ABSTRACT
Abstract X irradiation of sucrose single crystals at room temperature leads to the production of stable radicals, which give rise to the dosimetric electron paramagnetic resonance (EPR) signal. In the first few hours after irradiation, however, the shape of the EPR spectrum changes drastically. Based on two-dimensional field-frequency electron nuclear double resonance (FF-ENDOR) measurements, we demonstrate that, after high-dose ( approximately 5 kGy) and high-dose-rate irradiation, several species with limited stability at room temperature are produced next to the stable radicals. For two of these species, the main characteristics could be determined. Analysis of the time evolution of the FF-ENDOR and room-temperature EPR spectra in the first few hours after irradiation leads to the conclusion that these meta-stable radicals mainly recombine into diamagnetic species, while transformation into stable radicals is at most a marginal process.
Subject(s)
Electron Spin Resonance Spectroscopy/methods , Sucrose/chemistry , Sucrose/radiation effects , Crystallization , Temperature , X-RaysABSTRACT
Photolysis of the ternary system consisting of diethyldithiocarbamate (Et2dtc), diethyldiselenocarbamate (Et2dsc) and copper(II) (1:1:1) has been studied in isobutylmethylketone (IBMK), toluene, chloromethane and chloromethane/ROH solutions (chloromethane = CCl4, CHCl3 or CH2Cl2 and ROH = EtOH or i-PrOH). The results obtained by EPR techniques and UV-Vis data indicate that a homolytic Cu-S bond cleavage involving the dithiocarbamate (dtc) ligand appears as the primary photo-process in Cu(Et2dtc)(Et2dsc) photolysis. Further conversion of the primary photoproduct Cu(I)(Et2dsc) is discussed in terms of a specific interaction with the solvent. In chloromethanes and chloromethane/ROH Cu(I)(Et2dsc) is oxidised by the solvent to give the corresponding paramagnetic mixed-ligand Cu(II)(Et2dsc)Cl complex and/or its chloride-bridged and EPR silent dimer Cu2(Et2dsc)2Cl2. The formation of the monomeric species occurs through a co-ordination of the alcohol molecule in the xy plane of the complex. Because of its co-ordination inertness, toluene poorly stabilises the primary photoproduct Cu(I)(Et2dsc), thus providing an effective primary recombination process and lower efficiency of Cu(Et2dtc)(Et2dsc) photolysis. The formation of the bis-solvated mixed-ligand complex Cu(II)(Et2dsc)+ in IBMK is also discussed.
Subject(s)
Copper/chemistry , Carbamates/chemistry , Chemistry, Physical/methods , Chlorine/chemistry , Free Radicals , Ketones/chemistry , Ligands , Light , Methane/chemistry , Methyl Chloride/chemistry , Models, Chemical , Organometallic Compounds/chemistry , Oxygen/metabolism , Spectrophotometry , Thiocarbamates/chemistry , Toluene/chemistryABSTRACT
The interaction of bis(diethyldithiocarbamato)copper(II), Cu(Et2dtc)2, and bis(diethyldiselenocarbamato)copper(II), Cu(Et2dsc)2, complexes with solvents is studied by EPR and electronic spectroscopy. The solvents used are CCl4, CHCl3, CH2Cl2, C6H5 x CH3, DMFA and DMSO. It is found that Cu(Et2dsc)2 is destroyed in a first order reaction in CCl4 with an activation energy of 5.2 kcal/mol. The other complex, Cu(Et2dtc)2, is only destroyed in DMSO. The observed effects and reaction pathways are discussed in terms of solute-solvent donor-acceptor interactions taking into account the differences in the electronic structures of both complexes.
Subject(s)
Carbamates/chemistry , Electron Spin Resonance Spectroscopy/methods , Organometallic Compounds/chemistry , Carbamates/analysis , Chemical Phenomena , Chemistry, Physical , Electrons , Kinetics , Ligands , Organometallic Compounds/analysis , Solvents/chemistry , Temperature , Time FactorsABSTRACT
We report on the possibility of identification by EPR spectroscopy of some irradiated cellulose-containing foodstuffs, at a relatively long time after the irradiation, when the characteristic EPR spectral lines of the cellulose free radical have essentially disappeared. In such cases rather expensive and time-consuming methods (e.g. thermoluminescence analysis) have to be applied. The present communication demonstrates with some pre-irradiated spices, dried medicinal and sweet herbs that simply heating the samples to 60 degrees C for one hour leads to a significant (50% or more) decrease of the EPR intensity of the remaining central line of the samples. For comparison, the loss in the intensity of the same line upon heating non-irradiated samples at 60 degrees C for one hour was only about 10%. This inexpensive new procedure will extend the post-irradiation period in which EPR can be used for distinguishing irradiated from non-irradiated samples, of certain cellulose-containing foodstuffs.
Subject(s)
Cellulose/analysis , Food Analysis/methods , Food Irradiation , Electron Spin Resonance Spectroscopy/methods , Hot Temperature , Magnoliopsida , Plants, Medicinal , SpicesABSTRACT
The photochemical reactions of bis(diethyl-diselenocarbamato)copper(II), Cu(Et2dsc)2, complex have been studied in toluene, CH2Cl2, CHCl3 and chloroalkane/EtOH mixed solvents. Charge-transfer irradiation induces intramolecular oxidation of the ligand and reduction of copper(II) to copper(I) as evidenced by EPR and UV-Vis spectra of the complex as well as quantum yield results. When photolysis is carried out in CHCl3 or CH2Cl2 or in the solvent mixture CHCl3/EtOH resp. CH2Cl2/EtOH of lower than 1:1 EtOH content, the primary photoproduct CuI(Et2dsc) is further oxidised in a dark reaction with the chloroalkane producing the corresponding paramagnetic mixed-ligand CuII(Et2dsc)Cl complex in equilibrium with its chloride-bridged and EPR silent, dimeric form Cu2(Et2dsc)2Cl2. At low concentration of EtOH the equilibrium is shifted to the dimeric form whereas at higher than 1:1 EtOH content in the mixed solvent CHCl3/EtOH it is shifted to CuII(Et2dsc)Cl. A reaction mechanism is proposed and the role of ethanol is discussed.
Subject(s)
Carbamates/chemistry , Organometallic Compounds/chemistry , Carbamates/radiation effects , Electron Spin Resonance Spectroscopy , Organometallic Compounds/radiation effects , Oxidation-Reduction , Photochemistry , Solvents , Spectrophotometry , Spectrophotometry, UltravioletABSTRACT
The first quantitative estimation of the stable free radical 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (TEMPOL) simultaneously performed by electron paramagnetic resonance (EPR) and visible spectrophotometric titration is reported. The obtained molar absorptivity of TEMPOL 13.2 +/- 0.1 l(-1) m(-1) cm(-1) at 22,900 cm(-1) may be used as the future criterium about the purity of the EPR active substance. The studied compound may be considered as the second (after 1,1-diphenyl-2-pikrilhydrazil) material calibrated as the primary standard for quantitative EPR spectrometry.
Subject(s)
Cyclic N-Oxides/analysis , Electron Spin Resonance Spectroscopy/standards , Cyclic N-Oxides/standards , Free Radicals/chemistry , Reference Standards , Spectrophotometry , Spin LabelsABSTRACT
Electron paramagnetic resonance and thermoluminescence signals induced by gamma irradiation in some herbs, spices and fruits were systematically studied in order to detect the treatment. Using European protocols the validity and effectiveness of these two techniques are compared in regard to time of storage after irradiation.
Subject(s)
Food Irradiation , Fruit/radiation effects , Magnoliopsida/radiation effects , Spices/radiation effects , Electron Spin Resonance Spectroscopy , Food Analysis/methods , Fruit/chemistry , Luminescence , Magnoliopsida/chemistry , Reproducibility of Results , Spices/analysisABSTRACT
A method is described for determining NO(2) in workplace atmospheres, based on its reaction with bis(diethyldithiocarbamato)copper(II) in toluene. NO(2) is absorbed from an air sample by a toluene solution of Cu(dtc)(2) and the decrease in the initial absorbance at 437 nm is measured. The method has been compared with the Saltzman method. The interference of NO, Cl(2), O(3), SO(2) and other gases has been studied. The NO(2) concentration range of the method is 1-500 mg m (3).
