Abstract:The time-resolved fluorescence quenching method was applied to determine the micelle aggregation number of cationic single-chain surfactants dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS). The concentration dependence of micelle aggregation number was found to be linear for all investigated surfactants in the concentration range 2-15 × the value of critical micelle concentration of the respective surfactant. The values of micelle aggregation number were found in the range 30-77. Different trends in the linear concentration dependence of micelle aggregation number were observed for cationic surfactants and for the anionic surfactant SDS. A small slope value was found for cationic surfactants, while the SDS micelle aggregation number concentration dependence showed significantly a larger slope value. The aggregation number increase with the increasing SDS concentration results in the micellar growth. Results from a simple analysis based on computer models of cationic and anionic surfactant molecules with dodecyl chains supports, the formation of intramicellar hydrogen bonding between surfactant molecules in SDS micelle shell.

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with the maximum antimicrobial activity found at the spacer length of 6 CH2 groups for bacteria and 8 CH2 groups for fungi. This is related to a different composition of cell membrane of the used microorganisms.

Cationic gemini surfactants with polymethylene spacer and linear alkyl chains containing an even number of carbon atoms have been extensively studied in the recent past, with the emphasis put on the determination of their aggregation behaviour in aqueous solution and their biological properties. However, the information on the aggregation of branched gemini surfactants with an odd number of carbon atoms in their alkyl chains is only sparsely reported in the literature. To help cover this gap in the research of cationic gemini surfactants, a series of branched bisammonium cationic gemini surfactants with an odd number of carbon atoms in alkyl chains (tridecane-2-yl chains) and a polymethylene spacer with a variable length ranging from 3 to 12 carbon atoms have been synthesized and investigated. Critical micelle concentration, which was determined by three methods, was found to be in the order 10−4 mol/L. A comparison of the obtained data of the novel series of tridecyl chain geminis with those of gemini surfactants with dodecyl chains and an identical spacer structure revealed that structural differences between both series of gemini surfactants result in different aggregation and surface properties for surfactants with 6 and 8 methylene groups in the spacer (N,N’-bis(tridecane-2-yl)-N,N,N’,N’-tetramethylhexane-1,6-diaminium dibromide and N,N’-bis(tridecane-2-yl)-N,N,N’,N’-tetramethyloctane-1,8-diaminium dibromide) with the cmc values 8.2 × 10−4 mol/L and 6.5 × 10−4 mol/L, respectively, as determined by surface tension measurements. Particle size analysis showed the formation of small stable spherical micelles in the interval between 2.8 and 5 nm and with zeta potential around +50 mV, which are independent of surfactant concentration and increase with the increasing spacer length. Microbicidal activity of 13-s-13 gemini surfactants was found to be efficient against Gram-positive, Gram-negative bacteria and yeast.

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