Delta chirality ruthenium 'light-switch' complexes can bind in the minor groove of DNA with five different binding modes.

[Ru(phen)(dppz)] has been studied since the 1990s due to its 'light-switch' properties. It can be used as a luminescent DNA probe, with emission switched on through DNA binding. The luminescence observed is dependent on the solvent accessibility of the pyrazine nitrogen atoms, and therefore is sensitive to changes in both binding site of the cation and chromophore orientation.

X-ray crystal structure of rac-[Ru(phen)2dppz]2+ with d(ATGCAT)2 shows enantiomer orientations and water ordering.

We report an atomic resolution X-ray crystal structure containing both enantiomers of rac-[Ru(phen)2dppz](2+) with the d(ATGCAT)2 DNA duplex (phen = phenanthroline; dppz = dipyridophenazine). The first example of any enantiomeric pair crystallized with a DNA duplex shows different orientations of the Λ and Δ binding sites, separated by a clearly defined structured water monolayer. Job plots show that the same species is present in solution.

Preferred orientation in an angled intercalation site of a chloro-substituted Λ-[Ru(TAP)2(dppz)]2+ complex bound to d(TCGGCGCCGA)2.

The crystal structure of the ruthenium DNA 'light-switch' complex Λ-[Ru(TAP)2(11-Cl-dppz)](2+) (TAP=tetraazaphenanthrene, dppz=dipyrido[3,2-a':2',3'-c]phenazine) bound to the oligonucleotide duplex d(TCGGCGCCGA)2 is reported. The synthesis of the racemic ruthenium complex is described for the first time, and the racemate was used in this study. The crystal structure, at atomic resolution (1.