The influence of H/D kinetic isotope effect on radiation-induced transformations of hydroxyl-containing compounds in aqueous solutions

Article abstract of DOI:10.1080/10715762.2020.1838502

Vicinal diols and its derivatives can be exploited as model compounds for the investigation of radiation-induced free-radical transformations of hydroxyl-containing biomolecules such as carbohydrates, phospholipids, ribonucleotides, amino acids, and peptides. In this paper, for the first time, the prospects of isotope reinforcement approach in inhibiting free-radical transformations of hydroxyl-containing compounds in aqueous solutions are investigated on the example of radiolysis of 1,2-propanediol and 1,2-propanediol-2-d₁ aqueous solutions. At an absorbed dose rate of 0.110 ± 0.003 Gy·s^?1 a profound kinetic isotope effect (KIE) is observed for the non-branched chain formation of acetone, which is a final dehydration product of predominant carbon-centred radicals CH₃·C(OH)CH₂OH. In 0.1 and 1 M deaerated solutions at pH 7.00 ± 0.01, the values of KIE are 8.9 ± 1.7 and 15.3 ± 3.1, respectively. A rationale for the fact that a strong KIE takes place only in the case of chain processes, which may occur during free-radical transformations of vicinal diols, is also provided herein based on the results of 2-propanol and 2-propanol-2-d₁ indirect radiolysis. Lastly, the lack of KIE is shown in the case of 2-butanone formation from 2,3-butanediol or 2,3-butanediol-2,3-d₂. This indicates that the type (primary, secondary) of the β-carbonyl radicals formed as a result of CH₃·C(OH)CH(OH)R (R = H, CH₃) dehydration determines the manifestation of the effect.

Full text of DOI:10.1080/10715762.2020.1838502

Free Radical Research
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/ifra20
The influence of H/D kinetic isotope effect on
radiation-induced transformations of hydroxyl-
containing compounds in aqueous solutions
Palina S. Nepachalovich , Oleg I. Shadyro , Andrei V. Bekish & Vadim V.
Shmanai
To cite this article: Palina S. Nepachalovich , Oleg I. Shadyro , Andrei V. Bekish & Vadim V.
Shmanai (2020): The influence of H/D kinetic isotope effect on radiation-induced transformations
of hydroxyl-containing compounds in aqueous solutions, Free Radical Research, DOI:
10.1080/10715762.2020.1838502
To link to this article: https://doi.org/10.1080/10715762.2020.1838502
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The influence of H/D kinetic isotope effect on radiation-induced
transformations of hydroxyl-containing compounds in aqueous solutions
Journal: Free Radical Research
a
a,b,*
c
Palina S. Nepachalovich , Oleg I. Shadyro , Andrei V. Bekish ,
c
Vadim V. Shmanai
a
Research Institute for Physical Chemical Problems, Belarusian State University, Leningradskaya st., 14,
b
2
2
20050, Minsk, Belarus; Department of Chemistry, Belarusian State University, Leningradskaya st., 14,
c
20050, Minsk, Belarus; Institute of Physical Organic Chemistry, National Academy of Science,
Surganova st., 13, 220072, Minsk, Belarus
*
Correspondence should be addressed to: Oleg I. Shadyro
Research Institute for Physical Chemical Problems, Belarusian State University, Leningradskaya st., 14,
20050, Minsk, Belarus
2
Tel: +375-17-2095464
Fax: +375-17-2095464
E-mail: shadyro@tut.by
Co-Authors’ e-mail addresses:
Palina S. Nepachalovich: pol.nepochelovich@gmail.com
Andrei V. Bekish: andreibekish@yahoo.com
Vadim V. Shmanai: shmanai@ifoch.bas-net.by

Abstract
Vicinal diols and its derivatives can be exploited as model compounds for the investigation of
radiation-induced free-radical transformations of hydroxyl-containing biomolecules such as
carbohydrates, phospholipids, ribonucleotides, amino acids and peptides. In this paper, for the
first time, the prospects of isotope reinforcement approach in inhibiting free-radical
transformations of hydroxyl-containing compounds in aqueous solutions are investigated on the
example of radiolysis of 1,2-propanediol and 1,2-propanediol-2-d aqueous solutions. At an
1
-1
absorbed dose rate of 0.110±0.003 Gy·s a profound kinetic isotope effect (KIE) is observed for
the non-branched chain formation of acetone, which is a final dehydration product of
predominant carbon-centered radicals CH ·C(OH)CH OH. In 0.1 and 1 M deaerated solutions at
3
2
pH 7.00±0.01, the values of KIE are 8.9±1.7 and 15.3±3.1, respectively. A rationale for the fact
that a strong KIE takes place only in the case of chain processes, which may occur during free-
radical transformations of vicinal diols, is also provided herein based on the results of 2-propanol
and 2-propanol-2-d indirect radiolysis. Lastly, the lack of KIE is shown in the case of 2-
1
butanone formation from 2,3-butanediol or 2,3-butanediol-2,3-d . This indicates that the type
2
(
primary, secondary) of the -carbonyl radical formed as a result of CH ·C(OH)CH(OH)R (R =
3
H, CH ) dehydration determines the manifestation of the effect.
3
Keywords: 1,2-propanediol, 2,3-butanediol, 2-propanol, steady-state radiolysis, deuterium,
kinetic isotope effect.

Introduction
Classical radiobiology interprets the direct ionization of a cell nucleus and particularly nuclear
DNA as the main process of the cell damage arising from exposure to ionizing radiation (IR) [1].
However, with the development of the field and the accumulation of experimental data, it was
shown that indirect damage by cellular water radiolysis products can make a much greater
contribution to the modification of biomolecules [2–4]. This is especially true for biological
membranes [5], which can be considered the second most important localization of IR-induced
cell defects. The major components of a mammalian cell membrane are lipids (phospho-, glyco-,
sphingo-, cholesterol), and it also contains carbohydrates and proteins in integrated or linked
forms [6]. In the presence of oxygen, with which the lipid bilayer is enriched in comparison to
the surrounding aquatic medium [7,8], chain lipid peroxidation (LPO) occurs, affecting
polyunsaturated fatty acid (PUFA) moieties. Though there are a plethora of other free-radical
degradation and modification processes affecting biomolecules [9], LPO is arguably the most
studied one [10].
However, in different tissues, the oxygen level varies in a wide range [11]. At low (hypoxic)
oxygen levels, the role of LPO reduces significantly, which provokes other pathways of free-
radical damage to biomolecules. Our research group develops the idea that in addition to well-
characterized LPO, free-radical fragmentation processes also occur with varying probability in
biological systems exposed to IR. This fragmentation is characteristic of compounds containing a
free hydroxyl group adjacent to a hydroxyl/ester/amino/amide group [12]:
(1)
It is reliably established that physiologically active carbonyl and HX products of the process (1)
are formed in various systems of glycerophospholipids and lysophospholipids [13–20],
sphingolipids [13,18,20], carbohydrates [21,22] and glycolipids [23,24], amino acids and their
derivatives [25–27]. The accumulation of fragmentation products is particularly noticeable in
hypoxic irradiation conditions since O is known to inhibit the elimination of HX in the process
2
(1). Substances, such as quinones and phenolic compounds, capable of forming quinoid
structures [28–32], B group vitamins [33], and nitroazoles [31,32], also suppress the process (1)
due to oxidation of intermediate α-hydroxyalkyl radicals or by scavenging the initiators (mainly

·OH). Nevertheless, the development of new ways to regulate the probability of the process (1)
remains pertinent.
Relatively recently, a fundamentally different approach to suppression of free-radical reactions
has emerged, the concept of which consists of increasing the resistance of substrates themselves,
1
based on KIE . It was shown [34–37] that PUFAs reinforced site-specifically with deuterium in
the bis-allylic methylene groups (namely in there) are profoundly protected from LPO due to the
KIE arising from the rate-limiting propagation step.
It was uncovered that a linoleic acid sample enriched with linoleic acid-11,11-d by a fifth is
2
profoundly resistant to the chain oxidation as a whole. The observed “20% effect” means that the
therapeutic effect of the isotope reinforcement can be reached practically in vivo by proper
dietary supplementation [34]. Studies in yeast and mammalian myoblast models, as well as
atherosclerosis and Alzheimer’s disease models in mice, have shown that feeding living
cells/oral supplementation with deuterated PUFAs (D-PUFAs) is safe and reduces pro-oxidant
and iron-induced injury [34,36,37]. Moreover, the use of ethyl linoleate-11,11-d (known as
2
RT001) in clinical trials was approved by the United States Food and Drug Administration
agency (FDA), and some results have been obtained. Thus, the beneficial effect of RT001 has
been recognized in patients with neurodegenerative conditions known to involve LPO, such as
Friedreich Ataxia and Infantile Neuroaxonal Dystrophy [38,39].
The aforementioned LPO studies have shown that the isotope reinforcement approach is the
promising modality for the protection of biomolecules from free-radical degradation. Thus, the
objective of the present work is to find out how the H/D substitution in the α-C position to the
OH group affects the fragmentation of hydroxyl-containing compounds (Scheme (1)) induced by
γ-rays. Here we mainly focus on the protiated (ordinary) and deuterated forms of 1,2-propanediol
and 2,3-butanediol, which are prone to dehydration, and 2-propanol, which, in contrast,
possesses simpler radiation chemistry. This research provides a quantitative comparison of the
processes taking place during the steady-state indirect radiolysis of these compounds in
deaerated aqueous solutions.
1
KIE describes rate change due to isotopic substitution at a site of bond breaking/formation (primary KIE) or
another site (secondary KIE) in the rate-determining step (RDS) of a mechanism. The KIE value is defined as the
ratio of rate constants belonging to the reaction with the unsubstituted and substituted reactant. The RDS is usually
slowed down in the case of H/D substitution.

Materials and methods
Chemicals
The substrates were 1,2-propanediol (≥ 99.5%, racemic mixture, Aldrich), 2-propanol (≥99.8%,
Sigma-Aldrich) and 2,3-butanediol (≥98.0%, mixture of D-, L- and meso- isomers, Aldrich
Chemistry) as well as their deuterated analogues. Monopotassium phosphate (≥ 99.0%, Sigma
Life Sciences) and disodium phosphate (≥ 99.0%, Sigma-Aldrich) were used to prepare buffer
solutions. Formaldehyde (37 wt. % solution in water containing 10-15% methanol as a stabilizer,
Sigma-Aldrich), acetaldehyde (≥99.5%, Sigma-Aldrich), propanal (≥ 98.0%, Supelco
Analytical), acetone (≥99.9%, AppliChem), hydroxyacetone (≥95%, Fluka Chemika), 2-
butanone (≥99.0%, Sigma-Aldrich), were utilized as analytical standards in chromatographic
assays. Methanol (MeOH) (AppliChem) and 2,4-dinitrophenylhydrazine (DNPH) (Sigma-
Aldrich) were HPLC and reagent grade (97%), correspondingly, sulfuric acid – 96 wt. %
solution in water (Acros Organics). Water was purified and deionized using a Siemens Ultra
Clear TWF Water Purification System (France). Other chemicals used in this study were of the
highest quality available.
Synthesis of deuterated substrates
Reagents from commercial suppliers were used without further purification. Diethyl ether (Et O)
2
1
13
and tetrahydrofuran (THF) were dried over LiAlH . H (500 MHz) and C (126 MHz) NMR
4
spectra were recorded with a Bruker DRX-500 spectrometer (Bruker, USA). Chemical shifts
1
were referenced to the residual solvent signals of CDCl (7.26 ppm for H and 77.16 ppm for
3
1
3
C). Column chromatography was performed using 60 Å silica gel (40–63 µm). Analytical thin-
layer chromatography was performed on Kieselgel 60 F254 precoated aluminium TLC plates
Merck).
(
2
-Propanol-2-d1
This compound was synthesized according to the published procedure [40]. NaBD (2.0 g, 47.6
4
mol) was dissolved in NaOH aqueous solution (60 ml, 0.1 M). Acetone (14.0 ml, 18.9 mmol)
о
was added dropwise to the solution of NaBD , keeping the solution temperature below 20 С. The
4
reaction mixture was additionally stirred at room temperature for 2 h, then sulfuric acid (5 M)
was added until the pH of the solution reached a value of 1-2. A crude product was distilled off
о
о
at 80-83 С. The product was redistilled at 80-81 С with the addition of a small amount of
anhydrous calcium chloride. Thus, 2-propanol-2-d (5.8 g, 50%) was obtained as a colorless
1
liquid. Chemical purity (determined by the GC-MS method described in section 2.7): 95 wt. %

1
of 2-propanol-2-d , 0.06 wt. % of acetone. H NMR (CDCl , 500 MHz): δ 1.14 (s, 6H), 2.47 (br
1
3
s, 1H) (Fig. S1 in Supplemental materials).
1
,2-Propanediol-2-d1
A solution of hydroxyacetone (0.74 g, 10 mmol) in THF (5 ml) was added dropwise for 10 min
to a suspension of LiAlD (0.54 g, 12.9 mmol) in THF (15 ml) cooled to –20 °C. The reaction
4
mixture was slowly (30 min) warmed to room temperature, after which it was further stirred for
1
2 h. The reaction mixture was treated while cooling in an ice bath by sequential careful addition
of water (0.6 ml), 15% NaOH solution (0.6 ml), and again water (1.7 ml), followed by stirring at
room temperature for 2 h. The reaction mixture was filtered, the precipitate was additionally
washed with THF (4 × 10 ml), after which the solvent was removed under reduced pressure to
obtain 0.56 g of the relatively pure product. Additional purification was carried out by column
chromatography on silica gel (eluent CH Cl /ethyl acetate (EtOAc)/hexane from 1:1:0.5 to 1:1:0,
2
2
and then pure EtOAc), which led to 0.40 g (52%) of the colorless oily product. Chemical purity
(determined by the LC-UV method described in section 2.5): 97 wt. % of 1,2-propanediol-2-d1,
1
≤
2 mol.% of hydroxyacetone. H NMR (CDCl , 500 MHz): δ 1.06 (s, 3H), 3.30 (d, 1H, J = 11.5
3
1
3
Hz), 3.50 (d, 1H, J = 11.5 Hz), 4.28 (br s, 2H) (Fig. S2 in Supplemental materials). C NMR
CDCl , 126 MHz): δ 18.6 (s), 67.8 (m), 77.1 (t, J = 22 Hz) (Fig. S3 in Supplemental materials).
(
3
2
,3-Butanediol-2,3-d (mixture of diastereomers)
2
A solution of 2,3-butanedione (0.86 g, 10 mmol) in THF (5 ml) was added dropwise for 10 min
to a suspension of LiAlD (0.54 g, 12.9 mmol) in THF (15 ml) cooled to –20 °C. The reaction
4
mixture was slowly (30 min) warmed to room temperature, after which it was further stirred for
1
2 h. The reaction mixture was treated while cooling in an ice bath by sequential careful addition
of water (0.6 ml), 15% NaOH solution (0.6 ml), and again water (1.7 ml), followed by stirring at
room temperature for 2 h. The reaction mixture was filtered, the precipitate was additionally
washed with THF (4 × 10 ml), after which the solvent was removed under reduced pressure to
obtain 0.68 g of the relatively pure product. Additional purification was carried out by column
chromatography on silica gel (eluent CH Cl /EtOAc/hexane from 1:1:0.5 to 1:1:0, and then pure
2
2
EtOAc), which led to 0.52 g (57%) of the product (colorless oil) as a mixture of diastereomers in
1
a 6.5:1 ratio. H NMR (CDCl , 500 MHz) of major diastereomer: δ 1.05 (s, 6H), 3.66 (br s, 2H)
3
13
(
Fig. S4 in Supplemental materials). C NMR (CDCl , 126 MHz) of major diastereomer: δ 16.7,
3
7
0.4 (t, J = 21.6 Hz) (Fig. S5 in Supplemental materials).

Sample preparation
All solutions (including standard ones for chromatographic analysis) were prepared
gravimetrically and necessary concentrations were obtained by serial dilution in 50 mM
phosphate buffer (pH 7.00±0.01). The buffer was prepared by mixing 50 mM solutions of
KH PO and Na HPO in deionized water under pH control using a Hanna HI 9321 pH-meter.
2
4
2
4
Before each use, the instrument was calibrated using standard Hamilton Duracal buffers
Hamilton Bonaduz AG, Switzerland), which have pH values of 4.01±0.01 and 10.01±0.01. The
(
derivatization reagent for HPLC analysis was prepared by dissolving 0.03 g DNPH in 6.2 mL 36
wt. % HCl solution followed by dilution up to 100 mL by MeOH.
Irradiation
Irradiation experiments were carried out once (1 M 1,2-propanediol-2-d ), twice (1 M 1,2-
1
propanediol, 0.01 and 0.1 M 1,2-propanediol-2-d ), three (0.01 and 0.1 M 1,2-propanediol, 0.1 M
1
2
-propanol, 0.1 M 2-propanol-2-d ) or four (0.1 M 2,3-butanediol and 0.1 M 2,3-butanediol-2,3-
1
6
0
d ) times (irradiation on different days) with a Co γ-radiation source MPX-γ25M (Belarus) at
2
-1
the adsorbed dose rate of 0.110±0.003 Gy·s , which had previously been established by the
3
+
-1
standard ferrous sulfate (Fricke) dosimetry (G(Fe ) = 1.62 μmol·J ). Doses ranging from 0
control) to 660 Gy were applied in increments of 132 Gy. The samples were irradiated under
(
normal conditions for temperature and pressure (25°C and 1 atm). The radiolysis was performed
in glass vessels (the sample volume was of 1.0 ml) sealed after being subjected to argon
(≥99.993% purity) purge for 60 min to remove dissolved oxygen.
Analysis of irradiated 1,2-propanediol and 1,2-propanediol-2-d solutions
1
Detection and quantification of carbonyl products were performed after the pre-column
derivatization with DNPH (R , R = H, Alk):
1
2
(2)
For this purpose, the derivatization reagent, preparation of which is described in the Sample
preparation (section 2.3), was used.
The analysis was performed using a Shimadzu VP series LC system (Shimadzu, Japan), which
includes the following integrated units: an LC-10AD VP pumping unit, an SCL-10A VP system
controller, a CTO-10A column oven equipped with a manual injector, an SPD-10A VP UV–Vis

detector and a DGU-14A degasser. Chromatographic separation was carried out in a
LiChrospher 100 RP-18e column (25 cm × 4.6 mm ID; 5 μm particle size, 100 Å pore size) in
о
the isocratic mode of elution at 40 С. The mobile phase consisted of MeOH and water (60:40,
-1
v/v) and the flow rate was equal to 1.0 mL·min . The injection volume was 5 μL. The detection
of hydrazone derivatives was performed at 366 nm.
A sample solution and the derivatization reagent were mixed in a 1:1 (v/v) ratio, incubated for 15
min and then 5 μL of the mixture was manually entered into the injector using a 25 μL Hamilton
syringe (Hamilton Company, USA). Concentrations of the products were calculated using
calibration curves obtained in the concentration range of 10-1000 μM for each substance.
Analysis of irradiated 2-propanol and 2-propanol-2-d solutions
1
The accumulation of acetone in 2-propanol or 2-propanol-2-d solutions was determined by gas
1
chromatography using a Shimadzu GC-2010 (Japan) instrument equipped with an AOC-5000
auto-injector (Shimadzu, Japan) and a flame ionization detector (FID) (Shimadzu, Japan).
Compounds were separated using a Supelcowax 10 (Supelco, USA) capillary column (30.0 m х
0
.25 mm ID, 0.50 μm film thickness) with helium as a carrier gas in a constant flow rate of 1.28
-1
о
mL·min . The temperature of the injector port was set at 250 С. The column temperature
о
о
о
-1
о
increased from 40 С to 80 С in increments of 5 С·min , then it rose to 210 С at a rate of
о
-1
о
8
C·min and finally was maintained at 210 С for 5 min. The injection volume was 1 μL. The
о
detector temperature was adjusted to 220 С. The acetone concentrations were calculated using
the calibration curve obtained in the concentration range of 10-1000 μM.
Analysis of irradiated 2,3-butanediol and 2,3-butanediol-2,3-d solutions
2
The irradiated solutions were analyzed by GS-MS using a Shimadzu GC-2010 (Japan)
instrument equipped with an AOC-20i auto-injector (Shimadzu, Japan) and fitted to a GCMS-
QP2010 Plus quadrupole mass detector (Shimadzu, Japan). Compounds were separated using a
Stabilwax-DA (Restek, USA) capillary column (30.0 m х 0.25 mm ID, 0.25 μm film thickness)
-1
with helium as a carrier gas in a constant flow rate of 1.02 mL·min . The temperature of the
о
injector port was set at 250 С and the column temperature was programmed to increase from
о
о
о
-1
4
0 С to 150 С in increments of 5 С·min . The injection volume was 1 μL. The MS operated in a
positive electron impact (EI) mode with an electron energy of 70 eV (full scan, 40–200 m/z) and
о
at the ion source temperature equal to 200 С. Concentrations of the products were calculated
using calibration curves obtained in the concentration range of 10-500 μM for each substance.
Use of chromatograms and statistical treatment of the results

In the case of symmetrically shaped peaks rising above a stable horizontal baseline, well
separated from one another, concentration values were derived from both calculations using
areas and heights of the peaks, otherwise, only peak areas were used to calculate concentrations.
Preprocessing of chromatograms was performed in OriginPro software, Version 2019b (9.65),
OriginLab Corporation, Northampton, MA, USA, https://www.originlab.com/.
Each G-value (and its standard error) was calculated as a best-fit value of the linear regression
slope (and its standard error) of c(product) [μM] = f(D) [Gy]. Each linear regression analysis was
performed on a dataset of 5 or 6 points (including 0 values) using the method of least squares.
An error given for a specific G-value in Results (section 3) refers to the 95% confidence interval
of the pooled mean calculated from the t-distribution using a set of G-values possessing the
standard errors. To compare the radiation chemical yields of products for protiated and
deuterated substrates, unpaired parametric t-tests were executed and two-tailed P values (95%
confidence level) were reported. The null hypothesis is that two populations have the same mean
(
or that the isotopic substitution has no effect). A P-value, which is less than the threshold (α =
.05) leads to the rejection of the null hypothesis and means that the difference is significant
statistically. All the above-mentioned processing was performed using GraphPad Prism, version
.0.1 for Windows, GraphPad Software, San Diego, California USA, www.graphpad.com.
0
8

Results
Effects of the H/D substitution in the position C of 1,2-propanediol on its radiation-induced
2
transformations in deaerated aqueous solutions
To assess the effect of deuterium introduction into the position C of 1,2-propanediol, we
2
performed radiolysis of 1,2-propanediol and 1,2-propanediol-2-d deaerated solutions (pH =
1
7
.0±0.1). Among six major compounds, which are formed from 1,2-propanediol during its
indirect radiolysis [12], five products (hydroxyacetone, formaldehyde, acetaldehyde, acetone,
and propanal) were detected using LC-UV assay following the pre-column derivatization with
DNPH. Another product, 2-hydroxypropanal, has not been defined due to the lack of an
analytical standard. Anyway, no clear peaks, which might belong to 2-hydroxypropanal, were
observed in the full chromatograms recorded. Fig. 1 shows the difference between the ratio of
carbonyl products formed from the protiated and deuterated substrates. Moreover, the
chromatograms also demonstrate the effect of the substrate concentration on the amount of the
substances produced.
<Fig. 1>
G-values of the carbonyl products related to different substrate concentrations are shown in
Table 1.
<Table 1>
By definition, the value of the kinetic isotope effect is the ratio of rate constants of the
corresponding reactions (k /k ). In radiation-chemical experiments, the observed G-values of
H
D
product accumulation/substrate decomposition are more often used, and under certain conditions,
k /k is G (X)/G (X) since the radiation-chemical yield is a kinetic parameter that describes the
H
D
H
D
rate of product accumulation or substrate decomposition depending on the absorbed dose. Thus,
in the case of stationary radiolysis of aqueous solutions of organic substances, this equality is
observed when comparing G-values (except those of pure water radiolysis products, such as H2)
at the same substrate concentrations and experimental conditions [41]. Therefore, the value of
KIE will be understood further as the ratio G (X)/G (X) and can be found in the result tables
H
D
after the corresponding P-value, if applicable.
Two main results follow from the analysis of Table 1 and Fig. 1. Firstly, the yields of products 4-
do not depend significantly on the 1,2-propanediol concentration, whereas for product 1, and
6

especially for product 2, this subjection is pronounced. The latter feature is known to be
characteristic of chain processes [42]. Secondly, the H/D substitution drastically suppresses the
formation of acetone, the key product of the free-radical substrate dehydration. Thus, we can
firmly state that the pronounced KIE is observed for this product, reaching the value of 15.3±3.1
at the substrate concentration of 1 M.
Effects of the H/D substitution in the position C of 2-propanol on its radiation-induced
2
transformations in deaerated aqueous solutions
In our opinion, the observed KIE in the case of acetone formation from 1,2-propanediol/1,2-
propanediol-2-d cannot be fully explained by the different attitudes of initiators to the substrate.
1
And this part aims to justify this point of view.
To assess the contribution of the initiation step to the observed KIE on the chain acetone
formation (step 1 in Scheme (1)), a similar experiment with 2-propanol and 2-propanol-2-d was
1
carried out. The radiation chemistry of this substance is much simpler than that of 1,2-
propanediol. The main product of radiolysis here is acetone, which is formed as a result of the
disproportionation of prevailing CH ·C(OH)CH radicals following the interaction of the
3
3
substrate with ·H/·OH [12]. The radiation-chemical yields of acetone formation are presented in
Table 2.
<Table 2>
In contrast to vicinal diol radicals, alcohol radicals such as CH ·C(OH)CH do not form -
3
3
carbonyl radicals, which can accumulate as a result of a chain reaction with the substrate. The
difference in G(acetone), equal to 1.2±0.2 times, indicates the negligible effect of the substrate
reaction with radical water radiolysis products on the possible KIE. Although the calculated KIE
value is 1.2, the 95% confidence interval from 1.0 to 1.4 does not allow us to claim an
unambiguous KIE (despite P-value formally points to the difference in the G-values).
Effects of the H/D substitution in the positions C of 2,3-butanediol on its radiation-induced
2,3
transformations in deaerated aqueous solutions
The next issue to be addressed: is it crucial to have primary C-centered radicals after the
radiation-induced dehydration of vicinal diols to observe a chain mechanism and pronounced
KIE? To answer this, we conducted the radiation-chemical experiment with 2,3-butanediol and

2
,3-butanediol-2,3-d , where secondary C-centered radicals are obtained during the course of the
2
substrate transformations [12].
<Fig. 2>
The results obtained are presented in Fig. 2, from which it is evident that there is no KIE on the
formation of 2-butanone, the product of interest.
Discussion
6
0
Radiolysis of pure water under the action of Co γ-rays can be represented by the following
scheme, which is also applicable in the case of dilute aqueous solutions (the primary G-values
-1
(
μmol·J ) at pH of 4-9 are specified in the brackets [43]):
훾
-
aq
+
-
aq
H O → e (0.28), ·OH (0.29), ·H (0.06), H O (0.08), H (0.05), H (0.36), OH (0.06) (3)
2
2
2
2
aq
It should be noted that the molecular products (H O , H ) practically do not interact with the
2
2
2
-
aq
solutes studied in the present work. On the contrary, the radical products (·OH, ·H, e ) are very
active. So, ·OH radicals detach hydrogen atoms from an alcohol molecule with the rate constant
8
9
-1 -1
5
7
-1 -1
of 10 -10 M ·s , and ·H – with the rate constant of 10 -10 M ·s [43], but hydrated electrons
-
are inactive in relation to substrates that do not possess acceptor properties (alcohols, diols). If e
is not scavenged it can still interfere by reacting with the radicals or stable products formed
aq
from such substrates. But in dilute aqueous solutions with pH near 7 and in the absence of
-
aq
+
10
-1 -1
oxygen, e can react primarily with H (k = 2.3·10 M ·s [44]):
aq
-
+
e + H → ·H
(4)
aq
aq
and, in less degree, with H O molecules, which leads to the additional formation of hydrogen
2
atoms.
Besides, the solvated electrons can interact with hydrogen peroxide (Equation (5),
1
0
-1 -1
k = 1,3·10 M ·s , [43]) and carbonyl compounds, if the latter are present in sufficient
concentrations in the solution.
-
-
e + H O → ·OH + OH
aq
(5)
aq
2
2

Thus, during the short-term radiolysis of aqueous, comparably diluted (≤ 1 M), deaerated
solutions containing alcohols or diols, one can consider only the interactions of the substrate with
·OH and ·H radicals.
Schemes in Fig. 3 describe well-studied free-radical processes, which take place during the
radiolysis of 1,2-propanediol in deaerated aqueous solutions. It has been reliably established by
methods of pulse radiolysis, EPR, and with the use of spin traps and other acceptors, that radicals
of vicinal diols (RC·(OH)-CH(OH)R’) are unstable and they transform into the corresponding β-
carbonyl radicals (RC(O)-·CH-R’) with the simultaneous elimination of H O [12,45].
2
<Fig. 3>
In addition to radicals C1 and C2, the formation of radical C5 (·CH -CH(OH)-CH OH/·CH -
2
2
2
CD(OH)-CH OH) is also possible, but, as shown by the method of EPR, it is minor compared to
2
the former radicals [45,46], and converted into C2 and C1 by reacting with the substrate or
undergoes β-fragmentation with the formation of 5 and ·CH OH. Although the reaction of
2
recombination (dimerization) of C1–C4 radicals cannot be excluded, the products formed during
this process are also minor due to the low probability of the event when the radicals are in close
proximity to each other (in other words, due to the low stationary concentration during
radiolysis). It should be noted that the transformation of oxygen-centered radicals O1 and O2
into carbon-centered radicals C1–C4 (via interaction with the substrate) is also observed. With
-
the sufficient accumulation of carbonyl products, the processes of their interaction with e aq
should occur, but this is observed only under very long-term exposure to γ-rays.
1
,2-Propanediol radiation-induced dehydration with the formation of acetone at an absorption
-1
dose rate of 0.110±0.003 Gy·s in aqueous solutions is a non-branched chain process
The formation of a dehydration product in a straight (non-branched) chain reaction was shown
by the example of indirect radiolysis of ethylene glycol deaerated aqueous solutions at a dose
rate of ca. 0.64 Gy/s [43,47]. However, the values of G(dehydration product) characteristic of
chain processes were not obtained at this dose rate in the case of 1,2-propanediol. At a dose rate
of 0.64 Gy/s, G(acetone) in 0.1 M 1,2-propanediol solution (pH 6.0-6.5) did not exceed the sum
-
aq
of GOH + G + G (taking into account the transformation of e to ·H by reaction (4)) and was
H
e
-1
equal to 0.249-0.280 μmol·J [12].
However, the radiation-chemical yields of acetone obtained in our (present) work for 0.1 and 1
-1
M 1,2-propanediol solutions at pH 7.0±0.1, equal to 0.719±0.065 and 2.07±0.16 μmol·J (Table

1
), respectively, indicate the chain nature of acetone formation at the relatively low dose rate. In
the work of Jiang and colleagues [48], the radiolysis of 1,2-propanediol solutions saturated with
-
aq
-1
60
N O (to convert e to ·OH) was studied at a dose rate of 0.1 Gy·s (γ-rays of Co), which is
2
quite close to the value at which we conducted our radiation-chemical experiments. For the
substrate concentrations of 0.2 and 2 M, the authors obtained G(acetone) equal to 1.55 and 3.05
-1
μmol·J , respectively. Despite i) the unequal activity of the free radical system (in a system with
N O there are much more ·OH radicals), ii) the concentration of substrates, iii) and some minor
2
differences in the experimental conditions, we can say that the results of our work are consistent
with the results of [48], which also demonstrate the chain formation of acetone. Indeed, G-values
of radiolysis products may depend on the radiation dose rate inversely, i.e. increasing
significantly with the decrease in dose rate [49].
Thus, the dose rate strongly affects G-values of the molecular products formed from vicinal
diols. The point is that the increase in dose rate leads to a decrease in primary yields of water
radiolysis radical products and, in contrast, the increase in primary yields water radiolysis
molecular products. In other words, in diluted aqueous solutions the “radical-radical”
recombination of corresponding water radiolysis products competes and may even prevail over
the “radical-diluted compound” interactions [12,43]. For instance, it was shown on the example
of deaerated 1.2 M ethylene glycol aqueous solutions that the total radiation-chemical yield of
products decrease noticeably with increasing dose rate [12]. This dependence is particularly
pronounced in the case of chain processes, as was shown for acetaldehyde formed from ethylene
glycol at low dose rates [47], when the reaction rate depends on the concentration of initiators
(·OH and ·H).
Deuteration of 1,2-propanediol in the α-C position relative to the secondary OH-group can
quench its radiation-induced chain dehydration at an absorption dose rate of 0.110±0.003
-1
Gy·s in aqueous solutions
Once again, it is safe to postulate the chain mechanism of acetone radiation-induced formation
from 1,2-propanediol. We suppose this effect is observed due to the different reactivity of the
acetonyl radical C4 in relation to the C–H/C–D bonds of the initial molecules. Thus, the
introduction of deuterium into position C of 1,2-propanediol slows the rate-limiting step of the
2
acetone formation down.

(
6)
7)
(
(8)
From comparing the rate constants of the reactions of alcohols with ·OH, ·H, and carbon-
centered radicals, it can be concluded that the latter will define the rate-limiting step in the
acetone formation. One of the most active aliphatic C-centered radicals is ·CH . Although the
3
rate of hydrogen atom transfer from an alcohol molecule also depends on the substrate structure,
the following data [50] demonstrate that rate constants of such processes are much lower than
9
7
-1 -1
those involving ·OH and ·H (
̴1 0 and 10 M ·s , correspondingly):
2
-1 -1
·
CH + CH OH → CH + ·CH OH (k = 2·10 M ·s )
(9)
3
3
4
2
2
-1 -1
·
CH + CH CH OH → CH + CH ·CHOH + ·CH CH OH (k = 6·10 M ·s )
(10)
3
3
2
4
3
2
2
3
-1 -1
·
CH + CH CH(OH)CH → CH + CH ·C(OH)CH + ·CH CH(OH)CH (k = 3.4·10 M ·s ) (11)
3 3 3 4 3 3 2 3
Taking into account the reduced reactivity of acetonyl and similar ·CH C(O)R species (because
2
of the resonance stabilization of acetonyl radical by the adjacent carbonyl group [51]), one can
3
-1 -1
expect the rate constant of reaction (6) being not higher than ̴1 0 M ·s The conclusion is that
.
reaction (6) ((7)) is the rate-limiting step of the acetone formation process studied. And the
significant KIE is related to this interaction. In addition, the H/D substitution blocks another
secondary way of C2 formation, which may also affect G (acetone)/G (acetone): the
H
D
transformation of C3 to 1 through interaction with the substrate. In the case of 1,2-propanediol-
d1, the formation of C1 is predominant here, whereas the non-substituted substrate gives rise to
both C1 and C2 radicals in this reaction, with C2 being prevalent. The fact that C3 abstracts H in

the tertiary position more actively than in the secondary one also leads to a “leak” of the radical-
propagator from the hypothetical chain, which might describe the formation of 1. This is one of
the reasons why we do not observe G(propanal) characteristic for a chain process, whereas
-1
G(acetone) reaches the value of 2.07±0.16 μmol·J at c(1,2-propanediol) = 1 M.
The next quite significant point concerning the results of the experiment is the influence of the
hydroxyacetone impurity in the deuterated substrate on G(products). Hydroxyacetone contributes
-
aq
to the formation of acetone by reacting with e :
(12)
This leads to the overestimation of G(acetone) in 1,2-propanediol-2-d samples. In fact, in the
1
presence of this carbonyl impurity, the strong KIE of acetone formation is observed, and in the
case of ultimately pure 1,2-propanediol-2-d1 one should expect even a greater
G (acetone)/G (acetone) value.
H
D
Alcohols that are not characterized by chain radiation-chemical transformations, do not show
a significant KIE when deuterated in the α-C position relative to the OH-group
One can expect that not only reactions (6) and (7) but also the abstraction of H or D by the
radical water radiolysis species from 1,2-propanediol or 1,2-propanediol-2-d , respectively, are
1
the steps sensitive to isotope substitution.
Concerning the radical water radiolysis species, we must exclude from consideration ·OH-
radicals. These well-known " furious killers” in all free-radical reactions are too active to
differentiate energetically hydrogen and deuterium atom transfer processes. At the same time,
hydrogen atoms (·H) are less reactive than ·OH radicals, since H–H bond formation is less
exothermic than that of H–OH, and therefore ·H are likely more selective. Indeed, this selectivity
was shown in some works devoted to H/D abstraction by ·H from 2-propanol/2-propanol-d in
7
aqueous solutions [52–54]. However, the results of our research (Table 2) show that when both
·H and ·OH radicals are present in the solution, no KIE on the formation of acetone from 2-
propanol and 2-propanol-2-d is observed. This finding rejects the idea that the interaction of the
1
radical water radiolysis species with the C–H/C–D bonds plays a key role in the manifestation of
the KIE related to the formation of carbonyl products in (1). Therefore, we assume the carbon-

centered acetonyl radical is the one that differentiates C–H/C–D bonds in 1,2-propanediol/1,2-
propanediol-2-d molecules.
1
Propagating the chain process of carbonyl product formation is characteristic only for the
primary carbon-centered radicals derived from vicinal diols
In the systems studied, ·OH and ·H radicals react with 2,3-butanediol/2,3-butanediol-2,3-d2
molecules, forming mainly radicals C6 (Fig. 4). Radicals C6 are involved in two processes:
disproportionation (formation of 3-hydroxybutanone (acetoin), product 8), and dehydration
(formation of 2-oxobutyl radicals C7). 2-Butanone (methyl ethyl ketone, product 7) is obtained
by reactions of C7 with either the initial substrate molecules (С6 are also regenerated) or C6
radicals (disproportionation that yields product 8 as well). Besides, a certain quantity of C-C
destruction product 9 is observed in the system after irradiation.
<Fig. 4>
The observed “ordinary” values of radiation-chemical yields of 2-butanone formation from 2,3-
butanediol and 2,3-butanediol-2,3-d and their statistical similarity are explained as follows. C7
2
is additionally stabilized by the adjacent methyl group compared to C4, thus less reactive
towards H(D) abstraction from the corresponding substrate molecule. So, one should expect less
contribution of the chain process, which is analogous to that of 1,2-propanediol conversion to
acetone, to the reduction of C7 to 7. G(2-butanone) obtained at a dose rate of 0.110±0.003 in the
-1
present study is consistent with the value of 0.126-0.162 μmol·J found in earlier works at 0.64
-1
Gy·s [12]). Thus, the independence of G(2-butanone) from the dose rate may in some way
indicate a low contribution or even the absence of the chain process in the formation of 7 from
2
,3-butanediol.
To sum up, when switching from primary to secondary radicals in (1), the probability of the
chain formation of the corresponding carbonyl product is reduced sharply, and the isotopic
substitution does not affect free radical dehydration of vicinal diols of the R CH(OH)CH(OH)R
1
2
(
R , R ≠ H) type.
1 2

Conclusion
The studies shown here clearly indicate the chain nature of the radiation-induced formation of
acetone in 1,2-propanediol deaerated aqueous solutions and quenching the process by replacing
hydrogen with deuterium in position C of the initial compound. This is due to the formation of
2
acetonyl radicals, which propagate the chain mechanism and abstract hydrogen atoms from the
substrate molecule more likely than deuterium atoms. Propanal, the second product of 1,2-
propanediol dehydration, is characterized by lower G-values of its formation since the precursor
CH ·CHCHO radicals are less active and do not participate in the corresponding chain
3
propagation reaction. The exceptional role of primary β-carbonyl radicals in the radiation-
induced chain dehydration of diols and, as a result, in the appearance of a strong KIE, is also
demonstrated by the absence of a KIE when 2-butanone is formed from 2,3-butanediol or 2,3-
butanediol-2,3-d in deaerated aqueous solutions.
2
Some general considerations can be drawn from the observed effects, which affords a deeper
insight into the reactivity of hydroxyl-containing compounds with radical species. By
substituting H with D in the positions geminal to OH and functional groups we can expect the
suppression of free radical fragmentation in compounds prone to the radiation-induced 2β-
cleavage followed by the formation of corresponding primary β-carbonyl radicals. Examples of
such compounds are mono- and diglycerides (but not triglycerides), lysophospholipids,
phosphatidylglycerol. For similar substances, but capable of forming only secondary β-carbonyl
radicals (carbohydrates, glycolipids, ceramides, sphingomyelins, ribonucleotides) there is no
reason to assume the same.

Disclosure of interest
The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
Author contributions
Palina Nepachalovich: Investigation, Visualization, Formal analysis, Writing – Original draft
preparation and Editing; Oleg Shadyro: Supervision, Conceptualization, Writing – Review;
Andrei Bekish: Resources (synthesis of deuterated substrates), Conceptualization. Vadim
Shmanai: Conceptualization.

References
[
[
1] Iyer R, Lehnert BE. Effects of Ionizing Radiation in Targeted and Nontargeted Cells. Arch
Biochem Biophys 2000;376:14–25.
2] Reisz JA, Bansal N, Qian J, et al. Effects of Ionizing Radiation on Biological Molecules—
Mechanisms of Damage and Emerging Methods of Detection. Antioxid Redox Signal
2
014;21:260–292.
[
[
[
3] Chapman JD, Gillespie CJ. Radiation-Induced Events and Their Time Scale in Mammalian
Cells. In: Advances in Radiation Biology. Elsevier; 1981. p. 143–198.
4] Waldren CA. Classical radiation biology dogma, bystander effects and paradigm shifts.
Hum Exp Toxicol 2004;23:95–100.
5] Benderitter M, Vincent-Genod L, Pouget JP, et al. The Cell Membrane as a Biosensor of
Oxidative Stress Induced by Radiation Exposure: A Multiparameter Investigation. Radiat
Res 2003;159:471–483.
[
[
6] Lehninger AL, Nelson DL, Cox MM. Lehninger principles of biochemistry. 6th ed. New
York: W.H. Freeman; 2012.
7] Subczynski WK, Widomska J, Feix JB. Physical properties of lipid bilayers from EPR spin
labeling and their influence on chemical reactions in a membrane environment. Free Radic
Biol Med 2009;46:707–718.
[
8] Dotson RJ, Smith CR, Bueche K, et al. Influence of Cholesterol on the Oxygen
Permeability of Membranes: Insight from Atomistic Simulations. Biophys J
2
017;112:2336–2347.
[
[
9] von Sonntag C. The chemical basis of radiation biology. London: Taylor & Francis; 1987.
10] Stark G. The effect of ionizing radiation on lipid membranes. Biochim Biophys Acta BBA -
Rev Biomembr 1991;1071:103–122.
[
11] Carreau A, Hafny‐ Rahbi BE, Matejuk A, et al. Why is the partial oxygen pressure of
human tissues a crucial parameter? Small molecules and hypoxia. J Cell Mol Med
2
011;15:1239–1253.
[
[
[
[
[
12] Petryaev EP, Shadyro OI. Radiation chemistry of bifunctional organic compounds. Minsk:
Universitetskoe; 1986.
13] Edimecheva IP, Kisel MA, Shadyro OI, et al. The damage to phospholipids caused by free
radical attack on glycerol and sphingosine backbone. Int J Radiat Biol 1997;71:555–560.
14] Shadyro OI, Yurkova IL, Kisel MA. Radiation-induced peroxidation and fragmentation of
lipids in a model membrane. Int J Radiat Biol 2002;78:211–217.
15] Shadyro OI, Yurkova IL, Kisel MA, et al. Radiation‐ induced fragmentation of cardiolipin
in a model membrane. Int J Radiat Biol 2004;80:239–245.
16] Yurkova I, Shadyro O, Kisel M, et al. Radiation-induced free-radical transformation of
phospholipids: MALDI-TOF MS study. Chem Phys Lipids 2004;132:235–246.

[
17] Yurkova IL, Kisel MA, Arnhold J, et al. Effect of structure of polar head of phospholipids
on their fragmentation during γ-irradiation of model membranes. High Energy Chem
2
006;40:300–303.
[
[
[
[
18] Yurkova IL. Free-radical reactions of glycerolipids and sphingolipids. Russ Chem Rev
012;81:175–190.
2
19] Shadyro O, Samovich S, Edimecheva I. Free-radical and biochemical reactions involving
polar part of glycerophospholipids. Free Radic Biol Med 2019;144:6–15.
20] Shadyro O, Lisovskaya A. ROS-induced lipid transformations without oxygen
participation. Chem Phys Lipids 2019;221:176–183.
21] Edimecheva IP, Kisel RM, Shadyro OI, et al. Homolytic Cleavage of the O-glycoside Bond
in Carbohydrates: A Steady-state Radiolysis Study. J Radiat Res (Tokyo) 2005;46:319–
3
24.
[
[
22] Shadyro OI, Kisel RM. Glycoside bond cleavage in the radiolysis of aqueous solutions of
methylglycosides and disaccharides. High Energy Chem 2007;41:318–323.
23] Shadyro O, Yurkova I, Kisel M, et al. Formation of phosphatidic acid, ceramide, and
diglyceride on radiolysis of lipids: identification by MALDI-TOF mass spectrometry. Free
Radic Biol Med 2004;36:1612–1624.
[
[
24] Yurkova I, Kisel M, Arnhold J, et al. Free-radical fragmentation of galactocerebrosides: a
MALDI-TOF mass spectrometry study. Chem Phys Lipids 2005;134:41–49.
25] Shadyro OI, Sosnovskaya AA, Vrublevskaya ON. C-N bond cleavage reactions on the
radiolysis of amino-containing organic compounds and their derivatives in aqueous
solutions. Int J Radiat Biol 2003;79:269–279.
[
[
[
[
[
26] Sosnovskaya AA, Sladkova AA, Dobridenev IS, et al. Radiation-induced transformations
of threonine and its derivatives in aqueous solutions. High Energy Chem 2009;43:431–434.
27] Sladkova АА, Sosnovskaya АА, Edimecheva IP, et al. Radiation-induced destruction of
hydroxyl-containing amino acids and dipeptides. Radiat Phys Chem 2012;81:1896–1903.
28] Shadyro OI, Glushonok GK, Glushonok TG, et al. Quinones as Free-radical Fragmentation
Inhibitors in Biologically Important Molecules. Free Radic Res 2002;36:859–867.
29] Shadyro OI, Edimecheva IP, Glushonok GK, et al. Effects of Phenolic Compounds on
Reactions Involving Various Organic Radicals. Free Radic Res 2003;37:1087–1097.
30] Shadyro OI, Sosnovskaya AA, Edimecheva IP, et al. Effects of quinones on free-radical
processes of oxidation and fragmentation of hydroxyl-containing organic compounds.
Bioorg Med Chem Lett 2007;17:6383–6386.
[
[
31] Samovich SN, Sladkova AA, Sverdlov RL, et al. Effects of quinones and nitroazoles on
free-radical fragmentation of glycerol-1-phosphate and 1,2-dimyristoyl-glycero-3-
phosphatidyl-glycerol. Chem Phys Lipids 2019;222:8–14.
32] Samovich SN, Sverdlov RL, Voitekhovich SV, et al. Effects of quinones and azoles on
radiation-induced processes involving hydroxyl-containing carbon-centered radicals. Radiat
Phys Chem 2018;144:308–316.

[
[
33] Lagutin PYu, Shadyro OI. Effects of B group vitamins on reactions of various α-hydroxyl-
containing organic radicals. Bioorg Med Chem Lett 2005;15:3797–3800.
34] Shchepinov MS, Roginsky VA, Brenna JT, et al. Deuterium Protection of Polyunsaturated
Fatty Acids against Lipid Peroxidation. In: Omega-3 Fatty Acids in Brain and Neurological
Health. Elsevier; 2014. p. 373–383.
[
[
35] Andreyev AY, Tsui HS, Milne GL, et al. Isotope-reinforced polyunsaturated fatty acids
protect mitochondria from oxidative stress. Free Radic Biol Med 2015;82:63–72.
36] Berbée JFP, Mol IM, Milne GL, et al. Deuterium-reinforced polyunsaturated fatty acids
protect against atherosclerosis by lowering lipid peroxidation and hypercholesterolemia.
Atherosclerosis 2017;264:100–107.
[
37] Raefsky SM, Furman R, Milne G, et al. Deuterated polyunsaturated fatty acids reduce brain
lipid peroxidation and hippocampal amyloid β-peptide levels, without discernable
behavioral effects in an APP/PS1 mutant transgenic mouse model of Alzheimer’s disease.
Neurobiol Aging 2018;66:165–176.
[
[
38] Shchepinov MS. Polyunsaturated Fatty Acid Deuteration against Neurodegeneration.
Trends Pharmacol Sci 2020;41:236–248.
39] Adams D, Midei M, Dastgir J, et al. Treatment of infantile neuroaxonal dystrophy with
RT001: A di‐ deuterated ethyl ester of linoleic acid: Report of two cases. JIMD Rep
2
020;54:54–60.
[
[
40] Thompson MS, Meyer TJ. Mechanisms of oxidation of 2-propanol by polypyridyl
complexes of ruthenium(III) and ruthenium(IV). J Am Chem Soc 1982;104:4106–4115.
41] Fujisaki N, Gäumann T. Kinetic Isotope Effect for the Reaction of a Hydrogen Atom with
Cyclohexane-h12, Cyclohexane-d12 and Cyclohexane-1, 1, 2, 2, 3, 3-d6 as Studied by the
Radiolysis of Water Vapor-Cyclohexane Mixtures. Berichte Bunsenges Für Phys Chem
1
977;81:544–550.
[
[
42] Atkins PW, De Paula J. Physical chemistry. 9th ed. New York: W.H. Freeman; 2010.
43] Pikaev AK. Modern radiation chemistry: radiolysis of gases and liquids. Moscow: Nauka;
1
986.
[
[
44] Buxton GV, Greenstock CL, Helman WP, et al. Critical Review of rate constants for
−
reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (⋅OH/⋅O
Aqueous Solution. J Phys Chem Ref Data 1988;17:513–886.
in
45] Gilbert BC, Larkin JP, Norman ROC. Electron spin resonance studies. Part XXXIII.
Evidence for heterolytic and homolytic transformations of radicals from 1,2-diols and
related compounds. J Chem Soc Perkin Trans 2 1972;794.
[
[
46] Asmus KD, Moeckel H, Henglein A. Pulse radiolytic study of the site of hydroxyl radical
attack on aliphatic alcohols in aqueous solution. J Phys Chem 1973;77:1218–1221.
47] Pikaev AK, Kartasheva LI. Radiolysis of aqueous solutions of ethylene glycol. Int J Radiat
Phys Chem 1975;7:395–415.

[
[
[
[
[
48] Jiang D, Barata-Vallejo S, Golding BT, et al. Revisiting the reaction of hydroxyl radicals
with vicinal diols in water. Org Biomol Chem 2012;10:1102–1107.
49] Bugaenko LT, Kabakchi SA. Steady state method in radiation chemistry. Moscow:
Moscow State University; 1971.
50] Neta P. Application of Radiation Techniques to the Study of Organic Radicals. In:
Advances in Physical Organic Chemistry. Elsevier; 1976. p. 223–297.
51] Espinosa-Garcıa J, Márquez A, Dóbé S. Theoretical enthalpy of formation of the acetonyl
́
radical. Chem Phys Lett 2003;373:350–356.
52] Geimer J, Beckert D, Jenichen A. Kinetic isotope effect in hydrogen abstraction from 2-
propanol by hydrogen and deuterium radicals. A pulse radiolysis Fourier transform electron
spin resonance study. Chem Phys Lett 1997;280:353–358.
[
[
53] Madden KP, Mezyk SP. Critical Review of Aqueous Solution Reaction Rate Constants for
Hydrogen Atoms. J Phys Chem Ref Data 2011;40:023103.
54] Mezyk SP, Bartels DM. Rate of Hydrogen Atom Reaction with Ethanol, Ethanol- d , 2-
5
†
Propanol, and 2-Propanol- d in Aqueous Solution . J Phys Chem A 1997;101:1329–1333.
7

Figure legends
Fig. 1. LC-UV analyses of irradiated 0.01 M and 0.1 M solutions of 1,2-propanediol and 1,2-
-1
propanediol-2-d at various doses (dose rate = 0.110±0.003 Gy·s ) after the derivatization of the
1
carbonyl compounds with DNPH. Peaks from left to right: hydroxyacetone (turquoise),
formaldehyde (green), acetaldehyde (yellow), acetone (purple), propanal (blue). Each
chromatogram presented is the result of subtracting the corresponding control chromatogram (a
non-irradiated sample within the set, 0 Gy) from the original chromatogram of a given dose. The
aim of this pre-processing is to visualize the radiolytic accumulation of products only, where any
interference coming from the derivatization step is excluded.

Fig. 2. Accumulation curves for 2-butanone formed during the radiolysis of 2,3-butanediol and
its deuterated analogue solutions in 50 mM phosphate buffer (pH 7.0±0.1). Dose rate =
-1
0
.110±0.003 Gy
·
s . Radiation-chemical yields of 2-butanone and the t-test result are presented
on the right (p = 0.95).

Fig. 3. Schemes describing the indirect radiolysis of 1,2-propanediol and its deuterated analogue
in a deaerated aqueous solution. А: formation and dehydration of major carbon-centered radicals;
B: disproportionation of major carbon-centered radicals; C: formation and destruction of major
oxygen-centered radicals.

Fig. 4. Schemes describing the indirect radiolysis of 2,3-butanediol and its deuterated analogue
in a deaerated aqueous solution. А: formation and dehydration of a major carbon-centered
radical; B: disproportionation of the major carbon-centered radical; C: formation and destruction
of an oxygen-centered radical.

-1
Table 1. G-values (μmol·J ) of the products formed during the radiolysis of 1,2-propanediol and
its deuterated analogue solutions in 50 mM phosphate buffer (pH 7.0±0.1). Dose rate =
-1
0
.110±0.003 Gy·s .
c(substrate),
M
0
.01
0.1
1
1
,2-
propanediol-
-d1
1,2-
propanediol-
2-d1
1,2-
propanediol-
2-d1
Product \
Substrate
1,2-
propanediol
1,2-
propanediol
1,2-
propanediol
2
0
.050±0.008 0.056±0.007 0.094±0.011 0.093±0.011 0.183±0.027 0.131±0.020
(
1)
Statistically
different?
No, P = 0.469439
No, P = 0.923059
Yes, P = 0.013525
1.4±0.4 times
0
.170±0.018 0.041±0.005 0.719±0.065 0.081±0.008
2.07±0.16
0.135±0.017
(
2)
Statistically
different?
Yes, P<0.000001
4.10±1.0 times
Yes, P<0.000001
8.9±1.7 times
Yes, P<0.000001
15.3±3.1 times
0
0
.097±0.029
–*
0.094±0.037
–*
0.145±0.015
–*
(
4)
–
–
–
.044±0.005 0.040±0.014 0.052±0.005 0.056±0.007 0.071±0.008 0.048±0.008
(
5)
Statistically
different?
No, P = 0.619761
No, P = 0.290156
Yes, P = 0.000831
1.5±0.4 times
0
.028±0.011 0.025±0.005 0.030±0.004 0.035±0.011 0.040±0.007
No, P = 0.687394 No, P = 0.428283
-
(
6)
Statistically
different?
-
p = 0.95
*
Hydroxyacetone was not quantified due to its presence as an impurity in the deuterated substrate

-1
Table 2. G-values (μmol·J ) of acetone formed during the radiolysis of 2-propanol and its
deuterated analogue solutions in 50 mM phosphate buffer (pH 7.0±0.1). Dose rate = 0.110±0.003
-
1
Gy s .
·
c (substrate), M
0.1
Product \ Substrate
2-propanol
.177±0.015
2-propanol-2-d
0.145±0.015
1
0
Statistically different?
Yes, P = 0.002025, 1.2±0.2 times
p = 0.95