A Unique Helicate Comprised of Four Cytosine Nucleobases and Four Metal Entities (PtII, PtII, AuIII, AuI). Implications for the Interactions of Linearly Coordinated Metal Ions with Nucleotide Duplexes
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AbstractAbstract. Reaction of trans‐[Pt(CH3NH2)2(1‐MeC‐N3)2]X2 (1‐MeC = 1‐methylcytosine; X = NO3– or ClO4–) with Na[AuCl4] in strongly alkaline aqueous solution yields an asymmetrical double helicate containing two central PtII as well as AuIII and AuI atoms, four 1‐methylcytosinato bridges (1‐MeC–‐N3, N4), two terminal methylamine and two bridging methylamido ligands, [Au2Pt2(CH3NH2)2(CH3NH)2(1‐MeC–)4]Cl2·2H2O (2). The four 1‐MeC– ligands, which are pairwise oriented in head‐head fashion, are deprotonated at their N4 positions and cross‐linked by the gold ions. While one of the gold ions, AuI, adopts a linear coordination arrangement, the second, AuIII, is square‐planar and completes its coordination arrangement through two methylamido ligands, which behave as bridging species between AuIII and Pt. As a consequence of deprotonation of the original methylamine ligands, the nitrogen atoms of the CH3NH– bridges have become chiral. The four heavy metals form a diamond‐shaped plane, with an intramolecular AuIII···AuI distance of 3.053(4) Å. On the basis of the structure of cation 2 a new model is proposed how linear transition metal ions (M) might interact with (natural or artificial) nucleobases (L) within a double helix to produce compact M4L4 adducts.
