Thermogravimetric analysis of human femur bone

Thermal decomposition analysis of human femur bone has been carried out in the temperature range between 25°C and about 1000°C. In this temperature range, the differential primary weight loss curve yielded four distinct peaks for the femur bone. Each minimum inflexion point was arbitrarily chosen as the temperature at which the thermal decomposition of the component responsible for the peak had been completed. Aided by the thermogravimetric data on tendon collagen, the observed four peaks have been identified as follows: First: dissociation of water from the collagen; second: decomposition of collagen molecule itself; third: residual organic components associated with the collagen; fourth: water loss accompanied with the transformation of inorganic apatite and residual protein that were not decomposed at lower temperature. The fourth peak identified with the crystal transformation has been linked to the transformation ofα-tricalcium phosphate, which is known to have a hexagonal structure, toβ-tricalcium phosphate, which has a rhombohedral structure. This transformation has been observed between 700°C and 780°C which is in accord with the range observed in the transformation of synthetic apatite crystals. The experiments were performed under two different conditions: in normal pressure (in air) and in a reduced pressure of about 30μ Hg. In the average, the total weight loss up to the temperature of about 1000°C was about 35.64% for the heating in air and 36.45% for the heating in the reduced pressure. The weight loss has been carefully analyzed in the different temperature intervals and has been compared with an expected weight loss predicted by three most quoted formulas advanced for the apatite in bone. In addition to this, the conventional thermogravimetric analysis has been carried out in order to retrieve the thermal kinetic decomposition parameters corresponding to each peak. The activation energies corresponding to the first, second, and third peaks have been found to be slightly higher than those of tendon collagen. A detailed analysis showed that the bone contains about 28% protein and about 8% water (apatite crystalline water included).     

Kinetic and thermodynamics study of the pyrolytic process of the freshwater macroalga,Chara vulgaris

This is the first study where the pyrolysis of the freshwater macroalga Chara vulgaris was explored to reveal its bioenergy potential. The suitability of C. vulgaris to bioenergy conversion via pyrolysis was accessed in terms of kinetic triplet and thermodynamic parameters. For this purpose, pyrolysis experiments under a thermogravimetric scale were conducted at multiple heating rates (5, 10, and 20 °C min^?1) in an inert atmosphere. The mass-loss profiles of C. vulgaris pyrolysis showed that there are two dominant decomposition stages that are related to distinct chemical components inside its structure and that directly affect the calculated kinetic triplet and thermodynamics parameters. The average activation energy obtained using isoconversional methods of Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Starink, and Friedman was in the range of 52.87–72.91 kJ mol^?1 for the first decomposition stage and 156.14–174.65 kJ mol^?1 for the second decomposition stage. The pyrolytic conversion of C. vulgaris initially follows a second-order reaction model (first decomposition stage), while in second decomposition stage is controlled by a second-order Avrami-Erofeev reaction model. The kinetic results derived from the non-isothermal decomposition of C. vulgaris proved its suitable characteristics for pyrolysis. Additionally, multi-stage kinetic interpretation was successfully attained based on two kinetic triplets, where reconstructed pyrolysis behavior correlated well with experimental pyrolysis behavior. The changes in enthalpy, Gibbs free energy, and entropy for first decomposition stage were 67.58±0.25 kJ mol^?1, 180.77±5.30 kJ mol^?1, and ?176.65±0.41 J mol^?1 K^?1, and for the second decomposition stage the values were 166.70±0.09 kJ mol^?1, 285.51±1.29 kJ mol^?1, and ?124.29±0.09 J mol^?1 K^?1, respectively. Based on thermodynamic aspects, C. vulgaris is particularly interesting for use as a raw material to produce biofuels and bioenergy.

     

Thermoluminescence glow curve deconvolution and kinetic parameter determination of samarium-doped lithium borosilicate glass

Thermoluminescence glow curves of gamma-irradiated samarium-doped lithium borosilicate glass were investigated. The number of overlapping peaks was determined using the repeated initial rise method. The glow curves were deconvoluted into four overlapping peaks. The trapping parameters such as activation energy E, frequency factor (s), and kinetic order (b) for each peak were determined. The obtained results indicated that the lithium borosilicate glass doped with samarium had four electron trap levels with the average activation energies of 0.82, 1.01, 1.21, and 1.31 eV. Thermal fading analysis of the individual peaks based on the deconvolution data was performed. The obtained results showed high thermal fading of the first peak, but high thermal stability of the second and third peaks compared with the other peaks. These results could be used to explain some observed properties such as high thermal fading and light sensitivity for this thermoluminescent material. Moreover, the obtained results may be helpful in minimizing fading corrections in dosimetric applications.     

Thermal Stability Investigation and the Kinetic Study of Folnak<Superscript>®</Superscript> Degradation Process Under Nonisothermal Conditions

The nonisothermal degradation process of Folnak^® drug samples was investigated by simultaneous thermogravimetric and differential thermal analysis in the temperature range from an ambient one up to 810°C. It was established that the degradation proceeds through the five degradation stages (designated as I, II, III, IV, and V), which include: the dehydration (I), the melting process of excipients (II), as well as the decomposition of folic acid (III), corn starch (IV), and saccharose (V), respectively. It was established that the presented excipients show a different behavior from that of the pure materials. During degradation, all excipients increase their thermal stability, and some kind of solid–solid and/or solid–gas interaction occurs. The kinetic parameters and reaction mechanism for the folic acid decomposition were established using different calculation procedures. It was concluded that the folic acid decomposition mechanism cannot be explained by the simple reaction order (ROn) model (n?=?1) but with the complex reaction mechanism which includes the higher reaction orders (RO, n?>?1), with average value of <n?>?=?1.91. The isothermal predictions of the third (III) degradation stage of Folnak^® sample, at four different temperatures (T _iso?=?180°C, 200°C, 220°C, and 260°C), were established. It was concluded that the shapes of the isothermal conversion curves at lower temperatures (180–200°C) were similar, whereas became more complex with further temperature increase due to the pterin and p-amino benzoic acid decomposition behavior, which brings the additional complexity in the overall folic acid decomposition process.     

X-ray diffraction studies on the structure of hydrated collagen

The temperature dependence of the humidity-sensitive spacing, d, related to the lateral packing of collagen molecules was measured for fully hydrated collagen. In the vicinity of 0°C, a sudden change in d was observed, which was reversible with temperature. In the diffraction profile, below 0°C, a set of diffraction peaks identified with the hexagonal crystalline form of ice was observed. With the reduction in water content, the intensity of the set of diffraction peaks decreased and was found to be zero at a water content of 0.38 g/g collagen. These results were considered to be caused by the frozen water in collagen fibril below 0°C. According to the water content dependence of d, it was considered that up to a certain water content water absorbed would be stowed in the intermolecular space of collagen and above that water content water molecules would aggregate to make pools, i. e., extrafibrillar spaces. The unfreezable bound water was considered to be located in the intermolecular space of collagen. Size of the extrafibrillar space, determined from the intensity analysis of a smallangle x-ray scattering pattern, corroborates the speculation that the water showed in the extrafibrillar space is freezable and free. The formation of the hexagonal crystalline form of ice in the extrafibrillar space was considered to cause the sudden change in d at 0°C.     

Calorimetry of rat tail tendon collagen before and after denaturation: the heat of fusion of its absorbed water

The specific heat, of rat tail tendon at various water contents was measured as a function of temperature. The resulting graphs showed peaks arising from the melting, near 50°C, of helical material in the collagen, and from the melting of absorbed water in the range -40°C to 0°C. The heat of melting of helical material was 11.7 cal per gram of dry tendon. Determination of the heat and temperature of fusion of the absorbed water allowed resolution of the water into four states in the case of tendon before denaturation, and three states after denaturation. The four states are (1) water not freezable on cooling to - 70°C, (2) freezable water with-both heat and temperature of fusion different from the values for ordinary water, (3) freezable water with the heat of fusion of ordinary water, but a different temperature of fusion, and (4) water not distinguished from ordinary water. The fourth state was absent in denatured tendon. The results are discussed in terms of increasing size of clusters of absorbed water molecules.     

Reproduction of the introduced oyster Crassostrea gigas (Bivalvia: Ostreidae) cultured on rafts in Spain

The oyster Crassostrea gigas was introduced in Spain for aquaculture purposes; however, until now, it is not known whether populations are established in the wild, being necessary to define whether this species is spawning and which environmental variables trigger this process. The influence of environmental parameters on the reproduction of C. gigas was evaluated from January 2008 to October 2009 with oysters grown on a raft in the Ría de Arousa (Galicia, NW Spain). Temperature and chlorophyll a are directly correlated to sexual maturation. Oysters can mature at temperatures below 14°C. The temperature necessary for spawning differs between the sexes, requiring a temperature above 15°C for males and 18°C for females. Females had a single massive spawn between June and September, while males had partial spawning from May to December with two peaks, one in May–September and another in October–December, with the second peak more pronounced. The first spawning peak is related to high temperatures and concentrations of chlorophyll a, and the second spawning peak is mainly related to the food availability in the water. The spawning asynchrony may be impeding establishment of wild C. gigas populations in Spain.     

Biochemical and molecular characterization of a cellobiohydrolase from <Emphasis Type="Italic">Trametes versicolor</Emphasis>

A cellobiohydrolase-encoding cDNA, Tvcel7a, from Trametes versicolor has been cloned and expressed in Aspergillus niger. The deduced amino acid sequence shows that Tvcel7a encodes a 456-amino acid polypeptide belonging to glycosyl hydrolase family 7. TvCel7a possesses a 19-amino acid secretion signal but does not possess a linker region nor a carbohydrate-binding domain. Two peaks of activity were obtained after TvCel7a was purified to apparent homogeneity by gel-filtration followed by anion-exchange chromatography. Mass spectrometry performed on the purified proteins confirmed that both peaks corresponded to the predicted sequence of the T. versicolor cellulase. The biochemical properties of the purified TvCel7a obtained from both peaks were studied in detail. The pH and temperature optima were 5.0 and 40°C, respectively. The enzyme was stable over a pH range extending from pH 3.0 to 9.0 and at temperatures lower than 50°C. The kinetic parameters with the substrate p-nitrophenyl β-d-cellobioside (pNPC) were 0.58 mM and 1.0 μmol/min/mg protein for the purified TvCel7a found in both peaks 1 and 2. TvCel7a catalyzes the hydrolysis of pNPC, filter paper, β-glucan, and avicel to varying extents, but no detectable hydrolysis was observed when using the substrates carboxymethylcellulose, laminarin and pNPG.     

Structural changes in cartilage and collagen studied by high temperature Raman spectroscopy

Understanding the high temperature behavior of collagen and collagenous tissue is important for surgical procedures and biomaterials processing for the food, pharmaceutical, and cosmetics industries. One primary event for proteins is thermal denaturation that involves unfolding the polypeptide chains while maintaining the primary structure intact. Collagen in the extracellular matrix of cartilage and other connective tissue is a hierarchical material containing bundles of triple‐helical fibers associated with water and proteoglycan components. Thermal analysis of dehydrated collagen indicates irreversible denaturation at high temperature between 135°C and 200°C, with another reversible event at ～60‐80°C for hydrated samples. We report high temperature Raman spectra for freeze‐dried cartilage samples that show an increase in laser‐excited fluorescence interpreted as conformational changes associated with denaturation above 140°C. Spectra for separated collagen and proteoglycan fractions extracted from cartilage indicate the changes are associated with collagen. The Raman data also show appearance of new features indicating peptide bond hydrolysis at high temperature implying that molecular H₂O is retained within the freeze‐dried tissue. This is confirmed by thermogravimetric analysis that show 5‐7 wt% H₂O remaining within freeze‐dried cartilage that is released progressively upon heating up to 200°C. Spectra obtained after exposure to high temperature and re‐hydration following recovery indicate that the capacity of the denatured collagen to re‐absorb water is reduced. Our results are important for revealing the presence of bound H₂O within the collagen component of connective tissue even after freeze‐drying and its role in denaturation that is accompanied by or perhaps preceded by breakdown of the primary polypeptide structure.     

Structural Changes in Starch Granules of Low Moisture Content during Heating

The thermal behavior of the starch structure was determined successfully under low moisture conditions by differential thermal analysis (DTA) using an anti-leak cell (resistant to an internal pressure of about 40 kg/cm²). Three kinds of starch, potato, kuzu and corn, with a low moisture content less than 12% indicated two strong endothermic peaks, one at the lower temperature (A) and the other at the higher temperature (B) in a temperature range approximately from 20 to 250°C. From microscopic observations and determinations of intrinsic viscosity, blue value and the solubility of heated starch, it is considered that peak A reflects an endothermic process accompanied by dextrinization involving the collapse of the ordered structure of starch with a limited breakdown in the polysaccharide chain. On the other hand, peak B corresponds to a thermal decomposition of the glucosyl residues, that is caramelization. The temperature at which such dextrinization takes place is markedly influenced by both the starch species and the moisture content of the starch.     

Changes in denaturation and rheological properties of collagen-hyaluronic acid scaffolds as a result of temperature dependencies

This report describes the effect of temperature on the mechanical viscoelastic properties such as: storage modulus (E′), loss modulus (E″), and loss tangent (tan δ) of the collagen sponges modified with hyaluronic acid (HA). In order to detect collagen–HA copolymer denaturation and to assess its thermal stability, the differential scanning calorimetry (DSC) supplemented by thermogravimetric (TG) measurements was used. The denaturation temperature (T_d) of unmodified collagen samples increased from 69 to 86 °C for cross-linked samples, respectively. These temperature dependencies show remarkable changes in E′ and E″ at selected temperature up to 226 °C for all samples due to the release of loosely and strongly bound water. The influence of HA on the viscoelastic behavior of collagen is manifested by a shift of the tan δ peak associated with the process of decomposition towards higher temperatures resulting in a higher thermo-stability of the modified scaffolds.     

Rapid estimation of triacylglycerol content of <Emphasis Type="Italic">Chlorella</Emphasis> sp. by thermogravimetric analysis

A simple and reliable method based on thermogravimetric analysis has been developed for determining triacylglycerol content in Chlorella sp. KR-1. There are two decomposing steps during pyrolysis of the microalgal cells and the second step of weight loss may be attributed to degradation and volatilization of triacylglycerols. The second peak height in the temperature derivatives of weight loss increased with the triacylglycerol content of the microalgal cells and the peak was around 390°C regardless of the triacylglycerol contents. Based on these findings, a linear equation for determining triacylglycerol content was derived. The proposed method gives satisfactory results, showing small variance and a good interpolation capability.     

Electrical properties of hydrated collagen. I. Dielectric properties

The effect of water on the low-frequency (10²-10⁵ H_z) complex permittivitv of native, sold-state collagen has been investigated experimentally. Measurements at ambient temperature show that dry collagen exhibits essentially no frequency or temperature dependence. As water is absorbed, both dielectric constant and loss factor increase simultaneously and rise sharply upward at a hydration level which may be associated with the completion of the primary absorption layer as determined from independent water absorption studies. The behaviour is qualitatively identical to that observed for other proteins and related materials. Temperature-dependent measurements made under vacuum conditions in the range ?196°C to +100°C are characteristic of the dielectric properties of the water in the sample. Dehydration produced by successive temperature recycling to the maximum temperature effectively eliminates any temperature or frequency dependence. A maximum in the temperature-dependent curves is found at about +40°C and is explained as the superposition of two processes: (1) the transition of water molecules from bound to free states, and (2) the difffusion of water molecules out of the system. The dielectric constant of dry collagen, after desorption at ambient temperature, is about 4.5. Desorption at elevated temperatures reduced the room temperature value to about 2.3 and the liquid nitrogen temperature value to a number indistinguishable from the optical value of n² = 2.16.     

Structural analysis of turkey tendon collagen upon removal of the inorganic phase

Calcified leg flexor tendons in which the inorganic phase content had been lowered by progressive demineralization were studied by small angle X-ray diffraction and thermogravimetry. The X-ray diffraction results agree very well with the data previously obtained on calcified turkey tendon indicating that the method used to decalcify tendons provides good correspondence with the process of calcification. Up to five thermal processes can be detected in the thermogravimetric scans: (1) water release; (2) collagen decomposition; (3 and 4) combustion of the residual organic components; (5) carbonate removal from the apatitic phase. The temperature of collagen decomposition decreases at lower inorganic phase content in agreement with the higher thermal stability of calcified collagen fibrils compared with uncalcified ones. The decrease of collagen thermal stability upon decalification is paralleled by a decrease of the structural order of the collagen fibrils as indicated by small angle X-ray diffraction data. Decalcification down to about 40% wt of inorganic phase does not significantly alter the inorganic blocks that are regularly arranged inside the gap zone of the collagen. Further removal of inorganic phase down to about 15% wt provokes a variation of the intensity distribution of the small angle meridional reflections that can be ascribed to a reduction of the mean height of the inorganic blocks. At inorganic phase contents below 15% wt the gap region is more free to contract upon air drying as a result of the reduction of the mean length of the inorganic blocks.     

槲皮素的热降解机理及其分解动力学研究

利用TG-DTG技术测得槲皮素在氮气气氛中不同升温速率β下的热分解曲线,协同使用Achar法、Coats-Redfern法、Kissinger法和Ozawa法等4种方法同时进行动力学处理,根据热分解的表观活化能Eα和指前因子A计算推断槲皮素的贮存期.随着升温速率的提高,槲皮素的热分解温度逐渐升高;槲皮素热二步分解的机理依次是随机成核与随后生长控制和化学反应控制,对应的函数名称是Avrami-Erofeev方程和反应级数方程;经Gaussian模拟和热重数据结合分析,槲皮素在第一步分解时,失去两个O原子;第二步分解时失去一个苯环;根据第一步热分解的表观活化能Eα和指前因子A推断,在室温25℃下,槲皮素的贮存期为1.5 ～2年.     

Temperature-related heart rate in water and air and a comparison to other temperature-related measures of performance in the fiddler crab Leptuca pugilator (Bosc 1802)

Performance in poikilotherms is known to be sensitive to temperature, often with a low-sloping increase with temperature to a peak, and a steep decline with increasing temperature past the peak. We complemented past measures of performance by measuring heartbeat rates of the fiddler crab Leptuca pugilator in water and in air as a function of a range of temperatures previously shown to affect other measures of performance. In water over a range of 20–50 °C, heartbeat increased steadily to a peak at 40 °C and then steeply declined to near zero at 50 °C. In air, heartbeat also increased, but to a peak at 35 °C and then with a gentler decline than was found in water. Part of this different response may be due to evaporative water loss, which reduced body temperature in air, and therefore thermal stress, relative to body temperature when crabs were immersed in water. Increased availability of oxygen from air, according to the oxygen and capacity-limited thermal tolerance hypothesis, likely increased aerobic scope past the thermal peak, relative to within water, where oxygen delivery at higher temperatures may have been curtailed.We compared the heart rate performance relations to two previous measures of performance – endurance on a treadmill and sprint speed, both done in air. The peak performance temperature increased in the order: treadmill endurance time, sprint speed, heart rate in air, and heart rate in water, which demonstrates that different performance measures give different perspectives on the relation of thermal tolerance and fitness to temperature. Endurance may therefore be the limiting upper thermal stress factor in male fiddler crabs, when on hot sand flats. Temperature preference, found to be for temperatures <30 °C in air, could be a bet-hedging evolutionary strategy to avoid aerobic scope affecting endurance.     

Differential Thermal Analysis of Milk Proteins

Differential thermal analysis (DTA) was used for study of milk protein denaturation. Protein solutions produced an endothermic peak of characteristic shape and temperature of peak minimum. The peak minimum is considered the coagulation temperature of the protein.

The influence of pH and additives such as sugars and NaCl was clearly observed on the thermograms of β-lactoglobulin solution. Addition of κ-casein to β-lactoglobulin solution showed an inhibitory effect on the heat coagulation.

Solid proteins produced two-stage exothermic peaks between 200°C and 400°C.

DTA was a useful method in the study of heat denaturation and degradation of protein.     

Thermal behavior of biodegraded lime wood

The effects of the soft-rot fungus Trichoderma viride Pers., on the thermal behavior of lime wood (Tillia cordata Mill.) were investigated. The lime wood pieces were inoculated with the fungus over a 12-week period. At pre-established time intervals two samples were withdrawn from the medium and analyzed by thermogravimetry and differential calorimetry, and the results were correlated with mass loss. Fungal activity was indicated by continuous decrease of sample mass.Modification of the wood because of the presence of the fungus was evidenced by structural changes that affected its thermal properties, both in respect to the hydrophilicity of the wood (evidenced mainly in desorption process) and in its decomposition behavior. The shape of DTG curves depends on the exposure time of wood to the action of microorganisms. The peak temperature assigned to the decomposition of wood components increases, while the global kinetic parameters for the main peak decrease with increasing exposure time of the wood to the attack by microorganisms.The increased characteristic temperatures of water desorption and cellulose decomposition processes and lower thermal stability could be explained by newly formed structures, mainly the oxidized ones.     

Thermogravimetric kinetics of crude glycerol

The pyrolysis of the crude glycerol from a biodiesel production plant was investigated by thermogravimetry coupled with Fourier transform infrared spectroscopy. The main gaseous products are discussed, and the thermogravimetric kinetics derived. There were four distinct phases in the pyrolysis process of the crude glycerol. The presence of water and methanol in the crude glycerol and responsible for the first decomposition phase, were shown to catalyse glycerol decomposition (second phase). Unlike the pure compound, crude glycerol decomposition below 500 K leaves behind a large mass fraction of pyrolysis residues (ca. 15%), which eventually partially eliminate in two phases upon reaching significantly higher temperatures (700 and 970 K, respectively). An improved iterative Coats–Redfern method was used to evaluate non-isothermal kinetic parameters in each phase. The latter were then utilised to model the decomposition behaviour in non-isothermal conditions. The power law model (first order) predicted accurately the main (second) and third phases in the pyrolysis of the crude glycerol. Differences of 10–30 kJ/mol in activation energies between crude and pure glycerol in their main decomposition phase corroborated the catalytic effect of water and methanol in the crude pyrolysis. The 3-D diffusion model more accurately reproduced the fourth (last) phase, whereas the short initial decomposition phase was poorly simulated despite correlation coefficients ca. 0.95–0.96. The kinetics of the 3rd and 4th decomposition phases, attributed to fatty acid methyl esters cracking and pyrolysis tarry residues, were sensitive to the heating rate.     

Structural Contribution of the Carbohydrate Moiety to the Alkaline Hydrolysis of Aryl Glycosylamine Linkages

Differential scanning calorimetry (DSC) thermograms of soybean protein isolate developed two peaks corresponded to 11S and 7S globulin, the denaturation temperatures of which were 93.3 and 76.5°C, respectively, with 94% water. These peaks shifted to higher temperatures with lower water contents of the sample. At 47% water, there were two peaks, at 149 and 118.7°C, and at 11% water, there was one peak at 180°C. The DSC thermogram measured during cooling and reheating gave no peak. The soybean protein isolate was heated with 24.5% water at 100°C and then mixed with more water to the water contents of 94%. This sample gave two peaks at temperatures close to those of the original soybean protein, indicating that the soybean protein was not denatured at temperatures even above 100°C when the water content was low.