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排序方式: 共有159条查询结果,搜索用时 15 毫秒
71.
72.
Lima LS Weinert PL Lemos SC Sequinel R Pezza HR Pezza L 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2009,71(5):1999-2004
This paper describes an environmentally friendly method for quantitative determination of ranitidine using diffuse reflectance spectroscopy. This method is based on the reflectance measurements of the colored product produced from the spot test reaction between ranitidine and p-dimethylaminocinnamaldehyde (p-DAC), in acid medium, using filter paper as solid support. Experimental design methodologies were used to optimize the optimal conditions. All reflectance measurements were carried out at 590 nm and the linear range was from 1.42x10(-3) to 3.42x10(-2) mol L(-1), with a correlation coefficient of 0.997. The limit of detection was estimated to be 1.09x10(-3) mol L(-1) (R.S.D.=1.9%). The proposed method was successfully applied to the determination of ranitidine in commercial brands of pharmaceuticals and no interferences were observed from the common excipients in formulations. The results obtained by the proposed method were favorably compared with those obtained by an official procedure at 95% confidence level. Additionally, the method was also applied to the determination of ranitidine in human urine showing excellent recoveries (99.6-100.3%). 相似文献
73.
Weinert EE Dondi R Colloredo-Melz S Frankenfield KN Mitchell CH Freccero M Rokita SE 《Journal of the American Chemical Society》2006,128(36):11940-11947
Electronic perturbation of quinone methides (QM) greatly influences their stability and in turn alters the kinetics and product profile of QM reaction with deoxynucleosides. Consistent with the electron-deficient nature of this reactive intermediate, electron-donating substituents are stabilizing and electron-withdrawing substituents are destabilizing. For example, a dC N3-QM adduct is made stable over the course of observation (7 days) by the presence of an electron-withdrawing ester group that inhibits QM regeneration. Conversely, a related adduct with an electron-donating methyl group is very labile and regenerates its QM with a half-life of approximately 5 h. The generality of these effects is demonstrated with a series of alternative quinone methide precursors (QMP) containing a variety of substituents attached at different positions with respect to the exocyclic methylene. The rates of nucleophilic addition to substituted QMs measured by laser flash photolysis similarly span 5 orders of magnitude with electron-rich species reacting most slowly and electron-deficient species reacting most quickly. The reversibility of QM reaction can now be predictably adjusted for any desired application. 相似文献
74.
Insect‐Derived Proline‐Rich Antimicrobial Peptides Kill Bacteria by Inhibiting Bacterial Protein Translation at the 70 S Ribosome 下载免费PDF全文
Andor Krizsan Dr. Daniela Volke Stefanie Weinert Prof.Dr. Norbert Sträter Dr. Daniel Knappe Prof.Dr. Ralf Hoffmann 《Angewandte Chemie (International ed. in English)》2014,53(45):12236-12239
Proline‐rich antimicrobial peptides (PrAMPs) have been investigated and optimized by several research groups and companies as promising lead compounds to treat systemic infections caused by Gram‐negative bacteria. PrAMPs, such as apidaecins and oncocins, enter the bacteria and kill them apparently through inhibition of specific targets without a lytic effect on the membranes. Both apidaecins and oncocins were shown to bind with nanomolar dissociation constants to the 70S ribosome. In apidaecins, at least the two C‐terminal residues (Arg17 and Leu18) interact strongly with the 70S ribosome, whereas residues Lys3, Tyr6, Leu7, and Arg11 are the major interaction sites in oncocins. Oncocins inhibited protein biosynthesis very efficiently in vitro with half maximal inhibitory concentrations (IC50 values) of 150 to 240 nmol L ?1. The chaperone DnaK is most likely not the main target of PrAMPs but it binds them with lower affinity. 相似文献
75.
Christoph Helling George E. Cutsail Hanns Weinert Christoph Wlper Stephan Schulz 《Angewandte Chemie (International ed. in English)》2020,59(19):7561-7568
We report on the structures of three unprecedented heteroleptic Sb‐centered radicals [L(Cl)Ga](R)Sb. ( 2‐R , R=B[N(Dip)CH]2 2‐B , 2,6‐Mes2C6H3 2‐C , N(SiMe3)Dip 2‐N ) stabilized by one electropositive metal fragment [L(Cl)Ga] (L=HC[C(Me)N(Dip)]2, Dip=2,6‐i‐Pr2C6H3) and one bulky B‐ ( 2‐B ), C‐ ( 2‐C ), or N‐based ( 2‐N ) substituent. Compounds 2‐R are predominantly metal‐centered radicals. Their electronic properties are largely influenced by the electronic nature of the ligands R, and significant delocalization of unpaired‐spin density onto the ligands was observed in 2‐B and 2‐N . Cyclic voltammetry (CV) studies showed that 2‐B undergoes a quasi‐reversible one‐electron reduction, which was confirmed by the synthesis of [K([2.2.2]crypt)][L(Cl)GaSbB[N(Dip)CH]2] ([K([2.2.2]crypt)][ 2‐B ]) containing the stibanyl anion [ 2‐B ]?, which was shown to possess significant Sb?B multiple‐bonding character. 相似文献
76.
The results of low temperature (4.2K) stimulated emission and optical gain dynamics in highly photoexcited AlxGa1−xAs/As type I superlattices are presented. It was established that the increase of the pump quantum energy leads to the essential (more than one order) reduction of the stimulated emission intensity. The effect is explained in terms of quasiparticle system heating peculiarities in two-dimensional semiconductor structure. 相似文献
77.
78.
Lg-splines find application in many areas of mathematics, physics, and engineering. Especially in the last, there is need for recursive algorithms suitable for real-time application. In this paper we investigate a dynamical structure of the Hilbert space underlying the spline interpolation problem. We use these insights to develop a recursive algorithm for computing Lg-splines interpolating extended Hermite- Birkhoff data. We also investigate the relationship of our algorithm to a basic theorem due to Jerome and Schumaker regarding the smoothness properties of such splines and to algorithms based on their theorem. 相似文献
79.
S-sets and semigroups of quotients 总被引:1,自引:0,他引:1
H. J. Weinert 《Semigroup Forum》1980,19(1):1-78
During the last two decades, a good deal of work has been conducted on S-sets and semigroups of quotients, establishing several
concepts and results which are more or less analogous to the classicalas well as ring-theoretical ones. Clearly there are
different (and sometimes, we feel, too restrictive) assumptions in these papers, in particular on the semigroups S and on
the S-sets under consideration, and various notations need to be unified. Generalizing diverging dispositions, we try to give
a self-contained survey of the most fundamental parts (and other considerable parts) of these investigations, and add some
new results. A forthcoming paper will deal with S-semimodules over semirings S, including some relationships with rings and
modules. 相似文献
80.
A.J. Freeman M. Weinert J.P. Desclaux J.V. Mallow 《Journal of magnetism and magnetic materials》1980,22(1):L1-L5
Muon-nuclear-hyperfine anomalies are determined from Breit interaction calculations based on unrestricted Dirac-Fock solutions which explicitly include all electrons and the negative muon. We obtain anomalies of a few (3) percent, which are much larger than corresponding Bohr-Weisskopf electron-nuclear anomalies, but are much smaller than the giant, ≈(36 ± 5)%, anomaly reported by Yamazaki et al. for μ-Pd+ vs. Rh. We suggest the possibility that interstitial μ-Pd+ was observed and that the small anomaly for substitutional μ-Pd+ may also be seen at higher temperatures. 相似文献