Canonical purine−pyrimidine base pairs, the key to the complementary hydrogen bonding in nucleic acids, are fundamental molecular recognition motifs crucial for the formation and stability of double-helical DNA. Consequently, focused study and modeling of nucleobase hydrogen-bonding schemes have spawned a vast array of chemical and biophysical investigations. The Watson−Crick, reverse Watson−Crick, Hoogsteen, and reverse Hoogsteen hydrogen-bonding schemes stabilize various nucleic acid structures. As a result, numerous modified bases have been designed to maximize such interactions, addressing specific problems related to base pairing and giving rise to supramolecular ensembles in solution or in the solid state. It is also important to realize that suitably predisposed imino nitrogens and other functional groups present in heterocyclic nucleobases present a versatile molecular framework for the construction of coordination architectures, which may be harnessed to mimic base polyads and higher order nuclei...

The many facets of adenine: coordination, crystal patterns, and catalysis

The introduction of new noncovalent interactions to build functional systems is of fundamental importance. We here report experimental and theoretical evidence that anion−π interactions can contribute to catalysis. The Kemp elimination is used as a classical tool to discover conceptually innovative catalysts for reactions with anionic transition states. For anion−π catalysis, a carboxylate base and a solubilizer are covalently attached to the π-acidic surface of naphthalenediimides. On these π-acidic surfaces, transition-state stabilizations up to ΔΔGTS = 31.8 ± 0.4 kJ mol–1 are found. This value corresponds to a transition-state recognition of KTS = 2.7 ± 0.5 μM and a catalytic proficiency of 3.8 × 105 M–1. Significantly increasing transition-state stabilization with increasing π-acidity of the catalyst, observed for two separate series, demonstrates the existence of “anion−π catalysis.” In sharp contrast, increasing π-acidity of the best naphthalenediimide catalysts does not influence the more than 12 0...

Anion−π Catalysis

Spectral characterization, cyclic voltammetry, morphology, biological activities and DNA cleaving studies of amino acid Schiff base metal(II) complexes

Interaction of water-soluble amino acid Schiff base complexes with bovine serum albumin: fluorescence and circular dichroism studies.

In this manuscript we report a high-level ab initio study of anion−π interactions involving N9-methyl-adenine, N6-methyl-adenine, N9-methyl-hypoxanthine, a dimer of N9-methyl-adenine, and N9,N9‘-trimethylene-bisadenine. DNA bases like adenine are electron-deficient arenes that are well suited for interacting favorably with anions. We demonstrate that these compounds are able to interact favorably with anions. N9-Methyl-adenine, N6-methyl-adenine, and the dimer of N9-methyl-adenine interact with the anion via the six-membered ring more strongly than adenine due to cooperativity effects between the noncovalent π−π and anion−π interactions. This pattern, i.e., coexistence of π−π and anion−π bonding, is observed experimentally in the solid state. Finally, we report the solid-state characterization of two new compounds N6,N6‘-dimethylene-bisadenine hydrochloride and an outer-sphere complex of protonated N9,N9‘-trimethylene-bishypoxanthine with zinc tetrachloride anion, that exhibit interesting anion−π interact...

Anion−π Interactions in Bisadenine Derivatives: A Combined Crystallographic and Theoretical Study

Crystal structures of two copper(II) ternary complexes of N -salicylidene-tryptophanato with 2-aminopyridine and 2-aminopyrimidine

X-ray diffraction structures of two N-salicylidene tryptophananato diaquocopper(II) complexes: erythro and threo isomers

The monomeric [M(ACV)2(H2O)4]Cl2·2ACV (M = NiII 1 or CoII 2), [Zn(ACV)Cl2(H2O)] 3 and the polymeric [Cd(ACV)Cl2]·H2O 4 [ACV = acyclovir = 9-(2-hydroxymethoxymethyl)guanine] complex have been prepared and characterised by X-ray diffraction and IR data; 1H and 13C NMR have been used to interpret the structural characteristics of the complexes in solution. Compounds 1 and 2 exist as octahedral complexes with four H2O ligands in the basal plane [Ni–OW 2.053(2) and 2.057(7) A] and two axial ACV molecules linked to Ni through N(7) [Ni–N(7) 2.160(2) A]. Two additional ACV molecules are included in the outer sphere of the complex, interacting by means of hydrogen bonds with the co-ordinated ACVs. This reveals the unprecedented recognition of free acyclovir molecules by Ni(or Co)-ACV (1 and 2). The monomeric zinc(II) complex 3 exhibits a distorted-tetrahedral geometry, involving two chlorides, the N(7) of the ACV ligand [Zn–N(7) 2.009(2) A] and a water molecule. The hydrogen bonding of two guanine bases via NH2 and N(3) (unit 1) with N(3) and NH2 (unit 2) represents a novel type of interaction between nucleobases. In the case of the cadmium(II) complex 4 the structure is built by polymeric (CdCl2)n chains which are held together by ACV ligands. The cadmium cation is octahedrically coordinated by four chlorides, the N(7) from an ACV molecule and the hydroxylic oxygen from another ACV molecule, the latter two atoms being placed in cis disposition. On the other hand, the complex [{Hg(ACV)Cl2}x] 5 can be tentatively assigned as a polymer by comparison with analogous guanosine systems and spectroscopic and conductometric data.

Synthesis and structural characteristics of metal–acyclovir (ACV) complexes: [Ni(or Co)(ACV)2(H2O)4]Cl2·2ACV, [Zn(ACV)Cl2(H2O)], [Cd(ACV)Cl2]·H2O and [{Hg(ACV)Cl2}x]. Recognition of acyclovir by Ni–ACV

Ferran Bádenas

Papers

Crystal structures of two copper(II) ternary complexes of N -salicylidene-tryptophanato with 2-aminopyridine and 2-aminopyrimidine

X-ray diffraction structures of two N-salicylidene tryptophananato diaquocopper(II) complexes: erythro and threo isomers

Synthesis and structural characteristics of metal–acyclovir (ACV) complexes: [Ni(or Co)(ACV)2(H2O)4]Cl2·2ACV, [Zn(ACV)Cl2(H2O)], [Cd(ACV)Cl2]·H2O and [{Hg(ACV)Cl2}x]. Recognition of acyclovir by Ni–ACV

Reaction of trimethylene–bisadenine with d10 divalent cations

Synthesis, equilibrium studies and structural characterisation of the Zn(II) complexes with trimethylene-N6,N6'-bisadenine.