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This paper presents the synthesis and a study of the aggregation behavior of 4-undecyl-1-methyl- and 4-undecenyl-1-methylpyridinium iodide surfactants. The effect of the position of the double bond in the alkyl chain of the surfactant on the critical micelle concentration (cmc), degree of counterion binding (β), Krafft temperature, and thermodynamic parameters of micelle formation has been investigated. Also, a pyridinium surfactant with a triple bond in the alkyl chain has been studied. The cmc values of the surfactants increase after the introduction of a double bond or a triple bond in the tail as compared to the saturated equivalents. The largest effect was observed for surfactants with a cis-oriented double bond in the alkyl chain. The enthalpies of micelle formation (ΔH°) were shown to be exothermic. Introduction of an unsaturation in the tail leads to an increase of the enthalpy of micelle formation. The largest effect is observed for 4-(1-undecynyl)-1-methylpyridinium iodide. The influence of a double bond in the tail of the surfactants on the absorption spectrum of methyl orange (MO) complexed to the surfactant was studied by UV-vis spectroscopy. Low concentrations of 4-alkyl-1-alkylpyridinium amphiphiles induce a new, ca. 80-nm, blue-shifted band. However, the surfactants 4-(10-undecenyl)-1-methylpyridinium iodide, 4-(5-cis-undecenyl)-1-methylpyridinium iodide, and 4-(5-trans-undecenyl)-1-methylpyridinium iodide do not induce this absorption band at short wavelengths. In contrast, 4-(1-undecenyl)-1-methylpyridinium iodide and 4-(1-undecynyl)-1-methylpyridinium iodide showed this short wavelength absorption band positioned at 383 nm.

The aggregation behavior of a series of alkyltrimethylammonium 5-ethylsalicylate surfactants (CnTA5ES, n = 12, 14, 16) in aqueous solution has been investigated employing turbidity measurements, fluorescence anisotropy experiments (using 3-hydroxynaphthalene-2-carboxylate, HNC-), and cryo transmission electron microscopy (cryo TEM). Critical aggregation concentrations (cac) were determined by surface tension experiments; they are smaller than those of their salicylate analogues. CnTA5ES surfactants form vesicles immediately above the cac rather than wormlike micelles such as their salicylate counterparts. C12TA5ES was found to form large unilamellar vesicles (LUVs) which transformed into surfactant layers upon increasing surfactant concentration. The transition was characterized by an increase in turbidity. C14TA5ES and C16TA5ES were found to form LUVs and long wormlike vesicles which are assumed to be responsible for the viscoelasticity of the solutions. Upon increase of the surfactant concentration, a t...

Herein we describe the synthesis and aggregation of the sodium salts of a series of 5-alkyl-2-hydroxy-1,3,2-dioxaphosphorinan-2-ones and 5,5-dialkyl-2-hydroxy-1,3,2-dioxaphosphorinan-2-ones in aqueous solution. The results are compared with properties of previously studied sodium di-n-alkyl phosphates. The single-tailed surfactants (6a, b, g) form micelles whereas the double-tailed ones (6f, h-k) form vesicles, as revealed by transmission electron microscopy (TEM). Critical micelle concentrations (CMC) for 6a, b, g were determined using different techniques: UV spectroscopy, microcalorimetry, and conductometry. Phase transition temperatures of the bilayers were measured by differential scanning calorimetry (DSC) and by fluorescence depolarization. Fusion of the vesicles was studied employing the resonance energy transfer (RET) assay based on lipid mixing and TEM. Vesicles of 6h-k fuse upon addition of Ca2+ or Mg2+ ions, to almost the same extent in each case. Fusion only takes place above the phase transition temperature (T-c) of the different bilayers. The threshold concentrations of Ca2+ and Mg2+ ions for fusion of the different vesicles are below 0.1 mM. The initial rate of fusion is high and precludes the measurement of accurate rate constants. Upon addition of calcium chloride different processes occur. Vesicle fusion, crystallization, and formation of multilamellar sheets were observed, as was apparent from experiments with vesicles formed from 6h. Leakage through the vesicular bilayer of 6h was determined by measuring the carboxyfluorescein release from the aqueous compartment of the vesicles, All data are consistent with the notion that the alkyl chain packing in the bilayers of the vesicles formed from the cyclic phosphates is less efficient than that in the bilayers of vesicles composed of di-n-alkyl phosphates.

Interactions between the azobenzene-containing amphiphile methyl octyl orange (MOO) and n-alkyltrimethylammonium bromides (CnTAB, n = 1, 6, 8, 10, 12, 16) in aqueous solution have been studied using UV−vis spectroscopy. Interactions occur at concentrations below the critical micelle concentrations of the individual cationic surfactants (n = 8, 10, 12, 16) as indicated by a ca. 80 nm blue shift of the main absorption band of MOO. In addition, aggregation of MOO with C6TAB, which is a hydrotrope rather than a surfactant, was also observed. The critical aggregation concentration (cac) of MOO determined by surface tension experiments was 0.68 mM. The cac's of aqueous mixtures of CnTAB and MOO (1:1) were considerably lower than those of the individual surfactants. The absorption spectrum of MOO at concentrations above the cac in the 1:1 mixtures was also blue shifted with respect to the absorption spectrum of MOO in aqueous solution. Vesicular aggregates formed in equimolar aqueous mixtures of CnTAB and MOO we...

The aggregation of a series of n-alkyltrimethylammonium bromide (CnTAB, n = 10, 12, 14, 16, and 18) and 4-n-alkyl-1-methylpyridinium iodide amphiphiles (CmpyI, m = 8, 10, 12, and 14) induced by low concentrations of azo dyes in aqueous solution has been investigated by means of ultraviolet (UV) spectroscopy. It was observed that aggregation takes place at surfactant concentrations far below the cmc of C12TAB, C14TAB, C16TAB, and C18TAB with methyl orange (MO), ethyl orange (EO), and para-methyl red (pMR). Aggregation below the cmc of C10TAB was also induced by EO. In the case of MO and pMR, however, higher dye concentrations were necessary to induce aggregation. Interactions at low surfactant concentrations have also been observed in aqueous solutions of C10pyI, C12pyI, and C14pyI with MO. Binding of methyl red (MR), methyl yellow (MY), and azobenzene sulfonate (ABS) with cationic surfactants below their cmc did not occur. Aggregation was reflected by the appearance of a blue-shifted absorption band in th...