Crystalline-Structure-Dependent Enzymatic Degradation of Polymorphic Poly(3-hydroxypropionate)

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• 作者：Bo Zhu ; Yong He ; Haruo Nishida ; Koji Yazawa ; Nariaki Ishii ; Ken-ichi Kasuya ; Yoshio Inoue
• 刊名：Biomacromolecules
• 出版年：2008
• 出版时间：April 2008
• 年：2008
• 卷：9
• 期：4
• 页码：1221 - 1228
• 全文大小：392K
• 年卷期：v.9,no.4(April 2008)
• ISSN：1526-4602

文摘

The crystalline structure dependence of enzymatic degradation behavior was investigated for the polymorphic poly(3-hydroxypropionate) (P3HP), which has a basic backbone chemical structure of bacterial poly(3-hydroxyalkanoate)s (P3HAs). The P3HP films consisting of the β-, γ-, and/or δ-form crystal were cast or melt-crystallized as reported previously (Macromolecules 2005, 38, 6455; Macromolecules 2006, 39, 194–203) by controlling the molecular weight, crystallization temperature, and/or temperature of the melt. Their thermal properties, crystalline structures, morphologies, and ¹³C solid spin–lattice relaxation dynamics were characterized by the differential scanning calorimetry, the wide-angle X-ray diffraction, the small-angle X-ray scattering (SAXS), and the ¹³C solid-state NMR spectra (SNMR), respectively. Both the crystallinities and the lamellar thicknesses of P3HP films were found to decrease roughly in the order of β-form > (or ≈) γ-form > δ-form. From previous work, which indicates that the P3HA enzymatic degradation depends only on the degree of crystallinity and the lamellar thickness, their enzymatic degradation rates are then expected to increase in the order of β-form < (or ≈) γ-form < δ-form. Unexpectedly, their experimental P3HP enzymatic degradation rates in the presence of P3HA depolymerase isolated from Ralstonia pickettii T1 increase in the reverse order, i.e., δ-form < γ-form < β-form. The weight loss rate of the δ-form film is almost 1 order of magnitude smaller than that of the fastest degraded β-form film. It is then strongly indicated that the crystalline structure plays a strikingly decisive role in the enzymatic degradation of P3HP. In particular, only when the conformation of crystalline chain accords with that of the bacterial poly(3-hydroxybutyrate) (P3HB) sample, i.e., the 2₁ helix conformation, is the P3HP sample degraded as slow as the P3HB sample. The inherent reason responsible for the unique P3HP enzymatic degradation behavior has been further clarified by comparing the molecular interaction and dynamics of polymorphic P3HP crystals.