Solid-State 23Na NMR Study of Sodium Lariat Ether Receptors Exhibiting Cation- Interactions
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- 作者：David L. Bryce ; Samyuktha Adiga ; Elizabeth K. Elliott ; George W. Gokel
- 刊名：Journal of Physical Chemistry A
- 出版年：2006
- 出版时间：December 21, 2006
- 年：2006
- 卷：110
- 期：50
- 页码：13568 - 13577
- 全文大小：306K
- 年卷期：v.110,no.50(December 21, 2006)
- ISSN：1520-5215
文摘
Noncovalent cation-
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 beenacquired at three magnetic field strengths (9.4, 11.75, 21.1 T) and analyzed to provide key information on thesodium electric field gradient and chemical shift (CS) tensors which are representative of the cation- bindingenvironment. Triple-quantum MAS NMR spectra acquired at 21.1 T clearly reveal two crystallographicallydistinct sites in both 1 and 2. The quadrupolar coupling constants, CQ(23Na), range from 2.92 ± 0.05 MHzfor site A of 1 to 3.33 ± 0.05 MHz for site B of 2; these values are somewhat larger than those reportedpreviously 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 thatthe spans of the sodium CS tensors are less than 20 ppm for 1 and 2 and that the largest components of theEFG and CS tensors are non-coincident. Quantum chemical calculations of the NMR parameters substantiatethe experimental findings and provide additional insight into the dependence of CQ(23Na) on the proximity ofthe indole ring to Na+. Taken together, this work has provided novel information on the NMR interactiontensors characteristic of a sodium cation interacting with a biologically important arene.
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 beenacquired at three magnetic field strengths (9.4, 11.75, 21.1 T) and analyzed to provide key information on thesodium electric field gradient and chemical shift (CS) tensors which are representative of the cation- bindingenvironment. Triple-quantum MAS NMR spectra acquired at 21.1 T clearly reveal two crystallographicallydistinct sites in both 1 and 2. The quadrupolar coupling constants, CQ(23Na), range from 2.92 ± 0.05 MHzfor site A of 1 to 3.33 ± 0.05 MHz for site B of 2; these values are somewhat larger than those reportedpreviously 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 thatthe spans of the sodium CS tensors are less than 20 ppm for 1 and 2 and that the largest components of theEFG and CS tensors are non-coincident. Quantum chemical calculations of the NMR parameters substantiatethe experimental findings and provide additional insight into the dependence of CQ(23Na) on the proximity ofthe indole ring to Na+. Taken together, this work has provided novel information on the NMR interactiontensors characteristic of a sodium cation interacting with a biologically important arene.