title: Multiple metal binding to the 9-methyladenine model nucleobase involving N1, N6, and N7: discrete di- and trinuclear species with different combinations of monofunctional Pd(II) and Pt(II) entities.
abstract: Several di- and trinuclear metal complexes consisting of the model nucleobase 9-methyladenine (9-MeA) or its mono-deprotonated form (9-MeA(-)) and monofunctional (dien)Pd(II), (dien)Pt(II), (NH(3))(3)Pt(II), or (trpy)Pd(II) in different combinations have been prepared and/or studied in solution by NMR spectroscopy: [{Pd(dien)}(3)(9-MeA(-)-N1,N6,N7)]Cl(3.5)(PF(6))(1.5)·3H(2)O (1), [(dien)Pd(N1-9-MeA-N7)Pt(NH(3))(3)](ClO(4))(4)·9.33H(2)O (2), [(dien)Pt(N1-9-MeA-N7)Pt(NH(3))(3)](ClO(4))(4)·H(2)O (3), and [{(trpy)Pd}(2)(N1,N6-9-MeA(-)-N7)Pt(NH(3))(3)](ClO(4))(5)·3H(2)O (4). A migration product of 3, [(dien)Pt(N6-9-MeA(-)-N7)Pt(NH(3))(3)](3+) (3a), has been identified in solution. Unlike Pt-adenine bonds, Pd-adenine bonds are substantially labile, and consequently all Pd-containing complexes discussed here (1, 2, 4) exist in aqueous solution in equilibria of slowly interconverting species, which give rise to individual resonances in the (1)H NMR spectra. For example, 1 exists in an equilibrium of five adenine-containing species when dissolved in D(2)O, 2 undergoes dissociation to [Pt(NH(3))(3)(9-MeA-N7)](2+) or forms the migration product [(dien)Pd(N6-9-MeA(-)-N7)Pt(NH(3))(3)](3+) (2a), depending on pD, and 4 loses both (trpy)Pd(II) entities as the pD is increased. In no case is Pd binding to N3 of the adenine ring observed. A comparison of the solid-state structures of the two trinuclear complexes 1 and 4 reveals distinct differences between the Pd atoms bonded to N1 and N6 in that these are substantially out of the nucleobase plane in 1, by ca. 0.6 Å and -1.0 Å, respectively, whereas they are coplanar with the 9-MeA(-) plane in 4. These out-of-plane movements of the two (dien)Pd(II) units in 1 are not accompanied by changes in hybridization states of the N1 and N6 atoms.
authors.affiliation: Fakultät Chemie, TU Dortmund, 44221 Dortmund, Germany.
authors.forename: Tímea
authors.initials: T
authors.lastname: Mihály
authors.forename: Marta
authors.initials: M
authors.lastname: Garijo Añorbe
authors.forename: Francisca M
authors.initials: FM
authors.lastname: Albertí
authors.forename: Pablo J
authors.initials: PJ
authors.lastname: Sanz Miguel
authors.forename: Bernhard
authors.initials: B
authors.lastname: Lippert
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000737:chemistry; D001665:Binding Sites; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009944:Organoplatinum Compounds / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D009944:Organoplatinum Compounds; D010165:Palladium; C013115:9-methyladenine; D000225:Adenine