COLL 153 |
| Three gemini surfactants with a non-Hückel diaza[12]annulene core were synthesized and examined by density functional theory, surface tension, conductivity, UV, 1H and 13C NMR, and PGSE NMR. The computations give a minimum-energy conformation with shorter bonds (averaging 1.33 Å) alternating with longer bonds (averaging 1.44 Å) and with the two N-substituents pointing away from each other. The latter feature renders intramolecular chain/chain contact in self-assemblies difficult. When the geminis aggregate in water, they form micelles with CMCs of 7.7 mM, 2.0 mM, and 0.55 mM for the didodecyl, ditetradecyl, and dihexadecyl derivatives, respectively. These are substantially higher than those of conventional geminis, a fact that indicates the annulene headgroups encounter packing difficulties at the micelle surface. UV spectra of the geminis at concentrations encompassing the CMCs show no evidence for ring/ring interactions at the micelle surface. Plots of 1H NMR shifts vs. ([gemini]/CMC)-1 for the terminal methyl group of the chains suggest the presence of transient contact between the methyl group and the annulene ring system. Diffusion coefficients from PGSE NMR experiments reveal that the annulene gemini micelles are similar in size and shape to those of simple mono-chained surfactants. |
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Fundamental Research in Colloid and Surface Chemistry
6:00 PM-8:00 PM, Monday, August 20, 2007 BCEC -- East Registration, Poster
Division of Colloid & Surface Chemistry |