Adding an acid such as hydrochloric acid or sulphuric acid to the sodium carboxylate would free the carboxylic acid.
2
Such hydrogen bonding induces a more negative charge on the carboxyl oxygen atoms leading to an increase in the carboxyl oxygen atoms leading to an increase in the carboxylate pK a.
3
The model of protein carboxylate - hydroxyapatite surface binding proposed from our recent work.