Authors:M. Ruiz, I. Reyes, A. Parera, and V. Gallardo
Differential scanning calorimetry was used to study the stability of omeprazole in two forms: granules and powder. The drug
was subjected to light, elevated temperature (40 and 60�C) and different pH values. The greatest alterations in stability
were caused by pH, followed by light.
Solid state reactions of sputter-deposited Nb/Al multilayer thin films, with periodicities in the range 10–333 nm, have been studied by differential scanning calorimetry. The first phase to form upon annealing the films in NbAl3. Constant-heating-rate calorimetric measurements show the presence of two peaks for the formation of this phase, while isothermal scans reveal that the first peak is associated with a nucleation and growth type transformation. The formation of NbAl3 is thus interpreted as a two-stage process of nucleation and growth to coalescence (first peak) followed by growth until the consumption of one or both reactants (second peak).
Authors:Réka Dudás, Tünde Kupi, Andrea Vig, J. Orbán, and D. Lőrinczy
The effect of phalloidin on the thermal stability of skeletal actin filaments polymerized from ADP-binding monomers was investigated
with the method of differential scanning calorimetry. Phalloidin shifted the melting temperature of the ADP-F-actin from 59.1±1.0
to 80.0±1.2°C. The stabilizing effect of phalloidin propagated cooperatively along the filament. The cooperativity factor
according to the applied model was 1.07±0.11. With these measurements it was possible to demonstrate that the binding of phalloidin
has lower influence on the adjacent protomers in ADP- (k=1) than in ATP-actin filaments (k=3).
Authors:Andrea Vig, Réka Dudás, Tünde Kupi, J. Orbán, G. Hild, D. Lőrinczy, and M. Nyitrai
The effect of phalloidin on filaments polymerized from ADP-actin monomers of the heart muscle was investigated with differential
scanning calorimetry. Heart muscle contains α-skeletal and α-cardiac actin isoforms. In the absence of phalloidin the melting
temperature was 55°C for the α-cardiac actin isoform and 58°C for the α-skeletal one when the filaments were generated from
ADP-actin monomers. After the binding of phalloidin the melting temperature was isoform independent (85.5°C). We concluded
that phalloidin stabilized the actin filaments of α-skeletal and α-cardiac actin isoforms to the same extent when they were
polymerized from ADP-actin monomers.
The single components of association colloids are amphiphilic molecules, which are held together by van der Waals forces and/or hydrogen interactions. The thermodynamic parameters associated with the aggregation behaviour of amphiphiles depend on the chemical nature of the molecules as well as their environmental conditions (temperature, ionic strength, etc.). The systems studied and presented in this paper are association colloids, also known as micellar systems, which are formed of biological relevant detergents (e.g. bile salts, fatty acids). Information concerning the self-organisation (self-aggregation) of such micellar colloids can be easily obtained from isothermal titration calorimetry (ITC), as the critical micelle/aggregation concentration, the number of molecules (n) associated in the aggregate and the heat of aggregation. A complete thermodynamic description (ΔH, ΔS, ΔG, ΔCp) of the micellar colloids can be derived from the ITC data, allowing insights into the formation and stability of these colloidal systems. Based on the mass action model, taking into account counter ion binding, the ITC titration curves were simulated, and the aggregation number n of the aggregates derived. Isothermal titration calorimetry has a considerable advantage compared to other methods, because the critical micellisation concentration, the thermodynamic parameters of the aggregation process, and the aggregation numbers can be determined directly from one experiment.
The physical aging characteristics of maltose glasses aged at two temperatures below the glass transition temperature, Tg, (Tg-10C and Tg-20C) from 5 to 10 000 min were measured by standard differential scanning calorimetry (SDSC) and modulated differential
scanning calorimetry (MDSC). The experimentally measured instrumental Tg, the calculated Tg, and the excess enthalpy values were obtained for aged glasses using both DSC methods. The development of excess enthalpy
as a function of aging time, as measured by both SDSC and MDSC, was fit using the Cowie and Ferguson and Tool-Narayanswamy-Moynihan
models. The change in the Tg values and the development of the excess enthalpy resulting from physical aging measured by the two DSC methods are discussed.
An uptake or a release of heat accompanies practically all molecular binding interactions. Therefore isothermal titration microcalorimetry is universally applicable for the characterisation of such binding processes. Calorimetric analyses do not require marker molecules or intrinsic spectroscopic reporter groups, which can modify the analysed interactions. Furthermore, measurements are carried out in solution and the adsorption of reactants to a solid phase is thus avoided. At variance with most other analytical approaches, titration calorimetry determines simultaneously enthalpy and entropy contributions of the binding interactions, as well as the binding constant and stoichiometry. In our analyses of the interactions between monoclonal antibodies and candidate antigens for vaccines vs. malaria and malignant melanoma, isothermal titration calorimetry has turned out to be a very valuable technique. The obtained quantitative data on biomolecular interactions can substantially support the rational design of epitope-focused vaccines.
Authors:C. Cardelli, G. Conti, P. Gianni, and R. Porta
The mixing enthalpies of blends of polymethylmethacrylate (PMMA) with poly(styrene-co-acrylonitrile) (SAN) were investigated
by analogue calorimetry through the determination of the excess enthalpies of pseudobinary model mixtures corresponding to
the addition of methyl-i-butyrate to a binary mixture of acetonitrile or propionitrile plus toluene or ethylbenzene.
A group contribution procedure, based on UNIQUAC equation, was also devised and the polymeric mixing enthalpies were calculated
from properly defined group contributions. Enthalpies for polymeric interactions were introduced into the Flory-Huggins equation
and the miscibility window of PMMA-SAN mixtures was calculated.
The results show a qualitative agreement with the experimental miscibility data and indicate that both the analogue calorimetry
and the group contribution procedures yield correct results when acetonitrile, and not propionitrile, is chosen as the model
for the polyacrylonitrile repeat unit of the copolymer.
Authors:T. Tsukame, M. Kutsuzawa, H. Sekine, H. Saitoh, and Y. Shibasaki
A forensic sample consisting of melt-recrystallized polymers that was recovered from the scene of a fire in a factory was identified by differential scanning calorimetry. The factory commonly used two kinds of film sheets, A and B, made by different manufacturers. It was necessary to decide whether the forensic sample related to material A or B. The forensic sample and reference samples of materials A and B were subjected to infrared spectroscopy and pyrolysis gas chromatograph mass spectrometry measurements, which revealed their polyethylene nature. The thermal behaviour of the samples was examined by differential scanning calorimetry (DSC) and they were found to be blends of two kinds of polyethylenes, low-density polyethylene and linear low-density polyethylene. The samples could be identified and distinguished from each other via the DSC measurements.
Authors:H. Tanaka, S. Sawai, K. Morimoto, and K. Hisano
The hemispherical total emissivity of partially stabilized zirconia has been obtained by a spectral analysis of the normal
emission spectra between 400–850 K. Thermal conductivity was evaluated with this emissivity and temperature gradient in the
sample. Effects of the scattering of the radiation in a ceramic sample are also investigated. In addition, specific heat capacity
was measured by thermal radiation calorimetry. Current results are compared with those reported for tetragonal zirconia with
the same yttria content and for monoclinic phase.