TY - JOUR
T1 - Absence of sum frequency generation in support of orthorhombic symmetry of α-chitin
AU - Ogawa, Yu
AU - Lee, Christopher M.
AU - Nishiyama, Yoshiharu
AU - Kim, Seong H.
N1 - Funding Information:
The SFG and Raman experiments were supported by The Center for Lignocellulose Structure and Formation, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences under Award DE-SC0001090. Y.O. was supported by Japan Society for the Promotion of Science (JSPS).
Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/9/27
Y1 - 2016/9/27
N2 - The native polymorphic structures of chitin, namely α- and β-chitin, were studied with X-ray diffraction (XRD), infrared and Raman spectroscopies, and sum-frequency generation (SFG) vibrational spectroscopy. The currently proposed model of α-chitin crystal based on X-ray and electron diffraction study has an antiparallel chain arrangement imposed by the orthorhombic symmetry in contrast to parallel chain arrangements in β-chitin and native cellulose; however, the natural occurrence of antiparallel chain arrangement for α-chitin is controversial to widely accepted biosynthetic mechanisms for structural polysaccharides such as chitin and cellulose, where chains are successively polymerized and crystallized in a unidirectional way. We compared the SFG signals among samples with similar crystallinity, morphology, and textures but differing in allomorphs. The SFG signal from α-chitin was ∼40-fold weaker compared to β-chitin having a similar lateral dimension. The strong SFG signals arising from β-chitin can be explained by a net polar ordering of parallel packed chains. These results strongly supports the antiparallel chain orientation and high symmetry (orthorhombic) of α-chitin suggested by diffraction analysis.
AB - The native polymorphic structures of chitin, namely α- and β-chitin, were studied with X-ray diffraction (XRD), infrared and Raman spectroscopies, and sum-frequency generation (SFG) vibrational spectroscopy. The currently proposed model of α-chitin crystal based on X-ray and electron diffraction study has an antiparallel chain arrangement imposed by the orthorhombic symmetry in contrast to parallel chain arrangements in β-chitin and native cellulose; however, the natural occurrence of antiparallel chain arrangement for α-chitin is controversial to widely accepted biosynthetic mechanisms for structural polysaccharides such as chitin and cellulose, where chains are successively polymerized and crystallized in a unidirectional way. We compared the SFG signals among samples with similar crystallinity, morphology, and textures but differing in allomorphs. The SFG signal from α-chitin was ∼40-fold weaker compared to β-chitin having a similar lateral dimension. The strong SFG signals arising from β-chitin can be explained by a net polar ordering of parallel packed chains. These results strongly supports the antiparallel chain orientation and high symmetry (orthorhombic) of α-chitin suggested by diffraction analysis.
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U2 - 10.1021/acs.macromol.6b01583
DO - 10.1021/acs.macromol.6b01583
M3 - Article
AN - SCOPUS:84989238596
SN - 0024-9297
VL - 49
SP - 7025
EP - 7031
JO - Macromolecules
JF - Macromolecules
IS - 18
ER -