Surfactants dissociation reaction

Vj stoichiometric coefficients of the dissociation reaction of a surfactant molecule V total number of ions (including micelles) arising as a result of dissociation of a surfactant molecule... 

The lanthanide complexes lack distinct ultraviolet-visible spectra and, hence, kinetic information on their complex formation and dissociation reactions was obtained indirectly by the metallochromic indicator method. These studies indicate that in the case of the Cyanex 272 complexes, the CPC efficiencies are mainly limited by the slow dissociation of the M(HL2)HL complex at the heptane-H20 interface. In the case of the complexes of the acylpyrazolones, the CPC efficiencies are again limited by the dissociation of the lanthanide-pyrazolone complexes at the organic-aqueous interface with the rate-limiting step being the dissociation of the ML complex. It was also shown that because the dissociation reactions are interfacial separations, efficiencies can be dramatically improved by the addition of surfactants like Triton X-100 to the organic phase and by... 

The central assumption in the AW treatment is that micelles form and break down via a series of stepwise asso-ciation/dissociation reactions (4.1) where one surfactant S at a time associates to aggregate or dissociates from aggregate Sg (s and s-1 are the numbers of surfactant making up aggregates Sg and Sg i). These reactions are also referred to as entry/exit or insertion/expulsion reactions ... 

Oshima et al. explored a cationic rhodium-catalyzed intramolecular [4+2] annulation of l,3-dien-8-ynes in water in the presence of sodium dodecyl sulfate (SDS), an anionic surfactant.132 When the substrate l,3-dien-8-yne was a terminal alkyne, the reaction provided an inter-molecular [2+2+2] product (Eq. 4.68). In water, a reactive cationic rhodium species was formed by the dissociation of the Rh-Cl bond in the presence of SDS. The SDS forms negatively charged micelles, which would concentrate the cationic rhodium species (Scheme 4.15). 

The CL enhancement of the lucigenin reaction with catecholamines in the presence of HTAH micelles was used for determination of dopamine, norepinephrine, and epinephrine [42], However, the presence of an anionic surfactant, SDS, inhibits the CL of the system. The aforementioned CL enhancement in the presence of HTAH can be explained in the following way the deprotonated forms of the catecholamines are expected to be the principal species present in aqueous alkaline solution due to the dissociation of the catechol hydroxyl groups, and to react with lucigenin to produce CL. The anionic form of the catecholamines and the hydroxide ion interact electrostatically with and bond to the cationic micelle, to which the lucigenin also bonds. Therefore, the effective concentration of the... 

The rate constants and k represent rate constants for a surface reaction and have units m mol s and s respectively. The accelerative effects are about 10 -10 fold. They indicate that both reactants are bound at the surface layer of the micelle (surfactant-water interface) and the enhanced rates are caused by enhanced reactant concentration here and there are no other significant effects. Similar behavior is observed in an inverse micelle, where the water phase is now dispersed as micro-droplets in the organic phase. With this arrangement, it is possible to study anion interchange in the tetrahedral complexes C0CI4 or CoCl2(SCN)2 by temperature-jump. A dissociative mechanism is favored, but the interpretation is complicated by uncertainty in the nature of the species present in the water-surfactant boundary, a general problem in this medium. 

A pseudophase ion exchange model has been applied to reactions in micellar systems with varying success (1-7). According to this model, the distribution of nucleophile is considered to depend on the ion-exchange equilibrium between the nucleophile and the surfactant counterion at the micelle surface. This leads to a dependence on the ion-exchange constant (K g) as well as on the degree of dissociation (a) of the surfactant counterion. The ion exchange (IE) model has recently been extended to oil in water microemulsions (8). 

Surfactants having an appropriate hydrophobic/hydrophilic balance (sodium bis(-2-ethylhexyl)sufosuccinate, or AOT, for example) undergo concentration-dependent self association in apolar solvents to form reversed or inverted micelles (Fig. 33) [256-262]. Reversed micelles are capable of solubilizing a large number of water molecules (AOT reversed micelles in hexane are able to take up 60 water molecules per surfactant molecule, for example). Reversed-micelle-entrapped water pools are unique they differ significantly from bulk water. At relatively small water-to-surfactant ratios (w = 8-10, where w = [H20]/[Surfactant]), all of the water molecules are strongly bound to the surfactant headgroups. Substrate solubilization in the restricted water pools of reversed micelles results in altered dissociation constants [256, 257, 263-265], reactivities [256, 258, 266], and reaction products [267]. 

Dihydropyridine 129 has been shown to catalyze Michael reactions in aqueous cationic micelles of cetyltri-methylammonium bromide (Scheme 34) <2003CL1064>. In the micelles, dihydropyridine 129 ionizes to form an acetophenone enolate salt 130. The highly basic enolate deprotonates the Michael donor which then rapidly reacts with the Michael acceptor. The use of anionic surfactants did not promote Michael reactions, suggesting that the cationic micelles promote the dissociation of salt 130. 

Why is it that the preadsorbed surfactant layer on the electrode (e.g., the DDAB), has such a helpful effect in facilitating the reactions of enzymes on electrodes For one thing, the surfactant is a good adsorber on the metal or graphitic electrode. Correspondingly, if, upon adsorption, there is some partial dissociation of the complex enzyme, the preadsorbed surfactant makes it difficult for such fragments to build up passive layers on the electrode, layers that could diminish electron transfer. 

H -tetramethylbenzidine in anionic-cationic mixed micelles has been studied in detail by ESR . The photochemistry of the semi-oxidised forms of eosin Y and rose bengal have been investigated in colloidal solutions. Relevant to the fluorescence of proteins is a study of fluorescence quenching of indolic compounds by amino-acids in SOS, CTAB, and CTAC micelles O Rate constants for proton transfer of several hydroxyaromatic compounds have been measured in a variety of surfactant solutions. Photoprotolytic dissociation does not require exit of the reactant molecules from the micelles. Micellar solutions can be used to improve the fluorescence determination of 2-naphthol by inhibiting proton transfer or proton inducing reactions z2. jpe decay of the radical pair composed of diphenylphosphonyl and 2,4,6-trimethyl benzoyl radicals in SDS is affected by magnetic... 

In cases where the particle charge is the result of adsorption of ionic surfactants, its sign depends on the absorbability of the surfactant cation and aifion. The most probable mechanism as elucidated by Fowkes and Pugh is the adsorption of the surfactant as an ion pair (neutral molecule) followed by a proton exchange reaction the direction of which depends on the relative acidity/basicity of the surfactant and the surface. The final step in the charge generation process is the dissociation... 

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