Calorimetric Values Research Articles

Addition of Zinc Improves the Physical Stability of Insulin in the Primary Emulsification Step of the Poly(lactide-co-glycolide) Microsphere Preparation Process

In this study, the effect of zinc on insulin stability during the primary emulsification step of poly(lactide-co-glycolide) microspheres preparation by the water-in-oil-in-water (w/o/w) double emulsion solvent evaporation technique was evaluated. Insulin was emulsified at homogenization speeds of 5000 and 10,000 rpm. Insulin was extracted from the primary w/o emulsion by a method previously reported from our laboratory and analyzed by comprehensive analytical techniques. The differential scanning calorimetry thermograms of insulin with zinc showed a single peak around 83 °C with calorimetric enthalpy values similar to native insulin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of extracted insulin showed a single intense band around 6 kDa, demonstrating the preservation of primary structure. High performance liquid chromatography (HPLC) analysis revealed that no degradation products were formed during the homogenization process. Insulin aggregates residing at the w/o interfaces were found to be of non-covalent nature. In addition, observation of a single characteristic peak for insulin at m/z 5808 in the matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrum confirmed the absence of insulin degradation products and covalent dimers. Presence of zinc preserved the secondary structure of insulin as indicated by circular dichroism. In conclusion, these results show that with the addition of zinc, insulin stability can be improved during the primary emulsification step.

Rheological, physical and sensorial evaluation of cookies supplemented with dairy powders.

The effect of dairy powders (skim milk powder, butter milk powder, sodium caseinate, yoghurt powder, milk powder and colostrum powder) on cookie quality was studied. Cookies were tested for aw, calorimetric energy, diameter, thickness, spread ratio, breaking strength, colour, dough consistency and sensory evaluation. The lowest aw values were obtained for cookies containing colostrum powder; also the highest calorimetric energy values were obtained from the colostrum powder-added cookies. Diameter values of cookies with the addition of skim milk powder, butter milk powder, yoghurt powder and milk powder were higher than that of sodium caseinate and colostrum powder. The lowest spread ratio was measured in the cookie samples with added skim milk powder. The addition of yoghurt powder gave the highest breaking strength of cookies. Cookies with sodium caseinate addition exhibited the highest lightness (L*) values than the other cookies with different dairy powders. Cookies prepared with butter milk powder received the highest scores for colour, appearance, texture, crispness and overall acceptability.

H233 直膨方式地中熱ヒートポンプの熱交換性能 : 室内機側での性能評価(一般講演(13))

A ground source heat pump (GSHP) is paying attention as one of the energy saving technologies. The purpose of this study is to investigate a heat exchanging performance of a ground source heat pump using direct expansion method. The direct expansion method for heat exchange will be more efficient comparing with the conventional indirect heat exchange method. However it is difficult to measure the calorimetric value of the heat pump system using direct expansion method because the refrigerant becomes two phase flow. Therefore, we evaluated the calorimetric value around the indoor unit of the heat pump system. We also improved the accuracy of the measurement of the velocity distribution using the traversing system of the hot wire anemometer.

Thermodynamics of host-guest interactions between fullerenes and a buckycatcher.

1H NMR and isothermal titration calorimetry (ITC) experiments were employed to obtain reliable thermodynamic data for the formation of the 1:1 inclusion complexes of fullerenes C60 and C70 with the buckycatcher (C60H28). NMR measurements were done in toluene-d8 and chlorobenzene-d5 at 288, 298, and 308 K, while the ITC titrations were performed in toluene, chlorobenzene, o-dichlorobenzene, anisole, and 1,1,2,2-tetrachloroethane at temperatures from 278 to 323 K. The association constants, Ka, obtained with both techniques are in very good agreement. The thermodynamic data obtained by ITC indicate that generally the host–guest association is enthalpy-driven. Interestingly, the entropy contributions are, with rare exceptions, slightly stabilizing or close to zero. Neither ΔH nor ΔS is constant over the temperature range studied, and these thermodynamic functions exhibit classical enthalpy/entropy compensation. The ΔCp values calculated from the temperature dependence of the calorimetric ΔH values are negative for the association of both fullerenes with the buckycatcher in toluene. The negative ΔCp values are consistent with some desolvation of the host-cavity and the guest in the inclusion complexes, C60@C60H28 and C70@C60H28.

용융염 코팅이 열지에 미치는 영향

Thermal batteries are primary reserve batteries that use inorganic salt as electrolytes which are inactive at room temperature. The two principal heat sources that have been used in thermal batteries are heat paper and heat pellets. As soon as the heat paper, which is ignited by the initiator, in turn ignites the heat pellets, all the solid electrolytes are melted into excellent ionic conductors. However, the high combustion temperature by heat papers in thermal batteries causes thermal decomposition at the cathode, eventually leading to a thermal runaway. In this paper, we have attempted to prepare <TEX>$Zr/BaCrO_4$</TEX> heat papers coated with KCl molten salt. We have also investigated the effect of a molten salt coating on the heat papers through the thermal characteristics such as calorimetric value, combustion temperature and burning rate. The calorimetric value and combustion temperature of heat papers were reduced with an increase in the molten salt coating. As a result, the molten salt coating on heat papers greatly reduced risk of a thermal runaway and improved the stability of thermal batteries.

Aprovechamiento de residuos de trucha arco iris Oncorhynchus mykiss: uso de tecnologías limpias para la extracción de aceite

La producción de trucha arco iris en Colombia soporta el 11,36 % de la producción nacional; los residuos del beneficio pueden ser utilizados para la extracción de aceites, ya sea por calentamiento (Soxhlet) o por Fluidos Supercríticos (FSc) (temperatura y presión crítica de los gases). Se planteó como objetivo extraer y caracterizar el aceite de pescado derivado de subproductos de trucha arco iris por medio de Soxhlet y FSc. Para ello, vísceras y carcasas de trucha arco iris se secaron, se molieron, se determinó humedad, valores bromatológicos (según la AOAC 1986) y microbiológicos (NMP para coliformes totales y fecales); a todas las muestras por triplicado se aplicó Soxhlet y FSc; al producto final se le hizo el perfil de ácidos grasos por cromatografía gaseosa (GC). Los análisis microbiológicos realizados a carcasas y vísceras no arrojaron presencia de E. Coli en ninguna de las muestras; los análisis bromatológicos fueron: humedad, 2.1 %; grasa, 34.2 %; cenizas, 17.3 %; proteína, 17.2 %; un valor calorimétrico de 5414,4 cal/g para carcasas y un valor de 6068,01 cal/g para vísceras. El perfil lipídico del aceite obtenido por Soxhlet presenta 68.6 % de grasa insaturada (%GI), 27.73 % de grasa saturada y 0.85% de ácidos grasos omega 3; para el aceite obtenido por fluidos supercríticos se obtuvieron 69.14 %, 26.71 % y 4.99% de grasa insaturada, grasa saturada y ácidos grasos omega 3, respectivamente. Además, solamente por extracción con fluidos supercríticos se logró la recuperación de 2.88% de DHA (ácido docosahexanóico) y 0.67% de EPA (ácido eicosapentanóico). Se presentaron diferencias significativas (p&lt;0,05) para los valores de %GI y para los valores en % de DHA y EPA, al compararse Soxhlet vs Fluidos Supercríticos. Se evidenció que FSc es determinante para obtener una composición adecuada de ácidos grasos omega 3 (DHA y EPA).

Oxygen restriction as challenge test reveals early high-fat-diet-induced changes in glucose and lipid metabolism.

Challenge tests stress homeostasis and may reveal deviations in health that remain masked under unchallenged conditions. Ideally, challenge tests are non-invasive and applicable in an early phase of an animal experiment. Oxygen restriction (OxR; based on ambient, mild normobaric hypoxia) is a non-invasive challenge test that measures the flexibility to adapt metabolism. Metabolic inflexibility is one of the hallmarks of the metabolic syndrome. To test whether OxR can be used to reveal early diet-induced health effects, we exposed mice to a low-fat (LF) or high-fat (HF) diet for only 5 days. The response to OxR was assessed by calorimetric measurements, followed by analysis of gene expression in liver and epididymal white adipose tissue (eWAT) and serum markers for e.g. protein glycation and oxidation. Although HF feeding increased body weight, HF and LF mice did not differ in indirect calorimetric values under normoxic conditions and in a fasting state. Exposure to OxR; however, increased oxygen consumption and lipid oxidation in HF mice versus LF mice. Furthermore, OxR induced gluconeogenesis and an antioxidant response in the liver of HF mice, whereas it induced de novo lipogenesis and an antioxidant response in eWAT of LF mice, indicating that HF and LF mice differed in their adaptation to OxR. OxR also increased serum markers of protein glycation and oxidation in HF mice, whereas these changes were absent in LF mice. Cumulatively, OxR is a promising new method to test food products on potential beneficial effects for human health.

Pyrolysis kinetics of hazelnut husk using thermogravimetric analysis

This study aims at investigating physicochemical properties and pyrolysis kinetics of hazelnut husk, an abundant agricultural waste in Turkey. The physicochemical properties were determined by bomb calorimeter, elemental analysis and FT-IR spectroscopy. Physicochemical analysis results showed that hazelnut husk has a high calorimetric value and high volatile matter content. Pyrolysis experiments were carried out in a thermogravimetric analyzer under inert conditions and operated at different heating rates (5, 10, 20°C/min). Three different kinetic models, the iso-conversional Kissinger-Akahira-Sunose (KAS) and Ozawa-Flynn-Wall (OFW) models and Coats-Redfern method were applied on TGA data of hazelnut husk to calculate the kinetic parameters including activation energy, pre-exponential factor and reaction order. Simulation of hazelnut husk pyrolysis using data obtained from TGA analysis showed good agreement with experimental data. Combining with physicochemical properties, it was concluded that this biomass can become useful source of energy or chemicals.

Effects of supported (nBuCp)2ZrCl2 catalyst active center multiplicity on crystallization kinetics of ethylene homo- and copolymers

Two different supported zirconocene, that is, bis(n-butylcyclopentadienyl) zirconium dichloride (nBuCp)2ZrCl2, catalysts were synthesized. Each catalyst was used to prepare one ethylene homopolymer and one ethylene–1-hexene copolymer. Catalyst active center multiplicity and polymer crystallization kinetics were modeled. Five separate active center types were predicted, which matched the successive self-nucleation and annealing (SSA) peak temperatures. The predicted crystallinity well matched the differential scanning calorimetric (DSC) values for a single Avrami–Erofeev index, which ranged between 2 and 3 for the polymers experimented. The estimated apparent crystallization activation energy Ea did not vary with cooling rates, relative crystallinity α, and crystallization time or temperature. Therefore, the concept of variable/instantaneous activation energy was not found to hold. Ea linearly increased with the weight average lamellar thickness Lwav DSC-GT; and for each homopolymer, it exceeded that of the corresponding copolymer. Higher Ea, hence slower crystallization, was identified as a pre-requisite to attain higher crystallinity. Crystallization parameters were correlated to polymer backbone parameters, which are influenced by catalyst active center multiplicity.

Molecular Mobility of Amorphous S-Flurbiprofen: A Dielectric Relaxation Spectroscopy Approach

Amorphous S-flurbiprofen was obtained by the melt quench/cooling method. Dielectric measurements performed in the isochronal mode, conventional and temperature modulated differential scanning calorimetry (TMDSC) studies showed a glass transition, recrystallization, and melting. The different parameters characterizing the complex molecular dynamics of amorphous S-flurbiprofen that can have influence on crystallization and stability were comprehensively characterized by dielectric relaxation spectroscopy experiments (isothermal mode) covering a wide temperature (183 to 408 K) and frequency range (10(-1) to 10(6) Hz): width of the α-relaxation (βKWW), temperature dependence of α-relaxation times (τα), fragility index (m), relation of the α-relaxation with the β-secondary relaxation, and the breakdown of the Debye-Stokes-Einstein (DSE) relationship between the structural relaxation time and dc-conductivity (σdc) at deep undercooling close to Tg. The β-relaxation, observed in the glassy as well as in the supercooled state was identified as the genuine Johari-Goldstein process, attributed to localized motions and regarded as the precursor of the α-relaxation as suggested in the coupling model. A separation of about 6 decades between the α- and β-relaxation was observed at Tg; this decoupling decreased on increasing temperature, and both processes merged at Tαβ = 295 K. The temperature dependence of the α-relaxation time, τα, was described by two Vogel-Fulcher-Tammann-Hesse equations, which intercept at a crossover temperature, TB = 290 K, close to the splitting temperature between the α- and β-relaxation. From the low temperature VFTH equation, a Tg(DRS) = 265.2 was estimated (at τα =100 s) in good agreement with the calorimetric value (Tg,onset,TMDSC = 265.6 K), and a fragility or steepness index m = 113 was calculated allowing to classify S-flurbiprofen as a fragile glass former. The α-relaxation spectra were found to be characterized by a relatively large degree of nonexponentiality (βKWW = 0.52). A breakdown of the DSE log10 σdc - log10 τ relation was observed revealing an enhancement of translational ionic motions in comparison with the orientational molecular motions as the glass transition temperature Tg is approached from above.

An Overview of the Recent Developments on Fructooligosaccharide Production and Applications

Over the past years, many researchers have suggested that deficiencies in the diet can lead to disease states and that some diseases can be avoided through an adequate intake of relevant dietary components. Recently, a great interest in dietary modulation of the human gut has been registered. Prebiotics, such as fructooligosaccharides (FOS), play a key role in the improvement of gut microbiota balance and in individual health. FOS are generally used as components of functional foods, are generally regarded as safe (generally recognized as safe status—from the Food and Drug Administration, USA), and worth about 150€ per kilogram. Due to their nutrition- and health-relevant properties, such as moderate sweetness, low carcinogenicity, low calorimetric value, and low glycemic index, FOS have been increasingly used by the food industry. Conventionally, FOS are produced through a two-stage process that requires an enzyme production and purification step in order to proceed with the chemical reaction itself. Several studies have been conducted on the production of FOS, aiming its optimization toward the development of more efficient production processes and their potential as food ingredients. The improvement of FOS yield and productivity can be achieved by the use of different fermentative methods and different microbial sources of FOS-producing enzymes and the optimization of nutritional and culture parameter; therefore, this review focuses on the latest progresses in FOS research such as its production, functional properties, and market data.

Effect of Experiment Environment on Calorimetric Value of Composite Solid Propellants

The calorimetric value (cal-val) of solid rocket propellants and explosives is determined in the presenceof inert atmosphere using industrial nitrogen gas. However, due to presence of trace amount of oxygen, the cal-val is not always correct. To avoid such inaccuracy in cal-val, a systematic study has been carried out by takingdifferent types of solid propellant samples having burning rate in the range of 5 mm/s − 30 mm/s at different pressures.The data obtained were acquired using industrial nitrogen, ultra high pure nitrogen (UHP-N2), ultra high pureargon (UHP-Ar), air and ultra high pure oxygen (UHP-O2). The data reveal that cal-val is highest in the case ofUHP-O2 due to complete combustion while in the case of air and industrial nitrogen it is found to be substantiallyless. Moreover, the cal-val in the presence of UHP-N2 and UHP-Ar meets the standard value with reproducibility.The results, further, confirm that for authentic cal-val, the most suitable environment is UHP-N2/UHP-Ar. Defence Science Journal, 2013, 63(5), pp.467 -472 , DOI:http://dx.doi.org/10.14429/dsj.63.2896

Solubility and solution thermodynamics of sulfamerazine and sulfamethazine in some ethanol + water mixtures

The solubility of sulfamerazine (SMR) and sulfamethazine (SMT) in some ethanol+water cosolvent mixtures was measured at five temperatures from 293.15 to 313.15K in all the polarity range provided by the aqueous mixtures. The mole fraction solubility of both drugs was maximal in the mixture 0.80 in mass fraction of ethanol (δ=30.0MPa1/2) and minimum in pure water (δ=47.8MPa1/2) at all the temperatures studied. The thermodynamic functions Gibbs energy, enthalpy, and entropy of solution were obtained from these solubility data by using the van’t Hoff and Gibbs equations. Thermodynamic quantities of mixing were also calculated by using some calorimetric values related to the drugs fusion process reported in the literature. Non-linear enthalpy–entropy relationships were observed for both drugs in the plot of enthalpy vs. Gibbs energy of mixing. The plot of ΔmixH° vs. ΔmixG° shows three different trends according to the slopes obtained when the mixtures composition changes. Accordingly, the driving mechanism for SMR solution process in water-rich is the entropy; whereas, from 0.20 mass fraction of ethanol to neat ethanol the process is enthalpy-driven. For SMT the process is driving by entropy in water-rich and ethanol-rich mixtures but driven by enthalpy in mixtures from 0.30 to 0.80 mass fraction of ethanol. The behavior of SMT is similar to the ones exhibited by the similar drugs sulfapyridine and sulfadiazine in the same co-solvent mixtures.

Solution thermodynamics of sulfadiazine in some ethanol + water mixtures

The solubility of sulfadiazine (SD) in several cosolvent mixtures was measured at temperatures from 293.15 to 313.15K in all the polarity range provided by aqueous mixtures conformed by ethanol and water. The solubility was maximal in the mixture 0.80 in mass fraction of ethanol (δ=30.0MPa1/2) and minimum in pure water (δ=47.8MPa1/2) at all the temperatures. The thermodynamic functions Gibbs energy, enthalpy, and entropy of solution were obtained from these solubility data by using the van't Hoff and Gibbs equations. Thermodynamic quantities of mixing were also calculated by using calorimetric values related to a drug fusion process reported in the literature. A nonlinear enthalpy–entropy relationship was observed in a plot of enthalpy vs. Gibbs energy of mixing. The plot of ΔmixH° vs. ΔmixG° shows two different trends according to the slope obtained; that is, i) one with a negative slope from pure water up to 0.20 in mass fraction of ethanol and another one from the mixture 0.80 in mass fraction of ethanol up to pure ethanol; and ii) one with a positive slope from the mixture 0.20 in mass fraction of ethanol up to the mixture 0.80 in mass fraction of ethanol. Accordingly, the driving mechanism for SD solubility in water-rich and ethanol-rich mixtures is the entropy, whereas, between 0.20 and 0.80 mass fraction of ethanol the driving mechanism is the enthalpy. This behavior is similar to the one exhibited by the similar drug sulfapyridine.

Solubility of sulfapyridine in propylene glycol + water mixtures and correlation with the Jouyban–Acree model

The solubility of sulfapyridine (SP) in propylene glycol+water mixtures was determined at temperatures from 293.15K to 313.15K. The solubility was maximal in pure propylene glycol and minimum in pure water at all the temperatures. The thermodynamic functions; Gibbs energy, enthalpy, and entropy of solution were obtained from these solubility data by using the van’t Hoff and Gibbs equations. Thermodynamic quantities of mixing were also calculated by using calorimetric values related to drug fusion process. A nonlinear enthalpy–entropy relationship was observed from a plot of enthalpy vs. Gibbs energy of solution. The plot of ΔsolnH° vs. ΔsolnG° shows two different trends, one with negative slope from pure water up to 0.30 mass fraction of propylene glycol and the other one positive beyond this composition up to pure propylene glycol. Accordingly, the driving mechanism for SP solubility in water-rich mixtures is the entropy, probably due to water-structure loss around the drug non-polar moieties by effect of propylene glycol, whereas, above 0.30 mass fraction of propylene glycol the driving mechanism is the enthalpy, probably due to SP solvation increase by the co-solvent molecules. This behavior is similar to the one exhibited by sulfanilamide, sulfamethizole and other drugs in the same co-solvent mixtures. The Generated solubility data were calculated (correlated and/or predicted) with the Jouyban–Acree model in which the mean percentage deviation (MPD) of the correlated and predicted data were 9.3±8.6%, and 12.1±9.9%, respectively. The corresponding MPDs for the correlated and predicted solubilities using the log-linear model were 25.1±19.8%, and 55.1±32.4%. The density of saturated solutions was predicted using a previously trained model. The ΔsolnH° and ΔsolnG° values were also correlated using a proposed model.

Non-exponential nature of calorimetric and other relaxations: Effects of 2 nm-size solutes, loss of translational diffusion, isomer specificity, and sample size

Certain distributions of relaxation times can be described in terms of a non-exponential response parameter, β, of value between 0 and 1. Both β and the relaxation time, τ0, of a material depend upon the probe used for studying its dynamics and the value of β is qualitatively related to the non-Arrhenius variation of viscosity and τ0. A solute adds to the diversity of an intermolecular environment and is therefore expected to reduce β, i.e., to increase the distribution and to change τ0. We argue that the calorimetric value β(cal) determined from the specific heat [Cp = T(dS∕dT)p] data is a more appropriate measure of the distribution of relaxation times arising from configurational fluctuations than β determined from other properties, and report a study of β(cal) of two sets of binary mixtures, each containing a different molecule of ∼2 nm size. We find that β(cal) changes monotonically with the composition, i.e., solute molecules modify the nano-scale composition and may increase or decrease τ0, but do not always decrease β(cal). (Plots of β(cal) against the composition do not show a minimum.) We also analyze the data from the literature, and find that (i) β(cal) of an orientationally disordered crystal is less than that of its liquid, (ii) β(cal) varies with the isomer's nature, and chiral centers in a molecule decrease β(cal), and (iii) β(cal) decreases when a sample's thickness is decreased to the nm-scale. After examining the difference between β(cal) and β determined from other properties we discuss the consequences of our findings for theories of non-exponential response, and suggest that studies of β(cal) may be more revealing of structure-freezing than studies of the non-Arrhenius behavior. On the basis of previous reports that β → 1 for dielectric relaxation of liquids of centiPoise viscosity observed at GHz frequencies, we argue that its molecular mechanism is the same as that of the Johari-Goldstein (JG) relaxation. Its spectrum becomes broader on cooling and its unimodal distribution reversibly changes to a bimodal distribution, each of β < 1. Kinetic freezing of the slower modes of the bimodal distribution produces a glass. After this bifurcation, the faster, original relaxation persists as a weak JG relaxation at T → T(g), and in the glassy state.

Thermodynamic study of the solubility of sulfapyridine in some ethanol + water mixtures

The solubility of sulfapyridine (SP) in ethanol+water cosolvent mixtures was measured at temperatures from 293.15 to 313.15K in all the polarity range provided by aqueous mixtures conformed by ethanol and water (solubility parameter, δmix=26.5–47.8MPa1/2). The solubility was maximal in the mixture with 0.80 in mass fraction of ethanol (δ=30.0MPa1/2) and very low in pure water (δ=47.8MPa1/2) at all the temperatures. The thermodynamic functions Gibbs energy, enthalpy, and entropy of solution were obtained from these solubility data by using the van't Hoff and Gibbs equations. Thermodynamic quantities of mixing were also calculated by using calorimetric values related to the drug fusion process. A nonlinear enthalpy–entropy relationship was observed in a plot of enthalpy vs. Gibbs energy of solution. The plot of ΔsolnH° vs. ΔsolnG° shows two different trends according to the slope obtained; that is, i. one with negative slope from pure water up to 0.20 in mass fraction of ethanol and another one from the mixture with 0.80 in mass fraction of ethanol up to pure ethanol; and ii. one with positive slope from the mixture with 0.20 in mass fraction of ethanol up to the mixture with 0.80 in mass fraction of ethanol. Accordingly, the driving mechanism for SP solubility in water-rich and ethanol-rich mixtures is the entropy, whereas, between 0.20 and 0.80 mass fractions of ethanol the driving mechanism is the enthalpy.

Ballistic Modification of Nitramine Propellants with Special Reference to NG-PE-PCP-Based High Energy Propellants

The burning rate pressure relationship is one of the important criteria in the selection of the propellant for particular applications. The pressure exponent (η) plays a significant role in the internal ballistics of rocket motors. Nitramines are known to produce lower burning rates and higher pressure exponent (η) values. Studies on the burning rate and combustion behavior of advanced high-energy NG/PE-PCP/AP/Al- and NG/PE-PCP/HMX/AP/Al-based solid rocket propellants processed by a conventional slurry cast route were carried out. The objective of present study was to understand the effectiveness of various ballistic modifiers viz. iron oxide, copper chromite, lead/copper oxides, and lead salts in combination with carbon black as a catalyst on the burning rate and pressure exponent of these high-energy propellants. A 7–9 % increase in the burning rates and almost no effect in pressure exponent values of propellant compositions without nitramine were observed. However, in case of nitramine-based propellants as compared to propellant compositions without nitramines, slight increases of the burning rates were observed. By incorporation of ballistic modifiers, the pressure exponents can be lowered. The changes in the calorimetric values of the formulations by addition of the catalysts were also studied.

Mechanical spectra and calorimetric evaluation of gelatin–xanthan gum systems with high levels of co-solutes in the glassy state

Mechanical properties of gelatin–xanthan gum (XG) mixtures with high levels of co-solutes were examined by dynamic mechanical analysis (DMA). The mechanical spectra of the samples were modeled according to the Williams–Landel–Ferry (WLF) equation/free-volume theory, which requires an entropic lightly cross-linked network. For the α dispersion, E′ and E′′ superposed with the horizontal shift factor aT, which was temperature-dependent according to the WLF equation; no other secondary dispersion mechanism was detected. The addition of XG to gelatin networks with high levels of co-solutes changed the glass transition temperature (Tg) and kinetics of glass transition and glassy states. In the glassy state, the WLF equation was unable to follow progress in the mechanical properties, which were better described by the Andrade equation. The calorimetric measurements of the gelatin–XG systems were made using a modulated temperature differential scanning calorimetry (MTDSC) to improve the determination of Tg. The samples were exposed to two cooling and heating cycles to provide a controlled recent thermal history in the temperature range of 40 °C to −70 °C. The Tg values of the samples were determined from the second heating cycle in the reversing heat signal. The calorimetric Tg values increased with increasing glucose syrup:sucrose ratio due to increased crosslinking, whereas mechanical Tg decreased with increased XG content due to network formation.

Solubility of sulfamethizole in some propylene glycol + water mixtures at several temperatures

The solubility of sulfamethizole (SMZ) in propylene glycol+water cosolvent mixtures was determined at temperatures from 293.15 to 313.15K. The solubility was maximal in pure propylene glycol and very low in pure water at all the temperatures. The thermodynamic functions: Gibbs energy, enthalpy, and entropy of solution and of mixing were obtained from these solubility data by using the van’t Hoff and Gibbs equations. Thermodynamic quantities of mixing were also calculated by using calorimetric values related to drug fusion process. A nonlinear enthalpy–entropy relationship was observed from a plot of enthalpy vs. Gibbs energy of solution. The plot of ΔsolnH° vs. ΔsolnG° shows two different trends, one with negative slope from pure water up to 0.20 mass fraction of propylene glycol and the other one positive beyond this composition up to pure propylene glycol. Accordingly, the driving mechanism for SMZ solubility in water-rich mixtures is the entropy, probably due to water-structure loss around the drug non-polar moieties by effect of propylene glycol, whereas, above 0.20 mass fraction of propylene glycol the driving mechanism is the enthalpy, probably due to SMZ solvation increase by the co-solvent molecules. This behavior is similar to the one exhibited by sulfanilamide and other drugs in the same co-solvent mixtures.