Effect of the Solvent and Substituent on Tautomeric Preferences of Amine-Adenine Tautomers.

Adenine is one of the basic molecules of life; it is also an important building block in the synthesis of new pharmaceuticals, electrochemical (bio)sensors, or self-assembling molecular materials. Therefore, it is important to know the effects of the solvent and substituent on the electronic structure of adenine tautomers and their stability. The four most stable adenine amino tautomers (9H, 7H, 3H, and 1H), modified by substitution (C2- or C8-) of electron-withdrawing NO and electron-donating NH groups, are studied theoretically in the gas phase and in solvents of different polarities (1 ≤ ε < 109).

Effect of Alkali Metal Cations on Length and Strength of Hydrogen Bonds in DNA Base Pairs.

For many years, non-covalently bonded complexes of nucleobases have attracted considerable interest. However, there is a lack of information about the nature of hydrogen bonding between nucleobases when the bonding is affected by metal coordination to one of the nucleobases, and how the individual hydrogen bonds and aromaticity of nucleobases respond to the presence of the metal cation. Here we report a DFT computational study of nucleobase pairs interacting with alkali metal cations.

Aromaticity Induced by Electric Field: The Case of Polycalicenes.

Local and global π-electron delocalization occurring in planar poly-1,7-[N]calicenes is investigated with use of 10 aromaticity measures based on different physical properties. Systematic change of aromatic character is observed along chains of connected calicene units. Multidimensionality of the aromaticity phenomenon is studied with use of principal component analysis (PCA).

Hydrogen bonding as a modulator of aromaticity and electronic structure of selected ortho-hydroxybenzaldehyde derivatives.

Properties of hydrogen bonds can induce changes in geometric or electronic structure parameters in the vicinity of the bridge. Here, we focused primarily on the influence of intramolecular H-bonding on the molecular properties in selected ortho-hydroxybenzaldehydes, with additional restricted insight into substituent effects. Static models were obtained in the framework of density functional theory at B3LYP/6-311+G(d,p) level.

Interference of H-bonding and substituent effects in nitro- and hydroxy-substituted salicylaldehydes.

Two intramolecular interactions, i.e., (1) hydrogen bond and (2) substituent effect, were analyzed and compared.

Hydroxyl group as a substituent with varying electronic properties: effect of strength of H-bonding on charge density changes in Ph-OH…F⁻ complexes.

Due to gradual and controlled changes of interatomic distances between heavy atoms in OH…F⁻ of C(6)H(5)OH…F⁻ systems it was possible to study the electronic structure evolution. Computation at B3LYP/6-311+G(d,p) level of theory was performed for this purpose. Changes in charges at atoms and characteristics at bond critical points (BCPs) of the H-bond region and also in distant parts of the systems were investigated by means of natural bond orbitals (NBO) and atoms in molecules (AIM) analyses.

On the aromatic character of the heterocyclic bases of DNA and RNA.

Studies based on ab initio optimized geometries (at B3LYP/6-311+G** and MP2/6-311+G** levels) and on experimental structures retrieved from the Cambridge Structural Database (CSD) reveal that the nucleobases constituting DNA and RNA differ significantly in their aromatic character, as shown by the geometry-based index of aromaticity HOMA that ranges from 0.466 for thymine to 0.917 for adenine, based on B3LYP/6-311+G** calculations, and 0.