Supramolecular architectures assembled by the interaction of purine nucleobases with metal-oxalato frameworks. Non-covalent stabilization of the 7H-adenine tautomer in the solid-state

Abstract

The synthesis, crystal structure and variable-temperature magnetic measurements of the compounds [Mn(mu-ox)(H2O)(7H-pur-kappaN9)]n (1), {[Mn(mu-ox)(H2O)2].(7H-ade).(H2O)}n (2) and {[Cu(mu-ox)(H2O)(7H-ade-kappaN9)][Cu(mu-ox)(mu-H2O)(7H-ade-kappaN9)]. approximately 10/3H2O}n (3), (where ox: oxalato dianion, pur: purine, and ade: adenine) are reported. Compounds 1and 2 contain one-dimensional chains in which manganese(II) atoms are bridged by bis-bidentate oxalato ligands. The distorted octahedral geometry around each metal centre is completed in compound 1 by one water molecule and the imidazole N9 donor site of the purine ligand, which is a rare example of direct binding between the Mn(II) ion and the N donor site of an isolated nucleobase. Unlike 1, the adenine moiety in compound 2 is not bonded to manganese atoms and the metal coordination polyhedron is filled by two water molecules in a cis-arrangement. Its crystal building is constructed from pi-stacked layers of Watson-Crick hydrogen-bonded adenine...(H2O2)...adenine aggregates and zig-zag Mn(II)-oxalato chains held together by means of a strong network of hydrogen bonding interactions. The nucleobase exists in the lattice as the 7H-adenine tautomer which represents an unprecedented solid-state characterization of this minor tautomer as free molecule (without metal coordination) stabilized through non-covalent interactions. Compound consists of two slightly different [Cu(ox)(H2O)(7H-ade-kappaN9)] units in which the nucleobase coordinates through the imidazole N9 atom. The planar complex entities are parallel stacked and joined by means of long Cu-O bonds involving oxygen atoms from the oxalato and the aqua ligands, giving one-dimensional chains with a [4 + 1] square-planar pyramidal and a [4 + 2] octahedral coordination around the metal centre, respectively. Self-assembled process of compound 3 is further driven by an in-plane network of hydrogen bonding interactions to generate a porous 3D structure containing parallel channels filled by guest water molecules. Variable-temperature magnetic susceptibility measurements of all the complexes show the occurrence of antiferromagnetic interactions between the paramagnetic centres. DFT calculations have been performed to check the influence of packing in the stability of the 7H-amino tautomer of 2 and in the complex geometry of 3.

Elementary Molecular Mechanisms of the Spontaneous Point Mutations in DNA: A Novel Quantum-Chemical Insight into the Classical Understanding

“…The existence of other Ade tautomers was evidenced by experimental studies (García-Terán et al, 2006;Gu & Leszczynski, 1999;Lührs et al, 2001;Stepanyugin et al, 2002a;Sukhanov et al, 2003), often in the presence of a metal (Samijlenko et al, 2004;Vrkic et al, 2004). It was also found that the Ade imino tautomer is more stabilized under the influence of charged platinum (Burda et al, 2000) or mercury (Zamora et al, 1997) cations.…”

Supramolecular Structures and Tautomerism of Carboxylate Salts of Adenine and Pharmaceutically Relevant N6-Substituted Adenine

“…[23][24][25][26] In recent years the influence of hydrogen bonding interactions and molecular recognition on tautomeric and protonation equilibria has received growing interest and a few examples have been reported in the literature, where a noncanonical nucleobase tautomer is stabilized by a properly positioned H bond acceptor. [27][28][29] Salt and co-crystal formation are popular approaches to optimize the physicochemical properties of a pharmaceutically relevant solid without modifying the molecule itself. [30][31][32] It is well-established that the solid-state properties of a pharmaceutical solid have a significant impact on drug performance.…”

Molecular Recognition of Protonated Cytosine Ribbons by Metal–Oxalato Frameworks

“…3 The interest of these systems stems from the desire to better understand the complex interactions often present in a great diversity of molecular biorecognition processes 4 and to offer a powerful tool for the efficient synthesis of advanced functional materials with tailor-made properties and potential applications for the therapeutic medicine 5 and the material sciences. 6 Most of the studies concerning DNA/RNA nucleobases have been realized in gas phase or aqueous media, 7 but notable advances have been made in the solid-state chemistry such as (without being exhaustive): (a) the design and improvement of chemical biology tools and/or pharmaceutical agents, 8 (b) the building of high-dimensional covalent architectures containing nucleobases as bridging or terminal ligands, 9 (c) the stabilization of noncanonical tautomers through interactions with metallic ions 10 and/or hydrogen-bonding donor/acceptor species, 1,11 and (d) the development of artificial receptors for specific DNA/RNA bases recognition for their use as nucleotide sensors or for the determination of low concentrations of therapeutic agents. 12 Following these lines of investigation, we have recently reported the elaboration and solid-state characterization of supramolecular architectures isolated from aqueous solution at physiological pH in which adenine aggregates reside between neutral one-dimensional (1D) metal-oxalato-water complexes to build sheetlike structures containing sequentially arranged organic and inorganic layers.…”