CRYSTALLINE FEATURES OF CHITOSAN-L-LACTIC AND D-LACTIC ACID SALTS

The crystal structures of chitosan-L- and D-lactate salts mere studied by X-ray diffraction measurements on fiber diagrams. In each lactate, chitosan took on a different crystalline polymorph depending on the p reparation temperature. At low temperature, they pave a similar fiber pattern to that of Be type IZ salt which has been found to be one of t he two farms of chitosan acid salts in which the backbone chitosan mol ecules take on an eight-fold helix. At high temperature, however, the fiber pattern was that of the type I salt, another form of chitosan sa lt in which the backbone chains apparently retain the 2(1) symmetry of chitosan itself, The high-temperature polymorph of the L-lactate was a monoclinic (pseudoorthorhombic) unit cell whose lattice parameters w ere a = 10.51, b = 10.85, c(fiber axis) = 10.34 Angstrom and gamma = 9 0 degrees. That of the D-lactate was also a monoclinic cell having par ameters a = 11.20, b = 11.60, c(fiber axis) = 10.38 Angstrom and gamma = 93.0 degrees. Their unit cell volumes coupled with their observed d ensity values indicate that two drains of chitosan lactate were accomm odated in each unit cell, that the L-lactate was an anhydrous crystal, but that the D-lactate was hydrated, The preparation temperature at w hich the salt changed from type II to type I was different between the D- and L-lactate, suggesting that these acids had different affinity to the chitosan molecule. When chitosan powder was suspended in a race mic lactic acid solution, the resultant solution always showed a minus sign for the rotation angle, indicating that D-lactic acid had higher sanity to chitosan than the L-isomer.