Differential Scanning Calorimetric and Circular Dichroistic Studies on Plant Antifreeze Proteins

Antifreeze protein (AFP) can lower the freezing point by inhibiting the growth of ice crystals. In this article, the thermal hysteresis activity (THA) of a plant AFP was measured with differential scanning calorimetry (DSC). As is shown, when the amount of ice in the sample was less than 5% THA of this AFP reached as high as 0.35°C. The secondary structure of this AFP was studied with circular dichroism (CD). The CD spectrum from 195to 240 nm indicated a well-defined secondary structure consisting 11% α-helix, 34%antiparallel β-sheet and 55% random coil. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparative Study on Triclosan Interactions in Solution and in the Solid State with Natural and Chemically Modified Cyclodextrins

The aim of this study was to investigate the interactions of triclosan (TRI), a poorly water-soluble antimicrobial drug, with natural crystalline cyclodextrins (α-, β- and γ-Cd) and the corresponding hydroxypropylated amorphous derivatives (HPα-, HPβ-, and HPγ-Cd) and evaluate their effectiveness as complexing and solubilizing agents towards the drug. Equimolar solid systems were prepared using different techniques (physical mixing (PM), kneading (KN) and coevaporation (COE)) in order to evaluate the influence of the preparation method on the performance of the end products. Drug–carrier interactions were investigated both in aqueous solution, using phase-solubility analysis, fluorescence and circular dichroism (CD) techniques, and in the solid state, using differential scanning calorimetry (DSC) supported by thermograumetric analysis (TGA), X-ray powder diffractometry (XRPD) and scanning electron microscopy (SEM) analysis. Among the native cyclodextrins, β-Cd seemed to have the most suitable cavity to fit the drug molecule, whereas the α-Cd cavity was too small and the γ-Cd cavity too large to establish stable interactions with the guest. However, due to the B _S -type phase solubility diagram, its solubilizing efficiency was very limited. The presence of the hydroxypropylic substituents improved, in all cases, Cd solubilizing and complexing efficacies towards the drug. This was particularly evident in the case of HPγ-Cd, whose stability constant was about 200-fold higher than that of the native γ-Cd. HPβ-Cd was the most effective carrier for TRI, showing a solubilizing power about 20 times higher than the corresponding native Cd and about 2-fold that of the other hydroxypropyl derivatives. Moreover, a clear influence of the preparation method on the properties of the final products was observed. The COE method with hydroxypropylated cyclodextrins seemed the most suitable technique in achieving the complete drug amorphization and/or inclusion complexation. Received in final form: 24 January 2005     

The Thermal Degradation of Poly(dimethyl Itaconate-co-4-vinylpyridine)

Copolymers of dimethyl itaconate (DMI) and 4-vinylpyridine (4VP) were synthetized in toluene at 60°C with0.26 mol% of AIBN as initiator. Their compositions were determined by differential refractometry and by differential scanning calorimetry. The 4VP contents of the copolymer samples ranged between 7 and 75 mol%. The reactivity ratios calculated via the Fineman-Ross method were r ₁=0.24 (DMI) and r ₂=0.57 (4VP). The thermal degradations of these copolymers were studied. The results of thermogravimetric measurements indicated that the copolymers degrade at lower temperatures than those of their parent homopolymers. A possible explanation of this anomalous behaviour is the formation of thermally unstable structures during the copolymerisation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of the stability of omeprazole by means of differential scanning calorimetry

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.     

Effect of hydration andpH on the thermal stability of proteinase K

The effect of hydration andpH on the thermal stability of proteinase K was studied in the temperature range 310–450 K by differential scanning calorimetry. The dependences of the denaturation temperatureT _d, the specific enthalpy of denaturation H _d and the maximum of excess apparent specific heat capacityC _ex ^max upon the degree of hydrationh and thepH of the buffers used are presented. The relation betweenT _d andh is of the Flory-Garrett's type. By means of Ooi's model, the two components of the denaturation enthalpy arising from hydration and conformational change, respectively, were estimated. The fact that the specific denaturation enthalpy of proteinase K is very low may be attributed to its very low enthalpy of conformational change per heavy atom.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthdayThis major project was supported by the National Natural Science Foundation of China.     

Synthesis and thermal stability of xylene-formaldehyde resins

o-,p- andm-xylene have been condensed with formaldehyde using paratoluene sulphonic acid as a catalyst and acetic acid/acetic anhydride as a solvent. The xylene-formaldehyde resins thus obtained have been characterised by IR and NMR spectra. The average molecular weight of the resin samples was determined by vapour pressure osmometry. Kinetic parameters were determined by differential thermal analysis, thermogravimetry and differential scanning calorimetry.     

DSC analysis of the anti-HIV agent loviride as a preformulation tool in the development of hot-melt extrudates

Thermal analysis was performed on the anti-HIV agent loviride in order to test its suitability to be processed using hot-melt extrusion. Temperature characteristic parameters of crystallization were determined to quantify the stability of amorphous loviride. The present study has shown that cooling and heating loviride at different rates influenced its thermal stability. At high cooling rates melted loviride did not crystallize during cooling, and formed a glass that recrystallized during reheating. Very low cooling rates resulted in significant decomposition of the drug. The glass transition temperature was found to increase as a function of increasing heating rates and the activation energy for the transition from the glassy to the super-cooled liquid state was relatively high, indicating good stability of the glass. This revised version was published online in July 2006 with corrections to the Cover Date.     

Design and development in self-reference differential scanning calorimetry

An intermediate range (50–1000°C) self-referencing differential scanning calorimeter (SR-DSC) has been built and its performance evaluated. The SR-DSC measures heat flow across a heat flow metal plate, and any changes to the heat flow caused by a thermal transition occurring in a centrally placed sample is monitored by a temperature difference across the plate. The criteria for high sensitivity are that the circular plate should be as thin as possible and have a low thermal conductivity. The best sensitivity conducive with robust behaviour was achieved with an inconel thermal plate of uniform thickness, 75 m, this gave reproducible results, and the enthalpy of the thermal transition was proportional to sample mass. Calorimeter sensitivity decreased with increasing temperature and a sloped baseline was observed. Both of these effects can be corrected mathematically. An example of the use of the SR-DSC in polymer characterisation was limited to a study of the physical ageing of PET.This revised version was published online in November 2005 with corrections to the Cover Date.Paper was read at the TAC2001 Conference in Liverpool.     

The effect ofpH on thermal stability of globular proteins

In this study we try to re-analyze thepH dependence of thermal stability of small globular proteins. From the thermodynamic point of view a long series of calorimetric and spectroscopic investigations has shown that the decreased stability in very acidic conditions can be ascribed to entropic effects. The same conclusion is reached, from a microscopic point of view, by assuming that a binding of protons on equal and noninteracting sites takes place as a consequence of unfolding process. By linking the conformational unfolding equilibrium to the proton binding equilibrium, a model is developed that is able to describe the dependence on thepH of the thermal denaturation processes of small globular protiens. The application of the model to hen lysozyme and T4 lysozyme correctly accounts for the experimental results.     

The effect of zeolite on the curing of epoxy resin by polyaniline: a kinetic study

Polyaniline sulfate‐zeolite composite was prepared by emulsion polymerization. Epoxy resin was cured using polyaniline‐sulfate salt and various amounts of polyaniline sulfate‐zeolite composite. The kinetics of the cure reaction for an epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) with polyaniline‐sulfate and polyaniline sulfate‐zeolite composite have been studied using differential scanning calorimetry (DSC) under isothermal and dynamic conditions. Isothermal kinetics analysis was performed using the phenomenological model of Kamal. Dynamic kinetic analysis was performed using Kissinger's method. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis and characterization of chiral poly(alkyl isocyanates) by coordination polymerization using a chiral half‐titanocene complex

A new chiral half‐titanocene complex, [CpTiCl₂(O‐(S)?2‐Bu)], is synthesized and characterized by ¹H and ¹³C NMR spectroscopy. This complex is employed for the coordination polymerization of n‐butyl and n‐hexyl‐ isocyanate leading to chiral polymers, as revealed by their CD spectra. Only the left‐handed helix is produced, due to the chiral (S)?2‐butoxy group, which is bound to the polymer chain end. The polymerization of 3‐(triethoxysilyl)propyl isocyanate produces less soluble polymers. On the other hand, phenyl isocyanate reacts slowly with the complex leading quantitatively and selectively to triphenyl isocyanurate. 2‐Ethylhexyl isocyanate is slowly and selectively cyclotrimerized in the presence of the half‐titanocene complex. However, a statistical copolymer of 2‐ethylhexyl isocyanate and hexyl isocyanate is produced. The reaction of benzyl isocyanate with the complex leads to a mixture of low molecular weight polymer and cyclotrimer. The polymers are characterized using SEC, NMR, and CD spectroscopy and their thermal properties are investigated by TGA/DSC analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2141–2151     

The structural influence in the stability of polymer-bound diazonium salts

Various new diazonium ions on a polymeric support that have a variety of counterions and complexation with crown ethers have been prepared, and the thermal stability of these resins over a larger temperature interval has been investigated. Nonisothermal kinetics applied to DSC data have been used predicting the lifetime of the resins.     

Thermodynamics of a 24-Mer Triple Helix Formation and Stability

In this work we report a thermodynamic characterization of stability and melting behaviour of two 24-mer DNA triplexes. The third strand, that binds the Watson-Crick double helix with Hoogsteen hydrogen bonds, contains 3′-3′ phosphodiester junction that determines the polarity inversion. The target double helix is composed of adjacent and alternate fragments of oligopurine-oligopyrimidine tracts. The two helices differ from the substitution of the cytosine, involved in the junction, with the thymine. Calorimetric data reported here provide a quantitative measure of the influence of pH and base modification on the stability of a DNA triplex. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Stability of Heteropoly Acids and Characterization of the Water Content in the Keggin Structure

The thermal stability of heteropoly acids of the Keggin type (H₄[SiMo₁₂O₄₀], H₃[PMo₁₂O₄₀], H₄[SiW₁₂O₄₀] and H₃[PW₁₂O₄₀]), being important new catalytic materials, was studied by DSC. Two groups of signals were observed: the low temperature endothermic peak group belongs to the water content, while the high temperature one is exothermic and indicates the thermal decomposition of the acids. The effect of microwave irradiation on the target compounds was also studied. The emphasis, however, was placed on the characterization of the water content of the acids. Several types of water can be classified and DSC curves provide additional information to explain the differences in the catalytic behavior. The study of the effect of heat treatment and the subsequent water absorption of the acids provided additional unique information concerning the pseudoliquid phase in the secondary structure of heteropoly acids. This revised version was published online in July 2006 with corrections to the Cover Date.     

差示扫描量热法测定食用油脂的热氧化稳定性及氧化寿命

利用差示扫描量热法（DSC）测定了四种食用花生油的热氧化稳定性,用Ozawa法和Kissinger法计算了四种食用花生油热氧化反应的动力学参数,推算了不同温度下的氧化寿命。     

差示扫描量热法研究丙烯腈-衣康酸共聚物的热稳定化

应用差示扫描量热法(DSC)研究了衣康酸(IA)、气氛、升温速率对丙烯腈-衣康酸共聚物[P(AN-IA)]热稳定化的影响. IA能够显著降低放热峰起始温度、放热量和放热速率. P(AN-IA)共聚物的放热峰起始温度受气氛影响不大, 却随着IA含量的增加而明显降低, 表明在热稳定化过程中它可能首先以离子机理发生氰基环化反应, 再发生氧化反应. 提高升温速率会导致放热峰向高温偏移和放热速率加快. 采用Kissinger法计算了不同IA含量共聚物的热稳定化活化能, 结果表明IA可以有效降低活化能.     

Effect of Molecular Crowding on the Temperature–Pressure Stability Diagram of Ribonuclease A

FT‐IR spectroscopic and thermodynamic measurements were designed to explore the effect of a macromolecular crowder, dextran, on the temperature and pressure‐dependent phase diagram of the protein Ribonuclease A (RNase A), and we compare the experimental data with approximate theoretical predictions based on configuration entropy. Exploring the crowding effect on the pressure‐induced unfolding of proteins provides insight in protein stability and folding under cell‐like dense conditions, since pressure is a fundamental thermodynamic variable linked to molecular volume. Moreover, these studies are of relevance for understanding protein stability in deep‐sea organisms, which have to cope with pressures in the kbar range. We found that not only temperature‐induced equilibrium unfolding of RNase A, but also unfolding induced by pressure is markedly prohibited in the crowded dextran solutions, suggesting that crowded environments such as those found intracellularly, will also oppress high‐pressure protein unfolding. The FT‐IR spectroscopic measurements revealed a marked increase in unfolding pressure of 2 kbar in the presence of 30 wt % dextran. Whereas the structural changes upon thermal unfolding of the protein are not significantly influenced in the presence of the crowding agent, through stabilization by dextran the pressure‐unfolded state of the protein retains more ordered secondary structure elements, which seems to be a manifestation of the entropic destabilization of the unfolded state by crowding.     

Binding properties and structural changes of human growth hormone upon interaction with cobalt ion

Binding properties and structural changes of human growth hormone (hGH) due to the interaction by cobalt ion (Co²⁺) were done at 27°C in NaCl solution, 50 mM, using different techniques of UV-Vis spectroscopy, circular dichroism (CD), isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC) techniques. There is a set of three identical and non-interacting binding sites for cobalt ions. The intrinsic association equilibrium constant and the molar enthalpy of binding obtained by ITC are 0.80 mM⁻¹ and −16.70 kJ mol⁻¹, respectively. The intrinsic association equilibrium constant obtained by a standard isothermal titration UV-Vis spectrophotometry method is also 0.79 mM⁻¹, which is in good agreement with the value obtained from ITC. The Gibbs free energy and entropy changes due to the binding of cobalt ion on hGH are −16.67 kJ mol⁻¹ and −0.1 J K⁻¹ mol⁻¹, respectively. Energetic domains analysis by DSC shows that phase transition of hGH in the presence of cobalt occurs at one main transition. Deconvolution of the main transition provides two sub-transitions with different values of the melting point and enthalpy of unfolding (33°C and 164 kJ mol⁻¹ for the first and 49°C and 177 kJ mol⁻¹ for the second, respectively). Interaction of cobalt ions with hGH prevents aggregation by an affect on the hydrophobicity of the protein macromolecule and provide useful information about its structure due to becoming reversible of protein thermal denaturation.