High magnetic field solid‐state NMR analyses by combining MAS, MQ‐MAS, homo‐nuclear and hetero‐nuclear correlation experiments

Abstract

A general strategy of structural analysis of alumina silicate by combining various solid-state NMR measurements such as single pulse, multi-quantum magic angle spinning, double-quantum homo-nuclear correlation under magic angle spinning (DQ-MAS), and cross-polarization hetero-nuclear correlation (CP-HETCOR) was evaluated with the aid of high magnetic field NMR (800 MHz for (1) H Larmor frequency) by using anorthite as a model material. The high magnetic field greatly enhanced resolution of (27) Al in single pulse, DQ-MAS, and even in triple-quantum magic angle spinning NMR spectra. The spatial proximities through dipolar couplings were probed by the DQ-MAS methods for homo-nuclear correlations between both (27) Al-(27) Al and (29) Si-(29) Si and by CP-HETCOR for hetero-nuclear correlations between (27) Al-(29) Si in the anorthite framework. By combining various NMR methodologies, we elucidated detailed spatial correlations among various aluminum and silicon species in anorthite that was hard to be determined using conventional analytical methods at low magnetic field. Moreover, the presented approach is applicable to analyze other alumina-silicate minerals.

Advances in the characterization of inorganic solids using NMR correlation experiments

“…These 2D spectra provided information about the location of hydrogen in hydrous wadsleyite (β-(Mg,Fe)2SiO4) 388 , which has received interest as a potential reservoir for hydroxyls (water) in Earth's mantle (see Figure 32a), as well as the cation clustering in Mg/Al layered double hydroxides (LDH) 386,387 . Homonuclear correlation experiments have also been applied to probe 31 P-O-31 P connectivities in calcium phosphate phases 391,392 and 29 Si- 29 Si proximities in a feldspar mineral 393 . Furthermore, the sensitivity gain offered by DNP allowed to record 2D 13 C 2Q-1Q homonuclear correlation of isotopically unmodified carbonated hydroxyapatite nanoparticles 394 .…”

“…This spectrum demonstrated the clustering of carbonate anions. Proximities between Al sites in minerals were also probed by 2D 27 Al 2Q-1Q homonuclear correlation 151,393,395 . Regarding heteronuclear correlation, 2D 31 P{ 1 H} CP-HETCOR experiment has widely used to investigate the nature of calcium phosphate phases in bones 197,[396][397][398][399] as well as the interaction of calcium phosphate surfaces with other compounds [400][401][402] .…”

“…Correlation between 1 H and 29 Si nuclei as well as 17 O{ 1 H} CP-HETCOR experiment has also provided information about the location of protons in magnesium silicate phases (see Figure 32b) 385,388,410 . In addition, correlation experiments between 27 Al isotope and spin-1/2 nuclei, such as 1 H 411,412 , 19 F 412 and 29 Si 187,293,393 , have been employed to gain insight into the location of cations, anions and vacancies in minerals and to identify impurities (see Figure 16).…”

Analyses of Aluminum Structures in a Chinese Coal Ash and Its Slag by STMAS NMR

“…The STMAS NMR experiment is beneficial not only on shorting the scanning times than that in the conventional MQMAS experiments, but also provides a high-resolution spectrum of rare spins (Amoureux et al, 2005). Moreover, the NMR experiments were performed at 18.8 T (800 MHz for 1 H Lamor frequency); such a high magnetic field offers traditional advantages of improved sensitivity, enhanced resolution, and increased chemical shift dispersion, which allow the structural analysis under stronger comprehension (Lin et al, 2012).…”