Rapid acquisition of data dense solid-state CPMG NMR spectral sets using multi-dimensional statistical analysis

Abstract

The development of multi-dimensional statistical methods has been demonstrated on variable contact time (VCT) 29Si{1H} cross-polarization magic angle spinning (CP/MAS) data sets collected using Carr-Purcell-Meiboom-Gill (CPMG) type acquisition. These methods utilize the transformation of the collected 2D VCT data set into a 3D data set and use tensor-rank decomposition to extract the spectral components that vary as a function of transverse relaxation time (T2) and CP contact time. The result is a data dense spectral set that can be used to reconstruct CP/MAS spectra at any contact time with a high signal to noise ratio and with an excellent agreement to 29Si{1H} CP/MAS spectra collected using conventional acquisition. These CPMG data can be collected in a fraction of time that would be required to collect a conventional VCT data set. We demonstrate the method on samples of functionalized mesoporous silica materials and show that the method can provide valuable surface specific information about their functional chemistry.

3D relaxation-assisted separation of wideline solid-state NMR patterns for achieving site resolution

“…Furthermore, if the effective T 2 's of two magnetically distinct sites at a given decoupling power are similar, it may be possible to differentiate them further by varying the heteronuclear dipolar decoupling RF fields; 60 variation in CP efficiency with variable contact times could serve to highlight similar site differences. 83 3D RAS is particularly useful for separating overlapping halfinteger spin CT powder patterns of quadrupolar nuclei with large C Q 's, of the kind that cannot be resolved with MQMAS or STMAS. The example of a histidine HCl:glycine HCl mixture demonstrates the improved site resolution capabilities of 3D RAS over 2D RAS.…”

“…Furthermore, if the effective T 2 's of two magnetically distinct sites at a given decoupling power are similar, it may be possible to differentiate them further by varying the heteronuclear dipolar decoupling RF fields; 60 variation in CP efficiency with variable contact times could serve to highlight similar site differences. 83…”

Blind Source Separation for NMR Spectra with Negative Intensity

“…In less common applications, blind source separation has also been instrumental in enabling scientists to extract additional molecular level insight from NMR data. Blind source methods have also been characterizing surface structure of silica materials using variable contact time 29 Si{ 1 H} crosspolarization (CP/MAS) data sets [12,13], determining the site preference of dopants in multiphase cements, ceramics, and minerals using 27 Al or 45 Sc NMR data sets [14], and reducing noise in 13 C NMR of multiphase thermoplastics [15]. In the majority of these demonstrations use or test only a single blind source separation algorithm, raising the questions of what is the best methods for analysis of NMR spectra databases?…”