Selenium-75 labeled tertiary diamines, bis [& (N, N-dimethy1amino) ethyll selenide (l), bis [p- (N, N-diisopropylamino) ethyl] selenide (2), bis (8-piperidinoethyl) selenide (3), and bis@ morpholinoethyl) selenide (4), were prepared by reducing [76Se] selenious acid with sodium borohydride and reacting the intermediate with the N, N-disubstituted aminoethyl chlorides. The effect of pH on lipid solubility (l-octanol/buffer distribution coefficient) was ...