Proton-bound dimers of nitrogen heterocyclic molecules: Substituent effects on the structures and binding energies of homodimers of diazine, triazine, and fluoropyridine

Vacuum Ultraviolet Photoionization Induced Proton Migration and Formation of a New C-N Bond in Pyridine Clusters Revealed by Infrared Spectroscopy and Mass Spectrometry

The structures and reactions of pyridine (Pyd) cluster cations in a supersonic molecular beam generated upon photoionization at 9.2-9.4 eV were investigated by infrared (IR) action spectroscopy. The mass spectrum showed prominent peaks of (Pyd)_m⁺ and H⁺(Pyd)_m, m = 1-5. In the pyridine/pyridine-d₅ mixture, the mass pattern indicated that H⁺ and D⁺ migrated during the formation and dissociation of the cluster cations. The IR photodissociation spectra of both (Pyd)₂⁺ and H⁺(Pyd)₂ revealed a N-H stretching band near 3400 cm^-1, indicating that their structures are 1-(2-pyridyl)pyridin-1-ium and pyridinium-pyridine, respectively. Observation of the former product implies that the reaction proceeds via an α-distonic cation intermediate, while the latter product is formed via proton migration. The IR spectra of (Pyd)_m⁺ and H⁺(Pyd)_m, m ≥ 3, suggested that these clusters consist of a covalently bound (Pyd)₂⁺ or H⁺(Pyd)₂ core, respectively, with additional pyridines attached to them via hydrogen bonds and/or weak dispersive interactions.

Actual Symmetry of Symmetric Molecular Adducts in the Gas Phase, Solution and in the Solid State

This review discusses molecular adducts, whose composition allows a symmetric structure. Such adducts are popular model systems, as they are useful for analyzing the effect of structure on the property selected for study since they allow one to reduce the number of parameters. The main objectives of this discussion are to evaluate the influence of the surroundings on the symmetry of these adducts, steric hindrances within the adducts, competition between different noncovalent interactions responsible for stabilizing the adducts, and experimental methods that can be used to study the symmetry at different time scales. This review considers the following central binding units: hydrogen (proton), halogen (anion), metal (cation), water (hydrogen peroxide).

Binding preference of nitroimidazolic radiosensitizers to nucleobases and nucleosides probed by electrospray ionization mass spectrometry and density functional theory

Nitroimidazolic radiosensitizers are used in radiation therapy to selectively sensitize cancer cells deprived of oxygen, and the actual mechanism of radiosensitization is still not understood. Selecting five radiosensitizers (1-methyl-5-nitroimidazole, ronidazole, ornidazole, metronidazole, and nimorazole) with a common 5-nitroimidazolic ring with different substitutions at N1 and C2 positions of the imidazole moiety, we investigate here their binding to nucleobases (A, T, G, and C) and nucleosides (As, Td, Gs, and Cd) via the positive electrospray ionization mass spectrometry experiments. In addition, quantum chemical calculations at the M062x/6-311+G(d,p) level of theory and basis set were used to determine binding energies of the proton bound dimers of a radiosensitizer and a nucleobase. The positive electrospray ionization leads to the formation of proton bound dimers of all radiosensitizers except 1-methyl-5-nitroimidazole in high abundance with C and smaller abundance with G. Ronidazole and metronidazole formed less abundant dimers also with A, while no dimers were observed to be formed at all with T. In contrast to the case of the nucleoside Td, the dimer intensity is as high as that with Cd, while the abundance of the dimer with Gs is smaller than that of the former. The experimental results are consistent with the calculations of binding energies suggesting proton bound dimers with C and G to be the strongest bound ones. Finally, a barrier-free proton transfer is observed when protonated G or C approaches the nitroimidazole ring.

Observation of covalent and electrostatic bonds in nitrogen-containing polycyclic ions formed by gas phase reactions of the benzene radical cation with pyrimidine

This work reports a new formation mechanism for the nitrogen-containing polycyclic ions in the gas phase.

Morphological self-assembly of enantiopure allenes for upstanding chiral architectures at interfaces

Upstanding chiral architectures (UCAs) were fabricated from chiroptically active allenes under surface-confined conditions with morphological complementarity being central to the self-assembly process.