Stabilisation of unusual simultaneous binding of four cytosine nucleobases to copper(II) by a novel network of bifurcated hydrogen bonding

Abstract

The crystal structure of tetrakis(cytosine)copper(rI) perchlorate dihydrate has been determined. All the hydrogen atoms were obtained from Fourier-difference synthesis. The geometry around copper is a bicapped octahedron (4 + 2 + 2*). The adjacent cytosine rings are oriented head-to-tail with respect to each other and are roughly at right angles to the co-ordination plane. The exocyclic 0x0 groups form an interligand, intracomplex hydrogen-bonding network above and below the co-ordination plane with the exocyclic amino groups of alternate cytosine bases. The EPR and electronic spectra are consistent with the retention of the solid-state structure in solution. The steric effect of the C(2)=0 group of cytosine is offset by the presence of the intracomplex hydrogen-bonding network. The trend in El values of Cu"-Cu' couples for 1 : 4 complexes of cytosine, cytodine, pyridine, 2-methylpyridine and N-methylimidazole suggests that both steric effects and n-delocalization in imidazole and pyridine ligands and the steric effect of C(2)=0 in pyrimidine ligands are important in stabilising Cu' relative to Cu".

Interaction of the DNA bases and their mononucleotides with pyridine-2-carbaldehyde thiosemicarbazonecopper(II) complexes. Structure of the cytosine derivative

“…Notwithstanding, the intramolecular 2.687(5) Å and 2.726(5) Å CuÁ Á ÁO12 distances for B and A, respectively, could be interpreted as a (4 + 1) pseudocoordination. In fact, these lengths fall inside the 2.55-2.80 Å range reported in the literature for the cytosine Cu-O bonds [21,[33][34][35][36]. This feature is also supported by the Cu-N13-C12 and Cu-N13-C14 angles: 108.1(4)/ 129.1(4)°and 106.3(4)/132.6(4)°for A and B, respectively.…”

The replacement of chlorides by cytosines in copper(II) complexes containing guanidine derivatives

“…It was found that the predominant metal binding site of cytosine nucleobase is the nitrogen atom N(3) (Scheme 2) [11,12,14,15,17,23,24]. In addition, the secondary interaction between copper and the O(2) exocyclic carbonyl group of cytosine also exists in a few cases [16,25,26].…”

“…These activities have guided us to prepare copper(II) complexes containing a CuN 2 Cl 2 chromophore analog to cisplatin and then to study their interactions with DNA nucleobases. Several studies have mainly focused on the direct interaction of metal salts, where M = Cu, Rh, Cd, Mn or Co, with the cytosine nucleobase and its derivative 1-methylcytosine [12][13][14][15][16][17][18][19], but not the direct nucleobase replacement of the anionic ligands on metal complexes like the cisplatin system. However, Reedijk and coworkers have studied on interactions of the octahedral ruthenium(II) complexes [cis-Ru(bpy) 2 Cl 2 ] [20] and [a-Ru(azpy) 2 -(NO 3 ) 2 ] [21] (bpy = 2,2 0 -bipyridine and azpy = 2-(phenylazo)pyridine) with 9-ethylguanine, 9-methylhypoxanthine and guanosine, which replace only one of the two anionic ligands to yield the monofunctional binding adducts.…”

Structures, spectra, and DNA-binding properties of mixed ligand copper(II) complexes of iminodiacetic acid: The novel role of diimine co-ligands on DNA conformation and hydrolytic and oxidative double strand DNA cleavage

“…The frozen solution EPR spectra of the complexes are axial with g i > g^> 2.0 and G = [(g i À 2)/ (g^À 2)] = 3.6 suggesting that the nearly square-based geometries observed in the solid state are retained in solution. Further, a square-based CuN 4 chromophore is expected [45,46] to show a g i value of 2.200 and an A i value of 180-200 · 10 À4 cm À1 (Table 3) and the replacement of nitrogen atom in this chromophore by an oxygen atom is expected to increase the g i value and decrease the A i value. On the other hand, incorporation of strong axial interaction as in the present complexes would increase the g i and decrease the A i values.…”