ABSTRACT
Ab initio calculations at the MP2/6-311++G** level on model systems (N-methylpyridinium complexes of dimethyl ether and dimethyl phosphate anion) provide quantitative measures of the large stabilization energies that arise from [C-H...O] contacts in charged systems. These attractive interactions control (i) the self-assembly of bipyridinium-based catenanes and rotaxanes in solution, (ii) the self-organization of left-handed Z-DNA with alternating [dC-dG] sequences in the solid state, and (iii) the binding of pyridinium derivatives with single- and double-stranded DNA. Slightly attractive interactions occur between the donor ether and phosphate moieties and a neutral pyridine molecule in the gas phase. Electrostatic potential and solvation calculations demonstrate that [C-H...O] interactions which involve a cationic [C-H] donor are dominated by electrostatic terms.
Subject(s)
Macromolecular Substances , Pyridinium Compounds/chemistry , DNA/chemistry , Hydrogen Bonding , Models, Molecular , Nucleic Acid Conformation , Static ElectricityABSTRACT
The gas phase and aqueous thermochemistry and reactivity of nitroxyl (nitrosyl hydride, HNO) were elucidated with multiconfigurational self-consistent field and hybrid density functional theory calculations and continuum solvation methods. The pK(a) of HNO is predicted to be 7.2 +/- 1.0, considerably different from the value of 4.7 reported from pulse radiolysis experiments. The ground-state triplet nature of NO(-) affects the rates of acid-base chemistry of the HNO/NO(-) couple. HNO is highly reactive toward dimerization and addition of soft nucleophiles but is predicted to undergo negligible hydration (K(eq) = 6.9 x 10(-5)). HNO is predicted to exist as a discrete species in solution and is a viable participant in the chemical biology of nitric oxide and derivatives.
