Denis E. Bergeron

Chemical formation of neutral complexes from charged metal clusters: reactions of pre-formed aluminum cluster anions with methyl iodide

Abstract Aluminum cluster anions were reacted with methyl iodide vapor in a fast-flow tube apparatus, yielding primarily I − and clusters of the type Al n I − . Based on thermodynamic considerations, the presence of I − is taken to indicate a neutralization reaction pathway whereby clusters of the type Al n CH 3 are formed. Comparison of relative reaction rates to previously measured electron affinities suggests that the Al n –CH 3 interaction is covalent, rather than ionic, in nature. It is suggested that the neutral cluster complexes reported here may hold potential as high energy fuel dopants.

Identification of Active Sites of Biomolecules. 1. Methyl-α-mannopyranoside and FeIII

Car-Parrinello molecular dynamics (CPMD) simulations, DFT chemical reactivity index calculations, and mass spectrometric measurements are combined in an integrated effort to elucidate the details of the coordination of a transition-metal ion to a carbohydrate. The impact of the interaction with the FeIII ion on the glycosidic linkage conformation of methyl-alpha-d-mannopyranoside is studied by classical molecular dynamics (MD) and CPMD simulations. This study shows that FeIII interacts with specific hydroxyl oxygen atoms of the carbohydrate, affecting the ground state carbohydrate conformation. These conformational details are discussed in terms of a set of supporting experiments involving electrospray ionization mass spectrometry, and CPMD simulations clearly indicate that the specific conformational preference is due to intramolecular hydrogen bonding. Classical MD simulations proved insensitive to these important chemical properties. Thus, we demonstrate the importance of chemical reactivity calculations and CPMD simulations in predicting the active sites of biological molecules toward metal cations.

Identification of Phase Boundaries in Surfactant Solutions via Compton Spectrum Quenching

The critical micelle concentration and the phase boundary between isolated surfactant molecules and aggregates are probed via fluorescence spectroscopy and a Compton spectrum quenching technique for aqueous and toluenic solutions of Triton X-100 (TX-100). The internal fluorophore of TX-100 provides a convenient probe for the fluorescence measurements, and the appearance of redder bands in the fluorescence spectra and their relationship with aggregation (clustering of TX-100) phenomena is addressed. The Compton spectrum quenching approach makes use of quench indicating parameters (QIPs) commonly measured in liquid scintillation counting experiments. Phase boundaries identified by the QIP-based approach are in excellent accord with the fluorescence-based approach.