Magnesium hydroxide is an inorganic compound widely used in biochemical and analytical laboratories due to its weak basicity, low solubility in water, and high biocompatibility. In research environments, it is commonly applied in antacid neutralization assays, magnesium phosphate precipitation, and controlled pH adjustment in enzymatic reactions. Its crystalline brucite-type structure contributes to its chemical stability and makes it a reliable reagent for laboratory applications requiring gradual hydroxide ion release.

Chemical Properties

Magnesium hydroxide (Mg(OH)₂, molecular weight 58.32 g/mol) appears as a white, odorless powder characterized by a layered brucite crystal structure with a density of approximately 2.34 g/cm³. In this structure, Mg²⁺ ions occupy octahedral coordination sites between hexagonally close-packed hydroxide layers linked by hydrogen bonding. The compound exhibits extremely low solubility in water (K_sp ≈ 5.61 × 10⁻¹²; approximately 0.0009 g/100 mL at 20 °C), producing mildly alkaline suspensions with a pH around 10.5. Under thermal conditions, magnesium hydroxide decomposes at approximately 350 °C to form magnesium oxide (MgO) and water without melting.

Biochemical Applications

Magnesium hydroxide is used in several biochemical and analytical procedures. In protein purification workflows, saturated Mg(OH)₂ suspensions containing free Mg²⁺ ions can selectively precipitate nucleic acids from alkaline lysates, facilitating RNA isolation without the use of organic solvents. In enzymology, controlled concentrations of magnesium ions help activate Mg²⁺-dependent enzymes such as kinases, while the compound can also neutralize phosphate buffers during dialysis procedures. In analytical chemistry, magnesium hydroxide participates in gravimetric determinations involving magnesium ammonium phosphate precipitation and is applied in assays evaluating oxidative processes such as lipid peroxidation.

Laboratory and Cell Culture Uses

In cell culture and biochemical buffer systems, dilute suspensions commonly referred to as “milk of magnesia” may be used to regulate acidic culture media while avoiding excess sodium ion concentrations. This buffering capability, combined with the compound’s low toxicity and controlled hydroxide release, makes magnesium hydroxide a useful reagent for maintaining stable pH conditions in sensitive biological and biochemical experiments.