Loss of Hoogsteen pairing ability upon N1 adenine platinum binding

Photoactivation of trans diamine platinum complexes in aqueous solution and effect on reactivity towards nucleotides

We show that UVA irradiation (365nm) of the Pt(IV) complex trans,trans,trans-[Pt(IV)Cl(2)(OH)(2)(dimethylamine)(isopropylamine)] (1), induces reduction to Pt(II) photoproducts. For the mixed amine Pt(II) complex, trans-[Pt(II)Cl(2)(isopropylamine)(methylamine)] (2), irradiation at 365nm increases the rate and extent of hydrolysis, triggering the formation of diaqua species. Additionally, irradiation increases the extent of reaction of complex 2 with guanosine-5'-monophosphate and affords mainly the bis-adduct, while reactions with adenosine-5'-monophosphate and cytidine-5'-monophosphate give rise only to mono-nucleotide adducts. Density Functional Theory calculations have been used to obtain insights into the electronic structure of complexes 1 and 2, and their photophysical and photochemical properties. UVA-irradiation can contribute to enhanced cytotoxic effects of diamine platinum drugs with trans geometry.

Cobalt(III) Complexes of Monodentate N(9)-Bound Adeninate (ade-), [Co(ade-κN9)Cl(en)2]+ (en = 1,2-Diaminoethane): Syntheses, Crystal Structures, and Protonation Behaviors of the Geometrical Isomers

In acidic aqueous solution, a cobalt(III) complex containing monodentate N(9)-bound adeninate (ade(-)), cis-[Co(ade-kappaN(9))Cl(en)(2)]Cl (cis-[1]Cl), underwent protonation to the adeninate moiety without geometrical isomerization or decomposition of the Co(III) coordination sphere, and complexes of cis-[CoCl(Hade)(en)(2)]Cl(2) (cis-[2]Cl(2)) and cis-[Co(H(2)ade)Cl(en)(2)]Cl(3) (cis-[3]Cl(3)) could be isolated. The pK(a) values of the Hade and H(2)ade(+) complexes are 6.03(1) and 2.53(12), respectively, at 20 degrees C in 0.1 M aqueous NaCl. The single-crystal X-ray analyses of cis-[2]Cl(2).0.5H(2)O and cis-[3]Cl(2)(BF(4)).H(2)O revealed that protonation took place first at the adeninate N(7) and then at the N(1) atoms to form adenine tautomer (7H-Hade-kappaN(9)) and cationic adeninium (1H,7H-H(2)ade(+)-kappaN(9)) complexes, respectively. On the other hand, addition of NaOH to an aqueous solution of cis-[1]Cl afforded a mixture of geometrical isomers of the hydroxo-adeninato complex, cis- and trans-[Co(ade-kappaN(9))(OH)(en)(2)](+). The trans-isomer of chloro-adeninato complex trans-[Co(ade-kappaN(9))Cl(en)(2)]BF(4) (trans-[1]BF(4)) was synthesized by a reaction of cis-[2](BF(4))(2) and sodium methoxide in methanol. This isomer in acidic aqueous solution was also stable toward isomerization, affording the corresponding adenine tautomer and adeninium complexes (pK(a) = 5.21(1) and 2.48(9), respectively, at 20 degrees C in 0.1 M aqueous NaCl). The protonated product of trans-[Co(7H-Hade-kappaN(9))Cl(en)(2)](BF(4))(2).H(2)O (trans-[2](BF(4))(2).H(2)O) could also be characterized by X-ray analysis. Furthermore, the hydrogen-bonding interactions of the adeninate/adenine tautomer complexes cis-[1]BF(4), cis-[2](BF(4))(2), and trans-[2](BF(4))(2) with 1-cyclohexyluracil in acetonitrile-d(3) were investigated by (1)H NMR spectroscopy. The crystal structure of trans-[Co(ade)(H(2)O)(en)(2)]HPO(4).3H(2)O, which was obtained by a reaction of trans-[Co(ade)(OH)(en)(2)]BF(4) and NaH(2)PO(4), was also determined.

Molecular Interactions of Nucleic Acid Bases. A Review of Quantum-Chemical Studies

Ab initio quantum-chemical calculations with inclusion of electron correlation significantly contributed to our understanding of molecular interactions of DNA and RNA bases. Some of the most important findings are introduced in the present overview: structures and energies of hydrogen bonded base pairs, nature of base stacking, interactions between metal cations and nucleobases, nonplanarity of isolated nucleobases and other monomer properties, tautomeric equilibria of nucleobases, out-of-plane hydrogen bonds and amino acceptor interactions. The role of selected molecular interactions in nucleic acids is discussed and representative examples where these interactions occur are given. Also, accuracy of density functional theory, semiempirical methods, distributed multipole analysis and empirical potentials is commented on. Special attention is given to our very recent reference calculations on base stacking and H-bonding. Finally, we briefly comment on the relationship between advanced ab initio quantum-chemical methods and large-scale explicit solvent molecular dynamics simulations of nucleic acids.

Association patterns of platinated purine nucleobases in metal-modified pairs and triples

Blocking of Watson-Crick or Hoogsteen edges in purine nucleobases by a metal entity precludes involvement of these sites in interbase hydrogen bonding, thereby leaving the respective other edge or the sugar edge as potential H bonding sites. In mixed guanine, adenine complexes of trans-a2PtII (a = NH3 or CH3NH2) of composition trans-[(NH3)2Pt(9-EtA-N1)(9-MeGH-N7)](NO3)2 (1a), trans-[(NH3)2Pt(9-EtA-N1)(9-MeGH-N7)](ClO4)2 (1b), and trans,trans-[(CH3NH2)2(9-MeGH-N7)Pt(N1-9-MeA-N7)Pt(9-MeGH-N7)(CH3NH2)2](ClO4)4*2H2O (2) (with 9-EtA = 9-ethyladenine, 9-MeA= 9-methyladenine, 9-MeGH = 9-methylguanine), this aspect is studied. Thus, in 1b pairing of two adenine ligands via Hoogsteen edges and in 2 pairing of two guanine bases via sugar edges is realized. These situations are compared with those found in a series of related complexes.