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Results for “Differential Thermal Analysis”

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At least 19 recordsLinked to original sources
PubMed1976

Polymorphism of erythromycin studied by differential thermal analysis.

The polymorphism of erythromycin has been studied by differential thermal analysis. Three main forms, two crystalline (I and SI) and one amorphous have been characterized. Solvation and imbibition water can be differentiated. Solvates from 2-propanol (SII), trichloromethane (SIII) and tetrachloromethane (SIV) have been characterized. The physical stability of the various forms both in the dry state and in aqueous suspension are discussed.

Chemical Phenomena↗
PubMed1982

The use of differential scanning calorimetry and differential thermal analysis in studies of model and biological membranes.

Differential scanning calorimetry (DSC), and to a lesser extent differential thermal analysis (DTA), are powerful yet relatively rapid and inexpensive thermodynamic techniques for studying the thermotropic phase behavior of lipids in model and biological membranes, without the introduction of exogenous probe molecules. In this review the principles as well as the scope and limitations of DSC and DTA are discussed first. The application of these techniques to the study of the thermotropic phase behavior of aqueous dispersions of various single synthetic phospholipids are then summarized, and the effects of cholesterol, free fatty acids, lysophospholipids, drugs, anesthetics and proteins on the gel to liquid-crystalline phase transitions exhibited by these model systems are discussed. The phase mixing properties of model membranes consisting of mixtures of two or more synthetic or natural phospholipids are considered next. Finally, the thermotropic phase behavior of prokaryotic plasma membranes and of the plasma, microsomal and mitochondrial membranes of eukaryotic cells are reviewed, and the applications of DSC and DTA to study the thermal behavior of specific membrane proteins, as well as the physical properties of the membrane lipid phase, are summarized.

Acholeplasma laidlawii↗
PubMed1998

Electroperturbation of human stratum corneum fine structure by high voltage pulses: a freeze-fracture electron microscopy and differential thermal analysis study.

Application of high voltage pulses (HVP) to the skin has been shown to promote the transdermal drug delivery by a mechanism involving skin electroporation. The aim of this study was to detect potential changes in lipid phase and ultrastructure induced in human stratum corneum by various HVP protocols, using differential thermal analysis and freeze-fracture electron microscopy. Due to the time involved between the moment the electric field is switched off and the analysis, only "secondary" phenomena rather than primary events could be observed. A decrease in enthalpies for the phase transitions observed at 70 degrees C and 85 degrees C was detected by differential thermal analysis after HVP treatment. No changes in transition temperature could be seen. The freeze-fracture electron microscopy study revealed a dramatic perturbation of the lamellar ordering of the intercellular lipid after application of HVP. Most of the planes displayed rough surfaces. The lipid lamellae exhibited rounded off steps or a vanished stepwise order. There was no evidence for perturbation of the corneocytes content. In conclusion, the freeze-fracture electron microscopy and differential thermal analysis studies suggest that HVP application induces a general perturbation of the stratum corneum lipid ultrastructure.

Electric Stimulation↗
PubMed1970

Study of the thermal denaturation of ribonuclease A by differential thermal analysis and susceptibility to proteolysis.

1. The thermally induced change in conformation of ribonuclease A in solution was investigated by differential thermal analysis and the susceptibility of the enzyme to proteolytic digestion by ficin. 2. A transition with a mid-point of 60.5 degrees C at pH4.2 was observed directly by differential thermal analysis and shown to be a property of the native structure. 3. At pH4.2 ribonuclease A is susceptible to ficin digestion at 60 degrees C but not at 18 degrees C. 4. Chromatographic analysis of the digestion products reveals that transient active intermediates are produced during the digestion. 5. Three of these intermediates were purified and partially characterized. 6. The nature of those sections of the ribonuclease molecule that are involved in the thermal transition is discussed.

Amino Acids↗
PubMed1980

[Reducing activity and differential thermal analysis of enterococci].

The reducing activity of 100 Streptococcus faecalis strains, 100 Streptococcus faecium strains and 100 enterococcal strains were studied by the quantitative method. The study revealed that all mobile enterococci, in contrast to S. faecium, reduce 2,3,5-triphenyltetrazolium chloride with the formation of triphenylformasan. Differential thermal analysis also indicated that S. faecalis, S. faecium and mobile enterococci had thermograms with definite mathematical characteristics and could be best differentiated by the indices of their form and the size of S3 areas. The quantitative methods of the investigation of reducing activity and differential thermal analysis can be used for the differentiation of enterococcal species. Mobile enterococci have definite characteristics allowing one to sharply differentiate them from S. faecium and S. faecalis.

Animals↗
PubMed1984

A differential thermal analysis (DTA) for the heats of reaction and temperature rises produced during the setting of tooth coloured restorative materials.

Differential thermal analysis (DTA) has been used to obtain the temperature rises produced during the setting of a range of tooth coloured restorative materials, which included silicates, glass ionomers and composites. These have been compared on the basis of the temperature rise per unit volume of material. Calibration of the areas under the reaction peaks (produced during this isothermal operation) to obtain heats of reaction is discussed and a method described. As for the temperature rises, values are given per unit volume of material. The results are compared with those reported in other studies from which DTA is seen to be a technique suited to the determination of these parameters and which might be considered for use a standard method.

Chemical Phenomena↗
PubMed1982

Diatomite as a source of cristobalite for dental investments a differential thermal analysis study.

Cristobalite can be obtained from diatomite by heat-treatment at relatively low temperatures and short times without the use of flux. The differential thermal analysis method used to examine the alpha leads to beta inversion was not as satisfactory as it might have been, and to determine the amount and crystallinity of cristobalite formed any such method should be supported by other techniques, in particular, X-ray diffraction. To determine the suitability or otherwise of cristobalite produced from diatomite for use in dental investments, dialatometric studies are indicated since the property of thermal expansion is of fundamental importance to a dental investment.

Chemical Phenomena↗
PubMed1977

Determination of phase transitions in gutta-percha by differential thermal analysis.

Pure gutta-percha was heat-treated in a differential thermal analyzer. The high melting form crystallized on cooling when gutta-percha was heated to 70 C or less. Above 74 C, crystallization into the low melting form predominated. Either polymorph can be selectively crystallized by control of the heat-treatment temperature before cooling.

Chemical Phenomena↗