Aberrant Aggregation Behavior in Cationic Gemini Surfactants Investigated by Surface Tension, Interfacial Tension, and Fluorescence Methods

Abstract

Bis(quaternary ammonium halide) surfactants (gemini surfactants) having, variously, diethyl ether, monohydroxypropyl, and dihydroxybutyl spacer groups have been investigated by surface tension, interfacial tension, and steady-state fluorescence techniques. The critical micelle concentration (cmc) and area per molecule (A min) are shown to deviate from the expected patterns of behavior as the number of carbon atoms in the alkyl chain (n) increases beyond a certain maximum. This aberrant behavior is observed at the hydrocarbon/water as well as the aqueous/air interface. The unexpected values of the physicochemical parameters at long alkyl chain length have been interpreted on the basis of a concentration region in which submicellar or multilayer structures are forming. Fluorescence measurements provide confirmation of cmc values by an alternative technique. Comparison of the fluorescence emission maxima profiles of the gemini surfactants with those of their monoquaternary analogues demonstrates that there is a continuously changing shape with change in n for the geminis, whereas the profiles for nongeminis are invariant. Long-chain geminis exhibit a gradually sloping sigmoidal profile, indicating a variety of environments experienced by pyrene-3-carboxaldehyde between the totally aqueous environment at low surfactant concentration and the hydrophobic (entirely micellar) environment at high surfactant concentration. The large variation in the polarity of the probe environment between these two extremes may be attributed to the formation of submicellar structures.

Synthesis and Biological Properties of Gemini Quaternary Ammonium Compounds, 5,5'-[2,2'-(.ALPHA.,.OMEGA.-Polymethylnedicarbonyldioxy)diethyl]bis-(3-alkyl-4-methylthiazolium iodide) and 5,5'-[2,2'-(p-Phenylenedicarbonyldioxy)diethyl]bis(3-alkyl-4-methylthiazolium bromide)

“…The gemini QACs possess a unique structure, a greater surface activity and greater antimicrobial potency than conventional mono-QACs. Chemists have studied their physicochemical properties [4][5][6] and greater effective antibacterial potency than the corresponding mono-QACs. [7][8][9] We have also described the syntheses of gemini QACs, which have two cationic pyridiniums, and discussed their antimicrobial activities and characteristics.…”

Diester-containing Zwitterionic Gemini Surfactants with Different Spacer and Its Impact on Micellization Properties and Viscosity of Aqueous Micellar Solution

“…This shows that influence of methyl group on spacer and chain branching brings about a decrease in cmc and γ cmc , a result that is not necessarily to be expected. As depicted in Table 1, all zwitterionic gemini surfactants decreases the surface tension to a great extent which is solely attributed to a tighter packing of the longer hydrophobic chains at air/water interface 25,26 .…”

Giant Micelles of Organoplatinum(II) Gemini Amphiphiles

“…They show the expected decrease with the increase in alkoxy chain length due to close packing of the longer chains. 75 The two probable orientations of the amphiphiles 5a and 5b during the initial rise are the "face-on" structure, in which the phenanthrene core lies parallel to the water interface, with the alkoxy tails extending into air, and the "edge-on" conformation, in which the phenanthrene core is normal to the interface, with the two hydrophilic Pt cations preferentially immersed in water. Although the occurrence of face-on conformational structures at the air-water interface have been previously indicated in amphiphilic group 10d metal complexes,48-50 their occurrence in the thin films of amphiphiles 5a and 5b are unlikely.…”