Application Of Differential Scanning Calorimetry Research Articles

Application of differential scanning calorimetry and high performance liquid chromatography to determine the effects of mixture composition and preparation during the evaluation of niclosamide-excipient compatibility

Application of differential scanning calorimetry and high performance liquid chromatography to determine the effects of mixture composition and preparation during the evaluation of niclosamide-excipient compatibility

Application of differential scanning calorimetry in food research and food quality assurance

Differential scanning calorimetry (DSC) is the most widely used thermal analytical technique in food research and it has a great utility in quality assurance of food. Proteins are the most studied food components by thermal analysis including studies on conformation changes of food proteins as affected by various environmental factors, thermal denaturation of tissue proteins, food enzymes and enzyme preparations for the food industry, as well as effects of various additives on their thermal properties. Freezing-induced denaturation of food proteins and the effect of cryoprotectants are also monitored by DSC. Polymer characterization based on DSC of polysaccharides, gelatinization behaviour of starches and interaction of starch with other food components can be determined, and phase transitions during baking processes can be studied by DSC. Studies on crystallization and melting behaviour of fats observed by DSC indicate changes in lipid composition or help characterizing products. Thermal oxidative decomposition of edible oils examined by DSC can be used for predicting oil stability. Using DSC in the freezing range has a great potential for measuring and modelling frozen food thermal properties, and to estimate the state of water in foods and food ingredients. Research in food microbiology utilizes DSC in better understanding thermoadaptive mechanisms or heat killing of food-borne microorganisms. Isothermic microcalorimetric techniques provide informative data regarding microbial growth and microbial metabolism.

Shell-modified Sikarex calorimeter as a screening tool for runaway reactions

Adiabatic or accelerating rate calorimetry and differential scanning calorimetry (DSC) are both used for the study of runaway reactions. The application of DSC is limited to the study of solids and homogeneous liquid mixtures and generally no information is obtained on pressure development. Adiabatic calorimetry is laborious and time consuming. This paper describes the development of the Shell-modified Sikarex calorimeter as a versatile screening tool for runaway reactions, combining advantages of both techniques. Its construction facilitates the study of multiphase systems. A case history on the treatment of an organic mixture with nitric acid demonstrates a few of the unique properties of the instrument.

Application of differential scanning calorimetry and X-ray powder diffraction to the solid-state study of metoclopramide

Application of differential scanning calorimetry and X-ray powder diffraction to the solid-state study of metoclopramide

Application of differential scanning calorimetry to the study of drug-excipient compatibility

Differential scanning calorimetry (DSC) has been used to investigate drug-excipient interactions and, in consequence, their compatibility. In particular, binary mixtures of nefazodone with magnesium stearate and lactose, and fosinopril with the same excipients were prepared and analysed, after proper conditioning. The thermoanalytical results were compared with those obtained by spectroscopic (UV, IR) and chromatographic (HPLC) analysis. We believe that changes in DSC runs cannot always be a sufficient condition to prove that some interaction occurs between drug and excipient during storage at room temperature. Some data on the spectroscopic characteristics of nefazodone and fosinopril drugs and their thermal behaviour are also reported.

Physicochemical characterization of the structural stability of some plant globulins

The fluorescence properties of amaranth, soybean, rice, sorghum and maize globulins, and cassava globulin-like proteins were measured as a function of fluorescent light intensity, peak response and shift in the maximum of emission using the fluorescence of tryptophan at 295 nm. Application of differential scanning calorimetry (DSC) of these globulins gave a quantitative estimation of their thermal stabilities in solid state. The thermodynamic data associated with transition and the number of ruptured hydrogen bonds were calculated. Differences in secondary structure and α-helical content were observed. Relative structural stabilities of native plant globulins were also estimated by X-ray diffractometry and Fourier transform infrared (FT-IR) measurements.

Structural Stability of Globulins

Application of differential scanning calorimetry (DSC) and the susceptibility of amaranth globulins (A-G) to α-chymotrypsin gave a quantitative estimation of protein denaturation in solid state. To compare effects of size and crystal structure, A-G, quinoa globulins (Q-G), and bovine γ-globulins (γ-G) were examined at similar conditions for the extent of denaturation. A-G and Q-G showed similar data, but γ-G exhibited maximal conformational changes. The larger percentage of denaturation in globulins that is associated with enthalpy and the number of ruptured hydrogen bonds correspond to the smaller crystallinity determined by X-ray diffraction and disappearance of the α-helix in Fourier transform-infrared spectra. Keywords: Amaranth; quinoa; calorimetry; denaturation; spectroscopy

Thermodynamics of denaturation of staphylococcal nuclease mutants: an intermediate state in protein folding.

A valuable approach to understanding the forces that maintain protein structure is to analyze the thermodynamic effects of mutations on protein folding. The folding process is most often described using an energetic model that assumes a two-state transition between the native and denatured states. However, some results obtained using this approach for mutants of the protein staphylococcal nuclease have contradicted expectations from our current understanding of protein energetics. The application of differential scanning calorimetry to a set of mutant nuclease proteins allowed us to measure directly the effects of mutations on the enthalpy and heat capacity changes of unfolding, as well as on the cooperativity. We found that most of these effects can be understood with a three-state model of folding including a distinct intermediate, but not with the two-state model. Use of a three-state instead of a two-state model leads to large differences in conclusions about the stability effects of some mutations, suggesting that reevaluation of the effects of mutations on this and other proteins may be necessary to achieve an accurate description of folding energetics. The two-state assumption commonly used in protein stability studies may be an oversimplification in many cases.

Application of dielectric spectroscopy and DSC to the study of relaxations in some copolymeric hydrogels

AbstractThe nature of water in copolymeric N‐vinyl pyrrolidone/methyl methacrylate hydrogels has been investigated using dielectric thermal analysis (DETA) and differential scanning calorimetry (DSC). Dielectric tan δ measurements are reported over a frequency range 500 Hz‐20 kHz and a temperature range of −140 to +20°C. The observed complex relaxations were attributed to the mobility of water and the relaxation processes of the copolymer matrix. In addition DSC was used to measure the melting endotherm of water in gels partially swollen to a pseudoequilibrium. The resultant data were fitted to a two‐phase approximation model. © 1995 John Wiley & Sons, Inc.

Hazard evaluation of polymerizable compounds

AbstractReactive monomers are a special class of materials used widely in the chemical industry in the production of polymers. Many of these materials are thermally unstable and may polymerize during handling and storage with a release of significant amounts of energy. If this energy is not controlled properly, it can lead to a runaway reaction. Compounding the concern for the stability of monomers is the fact that these materials are typically transported and stored in large volume. The undesired initiation of the polymerization reaction may be caused by a number of factors, including contamination, exposure to extreme environmental conditions, or inhibitor loss. For example, an “unintended” polymerization can result from a seemingly benign procedure such as spill control with common absorbents. These and other factors mean that the reactive chemicals evaluation of monomers presents special problems and concerns which require more detailed experimental design for reliable hazard testing. This paper discusses the practical aspects of reactive chemicals testing strategies for monomers and rules‐of‐thumb for monomer inhibition, compatibility, spill control, and so‐called quenching (also called short‐stopping) agents. The techniques discussed range from simple “age and observe” type tests to more sophisticated heat flux calorimetry evaluations. We also discuss the more routine application of Differential Scanning Calorimetry and Accelerating Rate Calorimetry to monomers. Vent sizing applications with the VSP device are also presented with emphasis on total containment during a runaway.

Simultaneous differential scanning calorimetry, X-ray diffraction and FTIR spectrometry in studies of ovalbumin denaturation.

The new application of differential scanning calorimetry (DSC) and the susceptibility of ovalbumin to alpha-chymotrypsin gave a quantitative estimation of protein denaturation in solid ovalbumin. Solid ovalbumin in granules with 11% of water was heated at 100 degrees C in closed and nonclosed ampules. In order to compare effects of size and crystal structure, two proteins (bovine albumin and gamma-globulin) were examined at similar conditions for the extent of denaturation. Ovalbumin and bovine albumin showed similar extents of denaturation, but gamma-globulin, with a very different molecular mass, showed the maximal conformational changes. The enthalpy of denaturation was measured to elucidate the conformational changes in solid proteins. Its value was used for calculation of the degree of denaturation. The thermodynamic data associated with transition were calculated and the number of bonds broken during denaturation was determined. Intrinsic fluorescence was utilized in order to compare these two methods. Moreover, X-ray diffraction and FTIR spectrometry were applied to native and denatured proteins.

Application of differential scanning calorimetry to the study of latex stability

Differential scanning calorimetry was used to study the effect of temperature, shaking, and pH on the stability of an aqueous dispersion of ethylcellulose latex particles (Aquacoat™, 0.3 μm in diameter) obtained by emulsion polymerization, and frequently used as an excipient in pharmaceutical formulations. Of the three factors studied, pH had the most marked effect on latex stability, followed by shaking and temperature. We conclude that differential scanning calorimetry is a reliable method for the study of factors that modify the stability of some components of pharmaceutical formulations.

Industrial standardization of thermal analysis in Japan

To satisfy the needs for industrial standards for thermal analysis in the Japanese polymer industry, round-robin tests of differential scanning calorimetry (DSC), thermogravimetry (TG), thermomechanical analysis (TMA) and thermodilatometry (TD) have been carried out recently. The results are discussed in this short review. The DSC applications tested were not only for determination of transition temperature but also for measurements of the transition heat and heat capacity. The TG task group did not aim at longterm thermal endurance studies, but relative thermal stability in molding and estimation of filler content, residual solvent content, etc. TMA was found to be a useful tool for measuring softening temperature and heat distortion temperature, especially for high-temperature engineering plastics, instead of the Vicat test which has temperature limitations. For temperature calibration of DSC and TG, ICTA-NIST certified reference materials were used together with other potential temperature standards; some inorganic substances and alloys were not found to be preferable to pure metals. For TMA and TD metal plates were found to be very useful for temperature calibration. Analysis of the round-robin test results also clarified present status of practical applications of thermal analysis, such as reproducibility and causes of errors.

New applications of differential scanning calorimetry and solvent swelling for studies of coal structure: Prepyrolysis structural relaxation

Differential scanning calorimetry and solvent swelling have been applied for identifying physical transition temperatures in the macromolecular structure of coals. The transition processes seem to be associated with physical relaxation of the coal structure and are irreversible processes. In Pittsburgh no. 8 coal, one physical transition was noted at 250–300 °C (at 8 °C min −1) without any significant accompanying weight loss. Illinois no. 6 coal does not exhibit such a relaxation process at these temperatures. Coals of higher rank than high volatile bituminous i.e. Upper Freeport and Pocahontas no. 3 coals, exhibit structural relaxation just before the major thermal decomposition process and a sharp increase in solvent swellability accompanies this relaxation. In the case of both the Pittsburgh no. 8 and the Upper Freeport coal, structural relaxations at around 360 °C seem to coincide with release of ‘guest molecules’. In addition, significant shifts in transition temperatures have been observed with heating rate. In coals of higher rank than high volatile bituminous, pyridine exposure prior to thermal treatment does not influence the transition temperatures, indicating that heat is more effective than pyridine in relaxing the macromolecular structure, as suggested by Sakurovs et al. On the other hand, CS 2 pyridine mixtures are effective at relaxing the structure of the Upper Freeport coal, even at room temperature.

Differential scanning calorimetry of the solid-state thermal polymerization of TV-tert-butylacrylamide-ZnCl 2 complex

The application of differential scanning calorimetry and thermogravimetry to the study of the solid-state polymerization of N- tert-butylacrylamide complexed with ZnCl 2 has been studied. The scanning rate has a pronounced effect on the calculated endotherm and exotherm enthalpies. The polymerization enthalpy of the amide complexed with ZnCl 2, was calculated as 18.4 kJ mol −1, using an extrapolation of the scanning rate to zero. It is shown that the higher the heating rate, the smaller the influence of the decomposition reaction of the complex on the total endothermic effect. For higher heating rates, the total endothermic value, due almost entirely to the melting process of the complex, is estimated as 28.2 kJ mol −1.

Thin binary In 1−xSb x films prepared by flash evaporation

Thin binary In 1− x Sb x films of 1000 Å thickness have been prepared by flash evaporation. The antimony concentration x has been controlled to vary from 0.23 to 0.70. Grain sizes and homogeneity of concentration both before and after annealing at 250 °C, 350 °C, and 450 °C were examined by both X-ray diffraction and transmission electron microscopy. Application of differential scanning calorimetry allows discussion of an atomic migration mechanism and phase transformation kinetics as a function of concentration. Also, the relationship between the microstructures and the optical properties, such as reflectances, transmittances and absorption coefficients at 830 nm, are presented. Both the grain sizes and the optical reflectances observed show that the In 1− x Sb x film with an antimony concentration x ≈ 0.54 is a candidate for phase change optical recording.

Mechanism and enhancement of solute transport across the stratum corneum

This paper summarizes recent biophysical investigations of (a) stratum corneum (SC) barrier function, and (b) percutaneous penetration enhancement. Specifically, applications of differential scanning calorimetry (DSC) and infrared spectroscopy (IR) to probe the intercellular lipid domains of the SC are described. In vitro DSC experiments on isolated SC have determined the thermal melting behavior of the membrane and have indicated the presence of lipid phase transitions in the range 65–85 °C. Corresponding IR studies have confirmed this observation and, in conjunction with measurements of tritiated water permeability (Kp), have shown that solute flux increases with the number of gauche conformers along the lipid acyl hydrocarbon chains. There is an excellent correlation between Kp and the absorbance shift (to higher wavenumber) of the C-H antisymmetric stretching vibration associated with the SC lipids. Furthermore, it was found that certain putative penetration enhancers (e.g., cis-unsaturated fatty acids, such as oleic and vaccenic acids) induced similar shifts when applied to excised SC at ambient temperature. Concomitantly, the flux of another model solute (salicylic acid) was significantly enhanced by the treatment. The implied mechanism of penetration promotion (i.e., through the overall increased freedom of motion of the lipid acyl chains) was then examined in vivo, in humans, using attenuated total reflectance IR. Again, significant and sustained lipid disordering was induced by (in this case) oleic acid. In addition, through the assignment of unique absorbances, it was possible to obtain semi-quantitative measurements of (1) the enhancer in the upper layers of the SC, (2) the co-applied penetrant (4-cyanophenol, unequivocally identified by the intense C  N absorbance) and (3) the major vehicle component used (namely, propylene glycol, via the C-O stretching vibration). In this way, we have (i) documented the effect of the enhancer on the SC lipids, (ii) assessed the relative amount of the enhancer responsible for this action, and (iii) observed the kinetics of penetrant (solute) and solvent transport (in the presence and absence of enhancer) through the SC, from a single series of spectroscopic experiments in vivo in man. We suggest, therefore, that biophysical measurements of this type have considerable potential, often in clinically relevant situations, to reveal the crucial details of the mechanism and enhancement of solute transport across the SC.

The application of DSC in identification of LDPE/LLDPE blends mulching film

AbstractThe mulching film samples of known and unknown composition LDPE/LLDPE blends have been analysed and the film samples of unknown composition have been identified by means of differential scanning calorimetry (DSC). The relationships between composition of film samples and melting enthalpy peak in their DSC thermograms have been discussed. The working curve for determining the composition has been given. The experimental results show that DSC is a quick, effective and accurate method for the analysis of main composition of LDPE/LLDPE blends mulching films.

Application of Differential Scanning Calorimetry to Amaranth Starch Gelatinization – Influence of Water, Solutes and Annealing

AbstractGelatinization phenomena of amaranth starch were investigated using differential scanning calorimetry. Slight variations in onset (To) and peak (Tpl) temperatures were observed at moisture contents over 0.48 g water/g total. However, completion temperature (Tc) increased significantly. The intermediate transition temperature (Tp2) appeared at 0.61 g water/g total and below. The degree of gelatinization decreased by decreasing the moisture content. The three transition temperatures (To. Tpl and Tc) were increased and gelatinization delayed as the concentration of sucrose was enhanced. The three latter transition temperatures tended to increase as the sodium chloride was raised to 0.066 g/g total, but further increases in salt reduced significantly these temperatures. The gelatinization was delayed by increasing the salt concentration. After annealing for 12 h at 25 to 65°C, starch samples exhibited higher To and Tpl values, and narrowed gelatinization ranges. The degree of gelatinization augmented up to the annealing temperature of 55ºC and significantly decreased thereafter.

Application of differential scanning calorimetry in the study of intrazeolite metallophthalocyanines

The authors report a differential scanning calorimetric method for the study of Co(II) phthalocyanine formation in zeolite NaY.