X-ray Crystal Structures of Some Arene Oxides

Using a recently disclosed modification to the dimethyldioxirane method we have synthesized four arene monooxides and one trioxide in good to excellent yield. The X-ray crystal structures have been determined for all of these compounds. In the case of the chrysene trioxide the X-ray determination reveals that the structure is bent out of the plane.     

Physicochemical Studies on the Adsorption Properties of Asbestos

Toxic asbestos fibers are known to be carriers of carcinogenic polyaromatic hydrocarbons (PAH) when ingested by human lungs. To clarify the asbestos-PAH interactions, the adsorption properties of four different asbestos, namely amosite, anthofillite, crocidolite, and chrysotile (termed AMOS, ANTHO, CROX, and CHRYS, respectively), toward pyrene (py) were investigated by electron paramagnetic resonance (EPR) and fluorescence spectroscopy, both steady state and time resolved. Pyrene was labeled with a nitroxide TEMPO radical (py-T) for the EPR study. EPR provided information on the adsorption ability of the surface toward py-T and on the interactions between py-T and surface sites, mainly cooperative in nature. Pyrene molecules organize on AMOS samples in a packed layer; the radical works as a separator and prevents the attaching of the py-T molecules at the surface, but the N-O groups of the few adsorbed molecules directly interact with the surface. The interacting sites at the ANTHO surface are quite far from each other; therefore py-T instead of py may form a monolayer at the asbestos surface. The surface of CROX strongly adsorbs both excimers of py and monomers of py-T, orienting the nitroxide groups toward the polar sites at the surface. The surface of CHRYS is the most adsorbing toward py and py-T, but the nitroxide group does not directly interact with the surface. By increasing concentration, py-T saturates the CROX and the CHRYS surface interacting sites, and then forms a disordered liquid-like multilayer. The close average distance calculated for py-T adsorbed at the CROX surface (12 ?) suggests that the py-T molecules intercalate in an "up-and-down" conformation. The chemical composition of the different asbestos and their different structural properties affect the distribution of the polar sites at the external surface, modifying the adsorption properties. This study confirms the synergetic effect between the toxicity of the asbestos fibers and the adsorption of polyaromatic hydro carbons at their surface, which mainly depends on the surface properties of the asbestos. Copyright 2001 Academic Press.     

Lanthanon (III) Derivatives of Monofunctional Bidentate Schiff Bases

The 1:1, 1:2 and 1:3 interactions of lanthanon (III) isopropoxide with monofunctional bidentate Schiff bases as salicylidene-o-toluidine (SOTH) and salicylidene-p-p-toluidine (SPTH) have been investigated. The resulting products Ln(OPr¹)₂(SB), Ln(OPr¹)(SB)₂ and Ln(SB)₃ (where Ln=Pr, Nd and Sm and SB^1? is the anion of the corresponding Schiff base) have been isolated in almost quantitative yields. The infrared spectra of these compounds have been recorded and plausible structures suggested.     

Diastereoselectivity in the Epoxidation of Substituted Cyclohexenes by Dimethyldioxirane(1)(,)(2)

Three series of compounds based on the cyclohexene framework have been epoxidized by dimethyldioxirane. A pronounced dependence of epoxide diastereoselectivity on substituent has been observed. In addition there is a solvent influence on this stereoselectivity. The results have been explained by invoking steric, H-bonding, and dipole-dipole influences on the epoxide stereochemistry.