Heat Absorption Peak Research Articles

Treatment and mechanism for hot melting starch by reducing the molecular chain winding and crystallinity

Unlike thermoplastic petroleum-based materials, starch-based materials rely on aqueous systems but are incapable of hot melting, resulting in low processing efficiency and limited large-scale industrial applications. In this study, the combination of α-amylase liquefaction and urea plasticization was used for the first time to obtain enzymatic thermoplastic starch (ETPS) for hot melting by changing the molecular chain of starch. ETPS showed an apparent hot melting phenomenon when heated below 200 °C. Differential scanning calorimetry revealed that heat absorption peaks were obviously reduced, and the hot melting phenomenon occurred easily depending on the combination of enzymatic hydrolysis and plasticization. Dynamic mechanical analysis indicated that the combined modification effectively increased the number of freely movable chains. The red shift of -OH stretching vibration peaks indicated the formation of strengthened hydrogen bonds in ETPS. X-ray diffraction showed that the crystallinity of ETPS was reduced to 5.68 %, effectively reducing the regenerative phenomenon. Gel permeation chromatography revealed that the molecular weight of ETPS decreased, and the entanglements between molecular chains were reduced. A tensile test showed that the elongation at break of ETPS was as high as 235.29 %, which was much higher than those of enzymatic hydrolysis starch and thermoplastic starch.

Effect of Sb content on the phase structure and interface structure of Sn1.0Ag0.5Cu lead-free solder

Based on the alloy Sn1.0Ag0.5Cu, Sb powder is added at a certain mass percentage to form the solder alloy Sn1.0Ag0.5CuxSb (x = 0 wt%, 0.5 wt%, 1.5 wt%). The melting point of the solder was determined by differential scanning calorimetry, the alloy interface morphology was observed by scanning electron microscopy, and energy-dispersive X-ray spectroscopy was performed to analyze phase compositions. Thermo-Calc software was used to calculate the variation in phase content, the solidification curve, Gibbs energy, the driving force, liquid/solid phase lines, the phase diagram, and the nucleation radius of Sn1.0Ag0.5CuxSb(wt%). In addition, the calculation results were used to explain the interface growth mechanism. According to the results, the precipitation/transition temperature of each phase and the content of the newly formed phase SnSb gradually increased with the increase in Sb content. After the addition of Sb, both temperatures of the liquid-phase line and the solid-phase line slightly increased, and the calculated values showed the same trend as the measured values. Two heat absorption peaks were observed during the melting process. The Gibbs energy and nucleation radius of the Cu6Sn5 phase increased with the increase in Sb content, indicating that Sb can inhibit the growth of the Cu6Sn5 phase. The addition of Sb rendered the Sn-rich phase denser and finer and reduced the thickness of the intermetallic compound layer and the generation of cracks; these changes intensified with increasing aging time. Comprehensive analysis revealed optimal reliability of the solder for an Sb content of 0.5 wt%.

Spray-Dried Quercetin-Lactose Powders for Oral Tablets with Improved Dissolution Rates and Modified Material Properties

This study is aimed at using spray drying method to codisperse it with the commonly used drug carrier lactose in different solvents and then pass it through a spray dryer to obtain different samples. The results showed that the dissolution rate and solubility of the samples obtained by dispersion in hot water and 25% ethanol were significantly higher. The water of crystallization peaks of the raw material disappeared at 105-125°C and 130-150°C (DSC). The excipient lactose had a small upward exothermic peak at 177°C and a significant heat absorption peak at 209°C before untreated (XRD). α-Lactose peaks were observed at 12.5°, 19.1°, 19.6°, and 19.9° at 2θ in both samples, and β-lactose peaks were found at 10.5° at 2θ in sample A, but not in sample B (FTIR). The complex sharp peaks of lactose at 1100 cm-1 and quercetin at 1700-1000 cm-1 became moderated (SEM). The sample obtained by spray drying has a slit-type mesoporous structure with an average pore size of about 9.3 nm.

Study the effect of alloying on the phase transition behavior and thermoelectric properties of Ag2S

Phase transition will lead to abrupt change of thermoelectric material’s properties, which will have a negative influence on the application of thermoelectric device. Therefore, avoiding the phase transition of Ag2S is particularly important for its heat collection applications. In this work, we reported, for the first time, that Cu-Se co-alloying in Ag2S can suppress phase transition and improve thermoelectric properties. Specifically, different elements and compounds alloying in Ag2S samples were prepared, and their influences on the phase change behavior and thermoelectric performance stability of Ag2S are systematically studied. It is found that the free enthalpy decreases and the heat absorption peak disappears for the Cu-Se co-alloyed Ag2S sample. In addition, the average lattice thermal conductivity is greatly reduced, and the κL of Ag1.8Cu0.2S0.5Se0.5 is around 0.27 Wm−1K−1 from 330 K to 450 K. Therefore, a high ZT is obtained for Cu-Se co-alloyed Ag2S.

Preparation and characterization of curdlan/nanocellulose blended film and its application to chilled meat preservation

In this study, to improve the mechanical and thermal properties of curdlan film, a curdlan/nanocellulose (NC) blended film was prepared and characterized for the first time. NC was successfully prepared from microcrystalline cellulose (MCC) with NaOH/urea treatment. The particle size of NC was observed to be 70–140 nm by cryo-electron microscope (cryo-EM). The blended film was prepared by adding the NC to curdlan solution. The tensile strength (TS) of the blended film reached the maximum value of 38.6 MPa, and the elongation at break (EB) was 40%. The DSC curve showed that the heat absorption peak of the film was 240 °C, indicating that the blended film has good temperature stability. Additionally, some other film properties were also improved, including gas barrier properties and transparency. Obvious morphological and molecular differences between the blended film and the pure curdlan film were discovered by SEM and FTIR analysis. Finally, the blended film was used for the preservation of chilled meat and extended the storage time of meat to 12 days. These results provided a theoretical basis for future application and development of biodegradable film.

SIMULTANEOUS EFFECTS OF Cd(II) AND Pb(II) IONS AND γ-IRRADIATION ON STABILITY OF Spirulina platensis

Effect of toxic metal ions Cd(II) and Pb(II) on cyanobacterium (blue-green algae) Spirulina platensis intact cells have been studied with optical and differential scanning microcalorimetry (DSC) methods after 7.2 kGy 137 Cs gamma irradiation and without irradiation. It is shown that the addition of metal ions causes a decrease in optical absorption spectra band intensities. In the case of irradiation, the absorption band intensity decreases higher than without irradiation. The binding constant of Pb(II) with Spirulina platensis is calculated for nutrition medium with pH 9.2. DSC data show that Cd(II) and Pb(II) ions do not change the integral heat of absorption (Δ H m ) that equals to 24.6 J g -1 . In the case of irradiation, the DSC melting curve profile changes significantly and Δ H m decreases two times, which indicates that 50 % of proteins are denaturated. The DSC method also gives a possibility to evaluate C-phycocyanin content from deconvoluted heat absorption peak at 50 °C, which equals to 35.5 %. In case of irradiated wet mass, sub-cultured wet mass, and wet mass re-irradiated with the same dose, contents of Spirulina platensis ingredients – C-phycocyanin, chlorophyll, and carotenoids – increase as a result of the simultaneous effect of the metal ions and irradiation.

Water resistance improvement by polyethyleneimine of tannin-furfuryl alcohol adhesives

ABSTRACTIn this research furfuryl alcohol (FA) and polyethyleneimine (PEI) in different ratio were added to a tannin based adhesive in order to improve its moisture resistance. In order to characterize the functional groups involved, Fourier-transform infrared spectroscopy (FTIR) was used. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study the thermal behaviour of the formulations. FTIR spectroscopy indicated the reaction of quebracho tannin with FA and PEI. The results of the TGA showed that the added FA and PEI increased the resistance to thermal degradation. DSC analysis showed that the added FA and PEI reduced the heat absorption peak. According to the tensile shear strength of the formulations, the adhesive formulation T1 F0.75 P20 (mixing proportion: Tannin 1, FA 0.75, PEI 20%) was able to satisfy the standards requirements (BS 1204-2) as a moisture resistant adhesive. Furthermore, this formulation presented the best tensile shear tests results and the least number of delaminated samples.

Rejuvenation of a Metallic and Oxide Glass by Cooling from the Supercooled Liquid State at Laboratory Rates

Calorimetric study of relaxation and rejuvenation of PdNiP and SiO2‐based glasses by cooling from the supercooled liquid state at laboratory rates is performed. For the former glass, cooling at the highest rate of 54 K min−1 recovers 34–36% of the enthalpy released upon relaxation. The interplay between relaxation and rejuvenation leads to a dependence of the heat absorption peak above the glass transition temperature Tg on the cooling rate. The oxide glass displays a similar effect with analogous dependence on the cooling rate. Qualitative explanations for the observed phenomena are presented.

Unusual Reversible Oligomerization of Unfolded Dengue Envelope Protein Domain 3 at High Temperatures and Its Abolition by a Point Mutation.

We report differential scanning calorimetry (DSC) experiments between 10 and 120 °C of Dengue 4 envelope protein domain 3 (DEN4 ED3), a small 107-residue monomeric globular protein domain. The thermal unfolding of DEN4 ED3 was fully reversible and exhibited two peculiar endothermic peaks. AUC (analytical ultracentrifugation) experiments at 25 °C indicated that DEN4 ED3 was monomeric. Detailed thermodynamic analysis indicated that the two endothermic peaks separated with an increasing protein concentration, and global fitting of the DSC curves strongly suggested the presence of unfolded tetramers at temperatures around 80-90 °C, which dissociated to unfolded monomers at even higher temperatures. To further characterize this rare thermal unfolding process, we designed and constructed a DEN4 ED3 variant that would unfold according to a two-state model, typical of globular proteins. We thus substituted Val 380, the most buried residue at the dimeric interface in the protein crystal, with less hydrophobic amino acids (Ala, Ser, Thr, Asn, and Lys). All variants showed a single heat absorption peak, typical of small globular proteins. In particular, the DSC thermogram of DEN4 V380K indicated a two-state reversible thermal unfolding independent of protein concentration, indicating that the high-temperature oligomeric state was successfully abolished by a single mutation. These observations confirmed the standard view that small monomeric globular proteins undergo a two-state unfolding. However, the reversible formation of unfolded oligomers at high temperatures is a truly new phenomenon, which was fully inhibited by an accurately designed single mutation.

Mechanical Property of M40Jf/5A06Al Composite at Elevated Temperatures

In this work, aluminum alloy with a high concentration of magnesium (5A06) was reinforced with 55 vol% unidirectional ultra-high modulus and highly graphitized carbon fiber (M40J) using pressure infiltration method. The effect of temperature on the bending strength of the Cf/Al composites was investigated from room temperature to 500 °C. The experimental results showed that the strength of M40Jf/5A06Al composites was not affected by temperature from room temperature to 200 °C. The bending strength of the composite at 300 °C was decreased by 30% compared with that at room temperature. In order to evaluate the extent of interface weakening, the length of fiber pullout was measured. The results showed that the pullout length reached the maximum at 300 and 500 °C, which indicated weak interface at the corresponding temperature. The DSC curve presented obvious heat absorption peak at around 300 °C, which may be attributed to the dissolution of the interfacial product β (Al3Mg2) phases at the C/Al interface. The bending fracture surfaces of the composites after three-point bending tests were observed by SEM, plastic-viscous flow of the matrix were observed at the samples tested at 500 °C. The predominant mechanisms for high-temperature damage of M40Jf/5A06Al composites are matrix softening caused by dislocation recovery and interface weakening caused by the dissolution of interfacial products.

Structural basis for the NAD binding cooperativity and catalytic characteristics of sperm-specific glyceraldehyde-3-phosphate dehydrogenase.

Catalytic properties of enzymes used in biotechnology can be improved by eliminating those regulatory mechanisms that are not absolutely required for their functioning. We exploited mammalian glyceraldehyde-3-phosphate dehydrogenase as a model protein and examined the structural basis of the NAD(+) cooperative binding exhibited by its homologous isoenzymes: the somatic enzyme (GAPD) and the recombinant sperm-specific enzyme (dN-GAPDS). Moreover, we obtained a mutant dN-GAPDS, which misses the cooperativity, but exhibits a twofold increase in the specific activity instead (92 and 45 μmol NADH/min per mg protein for the mutant and the wild type proteins, respectively). Such an effect was caused by the disruption of the interdomain salt bridge D311-H124, which is located close to the active site of the enzyme. The thermal stability of the mutant protein also increased compared to the wild type form (heat absorption peak values were 70.4 and 68.6 °C, respectively). We expect our findings to be of importance for the purposes of biotechnological applications.

Effects of NaCl concentration and potassium chloride substitutions on the thermal properties and lipid oxidation of dry-cured pork.

The thermal properties of cured meat are important for determining storage life and nutritional quality. However, few studies have focused on the thermal properties of dry-cured pork, particularly in relation to salt level and type. In order to study the thermal properties of dry-cured pork, we used differential scanning calorimetry (DSC) to evaluate the net heat energy (enthalpy, ΔH), onset (T(onset)), and maximum (T(max)) temperatures of different pork cuts salted with mixtures of chloride (NaCl and KCl) salts within the curing and ripening temperature range. Within the curing temperature range (-5 to 20 °C), the T(onset), T(max), and ΔH of cured meat treated with different NaCl : KCl mixtures were generally lower than for fresh meat, which indicates that the addition of NaCl or KCl can reduce the melting of lipids and water (especially lipids), in different pork cuts. Within the ripening temperature range (5 to 50 °C), heat absorption peaks in belly and leg cuts were between 29 and 33 °C. However, no obvious heat absorption peak was found in loin cuts. Compared to non-KCl substitutions, a slightly higher KCl substitution could significantly (P < 0.05) enhance ΔH values of dry-cured belly and leg cuts. The likely cause of this phenomenon is that high KCl substitutions promote lipid oxidation (r = 0.98, for belly; r = 0.95, for leg cuts). Therefore, KCl substitution should be no more than 30% (wt/wt), especially for high lipid pork, to prevent excessive melting and oxidation of lipids during the dry-curing process.

Relations between macro- and microstability of CH2 domains and human IgG2 and their biological activity: 1. Analysis of calorimetric and optical melting curves

Human myeloma immunoglobulin second subclass LOM and SIN, their Fc fragment and firstly obtained hFc fragment in which there is not only low portion of the hinge region, but also its core portion (Cys-Cys-Val-Glu-Cys-Pro-Pro-Cys), have been studied by number of physical methods (scanning calorimetry, fluorescence spectroscopy, analytical centrifugation). Joint analysis of calorimetric and optical melting curves revealed that only first (low-temperature) heat absorption peak at all the melting curves corresponds to the melting of the two CH2 domains. It was shown that CH2 domains of intact IgG2 are destabilized relative to those domains in hFc and Fc fragments.

Structure of drug delivery DPPA and DPPC liposomes with ligands and their permeability through cells

Dipalmitoylphosphatidylcholine (DPPC) and 1,2-palmitoyl-phosphatidic acid (DPPA) liposomes, prepared by conventional rotary evaporation method, have similar structural organization, though they have significant differences. The similarity is that both types of lipids create standard bilayer liposomes with strong hydrophobic forces between lipids tails and with homogeneous bonds of hydrogen and electrostatic nature between hydrophilic lipids heads. By the calorimetric method, it has been shown that hydrophobic bonds break but liposomes’ destruction does not occur by heating till 150 °C. As for bonds between lipid heads in liposomes, their cooperative destruction takes place at 41 °C for DPPC and 66 °C for DPPA liposomes. In the case of thermal distraction of DPPC liposomes, two so-called pre transitions peaks were observed before the main transition peak, which indicates that DPPC liposomes’ structure is multilamellar. DPPA liposomes have one cooperative heat absorption peak, which points to a unilamellar structure of such liposomes. Substances of hydrophobic/hydrophilic nature, incorporated into the liposomes, are placed in hydrophobic or hydrophilic parts of liposomes, which lead to a change in calorimetric peak shapes and thermodynamic parameters. It has been shown that gold nanoparticles, incorporated into the DPPC liposomes, are able to enter Caco-2 cells. In contrast, these nanoparticles do not enter red blood cells.

Effect of Compatibilizing Agent on Mechanical and Thermal Properties of Wood-Plastic Composites

Polypropylene and wood flour were used as raw materials,maleic anhydride grafted polypropylene(MAPP) as compatibilizing agent, wood-plastic composite(WPC) was prepared by compression molding process. The effects of the content of MAPP on the mechanical and thermal properties of WPC were investigated. The results show that, with the increase of the content of MAPP, both the tensile and flexural strengths of WPC will increase, and the impact strength of WPC increases first, then decreases, and the impact strength reaches the maximum of 1.18kJ/m2 when the content of MAPP is 4%,which is 76.7% increased from that of the composite without MAPP. Each composite has an obvious heat-absorption peak when melted during 140-170 and the melting enthalpy of WPC increases with the content of MAPP, the melting procedures of all the composites are quite similar with one another. Application of MAPP can improve the thermal stability of WPC

Energetic domains analysis of bovine α-lactalbumin upon interaction with copper and dodecyl trimethylammonium bromide

Domain analysis of the dialyzed form of α-lactalbumin (m-α-LA) with varying concentrations of Cu +2 and DTAB has been carried out by differential scanning calorimetry (DSC), circular dichroism (CD) and resonance Rayleigh scattering (RLS) to elucidate the effect of the ligands on the thermal and structural properties of m-α-LA. The DSC profile displayed two dissimilar temperature-induced heat-absorption peaks as well as two melting points ( T m = 305 K, T m = 333 K). The m-α-LA is not a new form of α-LA, but rather contains a mixture of the apo- and holo-forms of α-LA (i.e., a-α-LA and h-α-LA) at low and high temperatures, respectively. The presence of Cu +2 as the metal ion and DTAB as the non-metal ion altered the two heat-absorption peaks in such a manner that, with the addition of Cu +2 to m-α-LA, the excess molar heat capacity profile showed three sub-peaks, i.e., one sub-peak for a-α-LA at 303.2 K and two other sub-peaks for h-α-LA at 325 K and 334 K. The presence of these peaks was due to the molecular population of the a-α-LA form changing into h-α-LA. Contrarily, when it came to the interaction between DTAB and m-α-LA, the DSC thermogram showed two sub-peaks, i.e., one sub-peak for a-α-LA and another sub-peak for h-α-LA, resulting from the molecular population of the h-α-LA form changing into a-α-LA. The CD experiments on m-α-LA upon interaction with Cu +2 and DTAB demonstrated an increment and a decrement, respectively, of the α-helix content relative to that of the protein in the absence of the ligands. However, the α-helix induced by Cu +2 as a metal ion inspired one energetics domain in m-α-LA, wherefore it could be deduced that the helicity content caused an increment of the energetics content of α-LA. Hence, Cu +2 and DTAB at various concentrations played important roles as good probes for defining the electrostatic moiety for domains of m-α-LA initiated through a dissimilarity with regard to the α-helicity of these domains. The RLS intensity of m-α-LA upon interaction with Cu +2 and DTAB determine the DSC and CD results for inducing h-α-LA and a-α-LA respectively.

Intrinsically Disordered Proteins and Their Environment: Effects of Strong Denaturants, Temperature, pH, Counter Ions, Membranes, Binding Partners, Osmolytes, and Macromolecular Crowding

Intrinsically disordered proteins (IDPs) differ from "normal" ordered proteins at several levels, structural, functional and conformational. Amino acid biases characteristic for IDPs determine their structural variability and lack of rigid well-folded structure. This structural plasticity is necessary for the unique functional repertoire of IDPs, which is complementary to the catalytic activities of ordered proteins. Amino acid biases also drive atypical responses of IDPs to changes in their environment. The conformational behavior of IDPs is characterized by the low cooperativity (or the complete lack thereof) of the denaturant-induced unfolding, lack of the measurable excess heat absorption peak(s) characteristic for the melting of ordered proteins, "turned out" response to heat and changes in pH, the ability to gain structure in the presence of various counter ions, osmolytes, membranes and binding partners, and by the unique response to macromolecular crowding. This review describes some of the most characteristic features of the IDP conformational behavior and the unique response of IDPs to changes in their environment.

Calorimetric and spectrophotometric investigation of PLGA nanoparticles and their complex with DNA

The calorimetric investigation of non-coated and chitosan-coated PLGA nanoparticles (NP) shows that at initial temperatures of heating particle swelling takes place what results in an internal architectural change at lower than physiological temperature. It has shown that the temperature of NP tightness perturbing depends on solvent polarity: as more polar is the solvent more stable are particles. The break of existing bonds in NP shell is accompanied with heat absorption peak which undergoes significant changes depending on heating rate. In the wide pH 2–8 interval in transition temperature no changes occurred. The obtained results show that such NP could be used in acidic area for drug transfer, which gives possibility to take medicine orally. It was shown that DNA attaches only to chitosan-coated NP. The optimal ratio for DNA loading onto the NP was found to be 7:1 (WNP/WDNA).

Identification of Precipitates Appearing in Al-Li-Cu-Zr Alloy

Identification of precipitates appearing during DSC scan of Al-2.1Li-2.9Cu-0.12Zr(wt. pct) alloy has been conducted as a function of temperature by using a differential scanning calorimetry (DSC) and transmission electron microscopy(TEM). In the as-quenched specimen from 540°C, three couples of heat evolution and absorption peaks are observed during the heating period of DSC experiments. It is found from TEM works that these peaks are associated with the formation and dissolution of GP zone, δ‘, and T1(+θ') phases. The heat evolution peak appearing in the temperature range over 36~78°C is due to the formation of GP zone. Heat absorption peak appearing in 78~140°C is associated with the dissolution of GP zone. Heat evolution peaking at 166°C in the temperature range over 140~190°C and next heat absorption peak are attributed to the formation and dissolution of δ‘ phase. Heat evolution peaking at 288°C in the temperature range of 254~332°C and heat absorption at high temperature are attributed to the formation and dissolution of T1(+θ'). The hump in DSC curve at the temperature of 425°C is considered as the formation of hexagonal structure T2 phase.

A differential scanning calorimetric study of the influence of copper and dodecyl trimethyl ammonium bromide on the stability of bovine α-lactalbumin

Bovine α-lactalbumin (α-LA) has been studied by differential scanning calorimetry (DSC), fluorescence spectroscopy and viscometry with various concentrations of Cu 2+ and DTAB to elucidate the effect of these ligands on its thermal properties. The DSC profile of dialyzed form of α-lactalbumin (m-α-LA) contrary to the undialyzed form (holo-form, h-α-LA) shows two temperature induced heat absorption peaks. The m-α-LA is not a new form of α-LA. It contains mixture of the apo (a-α-LA) and holo (h-α-LA) forms of α-LA at low and high temperatures, respectively. Therefore, these two states of α-LA (apo and holo) are equilibrating with together after dialyze experiment. The Cu 2+ as a metal ion and DTAB as a non metal ion alter the two heat-absorption peaks, in such a manner that, the addition of Cu 2+ to the m-α-LA increases partial molar heat capacity and enthalpy change values of the h-α-LA form at high temperature because the molecular population of the a-α-LA form changes into the h-like-α-LA. On the contrary, the interaction between the DTAB and the m-α-LA increases these thermodynamic values for the a-α-LA at low temperature. However, DTAB bound to m-α-LA prevents from Ca 2+ binding to protein, because there are positive charges repulsion between them. The high temperature peak occurs at the same temperature as the unfolding of the h-α-LA, while the low temperature peak lies within the temperature range associated with the unfolding of the a-α-LA. The R s values of m-α-LA, h-α-LA and a-α-LA forms confirmed the folding and unfolding of the m-α-LA during the addition of Cu 2+ and DTAB at different concentration, respectively.