An in vitro investigation of human enamel wear by restorative dental materials

A radiometric method was applied to assess enamel wear by another enameland by restorative materials. The radioactive enamel was submitted to wearin a machine which allows sliding motion of an antagonistic surface in contactwith the radioactive enamel. The enamel wear was evaluated by measuring thebeta-activity of ³²P transferred to water from this irradiatedtooth. Results obtained indicated that dental porcelains cause pronouncedenamel wear when compared with that provoked by another natural enamel orby resin materials. Resin materials caused less enamel wear than another naturalenamel. Vickers microhardness data obtained for antagonistic materials showeda correlation with the wear caused to the enamel.     

Electrofugal Fragmentation of Alkylcobalamin Derivatives Using Cob(I)Alamin and Heptamethyl Cob (I)yrinate as Catalysts

The cob (I)alamin- ( 1(I) ) and the heptamethyl cob(I)ynnate- ( 2(I) ) catalyzed transformation of an epoxide to the corresponding saturated hydrocarbon 3→4→5 is examined (see Schemes 1 and 3–5). Under the reaction conditions, the epoxyalkyl acetate 3 is opened by the catalysts with formation of appropriate (b?-hydroxyalkyl)-corrinoid derivatives ( 13 , 14 , 17 , 18 , see Schemes 12 and 14). Triggered by a transfer of electrons to the Co-corrin-π system, the Co, C-bond of the intermediates is broken, generating the alkenyl acetate 4 (cf. Schemes 12 and 14) following an electrofugal fragmentation (cf. Schemes 2 and 12). The double bond of 4 is also attacked by the catalysts, leading to the corresponding alkylcorrinoids ( 15 , 19 , see Schemes 12 and 14) which in turn are reduced by electrons from metallic zinc, the electron source in the system, inducing a reductive cleavage of the Co, C-bond with production of the saturated monoacetate 5 (see Schemes 2, 5 and 12). In the cascade of steps involved, the transfer of electrons to the intermediate alkylcorrinoids ( 13–15 , 17–19 , see Schemes 12 and 14) is shown to be rate-limiting. Comparing the two catalytic species 1(I) and 2(I) , it is shown that the ribonucleotide loop protects intermediate alkylcobalamins to some extent from an attack by electrons. The protective function of the ribonucleotide side-chain is shown to be present in alkylcobalamins existing in the base-on form (cf. Chap. 4 and see Scheme 14).     

Cycloaddition reactions of 2,4-diphenyl-1,3-diazabuta-1,3-dienes with isocyanates and isothiocyanates

The cycloaddition reactions of 1-p-tolyl and 1-benzyl- 2,4-diphenyl-1,3-diazabuta-1,3-dienes with a variety of aryl and alkyl isocyanate and isothiocyanate are described. The reaction mechanism is also discussed.     

Construction of functional porphyrin polystyrene nano-architectures by ATRP

A series of mono-functionalized metallo-porphyrin polystyrenes have been synthesized using atom transfer radical polymerization and their self-assembling behavior was studied by electron microscopy showing that the polystyrene tail-length influences the aggregate architecture.