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Biomarkers in Occupational Neurotoxicology
Published in Lucio G. Costa, Luigi Manzo, Occupatinal Neurotoxicology, 2020
The biological monitoring of styrene has been extensively studied.60 Styrene is metabolized to styrene oxide by cytochrome P450s, in particular CYP2E1; styrene oxide is detoxified via glutathione transferases and/or epoxide hydrolase, the latter pathway being more significant in humans than rodents.61 Mandelic acid and phenyl-glyoxylic acid are the most prominent urinary metabolites, and, together with levels of styrene in blood or exhaled air, have been commonly used for biological monitoring.60,62,63 Three-fold differences in the relative urinary excretion of optical enan-tiomers of mandelic acid have been reported, which may be related to polymorphisms of cytochrome P450s, leading to R or S styrene 7,8-oxide, or of epoxide hydrolase.64 This observation may be relevant with regard to genotoxicity, as R-styrene 7,8-oxide has a stronger mutagenic effect than its S-enantiomer.65 Styrene oxide can form adducts to the N-valine residue on hemoglobin,66-68 and measurement of these adducts has been utilized to monitor exposure to styrene in animals and humans.69-71 However, styrene oxide is not considered an effective alkylator of hemoglobin compared to other toxicants such as ethylene oxide.72 Furthermore, the capacity of humans to form styrene oxide is much lower than rats or mice,61 which results in very low levels of styrene oxide in blood,73 as well as of styrene oxide-hemoglobin adducts.69,70
Clay Mineral Catalysis of Redox, Asymmetric, and Enantioselective Reactions
Published in Benny K.G. Theng, Clay Mineral Catalysis of Organic Reactions, 2018
Louloudi and Papayannakos (2000) impregnated Ni into Al-PILC and used the product to convert benzene into cyclohexane. Subsequently, Dhakshinamoorthy and Pitchumani (2008) reported that montmorillonite-supported nickel nanoparticles obtained by treating the Ni2+-exchanged (K10) clay with hydrazine could efficiently catalyze the hydrogenation of alkenes and alkynes. Ni nanoparticles supported on synthetic saponites are similarly active in promoting the hydrogenation of styrene oxide to 2-phenylethanol (Vicente et al. 2011). We refer to Table 3.5 for other examples of organic hydrogenation reactions catalyzed by metal-impregnated pillared smectites.
Unique Electronic and Stereochemical Properties of Salen Complexes
Published in Atsushi Nagai, Koji Takagi, Conjugated Objects, 2017
Stoichiometric reactions of the iodosylmesitylene adduct withthioanisole and styrenes were carried out. Enantioselectivity of thesingle-turnover reaction with thioanisole is negligibly small (3%ee),which is consistent with low enantioselectivity in the catalyticreactions of sulfides. In contrast, the single-turnover reactionswith styrenes yield moderate enantioselectivity. The reaction withczs-ß-methyl styrene gives a mixture of czs-ß-methyl styrene oxide(63%ee) and trazzs-ß-methyl styrene oxide (27%ee).
Synthesis, characterization, and catalytic oxidation of styrene, cyclohexene, allylbenzene, and cis-cyclooctene by recyclable polymer-grafted Schiff base complexes of vanadium(IV)
Published in Journal of Coordination Chemistry, 2018
Vijay Kumar Singh, Abhishek Maurya, Neha Kesharwani, Payal Kachhap, Sweta Kumari, Arun Kumar Mahato, Vivek Kumar Mishra, Chanchal Haldar
In synthetic organic chemistry, catalytic oxidation products of alkenes such as carbonyl compounds, epoxides, and diols are the major feedstock among the most effective synthetic intermediates in fundamental research as well as industrial commodities [1–4]. Particularly oxidation of cyclohexene, styrene, cis-cyclooctene, allylbenzene, etc. produces versatile and useful intermediates widely used in polymers, pharmaceuticals, fine chemicals, and biological materials [5–8]. Certain herbs and spices, like basil, cinnamon, nutmeg, ginger, black pepper, clove, tarragon, etc. carry naturally occurring allylbenzenes (such as eugenol, estragole, and safrole) in high concentration, which can be a promising green alternative source of renewable raw materials for chemical industry. Oxidation products of allylbenzenes are widely used in pharmacological, cosmetic, food, and fragrance industries [9–12] as well as direct synthetic intermediates in the production of biologically active compounds [13]. 2-Cyclohexene-1-ol and 2-cyclohexene-1-one formed through the allylic oxidation of cyclohexene are applied in the manufacture of spices, medication, pesticides, and insect pheromones [14, 15]. Oxidation of styrene is one of the most important research tasks for converting hydrocarbons into other valuable commodities such as benzaldehyde, styrene epoxide, and formaldehyde [16–20]. Styrene oxide is widely used for the synthesis of epoxy resin-diluting agents, ultraviolet absorbents, flavoring agents, etc.; benzaldehyde is a precious chemical mainly used in perfumery, pharmaceuticals, dyestuffs, and agrochemicals [21]. Likewise, the oxidation products of cyclooctene have widespread applications in industrially important pharmaceuticals and fine chemicals [22]. Conventionally, stoichiometric amount of oxidants such as permanganates, chromium reagents, ruthenium(VIII) oxide or activated DMSO were used to carry out the oxidation of alkenes. From the last few decades, metal complexes of Ti, V, Cr, Mn, Co, Ni, Cu, Mo, Ru, and Re were utilized for oxidation of alkenes in the presence of peroxides, peracids, and other oxidizing reagents [4, 23–30]. Vanadium complexes in high oxidation states have been widely used as effective catalysts in oxidation reactions of industrial as well as academic interest in the presence of a suitable oxidant [26, 30–34]. Moreover, the involvement of vanadium haloperoxidase, a vanadium-containing enzyme in a variety of biological processes, stimulated the application of vanadium-containing enzymes in various catalytic organic transformations [1–4, 23–38]. Flexible coordination number, easily interconvertible high oxidation states between +4 and +5, Lewis acidic nature of the vanadium center along with high affinity toward oxygen make high valent vanadium complexes promising agents for the catalytic oxidation of alkenes.