title: Acid dissociation and metal complex formation constants of penicillamine, cysteine, and antiarthritic gold complexes at simulated biological conditions.
abstract: Ionization constants for acid functions of D-penicillamine, L-cysteine, thiomalic acid, and thioglucose were measured by pH titration at 37 degrees and 0.15 M ionic strength. Chelate formation constants for these ligands with calcium(II), iron(III), and gold(I) were then determined under the same conditions chosen to approximate the in vivo situation. Only iron(III) formed both 1:1 and 1:2 chelates with D-penicillamine, L-cysteine, and thiomalate; calcium formed weak and gold strong 1:1 complexes with all ligands studied. Because of precipitate formation, the stability constants for the systems thioglucose-iron(III), D-penicillamine-gold(I), and L-cysteine-gold(I) had to be determined indirectly with thiomalic acid as the competing ligand. The in vivo fate of antiarthritic gold(I) compounds remained uncertain, but gold(I) chelates probably persist as such for extended periods.
mesh_terms: D000143:Acids; D002614:Chelating Agents; D055598:Chemical Phenomena; D002621:Chemistry; D003545:Cysteine; D006046:Gold; D009942:Organometallic Compounds; D010396:Penicillamine; D011199:Potentiometry
chemical_list: D000143:Acids; D002614:Chelating Agents; D009942:Organometallic Compounds; D006046:Gold; D010396:Penicillamine; D003545:Cysteine