Enthalpy relaxation in binary amorphous mixtures containing sucrose

PURPOSE: To compare the enthalpy relaxation of amorphous sucrose and co-lyophilized sucrose-additive mixtures near the calorimetric glass transition temperature, so as to measure the effects of additives on the molecular mobility of sucrose. METHODS: Amorphous sucrose and sucrose-additive mixtures, containing poly(vinylpyrrolidone) (PVP), poly(vinylpyrrolidone-co-vinyl-acetate) (PVPNA) dextran or trehalose, were prepared by lyophilization. Differential scanning calorimetry (DSC) was used to determine the area of the enthalpy recovery endotherm following aging times of up to 750 hours for the various systems. This technique was also used to compare the enthalpy relaxation of a physical mixture of amorphous sucrose and PVP. RESULTS: Relative to sucrose alone, the enthalpy relaxation of co-lyophilized sucrose-additive mixtures was reduced when aged for the same length of time at a comparable degree of undercooling in the order: dextran approximately PVP > PVPNA > trehalose. Calculated estimates of the total enthalpy change required for sucrose and the mixtures to relax to an equilibrium supercooled liquid state (deltaHinfinity) were essentially the same and were in agreement with enthalpy changes measured at longer aging times (750 hours). CONCLUSIONS: The observed decrease in the enthalpy relaxation of the mixtures relative to sucrose alone indicates that the mobility of sucrose is reduced by the presence of additives having a Tg that is greater than that of sucrose. Comparison with a physically mixed amorphous system revealed no such effects on sucrose. The formation of a molecular dispersion of sucrose with a second component, present at a level as low as 10%, thus reduces the mobility of sucrose below Tg, most likely due to the coupling of the molecular motions of sucrose to those of the additive through molecular interactions.     

Stabilization of lactate dehydrogenase following freeze thawing and vacuum-drying in the presence of trehalose and borate

PURPOSE: The purpose of this work was to investigate the effects of trehalose and trehalose/sodium tetraborate mixtures on recovery of lactate dehydrogenase (LDH) activity following freeze-thawing and centrifugal vacuum-drying/rehydration. The storage stability of LDH under conditions of either high relative humidity or high temperature was also studied. METHODS: LDH was prepared in buffered aqueous formulations containing trehalose alone and trehalose/"borate" mixtures. Enzymatic activity was measured immediately following freeze-thawing and vacuum-drying/rehydration processes, and also after vacuum-dried formulations were stored in either high humidity or high temperature environments. Also, glass transition temperatures (Tg) were measured for both freeze-dried and vacuum-dried formulations. RESULTS: The Tg values of freeze-dried trehalose/borate mixtures are considerably higher than that of trehalose alone. Freezing and vacuum-drying LDH in the presence of 300 mM trehalose resulted in the recovery of 80% and 65% of the original activity, respectively. For vacuum-dried mixtures, boron concentrations below 1.2 mole boron/ mole trehalose had no effect on recovered LDH. After several weeks storage in either humid (100% relative humidity) or warm (45 degrees C) environments, vacuum-dried formulations that included trehalose and borate showed greater enzymatic activities than those prepared with trehalose alone. We attribute this stability to the formation of a chemical complex between trehalose and borate. CONCLUSIONS: The high Tg values of trehalose/borate mixtures offer several advantages over the use of trehalose alone. Most notable is the storage stability under conditions of high temperature and high relative humidity. In these cases, formulations that contain trehalose and borate are superior to those containing trehalose alone. These results have practical implications for long-term storage of biological materials.     

Fe60CoxZr10Mo5W2B23-x(x=1,3,5,7,9)块状金属玻璃的非晶形成能力

The bulk Fe60CoxZr10Mo5W2B23-x (x= 1, 3, 5, 7, 9) amorphous rods with diameters of1.5 mm were successfully prepared by copper mold casting method with the low purity raw materials.The amorphous and crystalline states, and thermal parameters, such as the glass transition temperature (Tg), the initial crystallization temperature (Tx), the supercooled liquid region (ΔTx = TxTg), the reduced glass transition temperature Trg (Tg/Tm, Tm: the onset temperature of melting of the alloy, and Tg/T1, T1 : the finished temperature of melting of the alloy) were investigated by X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) analysis. Glass forming ability of Fe60CoxZr10Mo5W2B23-x (x=1, 3, 5, 7, 9)bulk metallic glasses has been studied. According to the results, the alloy (x=7) with the highest Trg (Tg/T1 =0. 607, Tg/T1 =0.590) value, has the strongest glass forming ability among these alloys because its composition is near eutectic composition.The wide supercooled liquid region over 72 K indicates the high thermal stability for this alloy system.This bulk metallic glass exhibits quite high strength (Hv 1020). The success of production of the Febased bulk metallic glass with industrial materials is of great significance for the future progress of basic research and practical application.     

Preparation of Fe-Based Bulk Amorphous Materials and Its Application to Sensors

The study of recent years found that big bulk amorphous alloys were formed for some multi-element compositions at rapid cooling speed such as Zr-, La-, Fe-, Mg-based alloys with wide undercooled liquid phase field and high trend of forming glass.( ATx = crystallization temperature Tx - glass transformation temperature Tg) Bulk amorphous copper mold upper suction casting with minus pressure while some new technical processes and adding new elements such as Co, Nb, Ca, etc.were used to improve magnetic properties and other performances of the materials.The results show that Fe-based bulk amorphous alloys have low coercive force and high permeability, which are successfully applied to magnetoelectric sensors with temperature ranges between -45 ℃ and 150 ℃ by special design of magnetic circuits.     

Thermophysical properties of trehalose and its concentrated aqueous solutions

PURPOSE: To address the lack of fundamental thermophysical data for trehalose and its aqueous systems by measuring equilibrium and non-equilibrium properties of such systems. METHODS/RESULTS: Differential scanning calorimetry (DSC) and dynamic mechanical analysis were used to measure glass transition temperatures of trehalose and its solutions. X-ray diffractometry was used to verify the structure of amorphous trehalose. Controlled-stress rheometry was used to measure viscosity of several aqueous trehalose systems at ambient and sub-ambient temperatures. Over this temperature range, the density of these solutions was also measured with a vibrating tube densimeter. The equilibrium phase diagram of aqueous trehalose was determined by measuring the solubility and freezing point depression. CONCLUSIONS: Our solubility measurements, which have allowed long times for attainment of chemical equilibrium, are substantially different from those reported earlier that used different techniques. Our measurements of the glass transition temperature of trehalose are higher than reported values. A simple model for the glass transition is presented to describe our experimental observations.     

Thermodynamic and Kinetic Study of Crystallization Reaction of Fe/Dy Multilayers Form Amorphous State

ＭａｇｎｅｔｉｃｆｉｌｍｓｏｆＴＭ/ＲＥｃａｎｔｒａｎｓｆｏｒｍｔｏａｍｏｒｐｈｏｕｓｓｔａｔｅｂｙｍｅａｎｓｏｆａｄｊｕｓｔｉｎｇｔｈｅｉｒｍｏｄｕｌａｔｉｏｎｐｅｒｉｏｄｉｃｉｔｙｄｕｒｉｎｇｄｅｐｏｓｉｔｉｏｎ .Ｔｈｅｆｉｌｍｓｉｎａｍｏｒｐｈｏｕｓｓｔａｔｅｅｘｈｉｂｉｔｐｅｒｐｅｎｄｉｃｕｌａｒａｎｉｓｏｔｒｏｐｙａｎｄａｒｅｐｒｏｍｉｓｉｎｇｃａｎｄｉｄａｔｅｓｆｏｒｍａｇｎｅｔｉｃｒｅｃｏｒｄｉｎｇｍｅｄｉａ .Ａｍｏｒｐｈｏｕｓｓｔａｔｅｉｓｔｈｅｒｍｏｄｙｎａｍｉｃａｌｌｙｍｅｔ…     

A mammary epithelial cell line is transiently stimulated towards milk lipid synthesis by lactogenic treatments

The effect of moisture sorption at different relative humidities on the tensile strength and the physical stability of compacts of crystalline and partly amorphous lactose, alone and in binary mixtures with PVP, has been studied. Furthermore, the role of moisture as a plasticizer and its effect on the glass transition temperature, Tg, are related to the compactibiltiy. Samples were conditioned for 2 hr using a climate test chamber at different relative humidities. Moisture sorption was determined, the radial crushing strength for compacts was measured immediately and after storage, and the tensile strength was calculated. The glass transition temperature, Tg, was determined using DSC. The tensile strength of the compacts was found to depend on both the conditioning humidity and the humidity during storage. An increase in humidity to a level at which the glass transition temperature, Tg, fell below the operating temperature, T, resulted in transition from a rigid glassy state to a mobile rubbery state. For compacts of partly amorphous lactose, an increase in the tensile strength was observed during storage of tablets, due to recrystallization of the amorphous regions above Tg. Tablets of mixtures of lactose and PVP exhibit a sharp decrease in tensile strength at humidities above 70% RH, due to the glass-to-rubber transition of PVP.     

Glass transition of gluten. 1: Gluten and gluten-sugar mixtures

The glass transition in hydrated wheat gluten has been studied using dynamic mechanical thermal analysis, differential scanning calorimetry, pulsed nuclear magnetic resonance and a three point bend test. The results for gluten alone are in good agreement with results obtained by other workers for gluten and glutenin. In contrast to their effect on the Tg of amylopectin, a gluten:sugar ratio of 10:1 (where the sugar is amorphous fructose, sucrose or glucose) has little effect on the glass transition temperature, as a function of water content. A sample containing gluten and fructose in the ratio 2:1 showed plasticization due to the sugar.     

The physical state of mannitol after freeze-drying: effects of mannitol concentration, freezing rate, and a noncrystallizing cosolute

The objectives of this study were to (1) measure the effects of freezing rate and mannitol concentration on the physical state of freeze-dried mannitol when mannitol is present as a single component, (2) determine the relative concentration threshold above which crystalline mannitol can be observed by X-ray powder diffraction in the freeze-dried solid when a variety of noncrystallizing solutes are included in the formulation, and (3) measure the glass transition temperature of amorphous mannitol and to determine the degree to which the glass transition temperature of freeze-dried solids consisting of mannitol and a disaccharide is predicted by the Gordon-Taylor equation. Both freezing rate and mannitol concentration influence the crystal form of mannitol in the freeze-dried solid when mannitol is present as a single component. Slow freezing of 10% (w/v) mannitol produces a mixture of the alpha and beta polymorphs, whereas fast freezing of the same solution produces the delta form. Fast freezing of 5% (w/v) mannitol results primarily in the beta form. The threshold concentration above which crystalline mannitol is detected in the freeze-dried solid by X-ray diffraction is consistently about 30% (w/w) when a second, noncrystallizing solute is present, regardless of the nature of the second component. The glass transition temperature of amorphous mannitol measured from the quench-cooled melt is approximately 13 degreesC. Accordingly, mannitol is an effective plasticizer of freeze-dried solids when the mannitol remains amorphous. Glass transition temperatures of mixtures of mannitol and the disaccharides sucrose, maltose, trehalose, and lactose are well predicted by the Gordon-Taylor equation with values of k in the range of 3 to 4.     

An evaluation of the sensitivity of subjects with peanut allergy to very low doses of peanut protein: a randomized, double-blind, placebo-controlled food challenge study

PURPOSE: To find out if the physical instability of a lyophilized dosage form is related to molecular mobility below the glass transition temperature. Further, to explore if the stability data generated at temperatures below the glass transition temperature can be used to predict the stability of a lyophilized solid under recommended storage conditions. METHODS: The temperature dependence of relaxation time constant, tau, was obtained for sucrose and trehalose formulations of the monoclonal antibody (5 mg protein/vial) from enthalpy relaxation studies using differential scanning calorimetry. The non-exponentiality parameter, beta, in the relaxation behavior was also obtained using dielectric relaxation spectroscopy. RESULTS: For both sucrose and trehalose formulations, the variation in tau with temperature could be fitted Vogel-Tammann-Fulcher (VTF) equation. The two formulations exhibited difference sensitivities to temperature. Sucrose formulation was more fragile and exhibited a stronger non-Arrhenius behavior compared to trehalose formulation below glass transition. Both formulations exhibited < 2% aggregation at t/tau values < 10, where t is the time of storage. CONCLUSIONS: Since the relaxation times for sucrose and trehalose formulations at 5 degrees C are on the order of 10(8) and 10(6) hrs, it is likely that both formulations would undergo very little (< 2%) aggregation in a practical time scale under refrigerated conditions.     

In vivo evidence of enhanced guanylyl cyclase activation during the hyperdynamic circulation of acute liver failure

The different efficiencies of sucrose and trehalose in protecting isolated spinach (Spinacia oleracea L.) thylakoids against freeze-thaw damage is quantitatively related to their ability to reduce the solute loading of the vesicles during freezing. In the present paper we show that this effect is based on a reduction of the solute permeability of the membranes. Permeability was measured with 14C-labeled glucose at temperatures between 0 and 10 degrees C. Glucose permeability was reduced by both sucrose and trehalose, with trehalose effective at much lower concentrations than sucrose. An analysis of the temperature dependence of glucose permeability in the presence and absence of trehalose revealed that a 50% reduction in permeability resulted from a 10% increase in activation energy and a 30% decrease in activation entropy. Using the fluorescence probe 1,6-diphenyl-1,3,5-hexatriene (DPH), we found that the reduced permeability of the membranes in the presence of trehalose was unaccompanied by a reduction in lipid fluidity. This also excluded the possibility of a solute-induced liquid crystalline to gel phase transition. A reduced partitioning of the hydrophobicity-sensitive dye merocyanine 540 into thylakoids and into membranes containing 50% digalactosyldiacylglycerol in the presence of trehalose as compared to sucrose and glucose showed that the lipid headgroup region of these membranes became less accessible for solutes. No significant difference in merocyanine partitioning in the presence of trehalose as compared to sucrose or glucose was apparent when monogalactosyldiacylglycerol dispersions or phosphatidylcholine vesicles were investigated.     

Effect of sugars on headgroup mobility in freeze-dried dipalmitoylphosphatidylcholine bilayers: solid-state 31P NMR and FTIR studies

The effect of the carbohydrates trehalose, glucose, and hydroxyethyl starch (HES) on the motional properties of the phosphate headgroup of freeze-dried dipalmitoylphosphatidylcholine (DPPC) liposomes was studied by means of 31P NMR, Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The results show that trehalose, which is a strong glass former (Tg = 115 degreesC), elevates the onset of the lipid headgroup rotations and preserves some rotational mobility of the phosphate headgroups after cooling from the liquid-crystalline state. Glucose (Tg = 30 degreesC), a very effective depressant of the phase transition temperature of freeze-dried DPPC, markedly elevates the initiation of the temperature of headgroup rotations. On the other hand, the monosaccharide does not preserve the headgroup disordering when cooled from the liquid-crystalline state. These effects are consistent with formation of hydrogen bonds between the OH groups of the sugar and the polar headgroups of DPPC. They show, however, that hydrogen bonding is not sufficient for preservation of the dynamic properties of freeze-dried DPPC. HES, although a very good glass former (Tg > 110 degreesC), does not depress the phase transition temperature and affects only slightly the rotational properties of freeze-dried DPPC. This lack of effect of HES is associated with the absence of direct interactions with the lipid phosphates, as evidenced by the FTIR results. These data show that vitrification of the additive is not sufficient to affect the dynamic properties of dried DPPC.     

Cochlear implantation in the deaf-blind

Due to its strong tendency to crystallize, the glass properties of mannitol cannot be measured directly. However, because mannitol can exist in a fully or partially amorphous state in drug formulations, it is important to determine the glass properties of mannitol. We obtained the glass properties of mannitol by introducing a small amount of sorbitol, an isomer of mannitol, to delay the onset of crystallization. Extrapolation to zero sorbitol concentration yielded the following properties for the mannitol glass: Tg onset = 10.7(o)C, Tg midpoint= 12.6( o)C, Tg end = 18.4 degreesC and DeltaCp = 1.27 J/g/K. In addition, we estimated the following parameters of the mannitol glass from the width of glass transition using the results of Moynihan (J. Am. Ceram. Soc. 1993, 76, 1081) and Angell (J. Phys. Chem. 1994, 98, 13780): DeltaH (at Tg onset) = 103 kcal/mol, D = 11, and T0 = 222 K. The value of T0 is consistent with the Kauzmann temperature TK (236 K) obtained calorimetrically. The properties of the mannitol glass may be useful for predicting the behavior of amorphous mixtures containing mannitol.     

Mycoplasma hyorhinis infection of pigs selectively bred for high and low immune response

Fourier transform infrared microspectroscopy (FTIR) was used to study glasses of pure carbohydrates and in the cytoplasm of desiccation tolerant plant organs. The position of the OH stretching vibration band (vOH) shifted with temperature. Two linear regression lines were observed in vOH against temperature plots. The temperature at the point of intersection between these two lines coincided with the glass transition temperature (Tg), as determined by other methods. The temperature at the intersection point decreased with increasing water content, which further validates that, indeed, Tg was observed. Tg values that were determined for dry glucose, sucrose, maltose, trehalose and raffinose glasses were 27, 57, 91, 108 and 108 degrees C, respectively. The shift of vOH with temperature, the wavenumber-temperature coefficient (WTC), was higher in sugar glasses having higher Tg. This suggests that glasses are more loosely packed when they have higher Tg. For Typha latifolia pollen and dried Craterostigma plantagineum leaves we obtained similar vOH vs. temperature plots as for carbohydrate glasses, indicating that a glass transition was observed. The Tg in dry pollen was ca. 45 degrees C and in dry plant leaves ca. 65 degrees C, with WTC values comparable to those observed in the carbohydrates. The Tg values in these tissues decreased with increasing water contents. Our data suggest that the carbohydrates that are present in the cytoplasm are primary factors contributing to the glassy state. We conclude that FTIR provides new insights in the structure of glasses in carbohydrates and in biological tissues.     

Ball-milling-induced crystallization and ball-milling effect on thermal crystallization kinetics in an amorphous FeMoSiB alloy

Microstructure evolution in a melt-spun amorphous Fe_77.2Mo_0.8Si₉B₁₃ alloy subjected to high-energy ball milling was investigated by means of X-ray diffraction (XRD), a transmission electron microscope (TEM), and a differential scanning calorimeter (DSC). It was found that during ball milling, crystallization occurs in the amorphous ribbon sample with precipitation of an α-Fe solid solution, and the amorphous sample crystallizes completely into a single α-Fe nanostructure (rather than α-Fe and borides as in the usual thermal crystallization products) when the milling time exceeds 135 hours. The volume fraction of material crystallized was found to be approximately proportional to the milling time. The fully crystallized sample with a single α-Fe nanophase exhibits an intrinsic thermal stability against phase separation upon annealing at high temperatures. The ball-milling effect on the subsequent thermal crystallization of the amorphous phase in an as-milled sample was studied by comparison of the crystallization products and kinetic parameters between the as-quenched amorphous sample and the as-milled partially crystallized samples. The crystallization temperatures and activation energies for the crystallization processes of the residual amorphous phase were considerably decreased due to ball milling, indicating that ball milling has a significant effect on the depression of thermal stability of the residual amorphous phase.     

Metastable crystalline and amorphous structures formed in the Cu-W system by vapor deposition

The possibility of producing nonequilibrium amorphous and crystalline phases in the Cu-W system is of interest because, under equilibrium conditions, no mutual solubility is expected between Cu and W. Triode sputtered coatings (45 to 150 μm thick, produced at deposition rates between 20 and 150 Å/s) consisted of amorphous and metastable crystalline phases. The latter remained decomposition-resistant on heating to various temperatures between 340 °C and 600 °C (the maximum temperature of exposure). The amorphous phase in such coatings crystallized on heating into a metastable body-centered cubic (bcc) phase, and the crystallization temperatureT _x was found to decrease across the phase diagram from 450 °C to 340 °C as the percentage of W increased from 26 to 60 at. pct. Samples containing amorphous phase regions, when subjected to heating between 150 °C and 250 °C, showed an unusual rapid precipitation of Cu at the sample surface, indicating an easy diffusion of the Cu component. This occurred without crystallization of the remaining slightly tungsten-enriched amorphous matrix. Microhardness measurements in sputtered two-phase amorphous and bcc regions have shown that in alloys of the same composition, the amorphous phase was always softer than the bcc solid solution phase. X-ray, microprobe, and optical evidence suggests that the amorphous films deposited at very low temperatures(i.e., at liquid N₂) may subsequently undergo a phase separation upon heating to room temperature and prior to crystallization. Earlier work and present studies of vapordeposited alloys in this system confirm that the observed phases and microstructures can be related to free energy trends estimated from thermodynamic considerations and to specific deposition parameters, such as the substrate temperature and the deposition rates, which influence the kinetics.     

Cu基块体非晶合金的高温均匀塑性流变行为研究

本文选用非晶形成能力高,且在玻璃转变区和过冷液相区有高热稳定性的Cu46Zr47-x Al7块体非晶合金为研究对象,利用差示扫描量热分析（DSC）、高温真空压缩实验等方法,对其高温均匀塑性流变行为进行研究。结果表明,Cu46Zr47Al7块体非晶合金的高温均匀塑性形变行为依赖于温度和应变速率,随着温度的降低或应变速率的增大呈现出牛顿流变向非牛顿流变的转变,该行为可以用基于自由体积的过渡态理论来进行定量描述。根据过渡态理论拟合出来的驱动体积大致相当于25~50个原子,驱动能为551kJ/mol,说明控制合金高温均匀形变的原子不会脱离周围原子而单独跃迁,其扩散涉及到多原子的协同运动。     

A novel way of amorphous phase formation during mechanical alloying of copper and cadmium powders

Phase formation during high-energy ball milling of copper and cadmium powders has been investigated. Both X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) have been used to characterize the resulting phases. An amorphous phase forms during milling in the copper-cadmium system by a reaction between the equilibrium δ phase and one of the constituent metals (copper). However, the amorphous phase cannot be produced by a direct reaction between the copper and cadmium powders, nor by milling of a powder consisting of only the δ phase. It appears most likely that the contribution from the generated copper/δ interfaces, and the accompanying increase in the total free energy, provide the additional driving force for the amorphous phase formation in this system.     

Kinetic study on the non-isothermal crystallization of Gd53Al24Co20Zr3 bulk metallic glass

Gd-based bulk metallic glass has drawn strong attention because of its large magnetic entropy changes. Thermal stability of metallic glass is a very important issue for its application. In the paper, crystallization behavior of Gd53Al24Co20Zr3 bulk metallic glass was investigated using non-isothermal differential scanning calorimetric (DSC) technique. Attention was given to the analytic details. The crystallized volume fractions as a function of temperature were derived from the DSC signals, where heat capacity change between amorphous phase and crystalline phase was considered. The local activation energies at different crystallized volume fraction were estimated using Doyle-Ozawa and Agrawal methods. The results suggested that the Doyle-Ozawa equation was appropriate to get local activation energy due to its simplicity and accuracy. The local activation energy depended on the crystallized volume fraction. Function reflecting crystallization mechanism was also deduced. The crystallization mechanism of the Gd-based bulk metallic glass was discussed.     

Small angle X-ray scattering from an embrittling metallic glass

The metallic glass Fe_79.3B_16.4Si_4.0C_0.3 was examined by small angle X-ray scattering (SAXS) in the as-quenched condition and after low temperature annealing. In all cases, the annealing temperature was well below the crystallization temperature of the material. There was no significant change in SAXS intensity as the sample transformed from the ductile to the brittle state. Partially crystallized specimens prepared by up-quenching were used as calibration samples to estimate an upper limit of 0.9 vol% of a possible second phase with the electron density of amorphous Fe₃B in the most embrittled samples. It was concluded that phase separation is not the cause of annealing embrittlement in this system. The weak SAXS intensity suggests that the phase separation and chemical inhomogeneity in both the as-quenched and the annealed state are limited.