Improved synthesis of conduritol B epoxide.
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Chemical Phenomena↗
Biomedical subjects
S A Boyd
Publications and source records attributed to S A Boyd.
Anaerobic biodegradation of chlorophenols in fresh and acclimated sludge.
We investigated the anaerobic biodegradation of mono- and dichlorophenol isomers by fresh (unacclimated) sludge and by sludge acclimated to either 2-chlorophenol, 3-chlorophenol, or 4-chlorophenol. Biodegradation was evaluated by monitoring substrate disappearance and, in selected cases, production of 14CH4 from labeled substrates. In unacclimated sludge, each of the monochlorophenol isomers was degraded. The relative rates of disappearance were in this order: ortho greater than meta greater than para. For the dichlorophenols in unacclimated sludge, reductive dechlorination of the Cl group ortho to phenolic OH was observed, and the monochlorophenol compounds released were subsequently degraded. 3,4-Dichlorophenol and 3,5-dichlorophenol were persistent. Sludge acclimated to 2-chlorophenol cross-acclimated to 4-chlorophenol but did not utilize 3-chlorophenol. This sludge also degraded 2,4-dichlorophenol. Sludge acclimated to 3-chlorophenol cross-acclimated to 4-chlorophenol but not to 2-chlorophenol. This sludge degraded 3,4- and 3,5-dichlorophenol but not 2,3- or 2,5-dichlorophenol. The specific cross-acclimation patterns observed for monochlorophenol degradation demonstrated the existence of two unique microbial activities that were in turn different from fresh sludge. The sludge acclimated to 4-chlorophenol could degrade all three monochlorophenol isomers and 2,4- and 3,4-dichlorophenol. The active microbial population in this sludge appeared to be a mixture of populations present in the 2-chlorphenol- and 3-chlorophenol-acclimated sludges, both of which could utilize 4-chlorophenol. Experiments with 14C-radiolabeled p-chlorophenol, o-chlorophenol, and 2,4-dichlorophenol demonstrated that these compounds were converted to 14CH4 and 14CO2.
Anaerobiosis↗
Anaerobic biodegradation of phenolic compounds in digested sludge.
We examined the anaerobic degradation of phenol and the ortho, meta, and para isomers of chlorophenol, methoxyphenol, methylphenol (cresol), and nitrophenol in anaerobic sewage sludge diluted to 10% in a mineral salts medium. Of the 12 monosubstituted phenols studied, only p-chlorophenol and o-cresol were not significantly degraded during an 8-week incubation period. The phenol compounds degraded and the time required for complete substrate disappearance (in weeks) were: phenol (2), o-chlorophenol (3), m-chlorophenol (7), o-methoxyphenol (2), m- and p-methoxyphenol (1), m-cresol (7), p-cresol (3), and o-, m-, and p-nitrophenol (1). Complete mineralization of phenol, o-chlorophenol, m-cresol, p-cresol, o-nitrophenol, p-nitrophenol, and o-, m-, and p-methoxyphenol was observed. In general, the presence of Cl and NO2 groups on phenols inhibited methane production. Elimination or transformation of these substituents was accompanied by increased methane production, o-Chlorophenol was metabolized to phenol, which indicated that dechlorination was the initial degradation step. The methoxyphenols were transformed to the corresponding dihydroxybenzene compounds, which were subsequently mineralized.
Anaerobiosis↗
Synthesis of charged amphipathic nitroxide lipid spin labels and an example of their application in membrane studies.
The synthesis of a series of amphipathic nitroxide lipid spin labels is reported. Thus, 12-proxylhexadecanol has been converted into the versatile fatty acid spin label 14-proxylstearic acid. This substance was used to prepare 14-proxylstearyltrimethylammonium methanesulfonate, a positively charged label, and 14-proxylstearylmethyl phosphate sodium salt, a negatively charged label. Also prepared in the doxyl series were quaternary ammonium salts derived from 16-doxyl- and 7-doxylstearic acid. The positively charged and negatively charged proxyl labels were used in a preliminary experiment to investigate the role of charge in their interaction with reconstituted cytochrome oxidase. The average binding affinity of the negatively charged label is approximately 2-fold higher than that of the positively charged label at pH 7.4. At pH 5.5 the average relative affinity for negatively charged label is about 3.5-fold higher than that of positively charged label, suggesting that the ionizable group(s) on the protein can interact with the lipid headgroup.
Cyclic N-Oxides↗
Transverse motion of chlorophyll derivatives in phospholipid bilayers.
Chlorophyll derivatives were synthesized with spin labels attached to the porphyrin ring. These labels were incorporated into egg phosphatidylcholine vesicles in order to estimate the transbilayer motion (flip-flop) of this class of photosynthetic pigments. Using the ascorbate reduction method, the upper limit to the spin label half-life is tau 1/2 approximately 4 min at 0 degrees C. The flip-flop rate is rapid compared to that of a phospholipid spin label under the same conditions. The presence or absence of magnesium in the center of the porphyrin ring had no measurable effect on the flip-flop rate.
Chemical Phenomena↗
Microbial reductive dechlorination of PCBs.
Reductive dechlorination is an advantageous process to microorganisms under anaerobic conditions because it is an electron sink, thereby allowing reoxidation of metabolic intermediates. In some organisms this has been demonstrated to support growth. Many chlorinated compounds have now been shown to be reductively dechlorinated under anaerobic conditions, including many of the congeners in commercial PCB mixtures. Anaerobic microbial communities in sediments dechlorinate Aroclor at rates of 3 micrograms Cl/g sediment x week. PCB dechlorination occurs at 12 degrees C, a temperature relevant for remediation at temperate sites, and at concentrations of 100 to 1000 ppm. The positions dechlorinated are usually meta > para > ortho. The biphenyl rings, and the mono-ortho- and diorthochlorobiphenyls were not degraded after a one year incubation. Hence subsequent aerobic treatment may be necessary to meet regulatory standards. Reductive dechlorination of Aroclors does reduce their dioxin-like toxicity as measured by bioassay and by analysis of the co-planar congeners. The most important limitation to using PCB dechlorination as a remediation technology is the slower than desired dechlorination rates and no means yet discovered to substantially enhance these rates. Long term enrichments using PCBs as the only electron acceptor resulted in an initial enhancement in dechlorination rate. This rate was sustained but did not increase in serial transfers. Bioremediation of soil contaminated with Aroclor 1254 from a transformer spill was dechlorinated by greater than 50% following mixing of the soil with dechlorinating organisms and river sediment.(ABSTRACT TRUNCATED AT 250 WORDS)
Bacteria, Anaerobic↗
Kinetic modeling of bioavailability for sorbed-phase 2,4-dichlorophenoxyacetic acid.
The degradation rate of 2,4-dichlorophenoxyacetic acid (2,4-D) was studied in silica-slurry systems to evaluate the bioavailability of sorbed-phase contaminant. After the silica particles were saturated with 2,4-D, the system was inoculated with the 2,4-D-degrading microorganism Flavorbacterium sp. strain FB4. The disappearance rate of 2,4-D was found to be greater than the rate predicted based upon liquid-phase 2,4-D concentrations. A kinetic formulation, termed the enhanced bioavailability model, was developed to describe the desorption and biodegradation processes in this batch system. The approach assumes that 2,4-D resides in both the liquid and solid phases and degradation occurs via both suspended and attached biomass. All biomass can degrade liquid-phase 2,4-D at one rate, while only attached biomass can degrade sorbed 2,4-D at another rate. An enhanced transformation factor (Ef) was introduced to express the increased biodegradation rate over that expected from the liquid phase only. This approach was able to account for the increased degradation rates observed experimentally. The results provide evidence that desorption to the bulk solution is not prerequisite to degradation, and that sorbed substrate may be available for degradation.
2,4-Dichlorophenoxyacetic Acid↗
The orally active renin inhibitor A-74273. In vivo and in vitro morpholine ring metabolism in rats, dogs, and humans.
The metabolism and disposition of [14C]A-74273--a potent, orally active renin inhibitor--were investigated in beagle dogs and Sprague-Dawley rats. Two male and two female dogs received a single 10 mg/kg oral or 1 mg/kg intravenous dose in a cross-over experiment and urine and feces were collected for 5 days. After both intravenous and oral dosing, > 92% of the dose was recovered in the feces and < 3% was recovered in the urine. The predominance of hepatobiliary elimination in the clearance of A-74273 was verified in a bile-exteriorized dog, where 79.8% of a 1 mg/kg intravenous dose was excreted in the bile within 6 hr after administration. Similarly, administration of a 1 mg/kg intravenous dose to a bile-exteriorized rat resulted in biliary excretion of 60.5% of the dose within 6 hr. Radio-HPLC analysis of bile and feces from both species indicated extensive metabolism of A-74273 to three major morpholine ring-opened metabolites; the ethanolamine A-78242, the amine A-78030, and the carboxylic acid A-81307. These three metabolites each contributed 12.0-20.2% of the biliary radioactivity after intravenous dosing, while unchanged A-74273 contributed 5-17%. Incubation of [14C]A-74273 with rat, dog, and human liver microsomes afforded nearly equal amounts of the three in vivo metabolites for all three species, suggesting that the in vitro system was representative of A-74273 in vivo metabolism and that humans should also convert A-74273 to the morpholine ring-opened metabolites in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)
Administration, Oral↗