Selenium

Selenium is an essential trace mineral that functions primarily as a co‑factor for a family of selenoproteins, many of which are antioxidant enzymes and thyroid‑hormone regulators. In humans, it is required in minute amounts but is critical for maintaining cellular redox balance, immune competence, and proper thyroid function.

• Elemental selenium: Atomic number 34, symbol Se.
• Molecular formula: For elemental selenium is Se₈ (a polymeric ring).
• Common supplement forms:
  • Sodium selenite (Na₂SeO₃) and sodium selenate (Na₂SeO₄) for inorganic.
  • Selenomethionine (C₅H₁₁NO₂Se) for organic.
• IUPAC name for selenomethionine: (2S)-2-amino-4-(selenyl)butanoic acid.
• Valence electron configuration: Selenium possesses a 4p⁴ valence electron configuration, enabling multiple oxidation states (+4, +6) that underpin its redox activity.
• Atomic mass: 78.96 g mol⁻¹.
• Melting point: 217 °C.
• Solubility: Low solubility in water (inorganic salts) dictates formulation choices.
• Selenocysteine pKa: Selenocysteine’s selenol group has a pKa ≈5.2, making it a potent nucleophile in enzyme active sites.

• Natural dietary sources:
  • Brazil nuts (up to 800 µg per nut).
  • Seafood (e.g., tuna, 60–120 µg/100 g).
  • Organ meats (liver, 30–50 µg/100 g).
  • Cereals (1–5 µg/100 g).
• Commercial supplements:
  • Extraction: Extraction of selenium from sulfide ores (e.g., copper‑sulfide) followed by chemical conversion to sodium selenite/selenate.
  • Biotechnological synthesis: Biotechnological synthesis of selenomethionine via fermentation of Saccharomyces cerevisiae grown in selenium‑enriched media, yielding a highly bio-available organic form.
• Quality control:
  • GMP manufacturing.
  • Verification of selenium species (organic vs inorganic) via ICP‑MS.
  • Absence of heavy-metal contaminants.
  • Third‑party certifications (USP, NSF) assure potency, purity, and consistent bioavailability across batches.