A new type of molecular probes for catching reactive radicals

Free radical intermediates play a key role in many chemical and biological processes, and their detection and quantification is critical for combustion, atmospheric and indoor chemistry, reaction mechanisms (including catalysis - such as heterogeneous catalysis and a recently developed area of photoredox catalysis), biological and medicinal chemistry (e.g., monitoring oxidative stress). However, free radicals are often very short lived, and cannot be observed directly, particularly in complex real systems. Free radicals are usually detected using spin trapping technique in conjunction with EPR spectroscopy, a method which has been successfully used since 1960s.

In recent years, mass spectrometry was proposed as a more sensitive and informative detection method for spin trapping. However, as mass spectrometry does not require unpaired electrons for detection (unlike EPR spectroscopy), the conventional spin traps are not well-suited for this purpose. This point has surprisingly been overlooked by the research community. We have recently designed a different type of traps for radical detection. Our new traps offer dramatic improvements in stability, sensitivity and selectivity of detection compared to the more conventional methods, providing previously unavailable speciated structural information about radical intermediates in the gas phase at concentrations well below the detection limit of current techniques.

In this project, we will expand our new method (which has so far been only used with gas phase radicals) to liquid phase reactions, where the most exciting applications include studying biochemical mechanisms (through oxidative stress monitoring or immuno spin trapping), exploring mechanisms of catalytic reactions and looking at reactions at air-water interface, relevant to atmospheric and plasma chemistry. We believe this will lead to a step change in our understanding of mechanisms of free radical processes and will open up opportunities to establish new collaborations and new areas of research. The challenges in this project include synthesis, design of appropriate analysis method, and stability of the new probes in real systems. However the overall risk of failure is low as the feasibility of the new method has already been established in our preliminary work.