Aqueous Photolysis of Benzobicyclon Hydrolysate.

Benzobicyclon [3-(2-chloro-4-(methylsulfonyl)benzoyl)-2-phenylthiobicyclo[3.2.1]oct-2-en-4-one] is a pro-herbicide used against resistant weeds in California rice fields. Persistence of its active product, benzobicyclon hydrolysate, is of concern. As an acidic herbicide, the neutral species photolyzed faster than the more predominant anionic species ( t1/2 = 1 and 320 h, respectively; natural sunlight), from a >10-fold difference in the quantum yield. Dissolved organic matter in natural waters reduced direct photolysis and increased indirect photolysis compared to high-purity water. Light attenuation appears significant in rice field water and can slow photolysis. These results, used in the pesticides in flooded applications model with other experimental properties, indicate that a floodwater hold time of 20 days could be sufficient for dissipation of the majority of initial aqueous benzobicyclon hydrolysate prior to release. However, soil recalcitrance of both compounds will keep aqueous benzobicyclon hydrolysate levels constant months after benzobicyclon application.

Dissipation of the Herbicide Benzobicyclon Hydrolysate in a Model California Rice Field Soil.

The herbicide benzobicyclon (BZB; 3-(2-chloro-4-(methylsulfonyl)benzoyl)-2-phenylthiobicyclo[3.2.1]oct-2-en-4-one) has recently been approved for use on California rice fields by the United States Environmental Protection Agency (U.S. EPA). Hydrolysis of BZB rapidly forms the active compound, benzobicyclon hydrolysate (BH), whose fate is currently not well understood. A model California rice soil was used to determine BH soil dissipation. The pKa and aqueous solubility were also determined, as experimental values are not currently available. Sorption data indicate BH does not bind tightly, or irreversibly, with this soil. Flooding resulted in decreased BH loss, indicating anaerobic microbes are less likely to transform BH compared to aerobic microorganisms. Temperature increased dissipation, while autoclaving decreased BH loss. Overall, dissipation was slow regardless of treatment. Further investigation is needed to elucidate the exact routes of loss in soil, though BH is expected to dissipate slowly in flooded rice field soil.

Aerobic versus Anaerobic Microbial Degradation of Clothianidin under Simulated California Rice Field Conditions.

Microbial degradation of clothianidin was characterized under aerobic and anaerobic California rice field conditions. Rate constants (k) and half-lives (DT50) were determined for aerobic and anaerobic microcosms, and an enrichment experiment was performed at various nutrient conditions and pesticide concentrations. Temperature effects on anaerobic degradation rates were determined at 22 ± 2 and 35 ± 2 °C. Microbial growth was assessed in the presence of various pesticide concentrations, and distinct colonies were isolated and identified. Slow aerobic degradation was observed, but anaerobic degradation occurred rapidly at both 25 and 35 °C. Transformation rates and DT50 values in flooded soil at 35 ± 2 °C (k = -7.16 × 10(-2) ± 3.08 × 10(-3) day(-1), DT50 = 9.7 days) were significantly faster than in 25 ± 2 °C microcosms (k= -2.45 × 10(-2) ± 1.59 × 10(-3) day(-1), DT50 = 28.3 days). At the field scale, biodegradation of clothianidin will vary with extent of oxygenation.

Photochemical degradation of imazosulfuron under simulated California rice field conditions.

BACKGROUND: The photodegradation of imazosulfuron (IMZ), a potent broad-spectrum herbicide, was investigated under simulated rice field conditions. Previous reports have indicated that it is photolabile, but have failed to report radiation intensity or determine a quantum yield, precluding extrapolation to environmental rates. Therefore, the objective of this investigation was to determine the photolytic rate of IMZ under simulated rice field conditions and how it is influenced by environmental factors such as turbidity, salinity and temperature. RESULTS: IMZ was efficiently photolyzed in all solutions and fitted pseudo-first-order kinetics. Degradation was faster in HPLC-grade water than in field water. Field-relevant variances in temperature, turbidity and salinity did not significantly influence degradation. The experimentally derived quantum yield for direct photolysis (2.94 × 10(3) ) was used to predict the half-life of IMZ in a California rice field (3.6 days). CONCLUSIONS: Aqueous photolysis is predicted to be an important process in the overall degradation of IMZ in the environment, regardless of variances in salinity, organic matter and temperature. Based on the predicted half-life of IMZ in a California rice field (3.6 days), state-mandated holding periods for field water post-IMZ application (30 days) are expected to allow for sufficient clearance of the herbicide (>98%), preventing significant contamination of the environment upon release of tailwater. © 2015 Society of Chemical Industry.

Photodegradation of clothianidin under simulated California rice field conditions.

BACKGROUND: Photodegradation can be a major route of dissipation for pesticides applied to shallow rice field water, leading to diminished persistence and reducing the risk of offsite transport. The objective of this study was to characterize the aqueous-phase photodegradation of clothianidin under simulated California rice field conditions. RESULTS: Photodegradation of clothianidin was characterized in deionized, Sacramento River and rice field water samples. Pseudo-first-order rate constants and DT50 values in rice field water (mean k = 0.0158 min(-1) ; mean DT50 = 18.0 equivalent days) were significantly slower than in deionized water (k = 0.0167 min(-1) ; DT50 = 14.7 equivalent days) and river water (k = 0.0146 min(-1) ; DT50 = 16.6 equivalent days) samples. Quantum yield ϕc values demonstrate that approximately 1 and 0.5% of the light energy absorbed results in photochemical transformation in pure and field water respectively. Concentrations of the photodegradation product thiazolymethylurea in aqueous photolysis samples were determined using liquid chromatography-tandem mass spectrometry and accounted for ≤17% in deionized water and ≤8% in natural water. CONCLUSION: Photodegradation rates of clothianidin in flooded rice fields will be controlled by turbidity and light attenuation. Aqueous-phase photodegradation may reduce the risk of offsite transport of clothianidin from flooded rice fields (via drainage) and mitigate exposure to non-target organisms. © 2015 Society of Chemical Industry.

Enzymatic production of (-)-indolactam V by LtxB, a cytochrome P450 monooxygenase.

The P450 cytochrome monooxygenase gene, ltxB, was cloned and overexpressed in Escherichia coli as a 6xHis-tagged protein. The resulting recombinant LtxB was purified by Ni-NTA affinity chromatography and characterized biochemically. Purified LtxB demonstrated typical cytochrome P450 spectroscopic properties including substrate-induced transition from a low-spin (lambdamax=414 nm) to high-spin state (lambdamax=386 nm) upon incubation with N-methyl-L-valyl-L-tryptophanol. The catalytic activity of LtxB was verified by demonstrating the oxidation/cyclization of N-methyl-L-valyl-L-tryptophanol to (-)-indolactam V. LtxB shows a relaxed specificity for analogue substrates in which the valyl group is substituted for other aliphatic groups. The relaxed substrate specificity of LtxB, along with the relaxed specificity of the prenyltransferase, LtxC, allowed for the enzymatic production of a series of (-)-indolactam V and lyngbyatoxin analogues.

New conjunctive reagents as cross-coupling partners en route to retinoid-like polyenes.

[structure: see text] New conjunctive reagents E-2 and Z-3 can be used, after transmetalation, in Negishi couplings with vinyl and aryl iodides. The subsequently unmasked terminal alkynes can be further manipulated to arrive at retinoid-like products.