Hydroxyalkanoate

Hydroxyalkanoate generally refers to hydroxy-substituted alkanoate units that form the monomers of the biopolymer family known as polyhydroxyalkanoates (PHAs). The most common monomer class is 3-hydroxyalkanoates, which have the structure HO−CH(R)−CH2−COO−, where R denotes an alkyl side chain. When these units polymerize via ester linkages, they produce PHAs, including polyhydroxybutyrate (PHB) and copolymers such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). The nature of the R group influences crystallinity, stiffness, and melting behavior of the resulting polymer.

In biology, hydroxyalkanoates are produced by many bacteria as intracellular carbon and energy reserves. Under nutrient limitation (for example, nitrogen or phosphorus) with excess carbon, cells channel carbon flux into hydroxyalkanoate monomers and polymerize them using the PHA synthase enzyme (PhaC). The polymer is stored in intracellular granules and can be mobilized by depolymerases (PhaZ) when needed. The diversity of hydroxyalkanoate side chains allows PHAs to exhibit a wide range of material properties, from rigid thermoplastics to flexible elastomers.

Applications and production: PHAs and their hydroxyalkanoate monomers are studied as biodegradable, biocompatible plastics for packaging, agricultural films, and medical devices. Industrial production employs bacteria such as Cupriavidus necator and engineered strains, using renewable feedstocks. Despite environmental advantages, production costs and processing challenges limit widespread adoption. Ongoing research seeks to improve yields, tailor monomer composition, and enable cheaper synthesis from waste streams or nonfood carbon sources.