Radiation Stability of Cations in Ionic Liquids. 5. Task-Specific Ionic Liquids Consisting of Biocompatible Cations and the Puzzle of Radiation Hypersensitivity

Abstract

In 1953, an accidental discovery by Melvin Calvin and co-workers provided the first example of a solid (the α-polymorph of choline chloride) showing hypersensitivity to ionizing radiation: under certain conditions, the radiolytic yield of decomposition approached 5 × 10(4) per 100 eV (which is 4 orders of magnitude greater than usual values), suggesting an uncommonly efficient radiation-induced chain reaction. Twenty years later, the still-accepted mechanism for this rare condition was suggested by Martyn Symons, but no validation for this mechanism has been supplied. Meanwhile, ionic liquids and deep eutectic mixtures that are based on choline, betainium, and other derivitized natural amino compounds are presently finding an increasing number of applications as diluents in nuclear separations, where the constituent ions are exposed to ionizing radiation that is emitted by decaying radionuclides. Thus, the systems that are compositionally similar to radiation hypersensitive solids are being considered for use in high radiation fields, where this property is particularly undesirable! In Part 5 of this series on organic cations, we revisit the phenomenon of radiation hypersensitivity and explore mechanistic aspects of radiation-induced reactions involving this class of task-specific, biocompatible, functionalized cations, both in ionic liquids and in reference crystalline compounds. We demonstrate that Symons' mechanism needs certain revisions and rethinking, and suggest its modification. Our reconsideration suggests that there cannot be conditions leading to hypersensitivity in ionic liquids.

Development of nanosecond time-resolved infrared detection at the LEAF pulse radiolysis facility

“…Conversely, the acetaldehyde C==O stretch at 1733 cm −1 (ε = 189 M −1 cm −1 ) can be easily resolved from the IL background absorption. 21 Based on the observed kinetics, our results suggested that most of the radiolytically induced C 1 -N fragmentation in choline NTf 2 occurs promptly (within 40 ns), and that there is a further ∼40% increase in the yield of vinyl alcohol over the following 400 µs. These results, combined with other data using different techniques, led to a revision of the previously accepted Symons mechanism of radiation hypersensitivity in choline chloride and a demonstration that the conditions that lead to hypersensitivity do not exist in ILs.…”

“…One example of this is our recent investigation of the mechanism of radiolytic decomposition of a choline-based ionic liquid (IL) in collaboration with Dr. Ilya Shkrob of Argonne National Laboratory. 21 There is great interest in ILs and deep eutectic mixtures that are based on choline ((2-hydroxymethyl)trimethylammonium), betainium (1-carboxy-N,N,N-trimethylmethanaminium), and other derivatized natural amino compounds as diluents in metal ion separations, 33 including nuclear separations where the constituent ions would be exposed to ionizing radiation that is emitted by decaying radionuclides. 34 Thus, it is critical to investigate the radiation stability of such ILs, particularly since they are compositionally similar to radiation hypersensitive solids such as choline chloride, which decomposes significantly upon irradiation.…”

“…Upon pulse radiolysis of argon-saturated choline NTf 2 at 50 • C (NTf 2 = bis(trifluoromethylsulfonyl)imide), we successfully monitored the prompt formation of vinyl alcohol and acetaldehyde via their C==C and C==O vibrational bands at 1649 and 1733 cm −1 , respectively. 21 These products cannot be detected by transient UV-Vis pulse radiolysis since their signals in the UV are weak (e.g., acetaldehyde, 35 ε 290nm = 13 M −1 cm −1 ) and obscured by the background absorption of the IL. Conversely, the acetaldehyde C==O stretch at 1733 cm −1 (ε = 189 M −1 cm −1 ) can be easily resolved from the IL background absorption.…”

“…19 Making use of high-power external-cavity quantum cascade lasers (EC-QCLs) as tunable IR sources, we previously demonstrated, for the first time, the feasibility of combining pulse radiolysis of condensed-phase samples with nanosecond TRIR spectroscopy, 13 and have since begun to apply this powerful technique to the identification of transient intermediates in a diverse range of radiation-induced chemical processes. [20][21][22] Since our initial feasibility study, 13 significant changes and improvements have been made to the technique, and this paper describes in detail our development of dedicated nanosecond TRIR instrumentation for the study of condensedphase samples that are subjected to pulse radiolysis on a new electron beam line at the BNL Laser-Electron Accelerator Facility (LEAF). 23 Construction and use of a dedicated TRIR experimental station enabled enormous progress in addressing technical challenges and improving the performance and sensitivity of the detection system.…”

Direct Observation of Solvated Electrons in Deep Eutectic Solvents: Efficient Capture of Presolvated Electrons by DNA Base

“…The hole-eliminated transient absorption spectrum of the solvated electron is thus solely represented by curve c of Figure A. The solvated electron in the IL, bearing a choline cation (NTf 2 anion) at 45 °C, shows a peak in the wavelength range of 630–650 nm in its absorption spectrum, close to that in alcohols and ILs containing alcohol-substituted ammonium cations . The solvated electron absorption peak in reline is thus red-shifted to 760 nm as compared to that in choline-NTf 2 .…”