The photoactivatable aryl ketone derivatives have been rediscovered as biochemical probes in the last 5 years. The expanding use of benzophenone (BP) photoprobes can be attributed to three distinct chemical and biochemical advantages. First, BPs are chemically more stable than diazo esters, aryl azides, and diazirines. Second, BPs can be manipulated in ambient light and can be activated at 350-360 nm, avoiding protein-damaging wavelengths. Third, BPs react preferentially with unreactive C-H bonds, even in the presence of solvent water and bulk nucleophiles. These three properties combine to produce highly efficient covalent modifications of macromolecules, frequently with remarkable site specificity. This Perspectives includes a brief review of BP photochemistry and a selection of specific applications of these photoprobes, which address questions in protein, nucleic acid, and lipid biochemistry.

No abstract

The widespread applications of benzophenone (BP) photochemistry in biological chemistry, bioorganic chemistry, and material science have been prominent in both academic and industrial research. BP photophores have unique photochemical properties: upon n-π* excitation at 365 nm, a biradicaloid triplet state is formed reversibly, which can abstract a hydrogen atom from accessible C-H bonds; the radicals subsequently recombine, creating a stable covalent C-C bond. This light-directed covalent attachment process is exploited in many different ways: (i) binding/contact site mapping of ligand (or protein)-protein interactions; (ii) identification of molecular targets and interactome mapping; (iii) proteome profiling; (iv) bioconjugation and site-directed modification of biopolymers; (v) surface grafting and immobilization. BP photochemistry also has many practical advantages, including low reactivity toward water, stability in ambient light, and the convenient excitation at 365 nm. In addition, several BP-containing building blocks and reagents are commercially available. In this review, we explore the "forbidden" (transitions) and excitation-activated world of photoinduced covalent attachment of BP photophores by touring a colorful palette of recent examples. In this exploration, we will see the pros and cons of using BP photophores, and we hope that both novice and expert photolabelers will enjoy and be inspired by the breadth and depth of possibilities.

No abstract