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there may be strong between-run correlation. Conclusions A practical approach for evaluating the uncertainty of results for determinations of the adiabatic (corrected) temperature rise in isoperibol calorimetry was
Abstract
In isoperibol temperature-rise calorimetry, different approaches can lead to the corrected temperature rise. The description of the methodology, as well as an improvement in the approach to the accurate numerical calculation of the corrected temperature rise in isoperibol calorimetry, based on the comparison between the exponential functional description of the initial and final periods and an independent third order polynomial fitting, is presented. The latter is focused on the strategy of minimizing the result dependency on the definition of the main period of the reaction. Furthermore, the dedicated software application Labtermo is introduced.
The quality of sour cream production from homogenised cream in the 1970's was highly improved. The heat resistance of product remained badly, that is, it precipitated in hot food. The Hungarian Dairy Research Institute (HDRI) has elaborated a technology that eliminates this disadvantageous characteristic: it is the use of exopolysaccharide (EPS)-producing lactic acid bacteria. This bacterium produces no aroma, and the proliferation optima of EPS-producing and aroma-producing lactic acid bacteria cultures do not coincide. Detection of these two bacteria was done until now by gene technology, that is expensive and long lasting one. We have applied (at first as we know) isotherm calorimetric method to follow the simultaneous proliferation of these bacteria and it was determined that: both lactic acid bacteria cultures proliferate well at the non-optimal temperature of 30°C and the thermophilic EPS-producing culture was faster than that of the mesophilic aroma-producer. The two cultures do not inhibit each other in mixed culture, and the ratio in mixed culture was 79% EPS-producer and 21% aroma-producer.
Abstract
The solid-state coordination reaction: Nd(NO3)36H2O(s)+4Ala(s) → Nd(Ala)4(NO3)3H2O(s)+5H2O(l) and Er(NO3)36H2O(s)+4Ala(s) → Er(Ala)4(NO3)3H2O(s)+5H2O(l) have been studied by classical solution calorimetry. The molar dissolution enthalpies of the reactants and the products in 2 mol L–1 HCl solvent of these two solid-solid coordination reactions have been measured using a calorimeter. From the results and other auxiliary quantities, the standard molar formation enthalpies of [Nd(Ala)4(NO3)3H2O, s, 298.2 K] and[Er(Ala)4(NO3)3H2O, s,298.2 K] at 298.2 K have been determined to be Δf H m 0 [Nd(Ala)4(NO3)3H2O,s, 298.2 K]=–3867.2 kJ mol–1, and Δf H m 0 [Er(Ala)4(NO3)3H2O, s, 298.2 K]=–3821.5 kJ mol–1.
Abstract
Sr2CeO4 has been prepared by sol-combustion and co-precipitate routes and the resulting products have been characterized by XRD analysis. The molar enthalpies of solution of Sr2CeO4, Sr(NO3)2(s) and Ce(NO3)36H2O(s) in 0.150 dm3 of (4.41 mol dm3 H2O2+4.23 mol dm-3 of HNO3) solvent as well as the molar enthalpies of solution of Sr2CeO4(s), SrCl2(s) and CeCl3(s) in 0.150 dm3of (1.47 mol dm-3 H2O2+3.05 mol dm-3 of HClO4) solvent have been measured using an isoperibol type calorimeter. From these results and other auxiliary data, the standard molar enthalpy of formation of Sr2CeO4 has been derived to be -2277.33.1 kJ mol-1 at 298.15 K. This is the first reported thermodynamic data on this compound.
Abstract
Tetronic® comprises X-shaped copolymers formed by four poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO) block chains bonded to an ethylene diamine central group. Micellization behaviour of three representative Tetronics (T304, T904 and T1307) was characterized to gain an insight into the interactions between the copolymer unimers and the state of water in their solutions. The enthalpy of demicellization, recorded at 37°C in an isoperibol microcalorimeter, indicated that the process was in all cases exothermic and the enthalpy ranked in the order T1307≥T904>>T304. Micellization is entropy-driven owing to hydrophobic interactions between the PPO chains. DSC analysis showed that the crystallization and melting peaks of the free water remaining in T304 and T904 solutions were progressively shifted toward lower temperatures as the surfactant proportion increased, owing to a colligative effect. Bound water corresponded to 3 water molecules per EO repeating unit. In the case of T1307, which has longer PEO chains, a splitting of the melting peak was observed, one peak appearing around 0°C due to free water and another at –15°C due to interfacial water. As T1307 proportion raised, the enthalpy of the former decreased, whilst the enthalpy of the latter increased. In 40% T1307 solutions, interfacial water overcame the proportion of free water; there being 1 interfacial and 3 bound water molecules per EO repeating unit. Gaussian deconvolution of FTIR spectra also enabled to characterize the evolution of free water as a function of Tetronic proportion. The dependence of micellization and water interaction behaviour on Tetronics structure should be taken into account to use these copolymers as drug solubilizers and micellar carriers.
Abstract
The tetra-alkyl-ammonium halides are electrolytes that have special characteristics due to the presence of hydrocarbon chains. They have been used asmodel compounds to study hydrophobic interactions due to their fairly large solubility in water and because of the possibility of change in the length and geometry of the alkyl chains. In this work the solution enthalpies of tetra-n-butyl-ammonium bromide, tetra-sec-butyl ammonium bromide, tetra-iso-butyl-ammonium bromide and di-n-butyl-di-sec-butyl ammonium bromide were determined at 298.15 K at concentrations between 0.001 and 0.01 mol kg−1. The experimental method used was isoperibol calorimetry. The results were extrapolated fitting the experimental data by least squares to obtain the solution enthalpies at infinite dilution. The hydrocarbon chains studied were so chosen because the tetra-n-butyl-ammonium ion is considered to be a structure maker for water. The results show that the geometry of the ion and of the hydrocarbon chains play an important role in the behavior properties of the solutions.
, Lorinczy , D 2005 Isoperibol calorimetry as a tool to evaluate the impact of the ratio of exopolysaccharide-producing microbes on the properties of sour cream . J Therm Anal Calorim 82 2 537 – 541 10.1007/s10973
Thermodynamics of the coordination compound Zn(Met)(NO3)2·1/2H2O(s) (Met = l-α-methionine)
Low temperature heat capacities and the standard molar enthalpy of formation
). The enthalpy change of the above proposed reaction and standard molar enthalpy of formation of the complex Zn(Met)(NO 3 ) 2 ·1/2H 2 O(s) were determined by a designed Hess thermochemical cycle using the experimental data of isoperibol calorimetry and
