Perylene as an Organic Photocatalyst for the Radical Polymerization of Functionalized Vinyl Monomers through Oxidative Quenching with Alkyl Bromides and Visible Light

The generation of carbon-centered radicals from alkyl bromides through an oxidative quenching pathway using perylene as an organic visible-light photocatalyst is described. This methodology is used to initiate the radical polymerization of methyl methacrylate and other functionalized vinyl monomers. The polymers possess bromide chain-end groups that can be used to reinitiate polymerization to produce block copolymers. Control over the polymerization propagation can be achieved through pulsed light sequences while the ability to use natural sunlight to promote carbon–carbon bond formation produces polymers with dispersity as low as 1.29

Response and Discrimination Performance of Arrays of Organothiol-Capped Au Nanoparticle Chemiresistive Vapor Sensors

The response and discrimination performance of an array that consisted of 20 different organothiol-capped Au nanoparticle chemiresistive vapor sensors was evaluated during exposure to 13 different organic vapors. The passivating organothiol ligand library consisted of collections of straight-chain alkanethiols, branched alkanethiols, and aromatic thiols. A fourth collection of sensors was formed from composites of 2-phenylethanethiol-capped Au nanoparticles and nonpolymeric aromatic materials that were coembedded in a sensor film. The organic vapors consisted of six hydrocarbons (n-hexane, n-heptane, n-octane, isooctane, cyclohexane, and toluene), three polar aprotic vapors (chloroform, tetrahydrofuran, and ethyl acetate), and four alcohols (methanol, ethanol, isopropanol, and 1-butanol). Trends in the resistance response of the sensors were consistent with expected trends in sorption due to the properties of the test vapor and the molecular structure of the passivating ligands in the sensor films. Classification algorithms including principal components analysis and Fisher’s linear discriminant were used to evaluate the discrimination performance of an array of such sensors. Each collection of sensors produced accurate classification of most vapors, with misclassification occurring primarily for vapors that had mutually similar polarity. The classification performance for an array that contained all of the sensor collections produced nearly perfect discrimination for all vapors studied. The dependence of the array size (i.e., the number of sensors) and the array chemical diversity on the discrimination performance indicated that, for an array of 20 sensors, an array size of 13 sensors or more produced the maximum discrimination performance

Metallosupramolecular helices constructed from nickel(II) and multidentate “click” triazole ligands

© 2020 Elsevier Ltd A series of binuclear metallosupramolecular helices [Ni2L3]4+ has been synthesized from Ni(II) salts and bis(bidentate) pyridyltriazole or aminomethyltriazole ligands, separated by ortho- (o-xpt and o-xamt, respectively), meta- (m-xpt, m-xamt), and para-xylylene (p-xpt, p-xamt) spacers. All complexes were characterized by elemental analysis, ESI-MS, and in four cases, the structures confirmed by X-ray crystallography. The xpt and xamt ligands, derived by “click” reactions, exhibit similar bonding behavior regardless of modifications in their coordination pockets and spacer groups, forming triple-helical binuclear complexes with pseudo-octahedral geometry at Ni. The crystallographically characterized complexes show shorter Ni···Ni separations with the ortho spacer ([Ni2(o-xpt)3]4+, 9.332(2); [Ni2(o-xamt)3]4+, 8.9718(10) Å) than with the para spacer ([Ni2(p-xpt)3]4+, 11.574(2); [Ni2(p-xamt)3]4+, 11.899(2), 11.924(2) Å)

Coral-reef diatoms (Bacillariophyta) from Guam: new records and preliminary checklist, with emphasis on epiphytic species from farmer-fish territories

The marine diatom flora of the tropical western Pacific island of Guam is all but unknown. Following several taxonomic/systematic papers, this floristics paper documents 179 new records of diatoms identified from light microscopy and/or scanning electron microscopy. Samples were collected from diverse habitats for several research projects in the authors’ laboratories, but the majority reported here are epiphytic, especially from pomacentrid farmer-fish territories. While many of the species are well known from other regions, some recently named, rarely seen, or poorly-described taxa include Amphora decussata Grunow;Ardissonea fulgens var. fulgens (Greville) Grunow and var. gigantea (Lobarzewsky) De Toni; Campylodiscus humilis Greville; Falcula paracelsianus Voigt; Hyalosira interrupta (Ehrenberg) Navarro; Olifantiella pilosella Riaux-Gobin; andTriceratium pulchellum (Grunow) Grunow. A preliminary checklist incorporating the new records and our previous records totals 237 taxa, which is a step towards the development of the regional flora. Many taxa remain to be identified from the documentation so far and few samples have been analyzed from other habitats such as sediments and mangroves. Only 28–42% of the species in this checklist also occurred in lists from the Society Islands, Mahé, Puerto Rico and The Bahamas—but all regions remain seriously undersampled. We do, however note some apparent differences in common and distinctive species

Intramolecular Charge Transfer and Ion Pairing in <i>N,N</i>-Diaryl Dihydrophenazine Photoredox Catalysts for Efficient Organocatalyzed Atom Transfer Radical Polymerization

Photoexcited intramolecular charge transfer (CT) states in <i>N,N</i>-diaryl dihydrophenazine photoredox catalysts are accessed through catalyst design and investigated through combined experimental studies and density functional theory (DFT) calculations. These CT states are reminiscent of the metal to ligand charge transfer (MLCT) states of ruthenium and iridium polypyridyl complexes. For cases where the polar CT state is the lowest energy excited state, we observe its population through significant solvatochromic shifts in emission wavelength across the visible spectrum by varying solvent polarity. We propose the importance of accessing CT states for photoredox catalysis of atom transfer radical polymerization lies in their ability to minimize fluorescence while enhancing electron transfer rates between the photoexcited photoredox catalyst and the substrate. Additionally, solvent polarity influences the deactivation pathway, greatly affecting the strength of ion pairing between the oxidized photocatalyst and the bromide anion and thus the ability to realize a controlled radical polymerization. Greater understanding of these photoredox catalysts with respect to CT and ion pairing enables their application toward the polymerization of methyl methacrylate for the synthesis of polymers with precisely tunable molecular weights and dispersities typically lower than 1.10

Seasonal progression of diatom assemblages in surface waters of Ryder Bay, Antarctica

Phytoplankton assemblages from seasonally sea-ice covered Ryder Bay (Adelaide Island, Antarctica) were studied over three austral summers (2004–2007), to link sea-ice variability and environmental conditions with algal speciation. Typical of near-shore Antarctic waters, biomass was dominated by large diatoms, although the prymnesiophyte Phaeocystis antarctica was numerically dominant. Although there was considerable interannual variability between main diatom species, high biomass of certain species or species groups corresponded consistently to certain phases of seasonal progression. We present the first documentation of an extensive bloom of the late-season diatom Proboscia inermis in February 2006, accounting for over 90% of diatom biomass. At this time, water column stratification and nutrient drawdown were high relative to other periods of the study, although carbon export was relatively low. Melt water flux in this region promotes well-stratified surface waters and high chlorophyll levels, but not necessarily concurrent increases in export production relative to seasons with lower freshwater inputs