The monitoring of biological systems requires agents that are small enough and similar enough to the system under study that the system is not disturbed during observation. Barbara Imperiali and co-workers, Massachusetts Institute of Technology, USA, have used sulfonamide oxines to monitor phosphorylation in real time.

To achieve high intensities suitable for monitoring, e.g., protein folding, a molecule needs to display a large fluorescence increase on complexation. Generally, this is only achieved with a large molecule. Imperiali has identified a selection of small molecules, including aminophthalimide- and naphthalimide-based compounds, with sufficiently large fluorophores through targeted combinatorial chemistry. She has used these to study the activity of kinases in lung and breast cancer cells, which show 2–3 times higher activity than non-cancer cells.

• Plenary lecture “Fluorescent Tools for Chemical Biology” given at 3rd EuCheMS Congress, Nuremberg, August 2010.