Sodium hydroxide (NaOH), commonly known as caustic soda or lye, is a strong alkaline compound widely used in biochemical and molecular biology laboratories. Due to its complete dissociation in aqueous solutions, sodium hydroxide provides a reliable source of hydroxide ions (OH⁻), making it essential for pH adjustment, protein extraction procedures, and saponification reactions in analytical and preparative protocols.
Chemical Properties
Sodium hydroxide forms colorless, odorless crystalline solids or pellets with a density of approximately 2.13 g/cm³ and a melting point of 323°C. When dissolved in water, the process is highly exothermic (ΔH ≈ −44.5 kJ/mol), producing strongly alkaline solutions. A 1 M NaOH solution typically reaches a pH close to 14 with a hydroxide ion concentration of about 1 M. The compound is hygroscopic and deliquescent, rapidly absorbing moisture and carbon dioxide from the atmosphere to form sodium carbonate and hydrated derivatives. Chemically, sodium hydroxide participates in numerous reactions, including ester hydrolysis (saponification), precipitation of metal hydroxides such as Al(OH)₃ and Fe(OH)₃, and reactions with silica in glass (SiO₂ → Na₂SiO₃), which is why it is generally stored in polyethylene or compatible plastic containers.
Biochemical Applications
In protein biochemistry, sodium hydroxide solutions in the range of 0.1–1 M are frequently used to extract membrane-associated proteins from biological tissues or to solubilize inclusion bodies following cell lysis. Concentrations around 0.2 M are also employed to terminate enzymatic reactions, such as protease activity, through rapid and irreversible protein denaturation. In nucleic acid purification protocols, alkaline solutions containing approximately 0.5 M NaOH combined with EDTA are used during plasmid extraction procedures, allowing selective RNA hydrolysis while maintaining the integrity of DNA strands. Sodium hydroxide is also applied in immunological assays, including ELISA plate stripping for reuse of microplates or antibody elution from antigen-affinity columns through high-pH disruption of antigen–antibody interactions. At lower concentrations (typically 10–50 mM), NaOH is used to adjust the pH of buffers required for optimal enzymatic activity, such as conditions suitable for DNA polymerases used in PCR-based techniques.
