... PCB's are chemically very inert and are stable to conditions of hydrolysis and oxidation in industrial use. Photochemical degradation may be one route of their breakdown in the environment. ...
PREDOMINANT ROUTE OF PCB METABOLISM IS HYDROXYLATION. SOME CHLOROBIPHENYLS MAY BE HYDROXYLATED VIA ARENE OXIDE INTERMEDIATES. IN THE RAT 3,3',4,4'-TETRACHLOROBIPHENYL IS HYDROXYLATED TO THE 2- & 5-HYDROXYLATED DERIVATIVE AND 3- & 5-HYDROXYLATED DERIVATIVE.
25 MG OF 3,3'4,4'-TETRACHLOROBIPHENYL (TCB) IN SOYBEAN OIL WAS ADMIN ORALLY TO RATS EVERY 3RD DAY FOR 9 DAYS, AFTER 12 DAYS ONLY THE CHLOROFORM EXTRACT OF FECES CONTAINED UNCHANGED TCB OR 3 TCB METABOLITES. THE MAJOR METABOLITE WAS EITHER 2-HYDROXY-3,3'4,4'-TETRACHLOROBIPHENYL OR 5-HYDROXY-3,3',4,4'-TETRACHLOROBIPHENYL. DURING 14 DAYS AFTER ORAL ADMIN OF SINGLE DOSE OF 25 MG TCB, 64% OF DOSE WAS EXCRETED UNCHANGED, MOST OF WHICH WAS UNABSORBED MATERIAL FROM GI TRACT. FECAL EXCRETION OF MAJOR METABOLITE ACCOUNTED FOR ONLY 3.3% OF DOSE.
OF 36 PURE ISOMERS (CHLORINE NUMBERS 1-5) OF POLYCHLORINATED BIPHENYLS EXAM, 23 COMPOUNDS WERE METABOLIZED BY ALCALIGENS SPECIES STRAIN Y42 & 33 COMPOUNDS WERE METABOLIZED BY ACINETOBACTER SPECIES STRAIN P6. MAJOR PATHWAY OF MANY POLYCHLORINATED BIPHENYL ISOMERS EXAM WAS CONSIDERED TO PROCEED THROUGH 2',3'-DIHYDRO-2',3'-DIOL COMPOUNDS, CONCOMITANT DEHYDROGENATED 2',3'-DIHYDROXY COMPOUNDS, SUBSEQUENTLY THE 1',2'-META-CLEAVAGE COMPOUNDS (CHLORINATED DERIV OF 2-HYDROXY-6-OXO-6-PHENYLHEXA-2,4-DIENOIC ACIDS), & THEN CHLOROBENZOIC ACIDS.
Incubation of (14)C-labeled 3,4,3',4'-tetrachlorobiphenyl with a reconstituted monooxygenase system containing cytochrome p450 isolated from 3-methylcholanthrene treated rats /was conducted/. ... Increases in incorporation and covalent binding to the proteins were dependent on incubation time and required cytochrome p450-linked monooxygenase activity. In the absence of erythrocytes, the reactive 3,4,3',4'-tetrachlorobiphenyl metabolites were bound to cytochrome p450, nicotinamide adenine dinucleotide phosphate reductase cytochrome p450, and high-mol wt aggregates whereas inclusion of the cells in the reaction mixt caused marked alkylation of Hb and a decrease in binding to the electron transfer proteins. Several metabolites other than protein-bound metabolites were detected.
PCBs are absorbed via inhalation, oral, and dermal routes of exposure. They are trasported in the blood, often bound to albumin. Due to their lipophilic nature they tend to accumulate in lipid-rich tissues, such as the liver, adipose, and skin. Metabolism of PCBs is very slow and varies based on the degree and position of chlorination. PCBs are metabolized by the microsomal monooxygenase system catalyzed by cytochrome P-450 enzymes to polar metabolites that can undergo conjugation with glutathione and glucuronic acid. The major metabolites are hydroxylated products which are excreted in the bile and faeces. The slow metabolism of PCBs means they tend to accumulate in body tissues. (L4, T6)
The mechanism of action varies with the specific PCB. Dioxin-like PCBs bind to the aryl hydrocarbon receptor, which disrupts cell function by altering the transcription of genes, mainly be inducing the expression of hepatic Phase I and Phase II enzymes, especially of the cytochrome P450 family. Most of the toxic effects of PCBs are believed to be results of Ah receptor binding. Other PBCs are believed to interfere with calcium channels and/or change brain dopamine levels. PCBs can also cause endocrine disurption by altering the production of thyroid hormones and binding to estrogen receptors, which can stimulate the growth of certain cancer cells and produce other estrogenic effects, such as reproductive dysfunction. They will bioaccumulate by binding to receptor proteins such as uteroglobin. (A3, A4, A30, A66)
The most common health effects of PCBs are skin conditions such as chloracne and rashes. Chronic PCB exposure has also been shown to cause liver, stomach and kidney, damage, jaundice, edema, anemia, changes in the immune system, behavioral alterations, and impaired reproduction. (L4)
3,3',4,4'-TETRACHLOROBIPHENYL (TCB) WAS ADMIN ORALLY TO ADULT FEMALE SPRAGUE-DAWLEY RATS IN DOSAGE REGIMENS OF 0.2, 0.5, & 2 MG/KG/DAY FOR 10 DAYS AT 5 MG/KG/DAY FOR 4 DAYS. IT WAS DISTRIBUTED PREFERENTIALLY INTO ADIPOSE TISSUE & LIVER, WHERE THE XENOBIOTIC CONCN WAS GREATER THAN IN ADIPOSE TISSUE. THE ADIPOSE TISSUE & HEPATIC TCB CONCN WERE DEPENDENT ON BOTH ABSOLUTE DOSE & DOSING SCHEDULE. ONLY TRACE AMOUNTS WERE DETECTABLE BY GLC IN THE SERUM, BRAIN, & KIDNEY. FECAL EXCRETION WAS GREATER THAN URINARY EXCRETION IN THOSE RATS ADMIN 5 MG/KG/DAY FOR 4 DAYS.
DISPOSITION OF 37 PCB CONGENERS & ADIPOSE TISSUE-PLASMA PARTITION OF 28 PCB CONGENERS WERE STUDIED IN 26 PERSONS OCCUPATIONALLY EXPOSED TO VARIOUS PCBS (20-54% CL). CONCN OF PCBS IN ADIPOSE TISSUE & PLASMA WERE RELATED TO DURATION & INTENSITY OF EXPOSURE. PCB CONCN IN ADIPOSE TISSUE WAS PROPORTIONAL TO THAT IN PLASMA, WITH A PARTITION FOR TOTAL PCBS OF APPROX 190:1 INDICATED FROM REGRESSION ANALYSIS. PCB CONGENERS WITH CL IN BOTH 4-POSITIONS OF BIPHENYL RING WERE MAJOR COMPONENTS IN PLASMA & ADIPOSE TISSUE. CONGENERS WITH UNSUBSTITUTED 3,4-POSITIONS ON 1 OR BOTH OF BIPHENYL RINGS WERE OBSERVED AT LOWER CONCENTRATIONS. IN CONTRAST, THOSE COMPOUNDS WITH SUBSTITUENTS AT 2,4- & 3,4-POSITIONS ON BOTH RINGS WERE PRESENT IN MUCH HIGHER PROPORTIONS IN BLOOD OR ADIPOSE TISSUE THAN IN PCB MIXTURES USED. THESE COMPONENTS ALSO HAD HIGHER ADIPOSE TISSUE-PLASMA PARTITION THAN THOSE WITH UNSUBSTITUTED 3,4-POSITIONS, REGARDLESS OF DEGREE OF CHLORINATION.
3,3'4,4'-TETRACHLOROBIPHENYL SHOWED RELATIVE ACCUMULATION FACTORS WHICH AT STEADY STATE WERE PRACTICALLY CONSTANT FOR ANY KIND OF FISH EXAMINED. THE ACCUMULATION FACTORS FOR A PARTICULAR PCB COMPOUND IN DIFFERENT FISH WERE PROPORTIONAL TO THE LIPID CONTENTS OF THE FISH.
A COMPARATIVE STUDY OF THE DISTRIBUTION & EXCRETION OF 3,4,3',4'-TETRACHLOROBIPHENYL (3,4,3'4'-TCB) WAS CONDUCTED IN MALE & FEMALE RATS & FEMALE RHESUS MONKEYS IN AN EFFORT TO ACCOUNT FOR THE TOXICITY OF THIS POLYCHLORINATED BIPHENYL (PCB). DISTRIBUTION & CLEARANCE OF 3,4,3',4'-TCB WERE SIMILAR IN MALE & FEMALE RATS. ALTHOUGH TCB WAS CLEARED MORE SLOWLY BY MONKEYS THAN BY RATS, THE MONKEYS WERE ABLE TO CLEAR IT AT AN APPRECIABLE RATE SO THAT TISSUE LEVELS WERE NEGLIGIBLE 6 WK AFTER ADMIN. TOXICITY COULD NOT BE ATTRIBUTED TO INABILITY OF THE ANIMALS TO METABOLIZE & EXCRETE IT OR TO ITS PERSISTENCE IN ANY TISSUE, WITH THE POSSIBLE EXCEPTION OF BLOOD. 3,4,3',4'-TCB &/OR ITS METABOLITES APPEARED TO BE MORE PERSISTENT IN BLOOD THAN ANY PCB STUDIED TO DATE.
Hydrodehalogenation of Polyhalogenated Aromatics Catalyzed by NiPd Nanoparticles Supported on Nitrogen‐Doped Graphene
作者：Xuefeng Guo、Chao Yu、Zhouyang Yin、Shouheng Sun、Christopher T. Seto
DOI：10.1002/cssc.201800289
日期：2018.5.25
hydrodehalogenation of halogenated aromatics under mild reaction conditions. It reduces mono‐ or dichloroarenes to the corresponding dehalogenated arenes in >90 % yield in 10 % aqueous isopropanol solvent at or below 50 °C within 5 h. Tests on a variety of substrates containingvariousfunctionalgroups show that the catalyst is selective for reduction of C−Cl and C−Br bonds. In addition, this catalyst completely hydrodehalogenates
Palladium Ion Catalysed Oxidative C–C Bond Formation Reactions in Arylboronic Acid: Application of Cordierite Monolith Coated Catalyst
作者：Shrikanth K. Bhat、Prasanna、Jagadeesh Prasad Dasappa、M. S. Hegde
DOI：10.1007/s10562-020-03194-z
日期：2020.10
Catalytic efficiency of palladium ion substituted in TiO2, Ti0.97Pd0.03O1.97 is successfully exploited for the oxidative homocoupling of arylboronicacid and oxidative Heck coupling reactions between arylboronicacid and olefins. The reaction protocol provides direct approach to synthesize biphenyls and cinnamates from moderate to good yield with good functional group tolerance. As a result, 11 symmetrical
Pd-Catalyzed desulfitative arylation of olefins by <i>N</i>-methoxysulfonamide
作者：Subhadra Ojha、Niranjan Panda
DOI：10.1039/d1ob02360h
日期：——
A novel Pd-catalyzed protocol for the desulfitative Heck-type reaction of N-methoxy aryl sulfonamides with alkenes was reported. The cross-coupling reaction was performed successfully with a variety of olefins to obtain aryl alkenes. Different substituents on the aromatic ring of N-methoxysulfonamides were also found to be compatible with the reaction conditions. Expectedly, the reaction proceeds through
Pd-catalyzed oxidative homocoupling of arylboronic acids in WEPA: A sustainable access to symmetrical biaryls under added base and ligand-free ambient conditions
report, a quick and eco-friendly protocol for the synthesis of biaryls by an oxidative (aerobic) homocoupling of arylboronicacids (ABAs) using Pd(OAc)2 in water extract of pomogranate ash (WEPA) as an efficient agro-waste(bio)-derived aqueous (basic) media. The reactions were executed at ambient aerobicconditions in the absence of external base and ligand to result symmetrical biaryls in excellent
Phosphine ligand triggered oxidative decarbonylative homocoupling of aromatic aldehydes: selectively generating biaryls and diarylketones
作者：Luo Yang、Tieqiang Zeng、Qi Shuai、Xiangyu Guo、Chao-Jun Li
DOI：10.1039/c0cc04921b
日期：——
A novel rhodium-catalyzed oxidative decarbonylative homocoupling of aromatic aldehydes to generate biaryls and diarylketones selectively and efficiently, triggered by the choice of different phosphine ligands.
