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We explore dynamic nuclear polarization using electron spins in the photo-excited triplet state (Triplet-DNP) in magnetically oriented microcrystal arrays (MOMAs) of pentacene-doped p-terphenyl, in which the individual crystallites are magnetically aligned and UV-cured. In contrast to the conventional approach to Triplet-DNP in powder, which suffers from reduced nuclear polarization due to the averaged electron polarization and the broadening of electron-spin resonance, Triplet-DNP of the MOMAs offers as high dynamic polarization as that attainable in single-crystals. In the case of pentacene-doped p-terphenyl, the enhanced 1 H polarization in the one-dimensional MOMA, prepared simply by leaving the suspension in a stationary magnetic field before UV curation, can be higher than that attainable in the powder sample by an order of magnitude and comparable to that in single crystals and in the three-dimensional MOMA made using a modulational rotating field. Triplet-DNP of the MOMAs may find potential applications, such as the polarization of the co-doped target molecules and dissolution experiments., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

In situ solid-state NMR measurements of a magnetically oriented microcrystal suspension (MOMS) were demonstrated. Under modulated rotation of the static field, or equivalently, of the sample tube, randomly oriented microcrystals in a viscous liquid medium feel a torque arising from the anisotropic bulk susceptibility and eventually aligned in the same direction. In this way, a three-dimensional MOMS (3D-MOMS) was obtained. To apply an elliptically rotating magnetic field to microcrystals in suspension, a probe to rotate the sample tube around an axis perpendicular to the static magnetic field was developed. Single-crystal (SC) rotation patterns were obtained from the 3D-MOMS by solid-state CP measurements triggered in synchronous with the sample-tube rotation. Unlike the traditional SC method, the 3D-MOMS approach presented here does not require the elaborate adjustment of the direction of the reference frame. The process of three-dimensional magnetic alignment was also studied by monitoring the spectral changes during continuous application of the modulated sample rotation., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The single-crystal rotation technique was applied to magnetically oriented microcrystal arrays (MOMAs) of cellobiose (monoclinic) to determine the principal values and principal axes of the chemical shift tensors of C1 and C1' carbons. Rotations were performed about the magnetic χ1, χ2, and χ3 axes of MOMA, and the measurements were taken at six different orientations with respect to the applied magnetic field. Under these rotations, crowded peaks were reduced and the peaks for the C1 and C1' carbons were identified by comparing with simulation results. Six components of the chemical shift tensor expressed with respect to the magnetic χ1χ2χ3-frame were determined. The tensors thus obtained were transformed into those relative to the molecular frame., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Chemical shift tensors for the carboxyl and methyl carbons of L-alanine crystals were determined using a magnetically oriented microcrystal array (MOMA) prepared from a microcrystalline powder sample of L-alanine. A MOMA is a single-crystal-like composite in which microcrystals are aligned three-dimensionally in a matrix resin. The single-crystal rotation method was applied to the MOMA to determine the principal values and axes of the chemical shift tensors. The result showed good agreement with the literature data for the single crystal of L-alanine. This demonstrates that the present technique is a powerful tool for determining the chemical shift tensor of a crystal from a microcrystal powder sample., (Copyright © 2012 Elsevier Inc. All rights reserved.)