Biosynthesis and biodegradation of 3-hydroxypropionate-containing polyesters

Abstract

3-Hydroxypropionate (3HP) is an important compound in the chemical industry, and the polymerized 3HP can be used as a bioplastic. In this review, we focus on polyesters consisting of 3HP monomers, including the homopolyester poly(3-hydroxypropionate) and copolyesters poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxypropionate-co-3-hydroxybutyrate-co-3-hydroxyhexanoate-co-3-hydroxyoctanoate), poly(4-hydroxybutyrate-co-3-hydroxypropionate-co-lactate), and poly(3-hydroxybutyrate-co-3-hydroxypropionate-co-4-hydroxybutyrate-co-lactate). Homopolyesters like poly(3-hydroxybutyrate) are often highly crystalline and brittle, which limits some of their applications. The incorporation of 3HP monomers reduces the glass transition temperature, the crystallinity, and also, at up to 60 to 70 mol% 3HP, the melting point of the copolymer. This review provides a survey of the synthesis and physical properties of different polyesters containing 3HP.

FIG. 1.

Artificial pathways for poly(HA-co-3HP) accumulation from different carbon sources. Acc_Cn, acetyl-CoA carboxylase (C. necator); Aco_Cn, acetyl-CoA synthase (C. necator); Acs_Ca, 3HP-CoA synthase domain of propionyl-CoA synthase (C. aurantiacus); DhaB_Cb, glycerol dehydratase (C. butyricum); Mcr_Ca, malonyl-CoA reductase (C. aurantiacus); OrfZ_Ck, acetyl-CoA:4-hydroxybutyrate-CoA transferase (C. kluyveri); Pct_Cp, propionyl-CoA transferase (C. propionicum); PduP_Se, propionaldehyde dehydrogenase (Salmonella enterica serovar Typhimurium LT2); PhaC_Cn, PHA synthase (C. necator); PrpE_Se, propionyl-CoA synthetase (S. enterica). The indices (n) at the hydroxyalkanoate moieties indicate the presence of lactate (n = 0), 3-hydroxyalkanoates (n = 1), and 4-hydroxybutyrate (n = 4).

FIG. 2.

Changes in the physical properties of the copolymer poly(3HB-co-3HP) by varying the 3HP content. The glass transition temperatures (Tg) and melting temperatures (Tm), crystallinity, crystal lattice type, and fusion enthalpy are plotted against the 3HP content. The figure compiles the data of Shimamura et al. (39), Ischikawa et al. (19), Cao et al. (7, 8, 9), Na et al. (33), Wang et al. (46), and Feng et al. (11). For the hatched area of the crystal lattice type, the data are contrary. Both the amorphous and the 3HP crystal lattice type have been reported.