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151.
A novel type of retention indices for alkylphenols and related compounds are proposed. The alkylphenol retention indices (APRI) use para-substituted n-alkylphenols as reference series. APRI for para-n-alkylphenols are per definition equal to the number of carbon atoms in the alkyl substituent; the value for phenol is zero. Application of the APRI system with different types of derivatisation of the phenolic hydroxy group showed that the derivatisation has limited influence on these indices. Especially para-substituted alkylphenols gave APRI values that could be transferred with high accuracy from one type of derivative to another. By comparing results obtained with different gradients in temperature-programmed GC, it was also shown that APRI is less affected by chromatographic conditions than retention indices based on n-alkanes. 相似文献
152.
Kosevich MV Boryak OA Orlov VV Shelkovsky VS Chagovets VV Stepanian SG Karachevtsev VA Adamowicz L 《Journal of mass spectrometry : JMS》2006,41(1):113-123
Satellite [M + 2](+*) and [M + 3](+) peaks accompanying the common peak of the protonated molecule [M + H](+) that are known to indicate the occurrence of a reduction process were observed in the fast atom bombardment (FAB) mass spectra of imidazophenazine dye derivatives in glycerol matrix. The distribution of the abundances in the [M + nH](+) peak group varied noticeably for different derivatives. This indicated different levels of the reduction depending on the different structure variations of the studied molecules. In the search for correlations between the mass spectral pattern and the structural features of the dyes, ab initio HF/6-31++G** quantum chemical calculations were performed. They revealed that the abundances of the [M + 2](+*) and [M + 3](+) ions show growth proportional to the decrease of the energy of the lowest unoccupied molecular orbital, i.e. proportional to the increase of the electron affinity of the dye molecule. A method for rapid screening of reductive properties of sets of dye derivatives on the basis of the FAB mass spectral data is discussed. 相似文献
153.
Diastereoselective aldol coupling reactions with butane-2,3-diacetal (BDA) protected glyceraldehyde derivatives are reported. Good selectivities of up to 20:1 for the homologated aldol products have been achieved in preparatively useful yields. 相似文献
154.
Stepan A. Ukhanev Sergei V. Fedorov Yuriy Y. Rusakov Irina L. Rusakova Leonid B. Krivdin 《Magnetic resonance in chemistry : MRC》2022,60(9):901-914
All possible spin–spin coupling constants, 19F–19F, 19F–13C, and 19F–1H, of pentafluorobenzene were calculated at five different levels of theory, HF, DFT, SOPPA (CCSD), CCSD, and the SOPPA (CCSD)-based composite scheme with taking into account solvent, vibrational, relativistic, and correlation corrections. Most corrections were next to negligible for the long-range couplings but quite essential for the one-bond carbon–fluorine coupling constants. Hartree–Fock calculations were found to be entirely unreliable, while DFT results were comparable in accuracy with the data obtained using the wave function-based methods. 相似文献
155.
Nicolaou KC Tang Y Wang J Stepan AF Li A Montero A 《Journal of the American Chemical Society》2007,129(48):14850-14851
The chemical synthesis and biological evaluation of carbaplatensimycin, the carbon analogue of the recently reported antibiotic platensimycin has been accomplished. Carbaplatensimycin exhibited similar potency to the natural product as an antibacterial agent against a variety of strains, including methicilin- and vancomycin-resistant bacteria. 相似文献
156.
Chuprakov S Malyshev DA Trofimov A Gevorgyan V 《Journal of the American Chemical Society》2007,129(48):14868-14869
The first example of sila-Morita-Bayis-Hillman reaction between 1-silylcyclopropenes and carbonyl compounds has been demonstrated. This novel phosphine-catalyzed transformation features a 1,3-Brook rearrangement/elimination cascade and provides convenient access to a variety of 1-(silyloxymethyl)cyclopropenes, which are not easily available via traditional methods. 相似文献
157.
The purpose of this review is to draw attention to the use of electrospray ionization mass spectrometry (ESI-MS) for monitoring the course of enzyme-substrate interactions, in the particular case of complex systems in which two substrates participate. The determination and characterization of intra-molecular reactions, especially those that occur in the enzyme active site, is not a trivial task in chemical kinetics, typically requiring long measurement times and relatively expensive techniques such as nuclear magnetic resonance (NMR), X-ray crystallography or electron microscopy (EM). However, nowadays almost all laboratories are equipped with or else have access to the ESI-MS technique. The aim of this review is to focus on the possibilities of employing even quite simple MS equipment to tackle different applications in studies of complex enzymatic systems. 相似文献
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