Isolating the Spectroscopic Signature of a Hydration Shell With the Use of Clusters: Superoxide Tetrahydrate

Abstract

Cluster spectroscopy, aided by ab initio theory, was used to determine the detailed structure of a complete hydration shell around an anion. Infrared spectra of size-selected O(2)-. (H(2)O)(n) (n = 1 to 4) cluster ions were obtained by photoevaporation of an argon nanomatrix. Four water molecules are required to complete the coordination shell. The simple spectrum of the tetrahydrate reveals a structure in which each water molecule is engaged in a single hydrogen bond to one of the four lobes of the pi* orbital of the superoxide, whereas the water molecules bind together in pairs. This illustrates how water networks deform upon accommodating a solute ion to create a distinct supramolecular species.

Role of a distal pocket in the catalytic O 2 reduction by cytochrome c oxidase models immobilized on interdigitated array electrodes

“…This may account for the apparent stabilization of the oxygen complex in 3 and provides a plausible explanation for the selectivity of this catalyst. Despite the fact that free superoxide disproportionates in water at high concentrations (20,21), at low concentrations, superoxide under basic conditions has been spectroscopically identified as superoxide di-, tetra-, and hexa-hydrate clusters (22)(23)(24)(25)(26). This observation is supported by ab initio calculations (22)(23)(24)(25)(26).…”

“…Despite the fact that free superoxide disproportionates in water at high concentrations (20,21), at low concentrations, superoxide under basic conditions has been spectroscopically identified as superoxide di-, tetra-, and hexa-hydrate clusters (22)(23)(24)(25)(26). This observation is supported by ab initio calculations (22)(23)(24)(25)(26). This is a surprising analogy with the oxygen complex of 3: (i) 4 molecules of water are found in the pocket surrounding the superoxide, (ii) the concentration of superoxide-bound porphyrin is low, and (iii) the network of hydrogen bonds are known to increase the basicity of water, a condition that is known to increase the kinetic stability of superoxide (27,28).…”

Real-time molecular monitoring of chemical environment in obligate anaerobes during oxygen adaptive response

“…In each time-difference spectrum, we minimize the water-continuum absorbance; a positive absorption band reflects the formation of intermediates while a negative band the depletion of an initial state. To interpret changes observed in the FTIR time-difference spectra and to link them to the presence of ions and other small molecules, we used results from previous infrared simulation studies and infrared measurements on aqueous liquid and water clusters (15)(16)(17)(18)(19)(20)(21)(22)(23). Because water molecules simultaneously can be hydrogen donors and acceptors, whether the water be liquid or small clusters, spectral information from vibrational spectra of water clusters can be applied to understand dynamics in liquid or other condensed phases (33,34) such as water in the cellular environment.…”

“…More than 70% of the cellular constituents are highly polar water molecules, and their hydrogen bonding is a useful reflection of the cellular chemical environment because it responds ''instantaneously'' to ions and other species in their surroundings (12,13). The infrared spectrum of OH stretch vibrations has been widely used to characterize the dynamics of hydrogen-bonding structures in pure water (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23). These infrared spectroscopy studies have revealed distinct shifts in vibration frequencies and changes in spectral shapes and intensities induced by the presence of ions and small molecules (e.g., radicals, small organic acids, and hydrogen gas) in water; similar small molecules are expected to be in cellular water during functional metabolism of the oxygenstress adaptive response.…”

Spektroskopische Charakterisierung der lösungsmittelinduzierten Faltung von Dicarboxylatdianionen

“…Um einen tieferen Einblick in den Faltungsmechanismus zu erhalten, werden aber Strukturinformationen benötigt, die sich nur schwer aus den Photoelektronenspektren ableiten lassen. Die IR-Photodissoziationsspektroskopie, kurz IRPD-Spektroskopie, an mikrohydratisierten Anionen in Kombination mit quantenchemischen Rechnungen [10][11][12] [14] werden zwar für n S erreicht, jedoch nicht für n A (Abbildung 2). Hieraus lässt sich schlussfolgern, dass n A empfindlicher als n S auf langreichweitige Lösungsmitteleffekte reagiert.…”