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Crystal Structure of Quinine: The Effects of Vinyl and Methoxy Groups on Molecular Assemblies of Cinchona Alkaloids Cannot Be Ignored

Authors

  • Dr. Ichiro Hisaki,

    Corresponding author
    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7406
    • Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7406

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  • Eri Hiraishi,

    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7406
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  • Toshiyuki Sasaki,

    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7406
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  • Dr. Hideo Orita,

    1. National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan). Fax: (+81) 29-851-5426
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  • Dr. Seiji Tsuzuki,

    1. National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan). Fax: (+81) 29-851-5426
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  • Dr. Norimitsu Tohnai,

    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7406
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  • Prof. Dr. Mikiji Miyata

    Corresponding author
    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7406
    • Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7406

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Abstract

Quinine, one of Cinchona alkaloids, has been of great interest from medical, synthetic, and supramolecular viewpoints. However, unaccountably, the guest-free (GF) crystal of quinine containing no solvent or other molecules has not been reported for nearly three decades, although GF crystals of other Cinchona alkaloids, such as quinidine, cinchonidine, and cinchonine, are already known. In this study, we successfully revealed the crystal structure of quinine, which belongs to the P21 space group with the cell parameters of a=6.0587(1), b=19.2492(5), c=22.2824(7) Å, β=92.1646(11)°, and V=2596.83(12) Å3. Interestingly, the crystal has three crystallographically independent molecules in the cell (Z′=3) that are connected through a N(quinoline)⋅⋅⋅H[BOND]O hydrogen bond to form a pseudo three-two-fold (32) double-helical motif. The helical motif is completely different from those observed in GF crystals of other Cinchona alkaloids. Hierarchical comparison on the crystal structures of a series of Cinchona alkaloids including quinine clearly demonstrated that only small structural differences of a molecule, particularly the position of the vinyl group, cause a significant variety of assembly manner in the crystalline state. There have been no reports systematically demonstrating such steric effect in crystals of Cinchona alkaloids, and, therefore, the present system contributes to the design of desired functional crystal structures.

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