Degradation 3-hydroxypropionic acid

But, both polymers, PHB and PLA, lead to conflicts in the context of assigning them as biodegradable polymers, because these are naturally occurring polymers, which like PHB were evolved in natural material cycles. However, in the case of PLA only the monomer, L-2-hydroxypropionic acid, (l-Lactic acid) can be found in the natural material cycle. On the other hand, both of them can be generated on a natural nonpetrochemical basis, with renewable resources, and they are degradable. This common denominator should justify the discussion of both polymers herein and makes a comparison meaningful. 

Organic acid oxidation in conjugation with oxidation of CaS03 slurry was studied for seven acids. Degradation of adipic acid and other aliphatic and sulfo carboxylic acids was least at pH 4.3 with 1.0 mM dissolved Mn and greatest at pH 5.5 without Mn. Hydroxypropionic and hydroxyacetic acids inhibited sulfite oxidation and were less subject to degradation. Fumaric acid degraded faster than the other alternatives. 

The hydroxy acids did not degrade as fast as the dicarboxylic and sulfocarboxylic acids. The maximum degradation constant observed with these acids was 0.2 M"1 with hydroxypropionic acid at pH 4.5 with no Mn. Run AA2 with 10 mM adipic, 10 mlj[ hydroxy-acetic, and 1 mM Mn at pH 5.5 gave k,j values of 0.5 M" for adipic and less than 0.1 for hydroxyacetic. 

The hydroxycarboxylic acids are uniquely inert to oxidative degradation and inhibit sulfite oxidation in the absence of Mn. Hydroxypropionic acid is economically attractive however, its synthesis from acrylic acid gives polyacrylic acid impurities that would probably have to be separated. Glycolic acid is commerically available but economically somewhat less attractive. 

Zhou, S., Ashok, S., Ko, Y., Kim, D.M., and Park, S. (2014) Development of a deletion mutant of Pseudomonas denitrificans that does not degrade 3-hydroxypropionic acid. AppL Microbiol. Biotechnol, 98 (10), 4389-4398. 

There are two pathways for the degradation of nitriles (a) direct formation of carboxylic acids by the activity of a nitrilase, for example, in Bacillus sp. strain OxB-1 and P. syringae B728a (b) hydration to amides followed by hydrolysis, for example, in P. chlororaphis (Oinuma et al. 2003). The monomer acrylonitrile occurs in wastewater from the production of polyacrylonitrile (PAN), and is hydrolyzed by bacteria to acrylate by the combined activity of a nitrilase (hydratase) and an amidase. Acrylate is then degraded by hydration to either lactate or P-hydroxypropionate. The nitrilase or amidase is also capable of hydrolyzing the nitrile group in a number of other nitriles (Robertson et al. 2004) including PAN (Tauber et al. 2000). 

Organic acids are normally stable to oxidation, but laboratory and pilot plant results (18) have shown that adipic acid oxidizes in conjugation with sulfite oxidation in the scrubber. This paper reports oxidative degradation rate of adipic acid as a function of pH and Mn concentration (19). Results are also presented on sulfopropionic, sulfosuccinic, succinic, hydroxypropionic, and hydroxyacetic acids (20). 

Formic and acetic acids are most attractive, but would probably be volatile under scrubber conditions (8). Succinic and lactic acids would not be cost-effective if purchased at market price. Fumaric acid is more subject to oxidative degradation. Phthalic and Benzoic acids may give undesirable aromatic degradation products. Therefore, the most useful buffers appear to be hydroxypropionic, sulfosuccinic, fumaric, sulfopropionic, adipic, and hydroxyacetic. 

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