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121.
Ana C. D. Medeiros Lidiane P. Correia Mônica O. da S. Simões R. O. Macêdo 《Journal of Thermal Analysis and Calorimetry》2007,88(2):311-315
A number of disintegrants
are available on the market. They improve tablets’ disintegration. The
objective of this work is the comparison of the technological quality parameters
of disintegrants using different analytical techniques. Three batches of disintegrants
and their binary mixtures (water:disintegrants) were investigated. Cooling
experiments were used from –30 up to 200°C. The data obtained showed
calorimetric differences between the samples. In the binary mixtures water
showed different crystallization behaviour from the one found in the literature.
According to the results DSC technique helped the quality control of different
disintegrants. 相似文献
122.
Baeten V von Holst C Garrido A Vancutsem J Michotte Renier A Dardenne P 《Analytical and bioanalytical chemistry》2005,382(1):149-157
In this paper we present an alternative method for detection of meat and bone meal (MBM) in feedstuffs by near-infrared microscopic (NIRM) analysis of the particles in the sediment fraction (dense fraction (d >1.62) from dichloroethylene) of compound feeds. To apply this method the particles of the sediment fraction are spread on a sample holder and presented to the NIR microscope. By using the pointer of the microscope the infrared beam is focussed on each particle and the NIR spectrum (1112–2500 nm) is collected. This method can be used to detect the presence of MBM at concentrations as low as 0.05% mass fraction. When results from the NIRM method were compared with the classical microscopic method, a coefficient of determination (R2) of 0.87 was obtained. The results of this study demonstrated that this method could be proposed as a complementary tool for the detection of banned MBM in feedstuffs by reinforcement of the monitoring of feeds. 相似文献
123.
Ruifeng Liu Paula R. Moody Alex S. Vanburen Jeffrey A. Clark Joel A. Krauser Dennis R. Tate 《Vibrational Spectroscopy》1996,10(2):325-329
Results of ab initio and density functional theory calculations on the structure and vibrational frequencies of hypophosphite anion indicate earlier experimental assignments of the fundamental vibrational modes are correct while the recent reassignments of several modes proposed by Bickley et al. are inconsistent with the calculated results. 相似文献
124.
The orientational order parameter of dense colloidal dispersions of plate-like particles as a function of volume fraction is measured using neutron diffraction. This non-invasive experimental approach directly provides the full particle orientation distribution from which the order parameters can be calculated. The orientation parameters are shown to be linked to the solids fractions of the cakes and the macroscopic permeability of the samples. However, this study suggests that, although orientation can be relevant for a given system, other factors can have a stronger influence, for example, the degree of dispersion or colloidal stability of the clay and may be the principle factor that controls permeability. In addition, we report enhanced ordering of these materials under the influence of an external cross-flow field. 相似文献
125.
An enhanced etched electrochemical (EC) detection technique has been developed for CE in micron inner diameter capillaries. The design improvements allow for better alignment between the capillary bore and the electrode. This new method involves utilizing a carbon fiber microelectrode and etching both the carbon fiber and the detection end of a micrometer-sized inner diameter capillary to limit dead volume and analyte diffusion at the amperometric EC detector. To understand the factors affecting enhanced detector efficiency, a detailed examination of the relationship between detector design and performance has been completed by exploring the effects of varying electrode diameter, tip shape, and size, in addition to the etch length of the capillary outlet. The enhanced detection provides peak efficiencies as high as 75000 theoretical plates and estimated detection limits as low as 40 nM for dopamine. This etched detection method should further facilitate volume-limited sample analysis by CE. 相似文献
126.
Nitroazobenzene films have been grafted to pyrolyzed photoresist films by electrochemical reduction of the corresponding diazonium salt in acetonitrile solution. Two component films were also prepared by electrochemically grafting methylbenzene layers to preformed NAB films. Voltammetric investigation of the films in aqueous acid medium and the measurement of film thickness using atomic force microscopy (AFM) lead to new insights into film structure. In aqueous acid solution, the azobenzene groups have no detectable electroactivity and not all nitro groups in the films can be reduced. These findings point to a compact film structure in which proton diffusion is limited. There may also be spatial inhibition of the conformational changes that accompany azobenzene reduction. For increasingly thick NAB films, the peak for reduction of the nitro groups moves to more negative potentials and the peaks become more asymmetric in shape. These changes are interpreted in terms of the dielectric properties and the rate of proton diffusion in the films. Film thickness was measured by ploughing through the film with an AFM tip. When an NAB film prepared in acetonitrile solution is reduced in aqueous acid, the film thickness decreases by more than 50%. The changes can be partially reversed by treatment in acetonitrile-electrolyte solution and hence are attributed to ion-solvent induced swelling and shrinking. Thus, the large decrease in thickness detected by AFM after treatment of the film in aqueous acid is consistent with the compact film structure revealed by electrochemistry. 相似文献
127.
Sandra Jiménez-Alonso Ana Estévez-Braun Ángel G. Ravelo Rafael Zárate Matías López 《Tetrahedron》2007,63(14):3066-3074
Several bis-pyrano-l,4-benzoquinones have been synthesized by a double domino Knoevenagel hetero Diels-Alder reaction. The synthetic approach is highly efficient allowing the construction of complex polycyclic scaffolds with six new σ-bonds. These reactions performed more efficiently and more rapidly using microwave irradiation. The resulting bis-pyrano-1,4-benzoquinones are the first examples of a double domino Knoevenagel hetero Diels-Alder reaction. Our approach represents a novel contribution to the chemistry of 2,5-dihydroxy-l,4-benzoquinones and the first general method for the synthesis of bis-pyranobenzoquinones. 相似文献
128.
Ana B. Gaspar 《Coordination chemistry reviews》2005,249(23):2661-2676
One of the most important trends in the spin crossover (SCO) field is focused on the synthesis of new molecule-based functional materials in which the SCO properties may be combined with other physical or chemical properties in a synergic fashion. The current stage of investigations regarding interplay and synergic effects between SCO, magnetic coupling, liquid crystalline properties, host-guest interactions, non-linear optical properties, electrical conductivity, and ligand isomerization is highlighted and discussed. 相似文献
129.
Q. Paula Lei I. Jonathan Amster 《Journal of the American Society for Mass Spectrometry》1996,7(8):722-730
A systematic investigation of the gas-phase reactions of Cu+ and Fe+ with the 20 common amino acids is reported. Metal ions are formed by laser ablation of a metal target and are trapped in the analyzer cell of a Fourier transform mass spectrometer. By using quadrupolar excitation to axialize the metal ions, tens of thousands of thermalizing collisions occur prior to their reactions with laser-desorbed amino acid neutral molecules. Amino acids with nonpolar side chains are found to be more reactive toward Cu+ and Fe+ than amino acids with polar side chain. Many of the nonpolar amino acids are found to undergo dissociative metal attachment with a neutral loss of 46 u. A 13C-labeling experiment shows that the carboxyl group is lost during dissociative metal attachment to amino acids. Together these results suggest that these metal ions interact primarily with the carboxyl functional group in these molecules. 相似文献
130.
Maurício Cavicchioli Antonio Carlos Massabni Luciana Rebelo Guilherme Eduardo Ernesto Castellano Armando Paduan-Filho Ana Maria da Costa Ferreira 《Transition Metal Chemistry》2007,32(3):355-361
Structural, electrochemical and spectroscopic data of a new dinuclear copper(II) complex with (±)-2-(p-methoxyphenoxy)propionic acid are reported. The complex {tetra-μ-[(±)-2-(p-methoxyphenoxy)propionato-O,O′]-bis(aqua)dicopper(II)} crystallizes in the monoclinic system, space group P21/n with a = 14.149(1) ?, b = 7.495(1) ?, c = 19.827(1) ?, β = 90.62(1) and Z = 4. X-ray diffraction data show that the two copper(II) ions are held together through four carboxylate bridges, coordinated
as equatorial ligands in square pyramidal geometry. The coordination sphere around each copper ion is completed by two water
molecules as axial ligands. Thermogravimetric data are consistent with such results. The ligand has an “L” type shape due
to the angle formed by the β-carbon of the propionic chain and the linked p-methoxyphenoxy group. This conformation contributes to the occurrence of a peculiar structure of the complex. The complex
retains its dinuclear nature when dissolved in acetonitrile, but it decomposes into the corresponding mononuclear species
if dissolved in ethanol, according to the EPR measurements. Further, cyclic voltammograms of the complex in acetonitrile show
that the dinuclear species maintains the same structure, in agreement with the EPR data in this solvent. The voltammogram
shows two irreversible reduction waves at E
pc = −0.73 and −1.04 V vs. Ag/AgCl assigned to the Cu(II)/Cu(I) and Cu(I)/Cu° redox couples, respectively, and two successive oxidation waves at E
pa =− 0.01 and +1.41 V vs. Ag/AgCl, assigned to the Cu°/Cu(I) and Cu(I)/Cu(II) redox couples, respectively, in addition to the oxidation waves of the
carboxylate ligand. 相似文献