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1.
The present studies are concerned with the influence of the nature of the solvent on the time-dependent stability of the absorption maxima of the free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) at 520 nm as well as the intensity of its EPR spectrum. The correlation between these two characteristics of DPPH, the behaviour of which is found to be unpredictably strange, unambiguously shows that the problem for calibration of DPPH in order to be used as a primary standard for quantitative EPR spectrometry purpose is not solved yet. This problem needs additional studies in order to find exact methods for examination of the data concerning DPPH quantitative characteristics before its use. 相似文献
2.
N. D. Yordanov 《Applied magnetic resonance》1994,6(1-2):241-257
3.
N.D. Yordanov V. Gancheva M. Radicheva B. Hristova M. Guelev O. Penchev 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1998,54(14):2413-2419
Non irradiated and γ-irradiated dry herbs savoury (Savoury), wild thyme (Thymus serpollorium) and marjoram (Origanum) with absorbed dose of 8 kGy have been investigated by the methods of elecrtron paramagnetic resonance (EPR) and thermoluminescence (TL). Non-irradiated herbs exhibit only one weak siglet EPR signal whereas in irradiated samples its intensity increase and in addition two satelite lines are recorded. This triplet EPR spectrum is attributed to cellulose free radical generated by irradiation. It has been found that upon keeping the samples under the normal stock conditions the life-time of the cellulose free radical in the examined samples is ∼60–80 days. Thus the conclusion has been made that the presence of the EPR signal of cellulose free radical is unambiguous indication that the sample under study has been irradiated but its absence can not be considered as the opposite evidence. In the case when EPR signal was absent the method of TL has been used to give the final decision about the previous radiation treatment of the sample. 相似文献
4.
The extraction of uranium(IV) from phosphoric acid solutions with PMBP and PMBP-TOPO mixtures has been studied. The synergic extraction with PMBP-TOPO is more effective than the simple chelate extraction with PMBP and both systems are more effective than the synergic extraction of uranium(VI) with DEHPA-TOPO. It is established that the complexes extracted are U(PMBP)(4) and U(PMBP)(4).TOPO for the chelate and synergic extraction respectively. The most probable uranium(VI) species in the aqueous phase (2.9-6.33M H(3)PO(4)) is the neutral complex U(H(5)P(2)O(8))(4). Analytical methods suitable for determination of uranium in phosphoric acid solutions have been developed. The highest sensitivity is achieved by combining the synergic extraction with the uranium(IV)-arsenazo III colour reaction. 相似文献
5.
Sarova G Roussanova D Jeliazkova B Yordanov ND Malik MA O'Brien P 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,(2):351-356
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. 相似文献
6.
Jeliazkova BG Dimitrova A Yordanov ND 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(6):1163-1170
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. 相似文献
7.
Yordanov ND Ranguelova K 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,(2):373-378
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. 相似文献
8.
9.
N. D. Yordanov 《Applied magnetic resonance》1996,10(1-3):339-350
The knowledge about the physico-chemical properties of the stable free radical DPPH as a primary standard for the Quantitative EPR spectrometry is summarized. It is shown how to calibrate DPPH in order to use it as a primary EPR standard for quantitative estimations. It is expected that the reported data will be useful for the EPR community specially in calibration and also for periodical checking of the standards used. 相似文献
10.
Module upgrading the existing IBM PC data acquisition and processing system for Bruker ER200D equipped with EN250 ENDOR attachment is described. The old ASPECT 2000 computer is fully replaced by a modern IBM PC without any modification of the Bruker EN003 ENDOR standard interface. Thus the spectrometer can operate under IBM PC control in ENDOR and TRIPLE modes. Moreover its features are extended with ENDOR INDUCED EPR operating mode which was not available before. 相似文献