Two polymorphs of 2,6-dichloropurine, C(5)H(2)Cl(2)N(4), have been crystallized and identified as the 9H- and 7H-tautomers. Despite differences in the space group and number of symmetry-independent molecules, they exhibit similar hydrogen-bonding motifs. Both crystal structures are stabilized by intermolecular N-H···N interactions that link adjacent molecules into linear chains, and by some non...

The hydrogen-bonding and stacking interactions of hypoxanthine, a potential universal nucleobase, were calculated using a variety of methodologies (CCSD(T), MP2, B3LYP, PWB6K, AMBER). All methods predict that the hydrogen-bonding interaction in the hypoxanthine-cytosine pair is approximately 25 kJ mol(-1) stronger than that in the other dimers. Although the calculations support suggestions from...

Stereoselective Diels-Alder cycloadditions that probe substituent effects in aryl-aryl sandwich complexes were studied experimentally and theoretically. Computations on model systems demonstrate that the stereoselectivity in these reactions is mediated by differential pi-stacking interactions in competing transition states. This allows relative stacking free energies of substituted and unsubsti...

Simple expressions for the bending and the base-stacking energy of double-stranded semiflexible biopolymers (such as DNA and actin) are derived. The distribution of the folding angle between the two strands is obtained by solving a Schrödinger equation variationally. Theoretical results based on this model on the extension versus force and extension versus degree of supercoiling relations of DN...

An elastic model for double-stranded polymers is constructed to study the recently observed DNA entropic elasticity, cooperative extensibility, and supercoiling property. With the introduction of a new structural parameter (the folding angle w), bending deformations of sugar-phosphate backbones, steric effects of nucleotide base pairs, and base-stacking interactions are considered. The comprehe...

p.1 Title Page p2. Computational Methods p3. Figure S1. Distance and angles used to search for non-covalent interactions involving aromatic rings; a) -stacking, b) amide stacking. The angle  is the planar angle between two rings or one ring and the amide bond p4. Figure S2. Distance and angles used to search for halogen bonding (a) and multipolar halogen interaction (b). p6. Table S2. Most fr...

-Intercalates of Georgia well-crystallized kaolinite with formamide, N-methylformamide (NMF), and dimethylsulfoxide (DMSO) were prepared at room temperature by dispersing the clay in the organic liquid. Several physical and chemical properties of the intercalated organic molecules and the clay, while intercalated and after de-intercalation, were examined using nuclear magnetic resonance (NMR), ...

The properties of doubly-expanded (xx-) purine analogues are compared to the natural and singly-expanded (x-) purines using quantum chemical (B3LYP, MP2) methods. Purine expansion upon incorporation of a benzene or naphthalene spacer affects the preferred orientation of the base about the glycosidic bond in the corresponding nucleoside to a similar extent. Although the natural purines preferent...