It is also typically necessary to stain the bilayer with a heavy metal compound such as osmium tetroxide or uranyl acetate because the low atomic weight constituents of lipids ( carbon, nitrogen, phosphorus, etc . ) offer little contrast compared to water.
42.
Catalysts may affect the reaction environment favorably, or bind to the reagents to polarize bonds, e . g . acid catalysts for reactions of carbonyl compounds, or form specific intermediates that are not produced naturally, such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause chemisorbed hydrogen in catalytic hydrogenation.
