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Author(s)
     David L. Bryce, Samyuktha Adiga, Elizabeth K. Elliott, George W. Gokel
Title
     Solid-State 23Na NMR Study of Sodium Lariat Ether Receptors Exhibiting Cation-pi Interactions
Publication Name
     Journal of Physical Chemistry A
Publication Type
     Journal
Publisher
     ACS
Place
     
Editor(s)
     
Number
     
School
     
Volume
      110
Chapter
     
Pages
      13568-13577
Other Publication Information
     
Publication Year
     2006
Abstract
     Noncovalent cation-pi interactions are important in a variety of supramolecular and biochemical systems. We present a 23Na solid-state nuclear magnetic resonance (SSNMR) study of two sodium lariat ether complexes, 1 and 2, in which a sodium cation interacts with an indolyl group that models the side chain of tryptophan. Sodium-23 SSNMR spectra of magic-angle spinning (MAS) and stationary powdered samples have been acquired at three magnetic field strengths (9.4, 11.75, 21.1 T) and analyzed to provide key information on the sodium electric field gradient and chemical shift (CS) tensors which are representative of the cation- binding environment. Triple-quantum MAS NMR spectra acquired at 21.1 T clearly reveal two crystallographically distinct sites in both 1 and 2. The quadrupolar coupling constants, CQ(23Na), range from 2.92 0.05 MHz for site A of 1 to 3.33 0.05 MHz for site B of 2; these values are somewhat larger than those reported previously by Wong et al. (Wong, A.; Whitehead, R. D.; Gan, Z.; Wu, G. J. Phys. Chem. A 2004, 108, 10551) for NaBPh4, but very similar to the values obtained for sodium metallocenes by Willans and Schurko (Willans, M. J.; Schurko, R. W. J. Phys. Chem. B 2003, 107, 5144). We conclude from the 21.1 T data that the spans of the sodium CS tensors are less than 20 ppm for 1 and 2 and that the largest components of the EFG and CS tensors are non-coincident. Quantum chemical calculations of the NMR parameters substantiate the experimental findings and provide additional insight into the dependence of CQ(23Na) on the proximity of the indole ring to Na+. Taken together, this work has provided novel information on the NMR interaction tensors characteristic of a sodium cation interacting with a biologically important arene.
Keywords
     
Website
     http://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/jp065171q
Paper Status
     Published
DOI / Publication ID
     



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