CONFORMATIONAL-ANALYSIS OF POLY(3-HYDROXYBUTYRATE-CO-3-HYDROXYVALERATE) IN SOLUTION BY H-1-NMR SPECTROSCOPY

It has been found that 3-hydroxybutyrate homopolymer (PHB) and its copolymers with 3- hydroxyvalerate (PHB-HV) are accumulated in some microorganisms. In this paper the conformational aspects of PHB and PHB-HV in chloroform were investigated on the basis of the vicinal coupling constants of the1H NMR spectrum. The two methylene proton resonances of PHB were assigned by using the two-dimensional1H-1H NOESY spectrum. The fractional populations of gauche and trans conformers around the main-chain CH-CH2 bond are estimated to be 0.6 and 0.4, respectively. The main-chain methylene resonances of PHB-HV are split by two factors, i.e., by the ABX spin-spin coupling between the methylene and methine protons and by the difference in the diad and/or triad monomer sequences. By separating these splitting factors, with the aid of the1H-13C COSY spectra, the conformational structures of PHB-HV were determined. In every diad and/or triad monomer sequence, the fractional populations of gauche and trans conformers around the main-chain CH-CH2 bond are also believed to be 0.6 and 0.4, respectively. It was confirmed that two kinds of monomer units, HB and HV, in PHB-HV assume almost the same conformation irrespective of HV mole fractions in chloroform solution. This result suggests the possibility that PHB-HV’[s with different HV mole fraction form isomorphic crystals. © 1990, American Chemical Society. All rights reserved.