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991.
Nitrogen in organic samples may be determined on a routine basis after combustion in elemental analyzer instruments. If elementary copper is used in the reduction column, it will be oxidized to copper(II) oxide by passing oxygen and nitrogen oxides. Instead of changing the reduction column it is possible to regenerate the copper(II) oxide to elemental copper with hydrogen gas without removing the column from the oven. A modification of the original instrument and procedure is described. In this method, the capacity of the column will decrease after regeneration, but time and chemical costs will be saved. 相似文献
992.
The metabolic response of normal rat brain to photodynamic therapy (PDT) was studied over a 1 week interval using in vivo 31P-NMR spectroscopy. Rats injected with 12.5 mg/kg Photofrin II were submitted to brain photoactivation 48 h after drug administration with either 140 or 70 J/cm2 light (630 +/- 1 nm) from an Argon dye laser. Control studies, animals not given drug or light, animals submitted only to brain illumination without drug, and animals given drug but no light, were also performed. The data revealed a transient metabolic degradation; a decrease in the ratio of beta-nucleotriphosphate to inorganic phosphate (P less than 0.001) at 24 h after PDT treatment was followed by a return to pretreatment spectral values. Brain tissue alkalosis was also noted, with significant (P less than 0.05) differences in brain tissue pH detected at 72 h post treatment between 70 J/cm2 PDT vs control studies and at 1 week post treatment between 140 J/cm2 vs 70 J/cm2, 140 J/cm2 vs no light-no drug and 140 J/cm2 vs drug only. The data suggest that there is no difinitive metabolic marker from 31P-NMR spectroscopy that can identify necrotic brain tissue caused by PDT. Phosphorus-31 NMR data are also presented which suggest that PDT damage to brain is not solely the result of microvascular occlusion causing ischemic necrosis. 相似文献
993.
O. V. Fedotova M. I. Skuratova M. A. Panov S. P. Mushtakova 《Russian Journal of Organic Chemistry》2005,41(11):1661-1665
Reactions were studied of fused spirodihydrofurans originating from 1,3-cyclohexanedione with hydrogen sufide arising in situ. Depending on a substituent at the atom C 3 of the heterocycle the reaction ended by thionation of the conjugated carbonyl group followed by heterocyclization involving the spirodimedonyl fragment. A quantum-chemical forecasting of the protonation stages of substrates and their thionated analogs was performed applying the semiempirical PM3 procedure. A probable mechanism of investigated transformations of the spirodihydrofurans was suggested. 相似文献
994.
I. L. Odinets O. I. Artyushin E. A. Antonov P. V. Petrovskii B. I. Freger T. A. Mastryukova M. I. Kabachnik 《Russian Chemical Bulletin》1994,43(1):121-124
It was shown by31P and13C NMR spectroscopy that methyl(3-carboxy-3-oxopropyl)phosphinic acid (4-methylhydroxyphosphinyl-2-oxobutyric acid) (1) and the amide (2) of the latter exist in keto forms in non-aqueous solutions. In aqueous solutions an equilibrium between the keto,gem-diol, and enol forms has been observed. The proportions of the diol and enol forms increase as the acidity of the media increases. Silylation of acid 1 with hexamethyldisilazane gives the tris(trimethylsilyl) derivative of enol form (3) (Z- andE-isomers).Translated fromIzyestiya Akadetnii Nauk. Seriya Khimicheskaya, No. 1, pp. 125–128, January, 1994. 相似文献
995.
Dr. A. Woppmann 《Monatshefte für Chemie / Chemical Monthly》1974,105(2):419-426
The kinetics of the diazotization of o-, m-, p-chloroaniline in 0.005n- to 0.4n-methanolic HCl-solution at 25, 15, 0, ?10 ?20, and ?30°C was invertigated. It was found that the nitrosation reaction (the same as in1) $$C_6 H_4 ClNH_2 + NOCl \mathop \rightleftharpoons \limits^k C_6 H_4 ClNH_2 NO^ + + Cl^ - $$ is a proceeding advance-back-reaction. The decomposition of C6H4ClNH2NO+ by splitting off a proton is the rate determining step. The free activation enthalpies ΔG * for the nitrosation reaction, the activation entropies ΔS *, the activation enthalpies ΔH * and the activation energiesE a at the given temperatures are calculated. The experimentally found and the calculated velocities are given in Tables 1–6. The equilibrium constants of the o-, m-, p-chloroanilinium ions, and nitrosyl-chloride in methanol are indicated in Table 7, diagram 1. TheK M values (the ionic products of methanol, extrapolated at infinite dilution) together with theK A values of Table 7 give theK B values (p. 2) using the table10. The ΔG B values can be calculated using equation ΔG B = ?RTlnK B Fig 2 shows the linear dependance of the logarithmus of the ΔG * values from the logarithmus of theK B values. 相似文献
996.
The model of Onsager in which a polar molecule undergoes a reaction field due to the polarization of the molecular surroundings is used to evaluate by a S.C.F. calculation (CNDO/2 approximation) the modifications of a molecular structure in the liquid state.Application to water molecule and to three polar dimers for values of the dielectric constant varying between 3 and 78, shows that most of geometric parameters and dipoles moments vary of few per cent when the molecule is inserted in a liquid. In the liquid state dipole moments do not depend very much on the dielectric constant but energies and relative stabilities of isomers are strongly dependent on the medium.[/p] 相似文献
997.
V. V. Ishchenko E. I. Nosichenko O. T. Fal'kovskaya V. P. Khilya 《Chemistry of Heterocyclic Compounds》1995,31(3):276-278
The synthesis of benzodioxane derivatives of 1-benzopyrilium salts is reported and their reaction with nucleophiles is investigated.Taros Shevchenko University, Kiev 252017. Translated from Khimiya Geterotsiklicheskikb Soedinenii, No. 3, pp. 322–324, March, 1995. Original article submitted February 6, 1995. 相似文献
998.
Yu. A. Davidovich V. I. Butaeva O. M. Galkin T. N. Sentsova S. V. Rogozhin 《Russian Chemical Bulletin》1977,26(7):1554-1556
Conclusions A convenient method was proposed for obtaining the esters of N-carbonyl--amino acids, which is based on the reaction of the esters of N-trimethylsilyl--amino acids with phosgene in the presence of a tertiary amine.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1682–1684, July, 1977. 相似文献
999.
Dr. Marita Fell 《Colloid and polymer science》1967,220(2):107-110
Zusammenfassung Aus einem durch Trypsinabbau von -Keratose erhaltenen Gemisch von Peptiden wurden 15 neutrale, 5 saure und 2 basische Peptide durch Kombination papierchromatographischer und papierelektrophoretischer Methoden getrennt und in sehr geringen Mengen isoliert. Es wurden neben der Aminosäurezusammensetzung 14N-terminale Aminosäuren sowie einige Teilsequenzen in den untersuchten Peptiden ermittelt.Die mittlere Kettenlänge der Peptide beträgt 5,8 Aminosäuren.Mit 1 Tabelle3. Mitt. über Untersuchungen an -Keratose. 2. Mitt.:M. Fell undE. Schnabel, Hoppe-Seyler's Z. physiol. Chem.333, 218 (1963). 相似文献
1000.
I. A. Litvinov O. N. Kataeva V. E. Kataev O. Yu. Butenko 《Russian Chemical Bulletin》1991,40(8):1607-1609
It was established by x-ray crystallographic analysis that the molecular o-nitrobenzyltriethylammonium cation has an orthogonal orientation of the benzene ring and the vicinal C-N+ bond (=93.8°). The nitro group deviates from the plane of the aromatic ring by an angle of 26.9°. One of the ethyl groups at the quaternary nitrogen atom is in an ap-conformation (=176.2°); the other two are in sc-conformations, characterized by torsional angles 65.1 and 69.4°.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1816–1818, August, 1991. 相似文献