Reactivity Control by Aqueous Amphiphilic Self-Assembling Systems

Savelli, Gianfranco; Brinchi, Lucia; Germani, Raimondo

doi:10.1201/9780203908662.ch8

Cited by 54 publications

(152 citation statements)

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“…These methods could not be easily applied to reactions in micelles, or other association colloids, where the surfactant is in large excess over the organic substrate to avoid perturbation of the colloidal structure. 1,2 The situation changed with the introduction of low cost uv/visible spectrophotometers so that reactions could be followed with very dilute substrate. Bimolecular reactions were usually followed with one reagent in large excess, giving first-order kinetics, and making nucleophilic reactions of nitrophenyl derivatives very popular.…”

Section: Discussionmentioning

confidence: 99%

“…These volumes depend on assumptions regarding this region and cited values vary between 0.14 and 0.5 M -1 , and probably depend on the reaction conditions, which limits comparisons of second-order rate constants in micelles and water. 2 Diazonium ions are very effective trapping agents for many nucleophiles and comparison of extents of this trapping in water and in micelles allows estimation of concentrations of nucleophiles in the two regions. 20 The location of the diazonium ion is controlled by the hydrophobicity of its substituent group, whose size should not affect trapping rates in either medium, so that the extent of trapping relates nucleophilic molarity in micelles to the known nucleophilic molarity in water.…”

Section: Discussionmentioning

confidence: 99%

“…The various treatments lead to similar values of second-order rate constants in the micellar pseudophase for reactions of dilute electrolytes in ionic micelles. 2 The various quantitative treatments of ion binding to micelles in water estimate relative ionic concentrations in water and micelles but give local concentrations as molarities in terms of assumed molar volumes, V m , of the micellar reaction region. These volumes depend on assumptions regarding this region and cited values vary between 0.14 and 0.5 M -1 , and probably depend on the reaction conditions, which limits comparisons of second-order rate constants in micelles and water.…”

Section: Discussionmentioning

confidence: 99%

“…Bimolecular reactions can be followed in micellar solutions with a reactive counterion, typically a nucleophile or base, e.g., OH -or Br -and no ionic competition. 2,10 In terms of the PIE model reaction rates with fully micellar bound substrate should become constant when the interfacial reaction region is saturated with reactive ion, but in some conditions reaction rates increase on addition of large amounts of the reactive ion. 24 This phenomenon, called "invasion"…”

Section: Discussionmentioning

confidence: 99%

“…There is extensive literature summarizing early and recent kinetic work and covering reactivity in micelles and other association colloids, such as microemulsions and vesicles, in water and organic solvents. 1,2 Most work has involved organic reactions, generally in water, mediated by organic micelles which absorb reactants, providing a reaction region distinct from the bulk solvent. The treatments which allow estimation of rate constants in the micelles were developed over many years and make it possible to relate micellar reactivities to reaction mechanism and well-studied kinetic solvent effects.…”

Section: Introductionmentioning

confidence: 99%

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Micellar rate effects-assumptions and approximations

Bunton¹

2011

Arkivoc

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Surfactants with ionic or polar head groups and extended apolar groups form micelles in water with hydrocarbon-like interiors and ionic or polar groups at the surface and bind ionic and nonionic solutes. They act as reaction regions, i.e., as pseudophases distinct from the bulk solvent, and can accelerate or inhibit reactions, depending on rate constants and reactant concentrations in the two regions. Theoretical treatments and experimental evidence of reactant partitioning between water and micelles allow estimation of rate constants in the micellar pseudophase for both uni-and bimolecular reactions, provided that they are slower than reactant transfers between water and micelles, but some treatments apply only to dilute electrolyte. Competition between reactive and inert ions inhibits bimolecular ionic reactions and is treated by ion-exchange equations and some local ionic concentrations can be estimated by dediazonization trapping or physical methods. Ionic micelles affect rates of unimolecular and bimolecular watercatalyzed reactions because the reaction region at the micelle-water interface is less polar than water. Zwitterionic micelles have no net charge but they interact with ions, although ion-binding is weaker than with ionic micelles and there are limitations in the use of the theoretical treatments applied to ionic micelles. Micelles can control product composition, but product isolation limits use of surfactants in some reactions

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Micellar rate effects-assumptions and approximations

Bunton¹

2011

Arkivoc

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Introduction to Surfactant Self‐Assembly

Romsted

2012

Supramolecular Chemistry

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Current models and concepts are introduced and used to characterize the physical properties of homogeneous, small molecule, surfactant solutions such as the critical micelle concentration (cmc), aggregation number, degree of ionization of ionic aggregates and the interactions that determine the size and shape of aggregates, various mesophases such as spherical and rodlike micelles, lamellar, vesicular, bicontinuous, and reverse micelles, and the chemical reactivity in surfactant solutions. Surfactant aggregation is a spontaneous process and a delicate balance of forces governs the size and shapes of the structures at equilibrium. Aggregation is driven by the hydrophobic effect, the minimization of surfactant tail‐water contact by transfer of the tail of the surfactant unimer from water to the aggregate core with the concomitant release of water of hydration, and an increase in the entropy of the system. Balance is provided by a combination of electrostatic, ion‐specific, and hydration interactions in the interfacial region of the aggregates. Two models are generally used to interpret surfactant aggregation and solution properties, the more generally applied pseudophase model and the mass action model. For example, pseudophase models provide a comprehensive interpretation of micellar effects on chemical reactivity. A major unsolved problem is developing a general interpretation of ion‐specific effects, as exemplified by the Hofmeister series on surfactant aggregate properties. The ion‐pair hydration model represents one potential solution.

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Reactions in Dynamic Self‐Assemblies

Moulin

Giuseppone

2012

Supramolecular Chemistry

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The dynamic processes in self‐assemblies are involved in numerous domains that span throughout the modern aspects of chemical sciences, going from fundamental investigations into the origin of life to the most striking technological applications in medicine or electronics. This chapter aims at providing the reader with a brief overview of the concepts that link chemical reactivity with dynamic templates and catalysts made of large supramolecular assemblies. Specifically, we discuss kinetic and thermodynamic aspects of selected examples depending on (i) the nature of the matrix — that is, micelles, vesicles, liquid crystals, and gels; (ii) the nature of their constituents — that is, surfactants, block copolymers, bioactive macromolecules; and (iii) the nature of the chemical transformations that are performed — that is, reaction of small organic molecules, biomolecules, polymerizations, nanoparticle formation, and also reactions that involve the constituents of the matrix themselves as observed, for instance, in self‐reproducing systems. In each section, we combine original papers that paved the field together with more recent works of particular interest; several reviews are also referenced to help in accessing a more comprehensive literature.

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Reactivity Control by Aqueous Amphiphilic Self-Assembling Systems

Cited by 54 publications

References 0 publications

Micellar rate effects-assumptions and approximations

Micellar rate effects-assumptions and approximations

Introduction to Surfactant Self‐Assembly

Reactions in Dynamic Self‐Assemblies

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