Determining α-tocopherol distributions between the oil, water, and interfacial regions of macroemulsions: Novel applications of electroanalytical chemistry and the pseudophase kinetic model

Gunaseelan, K.; Romsted, Laurence S.; Pastoriza-Gallego, María José; González-Romero, Elisa; Bravo‐Díaz, Carlos

doi:10.1016/j.cis.2006.05.007

Cited by 55 publications

(112 citation statements)

References 30 publications

(36 reference statements)

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“…Additionally they postulated that α-tocopherol distribution between the oil, interface and aqueous regions may depend on oil polarity and in general vitamin E may be more soluble in the oil regions of emulsions composed of triglycerides than in octane. Although Gunaseelan et al [26] investigations refer to systems containing water and used a different kind of surfactant (forming regular micelles) the results are consistent with our results. They confirmed an excellent solubility of α-tocopherol in surfactant solutions, which are known as excellent solvents [27] as well as our hypothesis on preferred localization in the palisade layer of AOT reversed micelles.…”

Section: Resultssupporting

confidence: 95%

Calorimetric study of the α-tocopherol solubility in reversed AOT micelles

Wilczura-Wachnik¹,

Yavuz²,

Myslinski³

2008

Journal of Colloid and Interface Science

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Section: Resultssupporting

confidence: 95%

Calorimetric study of the α-tocopherol solubility in reversed AOT micelles

Wilczura-Wachnik¹,

Yavuz²,

Myslinski³

2008

Journal of Colloid and Interface Science

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“…Similar situations where found when reacting ArN þ 2 ions with neutral nucleophiles such as MeOH [15] and EtOH [14] and in systems of restricted geometry [13]. We are also interested in determining the distribution of polar organic molecules such as antioxidants in emulsified systems by using arenediazonium ions as chemical probes that react with a given antioxidant, the kinetic results being interpreted in terms of a pseudophase model [24] [25]. Knowledge of antioxidant distribution in food emulsions is important because the efficiency of antioxidants in inhibiting lipid peroxidation depends, among others, on their distribution within the different regions of the system [25 -27].…”

mentioning

confidence: 92%

Kinetics and Mechanism of the Reaction between an Arenediazonium Ion and Methyl Gallate (=Methyl 3,4,5‐Trihydroxybenzoate) in Aqueous Solution: Evidence for Diazo Ether Formation through an O‐Coupling Reaction

Losada‐Barreiro

Sánchez-Paz

Bravo‐Díaz

2007

Helvetica Chimica Acta

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We have investigated the kinetics and mechanism of the reaction between 3-methylbenzenediazonium ions (3MBD) and methyl gallate (¼ methyl 3,4,5-trihydroxybenzoate; MG), in aqueous buffer solution by employing spectrophotometric (UV/VIS) and electrochemical (linear-sweep voltammetry, LSV) techniques and computational methods. Because the absorption band of MG overlaps that of 3MBD, the reaction was monitored spectrophotometrically by measuring the changes in absorbance with time due to product formation, and biphasic kinetic profiles, indicative of accumulation of an intermediate in the course of the reaction, were obtained. The formation of an intermediate was confirmed by LSV. The observed rate constants k obs for 3MBD disappearance were obtained by fitting the decrease in the peak current of the first reduction peak of 3MBD with time to the integrated firstorder equation. The variation of k obs with [MG] was determined at different pH values and follows a saturation kinetic pattern. Alternatively, at a fixed [MG], k obs values show an inverse dependence on [H þ ], suggesting that the reactive species is the anion and not the neutral form of MG. To discern which of the three OH groups of MG is the first one undergoing deprotonation, the geometries of the resulting anions were optimized by using B3LYP hybrid density functional theory (DFT) and a 6-31G(þ þ d,p) basis set. The deprotonation energies suggest that the OH group at the 4-position is first deprotonated. The kinetic results can be accommodated, therefore, by assuming two competitive mechanisms, the spontaneous D N þ A N decomposition involving 3MBD, and a mechanism involving an electrophilic attack at the O-atom at C(4) in a pre-equilibrium step, leading to the formation of a transient diazo ether of the type ArÀN¼NÀOÀR which further decomposes. All attempts to isolate and characterize the diazo ether failed.

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“…Gallic acid is a basic structural unit of hydrolyzable tannins widely distributed in the plant kingdom especially in tanniferous plants in conjunction with other important polyphenolic compounds widely used as antioxidants [27 -29]. Estimating its distribution (and that of its derivatives) in food emulsions is important because their efficiency in inhibiting lipid peroxidation depends, among other aspects, on their distribution within the different regions of the system [26] [30] [31].…”

mentioning

confidence: 99%

“…Secondly, knowledge of the reaction mechanism of polar organic molecules such as antioxidants may be valuable in determining their distribution in emulsified systems [25] [26]. Gallic acid is a basic structural unit of hydrolyzable tannins widely distributed in the plant kingdom especially in tanniferous plants in conjunction with other important polyphenolic compounds widely used as antioxidants [27 -29].…”

mentioning

confidence: 99%

Reactivity of 3‐Methylbenzenediazonium Ions with Gallic Acid. Kinetics and Mechanism of the Reaction

Losada‐Barreiro

2009

Helvetica Chimica Acta

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We investigated the kinetics and mechanism of the reaction between the 3-methylbenzenediazonium ions (3MBD), and gallic acids (¼ 3,4,5-trihydroxybenzoic acid; GA) in aqueous buffer solution under acidic conditions by employing spectrometric, electrochemical, and chromatographic techniques and computational methods. To discern which of the three OH groups of GA is the first one undergoing deprotonation, the geometries of the resulting dianions were optimized by using B3LYP hybrid densityfunctional theory (DFT) and a 6-31G(þ þ d,p) basis set, and the results suggest that the OH group at the 4-position is the first one which is deprotonated. The variation of the observed rate constant, k obs , with the acidity at a given [GA] follows an upward curve suggesting that the reaction takes place with the dianionic form of gallic acid, GA 2À , and rate enhancements of ca. 23000 fold are obtained on going from pH 3.5 up to pH 7.5. At relatively high acidities, the variation of k obs with [GA] is linear with an intercept very close to the value for the thermal decomposition of 3MBD; however, a decrease in the acidity leads to saturation-kinetics profiles with nonzero, pH-dependent intercepts. The saturation-kinetics patterns found suggest the formation of an intermediate in a rapid pre-equilibrium step, but the nonzero, pHdependent intercepts cause the double reciprocal plots of 1/k obs vs. 1/[GA] to curve. This prompts us to propose an alternative reaction mechanism comprising consecutive equilibrium processes involving the bimolecular, reversible formation of a highly unstable (Z)-diazo ether which undergoes isomerization to the (E)-isomer through a unimolecular step. The results obtained indicate the complexity of reactions of arenediazonium ions with nucleophilic arenes containing three or more OH groups.

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Determining α-tocopherol distributions between the oil, water, and interfacial regions of macroemulsions: Novel applications of electroanalytical chemistry and the pseudophase kinetic model

Cited by 55 publications

References 30 publications

Calorimetric study of the α-tocopherol solubility in reversed AOT micelles

Calorimetric study of the α-tocopherol solubility in reversed AOT micelles

Kinetics and Mechanism of the Reaction between an Arenediazonium Ion and Methyl Gallate (=Methyl 3,4,5‐Trihydroxybenzoate) in Aqueous Solution: Evidence for Diazo Ether Formation through an O‐Coupling Reaction

Reactivity of 3‐Methylbenzenediazonium Ions with Gallic Acid. Kinetics and Mechanism of the Reaction

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