Computational studies of gas-phase Ca3P2 and Ca6P4.

The electronic and molecular structures of Ca3P2 and Ca6P4 are investigated using high-level ab initio methods. The lowest energy structure for Ca3P2 is found to be a Jahn-Teller distorted triplet. An excited-state singlet is found with various post HF methods; however, DFT incorrectly predicts a closed shell singlet to be the ground state.

Cluster precursors of uncapped CdS quantum dots via electroporation of synthetic liposomes. Experiments and theory.

Subnanometer size cluster precursors of uncapped CdS quantum dots were produced via the electroporation of synthetic dioleoylphosphatidylcholine (DOPC) unilamellar bilayer vesicles of mean hydrodynamic diameter Dh = 175 nm. During electroporation, Cd2+ ions are ejected from the interior compartments of the vesicles into the bulk solution where they react with S(2-) ions to form CdS monomers. The monomers adsorb on the exterior surface of the vesicles, where their spontaneous self-aggregation to (CdS)n clusters occurs on the hour and day time scale.

Equilibrium conditions in laser-desorbed plumes: thermodynamic properties of alpha-cyano-4-hydroxycinnamic acid and protonation of amino acids.

The equilibrium nature of a plume of laser desorbed material is explored through the application of a simple equilibrium model to the ion signals observed in 355 nm laser desorption/ionization mass spectra of mixtures of the MALDI matrix alpha-cyano-4-hydroxycinnamic acid (alphaCHCA) with the amino acids glycine, alanine, valine, isoleucine, and phenylalanine. In these studies it is found that there are systematic and predictable increases in the relative yield of protonated amino acid with increases in amino acid gas-phase basicity. In addition, the thermodynamic values extracted from the equilibrium plot are shown to be in good agreement with values obtained from computational investigation of plausible alphaCHCA proton donor species.

Density functional study of the structures of lead sulfide clusters (PbS)n (n = 1-9).

The structures of (PbS)n (n = 1-9) clusters are investigated with density functional theory at the B3LYP level. Various pseudopotential basis sets on lead and the 6-31+G basis set on sulfur were employed. Full geometry optimization and extensive searches of the potential energy surface were carried out for clusters with n = 1-6.

Computational study of matrix-peptide interactions in MALDI mass spectrometry: Interactions of 2,5- and 3,5-dihydroxybenzoic acid with the tripeptide valine-proline-leucine.

The mechanism of matrix-to-analyte proton transfer in matrix-assisted laser desorption and ionization mass spectrometry (MALDI-MS) has been investigated computationally by modeling the matrix-analyte interaction of potential MALDI matrixes such as 2,5-dihydroxybenzoic acid (2,5-DHB) and 3,5-DHB with the tripeptide valine-proline-leucine (VPL). A combination of molecular dynamics/simulated annealing calculations followed by density functional theory geometry optimization using a reasonably large basis set has been done on a large number of clusters in an attempt to study the ionization energy of each matrix in the cluster environment and the intracluster proton transfer from the matrix to the tripeptide. The calculations show a substantial reduction in the IP for both matrixes in their cluster environments.