Molecular modelling of helical and extended-chain polyhydroxybutyrates and polytetramethylene succinate

Pazur, Richard J.; Raymond, Stéphane; Hocking, Philippa J.; Marchessault, R. H.

doi:10.1016/s0032-3861(97)10031-3

Cited by 30 publications

(47 citation statements)

References 15 publications

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“…These crystal transitions between a and b forms is reversible, and the mechanisms of the crystal transition were investigated by FT-IR and X-ray diffraction 95) . More recently, three plausible crystalline conformers with pitches (1.09, 1.16 and 1.22 nm) close to the experimental ones (1.09 and 1.19 nm) were predicted by molecular modeling by Pazur et al 55) Poly(tetramethylene adipate) (PTMA; x = 4, y = 4) crystallizes in two forms, designated as a and b forms 96) . The a form is obtained from a stretched and annealed film, and the unit cell is a P2 1 /a monoclinic space group with dimensions a = 0.670 nm, b = 0.800 nm, c (fiber axis) = 1.420 nm and b = 45.5 8.…”

Section: Linear Aliphatic Polyestersmentioning

confidence: 53%

“…In one unit cell there are two chains with a 2/1 helix conformation along the molecular axis 54) . Pazur et al reported the same result based on the X-ray fiber diagram and the energy calculation of P(4HB) single chain; that is, P(4HB) has not an all-trans planar zigzag conformation (fiber repeat of 1.240 nm) and the observed fiber repeat distance of 1.190 nm is due to an inherent regular torsion along the molecular backbone 55) . However, for this polymer there is no three-dimensional structure analysis by using the reflection intensities derived from X-ray fiber diagram.…”

Section: Poly(4-hydroxybutyrate)mentioning

confidence: 66%

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Crystal structure and biodegradation of aliphatic polyester crystals

Iwata¹,

Doi

1999

Macromol. Chem. Phys.

140

121

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SUMMARY: The biodegradability of aliphatic polyesters, which are produced by biosynthesis and chemosynthesis, strongly correlates to the polymer morphology such as crystallinity, molecular orientation, chain packing and crystal surface, in addition to the chemical structure. For elucidation of biodegradation mechanism of crystal regions on an atomic level, lamellar single crystals of poly([R]-3-hydroxybutyrate) (P(3HB)) and its copolymers, poly([R]-3-hydroxyvalerate) (P(3HV)), poly(4-hydroxybutyrate) (P(4HB)), poly(L-lactic acid) (PLLA) and poly(ethylene succinate) (PES) were prepared from dilute solution by isothermal crystallization, and the crystal structures and morphologies were investigated by means of mainly transmission electron microscopy and atomic force microscopy. All single crystals were intramolecular single crystals, with spiral growth in some cases, and these crystals gave well-resolved electron diffractograms. The enzymatic degradation of lamellar crystals of P(3HB) and its copolymers was carried out with extracellular PHB depolymerases, and it was revealed that enzymatic degradation of lamellar crystals progressed from crystal edges and ends rather than the chain-folding surfaces of crystals, in spite of the homogeneous adsorption of enzyme molecules on the crystal surfaces by substrate-binding domain. Furthermore, in the case of PLLA single crystals, single crystals were also degraded from the edges to yield a rounded shape without decreasing the molecular weights and lamellar thickness. These results suggest that the attack by the active site of enzyme takes place at disordered regions of the crystals, that is, disordered lateral sites with high mobility of molecular chains are preferentially degraded.

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Section: Linear Aliphatic Polyestersmentioning

confidence: 53%

Section: Poly(4-hydroxybutyrate)mentioning

confidence: 66%

Crystal structure and biodegradation of aliphatic polyester crystals

Iwata¹,

Doi

1999

Macromol. Chem. Phys.

140

121

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“…The octamer 18a with a syndiotactic sequence of (R)-and (S)-HB residues was studied by stretch-fiber and powder X-ray diffraction. Analysis of the powder data gave a new unit cell (with much better resolution, based on the Rietveld method), as compared to the one obtained from a sample of largely syndiotactic polymer prepared by Marchessault et al 21 ) [35].…”

Section: 4mentioning

confidence: 95%

“…NaHCO 3 and sat. NaCl soln., dried (MgSO 4 ), and evaporated at r.t. 35.56 g (90%) of 2c. Clear, faintly yellow oil, very pure by 1 …”

mentioning

confidence: 99%

Synthesis and Structure of Linear and Cyclic Oligomers of 3-Hydroxybutanoic Acid with Specific Sequences of (R)- and (S)-Configurations

Bachmann¹,

Seebàch²

1998

HCA

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“…The conformational properties of bacterial polyesters have been intensively investigated [6][7][8]. Mostly these studies include SANS [6], X-ray analysis [7], molecular modelling investigations [8] and have been focused on poly(3-hydroxybutyrate) (PHB).…”

Section: Introductionmentioning

confidence: 99%