Search Results
. 6. Kemp , RB . Nonscanning calorimetry 1999 Gallagher , PK eds. Handbook of thermal analysis and calorimetry Elsevier Amsterdam 1032 . 7. ASTM D3173–03 ( 2008
Differential scanning calorimetry
A tool to assess physical and chemical alterations in liposomes
Abstract
This study was aimed to investigate the physicochemical changes induced in 200 nm extruded oligolamellar DPPC:DPPG (10:1) liposomes by freezing, followed by γ-irradiation, in the absence and presence of 5 mM stable cyclic nitroxide radicals, 2,2,6,6-tetramethylpiperidine-1-oxyl (Tempo) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol). The characterization is based on the use of differential scanning calorimetry (DSC) and was aimed to differentiate the contribution of freezing and γ-irradiation in the presence and absence of nitroxides. Liposomal preparations of DPPC/DPPG which have sub-, pre- and main-phase transitions in the temperature range (0�C<T m<50�C) were used. Our results show that: (1) freezing modified and induced fusion to MLV as well as fission to SUV, (2) freezing did not fully prevent the radiation-induced changes in the thermotropic characteristics of the liposomes, and (3) Tempo and Tempol did not prevent the changes in thermotropic behavior caused as a result of freezing of the liposomal dispersion. These results demonstrate that DSC is a powerful and sensitive tool in both physical and chemical studies of lipid assemblies.
additions by conduction calorimetry ’, Ph.D. Tesis, ETS Ings. CCP, Polytechnic University of Madrid-Spain, 12 Dec. 2002 . 13 Larbi , J Fraay , A
Multicycle differential scanning calorimetry
Thermophysical procedures for research, development, and quality control of substances and materials
Abstract
Multicycle Differential Scanning Calorimetry (MCDSC) is a procedure where repeated temperature cycles are executed and the measured data are superimposed for a selected number of cycles. Temperature cycles with a single sample are executed under selected experimental conditions in one of these procedures, namely, the MCDSCs. The second one, MCDSCm is a procedure in which every identical temperature cycle starts with a new sample of the same substance of a similar mass. The procedure MCDSCs using the same sample for a number of cycles is only applicable for substances and materials which are chemically and physically stable under the selected experimental conditions. The application of MCDSC enhances two extremely important qualities of a DSC measurement, namely, the sensitivity and the statistical base, both qualities with respect to the final data elucidated. Another possibility by MCDSC also related to the enhanced sensitivity can lead the discovery of a phenomenon which hitherto has not been observed. The most important result of any MCDSC application is the determination of the mean DSC curve within the temperature interval of interest by superimposing the single curves point by point and by the division of the calorimetric values obtained with the number of scans evaluated. The signal-to-noise-ratio (SNR) for the mean curve can be compared with the value determined for one or even for all the single curves measured yielding the improvement factor achieved with a MCDSC measurement. This experimentally determined improvement of the SNR can be compared with the value given on a statistical consideration by Gauss as the square root of the number of cycles evaluated. The main aims of this article are to prove the practical application of the procedure and the efficiency in case of rather small sample masses. Substances were selected with known enthalpy transitions and, in addition, polystyrene was taken for a determination of the data for the glass transition by MCDSC. Rather small sample masses in the order of micrograms as well as the experimental conditions have been selected for the measurements with 4,4′-azoxyanisole and n-hexatriacontane with the expectation to get a value of SNR for the single curves of about unity or even below. Two aims should be achieved with these experiments. First, the multicycle procedures and the data evaluation developed should be capable of establishing, after performing of a certain number of cycles, a mean curve showing an improvement over the SNR with respect to the single curves. Second, we should be able to get a rough estimation of the lower limit of the SNR for a single curve, below the instrumental noise level of the DSC used, necessary to achieve with a MCDSC experiment a mean curve with a clearly visible peak.
include IR spectroscopy, X-ray diffraction, thermomicroscopy, and thermal methods, including differential scanning calorimetry [ 13 , 14 ]. The potential drugs studied in this article correspond to organosulfur and organoselenium compounds with
properties of the mixture [ 3 ]. For a determination of the effect of additive on the course of hydration, various methods based on calorimetry proved to be useful for their fastness, simplicity of analysis and high informative value [ 5 ]. From the
Abstract
Isothermal titration calorimetry (ITC) and reaction calorimetry (RC) have been used to construct the solid-liquid equilibrium line in ternary systems containing the solute to precipitate and an aqueous mixed solvent, and to study polymerization reactions under real process conditions, respectively. Phase diagrams have been established over the whole concentration range for some benzene substituted derivatives, including o-anisaldehyde, 1,3,5-trimethoxybenzene and vanillin, in {water + alcohol}mixtures at different temperatures. Acrylamide polymerization in aqueous solution using potassium permanganate/acid oxalic redox system as initiator was investigated on a homemade calorimeter, which works according to the isoperibolic mode. A Calvet type differential RC was used to illustrate the applicability of temperature oscillation calorimetry (TOC) for the evaluation of the heat transfer coefficient during the course of reaction.
-flow microcalorimeters of the Tian–Calvet type are most commonly used for this purpose. These high sensitive calorimeters need to be connected to a sensitive volumetric system in order to determine accurately the adsorbed amounts. The principles of calorimetry in the
Abstract
Polymorphism of trilaurin mixed with 4% of cholesterol was studied with a setup coupling calorimetry and phase characterisation by in-situ X-ray diffraction (Microcalix). Four polymorphic forms were identified. Monotropic and enantiotropic transitions were identified from the reconstruction of Gibbs free energy diagram which allows the control of trilaurin polymorphism.
Modulated temperature differential scanning calorimetry
Characterization of curing systems by TTT and CHT diagrams
Abstract
Modulated temperature differential scanning calorimetry (MTDSC) is used to study simultaneously the evolution of heat flow and heat capacity for the isothermal and non-isothermal cure of an epoxy-anhydride thermosetting system. Modelling of the (heat flow related) chemical kinetics and the (heat capacity related) mobility factor contributes to a quantitative construction of Temperature-Time-Transformation (TTT) and Continuous-Heating-Transformation (CHT) diagrams for the thermosetting system.
