Modeling Chemical Reactivity at the Interfaces of Emulsions: Effects of Partitioning and Temperature

Abstract

Bulk phase chemistry is hardly ever a reasonable approximation to interpret chemical reactivity in compartmentalized systems, because multiphasic systems may alter the course of chemical reactions by modifying the local concentrations and orientations of reactants and by modifying their physical properties (acid-base equilibria, redox potentials, etc.), making them—or inducing them—to react in a selective manner. Exploiting multiphasic systems as beneficial reaction media requires an understanding of their effects on chemical reactivity. Chemical reactions in multiphasic systems follow the same laws as in bulk solution, and the measured or observed rate constant of bimolecular reactions can be expressed, under dynamic equilibrium conditions, in terms of the product of the rate constant and of the concentrations of reactants. In emulsions, reactants distribute between the oil, water, and interfacial regions according to their polarity. However, determining the distributions of reactive components in intact emulsions is arduous because it is physically impossible to separate the interfacial region from the oil and aqueous ones without disrupting the existing equilibria and, therefore, need to be determined in the intact emulsions. The challenge is, thus, to develop models to correctly interpret chemical reactivity. Here, we will review the application of the pseudophase kinetic model to emulsions, which allows us to model chemical reactivity under a variety of experimental conditions and, by carrying out an appropriate kinetic analysis, will provide important kineticparameters.

Distributions of α- and δ-TOCopherol in Intact Olive and Soybean Oil-in-Water Emulsions at Various Acidities: A Test of the Sensitivity of the Pseudophase Kinetic Model

“…Not long ago, interpreting the inhibition of lipid oxidation processes between antioxidants and peroxyl radicals in lipid-based emulsions was intractable [ 16 , 17 , 18 , 19 ]. Part of the problem lied in the lack of methods allowing separation and quantification of the contributions of the distribution of reactants and of the medium effects to the total rate of inhibition [ 20 , 21 , 22 ]. Particularly, knowing the distributions of antioxidants in emulsions was challenging for a long time, preventing a full rationalization of their effects because emulsions have regions with different solvent properties that affect both the reactivity and concentrations of antioxidants.…”

Formulation, Characterization and Evaluation of Innovative O/W Emulsions Containing Curcumin Derivatives with Enhanced Antioxidant Properties

“…Specifically, blank emulsion presents a medium droplet size, stable until 60 days after fabrication, which was also confirmed by optical analysis. The obtained micrographs showed the formation of yellow solid agglomerates regarding the emulsions containing 0.5 and 2% p-Cur, with the ones at 0.5% emulsion being larger [ 38 ]. These results are attributed to the poor solubility and stability of p-Cur in aqueous media.…”

Unexpected Antioxidant Efficiency of Chlorogenic Acid Phenolipids in Fish Oil-in-Water Nanoemulsions: An Example of How Relatively Low Interfacial Concentrations Can Make Antioxidants to Be Inefficient

“…The antioxidant efficiency was determined as in previous works [20][21][22]24,25,28,29,31,39,43] by monitoring the formation of primary oxidation products (conjugated dienes, CDs) with time in the intact emulsified systems both in the absence (control) and in the presence of AOs. The emulsified systems were stored in an oven and allowed to oxidize spontaneously at T = 40 • C in the dark.…”