Iodide conversion to iodate in aqueous and solid aerosols exposed to ozone.

The aqueous-phase and surface reactions of ozone (O3) with iodide (I-) in/on seawater have been recently found to be a strong atmospheric source of iodine. In addition, ozone also reacts with I- in solid and aqueous sea-salt aerosol. However, the primary products of the heterogeneous reactions of ozone with I- have not been clarified. In this paper, solid and aqueous KI aerosols have been exposed to ozone in an aerosol flow tube system and I- and iodate (IO3-) concentrations have been measured by UV-Vis spectroscopy. The results of these experiments have been combined with a kinetic model to elucidate the primary products of the aqueous and surface reactions. The reaction of ozone with aqueous iodide has been inferred to originate different products depending on whether it occurs at the surface via O3 adsorption (product I2-) or in the aqueous phase via O3 solvation (product IO-). The surface reaction of ozone with solid KI in the presence of water vapor forms KIO3, and other species, which are likely to be gaseous. Although the reactions have been studied in aerosols, the results can be extrapolated to aqueous solutions as well.

Quantum Molecular Interaction Field Models of Substrate Enantioselection in Asymmetric Processes.

Computational models correlating substrate structure to enantioselection with asymmetric catalysts using the QMQSAR program are described. In addition to rapidly providing predictions that could be used to facilitate the screening of catalysts for novel substrates, the QMQSAR program identifies the portions of the substrate that most directly influence the enantioselectivity. The lack underlying relationship between all the substrates in one case, requires two quantitative structure selectivity relationships (QSSR) models to describe all of the experimental results.

De novo chiral amino alcohols in catalyzing asymmetric additions to aryl aldehydes.

[reaction: see text] A de novo structural class of chiral amino alcohol catalysts has been identified through a synergistic effort combining novel architectures from [4 + 3] cycloadditions and quantum mechanical interaction field predictions that closely match subsequent experimental measurements.

QMQSAR: utilization of a semiempirical probe potential in a field-based QSAR method.

A semiempirical quantum mechanical approach is described for the creation of molecular field-based QSAR models from a set of aligned ligand structures. Each ligand is characterized by a set of probe interaction energy (PIE) values computed at various grid points located near the surface of the ligand. Single-point PM3 calculations afford these PIE values, which represents a pool of independent variables from which multilinear regression models of activity are built. The best n-variable fit is determined by constructing an initial regression using standard forward stepwise selection, followed by refinement using a simulated annealing technique. The resulting fit provides an easily interpreted 3D physical model of ligand binding affinity. Validation against three literature datasets demonstrates the ability of the semiempirical potential to model critical binding interactions in diverse systems.

Is the A-ring of sparteine essential for high enantioselectivity in the asymmetric lithiation-substitution of N-Boc-pyrrolidine?

The simplest chiral portion of sparteine, N,N'-dimethyl-2-endo-methylbispidine, was prepared and evaluated in the asymmetric lithiation-substitution of N-Boc-pyrrolidine. The results indicate that the complete A-ring of sparteine is essential for high levels of asymmetric induction. DFT-QSSR analyses of the diamine/Li(+) complexes and DFT calculations of the pertinent i-PrLi/diamine/N-Boc-pyrrolidine complexes are predictive and provide complementary pictures of the stereochemical features critical to this transformation.