Probing Heteronuclear ¹⁵N−¹⁷O and ¹³C−¹⁷O Connectivities and Proximities by Solid-State NMR Spectroscopy

Abstract

Heteronuclear solid-state magic-angle spinning (MAS) NMR experiments for probing (15)N-(17)O dipolar and J couplings are presented for [(2)H(NH(3)),1-(13)C,(15)N,(17)O(2)]glycine.(2)HCl and [(15)N(2),(17)O(2)]uracil. Two-dimensional (15)N-(17)O correlation spectra are obtained using the R(3)-HMQC experiment; for glycine.(2)HCl, the intensity of the resolved peaks for the CO and C-O(2)H (17)O resonances corresponds to the relative magnitude of the respective (15)N-(17)O dipolar couplings. (17)O-(15)N REDOR curves are presented for glycine.(2)HCl; fits of the initial buildup (DeltaS/S < 0.2) yield effective dipolar couplings in agreement with (+/-20%) the root-sum-squared dipolar couplings determined from the crystal structure. Experimental (15)N-(17)O REAPDOR curves for the (15)N resonances in glycine.(2)HCl and uracil fit well to the universal curve presented by Goldbourt et al. (J. Am. Chem. Soc. 2003, 125, 11194). Heteronuclear (13)C-(17)O and (15)N-(17)O 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.(2)HCl, (1)J(CO) was determined as 24.7 +/- 0.2 and 25.3 +/- 0.3 Hz for the CO and C-O(2)H resonances, respectively, while for uracil, the average of the two NH...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.(2)HCl and uracil, respectively. Excellent agreement was found with J couplings calculated using the CASTEP code using geometrically optimized crystal structures for glycine.HCl [(1)J(CO)(CO) = 24.9 Hz, (1)J(CO)(COH) = 27.5 Hz, (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].

Efficient rotational echo double resonance recoupling of a spin-1/2 and a quadrupolar spin at high spinning rates and weak irradiation fields

“…Because the curve is universal, it was shown that performing multiple experiments at various spinning rates provided data points that fit to the universal curve, and therefore increase the reliability of the experiment [17]. A couple of applications have demonstrated the usefulness of this approach [18,19]. Recently, an approach that combines rotary resonance recoupling (R 3 ) and spin-polarization-inversion (SPI-R 3 ) with TRAPDOR has been proposed [35].…”

Recent Advances in Solid‐State MAS NMR Methodology for Probing Structure and Dynamics in Polymeric and Supramolecular Systems

“…Fits to the spin I ¼ 5/2 REAPDOR master curve [142] that also take into account the partial (36%) 17 O labelling are also shown in Figure 10 [Reprinted with permission from ref. [123] Copyright (2002) build-up data have also recently been presented for glycine Á HCl and uracil: [143] good fits to the experimental data considering an effective dipolar coupling [144][145][146] were again obtained.…”

“….O hydrogen bonds in uracil. [143] As discussed above (see Figure 7), uracil packs as a layered structure with the individual molecules within each plane held together by two NH. Figure 15b, the average value of the two 2h J NO couplings was determined experimentally as 5.1 AE 0.6 Hz, in excellent agreement with those determined by a CASTEP [193] calculation, namely 6.1 and 4.6 Hz.…”

“…Figure 15b, the average value of the two 2h J NO couplings was determined experimentally as 5.1 AE 0.6 Hz, in excellent agreement with those determined by a CASTEP [193] calculation, namely 6.1 and 4.6 Hz. [143] Dynamics: Introduction…”

Insights into the spin dynamics of a large anisotropy spin subjected to long-pulse irradiation under a modified REDOR experiment

“…In REAPDOR the length of the pulse on the coupled-spin is extended to one-third of the rotor period and its efficiency and universality are maintained as long as the ratio x 2 1 =ðx R Á x Q Þ is large enough (x R represents the rotor spinning frequency). Since the REAPDOR curve is very weakly dependent on the actual value of the spinning speed, RF or quadrupolar frequency, it is very efficient and robust and can readily be applied to a variety of samples [10][11][12][13]. One of the main drawbacks of REAPDOR is the adiabaticity regime limit, which normally requires spinning speeds that are less than $10 kHz.…”