Synthetic strategies for 5- and 6-membered ring azaheterocycles facilitated by iminyl radicals

The author thanks EaStCHEM for financial support.The totality of chemical space is so immense that only a small fraction can ever be explored. Computational searching has indicated that bioactivity is associated with a comparatively small number of ring-containing structures. Pyrrole, indole, pyridine, quinoline, quinazoline and related 6-membered ring-containing aza-arenes figure prominently. This review focuses on the search for fast, efficient and environmentally friendly preparative methods for these rings with specific emphasis on iminyl radical mediated procedures. Oxime derivatives, particularly oxime esters and oxime ethers, are attractive precursors for these radicals. Their use is described in conventional thermolytic, microwave-assisted and UV-vis based preparative procedures. Photoredox catalyzed protocols involving designer oxime ethers are also covered. Choice can be made amongst these synthetic strategies for a wide variety of 5- and 6-membered ring heterocycles including phenanthridine and related aza-arenes. Applications to selected natural products and bioactive molecules including trispheridine, vasconine, luotonin A and rutaecarpine are included.Publisher PDFPeer reviewe

Microhydration and the enhanced acidity of free radicals

The author thanks EaStCHEM for financial support.Recent theoretical research employing a continuum solvent model predicted that radical centers would enhance the acidity (RED-shift) of certain proton-donor molecules. Microhydration studies employing a DFT method are reported here with the aim of establishing the effect of the solvent micro-structure on the acidity of radicals with and without RED-shifts. Microhydration cluster structures were obtained for carboxyl, carboxy-ethynyl, carboxy-methyl, and hydroperoxyl radicals. The numbers of water molecules needed to induce spontaneous ionization were determined. The hydration clusters formed primarily round the CO2 units of the carboxylate-containing radicals. Only 4 or 5 water molecules were needed to induce ionization of carboxyl and carboxy-ethynyl radicals, thus corroborating their large RED-shifts.Publisher PDFPeer reviewe

Identification of products from canthaxanthin oxidation

John C. Walton and Raphael C. Mordi acknowledge the financial support of EaStCHEM.Canthaxanthin is a carotenoid that lacks pro-vitamin A activity but is known to have antioxidant activity. The products of its oxidation in oxygen were found to be mainly substituted apo-carotenals and apo-carotenones. The product profile resembles that obtained in the oxidation of β-carotene, except that with canthaxanthin these products are the 4-oxo-β-apo-carotenals and 4-oxo-β-apo-carotenones. Epoxides and diepoxides were clearly identified from β-carotene oxidation but in contrast, with canthaxanthin, apart from 5,6-epoxy-canthaxanthin, which was detected at the early stage of oxidation and minor quantities of 5,6-epoxy-β-ionone and 5,6-epoxy-4-oxo-β-apo-11-carotenal, no other epoxides were detected. The identities of these products lead us to suggest that the mechanism of canthaxanthin oxidation bears significant similarity to that of β-carotene.PostprintPeer reviewe

EPR and pulsed ENDOR study of intermediates from reactions of aromatic azides with group 13 metal trichlorides

The reactions of group 13 metal trichlorides with aromatic azides were examined by CW EPR and pulsed ENDOR spectroscopies. Complex EPR spectra were obtained from reactions of aluminium, gallium and indium trichlorides with phenyl azides containing a variety of substituents. Analysis of the spectra showed that 4-methoxy-, 3-methoxy- and 2-methoxyphenyl azides all gave ‘dimer’ radical cations [ArNHC6H4NH2]+• and trimers [ArNHC6H4NHC6H4NH2]+• followed by polymers. 4-Azidobenzonitrile, with its electron-withdrawing substituent, did not react. In general the aromatic azides appeared to react most rapidly with AlCl3 but this reagent tended to generate much polymer. InCl3 was the least reactive group 13 halide. DFT computations of the radical cations provided corroborating evidence and suggested that the unpaired electrons were accommodated in extensive π-delocalised orbitals. A mechanism to account for the reductive conversion of aromatic azides to the corresponding anilines and thence to the dimers and trimers is proposedPublisher PDFPeer reviewe

N- to C-sulfonyl photoisomerisation of dihydropyridinones : a synthetic and mechanistic study

The authors thank the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007–2013) ERC Grant Agreement no. 279850 (CF and JET) and EPSRC grant number EP/J018139/1 (DSBD) for funding. ADS thanks the Royal Society for a Wolfson Research Merit Award.The scope and limitations of a photoinitiated N- to C-sulfonyl migration process within a range of dihydropyridinones is assessed. This sulfonyl transfer proceeds without erosion of either diastereo- or enantiocontrol, and is general across a range of N-sulfonyl substituents (SO2R; R = Ph, 4-MeC6H4, 4-MeOC6H4, 4-NO2C6H4, Me, Et) as well as C(3)-(aryl, heteroaryl, alkyl and alkenyl) and C(4)-(aryl and ester) substitution. Crossover reactions indicate an intermolecular step is operative within the formal migration process, although no crossover from C-sulfonyl products was observed. EPR studies indicate the intermediacy of a sulfonyl radical and a mechanism is proposed based upon these observations.Publisher PDFPeer reviewe

Quantification of liquid phase faecal odourants to evaluate membrane technology for wastewater reuse from decentralised sanitation facilities

Public willingness to use decentralised sanitation facilities or arising water products is discouraged due to malodour, preventing improved sanitation practices or water reuse opportunities in low income countries Whilst odour is characterised in the gas phase, it originates in the liquid phase. Consequently, controlling odour at source could prevent gas-phase partitioning and limit produced water contamination. This study therefore developed an analytical method for the quantitation of a range of liquid phase volatile organic compounds (VOCs) classified into eight chemical groups, known to be primary indicators of faecal odour, to provide characterisation of real fluids and to permit evaluation of several potential membrane separation technologies for liquid phase odourant separation. The gas chromatography mass spectrometry method provided quantitation in the range of 0.005 mg L-1 to 100 mg L-1 with instrument detection limits ranging from 0.005 mg L-1 to 0.124 mg L-1. Linear calibration curves were achieved (r2 >0.99) with acceptable accuracy (77-115%) and precision (<15%) for quantitation in the calibration range below 1 mg L 1, and good accuracy (98-104%) and precision (<2%) determined for calibration in the range 1-100 mg L-1. Pre-concentration of real samples was facilitated via solid phase extraction. Subsequent application of the method to the evaluation of two thermally driven membranes based on hydrophilic (polyvinyl alcohol) and hydrophobic (polydimethylsiloxane) polymers evidenced contrasting separation profiles. Importantly, this study demonstrates the methods utility for liquid phase VOC determination which is of use to a range of disciplines, including healthcare professionals, taste and odour specialists and public health engineers

Data Acquisition Protocols and Reporting Standards for Studies of the Electrochemical Reduction of Carbon Dioxide

Objective evaluation of the performance of electrocatalysts for CO_2 reduction has been complicated by a lack of standardized methods for measuring and reporting activity data. In this perspective, we advocate that standardizing these practices can aid in advancing research efforts toward the development of efficient and selective CO_2 reduction electrocatalysts. Using information taken from experimental studies, we identify variables that influence the measured activity of CO_2 reduction electrocatalysts and propose procedures to account for these variables in order to improve the accuracy and reproducibility of reported data. We recommend that catalysts be measured under conditions which do not introduce artifacts from impurities, from either the electrolyte or counter electrode, and advocate the acquisition of data measured in the absence of mass transport effects. Furthermore, measured rates of electrochemical reactions should be normalized to both the geometric electrode area as well as the electrochemically active surface area to facilitate the comparison of reported catalysts with those previously known. We demonstrate that, when these factors are accounted for, the CO_2 reduction activities of Ag and Cu measured in different laboratories exhibit little difference. Adoption of the recommendations presented in this perspective would greatly facilitate the identification of superior catalysts for CO_2 reduction arising solely from changes in their composition and pretreatment

A DNA nanoswitch incorporating the fluorescent base analogue 2-aminopurine detects single nucleotide mismatches in unlabelled targets

DNA nanoswitches can be designed to detect unlabelled nucleic acid targets and have been shown to discriminate between targets which differ in the identity of only one base. This paper demonstrates that the fluorescent base analogue 2-aminopurine (AP) can be used to discriminate between nanoswitches with and without targets and to discriminate between matched and mismatched targets. In particular, we have used both steady-state and time-resolved fluorescence spectroscopy to determine differences in AP environment at the branchpoint of nanoswitches assembled using complementary targets and targets which incorporate single base mismatches

Reconnecting Downtown to the Riverfront. Springfield, MA. Senior Urban Design Studio,

The work of this urban design studio illustrates visions for the revitalization of Springfield’s downtown riverfront through landscape architecture facing the challenges of a dissecting I-91 highway corridor. Re-Connecting people to the riverfront capi­talizes on the great Connecticut River and will revitalize the city to attract and engage residents and visitors alike. The proposals foster creating spaces in Riverfront Park for multiple activities such as recreation, places for arts and culture, education and enhancement of the River’s ecology. They further promote pedestrian/bicycle arteries to and along the riverfront that are embedded in a livable, mixed-use, diverse neighborhood. The work explores a community service learning strategy within the framework of an urban design studio with the goal of revitalizing the city of Springfield, Massachusetts, through sustainable design, planning, and engagement with the community. This studio produced six tangible visions and are based on three scenarios; 1) Scenario 1keeps the highway I-91 on an elevated level above ground; 2) Scenario 2 lowers I-91 down to an on-ground level; 3) Scenario 3 lowers I-91 underground as a completely or partially covered corridor. All six design visions share the following recommendations and principles to create a livable and sustainable city that engages the riverfront as a place for people and as a landscape that will be crucial for a great future of Springfield’s downtown: Creating spaces in Riverfront Park that are more centered and generous for multiple activities; add floodplains to improve the ecology of the River and educate the public. Creating pedestrian/bicycle arteries from Main Street to the riverfront. Elimination of on- and off- ramps within the core of downtown to prioritize pedestrian movement to the Connecticut River and reduce noise. Eliminate parking structures underneath the highway for visibility of the River. Redesigning East and West Columbus Avenue as pedestrian- and bicycle-friendly corridors through a road diet and speed reduction. Foster mixed-use development along East Columbus Avenue at the edge of the South End Neighborhood. Connect the Connecticut River Walk and Bikeway to Forest Park in the south