Probing the intrinsic features and environmental stabilization of multiply charged anions

Abstract

Multiply charged anions (MCAs) represent exotic, highly energetic species in the gas-phase due to their propensity to undergo unimolecular decay via electron loss or ionic fragmentation. There is considerable fundamental interest in these systems since they display novel potential energy surfaces that are characterized by Coulomb barriers. Over recent years, considerable progress has been made in understanding the factors that affect the stability, decay pathways and reactivity of gas-phase MCAs, mainly as a result of the application of electrospray ionization as a generic technique for transferring solution-phase MCAs into the gas-phase for detailed characterization. We review contemporary work in this field, focusing on the factors that control the intrinsic stability of MCAs, both as isolated gas-phase ions, and on their complexation with solvent molecules and counter-ions. While studies of MCAs are primarily of fundamental interest, several classes of important biological ions are commonly observed as MCAs in the gas-phase (e.g. oligonucleotides, sugars). Recent results for biologically relevant ions are emphasised, since a fundamental understanding of the properties of gas-phase MCAs will be highly valuable for developing further analytical methods to study these important systems.

Role of Water in Stabilizing Ferricyanide Trianion and Ion-Induced Effects to the Hydrogen-Bonding Water Network at Long Distance

“…Auto-detachment of an electron was also reported for the following ions: the 3− and 4− charge states of oligonucleotides, 9 sulfonated pyrene trianion, 10 metal phthalocyaninetetrasulfonate tetraanions, 11 8 indicates that the lowestenergy dissociation process for this ion is loss of an electron. Sequential loss of water molecules as well as electron loss from the smaller clusters occurs with the higher-energy activation conditions of the IRPD experiments.…”

“…The IRPD spectrum of Fe(CN) 6 3− (H 2 O) 8 (Figure 4a) has a broad band that appears to be comprised of at least two separate absorption bands centered at 3471 and 3505 cm −1 . Two low-intensity absorptions at 3150 and 3270 cm −1 are within baseline noise in this region of the spectrum, where both the laser power and photon energy are lower.…”

“…In order to gain insight into the structure of Fe(CN) 6 3− (H 2 O) 8 , the smallest trianion formed directly by nESI, an IRPD spectrum in the hydrogen oscillator region from 3100 to 3800 cm −1 was obtained (Figure 4a). The vibrational modes for the O−H stretch of water are sensitive to the local hydrogen-bonding environment and can provide information about how water molecules organize around the ion.…”

“…Structures of Fe(CN) 6 3− (H 2 O) 8 were generated by initially positioning water molecules around the ion in Macromodel 9.1 (Schrodinger, Inc., Portland, OR). The structures were geometry optimized using Q-Chem 4.0 48 (Q-Chem, Inc., Pittsburgh, PA) at B3LYP/LACVP++** level of theory prior to vibrational frequency and intensity calculations at the same level of theory.…”

“…Fe(CN) 6 3− (H 2 O) 8 is the smallest hydrated cluster produced by electrospray ionization, and blackbody infrared dissociation of this ion results in loss of an electron and formation of smaller dianion clusters. Fe(CN) 6 3− (H 2 O) 7 is produced by the higher activation conditions of IRPD, and this ion dissociates both by loss of an electron and by loss of a water molecule.…”