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131.
Chemical syntheses of 2′-amino-2′-deoxyarabinonucleosides of uracil, thymine, cytosine, adenine, and guanine and their conversion into suitably protected 3′-phosphoramidite building blocks 24–28 for oligonucleotide synthesis are described. The 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) group was used for protection of the aglycon and the 2′-amino functions. 相似文献
132.
Wolfgang A. Herrmann 《Angewandte Chemie (International ed. in English)》1978,17(11):800-812
In recent years, aliphatic diazo compounds have proved to be more and more versatile as reagents in the preparative chemistry of organometallic complexes. As readily accessible compounds, they are not only suitable for the synthesis of known kinds of metal complexes but also open fresh routes to novel complex systems. The comparatively new field of diazoalkane complex chemistry exhibits numerous unexpected and novel reactions, and introduces interesting and promising aspects into the chemistry of carbonylmetal compounds. 相似文献
133.
A comparison of different nebulisers for direct hyphenation of capillary and nano liquid chromatography (Cap-LC, Nano-LC) and quadrupole-based collision cell inductively coupled plasma mass spectrometry (CC-ICP–MS) for phosphorylation profiling of tryptic protein digests is described. Helium was used as cell gas and specially tuned instrumental conditions were used to achieve background minimisation at the mass of phosphorus, because of kinetic energy discrimination of the interfering polyatomic ions. The proposed set-up is based on a modified capillary electrophoresis interface and a home-made 4 mL spray chamber. It enables the use of gradient conditions with a highly concentrated organic mobile phase as often used in protein phosphorylation analysis, without the need to apply membrane desolvation for removal of the organic phase or further background minimisation. No significant signal suppression or other negative effects caused by the organic mobile phase occur, because of the low flow rates used in Cap-LC and the robust plasma conditions of the CC-ICP–MS instrument. A tryptic digest of beta-casein was investigated as model compound to demonstrate the applicability of the proposed set-up for phosphorylation profiling in protein analysis using quadrupole based collision-cell ICP–MS as phosphorus-specific detector. Detection limits for phosphorylated peptides down to the sub picomole level were obtained. As a complementary technique, electrospray ionisation tandem mass spectrometry (ESI–MS–MS) with data base searching was used for further characterisation of the phosphorylated peptides detected. 相似文献
134.
2-C5H5(CO)2[P(OMe)3]Mo(W)-substituted 4,4,5,5-tetramethyl-1,3,2-dioxarsolanes and -dioxaphospholanes (Ia–Ic) are obtained from C5H5(CO)3M derivatives via CO/P(OMe)3 exchange. In all cases the phosphite ligand appears trans to the σ-bonded arsenic heterocycle, which prefers a conformation with the transition metal group in an axial position. The dioxaphospholane-metal (Ia) undergoes isomerization with alkyl migration at 0°C, which due to stereochemical reasons can only occur by an intermolecular mechanism. 相似文献
135.
The products of decomposition of solutions of p-chlorobenzenediazonium tetrafluoroborate in aqueous buffer solutions (pH 9.0–10.3; ionic strength 0.1–0.5) at 20.0° have been analyzed quantitatively. Up to eleven low molecular weight compounds could be identified besides the major product, the complex polymeric diazo tar. The distribution of products is influenced by trace amounts of oxygen as well as by p-chlorophenol and the radical trapping reagent iodoacetic acid. Mechanisms of formation of the products are discussed. 相似文献
136.
Peter Roschger Werner Fiala Wolfgang Stadlbauer 《Journal of heterocyclic chemistry》1992,29(1):225-231
4-Chloro-3-nitro-2-quinolones 3 obtained from the 4-hydroxy quinolones 1 by nitration and chlorination, reacted with sodium azide to the 4-azido derivatives 4 which cyclized on thermolysis to yield the furoxanes 5 . Nucleophilic substitution reactions of 3 led to the 4-amino-, 4-fluoro- and 4-alkoxy-3-nitroquinolones 7, 8 and 9 , respectively. With thiols either 4-thio-3-nitro- 10 or 3,4-dithioquinolones 11 were obtained depending on the basic catalyst. 相似文献
137.
Electronic determinants of photoacidity in cyanonaphthols 总被引:2,自引:0,他引:2
We present semiempirical AM1 calculations for the ground and excited state of 2-naphthol and some of its cyano derivatives in the gas phase. Following photoexcitation, the Mulliken electron density on the oxygen diminishes slightly for the acid and more conspicuously for the anionic conjugated base. This agrees with the measured solvatochromic parameters for 2-naphthol. In both electronic states, we find a nice correlation with the measured pK values in water. The electronic charge distribution on the distal ring of the anion agrees with the experimental acidity order in both S(0) and S(1). Upon excitation, it increases predominantly in positions 3, 5, and 8. The ring system of the anion assumes an alternate quinoidal structure in the ground state of the anion, which becomes more symmetric in the relaxed excited state. This suggests that the enhanced aromatic character of a 4n electron system in the excited state allows for better delocalization of the oxygen charge within the ring. 相似文献
138.
Qijin Chi Wolfgang Göpel Tautgirdas Ruzgas Lo Gorton Peter Heiduschka 《Electroanalysis》1997,9(5):357-365
The electrochemical properties of carbon paste electrodes (CPEs), including unmodified and modified with protein and polycations, were investigated by impedance spectroscopy (IS) using ferricyanide and ferrocene monocarboxylic acid (FcMA) as redox probes. Various electrochemical pretreatments were applied to the unmodified CPE. The heterogeneous charge transfer rate constant of ferro/ferricyanide couple is enhanced by 2 to 10 times compared with that obtained at untreated electrodes. It was found that for ferricyanide the more suitable pretreatments are successive cyclic voltammetric scans, cathodization and a square wave-like stepping rather than high-potential anodization. However, the pretreatment only exhibits a slight effect on the kinetics of FcMA. At the CPEs containing modifier, the electron transfer rate of the redox couple depends more on the pH of electrolyte solution if ferro/ferricyanide is used. The results can be explained by the differently charged states of the CPEs that were caused by the protonation or deprotonation of the modifiers in various pH solutions and demonstrate the importance of the electrostatic interaction on the kinetics of the highly polar species such as ferricyanide. The different adsorptive behavior of ferricyanide and FcMA is also discussed. 相似文献
139.
The absorption spectra of Ru(2,2′-bipyridine)2 (2,2′-bipyridine-4,4′-dicarboxylic acid)2+ (I) and its diethyl ester (II) are closely related and are both significantly different from the spectra of the mono-protonated (Ia) and deprotonated (Ib) complexes. Luminescence polarization measurements show that for I and II the luminescent states have the transferred electron in the bipy-4,4′(COOH)2 and bipy-4,4′(COOEt)2 ligands, respectively, rather than in the unsubstituted bipy ligands. 相似文献
140.
Natural irones from the essential oil of Iris rhizomes develop by oxidative degradation of C31-triterpenoids produced by the plant. Two enantiomeric forms of irones are found in Iris, oils of different origin. The optical properties and CD spectra of irones, dihydroirones and their C31-precursors are reported and their absolute stereochemistry is determined. 相似文献