Preformulation compatibility studies of etamsylate and fluconazole drugs with lactose by DSC

Chemical compatibility of two drugs, namely, etamsylate and fluconazole was studied with lactose as excipient, employing differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques. The DSC patterns recorded for the mixtures of both the drugs with the common excipient (lactose) indicated that fluconazole as well as etamsylate were incompatible with lactose at high temperatures. X-ray diffraction patterns recorded for pure drugs and lactose and the mixtures of individual drugs with lactose prepared at room temperature by intimate grinding of the components revealed incompatibility of both the drugs with lactose also at room temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Oxidation of Saturated Fatty Acids Esters DSC investigations

Oxidation of saturated fatty acids ethyl esters: laurate, myristate, palmitate and stearate was investigated by means of DSC techniques under isothermal and non-isothermal conditions. The activation energies of isothermal oxidation were similar to each other (112–123 kJ mol⁻¹) and no influence of carbon length on the rate of oxidative decomposition was observed. Results obtained from non-isothermal experiments were similar only for the first stage of oxidation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determination of crystalline content gradients in cold-drawn poly-L-lactic acid films by DSC

Poly-L-lactic acid (PLLA) is a semi-crystalline, optically active, biodegradable, and biocompatible polymer that has been utilized extensively in biomedical applications as an implantable artificial cell scaffold material. In its crystalline form, PLLA is piezoelectric and it has been implicated in the enhancement of electromechanically induced osteogenesis in vivo. In its amorphous state, however, PLLA does not exhibit piezoelectricity. By uniaxially cold-drawing the polymer, PLLA can be endowed with varying degrees of piezoelectricity. It is important to understand the crystalline architecture of drawn PLLA so that the osteogenic potential imparted by piezoelectricity, if any, can be differentiated from the effects of sample crystallinity. In our work we investigate the induced crystallinity for samples of drawn PLLA at draw ratios between 1.0 and 5.5 by differential scanning calorimetry (DSC). As long-range molecular ordering occurs along the draw axis, we observe an increase in the average percent crystallinity up to a draw ratio of 5.0 and a slight decrease at a draw ratio of 5.5. More importantly, we observe significant heterogeneity in the crystalline content along the draw axis of standard dumbbells cut from PLLA and cold-drawn to representative draw ratios of 2.5 and 4.0. On average, the highest percent crystallinity occurs nearest the dumbbell center, but the maximum crystallinity is independent of draw ratio. Therefore, the draw ratio should not be considered a semi-quantitative estimate of localized PLLA crystallinity and point-to-point analysis of crystallinity in PLLA samples is required for constructing scaffolds with enhanced cell growth properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Starch Gelatinization Kinetics in Bread Dough. DSC investigations on 'simulated' baking processes

Starch gelatinization in wheat flour dough of various moisture contents was quantitatively evaluated by means of DSC. The experimental records were worked out in the form of excess heat capacity vs. T traces which were deconvoluted to single out the contribution of starch gelatinization from that of the decomposition of amylose-lipid complexes. The quantitative procedure used put into evidence that a third endothermic process would take place in the dough with a poor moisture content. DSC runs carried out with sealed pans (i.e., at constant moisture level) and open pans (from which some water was free to evaporate) allow simulation of two extreme conditions of a real baking process, namely that relevant to the central core and to superficial layer of a dough loaf, respectively. The extent of starch gelatinization occurred in these conditions was quantitatively assessed. These data were collected at various heating rates and used to define temperature-time-transformation(TTT) diagrams which are useful tools to predict the progress of baking for any given thermal history of the system. This revised version was published online in July 2006 with corrections to the Cover Date.     

DSC study of radiostability of 1,4-dihydropyridine derivatives

The effect of sterilisation by irradiation has been studied for the seven most often used in medicine derivatives of 1,4-dihydropyridine (nifedipine, nisoldipine, nicardipine, nitrendipine, nimodipine, felodipine and amlodipine). The sterilisation was performed for the compounds in the solid phase with an electron beam of the energy 10 MeV, at room temperature, using the irradiation doses from 20 to 400 kGy. The effects of the irradiation were studied by the methods SEM, DSC, XRD and TLC. The sterilisation with doses 20-100 kGy was found to cause no changes in the physico-chemical properties of the compounds, while the irradiation with higher doses (200-400 kGy) was found to induce changes in the colour, DSC spectrum and TLC picture. As follows from the TLC results, the main product of radiolysis of the compounds studied was a pyridine nitrozoderivative, which indicates the same mechanism of decomposition as in the process of photodegradation. The results prove that the 1,4-dihydropyridine derivatives being highly sensitive to visible and UV radiation are generally resistant to ionising radiation and thus can be subjected to sterilisation by irradiation. This revised version was published online in July 2006 with corrections to the Cover Date.     

DSC study on the motor protein myosin in fibre system

We have examined by DSC the complexes of myosin with actin in fibre system in the absence of nucleotides and the intermediate state of ATP hydrolysis by mimicking stable complex with myosin and ADP and beryllium fluoride in muscle fibres. Comparing the DSC results with other structural analogues of phosphate P_i leads the conclusion that the AM.ADP.BeF_x complex favours the AM.ADP.P_i complex in fibre system. The deconvolution of DSC scans resulted in four transitions, the first three transition temperatures were almost independent of the intermediate state of the muscle, the last transition temperature was shifted to higher temperature, depending on the actual intermediate states of ATP hydrolysis. In AM.ADP.V_i state the transition temperature at the second and third transitions (actin binding domain and myosin rod) varied only slightly, whereas the last one (the fourth transition) shifted markedly to higher temperature depending on the ternary complex, e.g. in case of ADP plus BeF_x it was 77.7 °C, the highest value in weakly binding state of myosin to actin. The sum of calorimetric enthalpies of the first and last curves was practically constant, but their fractions depended on the state of the muscle. In strongly binding state of myosin to actin (rigor, ADP state) the fraction of the first transition was much larger, than the last one, whereas in weakly binding state of myosin to actin, the fraction of the first transition decreased at the expense of the last one. It supports also the view that these transitions are parts of the same portion of the myosin molecule.     

Kinetic investigations on the basis of isothermal DSC measurements of hydrogenation and dehydrogenation of magnesium hydride

Results of kinetic investigations on the basis of isothermal DSC measurements by means of defined pressure changes are presented and interpreted for the Mg/MgH₂ system. From an evaluation of the experimentally obtained DSC-signals, the dependence of reaction rate on hydrogen pressure p₀, temperature and sample morphology could be described. Under certain conditions, it is possible to visualise individual rate-determining steps and, thus, to arrive at conclusions on the reaction mechanism.     

Kinetic study of chitosane/genipin system using DSC

Knowledge of the the kinetic study of chitosan/genipin allow to know the different effects that time and temperature have on the cure reaction of the material. The total enthalpy of reaction, the glass transition temperature and the partial enthalpies have been determined using DSC in dynamic mode. Two models, one based on chemical kinetics and the other accounting for diffusion were used. The incorporation of the diffusion factor in the second model allowed for the cure kinetics to be predicted the whole range of conversion.     

DSC investigation of oxygen subsystem in Ba-Y-Cu-O superconductors

DSC investigations have been performed for a series of compounds Ba₂YCu₃O_y with the oxygen content varying in the rangey=6.0...6.9 by means of various heat treatments at 800–1200 K followed by quenching, or through the chemical extraction of oxygen by placing the sample in dihydrogen at 470–490 K. The sample preserving a constant oxygen content during heating in nitrogen exhibited exothermal effects between 450 and 850 K. It has been shown that the H vs. y function reaches maximum aty 6.5. Kinetic measurements have shown that the diffusive mobility of oxygen atoms in the lattice is responsible for these effects, viz. the Arrhenius and cooperative processes of reorganization in the non-equilibrium oxygen subsystem of the bulk.

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Zusammenfassung Für eine Reihe von Verbindungen der allgemeinen Formel Ba₂YCu₃O_y und einem Sauerstoffgehalt vony=6.0....6.9 wurden mittels verschiedener Wärmebehandlungen bei 800–1200 K, gefolgt durch Abschrecken oder beim chemischen Sauerstoffentzug durch Einbringen der Probe in Diwasserstoff bei 470–490 K DSC-Untersuchungen durchgeführt. Wird die Probe in Stickstoff erhitzt, so behält sie ihren Sauerstoffgehalt bei und zeigt bei 450–850 K einen exothermen Effekt. Es wurde gezeigt, daß die Funktion H(y) bei etwa y=6.5 ein Maximum erreicht. Kinetische Messungen zeigen, daß für diesen Effekt die diffusive Beweglichkeit der Sauerstoffatome im Gitter verantwortlich ist.

     

The utility of phase correction in modulated DSC

Traditionally, Modulated DSC (MDSC^®) [1] has been used to simultaneously measure the heat capacity and heat flow of a sample in a single experiment. As first proposed by Readinget at. in 1992 [2], this complex heat capacity signal (C_p ^*) can be further deconvoluted into components which are in-phase (C_p) or out-of phase (C_p with the imposed temperature modulation. The vector sum of these components, respectively termed the reversing C_p and kinetic C_p, is equal to the aforementioned complex C_p (C_p ^*).Recent research has centered around the analysis of these signals and their inclusion into MDSC experiments. For most polymer systems, the contribution of the kinetic C_p is negligible, except at the melt. This signal does contain a small peak at the T_g of PET, but the significance of this peak is to date not clear. Examples of further applications will be presented and discussed, as well as the derivation and interpretation of novel MDSC signals.     

DSC studies on long-term properties of nitrocellulose and SYM-diphenylurea system

Long-term investigations of the phase structure and pore structure of nitrocellulose and sym-diethyldiphenylurea (C1) mixtures were conducted for samples with C1 mass fractions w _C1=0.5, 0.6 and 0.8. The distribution of pore sizes and the composition of the nitrocellulose matrix were determined based on the melting enthalpy of C1. The three kinds of pores was observed with the characteristic size of about 7, 14 and 28 nm. Long-term storage of mixtures caused an increase in size of the smallest pores and a decrease of C1 concentration in the nitrocellulose matrix. The mechanism of changes in pore sizes is presented in term of multi-sheet model of NC fiber. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrogen determinations in a zirconium based alloy with a DSC

In the present work a method to measure hydrogen concentrations in zirconium-based alloys was developed measuring simultaneously both, the temperature of terminal solid solubility, T_TSSd, and the hydride dissolution heat, Q_δ→α, using a differential scanning calorimeter (DSC). The hydrogen concentration measured with that technique, [H]_Q, and the values obtained with a standard hydrogen gas meter, [H]_HGM, shows a linear relation: [H]_Q = (1.00 ± 0.03)[H]_HGM| + (9.2 ± 8.0) with a correlation factor of 0.99 in the entire solubility interval in the αZr phase, from 15 to 650 wt. ppm-H. The mean enthalpy value determined with two different criteria for T_TSSd and Q_δ→α measurements is  kJ/mol H. The present method is specially appropriate for alloys where a partition of the overall hydrogen concentration in two phases exists. It is applicable to all hydride forming metals which ideally follows the van’t Hoff law.     

DSC and X-ray Diffraction Study of Polymorphism in n-Alkylammonium Chlorides

The influence of the hydrocarbon chain length in the formation of interdigitated and non-interdigitated bilayers in n -alkylammonium chlorides has been investigated for chain lengths varying between 8 and 14 carbon atoms. The formation of non-interdigitated bilayers during crystallization from solution is favoured for shorter chains whilst the interdigitated structure is predominant for larger chains. The thermodynamic parameters of the solid to solid phase transitions in the non-interdigitated samples depend on chain length showing the odd-even alternation that characterized homologous series in n -paraffins. The solid to liquid crystal phase transition temperatures and enthalpies show a linear dependence with the chain length. This revised version was published online in July 2006 with corrections to the Cover Date.     

CoC2O4·2H2O在空气中的热分解动力学研究

纳米Co3O4具有尖晶石结构,Co3 占据八面体位,具有较高的晶体场稳定化能,在空气中低于800℃时十分稳定,是优良的催化材料[1]。Co3O4还可以作为高比能锂离子电池负极材料具有非常好的电化学活性,充放电容量高达960m A h·g-1。纳米Co3O4在紫外、可见及近红外区域都有良好的吸收效果,因此,在隐身技术、保温节能技术等领域具有潜在的应用前景。所以,Co3O4超细粉体的制备和应用研究具有十分重要的意义。我们合成了草酸盐先驱物制备纳米Co3O4用作隐身材料,因此对先驱物的热分解过程研究是十分必要的。热分析方法在了解先驱物热分解反应的物理…     

DSC in the Chemical Analysis of Drugs. Determination of diclofenac in pharmaceutical formulations

Differential scanning calorimetry was applied to the determination of diclofenac in three 'Voltaren' formulas. The pharmaceutical products (soluble tablets, suppositories and vials) were selected in order to show that calorimetric analysis is an easy technique to perform and can be competitive with other conventional methods. In the tablets diclofenac (DH) was determined, without any pre-treatment, from the area of the endothermic peak which occurs at about 180°C in the DSC curve obtained in N2 atmosphere. In the analysis of the suppositories and vials, nitrilotriacetic acid (NTA) was added to transform the diclofenac sodium salt (DS) into the thermally active form (DH). In both cases, it was necessary to eliminate the interference of excipient by cyclohexane extraction (suppositories) or by a multistep program for the DSC run (vials). The accuracy of the results and the simplicity of the procedure justify the important role of DSC in the analysis of these drugs and certainly of several other commercial products. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solid state reactions in the platinum–mercury system

Thermogravimetry, Differential Scanning Calorimetry and other analytical techniques (Energy Dispersive X-ray Analysis; Scanning Electron Microscopy; Mapping Surface; X-ray Diffraction; Inductively Coupled Plasma Atomic Emission Spectroscopy and Cold Vapor Generation Atomic Absorption Spectroscopy) have been used to study the reaction of mercury with platinum foils. The results suggest that, when heated, the electrodeposited Hg film reacts with Pt to form intermetallic compounds each having a different stability, indicated by at least three mass loss steps. Intermetallic compounds such as PtHg₄, PtHg and PtHg₂ were characterized by XRD. These intermetallic compounds were the main products formed on the surface of the samples after partial removal of bulk mercury via thermal desorption. The Pt(Hg) solid solution formation caused great surface instability, attributed to the atomic size factor between Hg and Pt, facilitating the acid solution’s attack to the surface.     

Decomposition of DSC curves of dairy products with Gaussian functions

Summary DSC measurements have wide application in the field of biochemical/biophysical research to look into the melting behaviour of muscle proteins in different intermediate states of ATP hydrolysis cycle as well as in the field to develop dairy products. It was a demand to develop a deconvolution program to evaluate and interpret the background of DSC scans such a way that the decomposition into a proper function has to be simple and quick. There should be possible to choose the proper parameters as well as to calculate the data of decomposing curves with the simultaneous graphic representation of them including the resultant DSC scan as the sum of decomposing functions. In most cases Gaussian function is used for this purpose. Our main field of interest is the food physics where e.g. the proliferation of different probiotic bacteria follows a lognormal distribution, its first derivative is a Gaussian one, for this reason we have chosen it. The main parts of this PC program are: -the process of fitting and calculation of Gaussian functions, a multiple step correction of these function (optimal fitting), graphic representation of all functions. An example is shown for its application how to analyse the melting of butter fat.     

New ta system for simultaneous determination of thermo-optical properties and DSC of different organic compounds

A new instrument for DSC in combination with thermomicroscopy in transmitted light is described, where a DSC device is in corporated within a commercially available hot stage.     

DSC study of melting and glass transition in gelatins

In the range from –50° to +130°C, the temperature dependence of the heat capacity for different kinds of gelatins with water contents of from 2 to 95% was studied by the DSC method. It was shown that, in all studied cases, metastable collagen-like structures are formed in gels or crystalline gelatins, with thermodynamic parameters depending on the formation conditions. The characteristic properties of the glass transitions in amorphous gelatins and crystalline gelatins with different melting heats and different contents of the ordered phase were established. Special attention is paid to the structural properties of free and bound water. The dependence of the glass transition temperatureT _g on the bound water content was shown to be of general applicability for many denatured biopolymers. Free water in gelatins, in distinction to the bound water, does not act as a plasticizer, but forms a rigid matrix inhibiting the glass transition.

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Zusammenfassung Mittels DSC wurde im Bereich –50° bis +130°C die Temperaturabhängigkeit der Wärmekapazität für verschiedene Arten von Gelantine mit einem Wassergehalt von 2 bis 95% untersucht. Es wurde gezeigt, daß in allen untersuchten Fällen metastabile kollagenähnliche Strukturen in Gelen oder kristallinen Gelantinen gebildet werden, deren thermodynamische Parameter von den Bildungsbedingungen abhängen. Es wurden die charakteristischen Eigenschaften der Glasumwandlungen in amorphen Gelantinen und kristallinen Gelantinen mit unterschiedlichen Schmelzwärmen und einem unterschiedlichen Gehalt an geordneter Phase bestimmt. Spezielle Aufmerksamkeit wurde den strukturellen Eigenschaften von freiem und gebundenem Wasser gewidmet. Es wurde gezeigt, daß die Ab-hängigkeit der GlasumwandlungstemperaturT _g vom Gehalt an gebundenem Wasser generell für viele denaturierte Biopolymere anwendbar ist. Im Unterschied zu gebundenem Wasser fungiert freies Wasser in Gelatinen nicht als ein Weichmacher, bildet aber eine starre Matrix, die die Glasumwandlung verhindert.

     

Characterization of water in polysaccharide hydrogels by DSC

Water molecules in hydrogels were classified into three categories according to phase transition behavior; non-freezing, freezing bound and free water. Melting, crystallization, and glass transition of water in hydrogels reflected the state of the water interacting with polysaccharides. Freezing bound water formed metastable ice by slow cooling and formed amorphous ice by quenching. From the isothermal crystallization measurement, nucleation rate and crystal growth rate were obtained. The crystal growth rate of freezing bound water was about ten times slower than that of free water. The DSC characterization of water in hydrogels was summarized.

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Zusammenfassung In übereinstimmung mit dem Phasenum wandlungsverhalten werden Wassermoleküle in Hydrogelen in drei Kategorien eingestuft; nicht gefrierendes, gefrierendes gebundenes und freies Wasser. Das Schmelzen, die Kristallisation und die Glasumwandlung von Wasser in Hydrogen wiederspiegeln den Zustand von Wasser, welches in Wechselwirkung mit Polysacchariden tritt. Gefrierendes gebundenes Wasser bildet metastabiles Eis durch langsames Abkühlen und amorphes Eis durch Abschrecken. Anhand isothermer Kristallisationsmessungen wurden Keimbildungsgeschwindigkeit und Kristallwachstumsgeschwindigkeit erhalten. Die Kristallwachstumsgeschwindigkeit von gefrierendem gebundenem Wasser liegt zehnmal niedriger als die von freiem Wasser.