Spectroscopic evidence for the formation of goldfingers.

Gold(I) has long been used in the treatment of rheumatoid arthritis, but the therapeutically relevant biological targets of gold(I) are not well understood. Here, we report the results of a spectroscopic investigation into the formation of goldfingers. By exploiting a thiolate to gold charge-transfer band in the UV, we observed that gold(I) interacts with zinc finger peptides with a stoichiometry of one gold ion for each two cysteine residues, forming 1:1, 1.5:1, and 2:1 adducts with zinc finger peptides containing CCHH, CCHC, and CCCC donor sets, respectively. In addition, circular dichroism experiments provided evidence that goldfingers are more ordered than the corresponding metal-free peptides but do not exhibit the canonical zinc finger structure.