Differential Scanning Microcalorimeter Research Articles

Study of phase equilibria in a two-component system diphenyloxide <i>- n -</i> nonadecane

Using the Schroeder, UNIFAC and UNIFAC Dortmund methods, the fusibility diagram of the diphenyloxide – n –nonadecane system was calculated and it was shown that it belongs to the eutectic type. Individual substances and their mixtures were studied experimentally using a differential scanning microcalorimeter. On the DTA heating curve of the eutectic alloy, two endo-effects are noted, corresponding to the polymorphic transition of n–nonadecane and the melting of the eutectic. A comparison of the eutectic coordinates calculated by these methods with experimental data is presented. For a eutectic alloy, the specific enthalpy of fusion, molar values of entropy and enthalpy of fusion, volumetric specific enthalpy of fusion and density for standard conditions are calculated. The eutectic mixture can be recommended for use as a coolant, as well as the working fluid of a heat accumulator.

Study of phase equilibria in the two-component organic system biphenyl – n-docosane

The fusibility diagram of the diphenyl – n-docosane system was calculated by Schroeder, UNIFAC and UNIFAC Dortmund methods, and it was shown that it belongs to the eutectic type. Individual substances and their mixtures were studied experimentally using a differential scanning microcalorimeter. The endo-effect corresponding to the melting of the eutectic was noted on the DTA heating curve of the eutectic alloy. A comparison of the eutectic coordinates calculated by these methods with experimental data is presented. Specific fusion enthalpy, molar values of entropy and enthalpy of fusion, volumetric specific fusion enthalpy and density for standard conditions were calculated for an eutectic alloy. The eutectic mixture can be used as a heat carrier, as well as a working fluid of a heat accumulator.

PHASE EQUILIBRIUM IN TWO-COMPONENT SYSTEMS: DIPHENYL – N-GENEICOSAN AND DIPHENYL – N-TRICOSAN

The melting curves of the diphenyl – n-geneucosane and diphenyl – n-tricosane systems were calculated using the Schroeder equation and using the UNIFAC and UNIFAC Dortmund methods. The results obtained by calculation methods showed that both systems are eutectic. The use of a differential scanning microcalorimeter made it possible to experimentally confirm the presence of phase equilibrium in these alloys. Experimentally, for each system, individual substances and compositions within each of the studied systems were studied. Based on the data obtained, phase diagrams were constructed for two systems diphenyl – n-geneucosane and diphenyl – n-tricosane. In each system, at temperatures of 29.94 °C and 40.6 °C, polymorphic transformations are observed for n-geneicosane and n-tricosane, respectively, which coincide with the literature data. The UNIFAC Dortmund method for both systems showed the smallest deviation of the composition of the eutectic alloy from the experimental data at relatively close calculated values of the melting temperature of the eutectic with the UNIFAC method. These methods can be used to preliminary estimate the coordinates of eutectics in organic systems before planning an experiment. Calculations were made of the specific enthalpy of melting, molar values of entropy and enthalpy of melting, volumetric specific enthalpy of melting and density under standard conditions for each eutectic composition. The study of the fusibility of diphenyl – n-heneicosane and diphenyl – n-tricosane systems is important for understanding its physical properties and possibilities of application in various technological processes. Eutectic mixtures can be used as coolants and heat-storing substances. Eutectic melts of diphenyl – n-heneicosane and diphenyl – n-tricosane systems are safe to use.

Physicochemical Analysis of Systems Containing Alkanes and Cyclododecane

Three-component systems containing cyclododecane and two n-alkanes are studied via differential thermal analysis (DTA) using a differential scanning microcalorimeter (DSC). It is concluded that thirteen experimentally studied three-component systems, n-CnH2n + 2–C12Н24–n-CmH2m + 2 (n, m = 2k, k = 5, …, 12), are characterized by the formation of triple eutectics. Most of the results obtained for these systems are in satisfactory agreement with the data predicted by the methods proposed and developed earlier.

HEAT CAPACITY PROPERTIES OF AQUEOUS BUFFER SOLUTIONS OF L-HISTIDINE IN A WIDE TEMPERATURE RANGE

The influence of temperature and concentration of L-histidine on the heat capacity properties of its aqueous buffer solutions was studied by differential scanning calorimetry. The investigations were carried out in aqueous buffer solutions (pH 7.4) containing monobasic sodium phosphate and dibasic sodium phosphate, which brings the environment closer to the conditions of real biological systems. The pH values of the solutions were fixed with a digital pH meter Mettler Toledo, model Five-Easy (Switzerland). The differential scanning microcalorimeter SCAL-1 (Biopribor, Pushchino, Russia) was used for measure the specific heat capacity of the system under study. It was equipped with Peltier thermoelectric elements, two measuring glass cells with an internal volume of 0.377 cm3, as well as a computer terminal and software for calculating heat capacity. The standard error of measurement of the specific heat for the studied solutions was within ±7·10-3 J·K-1·g-1. The experimental values of the specific heat of solutions of the amino acid in a phosphate buffer solvent in the temperature range (283.15 – 343.15) K were obtained. The concentration of histidine was varied from (0.00215 to 0.03648) mol·kg-1. All the studied solutions were prepared by the gravimetric method using Sartorius-ME215S scales (with a weighing accuracy of 1·10-5 g). The apparent molar heat capacities of L-histidine in the buffer solution, as well as its partial molar heat capacities at infinite dilution, were determined. The calculated molar parameters increase with an increase in both temperature and amino acid concentration. It was shown that the partial molar heat capacities transfers of L-histidine from water to the buffer solution have positive values in the temperature range studied. The results are discussed on base of the Gurney model.

Phase Equilibrium States in the n-Dodecane–n-Hexadecane–Cyclododecane System

A three-component system comprising cyclododecane and n-alkanes is studied by means of differential thermal analysis on a differential scanning microcalorimeter. It is concluded that the investigated system is of the eutectic type and the n-dodecane–n-hexadecane–cyclododecane eutectic mixture system is 73.0 wt % n-С12Н26, 9.0 wt % n-С16Н34, and 18.0 wt % С12Н24. Its melting point is found to be −17.7°C.

High-pressure differential scanning microcalorimeter.

A differential scanning microcalorimeter for studying thermotropic conformational transitions of biopolymers at high pressure has been designed. The calorimeter allows taking measurements of partial heat capacity of biopolymer solutions vs. temperature at pressures up to 3000 atm. The principles of operation of the device, methods of its calibration, as well as possible applications are discussed.

FEM-based Modeling of the Temperature Distribution Influence on Melting Process in Ceramic Differential Micro-calorimeter

Abstract The influence of temperature distribution on the melting process in a ceramic differential scanning micro-calorimeter (MC-DSC) is shown. The MC-DSC chip is manufactured in low temperature co-fired ceramics technology (LTCC) as a three-dimensional device that includes all functions of a conventional DSC device. This study deals with the simulation-based optimization of the heater geometry for the second MC-DSC-chip generation to improve both sensitivity and selectivity. The influence of the heater geometry improvement was evaluated by simulation of the melting process of indium. The results suggest both higher sensitivities and higher selectivities.

Effect of the Peptide Bronchogen (Ala-Asp-Glu-Leu) on DNA Thermostability

Thermodynamic parameters of DNA melting in the presence of a peptide bronchogen in various concentrations were estimated on a differential scanning microcalorimeter. Bronchogen was shown to serve as a DNA-stabilizing agent. Bronchogen increased the melting temperature of DNA from calf thymus and mouse liver by 3.1°C in a narrow range of r (molar ratio of bronchogen/DNA b.p., 0.01-0.055). A further increase in r was not accompanied by changes in the melting temperature. The complex melting enthalpy (ΔH(melt)) remained unchanged in this range of r (0.01-1.0). ΔH(melt) for DNA from the thymus and mouse liver was 11.4 and 12.7 cal/g, respectively. Our results indicate that bronchogen is not an adenine-thymine-specific or guanine-cytosine-specific ligand. The type of binding is considered as strong and occasional. The binding occurs with both strands of DNA (mainly with nitrogen bases).

Applications of Differential Scanning Microcalorimeter for Physical Stability Evaluation of Therapeutic Antibodies

Applications of Differential Scanning Microcalorimeter for Physical Stability Evaluation of Therapeutic Antibodies

Thermal behavior of ammonium-containing titanium and germanium fluoride complexes (NH4)4Li2(AF6)3 and NH4NaAF6 (A = Ge or Ti)

The compounds (NH4)4Li2A3F18 and NH4NaAF6 (A = Ge or Ti) were studied thermogravimetrically. These fluoro complexes are thermolyzed in the range 230–450°C. Measurements on a differential scanning microcalorimeter revealed reversible phase transitions in NH4NaAF6 at T 1 = 126°C and T 2 = 111°C.

Calcium dependent p21 cip1/waf1 stabilizer cyclin I (Ccni).

Cyclin I (Ccni), a new member of cyclin family which contains a typical cyclin box at N‐terminal and PEST sequences at its C‐terminal. Unlike other cyclins, the mRNA level of cyclin I is high in post‐mitotic tissues and expresses constantly during cell cycle progression. However, the function of cyclin I remains unknown until this study. In this study, we have cloned, expressed and refolded the recombinatant human cyclin I from E. coli system. Spectroscopy analysis by circular dichroism spectra and thermal stability analysis by differential scanning micro‐calorimeter indicated that cyclin I is a native disorder protein but with helical secondary structure. Both far western blot analysis and reaction heat measurement by isothermal titration calorimeter showed that cyclin I can bind with p21cip1/waf1directly only at the condition with calcium ion present. These results suggested that cyclin I prolongs the life time of p21 by calcium regulation at the early stage of apoptosis.

Studies of a reference sample of glycyrrhizic acid during the drying process

Qualitative and quantitative assessments of water content in a reference sample of glycyrrhizic acid (RS GA) are presented. A DSM-10M differential scanning microcalorimeter of Russian origin was used for thermal analysis of RS GA and identification of the temperature ranges for phase transitions of the reference sample of glycerrhizic acid during drying. RS GA was shown to contain two types of water: weakly bound and tightly bound. HPLC studies showed that drying for 3 h at 105°C had virtually no effect on the quality of the RS GA.

Heat capacity of indium nitride

The heat capacity of the solid indium nitride was measured, using the Calvet TG-DSC 111 differential scanning microcalorimeter (Setaram, France), in the temperature between (314–978 K). The temperature dependence of the heat capacity can be presented in the following form: Cp=41.400+0.499·10−3T−135502T−2−26169900 T−3.

Structure and function analysis of new member of cyclin family: Cyclin I

Cyclin I, a new member of cyclin family was identified at 1995, which contains a typical cyclin box near the N-terminal and a PEST sequences near the C-terminal. Meanwhile, it shows the highest sequence similarity in the cyclin box to cyclin G and E. However, the function and structure are still remaining unknown. Unlike other cyclins, the mRNA of cyclin I is expressed constantly during cell cycle progression. This indicates the function of cyclin I may independently of the cell cycle directly. However, cyclin I is expressed in human breast cancer and closely associated with VEGF and KDR expression. In order to reveal the structure function relationship of human Cyclin I, we have cloned, expression and refolded this protein in vitro. The circular dichroism spectra indicated that Cyclin I is a helix major protein. However, differential scanning micro-calorimeter measurement indicated that the Cyclin I is a native non-structure protein. By far-western blot analysis we found that the Cyclin I bound with p21 cip1, waf1, in vitro. It suggests that Cyclin I may be the p21 mediated cell cycle regulator.

Crystal Structure of the Biglycan Dimer and Evidence That Dimerization Is Essential for Folding and Stability of Class I Small Leucine-rich Repeat Proteoglycans

Biglycan and decorin are two closely related proteoglycans whose protein cores contain leucine-rich repeats flanked by disulfides. We have previously shown that decorin is dimeric both in solution and in crystal structures. In this study we determined whether biglycan dimerizes and investigated the role of dimerization in the folding and stability of these proteoglycans. We used light scattering to show that biglycan is dimeric in solution and solved the crystal structure of the glycoprotein core of biglycan at 3.40-angstroms resolution. This structure reveals that biglycan dimerizes in the same way as decorin, i.e. by apposition of the concave inner surfaces of the leucine-rich repeat domains. We demonstrate that low concentrations of guanidinium chloride denature biglycan and decorin but that the denaturation is completely reversible following removal of the guanidinium chloride, as assessed by circular dichroism spectroscopy. Furthermore, the rate of refolding is dependent on protein concentration, demonstrating that it is not a unimolecular process. Upon heating, decorin shows a single structural transition at a T(m) of 45-46 degrees C but refolds completely upon cooling to 25 degrees C. This property of decorin enabled us to show both by calorimetry and light scattering that dimer to monomer transition coincided with unfolding and monomer to dimer transition coincided with refolding; thus these processes are inextricably linked. We further conclude that folded monomeric biglycan or decorin cannot exist in solution. This implies novel interrelated functions for the parallel beta sheet faces of these leucine-rich repeat proteoglycans, including dimerization and stabilization of protein folding.

Study of the influence of the In 2O 3 loading on γ-alumina for the development of de-NO x catalysts

Alumina-supported indium oxide (In 2O 3) catalysts with In loadings between 2 and 22 wt% were prepared by impregnation and characterized for their main properties. Surface properties, such as the surface area; surface In content, measured by X-ray photoelectron spectroscopy (XPS); and acidity and basicity, measured both by adsorption microcalorimetry using ammonia and sulfur dioxide as probe molecules and by infrared spectroscopy of pyridine adsorption, were determined. Bulk properties, namely the crystallographic structure as determined by powder X-ray diffraction (XRD) analysis and the redox character of the In 2O 3-dispersed phase as determined by redox cycles performed both in a flow apparatus and in a thermobalance coupled with a differential scanning microcalorimeter (TG-DSC), were studied. The results obtained were interpreted in terms of In 2O 3 surface dispersion or aggregation. The catalysts tested in the reduction of NO x by ethene in an oxygen-rich atmosphere showed an interesting ability to selectively reduce NO x to N 2, independently of the In loading. The weakness of the oxidative properties of the In 2O 3 phases limited the ethene combustion and made the catalysts able to reduce NO x even at high temperature (up to 550 °C). The rates of nitrogen formation depended strongly on the In 2O 3 aggregation state; the In centers were very active even at low amounts.

Heat Capacities of α,ω-Dichloroalkanes at Temperatures from 284.15 K to 353.15 K and a Group Additivity Analysis

Heat capacities at constant pressure of five α,ω-dichloroalkanes (1,2-dichloroethane, 1,3-dichloropropane, 1,4-dichlorobutane, 1,5-dichloropentane, 1,6-dichlorohexane) were measured at temperatures ranging from 284 K to 353 K by using a highly sensitive Tian−Calvet differential scanning microcalorimeter (DSC). Changes in the standard procedures increased the accuracy of Cp measurements. The influence of the evaporation heat effect on the Cp value is analyzed. In the described method, the uncertainty of the measurements is estimated to be ±0.15% for uncertainties arising solely from the measurement system and method. The group contributions to Cp for CH2 and Cl and their temperature dependence were determined by a group additivity analysis.

New small endothermic peaks with hysteresis commonly observed in the differential scanning calorimetric study of biopolymer–water systems

New small endothermic transitions with remarkable hysteresis were found in many biopolymer–water systems including proteins and polysaccharides by using a high sensitivity differential scanning microcalorimeter. The transition temperatures are usually around 40°C for fresh samples and they shift to the temperatures from 20 to 60°C according to the preservation at various temperatures. The transition enthalpies per gram of water (Δ H w) in the samples lie between 2 and 20 J/g water, and are not so diverse from species to species for the fresh biopolymer–water systems. The Δ H w decreases rapidly with the increase of water content of the samples. The remarkable narrowing of the band width of 1H-NMR signals of lysozyme–water and starch–water systems were observed at the temperature ranges of the endothermic transitions. The band widths showed fine hysteresis corresponding to the hysteresis behavior observed in the DSC measurements. The endothermic transitions observed in the DSC measurements must be brought about by the release of the cooperative motion of water and the biological macromolecules.

DIFFERENTIAL SCANNING MICROCALORIMETER SCAL-1

The paper describes the design and the principle of operation of the differential scanning microcalorimeter SCAL-1. This instrument serves to measure thermal parameters of protein or biopolymer solutions of low concentration (from0.1 mg ml−1) in the temperature range from −10 to 130°C using different rates. A distinctive feature of the microcalorimeter is that its calorimetric cell is made of glass, it is highly sensitive and measuring results can be easily and reliably reproduced.