27Aluminum (27Al)is a high sensitivity nucleus that yields broad lines over a wide chemical shift range. 27Al is a spin 5/2 nucleus and is therefore quadrupolar. As a result, the signal width increases with asymmetry of the environment with somewhat broad lines in symmetrical environments (fig. 1) but very broad lines in asymmetric ones. The main use of aluminum NMR is to detect the presence of aluminum and measure its relaxation rate in order to detect binding. There is always a broad signal arising from the probe in the 27Al spectrum. There is little information available about aluminum chemical shifts (fig. 2).
Fig. 1. Chemical shift ranges for 27Al NMR
Fig. 2. 27Al-NMR spectrum of AlCl3 in D2O
|Chemical shift range||400 ppm, from -200 to 200|
|Frequency ratio (Ξ)||26.056859%|
|Reference compound||1.1 m Al(NO3)3 in D2O|
|Linewidth of reference||11 Hz|
|T1 of reference||0.03 s|
|Receptivity rel. to 1H at natural abundance||0.207|
|Receptivity rel. to 1H when enriched||0.207|
|Receptivity rel. to 13C at natural abundance||1220|
|Receptivity rel. to 13C when enriched||1220|
|Linewidth parameter||69 fm4|
Some of the materials mentioned here are very dangerous. Ask a qualified chemist for advice before handling them. Qualified chemists should check the relevant safety literature before handling or giving advice about unfamiliar substances. NMR solvents are toxic and most are flammable. Specifically, aluminum salts may be toxic in large doses.