Nucleobase and DNA Binding

We have investigated [83] reactions of complexes [(ri -arene)Ru(en)Xj , where arene = biphenyl (Bip), tetrahydroanthracene (THA), dihydroanthracene (DHA), p-cymene (Cym) and benzene (Ben), X = Cl or HgO, with nucleic add derivatives using H, and ( N-en) NMR spectroscopy. For mononucleosides, (ri -biphenyl)Ru(en) (Fig. 2.12) binds only to N7 ofguanosine (G base), to N7 

In competitive studies with G, A, T and C nucleotides (R = sugar phosphate), binding is observed only to G N7. 

The reactivity of the various binding sites of nucleobases towards Ru(II) at neutral pH decreases in the order  

Therefore, diamino Ru(II) arene complexes can be more highly discriminatory between G and A bases than square-planar Pt(II) complexes. The site-selectivity appears to be controlled by the en-NH2 groups, which H-bond with exocyclic oxygens (e.g. C60 of G, see Fig. 2.15) but are non-bonding and repulsive towards exocyclic amino groups of the nucleobases (e.g. G6NH2 of A, Fig. 2.13). For mononucleotides, the same pattern of site selectivity is observed, and significant amounts of the 5 -phosphate-bound species (40-60%) are present at equilibrium 

Fig- 2.13 H-bonding and steric interactions which give rise to strong binding of (r -atene)Ru(en) to guanine but very weak binding to adenine [83]. 

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