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1.
J. C. Masini Oswaldo E. S. Godinho Luiz M. Aleixo 《Fresenius' Journal of Analytical Chemistry》1998,360(1):104-111
A linearization method based on modified Gran functions, and a general nonlinear regression program were used to study potentiometric
titration curves of denatured ovalbumin and lysozyme in 6 mol L–1 guanidine hydrochloride medium with the aim of determining the ionizable species. With both numerical techniques it was possible
to determine the sum of the carboxylic groups, the imidazol, the α-amine, and the sum of ɛ-amine, phenolic and sulfhydryl
groups, if the protein is completely denatured, and assumes a randomly coiled conformation. A total of 87.8 ± 2.5 and 20.7
± 0.6 groups per mol were determined in the ovalbumin and lysozyme, respectively. These values are very close to the 88 and
21 groups expected by aminoacid composition of both proteins, indicating that all ionizable groups were exposed to the solvent.
For ovalbumin the distribution of groups was very similar to that expected by the aminoacid composition, but for lysozyme
some anomalies were observed, suggesting the existence of interactions between ionizable groups, altering the dissociation
constants.
Received: 9 December 1996 / Revised: 27 February 1997 / Accepted: 4 March 1997 相似文献
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A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed. 相似文献
4.
Influence of the Solvent on the “Casting” Methodology for MWCNT‐Modified Glassy Carbon and Platinum Electrodes
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Ana Carolina Ângelo Dorim Herbert Aleixo Edilton de Souza Barcellos Leonardo Luiz Okumura 《Electroanalysis》2015,27(11):2663-2669
The choice of electrode material and surface preparation method are usually dictated by the suitability of the electrode to observe an electrochemical parameter, such as heterogeneous electron transfer rate, surface coverage, or redox potential. Thus, the glassy carbon (GC) and platinum (Pt) electrodes were modified with multiwalled carbon nanotubes (MWCNT) by direct “casting” modification using nine different aliquots of solvents. After drying at room temperature, the modified electrode showed distinct redox peaks corresponding to ferrocyanide oxidation/reduction. Using chemometrics, the cyclic voltammograms with higher current intensity were obtained for those in which ethanol, water and acetone as dispersing agents were used for GCE and dimethylformamide, water and acetone for Pt electrode modification. 相似文献
5.
A titrimetric method for determination of lead(II), based on the reaction between plumbite and silver ions, is described. Sodium hydroxide solution is added to the sample until the precipitate of lead hydroxide has redissolved. The solution is then made 0.025M in sodium chloride and titrated with silver nitrate. The titration is monitored with a silver electrode. An error smaller than 0.5% has been obtained for 0.05M lead (II). 相似文献
6.
A square wave voltammetric method whith a static mercury drop electrode (SMDE) was developed for the quantitative determination
of iron (III) in Zn-Fe alloy galvanic baths. Real alloy bath samples were analyzed by the standard addition method and recovery
tests were carried out. 0.50 mol L–1 sodium citrate (pH 6.0) or 0.20 mol L–1 oxalic acid (pH 4.0) were applied as supporting electrolytes resulting in both cases in a peak potential of about –0.20 V
vs. Ag|AgCl (saturated KCl). The iron (III) concentration in the alloy bath was 9.0 × 10–4 mol L–1. A good correlation (r = 0.9999) was achieved between the iron (III) concentration and the peak current in the electrolytes
studied, with linear response ranges from 1.0 × 10–6 to 1.2 × 10–4 mol L–1. Interference levels for some metals such as copper (II), lead (II), chromium (III) and manganese (II) that can hinder the
Zn-Fe alloy deposition were evaluated; only copper (II) interferes seriously.
Received: 4 April 2000 / Revised: 19 June 2000 / Accepted: 22 June 2000 相似文献
7.
Amita Gupta Alexei Yu Ganin Parmanand Sharma Vikrant Agnihotri LM Belova KV Rao Mikhail E Kozlov AA Zakhidov RH Baughman 《Pramana》2002,58(5-6):1051-1059
We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show
a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are
found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there
exists no report in literature on any BiNi compound which is magnetic. 相似文献
8.
A square wave voltammetric method with a static mercury drop electrode (SMDE) was developed for the quantitative determination of iron (III) in Zn-Fe alloy galvanic baths. Real alloy bath samples were analyzed by the standard addition method and recovery tests were carried out. 0.50 mol L-1 sodium citrate (pH 6.0) or 0.20 mol L-1 oxalic acid (pH 4.0) were applied as supporting electrolytes resulting in both cases in a peak potential of about -0.20 V vs. AgIAgCl (saturated KCl). The iron (III) concentration in the alloy bath was 9.0 x 10(-4) mol L-1. A good correlation (r = 0.9999) was achieved between the iron (III) concentration and the peak current in the electrolytes studied, with linear response ranges from 1.0 x 10(-6) to 1.2 x 10(-4) mol L-1. Interference levels for some metals such as copper (II), lead (II), chromium (III) and manganese (II) that can hinder the Zn-Fe alloy deposition were evaluated; only copper (II) interferes seriously. 相似文献
9.
Melissa Grazielle Morais Guilherme Augusto Ferreira da Costa Álan Alex Aleixo Graziela Teixeira de Oliveira Lucas Ferreira Alves Joaquim Maurício Duarte-Almeida 《Natural product research》2015,29(5):480-483
Ethanol extract (EE) and fractions obtained from the ripe fruits of Solanum lycocarpum were examined in order to determine their phenolic composition, antioxidant capacity, antibacterial activities and cytotoxic potential. High-performance liquid chromatography coupled with DAD analysis indicated that caffeic and chlorogenic acids were the main phenolic compounds present in the EE, dichloromethane (DCM) and ethyl acetate (Ac) fractions. The antioxidant activity assessed by the scavenging ability on 1,1-diphenyl-2-picrylhydrazyl radical was significantly more pronounced for DCM and Ac fractions than that of the commercial antioxidant 2,6-di-tert-butyl-4-methylphenol (BHT). EE and fractions exhibited selective antibacterial activity against Gram-positive bacteria, especially the hexane (Hex) and DCM fractions. EE and fractions exhibited low toxicity towards the LLC-MK2 cell line, especially the Hex, DCM and Ac fractions. This work provides the knowledge of phenolic composition in the extract and fractions from the ripe fruits of S. lycocarpum and their antioxidant, antibacterial and cytotoxic activities. 相似文献
10.
A dam-break flow is an example of an extremely transient free-surface flow with various time and space scales. The importance of studying this type of flow is directly connected with the risk assessment of a dam and with the effects of such a catastrophe on human activities in the valley downstream. In this paper, an experimental study of the dam-break flow is presented. While a great part existing studies about dam-break flows are focused on variables such as the water-front velocity and the water level, the present paper is focused on the measurement of velocity profiles over the whole flow depth within the dam-break wave. For such study and due to the characteristics of the flow itself, image acquisition techniques were used. The velocity field was obtained by means of a Particle Tracking Velocimetry (PTV) algorithm based on Voronoï patterns’ matching. A comparison with the application of a PIV algorithm to the raw data is provided. Finally, results for the velocity profiles and water elevation are presented and discussed for two different flow conditions. 相似文献