Water Network Shape-Dependence of Local Interactions with the Microhydrated -NO and -CO Anionic Head Groups by Cold Ion Vibrational Spectroscopy.

We report the structural evolutions of water networks and solvatochromic response of the CHNO radical anion in the OH and CH stretching regions by analysis of the vibrational spectra displayed by cryogenically cooled CHNO·(HO) clusters. The OH stretching bands evolve with a surprisingly large discontinuity at = 6, which features the emergence of an intense, strongly red-shifted band along with a weaker feature that appears in the region assigned to a free OH fundamental. Very similar behavior is displayed by the perdeuterated carboxylate clusters, RCO·(HO) (R = CDCD), indicating that this behavior is a general feature in the microhydration of the triatomic anionic domain and not associated with CH oscillators.

On the Hydrogen Oxalate Binding Motifs onto Dinuclear Cu and Ag Metal Phosphine Complexes.

We report the binding geometries of the isomers that are formed when the hydrogen oxalate ((CO ) H=HOx) anion attaches to dinuclear coinage metal phosphine complexes of the form [M M dcpm (HOx)] with M=Cu, Ag and dcpm=bis(dicyclohexylphosphino)methane, abbreviated [MM] . These structures are established by comparison of isomer-selective experimental vibrational band patterns displayed by the cryogenically cooled and N -tagged cations with DFT calculations of the predicted spectra for various local minima. Two isomeric classes are identified that feature either attachment of the carboxylate oxygen atoms to the two metal centers (end-on docking) or attachment of oxygen atoms on different carbon atoms asymmetrically to the metal ions (side-on docking).

THE IMS PARADOX: A PERSPECTIVE ON STRUCTURAL ION MOBILITY-MASS SPECTROMETRY.

Studies of large proteins, protein complexes, and membrane protein complexes pose new challenges, most notably the need for increased ion mobility (IM) and mass spectrometry (MS) resolution. This review covers evolutionary developments in IM-MS in the authors' and key collaborators' laboratories with specific focus on developments that enhance the utility of IM-MS for structural analysis. IM-MS measurements are performed on gas phase ions, thus "structural IM-MS" appears paradoxical-do gas phase ions retain their solution phase structure? There is growing evidence to support the notion that solution phase structure(s) can be retained by the gas phase ions.

Characterization of the alkali metal oxalates (MCO) and their formation by CO reduction via the alkali metal carbonites (MCO).

The reduction of carbon dioxide to oxalate has been studied by experimental Collisionally Induced Dissociation (CID) and vibrational characterization of the alkali metal oxalates, supplemented by theoretical electronic structure calculations. The critical step in the reductive process is the coordination of CO2 to an alkali metal anion, forming a metal carbonite MCO2- able to subsequently receive a second CO2 molecule. While the energetic demand for these reactions is generally low, we find that the degree of activation of CO2 in terms of charge transfer and transition state energies is the highest for lithium and systematically decreases down the group (M = Li-Cs).

Molecular-level origin of the carboxylate head group response to divalent metal ion complexation at the air-water interface.

We exploit gas-phase cluster ion techniques to provide insight into the local interactions underlying divalent metal ion-driven changes in the spectra of carboxylic acids at the air-water interface. This information clarifies the experimental findings that the CO stretching bands of long-chain acids appear at very similar energies when the head group is deprotonated by high subphase pH or exposed to relatively high concentrations of Ca metal ions. To this end, we report the evolution of the vibrational spectra of size-selected [Ca·RCO]·(HO) and RCO·(HO) cluster ions toward the features observed at the air-water interface.

Trapping and Structural Characterization of the XNO·NO (X = Cl, Br, I) Exit Channel Complexes in the Water-Mediated X + NO Reactions with Cryogenic Vibrational Spectroscopy.

The heterogeneous reaction of NO with sea spray aerosols yields the ClNO molecule, which is postulated to occur through water-mediated charge separation into NO and NO ions followed by association with Cl. Here we address an alternative mechanism where the attack by a halide ion can yield XNO by direct insertion in the presence of water. This was accomplished by reacting X(DO) (X = Cl, Br, I) cluster ions with NO to produce ions with stoichiometry [XNO].

Hidden role of intermolecular proton transfer in the anomalously diffuse vibrational spectrum of a trapped hydronium ion.

We report the vibrational spectra of the hydronium and methyl-ammonium ions captured in the C binding pocket of the 18-crown-6 ether ionophore. Although the NH stretching bands of the CHNH ion are consistent with harmonic expectations, the OH stretching bands of HO are surprisingly broad, appearing as a diffuse background absorption with little intensity modulation over 800 cm with an onset ∼400 cm below the harmonic prediction. This structure persists even when only a single OH group is present in the HDO isotopologue, while the OD stretching region displays a regular progression involving a soft mode at about 85 cm These results are rationalized in a vibrationally adiabatic (VA) model in which the motion of the HO ion in the crown pocket is strongly coupled with its OH stretches.