= 3-hydroxypropionate
<3-hydroxypropionate> is the <conjugate base> formed when the <carboxyl group> of <3-hydroxypropionic acid> loses a proton. Its structure is
$$
\mathrm{HOCH_2CH_2COO^-}.
$$
The primary ChEBI record gives formula $\mathrm{C_3H_5O_3}$, 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.<3-hydroxypropionate in ChEBI>[CHEBI:16510, Definition, Formula, Net Charge, IUPAC Name and Ontology]{ref}
The acid–base pair can be represented as
$$
\mathrm{HOCH_2CH_2COOH}\rightleftharpoons
\mathrm{H^+}+\mathrm{HOCH_2CH_2COO^-}.
$$
In a dilute-solution approximation with activity coefficients treated as equal, the <Henderson-Hasselbalch equation> gives
$$
\frac{[\mathrm{A^-}]}{[\mathrm{HA}]}=10^{\mathrm{pH}-\mathrm pK_a}.
$$
At a pH one unit above the relevant $\mathrm pK_a$, 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 $\mathrm pK_a$ 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 $89.070\,\mathrm{g/mol}$ 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.<3-hydroxypropionate in ChEBI>[Average Mass and conjugate-acid relation]{ref}
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