3-hydroxypropionic acid

3-hydroxypropionic acid is a three-carbon beta-hydroxy acid with structureIts carboxyl group carbon is numbered 1; the additional hydroxyl group is on carbon 3. The primary ChEBI record identifies the systematic name 3-hydroxypropanoic acid, formula ${\mathrm{C}}_3{\mathrm{H}}_6{\mathrm{O}}_3$ and average molecular mass $90.078g/mol$. The acid and its conjugate base, 3-hydroxypropionate, are distinguished chemical species.^[ref]

Moving the hydroxyl group by one carbon gives the different connectivity of lactic acid, $\mathrm{C}{\mathrm{H}}_3\mathrm{CH}(\mathrm{OH})\mathrm{COOH}$. The two acids have the same molecular formula but are constitutional isomers. Molecular mass alone cannot decide which one a sample contains. The terminal alcohol and the carboxyl group also provide different sites for chemical transformation; the compound’s name specifies the initial structure rather than guaranteeing one reaction pathway.

An experimentally demonstrated motivation is production as a chemical building block by metabolic engineering. In the 2016 primary study by Chan Woo Song and colleagues, engineered Escherichia coli produced $31.1g/L$ of 3-hydroxypropionic acid in fed-batch culture. The study screened enzyme combinations and altered the strain, so the observation concerns a particular engineered production system rather than a universal property of the species.^[ref]

Using the record’s molecular mass, that mass concentration corresponds to approximatelyof acid equivalents. This conversion is an original calculation, not a separate measurement. Product concentration alone gives neither production rate without a time interval nor mass yield without substrate consumption. Chemical identity, accumulated amount and process performance remain different experimental questions.

3-hydroxypropionate is the conjugate base formed when the carboxyl group of 3-hydroxypropionic acid loses a proton. Its structure isThe primary ChEBI record gives formula ${\mathrm{C}}_3{\mathrm{H}}_5{\mathrm{O}}_3$, net charge $-1$ and the systematic name 3-hydroxypropanoate. The terminal hydroxyl group remains present; the acid-to-base change occurs at the carboxyl group, not by moving that hydroxyl or removing the carbon skeleton.^[ref]

The acid–base pair can be represented asIn a dilute-solution approximation with activity coefficients treated as equal, the Henderson-Hasselbalch equation givesAt a pH one unit above the relevant $\mathrm{p}{K}_a$, the ratio is $10:1$, so about $10/11$ of the acid-plus-conjugate-base pool is anionic in that model. This is an illustrative equilibrium calculation; no numerical $\mathrm{p}{K}_a$ for this compound is being supplied.

Speciation and total amount answer different analytical questions. If no other reactions occur, changing pH can redistribute $[\mathrm{HA}]$ and $[{\mathrm{A}}^{-}]$ while preserving their sum. A negatively charged 3-hydroxypropionate ion in a bulk solution is accompanied by compensating positive charge elsewhere; it is not the same molecular species as the neutral acid or a complete named salt.

The record’s average mass of $89.070g/mol$ applies to the anion’s composition. Reporting a concentration as acid equivalents instead uses the acid’s reference mass, while reporting a particular salt requires the salt’s complete composition. This distinction matters when comparing metabolic engineering measurements that use an acid name for a total analytical product pool.^[ref]