The Synthesis and Characterization of Highly Fluorescent Polycyclic Azaborine Chromophores.

Six new heteroaromatic polycyclic azaborine chromophores were designed, synthesized, and investigated as easily tunable high-luminescent organic materials. The impact of the nitrogen-boron-hydroxy (N-BOH) unit in the azaborines was investigated by comparison with their N-carbonyl analogs. Insertion of the N-B(OH)-C unit into heteroaromatic polycyclic compounds resulted in strong visible absorption and sharp fluorescence with efficient quantum yields. The solid-state fluorescence of the heteroaromatic polycyclic compounds displayed a large Stokes shift compared to being in solution. The large Stokes shifts observed offset the self-quench effect in the solid state.

Photochemical changes in water accommodated fractions of MC252 and surrogate oil created during solar exposure as determined by FT-ICR MS.

To determine effects of photochemical weathering of petroleum, surrogate and Macondo (MC252) crude oils were exposed to solar radiation during the formation of Water Accommodated Fractions (WAFs) in sterile seawater. Samples were incubated in either unfiltered sunlight, with ultraviolet radiation blocked (Photosynthetically Active Radiation [PAR] only), or in darkness. WAFs were collected at two time points over the course of a week. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) analyses of water soluble species formed during exposure to sunlight were compared for the different treatments. Photochemical alterations resulted in differences in compound class distributions. In general, surrogate oil was photo-oxidized across a wider carbon number range compared to MC252. While photochemical differences were observed between MC252 and surrogate oils, microbial production in seawater responded similarly to both WAFs from both types of oils with the majority of the inhibition resulting from oil exposure to visible light.

Bacterial growth response to photoactive quinones.

Quinones are known producers of reactive oxygen species (ROS) that may be toxic in natural aquatic environments. In this study, the effects of parent quinones and their photodegradation products on bacterial growth were determined, and photochemical ROS formation rates were measured. Using (3)H-leucine incorporation to measure growth of the bacterium Pseudomonas aeruginosa and natural seawater bacterioplankton, growth inhibition was observed when samples were exposed to dichlone, chloranil and sodium anthraquinone-2-sulfonate (AQ2S). For seawater, compared with other quinones tested, dichlone showed the greatest toxicity in the dark, and AQ2S toxicity was greatest during simultaneous exposure to sunlight. Photodegraded chloranil and dichlone showed decreased toxicity compared with nonirradiated samples. For P. aeruginosa, AQ2S and its photodegradation products showed the greatest toxicity during simultaneous exposure to sunlight. Chloranil photodegradation products showed reduced toxicity compared with the parent compound during simultaneous exposure to sunlight. Dichlone was the only compound to show any toxicity to P. aeruginosa in the dark, and its photodegradation products were more toxic than the parent compound. Based on the results of dark and light controlled experiments measuring bacterial growth and estimated ROS production rates, ROS alone does not account for relative differences in toxicity between these quinones.

Aqueous photochemistry of methyl-benzoquinone.

Chemical trapping studies combined with optical and electron paramagnetic resonance measurements were employed to examine the mechanisms of the aqueous photochemistry of methyl-benzoquinone (mBQ) at both low and high quinone concentrations. At low [mBQ], dimethylsulfoxide (DMSO) reacted with a photogenerated intermediate to form a methyl radical, but methane did not, thereby unequivocally excluding the hydroxyl radical. DMSO at concentrations between 50 mM and 2 M completely suppressed the formation of the hydroxylated quinone, while only slowing the formation of the hydroquinone, suggesting reaction with either the triplet state or an intermediate arising from the triplet. Addition of Cl-, a putative physical quencher of the triplet, inhibited the DMSO reaction both noncompetitively and competitively in a fashion similar to that observed previously with nitrite, formate, and salicylic acid, thus providing further evidence for a reactive intermediate distinct from the triplet. This intermediate is attributed to a water-quinone exciplex. The relative yield of the methyl radical from the DMSO reaction decreased with increasing [mBQ], suggesting that at high concentrations, a bimolecular reaction of the triplet with the ground-state quinone outcompetes the formation of the quinone-water exciplex.