title: Pt(II) coordination to N1 of 9-methylguanine: why it facilitates binding of additional metal ions to the purine ring.
abstract: The preparation and X-ray crystal structure analysis of {trans-[Pt(MeNH(2))(2)(9-MeG-N1)(2)]}⋅{3 K(2)[Pt(CN)(4)]}⋅6 H(2)O (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(MeNH(2))(2)(H(2)O)(2)](2+) at pH 9.6, 60 °C, and subsequent removal of the [(dien)Pt(II)] entities by treatment with an excess amount of KCN, which converts the latter to [Pt(CN)(4)](2-). Cocrystallization of K(2)[Pt(CN)(4)] with trans-[Pt(MeNH(2))(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 pK(a) values of trans-[Pt(MeNH(2))(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(MeNH(2))(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 [(NH(3))(3)Pt(II)], trans-[(NH(3))(2)Pt(II)], and [(en)Pd(II)] (en=ethylenediamine) by using (1)H NMR spectroscopy. Without exception, binding of the second metal takes place at N7, but formation of a molecular guanine square with trans-[(Me(2)NH(2))Pt(II)] cross-linking N1 positions and trans-[(NH(3))(2)Pt(II)] cross-linking N7 positions could not be confirmed unambiguously, despite the fact that calculations are fully consistent with its existence.
authors.affiliation: Fakultät Chemie, Technische Unversität Dortmund, Otto-Hahn-Strasse 6, 44221 Dortmund, Germany.
authors.forename: Barbara
authors.initials: B
authors.lastname: Müller
authors.forename: Wei-Zheng
authors.initials: WZ
authors.lastname: Shen
authors.forename: Pablo J
authors.initials: PJ
authors.lastname: Sanz Miguel
authors.forename: Francisca M
authors.initials: FM
authors.lastname: Albertí
authors.forename: Tushar
authors.initials: T
authors.lastname: van der Wijst
authors.forename: Marc
authors.initials: M
authors.lastname: Noguera
authors.forename: Luis
authors.initials: L
authors.lastname: Rodríguez-Santiago
authors.forename: Mariona
authors.initials: M
authors.lastname: Sodupe
authors.forename: Bernhard
authors.initials: B
authors.lastname: Lippert
mesh_terms: D003460:Crystallization; D006147:Guanine / Q000031:analogs & derivatives* / Q000737:chemistry; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry; D009944:Organoplatinum Compounds / Q000737:chemistry*; D010984:Platinum / Q000737:chemistry*
chemical_list: D009944:Organoplatinum Compounds; C116701:9-methylguanine; D010984:Platinum; D006147:Guanine; D009584:Nitrogen