Electron-Transfer-Induced Side-Chain Cleavage in Tryptophan Facilitated through Potassium-Induced Transition-State Stabilization in the Gas Phase

• Published in: The Journal of Physical Chemistry A
• Main Authors: da Silva, Filipe Ferreira, Cunha, Tiago, Rebelo, Andre, Gil, Adrià, Calhorda, Maria José, García, Gustavo, Ingólfsson, Oddur, Limão-Vieira, Paulo
• Other Authors: Raunvísindadeild (HÍ), Faculty of Physical Sciences (UI), Verkfræði- og náttúruvísindasvið (HÍ), School of Engineering and Natural Sciences (UI), Háskóli Íslands, University of Iceland
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Chemical Society (ACS) 2021
• Subjects: Physical and Theoretical Chemistry; Efnafræði; Vetni; Sameindir; Peptíð; Kalín; Iceland
• Online Access: https://hdl.handle.net/20.500.11815/3307; https://doi.org/10.1021/acs.jpca.1c00690

Fragmentation of transient negative ions of tryptophan molecules formed through electron transfer in collisions with potassium atoms is presented for the first time in the laboratory collision energy range of 20 up to 100 eV. In the unimolecular decomposition process, the dominating side-chain fragmentation channel is assigned to the dehydrogenated indoline anion, in contrast to dissociative electron attachment of free low-energy electrons to tryptophan. The role of the collision complex formed by the potassium cation and tryptophan negative ion in the electron transfer process is significant for the mechanisms that operate at lower collision energies. At those collision times, on the order of a few tens of fs, the collision complex may not only influence the lifetime of the anion but also stabilize specific transition states and thus alter the fragmentation patterns considerably. DFT calculations, at the BHandHLYP/6-311++G(3df,2pd) level of theory, are used to explore potential reaction pathways and the evolvement of the charge distribution along those. F.F.d.S., T.C., and A.R. acknowledge the Portuguese National Funding Agency FCT-MCTES for IF-FCT IF/00380/2014, SFRH/BD/52538/2014, and PD/BD/114449/2016 and together with P.L.-V. the research grants PTDC/FIS-AQM/31215/2017 and PTDC/FIS-AQM/31281/2017. This work was also supported by Radiation Biology and Biophysics Doctoral Training Programme (RaBBiT, PD/00193/2012); UIDB/00068/2020 (CEFITEC) and UIDB/04378/2020 (UCIBIO). M.J.C. and A.G. also thank FCT-MCTES UIDB/04046/2020 and UIDP/04046/2020, and A.G. thanks the SFRH/BPD/89722/2012 grant. G.G. is partially funded by the Spanish Ministerio de Ciencia, Innovacion y Universidades (project no. PID2019-104727RB-C21) and CSIC (Project LINKA20085). O.I. acknowledges the Icelandic Center of Research (RANNIS) and the University of Iceland Research Fund for financial support. The authors thank Ragnar Bjornsson for fruitful discussions while preparing this manuscript. Pre-print