A 19F and 1H goniometric split-millicoil NMR probe for solid-state NMR

To allow for single-crystal nuclear magnetic resonance (scNMR) investigations, an existing narrow bore high-field double-resonance millicoil F-19 and H-1 solid-state NMR probe was modified by adding a goniometer stage to the top. The goniometer was kept outside of the radiofrequency (RF) transceiver coil for improved filling factor and probe sensitivity. Because of the large size of single crystal grown, the transceiver coil was changed from a standard millicoil to a split-millicoil, or crude helmholtz coil, design with effects on probe performance further studied herein. The type of goniometer and crystal sample holder chosen allows for accurate rotation of the single crystal in all three orthogonal planes (x, y, and z) while allowing for the sample to be easily removed for X-ray diffraction study. Careful consideration was taken in selection of non-fluorinated materials making up the probe head to reduce unwanted F-19 background in the NMR signal. Goniometer functionality is demonstrated by F-19 scNMR rotation spectra of 5-fluoro-DL-tryptophan (5F-DL-Trp) required to determine the independent elements of its F-19 chemical shielding anisotropic tensor. (C) 2007 Wiley Periodicals, Inc.