Chemical kinetic and chemical trapping methods: Unique approaches for determining respectively the antioxidant distributions and interfacial molarities of water, counter-anions, and other weakly basic nucleophiles in association colloids
| Autor: | Nighat Nazir, Carlos Bravo-Díaz, Aijaz Ahmad Dar, Laurence S. Romsted |
|---|---|
| Rok vydání: | 2017 |
| Předmět: |
chemistry.chemical_classification
Aqueous solution Polymers and Plastics Inorganic chemistry 02 engineering and technology Surfaces and Interfaces 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences Micelle 0104 chemical sciences Hydrophobic effect Colloid Colloid and Surface Chemistry Reaction rate constant chemistry Microemulsion Physical and Theoretical Chemistry Counterion 0210 nano-technology Alkyl |
| Zdroj: | Current Opinion in Colloid & Interface Science. 32:84-93 |
| ISSN: | 1359-0294 |
| DOI: | 10.1016/j.cocis.2017.09.001 |
| Popis: | Two problems in colloid chemistry have proved difficult to solve. First the specific counterion and hydration effects on the properties of association colloids of ionic surfactants such as micelles, microemulsions and vesicles and second the efficiency of antioxidants, AOs, in fluid, opaque, usually nonionic emulsions. Specific ion and hydration effects are important because they contribute to the balance-of-forces determining association colloid properties along with the hydrophobic effect, however, few methods provide estimates of interfacial molarities. Determining antioxidant efficiencies in emulsions, an important problem in food science, is difficult because emulsions are opaque and antioxidant (AO) distributions are difficult to monitor. This review reports the development of two methods: chemical trapping (CT) and chemical kinetic (CK) methods for solving these problems, both based on the chemistries of arenediazonium ions. The CT method provides estimates of interfacial molarities of weakly basic nucleophiles including water, halides, alkyl carboxylates and sulfates, alcohols (including nonionic surfactants) and amide oxygen in the interfacial regions of association colloids. Results to date show that specific ion effects on association colloid properties, such as the sphere-to-rod transition concentration also involve displacement of interfacial water. The CK method, provides the observed rate constant, k obs , described by a pseudophase kinetic model for the reduction of the arenediazonium ion by an AO in intact emulsions to determine the oil/water partition constants by fitting kinetic data with two equations in two unknowns to obtain estimates of distributions and concentrations of AOs in the oil, interfacial and aqueous regions of nonionic emulsions. Part I of this review describes new insights obtained by the chemical trapping CT method, especially how changes in interfacial water and counterion molarities depend on their bulk solution concentrations. Part II reviews the chemical kinetic CK method based on the pseudophase kinetic model for determining the distributions of AOs in nonionic surfactant emulsions and provides a natural explanation for the cut-off effect. Part III describes a new combined application of the CT and CK methods for interpreting the complex kinetics of TBHQ reduction by the arenediazonium ion in mixed cationic/nonionic micelles. Perspectives and prospects complete the review in Part IV . |
| Databáze: | OpenAIRE |
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