Tag Archives: radiolysis

Quasi-Free Electron-Mediated Radiation Sensitizaion by C5-Halopyrimidines

by Jun Ma, Teseer Bahry, Sergey A. Denisov, Amitava Adhikary, Mehran Mostafavi

J. Phys. Chem. A 2021, 125, 36, 7967–7975; doi.org/10.1021/acs.jpca.1c05974

Substitution of the thymidine moiety in DNA by C5-substituted halogenated thymidine analogues causes significant augmentation of radiation damage in living cells. However, the molecular pathway involved in such radiosensitization process has not been clearly elucidated to date in solution at room temperature. So far, low-energy electrons (LEEs; 0–20 eV) under vacuum condition and solvated electrons (esol) in solution are shown to produce the σ-type C5-centered pyrimidine base radical through dissociative electron attachment involving carbon–halogen bond breakage. Formation of this σ-type radical and its subsequent reactions are proposed to cause cellular radiosensitization. Here, we report time-resolved measurements at room temperature, showing that a radiation-produced quasi-free electron (eqf) in solution promptly breaks the C5-halogen bond in halopyrimidines forming the σ-type C5 radical via an excited transient anion radical. These results demonstrate the importance of ultrafast reactions of eqf, which are extremely important in chemistry, physics, and biology, including tumor radiochemotherapy.

Reaction Mechanisms of Fluoroethylene Carbonate Degradation, an Additive of Lithium-Ion Batteries, Unraveled by Radiation Chemistry

by Marin Puget, Viacheslav Shcherbakov, Sergey A. Denisov, Philippe Moreau, Jean-Pierre Dognon, Mehran Mostafavi and Sophie LE CAER

Chemistry – A European Journal 2021; doi.org/10.1002/chem.202100562

Numerous additives are used in electrolytes of lithium‐ion batteries, especially for the formation of efficient solid electrolyte interphase at the surface of the electrodes. The understanding of the degradation processes of these compounds is thus important. They can be obtained through radiolysis. In the case of fluoroethylene carbonate (FEC), picosecond pulse radiolysis experiments evidenced the formation of FEC●‐ . This radical is stabilized in neat FEC, whereas the ring opens to form more stable radical anions when FEC is a solute in other solvents, as confirmed by quantum chemistry calculations. In neat FEC, pre‐solvated electrons primarily undergo attachment compared to solvation. At long timescales, produced gases (H2, CO, and CO2 ) were quantified. A reaction scheme for both the oxidizing and reducing pathways at stake in irradiated FEC was proposed. This work evidences that the nature of the primary species formed in FEC depends on the amount of FEC in the solution.

Real-Time Observation of Solvation Dynamics of Electron in Actinide Extraction Binary Solutions of Water and n-Tributyl Phosphate

by Teseer Bahry, Sergey A. Denisov, Philippe Moisy, Jun Ma, Mehran Mostafavi

J. Phys. Chem. B 2021, 125, 15, 3843–3849; doi.org/10.1021/acs.jpcb.0c10831

The excess electron in solution is a highly reactive radical involved in various radiation-induced reactions. Its solvation state critically determines the subsequent pathway and rate of transfer. For instance, water plays a dominating role in the electron-induced dealkylation of n-tributyl phosphate in actinide extraction processing. However, the underlying electron solvation processes in such systems are lacking. Herein, we directly observed the solvation dynamics of electrons in H-bonded water and n-tributyl phosphate (TBP) binary solutions with a mole fraction of water (Xw) varying from 0.05 to 0.51 under ambient conditions. Following the evolution of the absorption spectrum of trapped electrons (not fully solvated) with picosecond resolution, we show that electrons statistically distributed would undergo preferential solvation within water molecules extracted in TBP. We determine the time scale of excess electron full solvation from the deconvoluted transient absorption–kinetical data. The process of solvent reorganization accelerates by increasing the water molar fraction, and the rate of this process is 2 orders of magnitude slower compared to bulk water. We assigned the solvation process to hydrogen network reorientation induced by a negative charge of the excess electron that strongly depends on the local water environment. Our findings suggest that water significantly stabilizes the electron in a deeper potential than the pure TBP case. In its new state, the electron is likely to inhibit the dealkylation of extractants in actinide separation.

Presolvated electron reactivity towards CO2, N2O in the water

by Sergey A. Denisov  and  M. Mostafavi 

Phys. Chem. Chem. Phys., 2021, Accepted; doi.org/10.1039/D1CP00373A

The reactivity of presolvated electrons with CO2 and N2O was studied in the gas pressure range from 1 to 52 bar. To measure this reactivity, the home-made spectroscopic cell with liquid circulation was developed working up to 70bar of gas pressure. The efficiency of presolvated electron scavenging was determined from the decrease of solvated electrons yield after the 5ps electron pulse. In addition, the reaction rate between these molecules and solvated electrons was directly determined at gas pressures below the critical point, which is in agreement with those presented in the literature measured at gas pressures below <1atm.

How to conduct pulse radiolysis of a liquid-gas system under pressure

by DENISOV Sergey


In order to conduct pulse radiolysis experiments at high gas pressures, we designed the optical cell capable of withstanding pressures up to 70bar with a 1 mm entrance window. The need for high pressures of gases was determined by the need for a high concentration of gases in water solutions for conducting measurement on presolvated electron scavenging by dissolved gases. The system was supposed to be capable of guaranteeing solution circulation under the pressure of a gas.


The system consists of a closed water loop. The circulation of solutions, to guarantee refreshment of solution in measurement volume, was achieved using home made pump driven by electromagnets. The principle of action follows the sequence: 1) the current is applied to the electromagnets (1 and 2), working in the opposite direction: electromagnet 1 is pushing, while 2 is pulling the permanent magnets fixed on the piston; 2) once the piston is displaced, the current in electromagnets is reversed, and the piston goes down. The flow of solution during reverse movement of the piston is not affected since the lock-balls are released, letting the solution flow through the six holes in the piston.

The spectroscopic cell fracture test with Ar guaranteed the safe pressure to operate below 75 bar with 1 mm input window and 5 mm output one, respectively. The pressure was controlled by a gas pressure regulator (0-100 bar, Swagelok) directly attached to a gas cylinder.

Scheme of high-pressure gas system for gas-liquid binary systems radiolysis studies

Once the pressure of the gas was applied using (valve 3), the equilibration for 30 minutes were undertaken. To intensify a gas exchange, a bubble of gas was formed over the water to increase the surface area for an exchange. Each measurement with a different pressure was conducted with a freshwater volume (1.5 mL) pumped into the cell.

The filling of the closed water circuit was accomplished by a peristaltic pump (valve 1, 2); after that, the system was isolated and pressurized to a given pressure.


Drawing of pressure cell


All fittings purchased from Swagelok were made of stainless steel. The tubes of stainless steel (1/4 inch) were utilized for gas distribution and water circuits. Seals were made of rubber (xx).


The input/output windows were made of optical quartz of 1mm and 5mm, thickness, respectively.


Permanent magnets

4 Neodymium magnets (https://www.first4magnets.com/) were utilized, one pair was installed at one side of the piston and another pair on another.


In this project two electromagnets were used for magnetic pump operation. The magnets operated at 100V; thus, intense cooling was required even for operating non in continuous pumping mode. The development of liquid cooling seems to be necessary to make the system operate in a continuous regime. Another possibility to work in a continuous way more efficiently is to increase the force of permanent magnets, which is not easy to find on the market, and of course, to optimize the electromagnets’ magnetic field shape.

Power Supply Scheme

AC-DC conversion

AC-DC conversion was realized around the monophase diode bridge (35A 1000V) with a polypropylene condenser (XXX).


According to a classical scheme based on 4 relays, the H-bridge was realized as capable of commuting 10A in the pulse regime. The trick was to close relays of the H-bridge without applying the tension, so the arcs are not created on the electrical contacts. The 3 kW autotransformer was used as the primary source supplying AC-DC converter.

Firstly, to move the piston in the pump, 2 of 4 relays of the H-bridge were closed, and only after that two 220V relays before AC-DC converted were closed for 50ms for down movement and 950ms for up movement. When the direction of the piston was changed, the relays of AC-DC converter were opened. The plastic-filled condenser damped the inductance of the electromagnets. After 10 ms the different sets of relays of the H-bridge were closed, and the power was sent to AC-DC converter.


The control of the power supply scheme was made using Raspberry Pi 3 Model B by sending the commands utilizing GPIO to control power relays.

The simple python script is presented below.

import RPi.GPIO as GPIO            # import RPi.GPIO module  
from time import sleep             # lets us have a delay  

sleep_time = 1

GPIO.setmode(GPIO.BCM)             # choose BCM or BOARD
relayI_IV = 6
relayII_III = 13

major = 5

GPIO.setup(relayI_IV , GPIO.OUT)  
GPIO.setup(relayII_III, GPIO.OUT)
GPIO.setup(major, GPIO.OUT)  

On = 1
Off = 0

GPIO.output(relayI_IV, Off)
GPIO.output(relayII_III, Off)
GPIO.output(major, Off)

def switch_power_off():
    GPIO.output(major, Off)

def switch_power_on():
    GPIO.output(major, On)

def deactivate_all_relay():
    GPIO.output(relayI_IV, Off)
    GPIO.output(relayII_III, Off)

def dir(a):
    if a == 'a':
        GPIO.output(relayI_IV, On)
    elif a == 'b':
        GPIO.output(relayII_III, On)
        print('unknown direction')

com = []

    while 'stop' not in com:
        com = input('Type command (e.g., -help): ')
        com = " ".join(com.split())
        com = str.split(com)
        if 'dir' in com:
            except KeyError:
                print('nothing was passed to dir command')
        elif 'disconnect' in com:
        elif 'on_power' in com:
        elif 'off_power' in com:
        elif 'pump' in com:
                n = int(com[1])
                t = float(com[2])
            except (KeyError,ValueError, IndexError) :
                print('test command was not followed with number of runs. setting to 1')
                n = 1
                t = 30
            for i in range(n):
                if n!=1:

except KeyboardInterrupt:  # trap a CTRL+C keyboard interrupt
    print('Terminated by user')

print('all Done')

Confined Water Radiolysis in Aluminosilicate Nanotubes: The Importance of Charge Separation Effects

by Marie-Claire PIGNIE,   Viacheslav Shcherbakov,   Thibault Charpentier,   Mélanie Moskura,   Cedric Carteret,   Sergey A. Denisov,   M. Mostafavi,   Antoine Thill  and  Sophie LE CAER  

Nanoscale 2021, 13, 3092-3105; https://doi.org/10.1039/D0NR08948F

Imogolite nanotubes are potentially promising co-photocatalysts because they are predicted to have curvature-induced, efficient electron-hole pair separation. This prediction has however not yet been experimentally proven. Here, we investigated the behavior upon irradiation of these inorganic nanotubes as a function of their water content to understand the fate of the generated electrons and holes. Two types of aluminosilicate nanotubes were studied: one was hydrophilic on its external and internal surfaces (IMO-OH) and the other had a hydrophobic internal cavity due to Si-CH3 bonds (IMO-CH3), with the external surface remaining hydrophilic. Picosecond pulse radiolysis experiments demonstrated that the electrons are efficiently driven outward. For imogolite samples with very few external water molecules (around 1% of the total mass), quasi-free electrons were formed. They were able to attach to a water molecule, generating a water radical anion, which ultimately led to dihydrogen. When more external water molecules were present, solvated electrons, precursors of dihydrogen, were formed. In contrast, holes moved towards the internal surface of the tubes. They mainly led to the formation of dihydrogen and of methane in irradiated IMO-CH3. The attachment of the quasi-free electron to water was a very efficient process and accounted for the high dihydrogen production at low relative humidity values. When the water content increased, electron solvation dominated over attachment to water molecules. Electron solvation led to dihydrogen production, albeit to a lesser extent than quasi-free electrons. Our experiments demonstrated the spontaneous curvature-induced charge separation in these inorganic nanotubes, making them very interesting potential co-photocatalysts.

Oxidation of Silver Cyanide Ag(CN)2 by the OH Radical: From Ab Initio Calculation to Molecular Simulation and to Experiment

by Céline Léonard, Frédéric Le Quéré, Daniel Adjei, Sergey A. Denisov, Mehran Mostafavi and Pierre Archirel

J. Phys. Chem. A 2020, 124, 51, 10787–10798; doi.org/10.1021/acs.jpca.0c08038

We investigate the oxidation of silver cyanide  in water by the OH radical in order to compare this complex with the free cation Ag+ and to measure the influence of the ligands. High-level ab initio calculations of the model species  enable the calibration of molecular simulations and the prediction of the oxidized species:  and its absorption spectrum, with an intense band at 292 nm and a weaker one at 390 nm. Pulse radiolysis measurements of the oxidation of  by the OH radical in water yields a transient species with a broad, intense band at 290 nm and a weaker band at 410 nm at short times after the pulse and a blue shift of the spectrum at longer times. The prediction of the simulations, that the oxidized complex  is formed, is confirmed by thermochemistry. Our calculations also suggest that the formation of the OH-adduct is possible only in very basic solution and that the blue shift observed at long times after the pulse is due to disproportionation of the oxidized complex. We also perform molecular simulations of the oxidation of free Ag+ cations by the OH radical. The results are compared to that of the literature and to the results obtained with the  complex.

On the Primary Water Radicals’ Production in the Presence of Gold Nanoparticles: Electron Pulse Radiolysis Study

by Viacheslav Shcherbakov, Sergey A. Denisov  and Mehran Mostafavi 

Nanomaterials 2020, 10, 2478; https://doi.org/10.3390/nano10122478

Gold nanoparticles are known to cause a radiosensitizing effect, which is a promising way to improve radiation therapy. However, the radiosensitization mechanism is not yet fully understood. It is currently assumed that gold nanoparticles can influence various physical, chemical, and biological processes. Pulse radiolysis is a powerful tool that can examine one of the proposed effects of gold nanoparticles, such as increased free radical production. In this work, we shed light on the consequence of ionizing radiation interaction with gold nanoparticles by direct measurements of solvated electrons using the pulse radiolysis technique. We found that at a therapeutically relevant gold concentration (<3 mM atomic gold, <600 μg × cm−3), the presence of gold nanoparticles in solution does not induce higher primary radicals’ formation. This result contradicts some hypotheses about free radical formation in the presence of gold nanoparticles under ionizing radiation previously reported in the literature.

Mechanisms of metal nanoparticles nucleation and growth studied by radiolysis

by J.Belloni, J.-L.Marignier, M.Mostafavi

Radiation Physics and Chemistry 2020, 169, 107952; doi.org/10.1016/j.radphyschem.2018.08.001

The ultradivided matter is used for long in various applications, for example in colloids, inks and paints, cosmetics, stained glasses, catalysts, photographic emulsions, … But the progressive need of nanoparticles for various miniaturized devices and the different approaches for the synthesis have suddenly increased.

All of the bottom-up synthesis methods from a diluted precursor to metal nanoparticles imply several steps: a reduction reaction of ionic precursors by electron transfer, inducing the nucleation of atoms then the growth of the seeds into particles, more or less inhibited by stabilizers. The final size, shape, structure and dispersity of the particles strongly depend on the thermodynamics and the kinetics of these steps. The interaction of high energy radiation with the solvent provides, quantitatively and homogeneously distributed in the bulk, strong electron donors (solvated electrons, reducing radicals) which reduce metal ions as precursors into atoms. The radiation chemistry, on one hand in the steady state regime with an accurate knowledge of the yields of all the radiolytic products, and on the other hand in the pulse regime giving access to time-resolved data, constitutes a unique tool to elucidate the detailed mechanisms and to provide the keys of really controlling these processes in view of various applications.

Pulse radiolysis study on the reactivity of NO3˙ radical toward uranous(iv), hydrazinium nitrate and hydroxyl ammonium nitrate at room temperature and at 45 °C

by R. Musat, J. L. Marignier, C. Le Naour,  S. Denisov,  L. Venault, Ph. Moisy  and  M. Mostafavi

Phys. Chem. Chem. Phys., 2020, 22, 5188-5197; https://doi.org/10.1039/C9CP07034F

Concentrated nitric acid solutions subjected to radiation produce radicals of extreme importance in the reprocessing of spent nuclear fuel. Knowledge of the different rate constants of the reactions involved in this chemistry is needed to improve the efficiency of the process and to define safe operating practices. Pulse radiolysis measurements are performed to find the rate constant of the reaction between NO3˙ radicals and U(IV) in highly concentrated nitrate solution. The optimal stabilization conditions toward thermal oxidation are defined for the considered solutions at room temperature and at 45 °C by adding anti-nitrous agents such as hydrazinium nitrate (HN) and hydroxyl ammonium nitrate (HAN). The decay of the NO3˙ radical is monitored and its reaction rates with HN, HAN and U(IV) are found to be 1.3 × 105, 1.5 × 107 and 1.6 × 106 M−1 s−1 at room temperature. The latter value is more than 10 times lower than the one currently used in numerical codes for simulation of the long-term radiolytic degradation associated with the reprocessing and storage of spent nuclear waste. At 45 °C, conditions similar to the reprocessing of spent fuel, the values of the rate constants of NO3˙ radical toward HN, HAN and U(IV) increase and are found to be 2.6 × 105, 2.9 × 107 and 9.3 × 106 M−1 s−1.