The molecular and crystal structure of the hydrated form of chitosan, which was obtained by deacetylation of chitin from crab tendon, was determined by the X-ray fiber diffraction method and the linked-atom least-squares method. The chitosan chains crystallize in an orthorhombic unit cell with dimensions a = 8.95(4), b = 16.97(6), c (fiber axis) = 10.34(4) Å and a space group P212121. The chain conformation is a 2-fold helix stabilized by O3---O5 hydrogen bond with the gt orientation of O6. The unit cell contains four chains and eight water molecules. There are direct hydrogen bonds (N2---O6) between adjacent chains along the b-axis, which makes a sheet structure parallel to the bc-plane. These sheets stack along the a-axis. Each sheet is related to its neighboring sheet by 21-symmetry along the b-axis. Water molecules form columns between these sheets and contribute to stabilize the structure by making water-bridges between polymer chains.

No abstract

No abstract

No abstract

Photophysics and photochemistry of 2,2-diphenylhexamethyltrisilane (1) was investigated in detail. Diphenyltrisilane 1 showed an intense fluorescence band assignable to the intramolecular charge-transfer (ICT) band in a polar solvent. Whereas silylene extrusion and 1,3-silyl migration were the major photoreactions of 1 in a nonpolar solvent, solvolytic cleavage of the Si−Si bond occurred significantly in an ethanol−hexane mixture; the ICT state is responsible for the latter reaction. Solvent and temperature dependence of the product distribution has indicated that both the silylene extrusion and the 1,3-silyl migration take place from the nonpolar but electronically different excited states of 1. On the basis of the photoreactions of 1 using a nonresonant two-photon (NRTP) excitation method, it is suggested that the silylene extrusion occurs via the 1La state of 1 as a silyl-substituted benzene.