Broadening The View of Aryl Diazonium Ion Reactivity with Proteins and DNA

Aryl diazonium ions (ADIs) are well established for their reaction with both proteins and DNA, and yet these reactions have been studied independently without systematic comparison. When electrophilic bioconjugation probes are introduced to environments containing multiple macromolecules, questions of selectivity and competitive reactivity become critical. Here, we establish a systematic method to evaluate the selectivity of a series of ADIs toward proteins, specifically tyrosine and histidine residues, across varying pH and solvent conditions, while also looking at the ADI reaction with DNA. Electron-deficient ADIs preferentially modified tyrosine over histidine, but all tested ADIs reacted with and degraded DNA. We also observed strong pH- and hydrophobicity-dependent effects on amino acid selectivity. These findings provide a framework for understanding and controlling ADI reactivity in complex biological environments, informing the design of selective bioconjugation strategies.