. (2013). Formation of dimethylketene and methacrolein by reaction of the CH radical with acetone. Physical Chemistry Chemical Physics, 15 (11), 4049-4058. Formation of dimethylketene and methacrolein by reaction of the CH radical with acetone AbstractThe reaction of the methylidyne radical (CH) with acetone ((CH3)2CO) is studied at room temperature and at a pressure of 4 Torr (533.3 Pa) using a multiplexed photoionization mass spectrometer coupled to the tunable vacuum ultraviolet synchrotron radiation of the Advanced Light Source at Lawrence Berkeley National Laboratory. The CH radicals are generated by 248 nm multiphoton photolysis of bromoform and react with acetone in an excess of helium and nitrogen gas flow. The main observed reaction exit channel is elimination of a hydrogen atom to form C4H6O isomers. Analysis of photoionization spectra identifies dimethylketene and methacrolein as the only H-elimination products. The best fit to the data gives branching ratios of 0.68 ± 0.14 for methacrolein and 0.32 ± 0.07 for dimethylketene. A methylketene spectrum measured here is used to reanalyze the photoionization spectrum obtained at m/z = 56 for the CH + acetaldehyde reaction, (Goulay et al., J. Phys. Chem. A, 2012, 116, 6091) yielding new H-loss branching ratios of 0.61 ± 0.12 for acrolein and 0.39 ± 0.08 for methylketene. The contribution from methyleneoxirane to the reaction product distribution is revised to be negligible. Coupled with additional product detection for the CD + acetone reaction, these observations pave the way for development of general set of reaction mechanisms for the addition of CH to compounds containing an acetyl subgroup. The reaction of the methylidyne radical (CH) with acetone ((CH 3 ) 2 CQO) is studied at room temperature and at a pressure of 4 Torr (533.3 Pa) using a multiplexed photoionization mass spectrometer coupled to the tunable vacuum ultraviolet synchrotron radiation of the Advanced Light Source at Lawrence Berkeley National Laboratory. The CH radicals are generated by 248 nm multiphoton photolysis of bromoform and react with acetone in an excess of helium and nitrogen gas flow. The main observed reaction exit channel is elimination of a hydrogen atom to form C 4 H 6 O isomers. Analysis of photoionization spectra identifies dimethylketene and methacrolein as the only H-elimination products.The best fit to the data gives branching ratios of 0.68 AE 0.14 for methacrolein and 0.32 AE 0.07 for dimethylketene. A methylketene spectrum measured here is used to reanalyze the photoionization spectrum obtained at m/z = 56 for the CH + acetaldehyde reaction, (Goulay et al., J. Phys. Chem. A, 2012, 116, 6091) yielding new H-loss branching ratios of 0.61 AE 0.12 for acrolein and 0.39 AE 0.08 for methylketene. The contribution from methyleneoxirane to the reaction product distribution is revised to be negligible. Coupled with additional product detection for the CD + acetone reaction, these observations pave the way for development of general set of reaction mechanisms for the additi...

Reversible stimuli-responsive self-assembly systems, particularly those involving photo-controlled assemblies and disassemblies, have attracted much attention over recent years, due to their diverse potentials in the fi elds of drug delivery, [ 1 ] switchable catalysis, [ 2 ] tunable sol-gel transition [ 3 ] and so forth. Various building blocks containing photo-responsive groups, [ 4 ] such as metal and metal oxide nanoparticles, [ 5 ] silica microspheres, [ 6 ] and polymers, [ 7 ] as well as small molecules, [ 3 , 8 ] were used to induce aggregation and dispersion in solution in response to the light stimulus. However, the integration of the smart response with specialized functions in a single system still remains a challenge. Polyoxometalates (POMs) as a class of nanoscale inorganic polyanionic clusters possess versatile properties in catalysis, redox reactions, medicines, etc . [ 9 ] The surface modifi cation with organic cations through electrostatic interactions makes possible the ready integration of various additional functional properties into POMs, [ 10 ] in addition to the improvement of the solubility in weakly polar solvents and the structural stability for diverse chemical environments as well as the promotion of catalytic reaction effi ciency. [ 11 ] In contrast to that only giant POMs are found to show self-assembling behavior in water, [ 12 ] most of these surfactant-encapsulated POM (SEP) and covalent hybrid complexes can self-assemble in organic media and the states at which they exist are dominated by the nature of solvents, [ 11a , 13 ] the amphiphilicity and structure of surfactants, as well as the size and charge density of POMs. [ 14 ] Up to date, none of these complexes have been found to undergo reversible assembly and disassembly processes, although they are very important in governing the catalytic and separation performance of the POM-based catalysts. To realize the high effi cient catalysis of water insoluble substrates, POMs were usually transferred into organic phase through a hydrophobic surface modifi cation of organic cations. In some reaction systems, the control for the reaction process is critical. Up to date, almost all the controllable POM catalyzed reactions depend on the additional chemicals, the oxidant exhaustion, or the temperature control. [ 15 ] It is found that the catalysis and catalytic effi ciency of POMs in organic phase are still strongly relied on their existing states. If one can control the catalytic reactions of POMs through the responsive assembly and disassembly, POMs will become more useful catalysts in some specifi c systems, such as microfl uid, patterned local reactions and catalyst separations. It is usually critical to introduce responsive groups into the SEPs for smart and switchable assemblies. [ 16 ] Considering that light can offer a convenient pathway for the direct modulation of the assembled state of SEPs without introducing chemical additives, it is of interest to develop photo-responsive SEPs for the fabrication of POM-based functional m...

Many large-scale applications of the organophosphate pesticide malathion have led to widespread environmental contamination. Concentrations are found in the environment well above those which are harmful to humans and environmental organisms. No current method of detection for this pesticide is rapid, cost-effective, and specific for malathion. Therefore, we utilized a stringent Systematic Evolution of Ligands by Exponential Enrichment (SELEX) process to identify a Molecular Recognition Element (MRE) for malathion. This MRE was identified from a large ssDNA library and has an equilibrium dissociation constant (K_d) in the low-nanomolar range. Additionally, it has significant selectivity for malathion in comparison to various other pesticides and metabolites of malathion, which were used as negative targets of selection. The high affinity and selectivity of the ssDNA MRE for malathion is a product of the stringent SELEX selection scheme and will be useful for rapid, inexpensive, and specific detection of malathion in the environment.

Toxin B is one of the major virulence factors of Clostridium difficile, a bacterium that is responsible for a significant number of diarrhea cases in acute care settings. Due to the prevalence of C. difficile induced diarrhea, rapid and correct diagnosis is crucial in the disease management. In this study, we have employed a stringent in vitro selection method to identify single-stranded DNA molecular recognition elements (MRE) specific for toxin B. At the end of the 12-round selection, one MRE with high affinity (K d = 47.3 nM) for toxin B was identified. The selected MRE demonstrated low cross binding activities on negative targets: bovine serum albumin, Staphylococcus aureus alpha toxin, Pseudomonas aeruginosa exotoxin A, and cholera toxin of Vibrio cholera. A modified sandwich ELISA assay was developed utilizing the selected ssDNA MRE as the antigen capturing element and achieved a sensitive detection of 50 nM of toxin B in human fecal preparations.

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