Synthesis, structures, and physical properties of benzo[k]fluoranthene-based linear acenes.

This work describes the syntheses, crystal structures, photophysical properties, and electro-chemical analyses of benzo[k]fluoranthene-based linear acenes, together with ab initio density functional theory computations on them. The molecules were prepared in generally moderate to good yields through Pd-catalyzed cycloadditions between 1,8-diethynylnaphthalene derivatives and aryl iodides. This protocol is simpler and more efficient than conventional methods. The scope and limitations of this reaction were examined. The structures of compounds 4hb, 15ac, 17ab, 19ac, and 24je were determined by X-ray analysis; they are either bent or twisted, rather than planar. The photophysical and electrochemical properties of these cycloadducts were also investigated and compared with computational predictions based on density functional theory.

Application of rhamnolipid and surfactin for enhanced diesel biodegradation--effects of pH and ammonium addition.

This study investigated the effects of pH and ammonium concentrations on the potential application of two biosurfactants, surfactin (SF) and rhamnolipid (RL), for enhanced diesel biodegradation with a series of bench-scale experiments. In general, compared to the experiments without biosurfactant addition, adding RL or SF to diesel-water systems at concentrations above their critical micelle concentration (CMC) values benefited diesel emulsification, and therefore enhanced diesel biodegradation. The effects of pH on RL or SF-enhanced biodegradation of diesel were in good agreement with the trends of emulsion index values for RL or SF addition, respectively, under different pH conditions, suggesting that enhanced diesel emulsification by RL or SF addition promoted biodegradation of diesel. In diesel-water systems with 50mg/L of RL addition, an optimum pH condition for microbial growth and diesel biodegradation was found to be at a pH 7.2, while decreasing pH to 5.2 or increasing it to 8.4 reduced those parameters considerably. For the cases where 40 mg/L of SF was added, the enhancing ability shared a general trend with that observed for adding 50mg/L of RL as the pH increased from 5.2 to 7.2. Further increase of pH to 8.4, however, did not seem to negatively influence biodegradation and biomass growth. With respect to the effects of ammonium concentration on diesel biodegradation in diesel-water systems with 50mg/L of RL addition, an optimum ammonium addition for microbial growth and diesel biodegradation was found between 200 and 300 mg-N/L, but a dramatic decrease in growth and biodegradation occurred at ammonium addition up to 450 mg-N/L. For the cases where 40 mg/L of SF was added, an increase of ammonium addition from 50 to 200mg-N/L substantially increased microbial growth and biodegradation of diesel. Further increase of ammonium concentration to 450 mg-N/L, however, did not further improve diesel biodegradation.

Application of biosurfactants, rhamnolipid, and surfactin, for enhanced biodegradation of diesel-contaminated water and soil.

This study investigated potential application of two biosurfactants, surfactin (SF) and rhamnolipid (RL), for enhanced biodegradation of diesel-contaminated water and soil with a series of bench-scale experiments. The rhamnolipid used in this study, a commonly isolated glycolipid biosurfactant, was produced by Pseudomonas aeruginosa J4, while the surfactin, a lipoprotein type biosurfactant, was produced by Bacillus subtilis ATCC 21332. Both biosurfactants were able to reduce surface tension to less than 30 dynes/cm from 72 dynes/cm with critical micelle concentration (CMC) values of 45 and 50 mg/L for surfactin and rhamnolipid, respectively. In addition, the results of diesel dissolution experiments also demonstrated their ability in increasing diesel solubility with increased biosurfactant addition. In diesel/water batch experiments, an addition of 40 mg/L of surfactin significantly enhanced biomass growth (2500 mg VSS/L) as well as increased diesel biodegradation percentage (94%), compared to batch experiments with no surfactin addition (1000 mg VSS/L and 40% biodegradation percentage). Addition of surfactin more than 40 mg/L, however, decreased both biomass growth and diesel biodegradation efficiency, with a worse diesel biodegradation percentage (0%) at 400 mg/L of SF addition. Similar trends were also observed for both specific rate constants of biomass growth and diesel degradation, as surfactin addition increased from 0 to 400 mg/L. Addition of rhamnolipid to diesel/water systems from 0 to 80 mg/L substantially increased biomass growth and diesel biodegradation percentage from 1000 to 2500 mg VSS/L and 40 to 100%, respectively. Rhamnolipid addition at a concentration of 160 mg/L provided similar results to those of an 80 mg/L addition. Finally, potential application of surfactin and rhamnolipid in stimulating indigenous microorganisms for enhanced bioremediation of diesel-contaminated soil was also examined. The results confirmed their enhancing capability on both efficiency and rate of diesel biodegradation in diesel/soil systems.