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991.
Ellis WW Miedaner A Curtis CJ Gibson DH DuBois DL 《Journal of the American Chemical Society》2002,124(9):1926-1932
The hydride complex [Pt(dmpe)2H]+ (dmpe = 1,2-bis(dimethylphosphino)ethane) reversibly transfers H- to the rhenium carbonyl complex [CpRe(PMe3)(NO)(CO)]+, giving the formyl CpRe(PMe3)(NO)(CHO). From the equilibrium constant for the hydride transfer (16.2), the DeltaGdegrees for the reaction was determined (-1.6 kcal/mol), as was the hydride-donating ability of the formyl (44.1 kcal/mol). The hydride-donating ability, DeltaGdegrees(H-), is defined as the energy required to release the hydride ion into solution by the formyl complex [i.e. M(CHO) right arrow M(CO)+ + H-]. Subsequently, the hydride-donating ability of a series of formyl complexes was determined, ranging from 44 to 55 kcal/mol. With use of this information, two rhenium carbonyl complexes, [CpRe(NO)(CO)2]+ and [Cp*Re(NO)(CO)2]+, were hydrogenated to formyls, employing [Pt(dmpp)2]2+ and Proton-Sponge. Finally, the E(1/2)(I/0) values for five rhenium carbonyl complexes were measured by cyclic voltammetry. Combined with the known DeltaGdegrees(H-) values for the complexes, the hydrogen atom donating abilities could be determined. These values were all found to be approximately 50 kcal/mol. 相似文献
992.
993.
Using semiempirical and ab initio procedures, the most stable conformations of meso- and rac-bioxirane and of some substituted 1,2:3,4-diepoxides were calculated. For threo-diepoxides (having the same relative configurations as rac-bioxirane, 3 ), two stable conformations with CCCC dihedral angles of ca. 90 and ca. 270° were found. For erythro-diepoxides (derivatives of meso-bioxirane, 4 ) the calculations suggest three preferred conformations with corresponding dihedral CCCC angles of ca. 90°, ca. 180°, and ca. 270°. The calculations are in fair agreement with the experimental data available for the unsubstituted compounds 3 and 4 . 相似文献
994.
Renee J. Soukup-Hein Jeff Schneiderheinze Paul Mehelic Daniel W. Armstrong 《Chromatographia》2007,66(7-8):461-468
Previous work on the LC separation of peptides had shown that macrocyclic glycopeptide stationary phases to be selective for
peptides of five to thirteen amino acids in length. In this work, the selectivity of the teicoplanin stationary phase is compared
to that of a C18 stationary phase for seven diastereomeric enkephalin peptides. The teicoplanin stationary phase separated
all seven diastereomeric enkephalin peptides in a single chromatographic run. The insertion of d-amino acids into the primary enkephalin sequence produced areas of hydrophobicity that influenced retention order on the
C18 stationary phase. However, analogous trends are not observed on the teicoplanin stationary phase, which is more polar
and structurally diverse. Optimization of the mobile phase and the use of a step-gradient for the enkephalin separation on
the teicoplanin stationary phase is discussed. Also, the selectivity of macrocyclic glycopeptide stationary phases for peptides
of 14, 28, 30, and 36 amino acids also is investigated and compared to separation on a C18 stationary phase. A method for
eluting peptides with multiple basic amino acids, which tend to be strongly retained on the macrocyclic glycopeptide stationary
phases, is presented. 相似文献
995.
A dynamics study [cross section and microscopic mechanism versus collision energy (E(T))] of the reaction O+ + H2 --> OH+ + H, which plays an important role in Earth's ionosphere and interstellar chemistry, was conducted using the quasiclassical trajectory method, employing an analytical potential energy surface (PES) recently derived by our group [R. Martinez et al., J. Chem. Phys. 120, 4705 (2004)]. Experimental excitation functions for the title reaction, as well as its isotopic variants with D2 and HD, were near-quantitatively reproduced in the calculations in the very broad collision energy range explored (E(T) = 0.01-6.0 eV). Intramolecular and intermolecular isotopic effects were also examined, yielding data in good agreement with experimental results. The reaction occurs via two microscopic mechanisms (direct and nondirect abstraction). The results were satisfactorily interpreted based on the reaction probability and the maximum impact parameter dependences with E(T), and considering the influence of the collinear [OHH]+ absolute minimum of the PES on the evolution from reactants to products. The agreement between theory and experiment suggests that the reaction mainly occurs through the lowest energy PES and nonadiabatic processes are not very important in the wide collision energy range analyzed. Hence, the PES used to describe this reaction is suitable for both kinetics and dynamics studies. 相似文献
996.
Five new CuII complexes of general formula [Cu2(Rdtc)tpmc](ClO4)3, (1)–(5), where tpmc and Rdtc
– refer to N,N,N,N-tetrakis(2-pyridylmethyl)-1,4,8,11-teraazacyclotetradecane and piperidine- (Pipdtc), 4-morpholine- (Morphdtc), 4-thiomorpholine- (Timdtc), piperazine- (Pzdtc) or N-methylpiperazine- (N-Mepzdtc) dithiocarbamates, respectively, have been prepared. Elemental analyses, conductometric and magnetic measurements, u.v./vis, i.r., e.p.r. and mass spectroscopy have been employed to characterize them. The complexes adopt an exo coordination of CuII ions and tpmc. The dithiocarbamate ion joins both the sulphur and the copper atoms acting as a bridging ligand The presence of different heteroatoms in the piperidine ring influences the (C=N) and (C=S) vibrations which decrease in the order of the complexes: Pipdtc>N-Mepipdtc>Pzdtc>Morphdtc>Timdtc ligands. Attention has been paid to the detailed mechanism of the mass spectral fragmentation of the complexes. The g
eff factors of the complexes have been also estimated by e.p.r. spectra. Finally, the complexes obtained demonstrate microbiologycal activity against some bacteria. 相似文献
997.
Jorge Casas-Sanchez M. Asuncion Alsina Mathias K. Herrlein Concepció Mestres 《Colloid and polymer science》2007,285(12):1351-1360
Oleuropein, a secoiridoid glycoside extracted from the olive tree, Olea europaea L., has been described as showing antibacterial properties. However, the exact mechanism of these antimicrobial properties
is not yet well understood. In the present study, we have studied the interaction of oleuropein with phosphatidylglycerol
(PG) as a model membrane for Staphylococcus aureus (S. aureus) (Gram-positive bacteria) and phosphatidylethanolamine and Escherichia coli (E. coli) lipid extract as a model membrane for E. coli (Gram-negative bacteria). The study has been carried out using monolayers as model membranes and using kinetics at constant
area and compression isotherms with Brewster angle microscopy (BAM) observations. The results show that oleuropein interacts
in higher extent with PG monolayers, which is related with its stronger antibacterial effect against Gram-positive bacteria.
The effects on the membrane are probably produced at the cell surface because oleuropein did not form stable mixed monolayers
with the lipids assayed at the air/water interface. 相似文献
998.
A closed‐form expression has been derived to obtain the N‐dimensional rectangular atomic wave functions. The wave functions can be obtained straightforwardly with the knowledge of the angular momentum quantum numbers and the dimension and there is no need to employ recursive methods as in previous works. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 263–274, 2002 相似文献
999.
Aydin Tavman Naz M. Agh-Atabay Sadik Guner Fahrettin Gucin Basaran Dulger 《Transition Metal Chemistry》2007,32(2):172-179
2-(5-H/Me/Cl-1H-benzimidazol-2-yl)-phenol ligands form 1:1 electrolytes, 5-coordinate monometallic complexes with iron(III) nitrate. The geometry of the [Fe(L)(OH)(H2O)2](NO3) complexes was derived from theoretical calculation in DGauss/DFT level (DZVP basis set) on CACHE. In all of the complexes
the ligands are bidentate, via one imine nitrogen atom and phenolate oxygen atom. The coordination is completed with a hydroxide ion, and two water molecules,
adopting a distorted square pyramidal geometry. The structures of the compounds were confirmed on the basis of elemental analysis,
molar conductivity, magnetic moment, FT-Raman, FT-IR (mid-IR, far-IR), EPR and u.v.–vis. The antimicrobial activities of the
free ligands, their hydrochloride salts, and the complexes were evaluated using the disk diffusion method in dimethyl sulfoxide
(DMSO) as well as the minimal inhibitory concentration (MIC) dilution method, against nine bacteria and the results are compared
with several known antibiotic agents. Antifungal activities were reported for Candida albicans, Kluyveromyces fragilis, Rhodotorula rubra, Debaryomyces hansenii, Hanseniaspora guilliermondii, and the results were referenced against nystatin, ketaconazole, and clotrimazole antifungal agents. In most cases, the compounds
tested showed broad-spectrum (Gram+ & Gram− bacteria) activities that were either more active or as potent as the references. 相似文献
1000.
Vytautas Getautis Giedre Sinkeviciute Albina Stanisauskaite 《Monatshefte für Chemie / Chemical Monthly》2007,138(5):477-480
Summary. A synthesis of 1,2-diphenylpyrazolidin-4-ol via direct heterocyclization of 1,2-diphenylhydrazine with 1-chloro-2,3-epoxypropane, its O-epoxypropyl-, O-ethyl-, and O-benzylderivatives are described. Novel hydrazone derivatives with pyrazolidine units were also synthesized. The compounds
were characterized by spectroscopic methods as well as elemental analyses. 相似文献