Next Article in Journal
The Tyranny of Arm-Wrestling Methyls on Iron(II) Spin State in Pseudo-Octahedral [Fe(didentate)3] Complexes
Next Article in Special Issue
Before Radicals Were Free – the Radical Particulier of de Morveau
Previous Article in Journal / Special Issue
Amino Acids and Peptides as Versatile Ligands in the Synthesis of Antiproliferative Gold Complexes
Open AccessFeature PaperArticle

Topological Dynamics of a Radical Ion Pair: Experimental and Computational Assessment at the Relevant Nanosecond Timescale

by Helmut Quast 1,‡, Georg Gescheidt 2,* and Martin Spichty 3,*,§
1
Institute of Organic Chemistry, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
2
Institute of Physical and Theoretical Chemistry, Technical University of Graz, NAWI Graz, Stremayrgasse 9, 8010 Graz, Austria
3
Laboratoire de Biologie et Modélisation de la Cellule, Ecole Normale Supérieure de Lyon, CNRS, Université Lyon 1, Université de Lyon, 46 allée d’Italie, 69364 Lyon CEDEX 07, France
*
Authors to whom correspondence should be addressed.
Dedicated to Professor Bernd Giese on behalf of his 80th birthday.
Current address: Hoetgerstrasse 10, 49080 Osnabrück, Germany
§
Current address: Laboratoire d’Innovation Moléculaire et Applications, Site de Mulhouse – IRJBD, 3 bis rue Alfred Werner, 68057 Mulhouse Cedex, France
Chemistry 2020, 2(2), 219-230; https://doi.org/10.3390/chemistry2020014
Received: 28 February 2020 / Revised: 22 March 2020 / Accepted: 27 March 2020 / Published: 31 March 2020
Chemical processes mostly happen in fluid environments where reaction partners encounter via diffusion. The bimolecular encounters take place at a nanosecond time scale. The chemical environment (e.g., solvent molecules, (counter)ions) has a decisive influence on the reactivity as it determines the contact time between two molecules and affects the energetics. For understanding reactivity at an atomic level and at the appropriate dynamic time scale, it is crucial to combine matching experimental and theoretical data. Here, we have utilized all-atom molecular-dynamics simulations for accessing the key time scale (nanoseconds) using a QM/MM-Hamiltonian. Ion pairs consisting of a radical ion and its counterion are ideal systems to assess the theoretical predictions because they reflect dynamics at an appropriate time scale when studied by temperature-dependent EPR spectroscopy. We have investigated a diketone radical anion with its tetra-ethylammonium counterion. We have established a funnel-like transition path connecting two (equivalent) complexation sites. The agreement between the molecular-dynamics simulation and the experimental data presents a new paradigm for ion–ion interactions. This study exemplarily demonstrates the impact of the molecular environment on the topological states of reaction intermediates and how these states can be consistently elucidated through the combination of theory and experiment. We anticipate that our findings will contribute to the prediction of bimolecular transformations in the condensed phase with relevance to chemical synthesis, polymers, and biological activity. View Full-Text
Keywords: ion pairing; radical anion; kinetics; thermodynamics; molecular dynamics; QM/MM; EPR ion pairing; radical anion; kinetics; thermodynamics; molecular dynamics; QM/MM; EPR
Show Figures

Figure 1

MDPI and ACS Style

Quast, H.; Gescheidt, G.; Spichty, M. Topological Dynamics of a Radical Ion Pair: Experimental and Computational Assessment at the Relevant Nanosecond Timescale. Chemistry 2020, 2, 219-230.

Show more citation formats Show less citations formats

Article Access Map by Country/Region

1
Back to TopTop