Dodecylammonium propionate

The strong interactions between the water molecules also become obvious from NMR measurements by Tsujii et al..57) 13C-NMR experiments were used for determining the microviscosity of water in reversed micelles of dodecylammonium-propionate with 13C glycine cosolubilized. It was found that the apparent viscosity of the water-pool corresponds to the viscosity of a 78 % aqueous glycerol solution, obviously as a consequence of the extended network formation by strong hydrogen bonding. 

The monomer to inverse micelle transition of dodecylammonium propionate (DAP) in CH2G2 was monitored by tire shifts in the COO bands. Addition of water caused further decreases in the COO- band frequency due to headgroup hydration. Micelle formation in hexane yielded similar spectroscopic changes (83). Frequency shifts induced by hydrogen bonding to water in the inverse micelle core were illustrated for phosphonate, carboxylate, and sulfate headgroups (84). 

An inverse (or reverse) micelle, which forms in a non-polar solvent, will have the hydrophilic head groups oriented toward the inside of the sphere, where a water pool is formed and a hydrophilic probe can become associated [10]. Some surfactants commonly employed to stabilize reverse micelles include sodium diisooctylsulfosuccinate (AOT), benzylhexadecyldimethylammonium chloride (BHDC), and dodecylammonium propionate (DAP). Ionic surfactants induce formation of a larger water pool than non-ionic surfactants, but the size of the hydrophilic core also depends on temperature and on the ratio of water to surfactant. 

The rates of intermolecular proton-transfer reactions can be studied using similar techniques (Escabi-Perez and Fendler, 1978 Huppert el al., 1981 Hagopian and Singer, 1983 Webb et al., 1984). In an interesting example involving nanosecond time-resolved fluorescence, the rate of protonation of the excited state of pyrene-1-carboxylate (PyCO 2) was compared in aqueous solution and in a reversed micelle of 0.1 mol dm" dodecylammonium propionate with 0.55 mol dm" water in benzene (Escabi-Perez and Fendler,... 

FIG. 10 Regulation of the catalytic activity of solubilized enz5unes by variation of the surfactant concentration at a constant degree of hydration in the systems ( ) AOT-water-octane (A) dodecylammonium propionate-water-riiethyl ether/benzene (O) Brij 96-water-cyclohexane ( ) lecithin-water/methanol/pentanol-octane. Dashed lines show levels of corresponding catalytic activities in aqueous solution. (From Ref. 10.)... 

In the system dodecylammonium propionate-benzene-water, only the neutral spin probe is partitioned between benzene and water, whereas the anionic and cationic spin probes are essentially solubilized in water [84]. 

Solubilizate binding constants have been determined for a few reverse micelle -small molecule (phenols, imidazole, simple alcohols) combinations [60, 63, 64]. In the case of imidazole binding to dodecylammonium propionate (DAP) reverse micelles, the use of the chemical shift dependence on DAP concentration for imidazole protons led to nonunique (i. e., proton-dependent) binding constants, a physically unreasonable situation [64]. When one is studying chemical reactions involving reactants which partition among the water pools, with the surfactant layer on the... 

The aminolysis of 4-nitrophenyl acetate in reversed micelles of dodecyl-ammonium propionate (DAP) is dependent upon the chain length of the amine and shows a rate increase of up to 50-fold compared with that in the absence of surfactant, which is attributed to catalysis by the surfactant The addition of water decreases the observed rates owing to hydration of the dodecylammonium propionate head groups. In the presence of bis(2-ethylhexyl) sodium sulpho-succinate the rate of hydrolysis of 4-nitrophenyl carboxylates catalysed by A -methylimidazole decreases with increasing chain length of the ester group and increases as a function of added water reflecting the importance of distribution of the reactants between the bulk solvent and the micellar water pool . ... 

From a thermodynamic point of view, self-aggregation of amphiphilic molecules in apolar solvents involves a favorable enthalpic term due to intermolecular bonding counteracted by an unfavorable entropic term due to a partial loss of molecular translational and rotational degrees of freedom. Using vapor pressure osmometry, for example, it has been found that the enthalpies of formation of molecular aggregates of dodecylammonium propionate in benzene and cyclohexane are 83.4 kJ/mol and -57.4 kJ/mol, whereas the entropy changes for the same processes are -0.23 kJ/mol and -0.14 kJ/mol, respectively [2]. 

A very complex behavior has been reported for the aquation of [Cr(ox)3] ion in the reversed micellar systems benzene—dodecylammonium propionate or octylammonium tetradeconoate containing solubilized water. The results differ markedly from an earlier investigationand the reasons for the discrepancy and the complex rate behavior is not clear. 

Fig. 5.8. A proposed model for the ultrafast proton transfer at the hydration shell of the surfactant headgroups in reversed micellar DAP in benzene. Since the concentration of surfactant is in a very large excess over the probe, proton transfer must occur from dodecylammonium propionic acid to pyrene-1-carboxylate. For the sake of clarity, two pyrene moieties are drawn in the aggregate shown. In reality, there is much less than one probe per aggregate. The shaded area indicates the extent water which hydrates the surfactant headgroups (161). Reprinted with permission. Copyright 1978 by the...

The solubilization of dimethyl sulphoxide, imidazole, methanol, pyrazole, 2-pyridone and tetrabutylammonium perchlorate by dodecylammonium propionate in benzene, deuterochloroform and dichloromethane has been investigated using proton n.m.r. techniques [219]. The results suggest that hydrogen bonding is of primary importance for strong binding in these systems but weaker forces such as dipole-dipole interactions may also be of importance. 

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