A Conformationally Flexible Dinuclear PtII Complex with Differential Behavior of its Two States toward Quadruplex DNA |
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Authors: | Dr Philipp von Grebe Dr Kogularamanan Suntharalingam Prof Dr Ramon Vilar Dr Pablo J Sanz Miguel Prof Dr Sonja Herres‐Pawlis Prof Dr Bernhard Lippert |
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Institution: | 1. Fakult?t Chemie, Technische Universit?t Dortmund, Otto‐Hahn‐Str. 6, 44221 Dortmund (Germany);2. Department of Chemistry, Imperial College London, South Kensington, London SW7 2AZ (UK);3. Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Universidad de Zaragoza‐CSIC, 50009 Zaragoza (Spain);4. Fakult?t für Chemie und Pharmazie, Ludwig Maximilians Universit?t München, 81377 München (Germany) |
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Abstract: | The reaction of tetrakis(pyridine‐2‐yl)pyrazine (tppz) with 2 equiv of (2,2′‐bpy)PtII 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 Z isomer, {Pt(2,2′‐bpy)}2(tppz)](PF6)4 ? 3 CHCl3 ? 4 H2O ( 1 a ), and of the U isomer, {Pt(2,2′‐bpy)}2](PF6)4 ? 2 CH3CN ? 1.5 H2O ( 2 a ), were carried out. Co‐crystallization of compound 2 with PtCl2(2,2′‐bpy) yielded {Pt(2,2′‐bpy)}2(tppz)](BF4)4?PtCl2(2,2′‐bpy)] ? 4.5 H2O ( 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 U isomer was more stable than the Z 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 U isomer binds significantly more strongly to quadruplex DNA (DC50=0.38 μM ) than the Z isomer (DC50=8.50 μM ). |
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Keywords: | conformation analysis coordination modes DNA molecular tweezers platinum |
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