High-sensitivity modulation differential scanning calorimetry of protein denaturation

Method of high-sensitivity modulation differential scanning calorimetry was applied for investigation of the kinetically controlled irreversible thermal denaturation of the trypsin inhibitor from soybeans (Kunitz inhibitor, KI) in diluted solution. The measurements were carried out with a temperature-modulation capillary nanocalorimeter designed and produced by the Institute of Biological Instrumentation of the RAS (Pushchino, Russia). An algorithm of the experimental data processing and corresponding software were developed. It was shown that the modulation nanocalorimetry allows one to obtain in one experiment the temperature dependence of the rate constant for irreversible protein denaturation. The temperature dependence of the rate constant and the activation energy of the irreversible denaturation of Kunitz inhibitor were determined. The obtained value of the activation energy (E _a = 206 ± 6 kJ mol^?1) agrees with independent estimates of this kinetic parameter.     

Protein denaturation in dosage forms measured by differential scanning calorimetry

The stability of beta-galactosidase dosage forms was studied by differential scanning calorimetry (DSC). It was found that the observed enthalpy of thermal denaturation was approximately in proportion to remaining enzyme activity, and denaturation temperature was related to protein stability. These results suggest that DSC can be used to determine native proteins in dosage forms and to clarify the factors affecting protein stability. The DSC method seems to be more convenient than conventional activity assay methods, and useful to follow protein denaturation during the manufacturing process and storage of dosage forms.     

水合醛缩酶热变性的DSC研究

本文采用差示扫描量热法(DSC),研究了水合醛缩酶在含水量h从0.08g/g至2.28g/g范围内的热变性行为。实验结果表明,当h=0.08g/g时,水合醛缩酶样品的温度扫描热谱图呈现了两个吸热峰,其中低温峰很小,高温峰很大。随着h的增大,低温峰变得更小,高温峰则出现了分峰现象。当h=0.22g/g时,低温峰消失,高温峰则分裂成了两个独立的吸热峰。随着h的继续增大,其中前峰的位置不断移向低温,直至h_0.65g/g时,才不再变化。后峰的位置则始终保持不变。当再进行第二次温度扫描时,前峰消失,而后峰却能再现。本文给出了两峰在不同含水量时的转变温度、转变焓和转变焓之和,以及它们与含水量的关系。最后,对上述诸峰的起因作了分析讨论,认为低温峰可能起因于水合醛缩酶结晶的熔化作用,前峰和后峰可能起因于醛缩酶中两种A亚基的热变性。     

Measurement of thermal conductivity by differential scanning calorimetry

A technique of measurement of thermal conductivity of solid materials by differential scanning calorimetry is presented. It concerns small samples having a diameter less than 8.0 mm, a height less than 2.0 mm and a low thermal conductivity. This method requires many samples with different heights which are heated in such a way that a calibration substance put on their top undergoes a first-order phase transition. The analysis of heat transfer of a such experiment predicts that the slope of the differential power during the transition is proportional to the factor 2 and inversely proportional to the sum of the thermal resistances. A measurement of the thermal conductivity of samples made of polytetrafluoroethylene powder, compressed at the density of 2.10±0.03 g cm⁻³, has been performed; the value obtained is 0.33±0.02 W m⁻¹ K⁻¹. Measurements of thermal conductivity of small metal hydride pellets are also presented. The precision of the measurements are on average 10%.     

Measurement of the sensitization of nitrocompounds by amines using differential scanning calorimetry

We report a new method of making empirical measurements of the sensitization of nitrocompounds by amines based on thermal analysis. The method is sensitive, accurate and reproducible. We have used this method to measure the sensitization of nitromethane, N-methyl-N-(2,4,6-trinitrophenyl) nitramine (tetryl), picric acid and trinitrotoluene (TNT) by a number of aliphatic amines.     

Thermal denaturation ofTrichoderma reesei cellulases studied by differential scanning calorimetry and tryptophan fluorescence

The thermal denaturation of four purified Trichoderma reesei cellulase components, cellobiohydrolase (CBH) I, CBH II, endoglucanase (EG) I, and EG II, has been monitored using a combination of classical temperature/activity profiles, differential scanning calorimetry (DSC), and thermal scanning fluorescence emission spectrometry. Significant correlations were found between the results of enzyme activity studies and the results obtained through the more direct physical approaches, in that both DSC and the activity studies showed EG II (T_m = 75°C) to be much more thermostable (by 10–11 °C) than the other three enzymes, all three of which were shown by both activity profiles and DSC to be very similar in thermal stability. The temperature dependence of the wavelength of maximum tryptophan emission showed a parallel result, with the three enzymes exhibiting less thermostable activity being grouped together in this regard, and EG II differing from the other three in maintaining a less-exposed tryptophan microenvironment at temperatures as high as 73 °C. The DSC results suggested that at least two transitions are involved in the unfolding of each of the cellulase components, the first (lower-temperature) of which may be the one correlated with activity loss.

     

Temperatures in differential scanning calorimetry

A recently described method is used to characterise thermal gradients in a DSC-2 and the results are compared with a conventional temperature calibration. Under certain circumstances the latter may be in error by several degrees with consequent adverse effects on calculated heat capacities. The errors are removed when allowance is made for variations in thermal lag from sample to sample.     

Thermal and stability study of tetracene using differential scanning calorimetry

A thermal analysis study was made of tetracene using differential scanning calorimetry (DSC). The effect of different scan speeds was investigated. At scan speeds of 0.625 to 10°C min^?1 two large rounded exothermic peaks were produced. The peaks occurred at an increasingly high temperature as the scan speed increased (for example, the peaks occurred at 128 and 130°C at a scan speed of 0.625°C min^?1 and at 148 and 150°C at a scan speed of 10°C min^?1. When tetracene was heated at a scan speed of 80°C min^?1 only one large sharp exothermic peak was produced. It is believed that the two peaks obtained at scan speeds of 0.625 to 10°C min^?1 represent decomposition of the tetracene in two successive stages, while the one peak obtained at 80°C min^?1 represents an explosion. A stability test for tetracene is proposed that involves heating of the tetracene in aluminum pans from the DSC apparatus in ovens at 100, 75, and 60°C, removing the pans and samples at intervals of 30 min, 24 h, and 7 days, respectively, subjecting the samples to DSC at 1.25°C min^?1, and noting the time interval in the oven that produces a DSC curve that shows obliteration of the second peak. Two lots of tetracene made by different processes showed marked differences in stability characteristics.     

Measurement of heat capacities of ionic liquids by differential scanning calorimetry

Heat capacities for nine ionic liquids (IL) have been determined with the “three-step” method using two different differential scanning calorimeters (DSC). In addition, the heat capacities of these ionic liquids have been studied by the modulated-temperature differential scanning calorimetry (MDSC™). The measurements cover a temperature range from 315 to 425 K.     

Measurement of adsorption energy between a solid adsorbent and a liquid adsorbate using differential scanning calorimetry

We report on a novel method involving the use of differential scanning calorimetry (DSC) in evaluation of adsorption energy between a liquid adsorbate and a solid adsorbent. The proof of concept is demonstrated by measuring the exothermic heat release due to the adsorption of automotive transmission fluid (ATF), the adsorbate, to a paper-based friction material used in automotive torque converters, the adsorbent. The novelty of the measurement technique involves initial freezing of the liquid adsorbate so that the initiation of the adsorption process can be identified. Our experimental results and theoretical calculations reveal that the adsorption energy of the friction paper and the summation of adsorption energies of each friction paper ingredient are in good agreement.     

Measurement of dilute metallic impurity concentration in lead by differential scanning calorimetry

The traditional method for purity determination by analysis of the peak shape of the melting transition has included fitting to a linear relation between sample temperature (T) and the reciprocal fraction molten ($\text{1}\text{7}$). This technique, however, necessitates the use of a series of calibrants to determine the proper choice of limits for $\text{1}\text{7}$ as a function of purity. In this paper, a non-linear relation between T and $\text{1}\text{7}$ is developed and applied to the determination of metallic impurities in Pb in the range of a few to 1000 parts per million. The results are found to be independent of the range of $\text{1}\text{7}$ used. The use of differential scanning calorimety in this determination is discussed, and rate effects are also mentioned.     

Thermal gradients in differential scanning calorimetry

A combined static and dynamic temperature calibration is described. The static calibration corrects the instrumental dial temperature reading. The dynamic calibration has instrumental and material components and therefore varies from specimen to specimen. It is obtained from individual DSC curves and so removes uncertainties in sample temperature due to varying mass, geometry, and heating rate. The instrumental performance is improved and specific heats may be obtained to an accuracy of ±1%.     

Evaluation of acylphosphine oxide polymerization initiators using differential scanning calorimetry

This study examines the polymerization of dental monomers catalyzed by synthesized acylphosphine oxides in a differential scanning calorimetry (DSC) cell. This research focuses on establishing a relationship between radicals generated by the acylphosphine oxide photoinitiators and the kinetic reaction rates of methyl methacrylate (MMA) and acrylamide (ACM), a model monomer. The thermal stability of mono- and di-acylphosphine oxides was examined by DSC. Endothermic melting and exothermic polymerization reactions initiated with the two initiators were recorded. The acrylamide model system laid the ground work for the critical evaluation of the synthesized new initiators of mono (2,4,6-trimethylbenzoyl) diphenylphosphine oxide, and bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide. The bis(acyl) phosphine oxide photoinitiator was more reactive than the mono-(acyl) phosphine oxide with methyl methacrylates under laboratory conditions. In exothermic reactions, temperatures rose higher and more rapidly for bis(acyl) phosphine oxide initiated reactions than mono-(acyl) phosphine oxide initiated reactions.     

Kinetic study of polyurethanes formation by using differential scanning calorimetry

Kinetics of polyurethane formation between several polyols and isocyanates with dibutyltin dilaurate (DBTDL) as the curing catalyst, were studied in the bulk state by differential scanning calorimetry (DSC) using an improved method of interpretation. The molar enthalpy of urethane formation from secondary hydroxyl groups and aliphatic isocyanates is 72±3 kJ mol^-1 and for aromatic isocyanates it is 55±2 kJ mol^-1 . In the case of a single second order reaction for aliphatic isocyanates reaction, activation energy is 70±5 kJ mol^-1 with oxypropylated polyols and 50±3 kJ mol^-1 with Castor oil. For aromatic isocyanates and oxypropylated polyols the activation energy is higher around 77 kJ mol^-1 . In the case of two parallel reactions (situation for IPDI and TDI 2-4) best fits are observed considering two different activation energies.     

Detection of butter adulteration with water using differential scanning calorimetry

The study evaluated the applicability of differential scanning calorimetry (DSC) for the detection of water content in butter. High correlation coefficients were found between the water content and the enthalpies of the ice melting/water crystallization. The correlation equations were adopted to calculate the water content for seven tested kinds of butter, and the results were compared with the values, obtained by using the reference method. The difference between the water content determined by the reference method and by DSC ranged between 0.2 and 2.6% for the measured enthalpy of ice melting, and between 1 and 5.6% for the enthalpy of water crystallization. In relation to the data obtained, it can be concluded that the parameter of ice melting enthalpy can be used in the identification of adulterations or confirmation of butter authenticity.     

Study of gelation using differential scanning calorimetry (DSC)

A new method for determining the degree of conversion of gelation (_gel) and gel time (t _gel) at gel point using a single technology, DSC, is discussed in this work. Four kinds of thermoset resins are evaluated. It is found that the mutation points of reduced reaction rate (V _r ) vs. reaction conversion () curves, corresponding with the changes of reaction mechanism, represents the gelation of the reaction. The at the mutation point is defined as _gel. From isothermal DSC curves, the point at _gel is defined ast _gel. Traditional techniques (ASTM D3532 and DSC method) are also used to determine _gel andt _gel in order to demonstrate this new method. We have found that the results obtained from this new method are very consistent with the results obtained from traditional methods.     

Quantitative aspects of differential scanning calorimetry

The quantitative performance of differential scanning calorimeters is reviewed. Temperature calibration is discussed in terms of an isothermal correction plus a contribution from thermal lag, this can be derived from individual curves and is valid in both, heating and cooling. It is emphasised that baselines that are drawn to thermal events, such as melting and transition phenomena, must have thermodynamic significance and a general procedure is suggested. When this is used, a power compensation calorimeter calibrated for heat-capacity work can reproduce heats of fusion and transition for a diverse range of materials to better than 1%.     

Use of cyclic differential scanning calorimetry

Formation of an activated cellulose (Cellulose) species $$CELLULOSE\xrightarrow[{air}]{{heat}}CELLULOSE*$$ is the designated first stage of cellulose degradation in air [1]. Little is known about either the process or the nature of CELLULOSE^*. The transition, designatedT ₂, is observed as an exotherm around 300°C as the sample temperature is raised. No corresponding endotherm is observed on cooling. The process is therefore not reversible but is repeatable as subsequent reheating results in the exotherm being observed again. The exotherm is also found to be oxygen dependant. The effect of all the flame retardant treatments studied was to reduceT ₂ compared to the value for the untreated cotton.