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31.
[reaction: see text] Tetrasubstituted pyrazines containing two phosphonate groups 2 in positions 2 and 5 and trisubstituted pyrazines containing a phosphonate 5 or a phosphine oxide group 7 in position 2 are obtained by thermal treatment of 2H-azirine-2-phosphonates 1 and -phosphine oxides 6. These pyrazines can also be prepared from beta-ketoxime tosylates 9 and 10 or from oxime derived from phosphine oxide 11. 相似文献
32.
Belén Abarca Rafael Ballesteros Gurnos Jones 《Journal of heterocyclic chemistry》1984,21(6):1585-1588
A synthesis of the methylthieno[3,2-c]cyclohepteno[b]indole 7 from 2-methylthieno[3,2-b]cycloheptanone 3 is described. Unsuccessful attempts to prepare the isomeric thienocycloheptenoindole system present in formula 2 , from the dihydrobenzothiophenone 8 , and from derivatives of 5-(2-thienyl)-4-oxopentanoic acid, 17 and 18 , and from N-benzylcycloheptindol-1-one 22 were unsuccessful. The preparation of 4,5-dihydro-2-phenyl-1-thienylmethyl-3H-pyridazin-3-one 20 and of the 5-aminopyrazole 21 are reported. 相似文献
33.
Rafael Fogel Rafaela Rodrigues Garcia Rebeca da Silva Oliveira Denise Neves Menchero Palacio Luciana da Silva Madeira Nei Pereira Jr. 《Applied biochemistry and biotechnology》2005,122(1-3):741-752
The dilute-acid hydrolysis of sugarcane bagasse was optimized using a statistical experimental design resulting in hydrolysates
containing 57.25 g/L of xylose, which were fermented with a high inoculum concentration (10 g/L of the yeast Candida guilliermondii IM/UFRJ 50088). The addition of urea reduced the time of conversion (t
C) to 75 h (without nitrogen source addition t
C>127 h), and, consequently, improving the rates of xylitol bioproduction. Fermentator experiments, using the optimized conditions,
resulted in enhanced conversion rates, reducing t
C to 30 h. The stability of the yeast in the hydrolysate was also verified in a 480-h cultivation. 相似文献
34.
Manuel Cano Beatriz Palenzuela J. Luis Ávila Rafael Rodríguez‐Amaro 《Electroanalysis》2007,19(9):973-977
A PVC/TTF‐TCNQ composite electrode has been employed as detector in a flow injection system. The proposed method allows the simultaneous detection of ascorbic acid (AA) and uric acid (UA) in mixtures by using a FIA system in a simple manner, without pre‐treatment or modified electrode. This method is based on the amperometric determination of (a) ascorbic acid at 0.15 V and (b) both analytes at 0.35 V, being the response linear in the range 1×10?2–4×10?4 M for both analytes with detection limits (S/N=3) of 1.2×10?4 M and 8.1×10?5 M for AA and UA, respectively. 相似文献
35.
Bustamante JJ Garcia M Gonzalez L Garcia J Flores R Aguilar RM Trevino A Benavides L Martinez AO Haro LS 《Electrophoresis》2005,26(23):4389-4395
A method for separating proteins with a molecular mass difference of 2 kDa using SDS-PAGE under nonreducing conditions is presented. A sample mixture containing several human growth hormone (hGH) isoforms was initially separated on a weak anion-exchange column. Fractions rich in 24 kDa hGH as determined by analytical SDS-PAGE were pooled and further separated by cation-exchange chromatography. The fractions pooled from the cation-exchange chromatography contained two hGH isoforms with a 2 kDa molecular mass difference according to SDS-PAGE analysis, 22 and 24 kDa hGH. The 22 and 24 kDa hGH were separated using continuous-elution preparative double-inverted gradient PAGE (PDG-PAGE) under nonreducing conditions. The preparative electrophoresis gel was composed of three stacked tubular polyacrylamide matrices, a 4% stacking gel, a 13-18% linear gradient gel, and a 15-10% linear inverted gradient gel. Fractions containing purified 24 kDa hGH were pooled and Western blot analysis displayed immunoreactivity to antihGH antibodies. PDG-PAGE provides researchers with an electrophoretic technique to preparatively purify proteins under nonreducing conditions with molecular mass differences of 2 kDa. 相似文献
36.
Raymundo Cea-Olivares Jesús Wingartz Jorge Cárdenas Jesus Valdés-Martínez Thelma Alvarado 《Transition Metal Chemistry》1991,16(1):62-64
Summary The interaction of non-anhydrous solutions of the ligand 1,3-bis-(2-hydroxyphenyl)-1,3-propanedione (bhppH3) with hydrated rare earth chlorides resulted in the formation of anhydrous, non-solvated, complexes M(bhppH2)3 (M=Y, La, Nd, Pr, Sm or Yb). The complexes have been characterized by elemental analysis, t.g., i.r. and1H n.m.r. spectroscopy. The evidence suggests that the coordination is through the -diketone site. 相似文献
37.
Emmanuel Blas Patricio-Rangel Margarita Tlahuextl Hugo Tlahuext Antonio Rafael Tapia-Benavides 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(4):322-327
The synthesis and characterization of two new 1,3,5‐triazines containing 2‐(aminomethyl)‐1H‐benzimidazole hydrochloride as a substituent are reported, namely, 2‐{[(4,6‐dichloro‐1,3,5‐triazin‐2‐yl)amino]methyl}‐1H‐benzimidazol‐3‐ium chloride, C11H9Cl2N6+·Cl? ( 1 ), and bis(2,2′‐{[(6‐chloro‐1,3,5‐triazine‐2,4‐diyl)bis(azanediyl)]bis(methylene)}bis(1H‐benzimidazol‐3‐ium)) tetrachloride heptahydrate, 2C19H18ClN92+·4Cl?·7H2O ( 2 ). Both salts were characterized using single‐crystal X‐ray diffraction analysis and IR spectroscopy. Moreover, the NMR (1H and 13C) spectra of 1 were obtained. Salts 1 and 2 have triclinic symmetry (space group P) and their supramolecular structures are stabilized by hydrogen bonding and offset π–π interactions. In hydrated salt 2 , the noncovalent interactions yield pseudo‐nanotubes filled with chloride anions and water molecules, which were modelled in the refinement with substitutional and positional disorder. 相似文献
38.
Barro R Ares S Garcia-Jares C Llompart M Cela R 《Analytical and bioanalytical chemistry》2005,381(1):255-260
A combination of sorbent enrichment and ultrasound-assisted solvent extraction has been used to determine polychlorinated biphenyls in air. Analytes were sampled by pumping a known volume of air through a porous polymer (Tenax TA). The enriched adsorbent was transferred into a glass vial, and ultrasound-assisted extraction of the analytes was then performed in n-hexane. Quantification was carried out by using gas chromatography coupled to tandem mass spectrometry. Breakthrough volume of the sampling step was studied, indicating that 10 m3 of air could be processed without losses of the most volatile compounds. Good recoveries (75–96%) were obtained, and limits of detection at the sub ng m–3 were achieved for all the analytes. The proposed method is very simple and fast, avoiding the use of large solvent volumes and time-consuming preconcentration steps. 相似文献
39.
Rafael Mayorga-Gonzlez Miguel Rivera-Torrente Nikolaos Nikolopoulos Koen W. Bossers Roozbeh Valadian Joaquín Yus Beatriz Seoane Bert M. Weckhuysen Florian Meirer 《Chemical science》2021,12(24):8458
Metal–Organic Frameworks (MOFs) have the potential to change the landscape of molecular separations in chemical processes owing to their ability of selectively binding molecules. Their molecular sorting properties generally rely on the micro- and meso-pore structure, as well as on the presence of coordinatively unsaturated sites that interact with the different chemical species present in the feed. In this work, we show a first-of-its-kind tomographic imaging of the crystal morphology of a metal–organic framework by means of transmission X-ray microscopy (TXM), including a detailed data reconstruction and processing approach. Corroboration with Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) images shows the potential of this strategy for further (non-destructively) assessing the inner architecture of MOF crystals. By doing this, we have unraveled the presence of large voids in the internal structure of a MIL-47(V) crystal, which are typically thought of as rather homogeneous lattices. This challenges the established opinion that hydrothermal syntheses yield relatively defect-free material and sheds further light on the internal morphology of crystals.TXM-tomography unraveled large macropore defects within a MIL-47(V) MOF crystal. These pores do not seem to be well connected and they show a preferential orientation. 相似文献
40.
Vladimir A Escobar Barrios Alain Petit Rafael Herrera Nájera 《European Polymer Journal》2003,39(6):1151-1167
Three types of butadiene-styrene copolymers, diblock, triblock and random, were partially hydrogenated in their elastomeric units in order to determine the influence of hydrogenation extent on their thermal properties. The hydrogenation reactions were carried out using a Ziegler-Natta type catalyst and the extent of hydrogenation was evaluated by FTIR spectroscopic technique. The percentage of crystallinity was determined by differential scanning calorimetry (DSC), considering the low density polyethylene (LDPE) as reference since the saturation of elastomeric units with low content of 1,2-vinyl bonds gives a structure which resembles to LDPE, thus semi-crystalline polymers were obtained. On the other hand, the glass transition temperature (Tg) for the hydrogenated and non-hydrogenated copolymers as well as their heat of fusion, were also determined by DSC. An equation to evaluate the Tg of partially hydrogenated random copolymers is proposed considering both the saturated and unsaturated fractions. The thermo-oxidative behaviour of certain hydrogenated and non-hydrogenated copolymers was evaluated by thermogravimetric analyses (TGA). The results obtained by TGA suggest that a minimum saturation level is necessary in order to improve the thermo-oxidative resistance of the polymers. 相似文献