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The mechanisms of the viscoelastic crystalline absorption of polyglutamic acid ester

1975; Taylor & Francis; Volume: 11; Issue: 1 Linguagem: Inglês

10.1080/00222347508217857

1525-609X

T. Kajiyama, Masayuki Kuroishi, M. Takayanagi,

Antimicrobial agents and applications

Abstract The viscoelastic crystalline relaxation process has been newly observed for solid films of poly-γ-methyl-D-glutamate. The temperature range of the crystalline absorption corresponds to the temperature range in which the lattice distance deviates from linear expansion. The viscoelastic crystalline relaxation process was decomposed into the a, mechanism (150 to 170°C) and the α2 mechanism (180 to 190°C) which appear principally for solid poly-γ-methyl-D-glutamate cast from solutions in dichloroethane and chloroform, respectively. The contribution from the α1 and the α2 relaxation processes depends on such structural factors as alignment or packing state of the a-helix chains; these vary with the kind of solvent and the condition of sample preparation. Based on the experimental results for the anisotropy of mechanical loss and the relationships between the peak temperature of tan 6 and the interhelix distance or the peak magnitude of tan δ and the interhelix distance, it seems reasonable to conclude that the α1 relaxation process is associated with shear deformation in the interhelix region of the crystalline phase. Also, from a model calculation of the magnitude of the energy dissipation produced by shear deformation of the interhelix region, coaxially vibrations and torsional oscillations of the a-helices are both possible origins of the a, relaxation mechanism. In practice, these molecular motions correspond to the migrational slip and the rotational motion of the α-helices, respectively. The nature of the α2 relaxation process is discussed from the viewpoint of the anisotropy of mechanical loss and the stability of the helix core investigated by X-ray and IR techniques. It is concluded that the α2mechanism is associated with tensile or bending deformation of the α-helix chains represented by accordion-like, torsional extension or bending motions.