The toughening transition in hair keratin

In a recent paper, Milczarek et al. [1] describe the observation of a toughening transition in keratin by DSC. On the basis of their results it is shown that the hypothesis of the existence of this transition is based on the misinterpretation of the evaporation peak of residual water, still present in keratin fibers after mild drying procedures.     

Thermal transitions and state of water in binary mixtures of water andn-decanephosphonic acid or its sodium salts

The state of water and several transitions were examined in the systemsn-decanephosphonic acid (DPA)—water and the sodium salts of DPA—water. Temperature — composition phase diagrams are reported. The results show that several liquid crystalline phases plus isotropic liquid, and two solid phases (a waxy solid phase and a crystalline phase) are formed. Several types of water were detected: bulk-like water, interfacial water and hydration water. This work was supported by the Consejo Nacional de Ciencia y Technología de México (grant # 3319-E) and by the Consejo Nacional de Investigaciones Científicas y Técnicas de la República de Argentina.     

Water-dependent thermal transitions in quinoa embryos

The water-dependent thermal transitions of the embryos in the mature seeds of Chenopodium quinoa Willd., cv. Baer II were studied by differential scanning calorimetry in order to provide tools for analyzing seed deterioration during storage. For comparative purposes, Guggenheim-Anderson-de Boer (GAB) constants from water sorption isotherms were also obtained from other two cultivars. Glass transition temperatures (T_g), overlapped with lipid melting, could be detected in defatted embryos. Quinoa seeds storage temperature should remain below 0 °C in order to maintain them in a glassy state if relative humidity is higher than 59%. Frozen water was detected in defatted embryos at water contents above 47% (dry basis, d.b.) while protein denaturation occurred even at 5% (d.b.) water content, although at a low extent. The results suggested that protein denaturation, without the requirement of lipid removal, is a potential index to follow seed deterioration during storage.     

Differential scanning calorimetry study of haemin thermal stability

A differential scanning calorimetry study of the thermal behaviour of haemin in N,N-dimethylformamide solution was carried out. The samples were scanned with different scan rates in the temperature range 25-130°C. The UV VIS spectrophotometry was used as assistant measurement method. The scan rate dependent and irreversible exothermic peaks were found. The activation energies of observed transitions were calculated assuming kinetically controlled process. The nature of thermal behaviour of haemin in DMF solutions is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of the amphiprotic nature of human hair keratin on the adsorption of high charge density cationic polyelectrolytes

Adsorption of the cationic polymers poly(methacrylamidopropyltrimethyl ammonium chloride) (PMAPTAC) and poly(1,1-dimethylpiperidinium-3,5-diallylmethylene chloride) (PDMPDAMC) on human hair was studied by measurements of the amount of polymer adsorbed and by the streaming potential method. Results reflect the amphoteric nature of the keratin surface and show that the excess of anionic sites at pH values above 4 is the main driving force for the adsorption of cationic polyelectrolytes. Lowering the pH below 4 or addition of neutral salt (KCl) reduces the amount of adsorbed polymer. It was shown that the adsorption of cationic polymer in the concentration range 0.01 to 0.1 % and at neutral pH reverses the overall character of the surface from anionic to cationic. Keratin fibers modified in this manner do not exhibit amphoteric character and bear excess positive charge in the pH range 2–9.5. The value of the amount of the polymer adsorbed at saturation concentration (2 mg/g) as well as the lack of molecular weight effect in the range (5 · 10⁴ – 10⁶) on the amount of polymer adsorbed suggest that polymer chains adopt a rather extended conformation on the fiber surface. Some data concerning the formation of a complex between adsorbed cationic polymer and anionic detergents or polyelectrolytes are also presented.     

The influence of radio-frequency radiation on thermal stability of bovine serum albumin in aqueous solution

Protein unfolding events were studied by differential scanning calorimetry (DSC) for bovine serum albumin (BSA) aqueous solutions exposed to radio-frequency radiation. No immediate effect of this radiation on thermal unfolding of BSA was observed. The differences between irradiated and control samples have appeared during the storage of BSA solution. The irradiated samples changed faster than non-irradiated. Our results indicated that the age-related changes were stronger for 3.5 and 5 MHz than for 247 MHz frequency and dependent on energy power of radiation. Deconvolution of DSC traces allowed to study the effect of radio-frequency radiation on each component transition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of purity on the thermal stability of solid organic compounds

DSC method was used to study thermal stability of nitrocompounds. It was assumed the model to estimate stability of solid phase in which perfect solid phase is totally stable and amorphous-liquid domains connected with impurities decompose according to the kinetic model determined for the liquid phase above the melting point. The influence of sample purity on relative stability, which is k _l/k _s — ratio of decomposition rate constants in liquid and solid phase, at temperature 20 K below the melting point was predicted. The increase of liquid domains in solid phase causes decrease of k _l/k _s ratio (relative stability) at chosen temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phase transitions in ternary caesium lead bromide

Phase transitions in ternary caesium lead bromide (CsPbBr₃) were studied by means of DSC, TMA and high temperature X-ray diffraction. The samples were prepared from the solution by water evaporation and from the melt. on the DSC curves as well as on the temperature dependence of the lattice constants of CsPbBr₃ only two effects were found belonging to the earlier published phase transitions at 88 and 130°C and no further effects. Linear thermal expansion coefficient α of individual CsPbBr₃ modifications were calculated from both TMA and high temperature X-ray diffraction. The structural parameters of the room temperature orthorhombic phase were refined and the results are presented. CsPbBr₃ prepared from the solution contained about 10% of CsPb₂Br₅ and so the DSC curve of pure CsPb₂Br₅ was also measured and an effect at a temperature of 68.5°C was found. This revised version was published online in July 2006 with corrections to the Cover Date.     

合成榍石的抗辐照稳定性和热稳定性

以H2SiO3、CaCO3、TiO2为原料,通过固相反应合成榍石,并对合成的榍石进行热处理和60Co源辐照试验,借助X射线衍射(XRD)、扫描电子显微镜(SEM)、红外光谱(IR)、激光拉曼光谱(LRS)等分析手段,研究合成榍石的抗辐照稳定性和热稳定性.结果表明,辐照累计剂量为5.76×105Gy的60Co源辐照没有造成榍石晶格的辐射损伤,合成的榍石具有良好的抗辐照稳定性;在200℃、400℃、600℃、800℃热处理24h,榍石晶体没有发生物相变化,合成榍石晶体具有良好的热稳定性.     

Rheological investigation of thermal transitions in vesicular dispersion

The thermal behavior of unsonicated dispersions of a double-chained surfactant, Dioctadecyldimethylammonium bromide (DODAB), has been studied over a wide concentration range using DSC and dynamic rheology. All dispersions are characterized by the pre- and main transition peaks at 35 °C and 43 °C, respectively. But, only above 10 mM DODAB, a third endotherm at 52 °C appears which may correspond to the (ULVs + L_α fragments) → MLVs transition. The thermal-induced MLV’s size is proportionally dependent on the concentration. In addition, and in agreement with DSC data, dynamic rheology has proven to be an indirect way to elucidate the structural transitions in these DODAB vesicular dispersions.     

Thermal transitions and structure of epoxy networks based on α, ω‐diamino terminated poly(propylene oxide)‐block‐poly(ethylene oxide)‐block‐poly(propylene oxide) swollen in water

Thermal transitions in epoxy networks prepared by reaction of α, ω‐diamino terminated poly(propylene oxide)‐block‐poly(ethylene oxide)‐block‐poly(propylene oxide) and diglycidyl ether of brominated Bisphenol A, swollen in water, were studied by differential scanning calorimetry (DSC) in a broad temperature range (from ?100 °C to 20 °C). Networks of two different values of initial molar ratio of amino and epoxy groups were prepared, r (r = 1.00, 2.00), and swollen with different amounts of water up to equilibrium concentration values. The qualitatively different kinds of experimental thermograms have been obtained for two networks and classified according to the amount of water in the sample on the basis of the phase diagram of the system. Also, the concentration dependence of the curves in this diagram (glass transition, melting, and crystallization) as well as the fraction of noncrystallizable water supply some information about the morphology of the system. In this sense, the existence of a microphase separated structure of swollen networks is suggested. The structure consists of hydrophilic and hydrophobic domains and depends on the initial molar ratio of the reactive groups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 699–708, 2005     

Thermoanalytical characterisation of modified keratin fibres

In the wool textile industry, several processes serve to improve the commercial properties of the fibres such as fineness, softness, length, strength and lustrous. For example, wool is chemically treated with reductive agents then stretched and set. This leads to modifications of the original protein structure causing changes in thermal behaviour, dyeing, colouristic and wet resistance properties. A multidisciplinary approach was used to investigate treated and untreated wools, with the aim of exploiting the nature of the structural changes. SEM and TEM revealed changes on the cuticle and cortical cell morphology; structure modification were studied by FT-IR and DSC. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electric properties of non-irradiated and gamma-irradiated keratin

Dielectric measurements as a function of temperature and frequency are reported for non-irradiated and γ-irradiated keratin, the irradiation doses being 5 and 50 kGy. The effect of γ-irradiation on the dielectric permittivity of keratin is not observed up to 190°C. In this temperature range, the values of the relaxation time and dipole moment are similar for non-irradiated and irradiated keratin at the same temperature. The influence of irradiation is manifested as a shift of the parameter (_s−_∞) peaks associated with the process of denaturation, towards lower temperatures. This fact is supported by lower values of the dipole moment for irradiated than for non-irradiated keratin, as a result of a decrease in the number of polar groups in the side and main chains of the macromolecule in the irradiated samples.     

The thermal behavior of powder emulsion explosives

The determination of the most probable mechanism function and the calculation of kinetic parameters of thermal decomposition of powder emulsion explosives have been achieved by different kinetic equations and different kinetic methods from data non-isothermal SC-DSC curves, DSC curves, and thermal explosion delay curve. The courses which the reaction would follow under adiabatic conditions are predicted.

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Zusammenfassung Mittels verschiedener kinetischer Gleichungen und verschiedener kinetischer Methoden wurde anhand der Angaben aus nichtisothermen SC-DSC-Kurven, DSC-Kurven und thermischer Explosionsverzugskurven die wahrscheinlichste Mechanismusfunktion der thermischen Zersetzung von Pulveremulsions-Sprengstoffen ermittelt und die diesbezüglichen kinetischen Parameter berechnet. Der Reaktionsweg unter adiabatischen Bedingungen wird vorausgesagt.

     

Effect of ethanol on the thermal stability of human serum albumin

The effect of ethanol on human serum albumin stability in aqueous solution was studied by use of differential scanning calorimetry. A deconvolution of DSC traces in 2-state model with ΔC _p=0 and ΔC _p≠0 was performed and analysed to obtain information on the interaction of ethanol with different parts of albumin molecule both fatty acid containing and fatty acid free. The differences in ethanol binding affinity for both kinds of albumin were found. At very low concentrations ethanol was observed to be a stabilizer of the folded state of albumin contrary to the higher concentration where its binding to the unfolded protein predominates.     

Effect of blending ratio and oligomer structure on the thermal transitions of stereocomplexes consisting of a D‐lactic acid oligomer and poly(L‐lactide)

Poly(lactic acid) (PLA) stereocomplexes have high potential as renewable materials for advanced polymer applications, mainly due to their high melting temperature (T_m, typically 230–240°C). The properties of PLA stereocomplexes consisting of linear high molar mass homopolymers have been studied extensively in the past, but the available information about the possibilities to affect the thermal properties of the stereocomplex by varying the structure of the blend components has not been sufficient. Novel stereocomplexes containing linear or star‐shaped D ‐lactic acid (D ‐LA) oligomers and high molar mass poly(L ‐lactide) (L‐ PLA) were thus prepared. The T_m and melting enthalpy (ΔH_m) of the racemic crystallites were found to depend strongly on both the blending ratio and the arm‐length of the D ‐lactic acid oligomer. The preparation method of the oligomers, i.e. step‐growth polymerization or ring‐opening polymerization (ROP), did not affect the T_m or ΔH_m of the blends significantly. Slightly higher ΔH_m values were, however, obtained, when linear oligomers were used. The results thus indicated that the T_m and ΔH_m of PLA stereocomplexes could be optimized, simply by selecting a D ‐LA oligomer having a suitable arm‐length and structure as the other blend component. The possibility to adjust the melting behavior of the stereocomplex blend is a significant advantage and could make PLA suitable for a wider range of products used at elevated temperatures. Copyright © 2010 John Wiley & Sons, Ltd.     

Novel determination of the dimerization mechanism for thermal polymerization of α-methylstyrene

This study discussed the phenomena on thermal polymerization of α-methylstyrene (AMS). A curve scanned by temperature-programmed technique was performed by differential scanning calorimetry (DSC). Heat of polymerization (ΔH) and onset temperature of exothermic (T₀) behavior were determined to be 280±10 J g^-1 and about 138±1°C, respectively. A dimer formation mechanism was proposed for initiation of the propagating chain. Spectroscopic identification of dimer structure was conducted by infrared (IR) spectroscopy in the wavenumber from 650 to 1100 cm^-1associated with molecular fingerprint characteristics. The mechanism of thermal polymerization on α-methylstyrene proposed in this study was similar to that of styrene suggested by Mayo.     

DSC and X-ray study of structure and phase transitions of low molecular compounds incorporated into crazes

Orientation, phase composition and phase transitions of a series of long chain low molecular weight compounds (LMC), such as heneicosane, cetyl alcohol, normal fatty acids, introduced into porous structure (crazes) of polymeric matrices oriented in liquid medium have been studied by means of DSC and SAXS techniques. Different types of LMC crystallites orientation in crazes of polymeric matrices have been observed. LMC phase state in crazes is shown to be characterized by higher stability of high-temperature polymer midifications. LMC melting temperature in crazes usually decreases as well as melting enthalpy (heat) and entropy. The origin of LMC properties changes observed is high dispersity (40–100nm) of LMC particles in crazes resulting in a marked growth of polymer/LMC interface influence on principal thermodynamic parameters of the systems studied.

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Zusammenfassung Mittels DSC- uns SAXS-Techniken wurden die Orientierung, Phasenzusammensetzung und Phasenumwandlungen einer Reihe von langkettigen niedermolekularen Verbindungen (LMC) wie z.B. Heneikosan, Zetylalkohol und normalen Fettsäuren untersucht, die in porösen Strukturen (Haarrissen) von in flüssigem Medium ausgerichteten polymeren Matrizen eingebracht wurden. Es konnten verschiedene LMC-Kristallit-TVpen in Haarrissen von polymeren Matrizen beobachtet werden. Es wurde gezeigt, daß der LMC-Phasenzustand in Haarrissen durch eine höhere Stabilität der Hochtemperatur-Polymermodifikationen charakterisiert ist. Die LMC Schmelztemperatur in Haarrissen nimmt im allgemeinen ab, genauso wie die Schmelzenthalpie (Wärme) und die Entropie. Der Grund für die beobachteten Veränderungen der LMC-Eigenschaften liegt in der großen Dispersität (40–100 nm) der LMC-Partikel in den Haarrissen, woraus sich ein sichtbarer Anstieg der Polymer/LMC Grenzflächeneinwirkung auf die grundlegenden thermodynamischen Parameter des untersuchten Systemes ergibt.

     

Thermal transitions of actin

Actin is one of the main components in the eukaryote cells which plays significant role in many cellular processes, like force-generation, maintenance of the shape of cells, cell-division cycle and transport processes. In this study the thermal transitions of monomer and polymerized actins were studied to get information about the changes induced by polymerization and binding of myosin to actin using DSC and EPR techniques. The main thermal transition of F-actin was at 67.5°C by EPR using spin-labeled actin (the relative viscosity change was around 62°C), while the DSC denaturation T _ms were at 60.3d°C for G-actin and at 70.5°C for F-actin. Applying the Lumry-Eyring model to obtain the parameters of the kinetic process and calculate the activation energy, a ‘break’ was found for F-actin in the function of first-order kinetic constant vs. 1/T. This indicates that an altered interdomain interaction is present in F-actin. The addition of myosin or heavy meromyosin (HMM) in different molar ratio of myosin to actin has changed significantly the EPR spectrum of spin-labeled F-actin, indicating the presence of the supramolecular complex. Analyzing the DSC traces of the actomyosin complex it was possible to identify the different structural domains of myosin and actin.