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11.
Grotjahn DB Van S Combs D Lev DA Schneider C Incarvito CD Lam KC Rossi G Rheingold AL Rideout M Meyer C Hernandez G Mejorado L 《Inorganic chemistry》2003,42(10):3347-3355
Inter- and intramolecular hydrogen bonding of an N-H group in pyrazole complexes was studied using ligands with two different groups at pyrazole C-3 and C-5. At C-5, groups such as methyl, i-propyl, phenyl, or tert-butyl were present. At C-3, side chains L-CH(2)- and L-CH(2)CH(2)- (L = thioether or phosphine) ensured formation of chelates to a cis-dichloropalladium(II) fragment through side-chain atom L and the pyrazole nitrogen closest to the side chain. The significance of the ligands is that by placing a ligating side chain on a ring carbon (C-3), rather than on a ring nitrogen, the ring nitrogen not bound to the metal and its attached proton are available for hydrogen bonding. As desired, seven chelate complexes examined by X-ray diffraction all showed intramolecular hydrogen bonding between the pyrazole N-H and a chloride ligand in the cis position. In addition, however, intermolecular hydrogen bonding could be controlled by the substituent at C-5: complexes with either a methyl at C-5 or no substituent there showed significant intermolecular hydrogen bonding interactions, which were completely avoided by placing a tert-butyl group at C-5. The acidity of two complexes in acetonitrile solutions was estimated to be closer to that of pyridinium ion than those of imidazolium or triethylammonium ions. 相似文献
12.
13.
Urones JG Sexmero MJ Hernandez FA Basabe AB Diez D Marcos IS 《Natural product letters》2001,15(6):387-391
Two new diterpenic acids with an ent-halimane skeleton have been isolated from the aerial parts of Halimium viscosum (Villarino de los Aires chemotype) and separated as methyl esters. These diterpenes were 13-oxo-14, 15-dinor-1(10),11E-ent-halimadien-18-oic acid and 15-hydroxy-1(10),13Z-ent-halimadien-18-oic acid. 相似文献
14.
L. M. Razo S. Solis M. Asomoza A. Hernandez 《Journal of Thermal Analysis and Calorimetry》1995,45(6):1323-1330
The combination of a DuPont 942 thermomechanical analyzer with a CBM computer allowed the establishment of thermodynamic properties such as isobars, isobaric volumetric expansions, isothermal compressibilities, and the equation of stateV=V(p, T) in a limited region ofpVT space. 相似文献
15.
Y. BallesterosM.J. Gonzalez de la Huebra M.C. QuintanaP. Hernandez L. Hernandez 《Microchemical Journal》2003,74(2):193-202
The electrochemical behaviour of kinetin (6-furfurylaminopurine) on a carbon paste modified with OV-17 silicone electrode, is studied. The determination of kinetin is possible working in square wave voltammetric techniques, reaching limits of determination of 38.7 ng ml−1. The proposed method was successfully applied to determine the cytokinin in extracts of apples (previously spiked with kinetin) and the obtained results were in accordance with the results obtained with HPLC-UV. 相似文献
16.
Rodrigues JA Abramovitch RA de Sousa JD Leiva GC 《The Journal of organic chemistry》2004,69(9):2920-2928
In preliminary communications, we reported the diastereoselective synthesis of cularine and sarcocapnine via the intramolecular ring closure of nitrenium and oxenium ions, a new highly diastereoselective reductive methylation with (+)-8-phenylmenthyl chloroacetate followed by reduction with sodium borohydride, and a facile entry to the isoquinoline precursors by aza-Wittig electrocyclic ring closure. We now report the full details of the syntheses of (+)-O-demethylcularine, (+)-cularine, (+)-sarcocapnidine, (+)-sarcocapnine, and (+)-crassifoline and describe different methods of synthesis of their precursors. 相似文献
17.
L. Hernandez M. Rudolph R. Lammertink J. Kornfield C. Zurita F. A. Gomez 《Chromatographia》2007,65(5-6):299-303
Vancomycin (Van) from Streptomyces orientalis has been derivatized with polyethylene glycol [PEG; PEG-550 (1), 750 (2), 1,100 (3), 2,000 (4), 5,000 (5), and 8,000 (6) g mol−1] at the N-terminus of the glycopeptide backbone and their binding to d-Ala-d-Ala terminus peptides assessed using affinity capillary electrophoresis (ACE). Utilizing ACE, a plug of Van-PEG and non-interacting
standards are injected and electrophoresed. Analysis of the change in the relative migration time ratio of the Van-PEG species,
relative to the non-interacting standards, as a function of the concentration of peptide, yields a value for the binding constant
(K
b). Values of K
b for N-acetyl-d-Ala-d-Ala, 7 to the Van-PEG derivatives are weaker than those for N
α,N
ε-diacetyl-Lys-d-Ala-d-Ala, 8 (for example, values of K
b for 7-1 and 8-1 are 1.8 and 47.7 × 103 M−1, respectively). These results demonstrate that derivatization of Van with PEG has little effect on the affinity of d-Ala-d-Ala peptide ligands to it. The findings further prove the versatility of ACE and its ability to estimate binding parameters
of ligands to antibiotics. 相似文献
18.
Delgado Zamarreño MM Sanchez Perez A Sanchez Rodriguez M Gomez Perez MC Hernandez Mendez J 《Talanta》1996,43(9):1555-1563
A method employing HPLC with electrochemical detection for the rapid and simultaneous determination of vitamins A, D(3) and E is described. The method uses a C-18 reverse phase column and 2.5 mM HAcO-NaAcO in methanol-water (99:1, v/v) solution as the mobile phase. The compounds are quantified using amperometric detection with a glassy carbon electrode at a potential of + 1300 mV (vs. Ag/AgCl) and the results are compared with those obtained using UV detection at a wavelength of 280 nm. The method was successfully applied to the analysis of vitamins A, D(3) and E in yogurt samples. After saponification, fat-soluble vitamins were extracted and the methanolic solution of the extracts was injected directly into the chromatographic system, avoiding the clean-up step which is necessary when no electrochemical detection is used. Good recovery percentages were obtained. 相似文献
19.
J. Hernandez Mendez A. Sanchez Perez F. Lucena Conde 《Journal of Electroanalytical Chemistry》1975,66(1):53-65
The anodic oxidation of a dropping copper amalgam electrode in presence of dilute solutions of glycine in 0.50 M NaClO4 has been studied. An anodic wave at ?0.28V (SCE) is observed, yielded by diffusion of glycinate anion in the solution towards the electrode surface. The wave-heights increase with the glycinate concentration (function of glycine concentration and pH value) until the anodic oxidation is controlled by the metal diffusion into mercury. The effect of pH is interpreted by attributing it to the depolarizer effects at glycinate anion even though the zwitterion is present in much larger concentrations. The applicability of anodic oxidation of a dropping copper amalgam electrode in the determination of glycine in the range of concentrations 10?4–10?2M with a rigorous control of pH (8.0<pH<10.5) is shown. The standard deviation of the proposed method is 4.1% and the minimum concentration determinable is in the 1×10?4M range. 相似文献
20.
Osuna RM Ortiz RP Ruiz Delgado MC Sakamoto Y Suzuki T Hernandez V López Navarrete JT 《The journal of physical chemistry. B》2005,109(44):20737-20745
In this Article, we report on the synthesis and full characterization of three perfluorinated oligothiophenes, ranging in length from the trimer to the pentamer (PF-nT, with n = 3, 4, or 5). The differential pulse voltammetry (DPV) analysis of the compounds showed that they can be both oxidized and reduced (i.e., they display a dual or amphoteric electrochemical behavior), with the reduction peaks positively shifted relative to those of the corresponding unsubstituted oligothiophenes. The electrochemically determined energy gaps are in agreement with those measured from the UV-vis-NIR absorption spectra in solution. The conjugational properties have been investigated by means of FT-Raman spectroscopy, both as pure solids and as dilute solutes in CH(2)Cl(2), revealing that: (i) pi-conjugation does not still reach saturation with chain length for the longest oligomer, and (ii) conformational distortions from a nearly coplanar arrangement of the successive thiophene units upon solution are not too large. DFT and TDDFT quantum chemical calculations have been performed, at the B3LYP/6-31G level, to assess information about the optimized molecular structure, equilibrium atomic charges distribution, energies and topologies of the frontier molecular orbitals (MO) around the gap, vibrational normal modes associated with the most outstanding Raman scatterings, and vertical one-electron excitations that give rise to the main optical absorptions. 相似文献