Abstract
A series of new gemini surfactants without a spacer group, disodium 2,3-dialkyl-1,2,3,4-butanetetracarboxylates, were synthesized in a green chemistry context minimizing the use of organic solvents and applying microwaves (MW) when activation energy was required. Once the desired architecture was confirmed by means of the nuclear magnetic resonance technique (1H-NMR, 1H-1H COSY) for all the studied surfactants, the critical micellization concentration was determined by conductance measurements. The diffusion coefficient of micelles formed by the four compounds was characterized using pulsed field gradient (PFG)-NMR. Diffusion coefficients were found to be dependent on the concentration and on the number of carbon atoms in the alkyl chain. The absence of the spacer group, peculiar to this new series of gemini surfactants, may confer relatively low flexibility to the molecules, with potential implications on the interfacial properties, namely on micellization. These gemini surfactants might have interesting applications in the preparation of composite materials, in nanotechnology, in gene transfection and mainly, due to the low CMCs, as new interesting ingredients of cosmetics and toiletries.
Highlights
In recent years, research has been widely carried out on gemini surfactants, due to their advantages over monomeric surfactants with respect to different applications
The critical micelle concentration (CMC) of gemini surfactants is typically one or two orders of magnitude lower than the one of the corresponding monomeric surfactant [1,2]; this feature may be related to the lower environmental impact of the molecule, because a much smaller quantity will be required to perform the same function when compared to conventional surfactants
Novel molecular architectures differing with regard to the polar head groups, the hydrocarbon chains and the type and size of the spacers have been proposed [9,10]. Taking into account these previous statements, our attention has focused on a specific anionic gemini surfactant lacking the spacer group, namely, disodium 2,3-didodecyl-1,2,3,4butanetetracarboxylate [11] (4c), whose CMC and phase behavior have already been reported in the literature [12,13]
Summary
Research has been widely carried out on gemini surfactants, due to their advantages over monomeric surfactants with respect to different applications. Novel molecular architectures differing with regard to the polar head groups, the hydrocarbon chains and the type and size of the spacers have been proposed [9,10] Taking into account these previous statements, our attention has focused on a specific anionic gemini surfactant lacking the spacer group, namely, disodium 2,3-didodecyl-1,2,3,4butanetetracarboxylate [11] (4c), whose CMC and phase behavior have already been reported in the literature [12,13]. Its usage has increased considerably over the past decade with the introduction of reasonably linear, self-shielded gradient coils in high resolution NMR probes This makes it relatively straightforward to obtain quantitative translational diffusion coefficients for a wide variety of diffusing objects, ranging from solvent molecules to large particles or aggregates. The recorded data have been analyzed for a specific characterization of these new molecules with regard to the potential applications in various fields, especially the cosmetic one
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