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Abstract
When certain macrocyclic anion receptors are added to a chloroform solution of the nitrate form of a lipophilic quaternary ammonium salt (methyltri-C8,10-ammonium nitrate, Aliquat 336N), the extraction of sulphate from an aqueous sodium nitrate solution via exchange with the organic-phase nitrate is significantly enhanced. Eight macrocycles were surveyed, including two derivatives of a tetraamide macrocycle, five derivatives of calix[4]pyrrole and β-decafluorocalix[5]pyrrole. Under the hypothesis that the enhancement originates from sulphate binding by the anion receptors in the chloroform phase, it was possible to obtain reasonable fits to the sulphate distribution survey data based on the formation of 1:1 and 2:1 receptor:sulphate complexes in the chloroform phase. Apparent 1:1 sulphate-binding constants obtained from the model in this system fell in the range . Comparison of the results for the various anion receptors included in this study reveals that sulphate binding is sensitive to the nature of the substituents on the parent macrocycle scaffolds in a way that does not follow straightforwardly from simple chemical expectations, such as electron-withdrawing effects on hydrogen-bond donor strength.
Acknowledgements
Research at Oak Ridge National Laboratory (ORNL) was sponsored by the Division of Chemical Sciences, Geosciences and Biosciences, Office Basic Energy Sciences, US Department of Energy. Research at the University of Texas at Austin was supported by the US Department of Energy (Grant Nos DE-FG02-04ER63741 and DE-FG02-01ER15186 to J.L.S.). Work at the University of Kansas was supported by US Department of Energy (Grant No. DE-FG02-04ER63745 to K.B.-J.) and the National Science Foundation (Grant No. CHE-0316623 to K.B.-J.). M.M. gratefully acknowledges partial funding for this work from University of Malaga (Junta de Andalucia), Project P09-TEP-5369 in collaboration with Prof. Ignacio Loscertales.
Notes
3. Email: [email protected]
6. Email: [email protected]
1. Present address: Congden Hall 338, High Point University, 833 Montlieu Ave., High Point, NC 27262, USA.
2. Present address: Department of Chemistry, Jackson State University, 1325 Lynch St, Jackson, MS 39217, USA.
4. Present address: Central College, 812 University St, Pella, IA 50219, USA.
5. Present address: YNano LLC, 14148 Riverdowns S. Dr, Midlothian, VA 23113, USA.
