Ab initio dynamics and photoionization mass spectrometry reveal ion-molecule pathways from ionized acetylene clusters to benzene cation.

The growth mechanism of hydrocarbons in ionizing environments, such as the interstellar medium (ISM), and some combustion conditions remains incompletely understood. Ab initio molecular dynamics (AIMD) simulations and molecular beam vacuum-UV (VUV) photoionization mass spectrometry experiments were performed to understand the ion-molecule growth mechanism of small acetylene clusters (up to hexamers). A dramatic dependence of product distribution on the ionization conditions is demonstrated experimentally and understood from simulations.

Probing Ionic Complexes of Ethylene and Acetylene with Vacuum-Ultraviolet Radiation.

Mixed complexes of acetylene-ethylene are studied using vacuum-ultraviolet (VUV) photoionization mass spectrometry and theoretical calculations. These complexes are produced and ionized at different distances from the exit of a continuous nozzle followed by reflectron time-of-flight mass spectrometry detection. Acetylene, with a higher ionization energy (11.

Probing methanol cluster growth by vacuum ultraviolet ionization.

The ability to probe the formation and growth of clusters is key to answering fundamental questions in solvation and nucleation phenomena. Here, we present a mass spectrometric study of methanol cluster dynamics to investigate these two major processes. The clusters are produced in a molecular beam and ionized by vacuum ultraviolet (VUV) radiation at intermediate distances between the nozzle and the skimmer sampling different regimes of the supersonic expansion.

Evolution of oxidation dynamics of histidine: non-reactivity in the gas phase, peroxides in hydrated clusters, and pH dependence in solution.

Oxidation of histidine by (1)O2 is an important process associated with oxidative damage to proteins during aging, diseases and photodynamic therapy of tumors and jaundice, and photochemical transformations of biological species in the troposphere. However, the oxidation mechanisms and products of histidine differ dramatically in these related environments which range from the gas phase through aerosols to aqueous solution. Herein we report a parallel gas- and solution-phase study on the (1)O2 oxidation of histidine, aimed at evaluating the evolution of histidine oxidation pathways in different media and at different ionization states.

Guided-ion-beam scattering and direct dynamics trajectory study on the reaction of deprotonated cysteine with singlet molecular oxygen.

We present a study on the gas-phase reaction of deprotonated cysteine with the lowest electronically excited state of molecular oxygen O2[a(1)Δg], including the measurement of the effects of collision energy (E(col)) on reaction cross sections over a center-of-mass E(col) range from 0.1 to 1.0 eV.

Mass spectrometry study of multiply negatively charged, gas-phase NaAOT micelles: how does charge state affect micellar structure and encapsulation?

We report the formation and characterization of multiply negatively charged sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) aggregates in the gas phase, by electrospray ionization of methanol/water solution of NaAOT followed by detection using a guided-ion-beam tandem mass spectrometer. Singly and doubly charged aggregates dominate the mass spectra with the compositions of [Na(n-z)AOT(n)](z-) (n = 1-18 and z = 1-2). Solvation by water was detected only for small aggregates [Na(n-1)AOT(n)H(2)O](-) of n = 3-9.

Reactions of deprotonated tyrosine and tryptophan with electronically excited singlet molecular oxygen (a1Δ(g)): a guided-ion-beam scattering, statistical modeling, and trajectory study.

The reactions of deprotonated tyrosine ([Tyr-H](-)) and tryptophan ([Trp-H](-)) with the lowest electronically excited state of molecular oxygen O(2)[a(1)Δ(g)] have been studied in the gas phase, including the measurement of the effects of collision energy (E(col)) on reaction cross sections over a center-of-mass E(col) range from 0.05 to 1.0 eV.

Dissociative excitation energy transfer in the reactions of protonated cysteine and tryptophan with electronically excited singlet molecular oxygen (a1Δ(g)).

We report a study on the reactions of protonated cysteine (CysH(+)) and tryptophan (TrpH(+)) with the lowest electronically excited state of molecular oxygen (O(2), a(1)Δ(g)), including the measurement of the effects of collision energy (E(col)) on reaction cross sections over the center-of-mass E(col) range of 0.05 to 1.0 eV.

Experimental and trajectory study on the reaction of protonated methionine with electronically excited singlet molecular oxygen (a1Δg): reaction dynamics and collision energy effects.

The reaction of protonated methionine with the lowest electronically excited state of molecular oxygen O(2)(a(1)Δ(g)) was studied in a guided ion beam apparatus, including the measurement of reaction cross sections over a center-of-mass collision energy (E(col)) range of 0.1-2.0 eV.

Selective transport of amino acids into the gas phase: driving forces for amino acid solubilization in gas-phase reverse micelles.

We report a study on encapsulation of various amino acids into gas-phase sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) reverse micelles, using electrospray ionization guided-ion-beam tandem mass spectrometry. Collision-induced dissociation of mass-selected reverse micellar ions with Xe was performed to probe structures of gas-phase micellar assemblies, identify solute-surfactant interactions, and determine preferential incorporation sites of amino acids. Integration into gas-phase reverse micelles depends upon amino acid hydrophobicity and charge state.

Reaction of protonated tyrosine with electronically excited singlet molecular oxygen (a1Delta(g)): an experimental and trajectory study.

Reaction of protonated tyrosine with the lowest electronically excited singlet state of molecular oxygen, (1)O(2) (a(1)Delta(g)), is reported over the center-of-mass collision energy (E(col)) range from 0.1 to 3.0 eV, using an electrospray-ionization, guided-ion-beam scattering instrument, in conjunction with ab initio electronic structure calculations and direct dynamics trajectory simulations.