affecting the rate of the reaction was investigated. The method is simple, rapid, relatively sensitive and precise. The limit of detection is 7.6 x 10(-6) M and calibration rang is 8 x 10(-6)-1.2 x 10(-3) M ascorbic acid. The relative standard deviation of seven replication determinations of 8 x 10(-6) and 2 x 10(-5) M ascorbic acid was 2.8 and 1.7%, respectively. The influence of potential interfering substance was studied. The method was successfully applied for the determination of ascorbic acid in pharmaceuticals.     

ESR spectra of C60 in concentrated sulfuric acid

On dissolution of C₆₀ in concentrated sulfuric acid, ESR spectra of paramagnetic species, which were identified as dimers (C₁₂₀ ⁺) or oligomers (nC₆₀)⁺, were recorded. The ESR spectra recorded upon the reaction of a toluene solution of C₆₀ with sulfuric acid were assigned to the radical cation C₆₀ ⁺. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2373–2376, November, 1998.     

Rhenium deposition onto platinum surface by reduction of perrhenic acid with methanol in hydrochloric acid media

It has been demonstrated that rhenium deposition onto Pt surface in hydrochloric acid media can also be carried out by reduction of perrhenic acid with methanol. Above 0.5 M Cl⁻ ion concentration, however, it is practical to combine the use of methanol with hydrogen.     

Photoreduction of 99Tc pertechnetate by nanometer-sized metal oxides: new strategies for formation and sequestration of low-valent technetium

Technetium-99 ((99)Tc) (β(-)(max): 293.7 keV; t(1/2): 2.1 × 10(5) years) is a byproduct of uranium-235 fission and comprises a large component of radioactive waste. Under aerobic conditions and in a neutral-basic environment, the pertechnetate anion ((99)TcO(4)(-)) is stable. (99)TcO(4)(-) is very soluble, migrates easily through the environment and does not sorb well onto mineral surfaces, soils, or sediments. This study moves forward a new strategy for the reduction of (99)TcO(4)(-) and the chemical incorporation of the reduced (99)Tc into a metal oxide material. This strategy employs a single material, a polyoxometalate (POM), α(2)-[P(2)W(17)O(61)](10-), that can be photoactivated in the presence of 2-propanol to transfer electrons to (99)TcO(4)(-) and incorporate the reduced (99)Tc covalently into the α(2)-framework to form the (99)Tc(V)O species, (99)Tc(V)O(α(2)-P(2)W(17)O(61))(7-). This occurs via the formation of an intermediate species that slowly converts to (99)Tc(V)O(α(2)-P(2)W(17)O(61))(7-). Extended X-ray absorption fine structure and X-ray absorption near-edge spectroscopy analysis suggests that the intermediate consists of a (99)Tc(IV) α(2)- species where the (99)Tc is likely bound to two of the four W-O oxygen atoms in the α(2)-[P(2)W(17)O(61)](10-) defect. This intermediate then oxidizes and converts to the (99)Tc(V)O(α(2)-P(2)W(17)O(61))(7-) product. The reduction and incorporation of (99)TcO(4)(-) was accomplished in a "one pot" reaction using both sunlight and UV irradiation and monitored as a function of time using multinuclear nuclear magnetic resonance and radio thin-layer chromatography. The process was further probed by the "step-wise" generation of reduced α(2)-P(2)W(17)O(61)(12-) through bulk electrolysis followed by the addition of (99)TcO(4)(-). The reduction and incorporation of ReO(4)(-), as a nonradioactive surrogate for (99)Tc, does not proceed through the intermediate species, and Re(V)O is incorporated quickly into the α(2)-[P(2)W(17)O(61)](10-) defect. These observations are consistent with the periodic trends of (99)Tc and Re. Specifically, (99)Tc is more easily reduced compared to Re. In addition to serving as models for metal oxides, POMs may also provide a suitable platform to study the molecular level dynamics and the mechanisms of the reduction and incorporation of (99)Tc into a material.     

Flow-injection spectrophotometric determination of ascorbic acid by reduction of vanadotungstophosphoric acid

Ascorbic acid may be determined spectrophotometrically at 360 nm based on reduction of vanadotungstophosphoric acid using flow-injection analysis. The carrier stream was distilled water and the reagent streams were buffer solution (pH 3.0), 1.735 × 10^?3 M dodecatungstophosphoric acid and 1.735 × 10^?3 M sodium vanadate. The injection rate was 80 h^?1. The calibration graph was linear up to 80 μg ml^?1 ascorbic acid and the relative standard deviation for the determination of 20 μg ml^?1 ascorbic acid was 1.5% (n=10). The detection limit was 1.0 μg ml^?1 ascorbic acid, based on an injection volume of 250 μl. The system was applied to the determination of ascorbic acid in vitamin C tablets.     

ESR spectra of fullerence C70 in concentrated sulfuric acid

It was established by ESR spectroscopy that the reaction of C₇₀ with concentrated H₂SO₄ resulted in the formation of isomeric dimers C₁₄₀ ⁺, and the action of H₂SO₄ on a toluene solution of C₇₀ ⁺ gave the C₇₀ radical cation. The structure of dimers was discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 208–210, January, 1999.     

ESR study of electron interaction in a Tc/Al2O3 system

An investigation was made into the nature of paramagnetic centers in a Tc/Al₂O₃ system under varying conditions as to heat treatment and technetium content, and in O₂ and CO adsorption environments. It was found that in the case of reduction at 573 K Tc²⁺ ions and, conceivably, other ionic forms developed and stabilized on the carrier surface. After reduction at 973 K two types of electron center appeared, whose concentration increased as reduction was prolonged. Signals were observed in the low fields (3–20 mT) of the ESR spectra having g₁ 13.5 and g₂>30, which could be assigned to free charge carriers in a cluster of metal atoms or ions. Adsorption of O₂ at 300 K caused O ₂ ^– ion radicals to form on the surface of the reduced Tc/Al₂O₃ samples, both electron centers and technetium ions constituting the electron donors. In the case of CO adsorption paramagnetic (CO) ₂ ^– particles appeared on the Tc/Al₂O₃ samples after prolonged exposure. On reaction with O₂ two types of O ₂ ^– ion-radical with differing thermal stability were formed.Institute of Physical Chemistry, Russian Academy of Sciences, Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 1972–1978, September, 1992.     

Effect of hydrochloric acid on the mean solute species in copper(II) chloride/hydrochloric acid solutions

In the concentrated solutions of CuCl₂/HCl/H₂O examined in this study, Cu²⁺ has tetragonally distorted octahedral coordination on the average. In these solutions of ca. 2 molar concentration, solute association does not appear to be an important solution parameter. In all of the solutions, the linear Cl_axCuCl_ax network remains intact upon dissolution of anhydrous copper(II) chloride. Ligand occupation of the equatorial coordination sites apparently is dependent upon the chloride/copper and/or the water/chloride stoichiometric ratios in each solution. The Cu-ligand bond distances are calculated to be: CuO_eq, 1·95 Å; CuCl_eq, 2·35 Å; and CuCl_ax, 2·8 Å. The latter two distances are significantly different than those calculated for the highly associated solute species found in aqueous solutions of CuCl₂[1].     

Active intermediates in the oxidative bromochlorination of olefins in concentrated hydrochloric acid

A study was carried out on the oxidative bromochlorination of olefins in the presence of KBr using hydrogen peroxide and an electrochemical technique. Asymmetric trihalide anions, Br₂Cl⁻ and BrCl₂ ⁻, were found to be the active bromochlorination reagents. The reaction mechanism was discussed. Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanskaya St., 253660 Kiev-94. Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 4, pp. 248–251, July–August, 1997.