In recent years, methods for the asymmetric epoxidation of electron-deficient olefins, particularly a,b-enones, have attracted widespread attention. A critical review is presented of these methods, which include epoxidations with chiral metal hydroperoxides, asymmetric phase-transfer methods, the use of polyamino acid catalysts and the use of chiral dioxiranes.

We analyze aircraft observations obtained during INTEX‐A (1 July to 14 August 2004) to examine the summertime influence of Asian pollution in the free troposphere over North America. By applying correlation analysis and principal component analysis (PCA) to the observations between 6 and 12 km, we find dominant influences from recent convection and lightning (13% of observations), Asia (7%), the lower stratosphere (7%), and boreal forest fires (2%), with the remaining 71% assigned to background. Asian air masses are marked by high levels of CO, O3, HCN, PAN, C2H2, C6H6, methanol, and SO42–. The partitioning of NOy species in the Asian plumes is dominated by PAN (∼600 pptv), with varying NOx/HNO3 ratios in individual plumes, consistent with individual transit times of 3–9 days. Export of Asian pollution occurred in warm conveyor belts of midlatitude cyclones, deep convection, and in typhoons. Compared to Asian outflow measurements during spring, INTEX‐A observations display lower levels of anthropogenic pollutants (CO, C3H8, C2H6, C6H6) due to shorter summer lifetimes; higher levels of biogenic tracers (methanol and acetone) because of a more active biosphere; and higher levels of PAN, NOx, HNO3, and O3 reflecting active photochemistry, possibly enhanced by efficient NOy export and lightning. The high ΔO3/ΔCO ratio (0.76 mol/mol) in Asian plumes during INTEX‐A is due to strong photochemical production and, in some cases, mixing with stratospheric air along isentropic surfaces. The GEOS‐Chem global model captures the timing and location of the Asian plumes. However, it significantly underestimates the magnitude of observed enhancements in CO, O3, PAN and NOx.

The sensing and differentiation of explosive molecules is key for both security and environmental monitoring. Single fluorophores are a widely used tool for explosives detection, but a fluorescent array is a more powerful tool for detecting and differentiating such molecules. By combining array elements into a single multichannel platform, faster results can be obtained from smaller amounts of sample. Here, five explosives are detected and differentiated using quantum dots as luminescent probes in a multichannel platform: 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), tetryl (2,4,6-trinitrophenylmethylnitramine), cyclotrimethylenetrinitramine (RDX), and pentaerythritol tetranitrate (PETN). The sharp, variable emissions of the quantum dots, from a single excitation wavelength, make them ideal for such a system. Each color quantum dot is functionalized with a different surface receptor via a facile ligation process. These receptors undergo nonspecific interactions with the explosives, inducing variable fluorescence quenching of the quantum dots. Pattern analysis of the fluorescence quenching data allows for explosive detection and identification with limits-of-detection in the ppb range.

Measurements of CHMultiple tracers were used to arrive at a set of UT CH 2 O background and perturbed air mass periods, and 46% of the TDLAS measurements fell within the latter category. At least 66% to 73% of these elevated UT observations were caused by enhanced production from CH 2 O precursors rather than direct transport of CH 2 O from the boundary layer. This distinction is important, since the effects from the former can last for over a week or more compared to one day or less in the case of convective transport of CH 2 O itself.In general, production of CH 2 O from CH 4 was found to be the dominant source term, even in perturbed air masses. This was followed by production from MHP, methanol, PAN type compounds, and ketones, in descending order of their contribution. In the presence of elevated NO from lightning and potentially from the stratosphere, there was a definite trend in the CH 2 O discrepancy, which for the highest NO mixing ratios produced a median CH 2 O measurement/model ratio of 3.9 in the 10-12-km range. Discrepancies in CH 2 O and HO 2 in the UT with NO were highly correlated and this provided further information as to the possible mechanism(s) responsible. These discrepancies with NO are consistent with additional production sources of both gases involving CH 3 O 2 + NO reactions, most likely caused by unmeasured hydrocarbons.3

Herein, we report a novel intramolecular ring-closing reaction of biaryl thioethers that give access to highly functionalized dibenzothiophene sulfonium salts under mild conditions. The resulting precursors react regioselectively with [18F]fluoride to give [18F]fluoroarenes in predictable radiochemical yields. The strategy expands the available radiochemical space and provides superior labeling efficiency for clinically relevant PET tracers.