Authors:J. Canotilho, F. Costa, A. Sousa, J. Redinha, and M. Leitão
Several samples of terfenadine prepared by crystallization from different solvents under different experimental conditions
were studied. The DSC curves obtained at a heating rate of 1C min−1 afforded the temperature of melting and the mole fractions of the components of each sample. Certain of the samples were
composed of two solid phases mixed in molar ratios varying between nearly one and a single structural form. Three polymorphic
forms were identified.
Authors:M. Leităo, J. Canotilho, M. Cruz, J. Pereira, A. Sousa, and J. Redinha
Terfenadine samples prepared by crystallization in different media and supersaturation conditions were used to investigate
the polymorphism of the substance. The study was based on DSC melting curves. An empirical parametric equation was used for
modelling the experimental data. The signal recorded was resolved into the corresponding overlapping peak components by fitting
analysis. Four polymorphic phases were identified.
The example of polyethylene of low density (PELD) crystallization in ethylbenzene and some other alkylbenzenes presence demonstrates
the unsufficiency of formal liquidus curve knowledge for the description of phase equilibrium in amorphous-crystalline polymer-liquid
system. Experimental data affirming polymorphous structure of PELD crystalline phase and influence of the solvent on the order
of various regular structures formation in it are being reported.
It is shown that for porous systems filled with a solvent, if the temperature domains of crystallization and melting of the
solvent are well separated, DSC technique, combined with suitably chosen thermal cycles, provides crystallization and melting
curves which are independent of a) the mass of the material, b) the thermal contact between DSC pan and material and c) the
thermal conductivity of the material. This method called DSC fractionation is applied to butyl rubber containing small water
nodules. Thermoporosimetry is then applied to get the size distribution of mesoscopic solvent droplets.
Comparative analysis of several methods for purity determination using DSC is presented. This is based on a mathematical model including the construction of theoretical melting curves for two-component systems and the calculation of recorded melting curves with the help of a set of equations describing the formation of a DSC output signal. It is shown that the true accuracy of purity determinations in the range of impurity concentrations ¯x=0.005–0.02 does not exceed 30–50%.
Authors:Erika Orosz, Katalin Perkátai, Beatrix Kapusinszky, Ágnes Farkas, and István Kucsera
Simple real-time PCR assay with one set of primer and probe for rapid, sensitive qualitative and quantitative detection of Entamoeba histolytica has been used. Consensus sequences were used to amplify a species-specific region of the 16S rRNA gene, and fluorescence resonance energy transfer hybridization probes were used for detection in a LightCycler platform (Roche). The anchor probe sequence was designed to be a perfect match for the 16S rRNA gene of Entamoeba species, while the acceptor probe sequence was designed for Entamoeba histolytica, which allowed differentiation. The performed characteristics of the real-time PCR assay were compared with ELISA antigen and microscopical detection from 77 samples of individuals with suspected clinical diagnosis of imported E. histolytica infection. Stool and liver abscess pus samples were examined with analytical sensitivity of 5 parasites per PCR reaction. The melting curve means Tms (standard deviation) in clinical isolates were 54°C. The real-time assay was 100% sensitive and specific for differentiation of Entamoeba histolytica, compared with conventional ELISA or microscopy. This real-time PCR assay with melting curve analysis is rapid, and specific for the detection and differentiation of Entamoeba histolytica. The suitability for routine use of this assay in clinical diagnostic laboratories is discussed.
Authors:Y. Kawasaki, A. Kuboki, S. Ohira, and M. Kodama
properties of lipid bilayer systems are compared for symmetric chain sphingomyelin
(N-palmitoylsphingomyelin) and asymmetric chain sphingomyelin (N-lignoceroylsphingomyelin).
These sphingomyelins were semisynthesized by a deacylation- reacylation process
with a natural sphingomyelin used as a starting material. The number of differently
bound water molecules was estimated by a deconvolution analysis of the ice-melting
curves obtained by a differential scanning calorimetry (DSC) and was used
to construct a water distribution diagram for these water molecules. Similarly
to a natural sphingomyelin used for comparison, the asymmetric chain sphingomyelin
was found to form small size vesicles having an internal cavity and incorporate
15 water molecules per molecule of lipid into its cavity, in contrast with
5 H2O/lipid for freezable interlamellar water observed
for large size multilamellar vesicles formed by the symmetric chain sphingomyelin.
DSC purity determinations have become very popular today . The latest edition of the Mettler software package for thermal analysis, TA72.S GraphWare, now comprises a powerful purity evaluation program. It is based on the simultaneous calculation of the mole ratio of the sum of the eutectic impurities, the melting point of the pure component, the melting point of the substance present and the linearization term. The portion of the melting curve investigated is selected appropriately.
The melting process of constrained nylon 6 fibers has been studied to estimate the true melting point of its original crystals.
The melting peak became simpler in shape and shifted to higher temperature with increasing fiber-axis restricting force. When
heating rate, β, was increased, the temperature where the melting curve initially departs from its baseline, Tsm, decreased
steeply in the range of 45 to 60C min-1, and increased linearly with increasing β above 60C min-1. By linear extrapolation of Tsm to 0C min-1, the temperature of ca 190C was obtained for the melting temperature of the original nylon 6 crystals. This seems to correspond
to the zero-entropy-production melting of the most imperfect crystallites of the nylon 6 fabric.