Abstract
1. 1. To elucidate the reaction mechanisms responsible for the fixation of cellular materials by osmium tetroxide, as used in electron microscopy, the products resulting from the interaction of OsO 4 with various unsaturated substances were studied. By a spectrophotometric method, crotonic acid, oleic acid, linoleic acid and lecithin (phosphatidyl choline) were found to take up approx. 1 mole OsO 4 per double bond. In dilute solutions in water-containing media cyclic osmic acid mono-ester formation occurs. Cyclic osmic mono-esters were also found to be products of the reaction between cis-diols and potassium osmate. 2. 2. Cyclic osmic esters in watery media behave like acids, which means they probably have a hydroxylated structure. The corresponding anions readily combine by electrostatic interaction with quaternary ammonium groups in bipolar phosphatides. 3. 3. The reaction between OsO 4 and membrane phosphatides probably begins with the formation of cyclic mono-esters, the corresponding anions moving almost simultaneously into the two polar strata of the membrane bilayer. Although nonlipid substances and dehydrating solvents lead to further reduction, the ultimate location of osmium dioxide deposits may be determined by the reaction between OsG4 and membrane lipids occurring initially.
Published Version
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