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1.
2.
A method is described to separate trace amounts of selenium in biological samples without using a carrier. This method is based on the adsorption on active carbon of the complex ion formed with APDC /ammonium salt of l-pyrrolidine carbodithioic acid/ at pH 1. The efficiency of the radiochemical separation described is measured by using carrier-free75Se labelled solutions of sodium selenite at selenium concentrations from 3.5×10–8 to 3.5×10–11 g ml–1. The results were between 95% and 98% with statistical variations from 2% to 10%. The determination of selenium can be made following this separation either through75Se in the traditional way, or through77mSe if the separation is performed prior to irradiation. The detection limits on the available conditions were 0.01 ppm for75Se and 0.1 ppm for77mSe. When the analysis is performed through75Se /t=120 d/, the statistical error is notably smaller because the counting time may be considerable, whereas through77mSe/t=17.5 s/it is higher than 20%, depending on the concentration and the available neutron flux. However, the advantages of gaining time and the fact of performing the trace separation from a non radioactive material, make both procedures competitive as useful tools for the research on the function of Se in vertebrates.  相似文献   

3.
The high-pressure phases of group-VI elements sulfur and selenium in their spiral chain and ring structures are examined by in situ Raman and x-ray diffraction techniques combined with first principles electronic structure calculations. The S-II, S-III, Se-I, and Se-VII having spiral chain structures and S-VI with a molecular six-member ring structure are studied in a wide P-T range. The square spiral chain structure of S-III and Se-VII is characterized by seven Raman modes that harden with increasing pressure. The calculations reproduce the observed frequencies and allow the authors to make the mode assignment. The "p-S" and "hplt" phases of sulfur reported by previous Raman studies are identified as S-II and S-III with the triangular and square spiral chain structures, respectively. The phase relations obtained by the x-ray and Raman measurements show that the high-pressure high-temperature phases of sulfur, observed by x-ray, can be induced by laser illumination at room temperature.  相似文献   

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The method developed for the determination of the optical purity of L-selenomethionine-75Se is based on the conversion of the mixture of L-and D-amino acids into the diastereoisomeric derivatives by reaction with (−)-camphorsulphonyl chloride. The diastereoisomeric derivatives are separated by means of thin layer chromatography. From the ratio of the radioactivities of the two spots on the chromatogram, the optical purity is calculated, and given in % D. For a sample of L-methionine-14C the following value was found: 0.53±0.05 (S.D. of mean, n=7). For a sample of DL-methionine-14C the percentage of D found, was: 48.5±0.5 (S. D. of mean, n=7). Of 30 different samples of L-selenomethionine-75Se the percentages of D-isomer were determined in duplicate. From the 30 differences between duplicates the S. D. of a single measurement is calculated to be 0.2.  相似文献   

6.
Since the initial determination of the Q 0 and k 0 factors for 75Se systematic errors in Se determination in various matrices have been noticed by several users of the k 0 method. A number of publications have been made on this subject, resulting in different k 0 and Q 0 values for this radio-isotope. This work consists of a re-determination of Q 0 and k 0 values for 75Se using the bare and Cd-ratio methods making use of three different irradiation channels from the BR1 reactor. For this re-determination three different kinds of standards were used: a pure Se powder standard, an ICP standard solution and pure Se shots. Results were compared with previously published literary data. Differences in k 0 with the official published data ranging from 3.5 to 12 % were observed and potential reasons for this discrepancy are discussed. A good consistency with recent work was found. The impact on recent certification and intercomparison exercises demonstrates the effectiveness of the newly proposed values.  相似文献   

7.
We present herein a straightforward synthesis of N-Fmoc-protected synthons derived from a phosphinic analogue of methionine. These precursors were used successfully for the solid-phase synthesis of methionine-mimic phosphinopeptides using BOP-catalyzed coupling without protection of the phosphoryl moiety. We also prepared a new type of pseudopeptide derived from a phosphinic analogue of norleucine with a -PO(OH)-CH2-COOR moiety.  相似文献   

8.
The effect of confinement on the structural phase of Se clusters in zeolites (LTA and FAU) has been studied in the temperature range of 300 ~ 550K by Raman scattering and differential scanning calorimetry. It has been found in Raman spectra that the structural unit and phase stability of Se clusters are greatly affected by the geometrical restriction in the zeolites. No clear phase transformation was observed by DSC measurements for Se clusters in LTA zeolites, while Se clusters in FAU zeolites exhibit a distinct endothermic peak which is ascribed to a glass transition. The glass transition temperature of amorphous Se (320 K) is remarkably elevated when Se rings/chains are incorporated in FAU zeolites; the higher glass transition temperature for the smaller window diameter of zeolites. We have also found that the activation energy for the glass transition is decreased drastically in the zeolites; the smaller activation energy for the smaller window size. The observations imply that the kinetics of the structural relaxation at the glass transition of Se is significantly influenced by the absence of inter-cluster interaction and that the thermokinetic dimension becomes lower owing to the geometrical restriction in the zeolites.  相似文献   

9.
Extraction of actinides like neptunium, plutonium and americium have been performed using polyphosphine polyoxides. Phosphorus compounds with (O)PCP(O) linkage exhibit very high liquid-liquid extraction properties. They demonstrate also quantitative and selective transport properties of some actinides by supported liquid membrane (SLM) technology.  相似文献   

10.
Journal of Radioanalytical and Nuclear Chemistry - Two methods were used to evaluate the age of 75Se sealed source material. Both methods utilized gamma spectroscopy to determine the quantity of...  相似文献   

11.
《Polyhedron》1988,7(7):581-583
The natural abundance 77Se NMR spectra of Se7 (singlet at 996 ppm vs Me2Se) and of Se5S2 (singlets at 976, 1023 and 1085 ppm) show that these puckered seven-membered ring molecules undergo pseudorotation at 20°C in CS2 solution. This internal puckering motion makes all atoms of Se7 equivalent on the NMR time scale, and results in only three sets of non-equivalent Se atoms in Se5S2. The chemical shift of seven-membered Se-containing ring molecules is much larger than that of comparable six- or eight-membered homo- or heterocycles, reflecting the unique bonding situation.  相似文献   

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Different synthetic routes to the preparation of 4-ethyl-2,6,7-trioxa-1-phosphabicyclo[2,2,2]octane-1-thioxide labelled with sulfur-35 have been investigated since it is of considerable interest as radioligand for neurochemistry. The thiophosphate was successfully synthesized by sulfuration of the corresponding bicyclophosphite by elemental sulfur-35, however the radiochemical purity of the material obtained in this way proves to be low. Convenient methods for synthesis of the thioxide from [35S] thiourea, based on the results of the autoradiolysis of the starting [35S] thiourea, has been discovered giving rise to thioxide with high radiochemical purity. The autoradiolytic stability of the labelled thiophosphate has been studied.M. V. Lomonosov Moscow State University, Moscow 119899, Russia Translated from Khimiya Geterotsiklicheskikh Soedinenii, No 8, pp. 1107–1111, August, 1999.  相似文献   

14.
Macro-porous cation exchange resin Diaion CPK-08 and gel type cation exchange resin Dowex 50WX8 were irradiated with γ-rays from60Co, while soaked in distilled water, 0.5M HNO3 or 4M HNO3, and the ion-exchange properties, such as strong- and weak-acid capacities, moisture content and wet resin volume, were examined in relation to absorbed dose. There was no appreciable difference between the radiation stabilities of the two cation exchangers. Increase of HNO3 concentration reduced the loss of strong-acid capacity and increased the decross-linkage and the weak-acid capacity. Elution characteristics of137Cs and90Sr from columns packed with γ-irradiated resin were examined and the column distribution ratio of these radionuclides and the theoretical plate number were calculated. These values decreased with the increase of absorbed dose. Diaion CPK-08 was packed into a pressurized column and irradiated with γ-rays at a dose rate of 2·106 R/hr, while water was passed through the column at a constant flow rate. The greatest change of the resin properties was observed at an upper stream position from the position of the highest radiation dose of 2·106 R/hr.  相似文献   

15.
The effect of temperature on the crystallization kinetics of bulk amorphous S20Se80 has been studied using differential scanning calorimetry. Using the empricial Avrami expressions, a number of kinetic parameters has been determined. The order of the reactionn was found to be 2.3 for the range of temperature 340–365 K and 1.6 in the range of temperature between 370–400 K. This range ofn indicates that the crystallization process is diffusion controlled growth with decreasing nucleation rate. The activation energy was found to be 3, 1.1 ev depending on the same range of temperatures.A time-temperature-transformation (TTT) curves has been plotted from isothermal results over the temperature range 340 K to 400 K showing the presence of minimum at 374 K. From theTTT curves the critical cooling rate required to avoid 25, 50, 75 and 100% crystallization was found to be 2.4, 1.79, 0.72 and 0.42C/sec respectively.
Zusammenfassung Mittels DSC wurde der Einflu\ der Temperatur auf die Kristallisierungskinetik von amorphem S20Se80 untersucht. Unter Verwendung der empirischen Avrami Gleichungen wurde eine Anzahl kinetischer Grö\en ermittelt. Danach ergab sich die Reaktionsordnung n für den Temperaturbereich 340–365 K mit 2.3 und für den Temperaturbereich 370–400 K mit 1.6. Dieses Intervall fürn zeigt, da\ es sich beim Kristallisationsproze\ um ein diffusionsbestimmtes Wachstum mit sinkender Kristallkeimbildungsgeschwindigkeit handelt. Für die Aktivierungsenergie wurde für die gleichen Temperaturbereiche ein Wert von 3 bzw. 1.1 eV gefunden.Ausgehend von den isothermen Ergebnissen im Temperaturbereich 340–400 K wurde eine Zeit-Temperatur-Transformationskurve (TTT) dargestellt, die bei 374 K die Gegenwart eines Minimum aufweist. Auf der Basis derTTT-Kurven konnte für eine 25-, 50-, 75-bzw. 100-prozentige Kristallisation eine kritische Kühlgeschwindigkeit von 2.4, 1.79, 0.72 bzw. 0.42C/s ermittelt werden.


The author wish to thank Prof. Dr. M.F. Kotkata Department of Physics, at Ain Shams University in Cairo, for his valuable discussions, and also Dr. F. Sale the head of the Metallurgy department at UMIST in Manchester. Who gave the facility of doing the experimental work in his department.  相似文献   

16.
According to ab initio MO calculations at the G2(MP2) level of theory, branched isomers of dialkyl triselenides, R-Se(=Se)-Se-R (1; R = Me, Et), are less stable by more than 60 kJ mol(-1) than the isomeric unbranched chains R-Se-Se-Se-R (2). Therefore, species 1 cannot be generated in substantial concentrations under equilibrium conditions at moderate temperatures, as has recently been claimed by Meja and Caruso (Inorg. Chem. 2004, 43, 7486). Alternatively, the isomeric CH3-Se-CH2-Se-Se-Et (3) can be considered to explain the reported gas chromatograms and mass spectra previously assigned to Et-Se(=Se)-Se-Et (1b). However, the isomerization 2b --> 3 is also endothermic, by deltaG(o)298 = 63 kJ mol(-1). The isomeric selenols HSe-C2H4-Se-Se-Et (4) and CH3-CH(SeH)-Se-Se-Et (5) are also less stable than 2b (by ca. 56 kJ mol(-1)), but 4 is another candidate to explain the mass spectrum formerly assigned to 1b. The calculated structures of 1-5 are reported.  相似文献   

17.
Catalysis Institute, Siberian Branch, USSR Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 1, pp. 50–54, January–February, 1989.  相似文献   

18.
The recovery of selenium75Se added as selenite to human blood and to mixed food, and the recovery of biologically incorporated75Se from different rat tissues were determined by using four mineralization methods. The recoveries of75Se after dry ashing /HNO3, Mg/NO3/2/ and after three wet digestion methods — 1. HNO3, HClO4 2. HNO3, HClO4, H2SO4 3. HNO3, HClO4, MgCl2 were as follows: 50–106%, 96–99%, 92–99% and 97–100%, resp. Losses of75Se in wet digestion /HNO3, HClO4/ were observed at the end of the procedure, when an excess of acids was evaporated. The addition of MgCl2 to the digestion mixture prevented the escape of75Se and thus permitted the total evaporation of the digest without any loss of selenium.  相似文献   

19.
Correction equations of the coincidence-summing effect for efficiencies of HpGe detector based on the decay scheme were developed by considering the summing up to triple coincidence. The correction equations which do not dependent on the kind of the Ge detector are very useful for efficiency calibrations of a Ge detector in the energy region from 60 to 400 keV by using75Se radionuclide even with very short source-to-detector distances.  相似文献   

20.

The through-diffusion method and batch sorption experiments were used to explore the influence of pH on the diffusion behavior of 75Se(IV) in matrix Beishan granite (BsG). In the pH range of 2.0–8.5, the De values of 75Se(IV) in BsG decreased first and then increased with pH increasing, while the changing trend of Kd was nearly opposite. It was speculated that the influence of pH on the diffusion of 75Se(IV) in BsG was due to the joint effects of different species distribution of Se, change in surface charge of BsG and change in ionic strength at various pH values.

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