Kinetic study of azobenzene E/Z isomerization using ion mobility-mass spectrometry

International audienceIntroductionAzobenzene molecular switches can interconvert both photochemically and thermally. Due to their important development, their fast identification has become a challenge. Usually identified using UV-VIS spectrophotometry, we propose different coupling to MS such as ion mobility spectrometry and liquid chromatography to study the thermal Z to E back relaxation kinetic of isomers.MethodsDifferent synthetized isomerically pure azobenzenes were analysed in MS/MS using different cation adducts. LC experiments were performed using a 1260 series Infinity system packed with a Kinetex XB C-18 column coupled to an ion trap mass analyser (AmaZon speed ETD). Ion mobility-mass spectrometry experiments were carried out on a hybrid instrument (Synapt G2-Si HDMS) equipped with an ESI source. ResultsAnalyses of isomers by tandem mass spectrometry were carried out on different azobenzene pairs and an azobenzene sample consisting of three isomers. Differentiation of isomers was achieved for isomer couples using MS/MS. An upstream separation dimension was necessary to characterise the sample with three isomers. For these compounds, IMS-MS and LC-(UV)-MS were evaluated in parallel to study the kinetic of thermal Z to E isomerisation. Baseline separation of two isomers was achieved in IMS-MS from [M+Ag]+, while the third isomer was differentiated from [2M+Ag]+. In addition, LC separation of the three isomers was achieved in less than 10 minutes. These methodologies can be applied to different systems in order to determine their thermal back relaxation kinetic. IMS-MS and MS/MS methods will be preferred for fast systems as they allowed differentiation in the millisecond scale.Novel AspectFor the first time, the thermal back relaxation kinetic of azobenzene isomers is studied using hyphenated techniques (IMS and LC) to MS and MS/MS