Christina J. Booker

Tuning of Electrogenerated Silole Chemiluminescence

Increasing interest in p-conjugated compounds containing silole rings (1-silacyclopentadiene) is to a large extent due to recent exploitation for applications such as electrochemiluminescent sensors and light-emitting diodes. Their unique photophysical and electronic properties arise from the particularly low lying LUMO owing to s*–p* conjugation between the s* orbital of two exocyclic s bonds on the silicon atom and the p* orbital of the butadiene moiety. We recently reported the synthesis of donor–acceptor siloles and oligomeric ethynyl siloles, and the electrogenerated chemiluminescence (ECL) of several silole-based chromophores. We also reported a series of 2,5-bis(arylethynyl) siloles in which a curious improvement of photoluminescence (PL) quantum efficiency from 9 to 63% was achieved by increasing the steric bulk on the silicon atom and 2,5substituents. It seemed plausible that the enhanced luminescence resulting from the highly improved quantum efficiency was due to increasing the energy barriers for nonemissive decay processes. However, these electronic improvements did not translate to ECL, and the efficiencies of some ethyleneand ethynyl-substituted siloles were only in the range of 0.001 to 0.1 relative to 9,10-diphenylanthracene (DPA), owing to the instability of their radical cations needed for ECL generation. Herein we report that successful tuning of the electrochemical potentials and of silole–thiophene hybrid chromophores results in higher stability of the radical cations and ultimately in improved ECL efficiency. Considering that 1,1-dimethyl-2,5-bis(2-thienyl)-3,4diphenylsilole (3a) and 1,1-dimethyl-2,5-bis[(2,2’-bithiophen)-5-yl]-3,4-diphenylsilole (4a) are efficient electrontransporting materials, we expected that replacement of the methyl substituents with larger isopropyl, tert-butyl and nhexyl groups would augment the energy barriers for nonemissive decay processes, stabilize the radical cations generated electrochemically, and thus result in enhanced photoluminescence and ECL. Therefore the target chromophores, 3b–d and 4b–d, were prepared as shown in Scheme 1. Intramolecular cyclization of bis(phenylethynyl) dialkyl

Bioenergy II: Characterization of the Pesticide Properties of Tobacco Bio-Oil

Pyrolysis converts biomass such as agricultural and forestry waste into bio-oil, preserving some chemicals while creating other, new ones. Nicotine, a chemical present in tobacco leaves and a known pesticide, was found to remain intact during pyrolysis. As expected, insecticidal properties were observed for tobacco bio-oil. Pesticide characteristics of tobacco bio-oil have been observed on the Colorado potato beetle (CPB), a pest currently resistant to all major insecticides, as well as a few bacteria and fungi that do not currently respond well to chemical treatment. Unexpectedly, nicotine-free fractions of the bio-oil were also found to be highly lethal to the beetles and successful at inhibiting the growth of select microorganisms. Through GC-MS, it was found that the active, nicotine-free fractions were rich in phenolics, chemicals likely created from lignin during pyrolysis. While bio-oils in general are known to contain phenolic chemicals, such as cresols, to our best knowledge, quantitative analysis has not been performed to determine if these chemicals are solely responsible for the observed pesticide activities. Based on GC-MS results, ten of the most abundant chemicals, eight of which were phenolic chemicals, were identified and examined through bio-assays. A mixture of these chemicals at the concentration levels found in the bio-oil did not account for the bio-oil activity towards the microorganisms. Tobacco bio-oil may have potential as a pesticide, however, further analyses using liquid chromatography is necessary to identify the remaining active chemicals.

Insecticidal activity of bio-oil from the pyrolysis of straw from Brassica spp.

Agricultural crop residues can be converted through thermochemical pyrolysis to bio-oil, a sustainable source of biofuel and biochemicals. The pyrolysis bio-oil is known to contain many chemicals, some of which have insecticidal activity and can be a potential source of value-added pest control products. Brassicacae crops, cabbage, broccoli, and mustards, contain glucosinolates and isocyanates, compounds with recognized anti-herbivore activity. In Canada, canola Brassica napus straw is available from over 6 000 000 ha and mustard Brassica carinata and Brassica juncea straw is available from 200 000 ha. The straw can be converted by microbial lignocellulosic enzymes as a substrate for bioethanol production but can also be converted to bio-oil by thermochemical means. Straw from all three species was pyrolyzed, and the insecticidal components in the bio-oil were isolated by bioassay-guided solvent fractionation. Of particular interest were the mustard straw bio-oil aqueous fractions with insecticidal and feeding repellent activity to Colorado potato beetle larvae. Aqueous fractions further analyzed for active compounds were found not to contain many of the undesirable phenol compounds, which were previously found in other bio-oils seen in the dichloromethane (DCM) and ethyl acetate (EA) solvent phases of the present study. Identified within the most polar fractions were hexadecanoic and octadecanoic fatty acids, indicating that separation of these compounds during bio-oil production may provide a source of effective insecticidal compounds.

Removal of sample background buffering ions and myoglobin enrichment via a pH junction created by discontinuous buffers in capillary electrophoresis

Traditional CE sample stacking is ineffective for samples containing a high concentration of salt and/or buffer. We recently reported the use of a discontinuous buffer system for protein enrichment that was applicable to samples containing millimolar concentrations of salt. In this paper, the technique was investigated for samples containing unwanted buffering ions, including TRIS, MES, and phosphate, which are commonly used in biological sample preparation. Using myoglobin as a model protein, the results demonstrated that background buffering ions can be effectively removed or separated from the enriched protein. The key is to use either the acid or the base of the discontinuous buffers to adjust the pH of the sample, such that the net charge of the unwanted buffering ions is near-zero. The successful isolation and enrichment of myoglobin from up to 100 mM TRIS and 50 mM MES was demonstrated. The enrichment factors remained at approximately 200. Removal of phosphate was more challenging because its net charge was anionic in both the acid and the base of the discontinuous buffers. The enrichment was only achievable up to 30 mM of sodium phosphate, the enrichment factors observed were significantly lower, below 50, and the process was delayed due to the higher ionic strength resulted from phosphate. The migration of phosphate during enrichment was studied using a UV-absorbing analogue, phenyl phosphate. In addition, Simul 5.0 was used to simulate the discontinuous buffers in the absence and presence of TRIS and phosphate. The stimulated TRIS and phosphate concentration profiles were generally in agreement with the experimental results. The simulation also provided a better understanding on the effect of phosphate on the formation of the pH junction.