Self-Assembly in Mixtures of Sodium Alkyl Sulfates and Alkyltrimethylammonium Bromides:  Aggregation Behavior and Catalytic Properties

Abstract

Two aqueous mixtures of cationic and anionic surfactants have been studied by means of conductometry, transmission electron microscopy, and microcalorimetry. Their catalytic effects on the decarboxylation of the kinetic probe 6-nitrobenzisoxazole-3-carboxylate (6-NBIC) were also examined in some detail. The mixtures differ profoundly in the hydrophobic match between both surfactant tails, which is perfect for dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulfate (SDS) and poor for hexadecyltrimethylammonium bromide (CTAB) and sodium heptyl sulfate (SHS). This difference is reflected in the more pronounced synergism in critical aggregation concentration and catalytic efficiency of the DTAB/SDS mixture and in the phase behavior of the mixtures. CTAB and SHS can be mixed in a 1:1 ratio without precipitation, forming both small, unilamellar and large, multilamellar vesicles. In DTAB/SDS mixtures, however, precipitation of the catanionic surfactant occurs for a mole fraction of DTAB (x) between 0.3 and 0.7, while both vesicles and large bilayer fragments are formed for x = 0.8. The excess of DTAB in the x = 0.8 mixture results in the solubilization of the vesicles by DTAB micelles close to the cmc of pure DTAB. A network of interconnected threadlike cylindrical micelles was found as an intermediate stage of aggregation between the vesicles and the mixed micelles. These cylindrical micelles are formed exclusively on further increasing the surfactant concentration.

Compositional genomes: Prebiotic information transfer in mutually catalytic noncovalent assemblies

“…comparable to those observed for accelerated vesicle formation (31,49) and other lipid catalysis reactions (50)(51)(52). For computer simulations of the dynamics of such molecular assemblies, we use chemical kinetics rules based on the previously proposed Graded Autocatalysis Replication Domain (GARD) model (38,39).…”

Influence of Long-Tailed Alcohols on the Solubilisation of Cationic DHAB Bilayers

“…These compounds induce rate constants of an order of magnitude of 10 -3 s -1 [34][35][36]. In addition, the k obs found for cationic micelles formed from nhexadecyltrimethylammonium bromide (CTAB) at 30°C is in the order of magnitude of 10 -4 s -1 [25,37], which is comparable with the k obs found for DHAB at 35°C. Comparable k obs values at a temperature of 30° C are also found for vesicles containing different amounts of di-noctadecyldimethylammonium chloride (DODAC) [28].…”

“…Here we report the kinetic effects of two types of DHAB/C n OH (n= 10, 16) mixtures on the unimolecular decarboxylation of 6-nitrobenzisoxazole-3-carboxylate (6-NBIC) (Scheme 1). This kinetic probe has been widely used in biophysical studies and is sensitive to the local micropolarity [23][24][25][26], which makes it a proper model reaction for investigation of composition changes in membranes. In addition, the reaction is also highly sensitive to hydrogen-bonding interactions which stabilize 6-NBIC by forming hydrogen-bonds with the carboxylate group [23][24][25][26].…”

Vesicular catalysis of the decarboxylation of 6‐nitrobenzisoxazole‐3‐carboxylate. The effects of sugars, long‐tailed sugars, cholesterol and alcohol additives

“…6 It has been shown that such vesicles can accelerate the 6-NBIC reaction by approximately 30% compared to cationic micelles. 7 Synthetic cationic vesicles are also 4-15times more efficient for the decarboxylation than phospholipid vesicles. 8 The interaction between the cationic head group and the 6-NBIC anion promotes binding at the vesicular interface, thereby decreasing the number of hydrogen bonding opportunities between water and the substrate, with a concomitant increase of the rate constant.…”