Solvation of electrosprayed ions in the accumulation/collision hexapole of a hybrid Q-FTMS

Abstract

In an effort to spectroscopically determine the structures of solvated ions composed of nucleic acid bases and amino acids, methods for their gas-phase synthesis have been studied. Ions were electrosprayed and solvated in the accumulation cell of a hybrid Q-FTICR filled with methanol or water vapor at ϳ10 Ϫ2 bar. There were subsequently transferred to the FTICR cell at 10 Ϫ10 mbar. Following their isolation in the FTICR, they can be investigated by studying their unimolecular blackbody infrared radiative dissociation (BIRD) or infrared multiple photon dissociation (IRMPD) spectroscopy. The IRMPD spectra for (Ade) 2 Li ϩ and (Ade) 2 Li(H 2 O) ϩ are reported and compared as well as BIRD rate constants for multiply solvated and metalated adenine ions. . The structural properties are typically deduced from fundamental studies of their thermochemistries, reactivities, and more recently, the vibrational spectroscopy of gaseous ions [2]. The ultimate purpose and challenge for studying the physical properties of sequentially solvated ions is to extrapolate to, or contrast these properties with, those in the solution phase especially for biologically interesting ions. Mass spectrometry has become a powerful technique for investigating biomolecules following the development of electrospray ionization (ESI) [3] and matrix-assisted laser desorption/ionization (MALDI) [4 -6]. Noncovalently bound biological complexes can be transferred from aqueous solutions to the gas phase by ESI for further study of the completely desolvated complex. In some instances a small amount of solvated ions have been reported from electrospray allowing the structure, reactivity and thermochemistry of the hydrated ions to be studied [7]. Lee et al.[8] studied extensively hydrated peptides from an electrospray source by operating the capillary at room-temperature, with no nebulizer or drying gas, and optimizing the potentials in the electrospray source. These ions were found to be cooled to between 130 and 150 K by evaporation of water without drying gas, effectively freezing the biomolecules. RodriguezCruz et al. [9] studied doubly protonated gramicidin S ions with up to 50 water molecules attached in a modified instrument with a home-built electrospray source equipped with a heated capillary inlet. They formed the ions under "gentle" electrospray conditions and later described two possible mechanisms for formation of hydrated ions by ESI [10], condensation of solvent onto ions due to expansion inside the ESI interface, and/or solvent evaporation of more extensively hydrated ions or electrospray droplets. The extent of hydration of gas-phase gramicidin S (M ϩ 2H) 2ϩ ions was observed to decrease with an increase in the temperature of the capillary.Rodriguez-Cruz and Williams [11] also studied solvent exchange reactions of hydrated divalent alkaline earth metals with benzene by ESI Fourier-Transform mass spectrometry (FTMS) at room temperature. Aqueous solutions of metal chloride salts were introduced to the mass spectrometer by nanoelectrospray. Me...

Endo or Exo? Structures of Gas‐Phase Alkali Metal Cation/Aromatic Half‐Belt Complexes

“…[22d,28] The magnet was protected from the heat source using a watercooled heating jacket on the outside of the ICR cell vacuum tube. [29] Parent and fragment ion intensities were measured as a function of time.…”

The hydrated Li+–adenine–thymine complex by IRMPD spectroscopy in the N–H/O–H stretching region

“…Solutions were prepared using 18 M Millipore water. Hydration was performed in the accumulation/collision hexapole which was held at ∼10 −2 mbar with water vapor as described previously by Rajabi et al [74] [A-T-Li + ]-H 2 O, m/z 286, was then transferred to the ICR cell where it was isolated and irradiated for 3 s with the OPO laser.…”

Structures and Fragmentation of [Cu(Uracil‐H)(Uracil)]+ in the Gas Phase

“…[31] We believe that the inability to hydrate [Cu(Ura-H)(Ura)] + could be due to the charge being delocalized over the entire complex, unlike in Li + (Ura) 2 [24] and M + (Ade) 2 complexes (M = Li, Na, K, Cs), [32] whose hydrated complexes have been studied previously by the same method. We decided to probe the structure of [Cu(Ura-H)(Ura)] + through fragmentation and computational studies.…”