共查询到20条相似文献,搜索用时 15 毫秒
1.
Integral enthalpies of mixing of solid iron—manganese alloys have been obtained at 1443K, 1073K and 873K using a modified Dench-type calorimeter. The modifications in calorimetric technique required to cope with the high volatility of manganese are described. Results are presented and discussed.Dedicated to Prof. Dr.Kurt L. Komarek on the occasion of his 60th birthday on 23rd June 1986. 相似文献
2.
Enthalpies of proton transfer in methanol-water mixtures (0–90 wt.% methanol) have been measured by direct calorimetry for
the bases quinuclidine, triethylamine, t-butylamine and tris(hydroxymethyl)aminomethane. The results are discussed in terms
of an adaptation of classical electrostatic formula. 相似文献
3.
Fan HY Nazari M Chowdhury S Heerklotz H 《Langmuir : the ACS journal of surfaces and colloids》2011,27(5):1693-1699
We present the application of pressure perturbation calorimetry (PPC) as a new method for the volumetric characterization of the micelle formation of surfactants. The evaluation is realized by a global fit of PPC curves at different surfactant concentration ranging, if possible, from below to far above the CMC. It is based on the knowledge of the temperature dependence of the CMC, which can for example be characterized by isothermal titration calorimetry. We demonstrate the new approach for decyl-β-maltopyranoside (DM). It shows a strong volume increase upon micelle formation of 16 ± 2.5 mL/mol (+4%) at 25 °C, and changes with temperature by -0.1 mL/(mol K). The apparent molar expansivity (E(S)) decreases upon micelle formation from 0.44 to 0.31 mL/(mol K) at 25 °C. Surprisingly, the temperature dependence of the expansivity of DM in solution (as compared with that of maltose) does not agree with the principal behavior described for polar (E(S)(T) decreasing) and hydrophobic (E(S)(T) increasing) solutes or moieties before. The results are discussed in terms of changes in hydration of the molecules and internal packing of the micelles and compared with the volumetric effects of transitions of proteins, DNA, lipids, and polymers. 相似文献
4.
Haman Nabil Ferrentino Giovanna Imperiale Sebastian Scampicchio Matteo 《Journal of Thermal Analysis and Calorimetry》2018,132(2):1065-1075
Journal of Thermal Analysis and Calorimetry - This work aims to determine the antioxidant and prooxidant activity of spent coffee extracts obtained with (1) a low-pressure (LP) extraction with... 相似文献
5.
Enthalpies of proton transfer in methanol-water mixtures (0–90 wt. % methanol) have been measured by direct calorimetry for the bases 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1,3-propanediol and 2,2-bis(hydroxymethyl)-2,2,2-nitrilotriethanol at 25°C. Also reported are the data for 3-hydroxy-2-methyl-4-pyrone. The results are discussed in terms of an adaptation of classical electrostatic formula. 相似文献
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Lerchner J. Volpe P. O. L. Lanaro C. Fertrin K. Y. Costa F. F. Albuquerque D. M. Haenschke F. Mertens F. 《Journal of Thermal Analysis and Calorimetry》2019,136(2):771-781
Journal of Thermal Analysis and Calorimetry - A new calorimetric technique is described which allows the measurement of metabolic heat rates in biological materials which are triggered by changes... 相似文献
8.
Cadmium determination in biological samples by direct solid sampling flame atomic absorption spectrometry 总被引:1,自引:0,他引:1
rico Marlon de Moraes Flores Jos Neri Gottfried Paniz Ayrton Figueiredo Martins Valderi L. Dressler Edson Irineu Müller Adilson Ben da Costa 《Spectrochimica Acta Part B: Atomic Spectroscopy》2002,57(12):2187-2193
A direct solid sampling flame atomic absorption spectrometric procedure for trace determination of cadmium in biological samples has been developed. Test samples (0.05–2.00 mg) were ground and weighed into small polyethylene vials, which were connected to the device for solid sample introduction into a conventional air/acetylene flame. Test samples were carried as a dry aerosol to a quartz cell, placed between the burner and the optical path, which had a perpendicular entrance and a slit in the upper part. The atomic vapor generated in the flame produced a transient signal that was totally integrated within 1 s. The effect of operating conditions and the extent of grinding on the analytical signal were evaluated. Background signals were always low and a characteristic mass of 0.29 ng Cd was obtained. Calibration was performed using different masses of solid certified reference materials. Results obtained for certified and in-house reference materials were typically within the 95% confidence interval of the certified and/or reference value, and the precision, expressed as relative standard deviation, was between 3.8 and 6.7%. The proposed system is simple and it might be adapted to conventional atomic absorption spectrometers allowing the determination of Cd in more than 80 test samples per hour, excluding weighing. 相似文献
9.
Medhi Moezzi Andrea Ferencz Dénes Lőrinczy 《Journal of Thermal Analysis and Calorimetry》2014,116(2):557-562
Psoriasis is a chronic inflammatory skin disease, most commonly resulting in the occurrence of red and silver scaly plaques. Application of differential scanning calorimetry (DSC) should be used as a new method to detect the different stages of the disease and to monitor medications with different anti-psoriatic drugs using patient’s blood plasma. The study included 72 white adults (35 men and 37 women; median age 56 years) with diagnosed psoriasis. According to the psoriasis area severity index (PASI) patients were selected into three groups: symptomless (PASI: 0), mild (PASI: 1–15), and serious symptoms (PASI: >15). According to medication patients were divided into untreated (n = 39) and treated (n = 33) groups. For systemic drug treatment cytostatic therapy (methotrexate, n = 12), retinoid treatment (acitretin, n = 10), and biologic response modifiers (adalimumab, n = 5; infliximab, n = 5; ustekinumab, n = 1) were applied. Denaturation of human plasma components were detected in Setaram Micro DSC II calorimeter. The patients had no third denaturation peak in the untreated mild and serious symptoms groups. In mild symptoms all the thermal parameters altered significantly, while in serious symptoms only the first melting and the calorimetric enthalpy altered significantly compared with symptoms-free states. In case of systematic cytostatic and retinoid drug treatment (methotrexate, n = 12; acitretin, n = 10) cases the DSC scans of patients with symptoms exhibited significant differences (p < 0.05) in melting temperatures and in calorimetric enthalpy compared with the untreated symptoms-free patients. Using biologic response modifier agents (adalimumab, infliximab, and ustekinumab) we had no enough samples for a statistical evaluation for each one, but after the intervention a stronger effect can be seen as in case of systematic drug treatment. In this study blood plasma measurement in psoriatic patients by DSC showed differences between untreated, conventional systemic drug treatment, and application of biologic response modifier agents, but further studies are needed to elucidate these relationships (supported by grant OTKA CO-272). 相似文献
10.
Yan X Hill K Gao H Ji HF 《Langmuir : the ACS journal of surfaces and colloids》2006,22(26):11241-11244
A potential binding assay based on conformational-change-induced micromechanical motion is described. Calmodulin was used to modify a microcantilever (MCL) by a self-assembled layer-by-layer approach. The results showed that the modified MCL bent when the proteins changed their conformation upon binding with Ca2+. The cantilever deflection amplitudes were different under different ionic strengths, indicating different degrees of conformational change of the proteins in these conditions. On the contrary, cantilevers modified by proteins, such as hemoglobin and myoglobin, that do not change conformations upon binding with analytes do not cause the cantilever deflection. These results suggest that the conformational changes of proteins may be used to develop cantilever biosensors, and the MCL system has potential for use in label-free, protein-analyte screening applications. 相似文献
11.
Bárbara Anes Ricardo J. N. Bettencourt da Silva Hugo F. P. Martins Cristina S. Oliveira M. Filomena Camões 《Accreditation and quality assurance》2016,21(1):1-7
Calibration of pH meters is usually performed with reference pH buffer solutions of low ionic strength, I ≤ 0.1 mol kg?1. For seawater pH measurements (I ≈ 0.7 mol kg?1), calibration buffers in high ionic strength matrix are required. The Harned cell, in association with the Nernst equation and a model for estimating the chloride ion activity coefficient, \(\gamma_{{{\text{Cl}}^{ - } }} ,\) is the basis of the primary method for pH assignment to reference pH buffers. The semi-empirical Pitzer model is, in principle, adequate to estimate \(\gamma_{{{\text{Cl}}^{ - } }}\) of complex solutions, namely seawater. Nevertheless, no assessment of the validity of the model for this matrix is known to the authors. This work aims at estimating the adequacy of the Pitzer model by assessing the metrological compatibility of mean activity coefficients, in this case \(\gamma_{ \pm } = \sqrt {\gamma_{{{\text{H}}^{ + } }} \gamma_{{{\text{Cl}}^{ - } }} }\) estimated experimentally with the Harned cell, \(\gamma_{ \pm }^{\text{Exp}} ,\) and using the Pitzer model, \(\gamma_{ \pm }^{\text{Ptz}}\). The measurement uncertainty considered in the compatibility test was estimated using the bottom-up approach, where components were combined by the numerical Kragten method after checking its adequacy. The compatibility of the estimated \(\gamma_{ \pm }\) was assessed for solutions with increasing complexity and an ionic strength of 0.67 mol kg–1. \(\gamma_{ \pm }^{\text{Exp}}\) and \(\gamma_{ \pm }^{Ptz}\) are metrologically compatible for a confidence level of 95 % where the relative standard uncertainty of their difference ranged from 1.1 % to 3.1 % in all chloride solutions to approximately 6.3 % when sodium sulfate was also present. This led to assume the validity of the Pitzer model equations to estimate \(\gamma_{{{\text{Cl}}^{ - } }} ,\) required to define reference pH values of buffer solutions with high ionic strength. 相似文献
12.
We report the use of proteins, lipids, and enzymes for the preparation of surfaces with reversible wettability changes, in particular, surfaces capable of switching from hydrophobic to hydrophilic and back. We demonstrate that these reactions can be used for engineering capillary systems with gating properties. 相似文献
13.
Jonathan P. Williams Hazel I. A. Phillips Iain Campuzano Peter J. Sadler 《Journal of the American Society for Mass Spectrometry》2010,21(7):1097-1106
The three-dimensional conformation of a protein is an important property and plays a key role in its biological activity.
We show here that ion mobility-mass spectrometry (IM-MS) can be used to detect conformational changes in the protein ubiquitin
in the gas phase induced by reaction with the anticancer drug cisplatin. The primary adduct was ubiquitin-{Pt(NH3)2} under denaturing conditions. Up to three different conformations appear to be generated upon platination depending on the
charge state. The collision cross-sections (Ω) for each conformation indicate that the conformations of the platinated protein
are contracted in size compared with unmodified ubiquitin with generally smaller Ω values. Ion mobility-tandem MS allowed
determination of the platinum binding site without a requirement for prior Chromatographic separation. A rapid 30-min digestion
of cisplatin-modified ubiquitin with trypsin allowed the platination site to be identified as the N-terminal methionine following
low-energy collision-induced dissociation (CID) studies of the modified peptide. The data were generated using a Traveling-Wave
based ion mobility-MS approach. Such cisplatin-induced shape changes may have a significant effect on its function in vivo.
This work highlights the usefulness of the ion-mobility mass spectrometry technique for shedding new light on such protein
interactions. 相似文献
14.
Direct anodic oxidation oftrans-stilbene in lower alcohols and in some other solvents in the presence of KF or Bu4NBF4 is accompanied by its electrooxidatve rearrangement into diphenylacetaldehyde acetals; a competing reaction yields 1,2-dialkoxy-1,2-diphenylethanes.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2202–2205, December, 1997. 相似文献
15.
Samples of human serum albumin (HSA) obtained as a result of heat denaturation followed by refolding controlled by a cooling
of the protein solution were studied by several methods: chromatographic measurements, kinetic of the reaction with a water
soluble free radical and by electron paramagnetic resonance (EPR) spectroscopy. In this context the interaction of this protein
with β-cyclodextrin (β-CD) and sodium dodecyl sulfate (SDS) was also investigated. Reversed phase thin layer chromatography
(RP-TLC) showed changes in lipophylicity of HSA, which are related with the existence of different ensembles of conformers.
The UV-Vis absorption spectra had shown the broadening of absorption band of the protein and a hyperchrom effect in the presence
of SDS; β-CD reduces the effect of SDS on protein UV-Vis spectra. 相似文献
16.
We have studied hydration (and dehydration) of thermally denatured hen egg lysozyme using sorption calorimetry. Two different procedures of thermal denaturation of lysozyme were used. In the first procedure the protein was denatured in an aqueous solution at 90 degrees C, in the other procedure a sample that contained 20% of water was denatured at 150 degrees C. The protein denatured at 90 degrees C showed very similar sorption behavior to that of the native protein. The lysozyme samples denatured at 150 degrees C were studied at several temperatures in the range of 25-60 degrees C. In the beginning of sorption, the sorption isotherms of native and denatured lysozyme are almost identical. At higher water contents, however, the denatured lysozyme can absorb a greater amount of water than the native protein due to the larger number of available sorption sites. Desorption experiments did not reveal a pronounced hysteresis in the sorption isotherm of denatured lysozyme (such hysteresis is typical for native lysozyme). Despite the unfolded structure, the denatured lysozyme binds less water than does the native lysozyme in the desorption experiments at water contents up to 34 wt %. Glass transitions in the denatured lysozyme were observed using both differential scanning calorimetry and sorption calorimetry. Partial molar enthalpy of mixing of water in the glassy state is strongly exothermic, which gives rise to a positive temperature dependence of the water activity. The changes of the free energy of the protein induced by the hydration stabilize the denatured form of lysozyme with respect to the native form. 相似文献
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《Thermochimica Acta》1986,100(1):271-282
The field of calorimetry has changed in many dramatic ways during the past 25 years. The authors' observations of the changes in equipment, measurements made, and automation are recorded. The number of uses of calorimeters has increased as have the ranges of temperature and pressure over which they have been operated. Automation and the use of computers have made the operation of calorimeters and the reduction of calorimetric data less tedious and less time consuming. The authors see the future of calorimetry to be bright and expanding. 相似文献
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《Polymer Gels and Networks》1995,3(2):135-143
The phase transition of poly(L-lysine-alt-terephthalic acid) (PPL) microcapsules induced by changes in the pH of the medium was investigated. The total number of ionizable groups in one capsule or the charge density of the microcapsule membrane was found to be important for the phase transition phenomenon to occur. Thus, the existence of a minimum was suggested, for the total number of ionizable groups in one capsule or for the charge density of the microcapsule membrane, if a pH-induced phase transition of PPL microcapsules is to be caused.The presence of SDS at low concentrations brought about the phase transition of PPL microcapsules, even when the microcapsules were poorly charged at low pH values, through enhanced adsorption of the surfactant unions to the constituent polymers of the microcapsules at high ionic strengths of the medium. Addition of 1,4-dioxane to the microcapsule suspension prevented the phase transition phenomenon from taking place. 相似文献