PtII Coordination to N1 of 9‐Methylguanine: Why it Facilitates Binding of Additional Metal Ions to the Purine Ring |
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| Authors: | Dr Barbara Müller Dr Wei‐Zheng Shen Dr Pablo J Sanz?Miguel Dr Francisca M Albertí Dr Tushar van der Wijst Dr Marc Noguera Dr Luis Rodríguez‐Santiago Prof Mariona Sodupe Prof Bernhard Lippert |
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| Institution: | 1. Fakult?t Chemie, Technische Unversit?t Dortmund, Otto‐Hahn‐Strasse 6, 44221 Dortmund (Germany), Fax: (+49)?231‐755‐3797;2. Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Universidad de Zaragoza—CSIC, 50009 Zaragoza (Spain);3. Department de Química, Universitat Autónoma Barcelona, Bellaterra, 08193 Barcelona (Spain) |
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| Abstract: | The preparation and X‐ray crystal structure analysis of {trans‐Pt(MeNH2)2(9‐MeG‐N1)2]} ? {3 K2Pt(CN)4]} ? 6 H2O ( 3 a ) (with 9‐MeG being the anion of 9‐methylguanine, 9‐MeGH) are reported. The title compound was obtained by treating Pt(dien)(9‐MeGH‐N7)]2+ ( 1 ; dien=diethylenetriamine) with trans‐Pt(MeNH2)2(H2O)2]2+ at pH 9.6, 60 °C, and subsequent removal of the (dien)PtII] entities by treatment with an excess amount of KCN, which converts the latter to Pt(CN)4]2?. Cocrystallization of K2Pt(CN)4] with trans‐Pt(MeNH2)2(9‐MeG‐N1)2] is a consequence of the increase in basicity of the guanine ligand following its deprotonation and Pt coordination at N1. This increase in basicity is reflected in the pKa values of trans‐Pt(MeNH2)2(9‐MeGH‐N1)2]2+ (4.4±0.1 and 3.3±0.4). The crystal structure of 3 a reveals rare (N7,O6 chelate) and unconventional (N2,C2,N3) binding patterns of K+ to the guaninato ligands. DFT calculations confirm that K+ binding to the sugar edge of guanine for a N1‐platinated guanine anion is a realistic option, thus ruling against a simple packing effect in the solid‐state structure of 3 a . The linkage isomer of 3 a , trans‐Pt(MeNH2)2(9‐MeG‐N7)2] ( 6 a ) has likewise been isolated, and its acid–base properties determined. Compound 6 a is more basic than 3 a by more than 4 log units. Binding of metal entities to the N7 positions of 9‐MeG in 3 a has been studied in detail for (NH3)3PtII], trans‐(NH3)2PtII], and (en)PdII] (en=ethylenediamine) by using 1H NMR spectroscopy. Without exception, binding of the second metal takes place at N7, but formation of a molecular guanine square with trans‐(Me2NH2)PtII] cross‐linking N1 positions and trans‐(NH3)2PtII] cross‐linking N7 positions could not be confirmed unambiguously, despite the fact that calculations are fully consistent with its existence. |
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| Keywords: | bioinorganic chemistry guanine nucleobases platinum transition metals |
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