N,N,O and N,O,N Meridional cis Coordination of Two Guanines to Copper(II) by d(CGCGCG)2.

Many research groups study the generation of supramolecular n-dimensional arrays by combining metals with DNA building blocks. Most of the time, the natural nucleobases are modified to obtain higher-affinity metal binding sites. Using unmodified nucleobases avoids a potentially difficult synthesis; however, they have the possible disadvantage of a less defined and/or weaker coordination mode of the metal. Structural studies on the behavior of copper(II) as a linking metal and guanine as the natural ligand for metals in unmodified DNA are reported. Previously, the ability of mono- and dinuclear metal complexes to induce Z-DNA has been explored [Medina-Molner, A.; Spingler, B. Chem. Commun. 2012, 48, 1961; Medina-Molner, A.; Rohner, M.; Pandiarajan, D.; Spingler, B. Dalton Trans. 2015, 44, 3664]. Herein, X-ray crystallographic studies of the structures resulting from the combination of copper(II) ions with DNA hexamers of the general sequence d(CG)3 are presented. Three different packing motifs were observed in three crystal structures with resolutions ranging from 2.15 to 1.45 Å. The motifs are dependent upon other cations being present and/or the crystallization conditions. The first examples of intramolecular O6,N7-chelates of a neutral purine nucleobase to copper(II) were obtained as well as the first meridional N,N,O and N,O,N coordination modes of two guanines to copper(II). The fascinating coordination chemistry of copper(II) complexes generated by the Z-DNA oligonucleotides and the differences to simple nucleobases complexes with copper(II) are discussed in detail.

Mono- and dinuclear metal complexes containing the 1,5,9-triazacyclododecane ([12]aneN3) unit and their interaction with DNA.

The ability of mononucleating and dinucleating macrocylic polyamines and their novel nickel, copper and zinc complexes to induce the left-handed form of poly d(GC) was evaluated. The influence of the nuclearity, the presence or absence of metals ions, the linker length in the case of dinucleating ligands and the metal ion was determined. Almost all dinuclear metal complexes efficiently induced Z-DNA, the zinc ones being the least and the copper ones the most efficient ones. Additionally, the X-ray structures of three dinuclear metal complexes and one partially protonated ligand could be determined.