The Crystal Structure ofl-Cysteic Acid

Abstract The crystal structure of cysteic acid, C3H7NO5S, has been determined. The crystal is orthorhombic with a space group of P212121, and four molecules are in a unit cell with these dimensions: a=8.35, b=10.16, and c=7.44 Å. The molecule is a zwitter ion, −O3SCH2CH-(NH3+)COOH; its dimensions are generally similar to those found in other amino acids and sulfonic acids. The acidic groups occupy the trans positions with respect to the Cα–Cβ bond, while the amino group is in a gauche position to the sulfonic group and forms an intramolecular hydrogen bond between them.