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991.
To measure the hydrophobic character of the ribose moiety of doridosine on the adenosine receptors, 2′,3′-didehydro-2′,3′-dideoxydoridosine (2) and 2′,3′-dideoxydoridosine (3) were prepared. Initial treatment of doridosine with N,N-dimethylformamide diethylacetal, and subsequently with tert-butyldimethylsilyl chloride gave 5. Compound 5 was then reacted with 1,1′-thiocarbonyldiimidazole and the resulting thionocarbonate 6 was heated with triethyl phosphite at 135°C to afford 7. Treatment of compound 7 with tetrabutylammonium fluoride and methanolic ammonia furnished compound 2 in good yield. Compound 2 was subjected to catalytic hydrogenation affording compound 3 in 85% yield. 相似文献
992.
Sh. Sh. Nabiev I. I. Ostroukhova N. V. Revina L. P. Sukhanov 《Russian Chemical Bulletin》1998,47(3):417-422
The Raman spectra of ClOF2
+ cation in solutions of anhydrous HF were studied. In the ClOF2
+HF2
− and ClOF2
+BF4
−−HF systems, this cation exists as a pyramidal structure (C
s
symmetry), while in the ClOF2
+AuF6
−−HF system, it exists as a planar structure (C
2v
symmetry). Based on nonempirical calculations by the Hartree-Fock-Roothaan method, an explanation for the dependence of the
structure of the ClOF2
+ cation on the nature of the anion was proposed. For the Cl−O bond vibrations, the correlation functions of vibrational and
rotational relaxations were calculated, and the characteristic times of these processes were determined. The main contribution
to the formation of the band contours corresponding to the above-mentioned modes is made by the vibrational dephasing.
Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 432–437, March, 1998. 相似文献
993.
An investigation of the alkaloidal constituents of the leaves of Catharanthus roseus has led to the isolation of a new alkaloid, “rosicine”, to which structure (1) has been assigned on the basis of spectroscopic studies. Two other alkaloids isolated have been identified as 14, 15-dehydroepivincadine and 19-hydroxytabersonine. 相似文献
994.
A cation adsorption model is presented and its recent applications are discussed. The model combines electrostatic equations with specific binding, and considers neutral and positively charged complexes between the negative surface sites and organic cations in a closed system. Extensions in the model account for dye aggregation in solution, and for the formation of solution complexes of inorganic cations, such as [M++ Cl–]+. The amounts of 45Ca2+ adsorbed to vesicles extracted from the plasma membranes of melon root cells could be adequately simulated and predicted. The binding coefficients determined for Ca2+, Na+, and Mg2+ are in the range of values previously deduced for binding to phospholipid components. Model calculations were applied to the test of hypotheses on the effect of salt stress on the growth of roots. The adsorption of monovalent organic cations to montmorillonite is characterized by binding coefficients that are at least six orders of magnitude larger than those of Na+, Mg2+, Ca2+, and Cd2+, or those of CdCl+ or CaCl+. Monovalent organic cations were found to adsorb 140–200% of the cation exchange capacity of the clay and to cause charge reversal. Deductions from adsorption results of acriflavin are consistent with those drawn from the application of other experimental methods. Preliminary results on the adsorption of divalent organic cations are presented. Agro-environmental applications of organo-clays are discussed. 相似文献
995.
The effect of 1,1,2,2-tetrachloroethane (TCE) on the IR spectra of HCl complexes withN,N-dimethylformamide (DMF) and 1-methyl-2-pyrrolidone (N-MP) with strong quasisymmetric hydrogen bonds was studied using Multiple Attenuated Total Reflection (MATR) IR spectroscopy.
The addition of TCE does not change the background absorption spectra, but results in a change in the extinction coefficients
of some bands of these complexes. The analysis of the spectra shows that the HCl−DMF complexes interact only with one molecule
of TCE, and the HCl−N-MP complexes interact with two molecules of TCE. It is shown that the neutral component of the system (TCE) has no effect
on the parameters of the strong quasi-symmetric H-bond in the complexes studied.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 956–960, May, 1997. 相似文献
996.
Gerald Giester 《Monatshefte für Chemie / Chemical Monthly》1992,123(11):957-963
Summary The crystal structure of the hydrothermally synthesized compound Fe(SeO2OH) (SeO4) · H2O was determined by single crystal diffraction methods:a=8.355(2) Å,b=8.696(2) Å,c=9.255(2) Å, =93.72(1)°,V=670.95 Å3;Z=4, space group P21/c,R=0.029,R
w=0.027 for 2430 independent reflections (sin /0.76 Å–1). Isolated FeO5(H2O)-octahedra share five corners with [SeO2OH] and [SeO4] groups to form sheets parallel to (100). These sheets are interconnected via hydrogen bonds only.
Die Kristallstruktur von Fe(SeO2OH)(SeO4)·H2O
Zusammenfassung Die Kristallstruktur der hydrothermal dargestellten Verbindung Fe(SeO2OH) (SeO4)·H2O wurde mittels Einkristallbeugungsmethoden bestimmt:a=8.355(2) Å,b=8.696(2) Å,c=9.255(2) Å, =93.72(1)°,V=670.95 Å3;Z=4, Raumgruppe P21/c,R=0.029,R w=0.027 für 2 430 unabhängige Reflexe (sin / 0.76 Å–1). Isolierte FeO5(H2O)-Oktaeder teilen fünf Ecken mit [SeO2OH]- und [SeO4]-Gruppen, wobei sie Schichten parallel (100) bilden. Diese Schichten sind nur über Wasserstoffbrücken miteinander verbunden.相似文献
997.
von Niessen Wolfgang Cederbaum Lorenz S. Kraemer Wolfgang P. 《Theoretical chemistry accounts》1977,44(1):85-93
The vertical valence ionization potentials of cyclopropane, ethylene oxide and ethylene imine are calculated by a many-body Green's function method. For C3H6 the ordering of the ionization potentials is 2e(), 1e(), 2a1(), 1a2(), 1e(). The assignment of the 2a1 and the 1a2 ionization potentials which has been controversial is thus clarified. The ordering is in agreement with the result obtained via Koopmans' theorem. For ethylene oxide and ethylene imine Koopmans' theorem fails in predicting the correct order of ionic states. For C2H4O the ordering of the ionization potentials is 2b
1(), 4a
1, 1a
2(), 2b
2,3a
1, 1b
1(), 1b
2, 2a
1 and for C2H5N 6a, 5a, 3a, 2a, 4a, 3a, 1a, 2a. The agreement of the computed ionization potentials with the experimental values is very satisfactory. 相似文献
998.
Josef Scharf Karl Schlögl Michael Widhalm Johann Lex Werner Tückmantel Emanuel Vogel Franz Pertlik 《Monatshefte für Chemie / Chemical Monthly》1986,117(2):255-267
2,7-Dibromo-1,6-methano[10]anulene (3) and 2,9-Dibromo-syn-1,6:8,13-diimino[14]anulene (9) were quantitatively separated into their enantiomers by chromatography on triacetylcellulose (TAC) in ethanol. X-ray structure analysis (Bijvoet technique) established the chiralities (+)(R)-3 and (+)(S)-9 for the dextrorotatory enantiomers.Comparison of the CD spectra allowed the configurational assignment to further optically active [10] and [14] anulenes which were also accessible by chromatography onTAC. Conversion of (+)(R)-2-bromo-1,6-methano[10]anulene (2) into the corresponding methylester (–)-4 confirmed its previously proposed chirality (–)(R).2,7-Dibromo-1,6-oxido[10]anulene (7) and 2,9-dibromo-syn-diimino[14]anulene (9) are in contrast to the 2,9-dibromo-syn-dioxido[14]anulene (10) optically stable until 250°C. Consequently their inversion barriers are higher than 42 kcal (176 kJ) mol–1.The CD spectra of mono and disubstituted anulenes (with C1 and C2 symmetry, resp.) are compared: For the [10]anulenes theCotton effect around 330 nm seems to be specific for their configuration with a positive effect indicating (S)-chirality and vice versa. Some regularities concerning the chromatographic resolutions are discussed.
Stereochemie planar chialer Verbindungen, 10. Mitt.: Röntgenkristallstruktur und absolute Chiralität überbrückter [10]- und [14] Anulene
Zusammenfassung 2,7-Dibrom-1,6-methano[10]anulen (3) und 2,9-Dibrom-syn-1,6:8,13-diimino[14]anulen (9) wurden durch Chromatographie an Triacetylcellulose (TAC) in Ethanol quantitativ in ihre Enantiomeren getrennt. Röntgenstruktur-analyse (Bijvoet-Technik) bewies für die rechtsdrehenden Enantiomeren die Chiralität (+)(R)-3 bzw. (+)(S)-9.Ein Vergleich der CD-Spektren ermöglichte die Konfigurationszuordnung weiterer optisch aktiver [10]- und [14]Anulene, die gleichfalls durch Chromato-graphie anTAC erhalten worden waren. Umwandlung von (+)(R)-2-Brom-1,6-methano[10]anulen (2) in den entsprechenden Methylester (–)-4 bestätigte dessen schon früher vorgeschlagene Chiralität (–)(R).Dibrom-1,6-oxido[10]anulen (7) und Dibrom-diimino[14]anulen (9) sind im Gegensatz zum Dioxido[14]anulen (10) bis 250°C optisch stabil. Ihre Inver-sionsbarrieren liegen somit über 42 kcal (176kJ) mol–1.Die CD-Spektren von mono- und disubstituierten Anulenen (mit C1 bzw. C2-Symmetrie) werden verglichen: Für die [10]Anulene scheint derCottoneffekt um 330 nm konfigurationsspezifisch zu sein, wobei ein positiver Effekt (S)-Chiralität anzeigt — und vice versa. Einige Regelmäßigkeiten bezüglich der chromatographischen Enantiomerentrennung werden diskutiert.相似文献
999.
1000.