Studies on the subcellular localization of the porphycene CPO

This study was designed to provide more detailed information on the subcellular sites of binding of the porphycene, termed 9-capronyloxytetrakis (methoxyethyl) porphycene (CPO), with a fluorescence resonance energy transfer (FRET) technique. The proximity of CPO to two fluorescent probes was determined: nonyl acridine orange (NAO), a dye with specific affinity for the mitochondrial lipid cardiolipin, and dihexa-oxacarbocyanine iodide (DiOC6), an agent that labels the endoplasmic reticulum (ER). FRET spectra indicated energy transfer between DiOC6 and CPO but no significant transfer between NAO and CPO. These results confirm data obtained by fluorescence microscopy, suggesting a similar pattern of subcellular localization by CPO and DiOC6 but not by CPO and NAO. However, when cells containing CPO were irradiated and then loaded with NAO, FRET between the two fluorophores was observed. Hence, a relocalization of CPO can occur during irradiation. These data provide an explanation for recent studies on CPO-catalyzed photodamage to both ER and mitochondrial Bcl-2.     

Weak-Link Versus Active Carbon Degradation Routes in the Oxidation of Aromatic Heterocyclic Systems. III

A polybenzimidazolone prepared by the condensation of 1,45,8-naphthalene tetracarboxylic acid and 3,3′-diaminobenzidine and several model compounds were thermally degraded (300-500°C) under inert and oxidative conditions. In every case only small fragments, i.e., carbon oxides, cyanogen (trace), and water, were detected by spectroscopic and chromatographic analysis of all phases of the pyrolysis products. The significance of these results is discussed in light of the mechanism by which this aromatic heterocyclic system undergoes oxidative degradation.     

An Improved Synthesis of Ethylidenecyclobutane

In our studies of the chemistry of small rings, it was necessary to synthesize ethylidenecyclobutane 1. Repetition of the only method in the literature^2,3 was attempted, namely, the reaction of 1,1,1-tris-(hydroxymethyl)-propane 2 with phosphorus tribromide to give 1,1,1-tris-(bromomethyl)-propane 3 and the subsequent conversion of 3 to 1 with zinc. The reaction of 2 with phosphorus tribromide is exceedingly hazardous. In spite of the careful adherence to the conditions specified by Derfer, et. al.² there were several fires in the effluent gases and the reaction produced precipitates which ignited spontaneously in air.     

Polymerization of Ethylene by Silica‐Supported Dinuclear CrIII Sites through an Initiation Step Involving C?H Bond Activation

The insertion of an olefin into a preformed metal–carbon bond is a common mechanism for transition‐metal‐catalyzed olefin polymerization. However, in one important industrial catalyst, the Phillips catalyst, a metal–carbon bond is not present in the precatalyst. The Phillips catalyst, CrO₃ dispersed on silica, polymerizes ethylene without an activator. Despite 60 years of intensive research, the active sites and the way the first Cr C bond is formed remain unknown. We synthesized well‐defined dinuclear Cr^II and Cr^III sites on silica. Whereas the Cr^II material was a poor polymerization catalyst, the Cr^III material was active. Poisoning studies showed that about 65 % of the Cr^III sites were active, a far higher proportion than typically observed for the Phillips catalyst. Examination of the spent catalyst and isotope labeling experiments showed the formation of a Si–(μ‐OH)–Cr^III species, consistent with an initiation mechanism involving the heterolytic activation of ethylene at Cr^III O bonds.