Abstract
N-(4-(7 - Diethylamino - methylcoumarin - 3 yl)phenyl)maleimide (CPM) and the corresponding iodoacetamide are described. When applied to sections at pH 6 and 9, respectively, the two fluorogens are very similar in their reactivity and selectivity toward thiols with which they form adducts having much the same bright blue fluorescence. However, difference in other properties favor CPM for further study.