title: Dual mesomorphic assemblage of chitin normal acylates and rapid enthalpy relaxation of their side chains.
abstract: Chitin derivatives having normalacyl groups (C(n)H(2n-1)O-; n = 4-20) were synthesized with pyridine, p-toluenesulfonyl chloride, and normal alkanoic acid in an N,N-dimethylacetamide-lithium chloride homogeneous system. The products (C(n)-ACs; degree of acyl substitution, DS = 1.7-1.9) showed an n-dependent thermal transition behavior: no evident transition (n = 4-10), a glass transition (n = 12 and 14), and a pseudo-first-order phase transition (n = 16-20), the latter two occurring usually below room temperature when examined by differential scanning calorimetry. Wide-angle X-ray diffractometry (WAXD) at 20 degrees C displayed a sharp diffraction peak (2theta = 2 degrees -7 degrees ) and a diffuse halo (2theta approximately 20 degrees ) for the respective C(n)-ACs. The former d-spacing (1.5-3.6 nm) increased with an increase in n to yield two stages of mutually different increasing rates, which reflects a systematic n-dependence of the period of a layered structure of the main chains. The molecular assembly of C(n)-ACs exhibited "dual mesomorphy"; nematic ordering for the semirigid carbohydrate trunk and smectic one for the flexible side chains. On the other hand, WAXD profiles of C(n)-ACs (n = 14-18) indicated almost no temperature dependence from -150 to +220 degrees C. Therefore, it was reasonably assumed that the pseudo-first-order transition observed in thermograms of C(n)-ACs (n = 16-20) was due to the enthalpy relaxation of the side-chain assemblage. An insight was provided into the kinetics of the characteristic aging behavior as a liquid-crystalline glass, in comparison with the corresponding data for other noncrystalline macromolecules.
authors.affiliation: Division of Forest and Biomaterials Science, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Yoshikuni
authors.initials: Y
authors.lastname: Teramoto
authors.forename: Tomoya
authors.initials: T
authors.lastname: Miyata
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Nishio
mesh_terms: D000215:Acylation; D000818:Animals; D003386:Brachyura / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D002686:Chitin / Q000737:chemistry*; D003460:Crystallization; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D044367:Phase Transition; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: D002686:Chitin