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排序方式: 共有514条查询结果,搜索用时 31 毫秒
71.
72.
Fitch WL He L Tu YP Alexandrova L 《Rapid communications in mass spectrometry : RCM》2007,21(10):1661-1668
Polarity switching mass spectrometry is an efficient way to collect structural data on drug metabolites. The value of this approach is illustrated with the in vitro metabolism of RO9237. Metabolites are identified by positive and negative electrospray ionization (ESI) full scan mass spectrometry, MS/MS and MS(3) using unlabelled and (14)C-radiolabelled versions of the drug. Comparison of the relative detectability of these metabolites by +ESI and -ESI shows that neither ESI mode is universal. It is advantageous to screen for metabolites using both positive and negative ionization modes. This is especially true for phase II metabolism which tends to make molecules more polar and often more acidic. Identification of phase II metabolites also benefits greatly from MS(3) experiments because the conjugating groups typically are cleaved in MS/MS and information on the core structure is only obtained in MS(3). A special case of phase II metabolism is the generation of glutathione (GSH) conjugates from reactive metabolites. The detection of GSH conjugates also benefits from generating both positive and negative ESI mass spectral data. 相似文献
73.
Ostroumova OS Kaulin YA Gurnev PA Schagina LV 《Langmuir : the ACS journal of surfaces and colloids》2007,23(13):6889-6892
We evaluated the effect of agents modifying the membrane dipole potential: phloretin, 6-ketocholestanol and RH 421 on the properties of single channels formed by lipodepsipeptide syringomycin E (SRE) in planar lipid bilayers. SRE forms two conductive states in lipid bilayers: "small" and "large." Large SRE channels are clusters of several small ones, demonstrating synchronous openings and closures. The increase in the membrane dipole potential led to (i) an increase in SRE channel conductance, (ii) an increase in the channel's lifetime, and (iii) a decrease in a number of synchronously operating small channels in the clusters. Overall, the results support the model of the small SRE channel synchronization in the cluster as voltage-dependent orientation of the lipid dipoles associated with the channel pores. 相似文献
74.
Vytria Piscitelli Cavalcanti Smail Aazza Suzan Kelly Vilela Bertolucci Joo Pedro Miranda Rocha Adriane Duarte Coelho Altino Júnior Mendes Oliveira Laís Campelo Mendes Maysa Mathias Alves Pereira Ludmila Caproni Morais Moacir Rossi Forim Moacir Pasqual Joyce Dria 《Molecules (Basel, Switzerland)》2021,26(19)
Garlic is a health promoter that has important bioactive compounds. The bioactive extraction is an important step in the analysis of constituents present in plant preparations. The purpose of this study is to optimize the extraction with the best proportion of solvents to obtain total phenolic compounds (TPC) and thiosulfinates (TS) from dried garlic powder, and evaluate the antioxidant activities of the optimized extracts. A statistical mixture simplex axial design was used to evaluate the effect of solvents (water, ethanol, and acetone), as well as mixtures of these solvents, after two ultrasound extraction cycles of 15 min. Results showed that solvent mixtures with a high portion of water and pure water were efficient for TPC and TS recovery through this extraction procedure. According to the regression model computed, the most significant solvent mixtures to obtain high TPC and TS recovery from dried garlic powder are, respectively, the binary mixture with 75% water and 25% acetone and pure water. These optimized extracts presented oxygen radical absorbance capacity. Pure water was better for total antioxidant capacity, and the binary mixture of water–acetone (75:25) was better for DPPH scavenging activity. These optimized extracts can be used for industrial and research applications. 相似文献
75.
Alexander Fainleib Elena Slinchenko Olexander Brovko Ludmila Sergeeva Valentina Dubkova Harry Frisch 《Macromolecular Symposia》2001,169(1):179-184
The influence of carbon fibre on the curing kinetics of the prepolymer based on bisphenol A cyanurate and epoxy resin has been studied using infra‐red spectroscopy. It was found that curing process of prepolymer is very complicated. It is shown that in curing the prepolymer a number of the sequential transformations of ones cycle structure into others occurs. An introduction of the carbon fiber (CF) of two types, original CF and modified CF (MCF) containing phosphate groups, affect strongly the prepolymer curing. Both CF and MCF accelerate the conversion rate of epoxy groups. In the case of cyanate groups, the former does not practically affect their conversion whereas the latter decelerates strongly this process. In the paper the influence mechanism of CF is considered. 相似文献
76.
Alexander S. Lyakhov Pavel N. Gaponik Michail M. Degtyarik Ludmila S. Ivashkevich 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(6):m204-m206
In the polymeric title complex, [CuCl2(C3H6N4)2]n, there are two ligands in the asymmetric unit. The Cu atom adopts an elongated octahedral geometry, with two 2‐ethyltetrazole ligands [Cu—N = 2.0037 (16) and 2.0136 (16) Å] and two Cl atoms [Cu—Cl = 2.2595 (6) and 2.2796 (6) Å] in equatorial positions. A Cl atom and a symmetry‐related 2‐ethyltetrazole molecule [Cu—Cl = 2.8845 (8) Å and Cu—N = 2.851 (2) Å] lie in the axial positions of the octahedron. One of the two 2‐ethyltetrazole ligands of the asymmetric unit exhibits bidentate binding to two Cu atoms through two N atoms of the tetrazole ring, whereas the other ligand is coordinated in a monodentate fashion via one tetrazole N atom. The Cu‐atom octahedra form dimer entities by sharing edges with equatorial and axial Cl atoms. The dimers are linked together through the 2‐ethyltetrazole ligands to form one‐dimensional polymeric zigzag chains extending along the b axis. The chains are connected into infinite layers parallel to the (10) plane via the 2‐ethyltetrazole ligands. 相似文献
77.
Alexander D. Vasiliev Alexander M. Astachov Maxim S. Molokeev Ludmila A. Kruglyakova Rudolf S. Stepanov 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(9):o499-o501
The molecule of the title compound, C3H5N5O4, has a planar geometry. Due to the presence of a second nitro group, the lengths of the two conjugated C—N bonds are different. Nevertheless, the conjugation of the nitrimine group spreads to the nitramine group. Intermolecular N—H...O bonds connect molecules into dimers in the crystal structure. 相似文献
78.
Alexander D. Vasiliev Alexander M. Astachov Maxim S. Molokeev Ludmila A. Kruglyakova Rudolf S. Stepanov 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(10):o550-o552
The title compound, CH3N5O4, is almost planar, and the conformation is fixed by two intramolecular N—H⋯O hydrogen bonds. Owing to the delocalization of π‐electron density over the whole molecule, there is through‐conjugation, with the C—N, N—N and N—O bond lengths having values intermediate between those typical for the corresponding single and double bonds. 相似文献
79.
Alexander L. Rusanov Ludmila G. Komarova Tatyana S. Sheveleva Marina P. Prigozhina Svyatoslav A. Shevelev Michai L. D. Dutov Irina A. Vatsadze Olga V. Serushkina 《Macromolecular Symposia》1997,122(1):123-128
New aromatic diamines were obtained on the basis of available and inexpensive 2, 4, 6-trinitrotoluene (trotyl, TNT). Monomers obtained were used for the preparation of the new organo-soluble polyimides containing thiophenoxy and phenoxy side groups. 相似文献
80.
Carlos A. Crdoba Ludmila I. Ronco Celina E. Barrios Luis M. Gugliotta Roque J. Minari 《大分子反应工程》2019,13(2)
Miniemulsion polymerization is employed to produce high solid content (50%) acrylic/melamine latexes with varied crosslinking capability, for their potential application as waterborne crosslinkable coatings. This synthesis strategy allows the efficient incorporation of a hydrophobic crosslinker, iso‐butylated melamine (iBMF), into polymer particles, and to obtain latexes with different iBMF concentrations and acrylic polymer with varied content of hydroxylic groups (OH–). The involved crosslinking mechanisms and the physical transformations during film thermosetting of acrylic/iBMF nanocomposite are exhaustively investigated by combining thermal, spectroscopic, and thermo‐mechanical analyses. The influence of reactive groups concentration (iBMF and OH– content in the acrylic polymer) on the rate of curing, the crosslinking degree, and consequently onto the sensitive properties of cured films are discussed here. 相似文献