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11.
Chahal Parmimder S. Chahal Devinder S. Lê George B. B. 《Applied biochemistry and biotechnology》1996,57(1):433-442
Applied Biochemistry and Biotechnology - It is an accepted fact that ethanol production from lignocellulosic materials is not economical as yet because of the high cost of cellulase production. To... 相似文献
12.
Ronaldo Santos da Silva Maria Inês Basso Bernardi Antonio Carlos Hernandes 《Journal of Sol-Gel Science and Technology》2007,42(2):173-179
In this work, we have studied the influence of the pH on the synthesis and structural properties of the Ba0.77Ca0.23TiO3 nanopowders synthesized by a modified polymeric precursor method, in order to achieve non-agglomerated powders. Synthesis,
morphology, thermal reactions, crystallite and average particle size of the synthesized powders were investigated through
thermal analysis (DTA/TG), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and Infrared spectroscopy.
In summary, Ba0.77Ca0.23TiO3 nanopowders were synthesized for the first time at a relative low temperature (500 °C). It was also found that the alkalinity
and acidity of the solution presented a great influence on the powder properties. The best results were obtained from solutions
with pH = 8.5 and 11 whose nanopowders presented weakly agglomerate, with homogeneous particle size and a narrow size distribution
(30–40 nm). This behavior could be explained based on the FT-IR results in which it was possible to see the increased of the
chelation in higher pHs. 相似文献
13.
Marta M.?Conceio V. J.?Fernandes Jr. F. S. M.?Sinfrnio J. C. O.?Santos M. C. D.?Silva V. M.?Fonseca A. G.?Souza 《Journal of Thermal Analysis and Calorimetry》2005,79(2):263-266
Summary Sulfonylureas are widely used for the treatment of non-insulin dependent diabetes mellitus. Glibenclamide belongs to the group of substituted arylsulfonylureas. Many representative of this group shows polymorphism. The purpose of this work was to investigate the thermal behaviour and compatibility between glibenclamide and some excipients using thermoanalytical techniques (TG-DTG/DSC). The thermal and isothermal kinetics data showed incompatibility between glibenclamide and magnesium stearate. 相似文献
14.
Antonilêni F. D. Medeiros Ana Flávia O. Santos F. S. de Souza I. D. B. Júnior J. Valdilânio J. V. V. Procópio D. P. de Santana R. O. Macêdo 《Journal of Thermal Analysis and Calorimetry》2007,89(3):775-781
Compatibility studies between active drugs and excipients are substantial in the pharmaceutical technology. The objective
of the present work was to develop pre-formulated mixtures of metronidazole (MT) obtained by spray drying (SPDR) and their
thermoanalytical characterization. Dynamic and isothermal TG, conventional DSC and DSC coupled to a photovisual system were
used. DSC experiments with both techniques confirmed the homogeneity of the conventional and pre-formulated mixtures. The
TG data made possible the comparison the thermal stability of the different mixtures. Similar thermal stabilities were found
of the conventional and pre-formulated mixtures, with slower particles sizes of MT. 相似文献
15.
The palladium catalysed condensation of Grignard reagents with silyl derivatives of 8-bromopurine nucleosides and 8-bromoadenosine-3′,5′ cyclic monophosphate is a convenient method for the preparation of free 8-alkylpurine nucleosides and 8-alkyladenosine-3′,5′ cyclic monophosphate. 相似文献
16.
Larsen BR Astorga-Llorens C Florêncio MH Bettencourt AM 《Journal of chromatography. A》2001,926(1):167-174
With its detection limit well below 30 pg microl(-1) LC-MS-MS has become a sensitive and thus popular analytical technique for organoarsenical compounds. Collision induced dissociation (CID) is a valuable tool for speciation and facilitates a positive identification of the species detected. However, it is not straightforward to understand the fragmentation pathways of organoarsenical compounds when only CID-MS-MS data is available. In the present paper we have investigated multiple mass spectrometry (MSn, n=1, 2, 3, 4, 5, 6) with electrospray CID fragmentation for a number of organoarsenical compounds likely to occur in the environment. The investigated compounds were tetramethylarsonium, trimethylarsinoxide, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, arsenocholine, and dimethylarsinoylethanol. By CID of (protonated) organoarsenical cations mostly even-electron fragments are produced after neutral loss processes such as elimination of H2, H2O, CH4, C2H2, C2H4, C2H6, HCHO, CH3OH, C2H5OH, C2H4O, and CH2CO. However, abundant odd-electron fragments are also formed after elimination of radical species. Evidence for reduction of As(V) to As(III) as a driving force in the odd-electron ion formation is obtained. 相似文献
17.
Joaquim Branco Catarina de Jesus Dias Antnio Pereira Gonalves Teresa Almeida Gasche Antnio Pires de Matos 《Thermochimica Acta》2004,420(1-2):169-173
In our laboratories we have been studying the synthesis and reactivity of binary actinide and lanthanide intermetallic compounds. In this work, the air-oxidation of ThCu2 and AnNi2 (An = Th, U) was followed by thermogravimetry (TG) and the products were characterized by X-ray powder diffraction (XRD). The heterobimetallic oxides obtained are described by the formulas 2MO·ThO2 (M = Cu, Ni) and 2NiO·UO3. The thermogravimetric analysis under hydrogen of these heterobimetallic oxides show one mass loss for 2MO·ThO2 and two mass losses for 2NiO·UO3 over a wide range of temperature (293–1273 K). The characterization by XRD shows that the reduction products are 2M·ThO2 (M = Cu, Ni) and 2Ni·UO2, with all the actinides in the 4+ oxidation state. The actinide heterobimetallic oxides were described as copper or nickel supported catalysts. 相似文献
18.
Iványi T Vander Heyden Y Visky D Baten P De Beer J Lázár I Massart DL Roets E Hoogmartens J 《Journal of chromatography. A》2002,954(1-2):99-114
This paper focuses on the classification or differentiation of RP-HPLC columns based on measured chromatographic properties. A chemometric study has been conducted on a published data set consisting of 85 RP-HPLC columns and on a data set consisting of 47 self-tested columns. Principal component analysis enables determination of the number of parameters necessary for a rational differentiation. The results show that reducing the number of parameters for such differentiation still allows classification of the columns just as a higher number did. It is shown that three test parameters produce a classification similar to that obtained with five parameters. 相似文献
19.
Roman F. Nalewajski Sebastito J. Formosinho Ant
nio J.C. Varandas Janusz Mrozek 《International journal of quantum chemistry》1994,52(5):1153-1176
The recently introduced set of the quadratic, two-electron covalent and ionic valence indices is used to investigate the bond-breaking–bond-forming (BB-BF ) process in an atom exchange reaction between H2 and X (X = H, F—I) as well as in the O2—H system. Valence changes accompanying selected charge reorganizations are examined within the three-orbital model and valence diagrams for symmetric transition states (TS s) are given. The UHF valence data for Li2O and CO2 and the H—H—X, O—O—H, and O—H—O (ABC) TS s (collinear and angular) are reported and compared to valence data in the separated fragments limits (SFL ), AB and BC. The overall valence, ν(ABC), and the total (ionic plus covalent) diatomic valences, νAB and νBC, are used as measures of the overall bond-order in a concerted BB–BF reaction, to test the postulate of the bond-energy–bond-order (BEBO ) model. In collinear TS s of H2X, ν ? ?1, i.e., one bonding electron pari, is found to be roughly preserved, whereas in the angular H2X and in collinear O—H—O TS s, the effect of increased valence at the saddle-point is observed, relative to that of diatomic fragments (reactiants or products). For the angular O—O—H TS , a similar increase in | ν (ABC)| relative to both O2 and OH SFL s is detected; smaller changes relative to the O2 data are found in the collinear TS . This observation is in agreement with earlier predictions from the intersecting-state model. The relative diatomic valences, ν/ν and ν/ν, are shown to conserve the overall relative bond multiplicity around 1 in both collinear and angular TS s of the H2—X systems. © 1994 John Wiley & Sons, Inc. 相似文献
20.
Jo?o L M Santos Arnaud Clausse José L F C Lima M L M F S Saraiva António O S Rangel 《Analytical sciences》2005,21(4):461-464
A new flow methodology exploiting the multi-pumping approach was developed for the spectrophotometric determination of ambroxol hydrochloride in pharmaceutical preparations. The flow manifold was implemented by using, exclusively, multiple solenoid-actuated micro-pumps, which acted simultaneously as sample insertion, solutions propelling and reagents commutation units. Linear calibration plots were obtained over an ambroxol concentration ranging from 10 to 200 mg l(-1) (r.s.d. < 0.5%, n = 15) and a sampling rate of about 60 samples per hour (flow rate = 1.92 ml min(-1), sample volume = 80 microl). 相似文献