Variations in the Optical Activity of L-Arginine in Electrolyte and Nonelectrolyte Solutions

Specific rotations [α] of L-arginine in water and aqueous solutions of glycine, HCl, LiCl, KCl, NaOH, and Na₂SO₄ were measured at 405 nm. The [α] value is 34.7 ± 0.5 deg·mL·dm^-1·g^-1 in water and increases with the increasing acidity in accordance with the Clough-Lutz-Jirgensons (CLJ) rule. [α] changes little in glycine solutions, implying that the CLJ effect is the result of a proton-amino acid interaction. In the salt solutions, [α] gradually decreases with the increasing concentration, suggesting that binding between a metal ion and L-arginine produces a different structure from that of the protonated amino acid, producing the anti-CLJ effect.