Pharma & Specialty Chemical Standards

Cysteine (IUPAC: 2-Amino-3-mercaptopropanoic acid; molecular formula C₃H₇NO₂S, molecular weight 121.16 g/mol) is a non-essential thiol-containing amino acid. It belongs to the class of α-amino acids with a sulfhydryl (-SH) group in its side chain, enabling redox activity. Structurally, its thiol group imparts nucleophilicity and reactivity. Therapeutically, cysteine serves as an antioxidant precursor for glutathione synthesis and a mucolytic agent. It exhibits amphoteric properties, with pKa values of 1.96 (carboxyl) and 8.18 (amino/thiol). Its mechanism involves free radical scavenging via thiol oxidation to form disulfide bonds, critical for protein structure and cellular redox homeostasis.