Teresa Kasprzycka-Guttman

Effects of selected phenol derivatives on the autoxidation of linolenic acid investigated by DSC non-isothermal methods

Abstract The kinetic features of the thermoxidation of linolenic acid (LNA) was investigated under non-isothermal conditions (50–300°C) in the presence of the phenolic compounds: o -cresol, p -cresol, 2,4-dimethylphenol, 2,5-dimethylphenol, 3,5-dimethylphenol, 2,4,6-trimethylphenol and 2,6-di- t -butyl-4-methylphenol at concentrations 0.26–20 mmol of compound per mol of LNA. Temperatures of reaction onset at different heating rates were used to evaluate kinetic parameters of linolenic acid thermoxidation by the Ozawa-Flynn-Wall method. Activation energy ( E a ) of the pure linolenic acid thermoxidation was 70.4 ± 0.5 kJ/mol and at the tested concentrations range of the phenolic compound, E a increased maximally to 95.8 ± 5.1 kJ/mol for 2,6-di- t -buty1–4-methylphenol, 101.1 ± 3.0 kJ/mol for o -cresol, 90.9 ± 1.5 kJ/mol for 2,4,6-trimethylphenol, 89.9 ± 4.4 kJ/mol ( p -cresol), 80.7 ± 4.5 kJ/mol (2,5-dimethylphenol) 86.1 ± 3.6 kJ/mol (3,5-dimethylphenol) and 75.1 ± 3.0 kJ/mol for 2,4-dimethylphenol. At concentrations of the phenolic compound greater than 10 mmol per mol of LNA, a decrease of inhibitory effect was observed.

Dynamic and isothermal DSC investigation of the kinetics of thermooxidative decomposition of some edible oils

The kinetics of thermooxidation of edible oils: soybean oil, rapeseed oil, corn and peanut oil was investigated in two ways. The DSC and its pressure version (PDSC) were used for measurements under the isothermal and non-isothermal conditions in atmosphere of oxygen. Comparing these two methods for each oil the differences between the values of activation energies were observed. However, mechanism of oxidation in both method was different.ZusammenfassungAuf zwei verschiedene Arten wurde, die Kinetik der Thermooxidation von Speiseölen (Sojabohnenöl, Rapsöl, Weizenöl und Erdmußöl) untersucht. Zur Messung unter isothermen und nichtisothermen Bedingungen in einer Sauerstoffatmosphäre wurden DSC und deren Druckvariante (PDSC) eingesetzt. Im Vergleich dieser beiden Methoden wurden für jede Ölsorte die Unterschiede bei den Werten für die Aktivierungsenergien beobachtet. Der Oxidationsmechanismus ist in beiden Methoden unterschiedlich.

Specific heats and kinetic parameters of thermo-oxidative decomposition of peanut oil

Abstract The kinetics of thermo-oxidative decomposition of peanut oil have been investigated using a Du Pont differential scanning calorimeter. The measurements were carried out under dynamic conditions in an atmosphere of oxygen. The activation energy of oxidation of the oil is calculated using the Kissinger and ASTM methods. The specific heats of peanut oil have been measured at 70–140°C.

Antioxidant properties of lignin and its fractions

Antioxidant properties of lignin in edible oils such as arachide oil have been investigated. Reaction kinetics were measured by differential scanning calorimetry (DSC) and experiments entailed heating the pure oil or oil to which substances suspected of inhibiting oxidation, i.e. lignin or its fractions, had been added, with subsequent comparison of the thermograms obtained. Similar experiments were carried out for arachide oil with addition of the well known inhibitor 2,6-di-(ert-butyl-4-methylphenol (BHT). Measurements described in this report prove that lignin and its fractions can be regarded as inhibitors in free radical auto-oxidation.

Excess volumes of binary systems formed by a pyridine base and an n-alkane in terms of an association model

Abstract An approach proposed recently (Treszczanowicz and Benson, 1985) is applied to the description of the excess volumes of binary systems formed by mixing a pyridine base with an n-alkane. The pyridine bases are: pyridine, α-picoline, 2,4- and 2,6-lutidine and γ-collidine. n-Alkanes from n-hexane to n-decane are considered. The excess volumes are described as sums of two contributions. One arises from self-association of the pyridine base and is evaluated according to the Mecke—Kempter continuous association model. The other comprises equation of state and interaction effects, which are treated according to the Flory theory. Four parameters are used for each series of (pyridine base + n-alkane) systems. Three are the enthalpy, entropy, and volume of bond formation in the complex, and the fourth is the Flory interaction parameter X ‡ 12 for the system containing n-hexane. The model provides a good description of the excess volumes which are S-shaped (negative at low mole fractions of base) for n-hexane systems, changing to positive values for systems containing higher n-alkanes. With the same values of the parameters, the model also predicts excess enthalpies which are in reasonable agreement with experiment.

Specific heats of some oils and a fat

Abstract The specific heats of some edible oils, pharmaceutical oils and a fat were measured by differential scanning calorimetry at 70–140 °C.

Volumes of mixing of pyridine bases withn-alkanes: Comparison with the prigogine-flory-patterson theory

The excess molar volumes of binary mixtures pyridine and α-picoline + C6−C10 n-alkanes have been measured at 25°C over the whole composition range. For pyridine + n-hexane and + n-heptane and also α-picoline + n-hexane and n-heptane VE has an S-shaped behavior and is positive at low concentrations of the base. For the systems pyridine + n-octane + n-nonane + n-decane and α-picoline + n-octane, n-nonane, and n-decane VE is positive. The Prigogine-Flory-Patterson theory has been fitted to our results.

Mitochondrial localization of P2Y1, P2Y2 and P2Y12 receptors in rat astrocytes and glioma C6 cells.

We have previously shown that P2Y1, P2Y2 and P2Y12 nucleotide receptors are functionally expressed and active on the cell surface of rat glioma C6 cells. In the present study, we have immunocytochemically shown their sub-cellular colocalization with mitochondria in these cells. The same colocalization of above receptors has been found in rat astrocytes. Additionally, differences in intracellular distribution of examined receptors between both cell lines have been observed. This data indicates that P2Y1, P2Y2 and P2Y12 receptor proteins exist within mitochondria of astrocytes and C6 cells, although their role in these sub-cellular structures remains unclear.

Thermodynamic properties of solutions: enthalpy of mixing of 2,4-lutidine + n-alkanes

Abstract The main purpose of this work is the determination of the excess heat of mixing H E for binary mixtures of 2,4-lutidine and C 6 to C 10 n -alkanes at 298.15 K. Prigogine-Flory-Patterson theory and the extended real associated solutions (ERAS) method are applied to describe the excess heat of mixing of the mixtures investigated.

Thermoanalytical investigation of edible oils

Abstract The kinetics of thermo-oxidative decomposition of linseed, olive, castor and cod-liver oils have been investigated using a Du Pont differential scanning calorimeter by the Kissinger (Anal. Chem., 29 (1957) 1702) and ASTM (ANSI/ASTM E 698-79, 1979, standard method for Arrhenius kinetic constants for thermally unstable materials) methods.