title: Enzymatic degradation processes of lamellar crystals in thin films for poly[(R)-3-hydroxybutyric acid] and its copolymers revealed by real-time atomic force microscopy.
abstract: Enzymatic degradation processes of flat-on lamellar crystals in melt-crystallized thin films of poly[(R)-3-hydroxybutyric acid] (P(3HB)) and its copolymers were characterized by real-time atomic force microscopy (AFM) in a phosphate buffer solution containing PHB depolymerase from Ralstonia pickettii T1. Fiberlike crystals with regular intervals were generated along the crystallographic a axis at the end of lamellar crystals during the enzymatic degradation. The morphologies and sizes of the fiberlike crystals were markedly dependent on the compositions of comonomer units in the polyesters. Length, width, interval, and thickness of the fiberlike crystals after the enzymatic degradation for 2 h were measured by AFM, and the dimensions were related to the solid-state structures of P(3HB) and its copolymers. The width and thickness decreased at the tip of fiberlike crystals, indicating that the enzymatic degradation of crystals takes place not only along the a axis but also along the b and c axes. These results from AFM measurement were compared with the data on crystal size by wide-angle X-ray diffraction, and on lamellar thickness and long period by small-angle X-ray scattering. In addition, the enzymatic erosion rate of flat-on lamellar crystals along the a axis was measured from real-time AFM height images. A schematic glacier model for the enzymatic degradation of flat-on lamellar crystals of P(3HB) by PHB depolymerase has been proposed on the basis of the AFM observations.
authors.affiliation: Department of Innovative and Engineered Materials, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.
authors.forename: Keiji
authors.initials: K
authors.lastname: Numata
authors.forename: Takuya
authors.initials: T
authors.lastname: Hirota
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kikkawa
authors.forename: Takeharu
authors.initials: T
authors.lastname: Tsuge
authors.forename: Tadahisa
authors.initials: T
authors.lastname: Iwata
authors.forename: Hideki
authors.initials: H
authors.lastname: Abe
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Doi
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D002265:Carboxylic Ester Hydrolases / Q000494:pharmacology*; D003460:Crystallization; D018360:Crystallography, X-Ray; D004798:Enzymes / Q000378:metabolism; D006885:Hydroxybutyrates / Q000737:chemistry*; D046911:Macromolecular Substances; D018625:Microscopy, Atomic Force / Q000379:methods*; D011091:Polyesters / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry; D043367:Ralstonia / Q000201:enzymology; D012542:Scattering, Radiation; D013696:Temperature; D013997:Time Factors; D014961:X-Ray Diffraction; D014965:X-Rays; D000094122:Polyhydroxybutyrates
chemical_list: D002265:Carboxylic Ester Hydrolases; D004798:Enzymes; D006885:Hydroxybutyrates; D046911:Macromolecular Substances; D011091:Polyesters; D011108:Polymers; C003182:poly-beta-hydroxybutyrate; D000094122:Polyhydroxybutyrates; C022417:poly-beta-hydroxybutyrate depolymerase