Magnesium carbonate serves as a poorly soluble base and magnesium supplement in biochemical applications. Its controlled reactivity and calcite-like structure make it particularly suitable for antacid neutralization studies, protein desalting processes, and magnesium-dependent enzyme activation.
Chemical Properties
Magnesium carbonate (MgCO₃, molecular weight 84.31 g/mol) forms white trigonal crystals with a density of 2.96 g/cm³ and decomposes at approximately 350°C. It is isomorphous with calcite, where Mg²⁺ ions occupy octahedral coordination sites surrounded by six oxygen atoms from planar CO₃²⁻ anions (Mg–O distance: 2.10 Å; C–O distance: 1.28 Å).
The compound is practically insoluble in water (0.01 g/L at 20°C) but readily reacts with acids according to the reaction: MgCO₃ + 2H⁺ → Mg²⁺ + H₂O + CO₂. Upon heating above 300°C, it thermally decomposes into magnesium oxide (MgO) and carbon dioxide (CO₂). Hydrated forms such as trihydrate (nesquehonite) exhibit increased solubility compared to the anhydrous form.
Biochemical Applications
In protein chemistry, magnesium carbonate is used as a 5–10% suspension to remove sodium chloride from protein fractions through differential precipitation at alkaline pH (9–10). In enzymology, 1–5 mM suspensions are employed to provide Mg²⁺ cofactors essential for kinase and ATPase activity while minimizing interference from soluble salts.
In molecular biology, it is applied during plasmid DNA purification to neutralize alkaline lysates and facilitate SDS precipitation. In histological applications, its acid reactivity is exploited for carbonate endpoint detection, particularly in bone mineral analysis.
