Convenient syntheses of dibenzo[c,p]chrysene and its possible proximate and ultimate carcinogens: in vitro metabolism and DNA adduction studies

Dibenzo[c,p]chrysene (DB[c,p]C) is the only hexacyclic polycyclic aromatic hydrocarbon having two fjord regions, both in different chemical environments. Its environmental presence and relative tumorigenic potency are not known due to the lack of synthetic standards. We report here the synthesis of dibenzo[c,p]chrysene (1), its proximate carcinogens, i.e., trans-1,2-dihydroxy-1,2-dihydro-DB[c,p]C (2) and trans-11,12-dihydroxy-11,12-dihydro-DB[c,p]C (3), and possible ultimate carcinogens, i.e., anti-trans-1,2-dihydroxy-3,4-epoxy-1,2,3,4-tetrahydro-DB[c,p]C (4) and anti-trans-11,12-dihydroxy-13,14-epoxy-11,12,13,14-tetrahydro-DB[c,p]C (5). The syntheses of 1 and the appropriately methoxy-substituted DB[c,p]C (12 and 27), key intermediates for the synthesis of its proximate and ultimate metabolites, were tried first using a Suzuki cross-coupling reaction. However, the cyclization of olefins (10 and 11) gave poor yields of the desired products. An alternate method was thus developed employing a photochemical approach. The in vitro metabolism of DB[c,p]C was established with the S9 fraction of liver homogenate from phenobarbital/beta-naphthoflavone-induced Sprague-Dawley rats. The major dihydrodiol formed was identified as the fjord region 11,12-dihydroxy-11,12-dihydro-DB[c,p]C, while the major and minor phenols were identified as 11-hydroxy-DB[c,p]C and 12-hydroxy-DB[c,p]C, respectively. Further, the DNA adduction studies with the calf thymus DNA led to a mixture of dA and dG adducts for both fjord region diol epoxides (4 and 5). Interestingly, the dA to dG ratio for 1,2-dihydroxy-3,4-epoxide was much higher (3.2) compared to that of 11,12-dihydroxy-13,14-epoxide (0.5).     

Synthesis and application of functional polyethylene graft copolymers by atom transfer radical polymerization

This investigation attempts to elucidate the copolymerization reaction ethylene and p-methylstyrene via the homogeneous metallocene catalyst, Et(Ind)₂ZrCl₂. With increasing of p-methylstyrene concentration, the poly[ethylene-co-(p-methylstyrene)] copolymer shows systematical decrease of melting temperature and crystallinity and increase of glass transition temperature. The benzylic protons of p-methylstyrene are ready for numerous chemical reactions, such as halogenation and oxidation, which can introduce functional groups at the p-methyl group position under mild reaction conditions. With the bromination reaction of poly[ethylene-co-(p-methylstyrene)], polyethylene graft copolymers, such as polyethylene-g-poly(methyl methacrylate) and polyethylene-g-polystyrene can be prepared via atomic transfer radical polymerization. The following selective bromination reaction of p-methylstyrene units in the copolymer and the subsequent radical graft-from polymerization were effective methods of producing polymeric side chains with well-defined structure. The products were characterized by nuclear magnetic resonance, gel-permeation chromatography, differential scanning calorimetry, and thermal gravimetric analysis. Additionally, the morphology of PE/PMMA and PE/PMMA/PE-g-PMMA blend are compared by using scanning electron microscope.     

Facile soft solution synthesis of delafossite structured Cu(Cr1-xFex)O2 (x = 0, 0.5, and 1) materials and their supercapacitor application

Journal of Solid State Electrochemistry - The investigation of metal oxides with delafossite-type crystal structure for electrochemical energy storage applications is an emerging area....