Gas-Phase Experimental and Theoretical Studies of Adenine, Imidazole, Pyrrole, and Water Non-Covalent Complexes

Abstract

We present both experimental and theoretical gas-phase studies of several noncovalent complexes of elementary molecules of biological interest: adenine, imidazole, pyrrole, and water. By means of charge-transfer collisions between those complexes and laser-excited atoms, dipole-bound cluster anions are observed. This Rydberg electron transfer (RET) spectroscopic technique is used to experimentally determine the very weak excess electron binding energies of the complex anions. Theoretical calculations which rely on a homemade semiempirical intermolecular force field allow for the determination of the structures of the low-lying equilibrium configurations of the neutral complexes. The electrostatic properties of these configurations (dipole moments, quadrupole moments, etc.) lead to predicted excess electron binding energies which are compared to the experimental values. This comparison provides a test of the validity of the employed methods, as discussed in the case of the five studied complexes: adenine−imidazole, adenine−pyrrole, adenine−water, pyrrole−water, and imidazole−water.

Communication: Where does the first water molecule go in imidazole?

“…Due to the role of neutral imidazole in both biology 4 and materials science, 5 this preference is rather relevant 6 and has been addressed several times. [7][8][9][10][11] In relation to direct methanol fuel cells, comparison to the case of methanol (m) solvation is of interest. 5,12 Beyond classical hydrogen bonds, imidazole can also bind water via C−H hydrogen bonds.…”

“…Rydberg electron transfer spectroscopy suggests imidazole as the hydrogen bond acceptor, but remains ambiguous because of uncertainties in the experimental and calculated excess electron binding energies and dipole moments of the floppy dimers. 9 In contrast, a free jet study of the derivative 4-phenyl imidazole 17,18 only revealed water as a hydrogen bond acceptor, but the influence of the phenyl ring is unclear. Therefore, an independent and unambiguous free jet direct absorption study on the isolated parent compound imidazole appears timely and is provided in this work.…”

“…Figure 2 and Table S3 (Ref. 3) underline how uncertain the theoretical isomer preference is, when standard Pople basis sets are employed. [7][8][9][10][11] Using correlation consistent basis sets, the prediction becomes robust already at the double-zeta level. It is fully in line with our experimental finding of an enhanced stability for the water donor complex and is confirmed by coupled cluster corrections including single, double and perturbative triple excitations (see Tab.…”

Complexes of nitric oxide with water and imidazole

“…Similar complexes are reported by Carles et al using electron transfer spectroscopic techniques and semiempirical calculations. [35] The interaction of protonated imidazole with water was theoretically investigated [36] as well as the interactions of the imidazole dimers with water. [37] In both cases it was found that water preferably interacts with the nitrogen atoms of the imidazole ring.…”

Infrared Spectroscopy of Imidazole Trimer in Helium Nanodroplets: Free NH Stretch Mode

“…1 Therefore, IM and imidazole dimer (IMD) have been the subject of several investigations to get information about their intermolecular interactions. [1][2][3][4] Despite its importance, to the best of our knowledge no spectroscopic information concerning the imidazole trimer (IMT) is known. Recently, we have reported infrared spectroscopic studies of IM, IMD and its water complexes (IMW and IMDW) in helium nanodroplets.…”