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991.
Fondo M García-Deibe AM Ocampo N Sanmartin J Bermejo MR 《Dalton transactions (Cambridge, England : 2003)》2004,(14):2135-2141
The heptadentate Schiff base H(3)L can react with zinc acetate to form the discrete dinuclear complex Zn(2)L(OAc)(H(2)O), 1.H(2)O. The reaction of 1.H(2)O with NMe(4)OH.5H(2)O both in air and under an argon stream has been investigated. On one hand, this reaction in air yields the tetranuclear complex (Zn(2)L)(2)(CO(3))(H(2)O)(6), 2.5H(2)O, by spontaneous absorption of adventitious carbon dioxide. This process can be reverted in an acetic acid medium, whereas the treatment of 2.5H(2)O with methanoic acid yields crystals of [Zn(2)L(HCOO)].0.5MeCN.1.25MeOH.2H(2)O, 3.0.5MeCN.1.25MeOH.2H(2)O. On the other hand, the interaction under an argon atmosphere of 1.H(2)O with NMe(4)OH.5H(2)O in methanol allows the isolation of the dinuclear complex Zn(2)L(OMe)(H(2)O)(4), 4.4H(2)O. Recrystallisations of 1.H(2)O, 2.5H(2)O and 4.4H(2)O, in different solvents, yielded single crystals of 1.MeCN.2.5H(2)O, 2.4MeOH and 4.3MeOH.H(2)O, respectively. The crystal structure of 2.4MeOH can be understood as resulting from an unusual asymmetric tetranuclear self-assembly from two dinuclear units, and shows three different geometries around the four zinc atoms. 相似文献
992.
Combinatorial development of new catalysts with phosphodiesterase and esterase activities requires specific fluorescent probes for rapid visual detection of hydrolytic activity. Such fluorescent probes have been synthesized with special attention to solubility in water and stability towards spontaneous hydrolysis at a given pH. The probes reported here include compound 5 based on a fluorescein fluorophore, compound 12 for FRET-detection of phosphodiester hydrolysis and compound 25 based on a quinolinium fluorophore. 相似文献
993.
Manuel Snchez‐Chaves Gerardo Martínez Enrique Lpez Madruga Carmen Fernndez‐Monreal 《Journal of polymer science. Part A, Polymer chemistry》2002,40(8):1192-1199
Free‐radical copolymerization of glycidyl methacrylate (GMA) with N‐vinylpyrrolidone (VPD) was carried out at 50 °C using 3.0 mol · L?1 of N,N′‐dimethylformamide solution and 9.0 · 10?3 mol · L?1 of 2,2′‐azobisisobutyronitrile as an initiator. The modification reaction of GMA‐VPD copolymers with a model bioactive carboxylic acid, 6‐methoxy‐α‐methyl‐2‐naphthaleneacetic acid (naproxen), was studied in the homogeneous phase using basic catalysts. The influence of the type of catalyst and the GMA content was evaluated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1192–1199, 2002 相似文献
994.
V. Jedináková L. Kuča M. Vojtíšková 《Journal of Radioanalytical and Nuclear Chemistry》1980,59(1):125-132
We have investigated the effect of coextraction of lanthanides and yttrium on the distribution coefficients DAm in the extraction of americium by benzyldimethyldodecylammonium nitrate (BDMLNNO3) from nitrate solutions. In the coextraction of lanthanides, the extraction of Am(NO3)3 is suppressed, which is markedly manifested in the extraction of light lanthanides (La, Ce, Pr); of the series of lanthanides their extraction is the highest. The effect of nitric acid and the possibility of separation of lanthanides and americium by the application of three-stage multiple extraction is discussed. 相似文献
995.
Gracia CA Gómez-Barreiro S González-Pérez A Nimo J Rodríguez JR 《Journal of colloid and interface science》2004,276(2):408-413
Static (SLS) and dynamic (DLS) light-scattering techniques were applied to the study of the aggregation of dodecyl- (C12DBACl), tetradecyl- (C14DBACl), and hexadecyldimethylbenzylammonium (C16DBACl) chlorides in water and in 0.01 and 0.05 m NaCl aqueous solutions at 25 degrees C. Results of SLS measurements yielded critical micelle concentration (cmc) values for aqueous and NaCl solutions. The aggregation numbers of the micelles for the homologous surfactants are low but increase with chain length and ionic strength of the solution. Various patterns of changes of the diffusion coefficient, D, as a function of chain length, molality, and with ionic strength were found for the studied surfactants. Transformations in the structure of micelles of C14DBACl in 0.01 m NaCl occur at a concentration of surfactant of about 0.01 m. Such transformations, presumably due to rodlike structure, are the more extensive the higher the concentration of NaCl. The concentration of C16DBACl in 0.05 m NaCl covers the range where already repulsive interactions between micelles occur, as judged by the strongly negative slope of the D versus molality plot. To provide additional information on the suggested transformations, complementary viscosity measurements for C14DBACl in 0.01 m of NaCl have been performed. 相似文献
996.
Hevia E Pérez J Riera V Miguel D Campomanes P Menéndez MI Sordo TL García-Granda S 《Journal of the American Chemical Society》2003,125(13):3706-3707
As depicted in the scheme, the alkylidenamido complex 1, a N-rhenaimine, reacts with ketenes to afford the beta-lactams 2-4, which possess a {Re(CO)3(bpy)} fragment as substituent at nitrogen. Clean demetalations using HOTf or MeOTf yield the free beta-lactams or N-methyl-beta-lactams along with [Re(OTf)(CO)3(bpy)]. DFT calculations help to rationalize why the reaction is faster than those of non transition metal N-substituted imines. 相似文献
997.
Erik Rakovský Ľudmila Žúrková Jaromír Marek 《Monatshefte für Chemie / Chemical Monthly》2002,133(3):277-283
Summary. Anhydrous 1,6-hexanediammonium dihydrogendecavanadate ((HdaH2)2H2V10O28, 1) was prepared by reaction of V2O5 with 1,6-hexanediamine in aqueous solution. The crystal structure of 1 was determined, and the proton positions in the H2V10O28
4− anion were calculated by the bond length/bond number method. The protons are bound to the centrosymmetrically oriented μ–OV3 groups of the decavanadate anion. Based on the analysis of IR spectra of 1 prepared from H2O and D2O, the absorption band at 871 cm−1 can be attributed to δ(V–Ob–H) vibrations.
Received August 3, 2001. Accepted (revised) October 8, 2001 相似文献
998.
Rodríguez-Cea A de la Campa MR Sanz-Medel A 《Analytical and bioanalytical chemistry》2005,381(2):388-393
Cytochromes P-450 are members of a superfamily of hemoproteins involved in the oxidative metabolism of various physiological and xenobiotic compounds in eukaryotes and prokaryotes. The multiplicity of this group of enzymes has been widely studied by chromatographic techniques, mainly high-performance liquid chromatography (HPLC). Because these enzymes are membrane-bound proteins, sample preparation for chromatographic separation of P-450 enzymes requires a solubilization step. The sample-preparation procedures are critical, because detergents affect not only the efficiency of protein solubilization but also their further chromatographic resolution. Trout liver microsomes have been taken here as a model sample to investigate iron speciation in cytochrome P-450. Trouts were treated intraperitoneally with -naphthoflavone, a potent inducer of some P-450 enzymes, and a microsomal suspension containing 7.4±0.1 nmol mL–1 P-450 enzymes was obtained by ultracentrifugation. Lubrol PX was selected as detergent for solubilization, resulting in about 90% solubilization recovery. The solubilized cytochromes P-450 were further separated by AE–FPLC, with UV detection, or coupled to ICP–MS with an octapole reaction system, ICP–(ORS)MS (monitoring Fe signals at masses 54, 56, and 57). A sampling procedure and chromatographic conditions are developed and were successfully applied to iron speciation in trout liver P-450 enzymes. ICP–(ORS)MS detection of P-450 enzymes is Fe-specific and so will give accurate information on the prosthetic group of the protein, which can constitute an advantageous alternative to classical methods for detection of these hemoproteins. 相似文献
999.
Fourier-transform infrared (FTIR) spectroscopy has been a major point of development in many wine laboratories in recent years. It enables almost instant analysis of several properties of wine, usually with very good precision and accurate results. Nevertheless, validation procedures should not be forgotten and should be fully performed. Recovery experiments were performed by spiking wine samples with different amounts of organic acids (tartaric, malic, lactic, acetic and citric—the most prominent in wines). After FTIR analysis of the total acidity and of each organic acid concentration, recoveries were calculated. For total acidity recovery results were, in general, good and very close to 100% (64–111%). On the other hand, for individual organic acid concentrations, the recovery results were lower than 100% (11–73%) for all spiking additions. These results could be explained by spectroscopic interferences between the organic acids. Because they have similar infrared spectra, it is not easy to distinguish between them and, therefore, to achieve accurate calibration. When total acidity, with a different infrared spectrum from the other abundant compounds in the wine, was taken as a single property the recovery results were acceptable. 相似文献
1000.
The model proteins cytochrome c, myoglobin, ovalbumin, and beta-lactoglobulin were investigated with regard to their adsorption properties on capillaries for electrophoresis. The model compounds were selected to cover a wide range of properties. Cytochrome c is a basic protein (isoelectric point (pI): 9.6; M(r): 11.7 kDa), beta-lactoglobulin is rather acidic (pI: 5.4, M(r): 18.4 kDa), myoglobin was chosen as a neutral reference protein (pI: 6.8-7.4, M(r): 17.8 kDa), and ovalbumin (pI: 5.1, M(r): 45.0 kDa) was selected as a relatively larger analyte. First, the pH dependence of adsorption was investigated for the bare fused silica. A clear correlation to the respective pIs was noted. For myoglobin and ovalbumin, none or negligible adsorption was found above the pI, whereas strong adsorption was noted just below this parameter. Cytochrome c and beta-lactoglobulin already showed distinct adsorption above their pIs. However, none of the proteins showed any significant adsorption more than one pH unit above the pIs. For linear polyacrylamide-coated capillaries, a decreased but not a complete lack of adsorption was observed. Here, pH-dependent adsorption was noted as well. Regeneration of the capillaries by rinsing with buffers containing 200 mM SDS was also investigated. This method was completely successful for myoglobin, but that too for only freshly-adsorbed protein. After a storage time of 24 h and due to the aging of the adsorbate, a sufficient regeneration was no longer possible. 相似文献