CuSO4 (58 lM) and ascorbic acid (72.5 lM) were combined in MOPS buffer (10 mM) at pH 7 and allowed to stand for 3 min at room temperature. The sulfur compound (116 lM) was then added to the reaction mixture and the solution was allowed to stand for an additional 3 min. For spectra with only copper/ascorbic acid or sulfur compound, an equivalent volume of MOPS buffer was added. A similar procedure was used for CuðbipyÞII2 studies except CuðbipyÞII2 (29 lM), ascorbic acid (36.25 lM), and the sulfur compound (58 lM) were used. For