A bis(terpyridine) modified single-stranded DNA smoothly forms a stable cycle by Fe2+-assisted ring closure. A novel, complex type of allosteric behavior is observed with Zn2+, which reversibly off-regulates binding of a complementary oligonucleotide only in a narrow concentration range.

Seeing the light: Upon binding to a complementary nucleic acid, a metal‐complex–DNA conjugate releases copper(II) ions that activate the precatalyst 1,10‐phenanthroline (phen) and amplify the primary signal through catalytic production of a fluorescent dye (DCF). This combination of allosteric signal transduction and catalytic signal amplification imitates biological signaling cascades. tpy=2,2′:6′,2′′‐terpyridine.

Conjugation of usually impermeable peptide nucleic acids (PNA) to the chelator 2,2':6',2' '-terpyridine strongly promotes cellular and nuclear uptake by cultured HeLa cells. Cellular accumulation is further enhanced in the presence of extracellular Zn2+.

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