9962
J. Phys. Chem. C 2008, 112, 9962
COMMENTS Comment on “27Al, 47,49Ti, 31P, and 13C MAS NMR Study of VX, GD, and HD Reactions with Nanosize Al2O3, Conventional Al2O3 and TiO2, and Aluminum and Titanium Metal” George W. Wagner*,† and Boris Itin‡ U.S. Army Edgewood Chemical Biological Center, Aberdeen ProVing Ground, Maryland 21010-5424, and New York Structural Biology Center, 89 ConVent AVe., Park Building at 133rd St., New York, New York 10027-7566 ReceiVed: April 2, 2008; ReVised Manuscript ReceiVed: April 9, 2008 Wagner et al.1 recently reported 47,49Ti MAS NMR spectra for TiO2 (anatase) at 14, 17.5, and 21 T to assess anticipated line-narrowing for these nuclei at high magnetic field. As quadrupolar nuclei, 49Ti (I ) 7/2, Q ) 0.24) and 47Ti (I ) 5/2, Q ) 0.29) are susceptible to broadening by the second-order quadrupolar interactions that diminish with respect to the dominant NMR Zeeman interaction at higher magnetic fields.2 Although the lineshapes of both 49Ti and 47Ti were clearly evident in the 14 and 17.5 T spectra, only the 49Ti peak was detected in the 21 T spectrum because of the poor signal-tonoise ratio. By 21 T, the 49Ti resonance had narrowed to less than half of its width at 14 T, but the extent of narrowing of the 47Ti could not be ascertained. As shown in Figure 1, much better signal-to-noise 47,49Ti MAS NMR spectra have now been obtained3 for anatase at 21 T, which allow the line shape of the much broader 47Ti resonance to be observed. The better sensitivity was evidently provided by use of a larger-diameter 5 mm probe rather than the previous 3.2 mm probe.1 Spectra previously reported1 at 14 * To whom correspondence should be addressed. Phone: (410) 4368468. E-mail:
[email protected]. † U.S. Army Edgewood Chemical Biological Center. ‡ New York Structural Biology Center.
Figure 1. and 21 T.
47,49Ti
MAS NMR spectra obtained for anatase at 14, 17.5,
and 17.5 T are also shown for comparison. At 21 T, the line width of the 47Ti peak narrows to less than half of its width at 14 T, in agreement with the results previously noted1 for the sharper 49Ti resonance. Acknowledgment. Work at NYSBC was supported under U.S. Department of Defense Contract DAAD19201-1-0369. The Center is a STAR center supported by the New York State Office of Science, Technology, and Academic Research. The 900 MHz spectrometers were purchased with funds from NIH, USA, the Keck Foundation, New York State, and the NYC Economic Development Corp. References and Notes (1) Wagner, G. W.; Procell, L. R.; Munavalli, S. J. Phys. Chem. C 2007, 111, 17564–17569. (2) Gan, Z.; Gor’kov, P.; Cross, T. A.; Samoson, A.; Massiot, D. J. Am. Chem. Soc. 2002, 124, 5634–5635. (3) 47,49Ti MAS NMR spectra were obtained at 21 T with a Bruker AVANCE 900 NMR using a Doty Scientific 5 mm XC MAS NMR probe.
JP802847M
10.1021/jp802847m CCC: $40.75 2008 American Chemical Society Published on Web 06/07/2008
