RESUMO
The reaction of tetrakis(pyridine-2-yl)pyrazine (tppz) with 2â equiv of (2,2'-bpy)Pt(II) in water yields two isomeric dinuclear cations, [{Pt(2,2'-bpy)}2 (tppz)](4+) , in which Pt coordination exclusively takes place through the two pairs of pyridine-2-yl nitrogen atoms. The two conformational isomers differ in their overall shape, with the formation of "Z" and "U" shapes, which are formed at 40 °C (Z isomer, 1) and under reflux conditions (U isomer, 2), respectively. X-ray crystal-structure analyses of the Zâ isomer, [{Pt(2,2'-bpy)}2 (tppz)](PF6 )4 â 3 CHCl3 â 4 H2 O (1 a), and of the Uâ isomer, [{Pt(2,2'-bpy)}2 ](PF6 )4 â 2 CH3 CNâ 1.5 H2 O (2 a), were carried out. Co-crystallization of compound 2 with PtCl2 (2,2'-bpy) yielded [{Pt(2,2'-bpy)}2 (tppz)](BF4 )4 â [PtCl2 (2,2'-bpy)]â 4.5 H2 O (3), in which the PtCl2 (2,2'-bpy) entity was sandwiched between the two 2,2'-bpy faces of the U-shaped cation (2). Quantum chemical calculations revealed that the Uâ isomer was more stable than the Zâ isomer, both in the gas phase and in an aqueous environment. These two isomers display different affinities toward duplex DNA and human telomeric quadruplex DNA (Htelo), as concluded from CD spectroscopy and FID assays. Thus, the Uâ isomer binds significantly more strongly to quadruplex DNA (DC50 =0.38â µM) than the Zâ isomer (DC50 =8.50â µM).
Assuntos
Complexos de Coordenação/química , Quadruplex G , Platina/química , Cristalografia por Raios X , DNA/química , DNA/metabolismo , Humanos , Isomerismo , Conformação Molecular , Pirazinas/química , Teoria Quântica , Telômero/químicaRESUMO
Pt···Pt···Pt interactions via their d(8) orbitals, combined with π-π stacking of deprotonated, chelating 2-(3'-pyrazolyl)pyridine (pyzpy) ligands, are responsible for trans-Pt(pyzpy)(2) (2) crystallization in a stack of three molecules unsupported by any bridging ligand.