Structural Analysis, Thermal Properties, Second Harmonic Generation and In-Vivo Biodegradability

Pseudomonas putida KT 2442 was utilized as biocatalyst to form optoactive poly(/?-hydroxya1kanoate)s (PHAs) from a cosubstrate mixture of octanoate and the achiral polarizable carbon source 6(4-cyanophenoxy)hexanoate, CPH. COSY and heteronuclear multiplet quantum correlation experiments were used to assign ‘H and 13C NMR signals of 3-hydroxy-6(4cyanophenoxy)hexanoate (3HCPH) repeat units. The methine carbon of 3HCPH repeat units was sensitive to repeat unit sequence effects, indicating that a substantial fraction of 3HCPH centered triad sequences in the product contain neighboring 3-hydroxyoctanoate and 3-hydroxhexanoate repeat units. Comparing the thermal properties of 0 and 19.6mol% 3HCPH samples by differential scanning calorimetry shows that 3HCPH incorporation results in melting at temperatures > 64°C (not seen for the 0 mol% sample), more rapid crystallization and a new Tg transition at -21°C. These characteristics indicate that chains and/or chain segments are formed that are enriched in 3HCPH which phaseseparate and form a unique crystal structure. Measurements of second harmonic generation (SHG) intensities carried out using in-situ corona-poled samples showed weak SHG signals that increased by a factor of 8 for an increase in the 3HCPH content from 26 to 34mol%. Comparatively higher SHG intensities (5 times) were found for PHAs which contained 5.1 mol% 3-hydroxy-6(4nitrophen0xy)hexanoate (3HNPH) repeat units relative to a PHA with 17 mol% 3HCPH. In-vivo biodegradation studies of microbial polyesters prepared with and without 3HCPH repeat units showed that PHA chains with 3HCPH degraded to lesser extents (weight loss of -20 and 50% over 72 h incubations). The large increase in polydispersity from 1.9 to 4.3 observed during in-vivo biodegradation of microbial polyesters containing 3HCPH repeat units was attributed to the existence of chains with highly variable contents of 3HCPH repeat units.