Differential Scanning Calorimetry Values Research Articles

Impact of mobile and stationary phases on siRNA duplex stability in liquid chromatography

Nucleic acid duplexes are typically analyzed in non-denaturing conditions. Melting temperature (Tm) is the property used to measure duplex stability; however, it is not known how the chromatographic conditions and mobile phase composition affect the duplex stability. We employed differential scanning calorimetry (DSC) method to measure the melting temperature of chemically modified silencing RNA duplex (21 base pairs, 0.15 mM duplex concentration) in mobile phases commonly used in reversed-phase, ion-pair reversed-phase, size exclusion and hydrophilic interaction chromatography. We investigated mobile phases consisting of ammonium acetate, alkylammonium ion-pairing reagents, alkali-ion chlorides, magnesium chloride, and additives including methanol, ethanol, acetonitrile and hexafluoroisopropanol. Increasing buffer concentration enhanced the duplex stability (Tm was 67.1 – 78.2 °C for 10–100 mM [Na+] concentration). The melting temperature decreases with the increase in cation size (70.2 °C in 10 mM [Li+], 68.1 °C in 10 mM [NH4+], 65.6 °C in 10 mM [Cs+], and 56.6 °C in 10 mM [triethylammonium+] solutions). Inclusion of 20 % of organic solvent in buffer reduced the melting temperature by 1–3 °C, and denaturation power increases in the order MeOH<EtOH<MeCN. Next, we investigated the RNA duplex melting using selected chromatographic techniques and within the 10–90 °C column temperature range. Melting temperature obtained with size exclusion chromatography in 25 mM sodium phosphate buffer was ∼ 70 °C, about 5 °C lower compared to DSC values. The apparent melting temperature for a reversed-phase chromatography experiment was < 10 °C for 10 mM ammonium acetate mobile phase with acetonitrile eluent. Ion-pair reversed-phase with 10 mM triethylamine, 100 mM hexafluoroisopropanol and MeCN as eluent yielded Tm 49.3–54.9 °C. Hydrophilic interaction chromatography experiments with 10 mM ammonium acetate and ∼ 50 % acetonitrile mobile phase showed high duplex stability (Tm ∼ 80 °C). The observed chromatographic Tm values suggest that the formation of an organic/aqueous solvent layer on the chromatographic sorbent surface affects the duplex stability more significantly than the composition of the mobile phase alone.

Investigation of the Degree of Monomer Conversion in Dental Composites through Various Methods: An In Vitro Study

The degree of monomer conversion (DC) values of three different dental composites were examined using three different methods: surface microhardness (ratio of bottom/top), Fourier-transform infrared (FT-IR), and differential scanning calorimetry (DSC). Two of the dental composites included in the study were nanohybrid (Dentsply Neo Spectra ST HV and Omnichroma), and one was a microhybrid-labeled newly marketed composite containing nanoparticles (Dentac Myra). Composite discs were prepared according to the methodology for all methods and analyzed (2 mm thickness × 5 mm diameter). Surface microhardness values were measured in Vickers Hardness Number (VHN), while FT-IR and DSC values were obtained in percentage (%). Significant differences were observed in both bottom/top surface microhardness values and DC values obtained from FT-IR. However, there was no statistical difference in the ratio of bottom/top microhardness values. Neo Spectra ST HV exhibited superior performance in both microhardness and monomer conversion compared to the other two composites. Newly marketed Myra showed values close to Omnichroma. It was found that the values obtained by the DSC method were parallel to those obtained by FT-IR. In conclusion, the structure of dental composites leads to different mechanical properties. Additionally, DSC measurements and FTIR spectra were found to be complementary techniques for characterizing monomer conversion values.

Development of a low-medium temperature T-history setup for the thermal storage characterization of non-homogeneous mixtures containing PCMs

More attention has been paid to thermal energy storage in recent years for its advantages in heating and cooling applications to foster the use of renewable energies. As part of the design of new thermal energy storage materials, the characterization of specific heat capacity and phase change enthalpy is required. One of the most widespread methods for evaluating specific heat capacity and phase change enthalpy is differential scanning calorimetry (DSC). However, the small amount of required material means that DSC is not the most suitable method for non-homogeneous materials. This paper presents the development and validation of a low-medium temperature (<100 °C) T-history system for measuring specific heat capacity and phase change enthalpy as an economical alternative. Validation was carried out with paraffins used as phase change material and two data processing methods were applied. Only one of the methods was able to measure the specific heat capacity in the liquid and solid phases, and the phase change enthalpy. Acceptable deviations calculated as the relative error in relation to DSC and manufacturer values were obtained with values lower than 18.50 % and 14.58 % respectively. The new system was used to evaluate the thermal properties of a pure paraffin/water emulsion and a hybrid carbon-paraffin/water emulsion by corroborating its suitability for measuring non-homogeneous samples.

Antioxidant Effects of Rosemary Extract on the Accelerated Degradation of Ethylene‐Propylene‐Diene Monomer

AbstractThe influence of natural antioxidants (rosemary extract, capsaicin, quercetin, or oleanolic acid) in ethylene‐propylene‐diene‐monomer (EPDM) thermal behavior has been investigated by the means of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). EPDM and EPDM/rosemary (RM) composite are investigated with a thermogravimetric (TG) balance in dynamic heating conditions (25°C‐700°C). DSC analysis is also carried out from subambient to better highlight the melting of the polymer and the composite. The obtained DSC and TG values are discussed to have information about the effect of RM content in the polymer stability.

Differential scanning calorimetry and thermally stimulated depolarization currents study on the molecular dynamics in amorphous fenofibrate

The slow molecular mobility of the active pharmaceutical drug fenofibrate is studied by differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). The general kinetic features of the secondary relaxations and of the main relaxation, in particular their distribution of relaxation times, were determined by TSDC. Different experimental procedures were used to determine the fragility index by DSC and the obtained results were discussed. The TSDC fragility is in very good agreement with the value obtained by dielectric relaxation spectroscopy (DRS), and all the DSC, TSDC and DRS values indicate that fenofibrate is a very fragile liquid. Given that this means a strong aging sensitivity, we profited from this property to evaluate the influence of physical aging on the fragility values determined by TSDC. From the results of experiments designed to achieve this goal we can conclude that this influence can be considered as negligible.

Significance of Theoretical Decomposition Enthalpies for Predicting Thermal Hazards

Much effort is currently put into the development of models for predicting decomposition enthalpies measured using differential scanning calorimetry (DSC). As an alternative to the purely empirical schemes reported so far, this work relies on theoretical values obtained on the basis of simple assumptions. For nitroaromatic compounds (NACs) studied in sealed sample cells, our approach proves clearly superior to previous ones. In contrast, it correlates poorly with data measured in pin-hole sample cells. Progress might be obtained through a combination of the present approach with the usual Quantitative Structure-Property Relationships (QSPR) methodologies. This work emphasizes the significance of the theoretical decomposition enthalpy as a fundamental descriptor for the prediction of DSC values. In fact, the theoretical value provides a valuable criterion to characterize thermal hazards, as a complement to experimental decomposition temperatures.

Dislocation Density of FCC Metals Processed by ARB

Accumulative roll bonding (ARB) was applied to three FCC metals, such as Al, Cu and Ni. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were made to evaluate dislocation density ρ of the ARB processed FCC metals. The values of ρ of ARB processed Cu and Ni increased rapidly after the first ARB cycle, and then, tend to saturate after the following cycles. The evaluated values of ρ of both ARB 8-cycled Cu and Ni using DSC were around 2×1015 m−2. Whereas, those using XRD were around 5×1014m−2 (for Cu) and 3×1014m−2 (for Ni). Although the ρ values depend on the measurement methods, the trends that DSC values are about an order of magnitude higher than XRD values seem to be common. In the case of Al, dislocation density evaluated using XRD increased to about 1×1013m−2 at the first ARB cycle, and then gradually decreased to about 1×1012m−2 with increasing number of ARB cycles.

Replacement of Acetate with Ammonium Buffer to Determine Apparent Amylose Content of Milled Rice

An improved iodine colorimetric method based on ammonium-buffered pH 9 solution (NH4Cl-KI) is reported. The method produces blue color and measures apparent amylose contents (AC) of nonwaxy rice, using potato amylose standard, and results in values similar to those observed when using differential scanning calorimetry (DSC), based on the exotherm of amylose-lipid complex formation, which has no amylopectin and lipid interference. Using the iodine colorimetric method, waxy rice had AC values of 2-3%, while undefatted, milled rice samples had AC values similar to those observed using the DSC method, probably because interference from amylopectin-iodine and amylose-lipid complexes cancelled each other. Using the iodine-NH4I method, AC values for five nonwaxy rice varieties were identical to DSC values, while AC values for the iodine colorimetric method with acetate buffer were not identical to DSC values when amylose alone was used as the standard. Using an amylose-waxy rice standard, the ammonium buffer met...

Characterization of Almond Cultivars by the Use of Thermal Analysis Techniques. Application to Cultivar Authenticity

AbstractAlmonds are subjected to thermal processes in the production of processed food and this can affect their thermal stability and lead to oxidation processes. In this work, almond samples from three different cultivars (Spanish Guara and Marcona, and American Butte) were characterized by using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) at different heating rates. Crystallization and melting parameters were determined by DSC; whereas thermal stability was studied by TGA, showing no apparent degradation for all samples up to around 290 °C. Butte samples showed the lowest DSC values and TGA initial degradation temperature. These results were linked with differences in fatty acid profiles between Butte and Spanish almond cultivars, Butte presenting higher linoleic acid content. Successful discrimination was obtained for samples analyzed at 2 and 10 °C min−1 heating rates for DSC and TGA, respectively, by applying multivariate stepwise linear discriminant analysis (LDA). The results obtained proved the suitability of thermal analysis techniques combined with LDA for an easy and fast discrimination among different almond cultivars to control eventual adulteration in food processing.

Effects of various vessel materials on exothermic decomposition energy measurements

The United Nations Recommendations on the Transport of Dangerous Goods, 1999, has specified differential scanning calorimetry (DSC) measurements as a screening method for determining the explosive properties of chemicals. In this study, we have investigated the effects of different vessel materials on the exothermic decomposition energy ( Q DSC) of 49 chemical substances by performing measurements with DSC. Different Q DSC values were obtained for various types of sealed pressure vessels and a glass capillary tube vessel. To evaluate Q DSC, all the decomposition energy values (calorific values) obtained in this study were investigated in terms of the permissible fluctuation range specified by American Society for Testing of Materials (ASTM) standards. In this manner, we have demonstrated that the material and shape of a vessel affects the measurement of exothermic decomposition energy.

Melting the secrets of gelatinisation temperature in rice

Gelatinisation temperature (GT) is one of the key traits measured in programs for breeding rice (Oryza sativa L.). It is commonly estimated by the alkali spreading value (ASV), and less commonly by differential scanning calorimetry (DSC). Using a diverse set of germplasm, it was determined that DSC values associate poorly with ASV, are not correlated with amylose content but correlate with cooking time. Rice varieties are traditionally grouped into three classes of GT based on ASV: high, intermediate and low. However, the distribution of DSC values of 4000 samples shows only two classes: high and low. Large differences in the distributions of chain lengths synthesised by starch synthase IIa (SSIIa) support the two classes as the major grouping, two haplotypes associating with each peak. Each peak of DSC values spanned 10°C. The chain length distribution of the amylopectin molecules from varieties at the upper boundary of each peak showed significantly more chains that span both the crystalline and amorphous lamellae of a cluster than varieties at the other end of that distribution. Improved varieties, classified as intermediate GT by ASV, belong to both of the classes defined by DSC, implying that some enzyme, other than SSIIa is involved in intermediate GT.

Thermal Transition Properties of Spaghetti Measured by Differential Scanning Calorimetry (DSC) and Thermal Mechanical Compression Test (TMCT)

Glass transition temperature (Tg) of spaghetti sample was measured by thermal and rheological methods as a function of water content from 0 to 70 kg/100 kg spaghetti. In the cases of sample containing un-freezable water (i.e., amount of water which did not form ice even at very low temperature), calorimetric measurements performed by differential scanning calorimetry showed that the Tg values decreased from 142.8 to 42.7 °C when water content increased from 0 to 13.95 kg/100 kg spaghetti, respectively. Glass transition temperature increased with the increase of heating rate (2–50 °C/min) and reached to a nearly constant value above 30 °C/min. Thermal mechanical compression test showed relatively lower Tg values compared to the DSC values at low moisture contents, whereas at high moisture content Tg showed higher values. In the cases of samples containing freezable water (27–70 kg/100 kg spaghetti), glass transition shifts were merged with the ice melting endotherm. The freezing point, measured from the endothermic peak, decreased with the decrease of water content. In the state diagram, maximal freeze-concentration condition was determined as \( X_{\text{s}}^\prime \)=0.81 kg/kg spaghetti from the intersection of the extended freezing curve and a horizontal line passing thru \( T_{\text{m}}^\prime \) = −10.3 °C.

Microstructure evolution during cold rolling in a nanocrystalline Ni–Fe alloy determined by synchrotron X-ray diffraction

Stress softening after cold rolling is observed in an electrodeposited nanocrystalline Ni–Fe alloy. The grain-size distribution becomes much broader after the cold rolling. Microstructure changes, though moderate, such as simultaneously decreased dislocation and twin densities with grain growth during cold rolling, are systematically proved by synchrotron high-energy X-ray diffraction, transmission electron microscopy and differential scanning calorimetry (DSC). The amorphous fractions in the form of grain boundaries are evidenced by the diffuse-background scatterings and large DSC values. Partial dislocation separation calculation, a dislocation mean free path and annihilation model, and texture development together reveal that the current nanocrystalline Ni–Fe alloy exhibits the combined behavior of perfect dislocation slip and grain-boundary mediated deformation.

Calorimetric study of milk fat/rapeseed oil blends and their interesterification products

AbstractMilk fat (MF) and rapeseed oil (RO) blends were analyzed by differential scanning calorimetry (DSC). It was shown that peak and onset temperatures can be used to determine the percentage of each fat in the blend and that the relative enthalpy of one peak assigned to low‐melting triacylglycerols (TAG) can also be used to determine the percentage of RO in the blend. A linear relation was also established between MF content of the blend and its dropping point (DP), indicating that DP can be linearly related with the above DSC data. A blend of MF/RO 70 : 30 (wt/wt) was then chosen as a model system for enzymatic interesterification (EIE). The applicability of DSC analyses to EIE products was checked and a correct correlation could be established between DSC values and the interesterification degree and DP. Among the data from the DSC profiles, the peak associated with low‐melting TAG was the best indicator of the reaction course. In the same way, a high‐melting MF stearin fraction was interesterified with RO. In that case, onset temperatures and peak “a” were better reaction indicators than for the interesterified MF/RO blend. We therefore suggest that values from DSC endotherms could be used to monitor EIE of fat blends.

Vegetable fat hydrogenation in supercritical-fluid solvents: Melting behavior analysis by DSC and NMR

The melting behavior of six fat samples hydrogenated on Pd catalysts (uniform 2% Pd/C and eggshell 0.5% Pd/Al 2O 3) in supercritical dimethylether (DME) or propane as reaction solvents was investigated. Hydrogenation was carried out at 484 K, with pressures between 20 and 28 MPa and a molar hydrogen content ranging from 4 to 9%, and using a continuous internal-recycle reactor. The melting and crystallization behavior of the hydrogenated products was characterized by differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR), which allowed the determination of solid fat content (SFC). DSC values were generally higher than NMR values. Melting behavior is one of the most important characteristics of edible fats and margarines as it has an impact on their organoleptic properties. These are strongly affected by supercritical-fluid (SCF) processing, so readjustment is necessary. The results obtained show that supercritical hydrogenation on the eggshell 0.5% Pd/Al 2O 3 catalyst in supercritical DME leads to an improved melting profile of the hydrogenated products compared with uniform 2% Pd/C catalyst in propane. In addition, supercritical conditions have a greater influence on melting behavior than conventional hydrogenation.

Applications of the Cyclone Stickiness Test for Characterization of Stickiness in Food Powders

The cyclone stickiness test (CST) technique was applied to measure the stickiness temperature and relative humidity of whey, honey, and apple juice powders. A moisture sorption isotherm study was conducted to analyze the surface moisture content of whey powder. The glass transition temperatures of the sample powder were analyzed using differential scanning calorimetry (DSC). The stickiness results of these products were found within 20°C above their surface glass transition temperatures, which is well within the normal temperature range for glass transition in general. The results obtained by the CST technique were found consistent with DSC values.

Determination of melting point of vegetable oils and fats by differential scanning calorimetry (DSC) technique.

Melting point of fats is used to characterize oils and fats and is related to their physical properties, such as hardness and thermal behaviour. The present work shows the utilization of DSC technique on the determination of melting point of fats. In a comparison with softening point (AOCS method Cc 3-25), DSC values were higher than those obtained by AOCS method. It has occurred due to the fact that values obtained by DSC technique were taken when the fat had melted completely. DSC was also useful for determining melting point of liquid oils, such as soybean and cottonseed ones.

Structure and Functionality of Barley Starches

ABSTRACTAmylose contents of prime starches from nonwaxy and high‐amylose barley, determined by colorimetric method, were 24.6 and 48.7%, respectively, whereas waxy starch contained only a trace (0.04%) of amylose. There was little difference in isoamylase‐debranched amylopectin between nonwaxy and high‐amylose barley, whereas amylopectin from waxy barley had a significantly higher percentage of fraction with degree of polymerization &lt; 15 (45%). The X‐ray diffraction pattern of waxy starch differed from nonwaxy and high‐amylose starches. Waxy starch had sharper peaks at 0.58, 0.51, 0.49, and 0.38 nm than nonwaxy and high‐amylose starches. The d‐spacing at 0.44 nm, characterizing the amylose‐lipids complex, was most evident for high‐amylose starch and was not observed in waxy starch. Differential scanning calorimetry (DSC) thermograms of prime starch from nonwaxy and high‐amylose barley exhibited two prominent transition peaks: the first was &gt;60°C and corresponded to starch gelatinization; the second was &gt;100°C and corresponded to the amylose‐lipid complex. Starch from waxy barley had only one endothermic gelatinization peak of amylopectin with an enthalpy value of 16.0 J/g. The retrogradation of gelatinized starch of three types of barley stored at 4°C showed that amylopectin recrystallization rates of nonwaxy and high‐amylose barley were comparable when recrystallization enthalpy was calculated based on the percentage of amylopectin. No amylopectin recrystallization peak was observed in waxy barley. Storage time had a strong influence on recrystallization of amylopectin. The enthalpy value for nonwaxy barley increased from 1.93 J/g after 24 hr of storage to 3.74 J/g after 120 hr. When gel was rescanned every 24 hr, a significant decrease in enthalpy was recorded. A highly statistically significant correlation (r = 0.991) between DSC values of retrograded starch of nonwaxy barley and gel hardness was obtained. The correlation between starch enthalpy value and gel hardness of starch concentrate indicates that gel texture is due mainly to its starch structure and functionality. The relationship between the properties of starch and starch concentrate may favor the application of barley starch concentrate without the necessity of using the wet fractionation process.

Thermal Properties of Starch from 62 Exotic Maize (Zea mays L.) Lines Grown in Two Locations

ABSTRACTThe variability in thermal properties among 62 S3 lines derived from a high‐yielding exotic corn (Zea mays) population, Antigua 1 (PI 484990), was evaluated by differential scanning calorimetry (DSC). The S3 lines were grown in Puerto Rico (1990–1991) and Georgia (1994). Separate single‐kernel starch extractions for five kernels (five replicates) from each line grown in each location were performed, and the starch was analyzed. The DSC values reported included gelatinization onset (ToG), range (RG), enthalpy (ΔHG), and peak height index (PHI) and retrogradation onset (ToR), range (RR), enthalpy (ΔHR), and percent retrogradation (%R) (an indication of the stability of gelatinized starch after storing at 4°C for 7 days). Significant differences (P &lt; 0.05) were found among the 62 lines of Antigua 1 for ToG, RG, and PHI and highly significant differences (P &lt; 0.01) were found for ΔHG. The starches from plants grown in Georgia (1994) had significantly (P &lt; 0.05) greater ToG, ΔHG, and PHI but a significantly lower RG than those from Puerto Rico (1990–1991). These data suggest that the starch from plants grown in Georgia (1994) might have a greater degree of crystallinity than that from Puerto Rico (1990–1991). None of the retrogradation values were significantly different among starches of the 62 lines of Antigua 1 and the starches from plants grown in the two locations.

Thermal Properties of Starch from Selected Maize (Zea mays L.) Mutants During Development

ABSTRACTThe changes in thermal properties of maize starches during five stages of kernel maturity, (12, 18, 24, 30, and 36 days after pollination [DAP]), from three mutant genotypes, amylose extender (ae), sugary‐2 (su2), and waxy (wx) in an OH43 background, and the OH43 genotype were studied using differential scanning calorimetry (DSC). Within a genotype, DSC values of starches at 24, 30, and 36 DAP were similar to each other and often were significantly different (P &lt; 0.05) from the values at 12 DAP, indicating possible differences in the fine structure of starch during endosperm development. For su2 starches, the gelatinization onset temperature (ToG) significantly decreased after 12 DAP and remained low throughout the study. The gelatinization range (RG) had a similar pattern. For wx starches, ToG at 18 DAP was significantly lower than at 12 DAP but tended to increase after 18 DAP. The RG increased significantly after 12 DAP and significantly decreased after 30 DAP. Thus, thermal properties of starches during early development were different from those of their mature counterparts, and differences among the mutant genotypes and the normal starch originated from the earliest endosperm development stage studied (12 DAP).