Cu(I) Luminescence from the Tetranuclear Cu₄S₄ Cofactor of a Synthetic 4-Helix Bundle

The addition of Cu(I) to the random-coil peptide, C16C19-GGY, produces a self-organized, metal-bridged 4-helix bundle which displays an intense room-temperature luminescence at 600 nm. Emission, UV, and CD titrations along with X-ray absorption studies indicate that the luminescent cofactor is likely a Cu₄S₄ cluster in which each Cu atom is bridged by the side chains of two cysteine residues and has terminal N/O ligation.