Copper complex formation as indicated by color change. (a) Chemical structures of compounds referenced in the text: 5,7-DiCl-8-OHQ, 5,7-dichloro-8-hydroxyquinoline; 8-OHQ, 8-hydroxyquinoline; CQ, clioquinol; PDTC, pyrrolidine dithiocarbamate. (b) 50 mM of PDTC, CQ, or tetrathiomolybdate (TM) were mixed in a 1:1 molar ratio with CuCl2. All solutions were made in dimethylsulfoxide. In each case the appearance of intensified color indicated formation of a copper complex.