High-Resolution Heteronuclear Correlation between Quadrupolar and Spin-12 Nuclei Using Multiple-Quantum Magic-Angle Spinning
✍ Scribed by S.H. Wang; S.M. De Paul; L.M. Bull
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 242 KB
- Volume
- 125
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
Heteronuclear correlation (HETCOR) NMR spectroscopy
To achieve high resolution for quadrupolar nuclei in a has been used in both liquid and solid states to provide HETCOR experiment, it is necessary to construct an isoinformation on the proximity of different nuclei in a complex tropic t 1 dimension. Until recently, this construction was only spin system (1-5). In the solid state, the experiment is achieved by dynamic-angle spinning (8). A high-resolution generally carried out under magic-angle-spinning (MAS) HETCOR spectrum of sodium trimetaphosphate (Na 3 P 3 O 9 ) conditions, which average away the line broadening due to was measured by applying appropriate RF pulses to 23 Na chemical-shift anisotropy and heteronuclear dipolar coupling while spinning the sample sequentially around angles of (3). Although HETCOR experiments involving half-integer 79.19Њ and 37.38Њ with respect to the B 0 field during t 1 . The quadrupolar nuclei have been performed on certain systems evolution times at the first and second angles were chosen (6, 7), the resolution in the quadrupolar dimension of a such that an isotropic echo was formed at the end of the t 1 HETCOR spectrum is often poor since the second-order evolution period. This magnetization was stored along B 0 quadrupolar interaction is only partially averaged by MAS. using a z filter and was subsequently transferred via cross Recently, Jarvie et al. (8) demonstrated that a high-resolupolarization to 31 P with the sample spinning at an angle of tion HETCOR spectrum could be obtained from a quadrupo-0Њ. The 31 P signal was then detected at the magic angle. lar nucleus and a spin-1 2 nucleus by applying the principles While this experiment gives high resolution in both the 23 Na of dynamic-angle spinning (9-11) (DAS), which averages and 31 P dimensions, it requires three rotor-axis reorientations the second-order quadrupolar interaction, but requires samduring each scan and therefore cannot be used to study nuclei ple spinning at two different angles. The purpose of the with short T 1 values, such as 27 Al or 11 B. current Communication is to present an alternative method Recently, Frydman et al. (12) proposed an alternative of performing a high-resolution HETCOR experiment that approach for the removal of the second-order quadrupolar requires sample spinning at only one angle. Our approach interaction (13, 14). This method is analogous to DAS in is based on the method recently described by Frydman and that an isotropic echo is generated by sequential manipula-Harwood (12, 13) who exploited multiple-quantum cohertion of the Hamiltonian. However, in contrast to DAS, the ence in conjunction with magic-angle spinning to obtain sample in the MQMAS experiment is spun only at the magic high-resolution spectra of quadrupolar nuclei.
angle, and the magnetization evolves sequentially under the In a simple HETCOR experiment (1-3) between two triple-quantum Hamiltonian in the first part of t 1 and under spin-1 2 nuclei, I and S, a p/2 pulse is first applied to the I the single-quantum Hamiltonian during the second part. Juspins to bring the I-spin magnetization into the x-y plane. dicious selection of the length of these two evolution periods The magnetization evolves under the I-spin Hamiltonian for generates an isotropic echo. To date, MQMAS has been used a time t 1 , and then is transferred through cross polarization to study a number of materials and its advantages over DAS to the S spins and detected. After two-dimensional Fourier have been discussed (15)(16). This Communication demontransformation of the time-domain signal, cross peaks will strates that the MQMAS experiment combined with Hartappear between the resonances of dipolar-coupled nuclei. mann-Hahn cross polarization (19, 20) can give a high-These yield information about the proximity of different resolution HETCOR spectrum in which one of the dimenchemical sites.
sions is from a half-integer quadrupolar nucleus.