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PubMed2002

Thermal analysis and spectroscopic characterization of interactions between a naphthoquinone derivative with HP-beta-CD or PVP.

The purpose of the present study was to investigate the interaction between both hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and PVP-K30 with 2-hydroxy-N-(3-methyl-5-ethyl-4-isoxazolyl)-1,4-naphthoquinone-4-imina (I), a synthetic derivative of isoxazolylnaphthoquinones that has demonstrated to exhibit important biological activity against S. aureus and T. cruzi. The continuous variation plot for I-HP-beta-CD system showed a 1:1 stoichiometry for the complex. Ultraviolet absorption spectroscopy indicates that the isoxazole moiety of I is preferably incorporated in the cavity. Furthermore, proton nuclear magnetic resonance spectroscopy suggests that this incorporation is made from the primary hydroxyl group side of the cyclodextrin. The validation of this incorporation is further evidenced by thermal analysis (DSC and TGA) and infrared spectroscopy. I-PVP-K30 interactions in solid state were demonstrated by combining the infrared spectroscopy data with the results of thermal analysis (DSC, TGA). These methods suggest that drug-polymer interaction probably occurs via intermolecular hydrogen bonding between the drug hydroxyl and polymer carbonyl groups.

2-Hydroxypropyl-beta-cyclodextrin↗
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↗
PubMed2002

Electret-thermal analysis of blood.

The thermally stimulated discharge (TSD) method, intended for the analysis of charged dielectrics, was used for human blood research. Above-room-temperature TSD spectra of blood consist of three peaks. There are indications that the low-temperature peak (40-50 degrees C) corresponds to the thermally stimulated destruction of hydrate shells surrounding blood components while the mid-temperature peak (70-90 degrees C) is related to thermal denaturation of blood proteins. The intensive high-temperature peak (105-120 degrees C) is observed when a phase transition of blood, accompanied by the formation of a firm dry film of blood, occurs. The position of the high-temperature peak depends on the blood group. Data is discussed which suggests that the spontaneous "quasi-electret effect" of blood relates to the character of the biochemical processes taking place in human organisms. The TSD method might be used as simple and informative means of diagnostics in cooperation with medical and physical investigations.

Adult↗
PubMed2005

The evolving role of the dynamic thermal analysis in the early detection of breast cancer.

It is now recognised that the breast exhibits a circadian rhythm which reflects its physiology. There is increasing evidence that rhythms associated with malignant cells proliferation are largely non-circadian and that a circadian to ultradian shift may be a general correlation to neoplasia.Cancer development appears to generate its own thermal signatures and the complexity of these signatures may be a reflection of its degree of development.The limitations of mammography as a screening modality especially in young women with dense breasts necessitated the development of novel and more effective screening strategies with a high sensitivity and specificity. Dynamic thermal analysis of the breast is a safe, non invasive approach that seems to be sensitive for the early detection of breast cancer.This article focuses on dynamic thermal analysis as an evolving method in breast cancer detection in pre-menopausal women with dense breast tissue. Prospective multi-centre trials are required to validate this promising modality in screening.The issue of false positives require further investigation using molecular genetic markers of malignancy and novel techniques such as mammary ductoscopy.

Editorial↗
PubMed2001

Thermal behavior of ursodeoxycholic acid in urea: identification of anomalous peak in the thermal analysis.

The objective of this study was to clarify the thermal behavior of ursodeoxycholic acid (UDCA) in mixtures with urea. Physical mixtures of UDCA and urea in various ratios were prepared, and the thermal analysis of these sample mixtures was investigated using conventional differential scanning calorimetry (DSC) and variable-temperature powder X-ray diffractometry (VTXRD). The hot-stage microscopy (HSM) and powder X-ray diffractometry (PXRD) were used as complementary techniques. From the DSC results of all sample mixtures, it was found that there was no endothermic peak at the melting temperature of intact UDCA crystals. The DSC thermograms of each ratio showed only the endothermic peak at about 136 degrees C due to the melt of urea and the anomalous endothermic peak at about 155 degrees C 157 degrees C. The VTXRD study revealed that the crystals of urea completely disappeared at a temperature of 140 degrees C. At this temperature, it was identified that the VTXRD pattern obtained was of UDCA crystals. The crystalline peaks gradually decreased in intensity at a temperature of 150 degrees C When the temperature was up to 160 degrees C, the identical crystalline peaks of UDCA crystals completely disappeared. It was concluded that the anomalous endothermic peak at 155 degrees C-157 degrees C was the peak due to the dissolution of UDCA crystals in the surrounding melted urea.

Calorimetry, Differential Scanning↗
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↗
PubMed2003

Thermal analysis of poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels.

The influence of water on the physical properties of a hydrogel is important for understanding natural tissues and in designing synthetic materials to replace them. In this study, poly (2-hydroxyethyl methacrylate) (pHEMA) was used as a model system to understand how water interacts with the polymer of a hydrogel. Thermal analysis methods (thermogravimetric analysis coupled to mass spectrometry and differential scanning calorimetry) were used to determine: (i) the total water content of pHEMA gels; (ii) how this water was lost during heating; (iii) the relationship between water content of the gel and its glass transition temperature; and (iv) the behavior of the water in the gel on cooling. Previous researchers have invoked various models to describe the organization of water in a hydrogel. In this study, the simplest model which could explain all of the results from the different thermal analysis techniques was one which consisted of three classes of water: (i) hydration water in close proximity to the polymer; (ii) interstitial water in regions or cavities surrounded by polymer chains; and (iii) bulk water.

Journal Article↗
PubMed1999

Electromagnetic and thermal analysis for lipid bilayer membranes exposed to RF fields.

Experiments with pulsed radio frequency fields have shown influence on the low-frequency behavior of lipid bilayer membranes. In this paper, we present an electromagnetic and thermal analysis of the used exposure device to clarify whether the observed effects have a thermal cause and to determine the fields at the lipid bilayer. In order to model the very thin lipid bilayer (about 5 nm) accurately, the electromagnetic analysis is broken into several steps employing the finite difference time domain technique and a finite element/boundary element hybrid approach. Based on the obtained power loss due to the electromagnetic fields, the temperature change is calculated using the finite element method for the solution of the heat conduction equation. Both, the electromagnetic and the thermal analysis are performed for a variety of material parameters of the exposure device. The electromagnetic analysis shows that the exposure device is capable of producing voltages on the order of 1 mV across the lipid bilayer. The combined electromagnetic and thermal calculations reveal that the temperature oscillations due to the pulsed radio frequency fields are too small to directly influence the low-frequency behavior of the lipid bilayer.

Electromagnetic Fields↗
PubMed1988

Thermal analysis of water in p(HEMA) hydrogels.

Hydrogels composed of poly(hydroxyethyl methacrylate) (pHEMA) and water were investigated using differential thermal analysis (DTA) and adiabatic calorimetry (AC). The results show that the crystallization of water in the gels is a very gradual process, leading to the development of a metastable, non-equilibrium state. They are not in agreement with models that assume the actual presence of thermodynamically different classes of water in the gels, based on the abnormal melting behaviour of this water. The results indicate that the internal structure of these gels can be described as that of an elastic solution, in which the water molecules are distributed continuously over all possible orientations to and interactions with the polymer.

Calorimetry↗
PubMed1996

Characterization of steroid/cyclodextrin inclusion compounds by x-ray powder diffractometry and thermal analysis.

Two inclusion compounds, progesterone with beta- and gamma-cyclodextrin, were studied with X-ray powder diffractometry and thermal analysis. Disappearance of characteristic X-ray diffraction patterns of the two compounds as well as the appearance of a new diffraction pattern for each were found when formation of the inclusion compounds was completed. The X-ray diffraction patterns of beta-cyclodextrin measured at various temperatures showed a structural change occurring between 60 degrees C to 80 degrees C, which coincided well with the DSC endothermic peak around 75 degrees C. Results suggest that changes in the X-ray diffraction patterns of cyclodextrin during inclusion formation and during heating is due to the displacement of adsorbed water by progesterone in the cavity of cyclodextrin.

Crystallography, X-Ray↗
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↗
PubMed2002

Thermal analysis of dental resins cured with blue light-emitting diodes (LEDs).

Thermal analysis was used to measure the characteristics of dental resins cured with the use of a new light-activation unit equipped with high illuminant blue light-emitting diodes (LEDs). The characteristics were compared with those of resins cured with the use of two conventional halogen lamp units. The prepared base monomer consisted of a mixture of Bis-GMA and TEGDMA (60:40 by weight), with 0.5 wt% CQ/DMPT or CQ/DMAEMA. The two experimental visible-light-cured resins were polymerized for 40 s. Differential scanning calorimetry (DSC) was used to examine the thermal characteristics of the cured resins. The activation energy for the decomposition of the dental resin was calculated from the peaks of the endothermic curves obtained when the specimens were heated at three different rates (5, 10, and 15 C/min) during DSC. The activation energies calculated for the LED-cured specimens were more than 220 kJ/mol; specimens cured with the use of the halogen units had activation energies of less than 192 kJ/mol. The Knoop hardness number (KHN) of the same specimens was measured, and was higher with the blue LED units than with halogen lamp units. Therefore, dental resins cured using blue LEDs have a higher degree of polymerization and more stable three-dimensional structures than those cured with halogen lamps.

Calorimetry, Differential Scanning↗
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↗
PubMedDate not supplied

Microencapsulation of menadione sodium bisulphite with polydimethylsiloxane by the spray-drying process: characterization by thermal analysis.

Menadione sodium bisulphite was microencapsulated with a polydimethylsiloxane membrane using spray-drying technology. Tests were performed using laboratory equipment and a Niro Atomizer pilot plant to scale up the process. The products were characterized with differential thermal analysis (DTA) and chemical and physical methods. Many differences between raw material and microencapsulated powder result from DTA data. The thermal characterization confirms that the spray-drying microcoating could be used to protect powder from the oxidative actions of the atmosphere.

Chemistry, Pharmaceutical↗
PubMed2006

[Thermal analysis and the distribution rule of heavy metals during electroplating sludge combustion].

A representative hazardous waste containing heavy metal is electroplating sludge, Thermal characteristic and the distribution of different heavy metal elements (Pb, Cd, Cu, Zn, Ni and Mn) was studied. The results of experiment show that from thermal analysis, in the process of experiment of thermal gravity there are some peaks of weight loss as 100 degrees C, 150 degrees C and 600 degrees C among these peaks, the peaks of 100 degrees C and 150 degrees C is caused by that the volatile separated out and organic matter combusted and pyrolysed at the same time, the peak of 600 degrees C is produced by the carbonate decomposed. From EDS analysis, electroplating sludge is composed by these main elements which are O, S, Al, Ca, Cr and Fe, and other secondary elements such as Mg, Cu, Zn, P, Cl and C. In the process of temperature promoted, the quantity of nonmetal such as C and Cl is decreased, and the quantity of Cr, Fe, and Mg is steady within 900 degrees C. From the experiment of distribution rule, the quantity of Mn, Pb, Ni and Cu decreased in the process of combustion while the furnace temperature raised,among these heavy metal the quantity of Ni decrease most obviously,and on the contrary the quantity of Cd enrich obviously in this process.

Electroplating↗
PubMed1995

The combined use of DSC and TGA for the thermal analysis of atenolol tablets.

The New York Regional Laboratory's forensic pharmaceutical group used thermal analysis (TA) to ensure adherence to batch formulations by drug manufacturers. TA in our laboratory consisted of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC and TGA were used to analyse finished dosage forms and their components. In this study the components of atenolol formulations were qualitatively identified by analysing individual components and comparing with the finished product. DSC and TGA were used together to develop a profile of batch formulations, with each analytical technique giving complementary types of information. For example, the excipient sodium starch glycolate was identified by DSC and confirmed by TGA. These experimental results demonstrated the use of TA for the characterization of finished dosage forms and the qualitative identification of some of the individual components in batch formulations.

Atenolol↗
PubMed1999

Thermal analysis of hydroxypropylmethylcellulose and methylcellulose: powders, gels and matrix tablets.

This review focuses on the thermal analysis of hydroxypropylmethylcellulose (HPMC) and methylcellulose. Differential scanning calorimetry (DSC) of their powders is used to determine temperatures of moisture loss (in conjunction with thermogravimetric analysis) and glass transition temperatures. However, sample preparation and encapsulation affect the values obtained. The interaction of these cellulose ethers with water is evaluated by DSC. Water is added to the powder directly in DSC pans or preformed gels can be evaluated. Data quality depends on previous thermal history but estimates of the quantity of water bound to the polymers may be made. Water uptake by cellulose ethers may be evaluated by the use of polymeric wafers and by following loss of free water, over a series of timed curves, into wafers in contact with water. Cloud points, which assess the reduction of polymer solubility with increase of temperature, may be assessed spectrophotometrically. DSC and rheometric studies are used to follow thermogelation, a process involving hydrophobic interaction between partly hydrated polymeric chains. The advantages and disadvantages of the various methodologies are highlighted.

Calorimetry, Differential Scanning↗
PubMed1978

Thermal analysis of dental impression waxes.

Ten dental impression waxes were characterized by penetration and differential thermal analysis. Penetration and initial transition temperatures were directly correlated. Penetration at 37 C ranged from 2.5 to 22% for bite waxes and was 100% for corrective waxes. Distortion of an impression wax may occur upon removal from the mouth.

Bees↗