Calorimetric Curves Research Articles

454 ULTRASOUND PROPERTIES OF ARTICULAR CARTILAGE IN PATELLOFEMORAL JOINT IN KNEE OSTEOARTHRITIS: DIFFERENCE BETWEEN THE INTERNATIONAL CARTILAGE REPAIR SOCIETY GRADE-0 AND GRADE-1

Greater change in the enthalpy was observed in osteoarthritic cartilage: −1414.78 J/g compared to 1357.70 J/g in avascular necrosis. Consequently these samples required larger amount of energy for decomposition. Statistical tests proved these calculations to be significant (p< 0.05). All samples showed a clear denaturation peak on the calorimetric curve. Conclusions: This study clarifies the previously reported thermoanalytical results, with acquiring normal cartilage from live surgery, thus providing similar sample environment. The use of DSC as part of thermal analysis was a reliable method for differentiating osteoarthritic hyaline cartilage from necrotic samples. All samples showed a clear denaturation peak on the calorimetric curve, therefore volume of the curve was easily calculated giving the enthalpy change of the sample. These changes correlated with the water content of the samples. The calorimeter that was available for use proved to be adequate for these measurements. The use of thermal analysis could be a simple and effective method for differentiating between pathological disease progression. The relationship between the different pathomorphologic influences, and the role extracellular matrix homeostasis will be necessary to reveal potential targets of therapy. While there is rapid progress in understanding the complexities of joint diseases a simple basic research technique like thermal analysis can be an effective method for controlling the relationship between biomarkers and disease progression.

Structural Characterization of Co&lt;sub&gt;70-x&lt;/sub&gt;Ni&lt;sub&gt;x&lt;/sub&gt;Ga&lt;sub&gt;30&lt;/sub&gt; Ferromagnetic Shape Memory Alloys

Polycrystalline ingots of Co70–xNixGa30 (20 ≤ x ≤ 26) ferromagnetic shape memory alloy (FSMA) were prepared by arc melting elemental powders followed by homogenization at 1230 °C for 24 hrs and quenching in liquid nitrogen. Room temperature X-Ray diffraction (XRD) patterns of as-quenched samples exhibited single-phase tetragonal structure for alloy compositions with x = 21 to 26, and a two-phase structure (cubic A2-phase along with weak tetragonal phase) for the alloy with x = 20. Rietveld refinement was performed on the X-ray diffraction patterns to obtain the refined structural parameters. Differential Scanning Calorimeter (DSC) curves recorded from 30 °C to 250 °C revealed martensite-austenite and austenite-martensite transformations in all alloys except the alloy with composition x = 20. Low temperature ac magnetic susceptibility measurements confirmed the existence of martensitic transformations in the alloy with x = 20. The structural transformation temperatures show a linear variation with e/a ratio. All the alloys were ferromagnetic at room temperature. Curie temperature was determined using a high temperature ac magnetic susceptibility measurement set-up.

Titration Calorimetry Applied to the Thermokinetics Study of Consecutive First‐order Reactions

AbstractThe thermokinetic mathematical models for consecutive first‐order reactions in titration period and the stopped‐titration reaction period were proposed for titration calorimetry, based on which, thermodynamic parameters (reaction enthalpies, ΔrHm1and ΔrHm2) and kinetic parameters (rate constants, k1 and k2) of the consecutive first‐order reactions could be obtained by directly simulating the calorimetric curve from a single experiment with the method of nonlinear least squares regression (NLLS). The reliability of the model has been verified by investigating the reaction of the saponification of diethyl succinate in an aqueous ethanol solvent.

Real-time monitoring of the heat of transfer of a homologous series of m-alkoxy phenols from isotonic aqueous solution to bacterial cells

Heats of dissolution of a homologous series of m-alkoxy phenols in an osmotically stable isotonic solution and in the same media containing a suspension of Escherichia coli cells were obtained by a differential heat conduction batch calorimeter at 298 K. The calorimetric curves show an initial rapid endothermic dissolution of the solute, followed by an exothermic process. From the heats of solution, the heat of transfer (Qtrs) of these compounds from the aqueous solution to the cells was calculated. The heat of transfer is exothermic and increases with the hydrophobicity of the compounds due to the biological consequences of the interaction process with the lipidic phase.

Self-aggregation of hydrophobically modified dextrin and their interaction with surfactant

A series of newly hydrophobically modified polymers (dexC 16) with different degrees of substitution (DS C16) have been synthesized. They can self-assemble to form micelle-like aggregates through association of the hydrophobic alkyl chains in aqueous solution. The self-aggregation processes, i.e. the critical micelle concentrations (cmc's) of the polymers were characterized by steady-state fluorescence. Further, the interaction between these dexC 16 polymers and ionic surfactants (SOS, SDS and DTAC) was investigated by isothermal titration calorimetry (ITC). For the studied mixed systems some important parameters can be derived from calorimetric titration curves, such as interaction enthalpies, critical concentrations and enthalpies of aggregation. The critical concentrations and the aggregation behaviour for the dexC 16/SDS system were confirmed by fluorescence measurements. The effects of hydrophobic side group concentrations on the interaction were evaluated in detail. Importantly, we show that the aggregation behaviour of the mixed systems depends on the molar ratio of surfactant to hydrophobic side group ( R = n s/ n side group).

Kinetics analysis of precipitation in a quasi-binary Cu-1 at.% CoTi alloy

The precipitation process for a concentration of CoTi of super-saturated solutions of Cu-0.50 at.% Co-0.45 at.% Ti (Cu-1 at.% CoTi) was studied through differential scanning calorimetry (DSC) and microhardness measurements. The analysis of the calorimetric curves between the environmental temperature and 900 K shows the presence of only one exothermic reaction attributed to the formation of CoTi particles in the matrix of copper. The energy of activation estimated by using the modified Kissinger method came out much lower than the corresponding to the diffusion of the cobalt and titanium in copper. We may attribute this fact to the strong contribution of the vacancies introduced by quenching.

Efficient parallel tempering for first-order phase transitions

We present a Monte Carlo algorithm that facilitates efficient parallel tempering simulations of the density of states g(E) . We show that the algorithm eliminates the supercritical slowing down in the case of the Q=20 and Q=256 Potts models in two dimensions, typical examples for systems with extreme first-order phase transitions. As recently predicted, and shown here, the microcanonical heat capacity along the calorimetric curve has negative values for finite systems.

Effect of β nucleating agent on mechanical properties of PP/POE blends

Polypropylene/polyolefin elastomer (PP/POE) blends with and without β nucleating agent were prepared by injection moulding. Wide angle X-ray diffraction (WAXD) results are in agreement with differential scanning calorimetric (DSC) melting curves; both demonstrate the formation of the hexagonal β phase after adding β nucleating agent in PP/POE blends. The addition of β nucleating agent increases the toughness of PP and PP/POE blends but decreases their tensile strength. Brittle–ductile transition (BDT) occurs in PP/POE blends, but no obvious BDT point can be seen in β nucleated PP/POE blends. The toughening mechanism, morphology of the fractured surfaces after impact, was investigated by scanning electron microscope (SEM). From impact strength interparticle distance curves, a critical interparticle distance of ∼0·2 μm is seen in PP/POE blends, but no critical value is observed for β nucleated system, indicating better interaction between PP and POE, deduced by their good compatibility. The toughening and softening effect of β nucleating agent is also responsible.

Formation mechanism of super water-repellent fractal surfaces of alkylketene dimer

Alkylketene dimer (AKD), a kind of wax, has been known to form fractal surfaces spontaneously, and to show super water-repellent property. In order to understand further the super water-repellency of the AKD surfaces and to elucidate the mechanism of spontaneous formation of the fractal structures on the wax surfaces, a pure and a mixed AKD samples were employed to make the surfaces by the melt-solidification method. Time-dependent contact angles of water droplets on the AKD surfaces cured at several temperatures were systematically measured. It was found that spontaneous formation of super water-repellent surfaces was thermally induced quite effectively. For example, it took about 6 days for the pure AKD surface to show the super water-repellency at 40 °C but did just 1 h at 50 °C. The fractal dimension of the mixed AKD surface with super water-repellency was calculated to be 2.26 from the SEM images by the box-counting method which should be reasonably compared with 2.29 of pure AKD surface. The mechanism for the spontaneous formation of fractal structures was discussed from the results of the time-dependent contact angles, differential scanning calorimetric (DSC) curves and X-ray diffractometric (XRD) patterns. It has been made clear that the fractal AKD surface and its super water-repellency result from the phase transformation from the metastable state to the stable one of the AKD crystals.

Critical temperatures and a critical chain length in saturated diacylphosphatidylcholines: calorimetric, ultrasonic and Monte Carlo simulation study of chain-melting/ordering in aqueous lipid dispersions

Chain-ordering/melting transition in a series of saturated diacylphosphatidylcholines (PCs) in aqueous dispersions have been studied experimentally (calorimetric and ultrasonic techniques) and theoretically (an Ising-like lattice model). The shape of the calorimetric curves was compared with the theoretical data and interpreted in terms of the lateral interactions and critical temperatures determined for each lipid studied. A critical chain length has been found (between 16 and 17 C-atoms per chain) which subdivides PCs into two classes with different phase behavior. In shorter lipids, the transition takes place above their critical temperatures meaning that this is an intrinsically continuous transition. In longer lipids, the transition occurs below the critical temperatures of the lipids, meaning that the transition is intrinsically discontinuous (first-order). This conclusion was supported independently by the ultrasonic relaxation sensitive to density fluctuations. Interestingly, it is this length that is the most abundant among the saturated chains in biological membranes.

Thermodynamic Investigation of the Role of Contact Residues of β-Lactamase-inhibitory Protein for Binding to TEM-1 β-Lactamase

We have determined the thermodynamics of binding for the interaction between TEM-1 beta-lactamase and a set of alanine substituted contact residue mutants ofbeta-lactamase-inhibitory protein (BLIP) using isothermal titration calorimetry. The binding enthalpies for these interactions are highly temperature dependent, with negative binding heat capacity changes ranging from -800 to -271 cal mol(-1) K(-1). The isoenthalpic temperatures (at which the binding enthalpy is zero) of these interactions range from 5 to 38 degrees C. The changes in isoenthalpic temperature were used as an indicator of the changes in enthalpy and entropy driving forces, which in turn are related to hydrophobic and hydrophilic interactions. A contact residue of BLIP is categorized as a canonical residue if its alanine substitution mutant exhibits a change of isoenthalpic temperature matching the change of hydrophobicity because of the mutation. A contact position exhibiting a change in isoenthalpic temperature that does not match the change in hydrophobicity is categorized as an anti-canonical residue. Our experimental results reveal that the majority of residues where alanine substitution results in a loss of affinity are canonical (7 of 10), and about half of the residues where alanine substitutions have a minor effect are canonical. The interactions between TEM-1beta-lactamase and BLIP canonical contact residues contribute directly to binding free energy, suggesting potential anchoring sites for binding partners. The anti-canonical behavior of certain residues may be the result of mutation-induced modifications such as structural rearrangements affecting contact residue configurations. Structural inspection of BLIP suggests that the Lys(74) side chain electrostatically holds BLIP loop 2 in position to bind to TEM-1 beta-lactamase, explaining a large loss of entropy-driven binding energy of the K74A mutant and the resulting anti-canonical behavior. The anti-canonical behavior of the W150A mutant may also be due to structural rearrangements. Finally, the affinity enhancing effect of the contact residue mutant Y50A may be due to energetic coupling interactions between Asp(49) and His(41).

Modification of the physical, mechanical and thermal properties of poly(vinyl chloride) by blending with poly(ethyl methacrylate)

AbstractBlends of poly(vinyl chloride) (PVC) with different ratio of poly(ethyl methacrylate) were characterized with respect to their physical, mechanical, thermal, and morphological properties. The blends indicated a gradual rise in the modulus and ultimate tensile strength values followed by a reduction in the percent elongation at break and toughness values after an initial rise compared to the base reference compound PVC. The effect of composition of the PVC‐PEMA blends on the thermal stability was investigated. Differential scanning calorimetric curves of the blends showed an inward shift of the PVC glass transition temperature and an upward shift in the degradation temperature. The thermomechanical analysis results also indicated thermal stability over unmodified base reference compound PVC from the softening characteristics of the different samples under study. The biphasic cocontinuous systems as explicit from the scanning electron and optical micrographs supported phase‐mixing at the initial stages with subsequent phasing out tendency with increasing percentage of PEMA incorporation. The thermomechanical parameters are in conformity to their mechanicals, which have been further supported by their morphological studies. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Thermal unfolding of eosinophil cationic protein/ribonuclease 3: A nonreversible process

Eosinophil cationic protein (ECP)/ribonuclease 3 is a member of the RNase A superfamily involved in inflammatory processes mediated by eosinophils. ECP is bactericidal, helminthotoxic, and cytotoxic to tracheal epithelium cells and to several mammalian cell lines although its RNase activity is low. We studied the thermal stability of ECP by fourth-derivative UV absorbance spectra, circular dichroism, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The T (1/2) values obtained with the different techniques were in very good agreement (T (1/2) approximately 72 degrees C), and the stability was maintained in the pH range between 5 and 7. The ECP calorimetric melting curve showed, in addition to the main transition, a pretransitional conformational change with a T (1/2) of 44 degrees C. Both calorimetric transitions disappeared after successive re-heatings, and the ratio DeltaH versus DeltaH (vH) of 2.2 indicated a significant deviation from the two-state model. It was observed that the thermal unfolding was irreversible. The unfolding process gives rise to changes in the environment of aromatic amino acids that are partially maintained in the refolded protein with the loss of secondary structure and the formation of oligomers. From the thermodynamic analysis of ECP variants, the contribution of specific amino acids, such as Trp10 and the region 115-122, to thermal stability was also determined. The high thermal stability of ECP may contribute to its resistance to degradation when the protein is secreted to the extracellular medium during the immune response.

Hydration behavior of C2S and C2AS nanomaterials, synthetized by sol–gel method

Hydration behavior of dicalcium silicate (C2S) (Cement chemistry nomenclature is used where C=CaO, S=SiO2, A=Al2O3, \( \overline S \)S=SO3) and gehlenite (C2AS), synthesized by sol–gel method was investigated by means of isothermal heat flow calorimeter at different temperatures. These phases were obtained by crystallization processing at different temperatures from their xerogels (nano-crystalline) prepared by the sol–gel method at ambient temperature. The crystallization of C2S begins below 600°C and it is well crystallized at 900°C. X-ray diffraction patterns reveal that β-C2S is formed and it remains stable since after slow cooling. The crystallization of C2AS xerogels starts with the formation of C2S, then it reacts with alumina to form mineral C2AS at 1100°C. The effect of hydration temperature upon the hydration reaction of C2S obtained at 600 and 900°C and C2AS annealed at 600 and 1100°C was investigated by means of isothermal calorimeter. An increase in the temperature of hydration brought about initial acceleration of all samples, as indicated by the increased magnitude of peak of calorimetric curves. The microstructure of the samples cured at hydrothermal condition after 1 and 7 days has been examined by means of scanning electron microscopy (SEM). Fine crystals of calcium silicate hydrate (C–S–H) were developed in C2S samples, while C2AS has been hydrated to form gehlenite hydrate supplemented by C–S–H.

Preparation and Characterization of Nano‐TATB Explosive

AbstractNano‐TATB was prepared by solvent/nonsolvent recrystallization with concentrated sulfuric acid as solvent and water as nonsolvent. Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) were used to characterize the appearance and the size of the particles. The results revealed that nano‐TATB particles have the shape of spheres or ellipsoids with a size of about 60 nm. Due to their small diameter and high surface energy, the particles tended to agglomerate. By using X‐ray powder diffraction (XRD), broadening of diffraction peaks and decreasing intensity were observed, when the particle sizes decreases to the nanometer size range. The corrected average particle size of nano‐TATB was estimated using the Scherrer equation and the size ranged from 27 nm to 41 nm. Furthermore, the specific surface area and pore diameter of nano‐TATB were determined by BET method. The values were 22 m2/g and 1.7 nm respectively. Thermogravimetric (TG) and Differential Scanning Calorimetric (DSC) curves revealed that thermal decomposition of nano‐TATB occurs in the range of 356.5 °C–376.5 °C and its weight loss takes place at about 230 °C. Furthermore, a slight increase in the weight loss was observed for nano‐TATB in comparison with micro‐TATB.

Optimizing conditions to study seed germination by calorimetry using soybean ( Glycine max [L.] Merr.) seeds

To establish the best conditions for germination, calorimetric experiments were conducted with individual soybean seeds ( Glycine max [L.] Merr.) under different conditions of imbibition at 24.7 °C. The calorimetric curves were analysed for imbibition and metabolic processes and compared with imbibition curves to establish a general methodology that could be used to evaluate inter- and intra-species physical and physiological variability. Measurements of pH were performed during the determination of the imbibition curves . The best experimental method for calorimetric investigations of seed germination is to insert the seed in 1% agar instead of placing the seed over wetted filter paper disks. Correlation of imbibition experiments and pH results with mass specific enthalpy of imbibition (determined in a KCN solution) or mass specific enthalpy of germination when seeds were germinated in 1% agar allowed determination of the water content needed for soybean seeds of the cultivar studied (A7636 RG) to activate their metabolic machinery (74–80% or 2.5–3 h) and the moment in which they are ready for root protrusion (122% or 9 h). The method presented here should be useful for evaluating soybean coat permeability to water and other factors related to seed damage before and during harvest and storage.

Solid Solution Characterization of Bi4Ti3O12 with Eu3+

Bi4− xEuxTi3O12 solid solution was synthesized by coprecipitation and characterized by X-ray powder diffraction, thermal analyses, Raman spectroscopy and scanning electron microscopy. Sintering temperature influence on microstructure is discussed in base of the scanning electron microscopy micrographs. Differential scanning calorimetric curves show a reversible phase transition around 665°C with an intensity changes as a function of the Eu3+ doping content. The transformation enthalpy has a maximum value for the undoped Bi4Ti3O12 samples and decreases with the increasing of Europium content. Finally, Raman studies of the samples show the vibrational changes induced by the Eu/Bi substituttion.

Microstructures and Properties of Melt-Spun and As-Cast Mg-20Gd Binary Alloy

Mg-20Gd(%, mass fraction) samples were prepared using melt-spinning and copper mold casting techniques. Microstructures and properties of the Mg-20Gd were investigated. Results show that the melt-spun ribbon is mainly composed of supersaturated α-Mg solid solution phase and the as-cast ingot mainly contains α-Mg solid solution and Mg 5Gd phase. The differential scanning calorimeter (DSC) curve of the ribbon exhibits a small exothermic peak in the temperature range from 630 to 680°K, which indicates that the ribbon contains a metastable phase (amorphous). Tensile strength at room temperature of the melt-spun ribbon and as-cast specimen are 308 and 254 MPa, respectively. The elongations of the two samples are less than 2%. The fracture surfaces demonstrate that the fracture mode of the as-cast Mg-20Gd is a typical cleavage fracture and that of the melt-spun sample is a combination of brittle fracture and ductile fracture.

Characteristic length of glass transition heterogeneity from calorimetry

The determination of the temperature fluctuation in a representative subsystem from experimental calorimetric curves is discussed. Contrary to the traditional fluctuation approach it is suggested to use the dispersion width of the corresponding relaxation spectrum and not the width of the peak in the imaginary part of the complex heat capacity as a measure of the temperature fluctuation in local subsystems. This leads to larger estimates for the length scales of the dynamic heterogeneity of the dynamic glass transition than originally supposed. A correction method for former results is given and the comparison with other experimental results is discussed.

The specific heat of Cu–Al–Ni shape memory alloys

The specific heat of Cu 81.8Al 13.7Ni 4.5 (AK10) shape memory alloy has been studied by means of conventional DSC and adiabatic calorimetry techniques. The transformation temperatures and the shape of the calorimetric curves obtained by adiabatic calorimetry do not show any noticeable dependence on the temperature measurement rates, contrarily to what is observed by other calorimetric techniques. The dynamical character of the various experimental methods together with the influence of the latent heat associated to the first order character of these phase transitions are discussed. The specific heat of AK10 has been measured from 50 to 350 K which covers the phase transformation temperature range. The forward and reverse martensitic transformation peaks were found at 299.5 and 304.6 K, showing a thermal hysteresis of 5.1 °C. The C p accuracy can be estimated in 0.1% of C p and permits a reliable assignment of the following values to the phase transition thermodynamic functions: Δ H = 7.4 ± 0.2 J/g and Δ S = 0.025 ± 0.001 J/gK.