1H NMR Studies of Aerosol-OT Reverse Micelles with Alkali and Magnesium Counterions: Preparation and Analysis of MAOTs
journal contributionposted on 17.06.2008 by Michelle L. Stahla, Bharat Baruah, Dustin M. James, Michael D. Johnson, Nancy E. Levinger, Debbie C. Crans
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Simple procedures and characterization of a series of well-defined precursors are described for preparation of a unique microenvironment in nanoreactors, reverse micelles. The Na+, K+, Rb+, Cs+, and Mg2+ surfactants were prepared using liquid–liquid ion exchange using chloride and nitrate salts. The surfactants were characterized using 1H NMR spectroscopy and a variety of other techniques. 1H NMR spectroscopy was found to be a sensitive probe for characterization of the size of the nanoreactor as well as its water content. 1H NMR spectra can be used for detailed characterization of reactions in confined environments when counterion effects are likely to be important. 1H NMR spectroscopy revealed two separate peaks corresponding to water in Mg(AOT)2 samples; one peak arises from water coordinated to the Mg2+ ion while the other peak arises from bulk water. The two water signals arise directly from the slow exchange of the water coordinated to Mg2+ in these microemulsions with water in the water pool, and provide an opportunity to study hydration of Mg2+. This work thus extends the potential use of MAOT microemulsions for applications such as in green chemistry.