Microhydration of Deprotonated Nucleobases

Abstract

Hydration reactions of deprotonated nucleobases (uracil, thymine, 5-fluorouracil,2-thiouracil, cytosine, adenine, and hypoxanthine) produced by electrospray have been experimentally studied in the gas phase at 10 mbar using a pulsed ion-beam high-pressure mass spectrometer. The thermochemical data, ΔHo, ΔSo, and ΔGo, for the monohydrated systems were determined. The hydration enthalpies were found to be similar for all studied systems and varied between 39.4 and 44.8 kJ/mol. A linear correlation was found between water binding energies in the hydrated complexes and the corresponding acidities of the most acidic site of nucleobases. The structural and energetic aspects of the precursors for the hydrated complexes are discussed in conjunction with available literature data.Graphical Abstractᅟ

Gas‐phase hydration of Mg2+ complexes with deprotonated uracil, thymine, uridine, and thymidine

“…Interactions of nucleic acids with Mg 2+ occur in water environment, which has stimulated a number of studies (including gas‐phase studies) concerning the interaction of hydrated Mg 2+ with nucleobases . Deprotonated nucleobases can be formed in living organisms, which has stimulated studies of hydration of deprotonated nucleobases . It is clear that studies of hydration of the complexes made by deprotonated nucleobases and metal cations are also of interest.…”

Crystallographic evidence of Watson–Crick connectivity in the base pair of anionic adenine with thymine

“…Since water is the natural component/medium of biological systems, investigation of the interactions of deprotonated nucleobases with it is of both fundamental and practical interest. Moreover, such interactions have also been studied in the gas phase for isolated deprotonated nucleobases ( 23 ). As discussed below and elsewhere ( 23 , 24 ), the most acidic gas-phase site in the adenine molecule is the N(9)-H of the imidazole ring ( Fig.…”

“…Whereas the gas-phase photoelectron spectra suggested that Thy − is formed by removal of a proton from the N(1) atom ( 23 , 27 ) that generally connects to the sugar in the nucleotide, both N(3) − and N(1) − deprotonated monoanions are indistinguishable in aqueous solution ( 28 ). Both sites show distinctive acidities in the gas phase (by 11.0 kcal/mol) as discussed below and in the literature ( 29 ), yet they are equivalent in water.…”

“…have also been studied in the gas phase for isolated deprotonated nucleobases (23). As discussed below and elsewhere (23,24), the most acidic gas-phase site in the adenine molecule is the N(9)-H of the imidazole ring ( Fig.…”

“…On the other hand, the [N 4444 ] + cations are also connected with two [Ad] − anions via the same CH•••π intermolecular interactions and with two water molecules via weak CH•••O hydrogen bonds. Whereas the gas-phase photoelectron spectra suggested that Thy − is formed by removal of a proton from the N(1) atom(23,27) that generally connects to the sugar in the nucleotide, both N(3) − and N(1) − deprotonated monoanions are indistinguishable in aqueous solution(28). Both sites show…”