Abstract: Reagents for cleaving or crosslinking of biomolecules using nondiffusible reactive intermediates and a method of using the reagents. In one embodiment, the DNA binding element includes a phenyl group on each end, and each terminal phenyl group contains at least one reactive group X: ##STR1## The reactive groups X may function to either cleave or crosslink the DNA to which the reagent is bound. Reactive groups that cleave the DNA include radical species formed by the decomposition of diazonium ions or the hydrolysis of azocarboxylates and cationic species formed, for example, by the photolysis of diazonium ions. Crosslinking moieties include nitrenes generated from the photolysis of azides.