Search Results
Abstract
The aim of the present work was the characterization of nonpregnant and early pregnant myometrium (days 3–6) of the rat by means of differential scanning calorimetry (DSC). The spontaneous motor activity as well as the KCl-evoked contractions of isolated uterine rings was additionally recorded. A relatively close correlation was found between calorimetric enthalpy (ΔH) and the contractility of the uterus samples. Our results indicate that DSC is a useful tool for the investigation of the functions of developing myometrium and it can be considered as supplementing the traditional structural and functional methods.
Summary
Treatment of a bacterial arthritis is a challenging task for a clinician as inadequate therapy can cause cartilage destruction and can result in severe osteoarthritis of the affected joint. The development of cartilage destruction in septic arthritis is not known in details. The aim of this study was to follow this process by calorimetric method. We induced experimental septic arthritis in knee joints of seven New Zealand rabbits by single inocculation of Staphylococcus aureusOKI 112001 culture (1.5 mL 81085% c.f.u.). The first rabbit died on the 11thday. At that time all the other subjects were made overslept and samples were isolated from the cartilage of the femurs for calorimetric measurement. The DSC scans clearly demonstrated the development of infective structural destruction in cartilage from the first to the tenth day of incubation. In case of healthy control the melting temperatures (T m) were: 49.7, 55 and 63.4C and the total calorimetric enthalpy change (ΔH) was 0.55 J g-1. After the first day the enthalpy decreased (0.375 J g-1), the first two transition temperature shifted towards higher temperature: 57 and 63.15C. Up to the fourth day the effect of infection culminated with T mof 49.3, 55.9, 59.4, 62.8C and further decrease of the ΔH. At the fifth day the effect of infection is culminated in two separable thermal denaturation events (with 55 and 63.3C T ms) with high jump in ΔHindicating the dramatic change of the structure of rabbit cartilage, so this time elapsed seems to be critical from the point of view of practical clinical relevance too. Between the 7thand 11thdays practically we had same melting temperatures (50 and 63C) with low (~0.24 J g-1) enthalpy.
Summary
While the basic fermented (sour) milk products, such as yogurt and kefir can be produced only in live flora version, the post heat-treatment is preferred in their flavored variations to increase the storage time. Casein being in sour coagulum precipitates during heat-treatment; therefore protective colloids surrounding the protein should be used to prevent it. Protective colloids are plant extracts, the most known of them are pectin and amylopectin. Basic requirement of protective colloid effect is the lower swelling temperature of hydrocolloid than the temperature of precipitation of sour coagulum. In this work we have examined the precipitation of sour coagulum as a function of the type of lactic acid bacteria cultures applied during fermentation as well as the swelling of heat protective plant hydrocolloids as a function of the composition (mainly of sugar content) of medium. To investigate the precipitation of fermented coagulum skimmed milk was fermented with mesophilic butter culture, thermophilic yogurt culture as well as with exopolysaccharide (EPS)-producing Prebiolact-2 culture. Precipitation was indicated in the increase of great extent of viscosity. Amylopectin was dispersed into aqueous solution of pH 4.5, the saccharose concentration of which was changed during the investigation of the swelling of heat protective hydrocolloids. A definite exothermic peak was assigned to the swelling of hydrocolloids during the DSC experiments. We could conclude that the precipitation temperature was increasing in the mesophilic-thermophilic-EPS producing microbes line, i.e. the heat stability and swelling temperature of hydrocolloids depend on the saccharose content of aqueous medium and they increase with rising the concentration of saccharose.
Abstract
The differential scanning calorimetry (DSC) technique was used to analyse the thermal effects and the irreversible processes associated with the dehydration of manganese ferrite powders coprecipitated from aqueous solution of salts obtained by simultaneous dissolution of MnO2 and FeSO4x7H2O.
Abstract
The compatibility of some technically important polymer blends, namely BR/NR, NR/NBR and CR/NBR, has been investigated using the DSC method. In addition, dynamic mechanical measurements have been carried out for the NR/NBR blends over the frequency range of 10−4 Hz –200 Hz and temperatures ranging from −70 to +70°C. The results obtained show that the three rubber blends are not compatible over the entire composition range as proven by the DSC and mechanical measurements. By analyzing the heat capacity increases at the glass transitions of the separate phases in the NR/BR blend, it was possible to suggest the presence of a limited compatibility at the boundaries of the two phases. By comparing this work with prior measurements, it was possible to conclude that the calorimetric method is a more efficient tool for the study of compatibility of polymer blends when compared to ultrasonic and viscosity methods. Furthermore, it was found that polymers that show compatibility when measured with an ultrasonic method could behave compatible, semicompatible or incompatible when analyzed by DSC. On the other hand, blends that show incompatibility by the ultrasonic method are always incompatible by the DSC method.
Abstract
DSC measurements in open pans are often disturbed by mass losses such as sublimation during melting or release of water during chemical reactions. By simultaneous DSC and TG measurements the DSC signal can be corrected. For this purpose, a temperature dependent calibration function has to be determined by which the SDTA signal from the TGA/SDTA851e measuring cell can be converted into a heat flow curve (DSC). By this procedure, accurate heat of melting can be determined despite ongoing sublimation in open pans. This method is illustrated with reference of the melting of anthracene. Additionally, condensation reactions were investigated and analyzed by DSC/TG even under ambient pressure, knowing the heat of evaporation. Using phenol formaldehyde resins the influence of the presence or the release of volatile reaction products on the reaction rate and kinetic parameters were studied. In general, the method can be used to correct DSC curves for thermal effects related to mass change.
Abstract
A calorimetric study of thermal denaturation of bovine serum albumin in aqueous solutions has shown essential differences in stability of fatty acid containing and defatted albumin. The first one shows a single endotherm peak in DSC curve near 69°C with enthalpy change about 1000 kJ mol-1. Defated albumin melts in two different temperature ranges: near 56 and 69°C with enthalpy changes about 300 and 200 kJ mol-1 respectively. Deconvolution analysis shows that the single endotherm is well approximated as the sum of three independent two-state transitions. Two transitions of bimodal DSC curve for defatted albumin are not of a two-state type. This molecule melts probably as two structurally independent parts.
Abstract
The objects for the studies of this paper are iron sulfates where the iron has second or third valences and where coordination between iron, sulfur and oxygen is different. DSC technique is used to investigate thermal stability and enthalpy changes when iron compounds are treated in different gas medium. The main objective is to compare thermal stability and enthalpy of iron oxy-sulphate, often detected as an intermediate, with commonly known iron sulphates. DSC curves of samples with equal mass under different gas medium, determining different partial pressure of oxygen in the gas phase, are the base for comparative study of the sample’s thermal properties. Obtained different values of the enthalpy and mass losses and kinetic parameters demonstrate that the stability of oxy-sulphate strongly depended on the value of oxygen partial pressure in the gas phase. The new evidences from the experimental study help to propose the mechanism of the decomposition and to compare some of the iron sulphates properties.
Abstract
DSC analysis is applied to investigate the precipitation reaction in the AA6005 extrusion alloy for different heat treatment practices often presented in commercial production. The quenching practice is shown to have a big impact on the response of the AA6005 alloy to an artificial ageing treatment. The range of β″ precipitation is displaced to lower temperatures in samples quenched in air following the solution treatment. This acceleration, however, does not produce a favorable effect on age hardening capacity since much of the solute Mg and Si is removed from the solid solution before the principal hardening phase can precipitate. The DSC results are in good agreement with the age hardening curves. Natural ageing before artificial ageing promotes clustering activities during a subsequent thermal exposure and produces a strong delay in β″ precipitation.
Abstract
The existence of multiple crystal forms in a drug substance poses interesting development challenges as the material is taken from discovery through formulation, manufacture and market. There are a number of factors why drug substances under development are screened for presence of multiple crystal forms. Different crystal forms may exhibit varied performance properties including bioavailability and solubility, as well as, differences in physical properties such as morphology and melting point. These properties can affect the design of the manufacturing processes for the bulk drug substance, the formulation and the performance of the drug product. This paper will focus on the application of differential scanning calorimetry (DSC) for the quantitation of pharmaceutical crystal forms. Feasibility studies were conducted on several pharmaceutical drug substances which were known to have multiple crystal forms, to determine if quantitative, semi-quantitative or limit of detection tests could be developed. The conclusion from these studies is that polymorphic crystal systems comprised of either close, or melting with decomposing, endotherms, competing transitions, or that contain sample contaminants, may not be optimum candidates for quantitation by DSC. Conversely, crystal systems that contain polymorphs that exhibit well-resolved endothermic or exothermic transitions, for either solvated vs. unsolvated species or both unsolvated, may be excellent candidates for crystal form quantitation by DSC.
