Probing heteronuclear N-15-O-17 and C-13-O-17 connectivities and proximities by solid-state NMR spectroscopy

Hung, Ivan and Uldry, Anne-Christine and Becker-Baldus, Johanna and Webber, Amy L. and Wong, Alan and Smith, Mark E. and Joyce, Sin A. and Yates, Jonathan R. and Pickard, Chris J. and Dupree, Ray and Brown, Steven P. (2009) Probing heteronuclear N-15-O-17 and C-13-O-17 connectivities and proximities by solid-state NMR spectroscopy. Journal of the American Chemical Society, 131 (5). pp. 1820-1834. ISSN 1520-5126

Abstract

Heteronuclear solid-state magic-angle spinning (MAS) NMR experiments for probing N-15-O-17 dipolar and J couplings are presented for [H-2(NH3),1-C-13,N-15,O-17(2)]glycine center dot(HCl)-H-2 and [N-15(2), O-17(2)]uracil. Two-dimensional N-15-O-17 correlation spectra are obtained using the R-3-HMQC experiment; for glycine center dot(HCl)-H-2, the intensity of the resolved peaks for the C=O and C-(OH)-H-2 O-17 resonances corresponds to the relative magnitude of the respective N-15-O-17 dipolar couplings. O-17-N-15 REDOR curves are presented for glycine center dot(HCl)-H-2; fits of the initial buildup (Delta S/S <0.2) yield effective dipolar couplings in agreement with (+/- 20%) the root-sum-squared dipolar couplings determined from the crystal structure. Experimental N-15-O-17 REAPDOR curves for the N-15 resonances in glycine center dot(HCl)-H-2 and uracil fit well to the universal curve presented by Goldbourt et al. (J. Am. Chem. Soc. 2003, 125,11194). Heteronuclear C-13-O-17 and N-15-O-17 J couplings were experimentally determined from fits of the quotient of the integrated intensity obtained in a heteronuclear and a homonuclear spin-echo experiment, S-Q(tau) = S-HET(tau)/S-HOM(tau). For glycine center dot(HCl)-H-2, (1)J(CO) was determined as 24.7 +/- 0.2 and 25.3 +/- 0.3 Hz for the C=O and C-(OH)-H-2 resonances, respectively, while for uracil, the average of the two NH center dot center dot center dot O hydrogen-bond-mediated J couplings was determined as 5.1 +/- 0.6 Hz. In addition, two-bond intramolecular J couplings, (2)J(OO) = 8.8 +/- 0.9 Hz and (2)J(N1,N3) = 2.7 +/- 0.1 Hz, were determined for glycine center dot(HCl)-H-2 and uracil, respectively. Excellent agreement was found with J couplings calculated using the CASTEP code using geometrically optimized crystal structures for glycine center dot HCl [(1)J(CO)(C=O) = 24.9 Hz, (1)J(CO)(C-OH) = 27.5 H Z, (2)J(OO) = 7.9 Hz] and uracil [(2h)J(N1,O4) = 6.1 Hz, (2h)J(N3,O4) = 4.6 Hz, (2)J(N1,N3) = 2.7 Hz].