Overtone solid-state NMR spectroscopy on Nitrogen-14

¹⁵N NMR is widely used because of the importance of nitrogen in chemistry, materials, biology, environment etc. However, very low abundance of ¹⁵N (<0.4%) results in poor sensitivity and thus makes observation time-consuming. On the other hand, the rest of nitrogen atoms are also NMR sensitive nucleus of ¹⁴N. Despite the high abundance of ¹⁴N (>99%), it’s application is rather limited due to the huge quadrupolar interactions and its spin quantum number I = 1. The introduction of very fast MAS (>70 kHz) enabled the ¹H detected ¹⁴N/¹H correlation spectroscopy (Nishiyama et al.,JMR 208 (2011) 44-48). However, it demands precise magic-angle adjustment, moreover, the sensitivity is largely affected by the molecular motion. It was shown that the use of ¹⁴N overtone transition avoids these difficulties under MAS (O’Dell et al. Chem. Phys. Lett. 514 (2011) 168-173) with a cost of sensitivities. Since the overtone transition between -1 and +1 energy level is forbidden, the low sensitivity fundamentally comes from small transition moment between these levels. Here, we have developed ¹H detected ¹⁴N overtone/¹H correlation spectroscopy under ultrafast MAS conditions > 70 kHz to achieve highly sensitive ¹⁴N NMR spectroscopy of rigid solid.

Y. Nishiyama, M. Malon, Z. Gan, Y. Endo, T. Nemoto, J. Magn. Reson. 230 (2013) 160-164.

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