= Iduronate
<Iduronate> is the <conjugate base> of <iduronic acid>, formed when its <carboxyl group> loses a proton. Starting from neutral $\mathrm{C_6H_{10}O_7}$, proton loss gives the free-monomer <molecular formula> $\mathrm{C_6H_9O_7^-}$. The usual biological discussion concerns the L-iduronate series.<Iduronic acid in ChEBI>[CHEBI:24769, Formula and conjugate-base relationship to CHEBI:33820]{ref}
Ionization and <epimerization> are different operations. Removing the acidic proton changes <electric charge> without changing the carbon stereochemistry. Conversely, <heparosan-N-sulfate-glucuronate 5-epimerase> converts D-<glucuronate> residues into L-<iduronate> residues by changing carbon-5 configuration within a polymer.<Heparosan-N-sulfate-glucuronate 5-epimerase in IUBMB Enzyme Nomenclature>[EC 5.1.3.17, Reaction]{ref}
Charge accounting makes the distinction quantitative. A solution containing $1\,\mathrm{mmol}$ of singly charged iduronate anions requires one millimole of monovalent positive <counterions> for electrical neutrality, if no other charged species contribute. That statement concerns charge balance, not a specification of which salt was prepared. In a <polysaccharide>, the iduronate name instead refers to a linked residue; its atom inventory cannot be substituted unchanged for a free monomer's formula.
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