High-field 19.6T 27Al solid-state MAS NMR of in vitro aluminated brain tissue

The combination of Al-27 high-field solid-state NMR (19.6 T) with rapid spinning speeds (17.8 kHz) is used to acquire Al-27 NMR spectra of total RNA human brain temporal lobe tissues exposed to 0.10mM Al3+ (as AlCl3) and of human retinal pigment epithelial cells (ARPE-19), grown in 0.10 mM AlCl3. The spectra of these model systems show multiple Al3+ binding sites, good signal/ noise ratios and apparent chemical shift dispersions. A single broad peak (-3 to 11 ppm) is seen for the aluminated ARPE-19 cells, consistent with reported solution-state NMR chemical shifts of Al-transferrin. The aluminated brain tissue has a considerably different Al-27 MAS NMR spectrum. In addition to the transferrin-type resonance, additional peaks are seen. Tentative assignments include: -9 to -3ppm, octahedral AlO6 (phosphate and water); 9ppm, condensed AlO6 units (Al-O-Al bridges); 24ppm, tetrahedral AlO3N and/or octahedral Al-carbonate; and 35ppm, more N-substituted aluminum and/or tetrahedral AlO4. Thus, brain tissue is susceptible to a broad range of coordination by aluminum. Furthermore, the moderate Al-27 C-Q values (all less than 10 MHz) suggest future NMR studies may be performed at 9.4 T and a spin rate of 20 kHz. (C) 2004 Elsevier Inc. All rights reserved.