Novel ammonium dichloroacetates with enhanced herbicidal activity for weed control

Article abstract of DOI:10.1039/d0ra08707f

Dichloroacetic acid (DCA) exhibits great potential as an herbicide (nontoxic, easily biodegradable), but its application in agriculture has scarcely been investigated. Since DCA readily undergoes photolysis when exposed to natural light or UV irradiation, there is a large activity loss in controlling weeds. To improve the activity of DCA, we proposed the transformation of DCA into an ionic salt form by using an herbicidal ionic liquids (HILs) strategy. Herein, fifteen novel ammonium dichloroacetates were designed and achieved for the first time. When compared to the anionic precursor DCA, three salts with longer alkyl chains ranging from dodecyl to hexadecyl chains were found to enhance not only the post emergence herbicidal activity but also the rates of activity against some broadleaf weeds under greenhouse conditions. The enhancement was due to the synergistic effect of structural factors, such as the surface activity, solubility and stability arising from their ionic nature. In addition, IL 13 possesses a low phytotoxicity to cotton plants with a favorable selectivity index above 2. This study will be useful for the design of new, high-performance herbicidal formulations.

Full text of DOI:10.1039/d0ra08707f

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Novel ammonium dichloroacetates with enhanced
herbicidal activity for weed control†
Cite this: RSC Adv., 2020, 10, 44512
a
a
a
a
a
*
Yajie Ma, Hongyan Hu, Xianpeng Song, Yan Ma
*
Huanhuan Li,
and Hong Yan
b
Dichloroacetic acid (DCA) exhibits great potential as an herbicide (nontoxic, easily biodegradable), but its
application in agriculture has scarcely been investigated. Since DCA readily undergoes photolysis when
exposed to natural light or UV irradiation, there is a large activity loss in controlling weeds. To improve
the activity of DCA, we proposed the transformation of DCA into an ionic salt form by using an
herbicidal ionic liquids (HILs) strategy. Herein, fifteen novel ammonium dichloroacetates were designed
and achieved for the first time. When compared to the anionic precursor DCA, three salts with longer
alkyl chains ranging from dodecyl to hexadecyl chains were found to enhance not only the post
emergence herbicidal activity but also the rates of activity against some broadleaf weeds under
greenhouse conditions. The enhancement was due to the synergistic effect of structural factors, such as
the surface activity, solubility and stability arising from their ionic nature. In addition, IL 13 possesses
a low phytotoxicity to cotton plants with a favorable selectivity index above 2. This study will be useful
for the design of new, high-performance herbicidal formulations.
Received 13th October 2020
Accepted 23rd November 2020
DOI: 10.1039/d0ra08707f
rsc.li/rsc-advances
properties make them have enhanced performance, better
biodegradability and lower toxicity than its model anionic
herbicides.7–24 For instance, Cojocaru et al. synthesized dicamba
1 Introduction
Weeds are an important biodisaster class in agriculture. They
intensely compete with crops for light, water and nutrients, and
also host crop pests, bacteria and fungi, therefore cause
a greater reduction in both the quantity and quality of crop
production.1 Currently, chemical herbicides remain the most
effective way to control weeds in agricultural practices.2
However, some failed to control weeds during application
because of issues with, volatility,3 solubility4 or stability,5 that
even adversely affect the bio-efficacy and agro-ecological
security.6
HILs to avoid high volatile dri problems of dicamba acid, and
found that dicamba tetrabutylammonium salt reduced volatility
with a 0.7% volatilization loss versus a 10.8% loss of dicamba
acid aer 12 h isotherms at 75 ꢀC.8 This can minimize the risk of
off-site movement to humans, non-target organisms and other
agricultural ecosystems via volatilization. Pernak et al. prepared
glyphosate HILs to solve the poor solubility of glyphosate acid
(only 1.2–1.4% soluble in water),4 among which, di(bis(2-
hydroxyethyl)-cocomethylammonium) glyphosate was shown
to improve the herbicidal efficacy by increasing the water
solubility by 2.5–3 times, much higher than the commercial
formulation Roundup 360 SL, and it would lower the dose of
glyphosate by more than 50%.9 Niemczak et al. changed auxin
herbicides (i.e., 2,4-D, MCPA) in to their ammonium salt, and
effectively reduced toxicity (acute oral LD50 300–2000 mg kgꢁ1
for rats) and enhanced biodegradability ($62% degradation
aer 28 days in an OECD 301F Test).10 Similar results had also
been observed in the other HILs based on clopyralid,11 benta-
zone,12 picloram,13 2,20-thiodiacetic acid,14 etc,15–24 which were
incorporated with special cations. Notably, not every HIL was
safe, and some HILs were still shown to inuence soil micro-
organism (Proteobacteria, Chlamydiae or Bacteroidetes).25
Although HILs have both advantages and disadvantages, but
the use of HILs in agricultural applications is well accepted.
Dichloroacetic acid (DCA) and its sodium or diisopropy-
lammonium salt, pyruvate dehydrogenase kinase (PDK)
To address these issues, herbicidal ionic liquids (HILs)
strategy can be employed early in 2011,7 in which the herbicides
are developed into new IL forms. Such HILs are ionic salts with
ꢀ
melting point below 100 C, usually composed of active herbi-
cidal anions and cations. These polar HILs are very soluble in
water, not volatile, and thermally/chemically stable. These
aPlant Protection Department, State Key Laboratory of Cotton Biology, Institute of
Cotton Research, The Chinese Academy of Agricultural Sciences, Henan, Anyang
455000, China. E-mail: aymayan@126.com; Fax: +86-372-2562294; Tel: +86-372-
2562294
bState Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical
Engineering, Nanjing University, Nanjing, Jiangsu 210023, P. R. China. E-mail:
hyan1965@nju.edu.cn
† Electronic supplementary information (ESI) available: 1H and 13C NMR spectra,
solubility and surface tension results, preliminary screening of herbicidal activity,
the image of the response of some broadleaf weeds aer treatments. See DOI:
10.1039/d0ra08707f
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inhibitors, have been well known to possess diverse pharma-
cologic properties, e.g., antitumor,26 anticancer,27 antimetabolic
agents,28 therapeutic agents,29 oral antidiabetic agents,30 and
more. However, the phytotoxicity of DCA to weed plants has
been barely investigated. Early in the mid-1980s, DCA was found
to have phytotoxicity, where it can inhibit electron transport
between menaquinone QA and ubiquinone QB at the reductase
side in plant photosystem II (PSII) reaction centers.31 Being
a potential herbicide, DCA has a short persistence (21 days) in
water and soil due to its easy biodegradation via microbial
dehalogenases, and has little impact on subsequent rotated
crops.32 However, if exposed to natural light or UV irradiation,
DCA is vulnerable to being dechlorinated and decomposing to
inactive products, such as hydrochloric acid and carbon
dioxide,33 which therefore largely affect its activity in controlling
weeds.
As the “HIL” strategy implied, the transformation of DCA
into a stable ionic salt form might improve its activity. DCA,
a strong acid (pKa ¼ 1.29), can be fully deprotonated as the
dichlorocetate anion to generate salts with ammonium cations.
Herein, we designed a novel and active class of ammonium
dichloroacetates ILs containing cations with biogenic 2-
hydroxyethylamine34 and a xed phytotoxic dichlorocetate
anion (Scheme 1) and demonstrate their abilities to enhance
herbicidal activity against weeds compared to that of the DCA
control.
2 Results and discussion
2.1 Synthesis and characterization of ILs
Fieen ammonium dichloroacetates were rst synthesized
through acid–base neutralization but in two different routes
(Scheme 1). In the rst, DCA was directly neutralized with
primary (1ꢀ), secondary (2ꢀ) and tertiary (3ꢀ) hydroxylalkyl-
amines in a 1.1 : 1.0 mole ratio to form ILs 1–12. In the second,
1-bromoalkanes with different linear alkyl chains (C12, C14 or
C
16) were converted to quaternary alkylammonium bromide by
the Menschutkin reaction with N-methyldiethanolamine, fol-
lowed by an anion-exchange with hydroxide and neutralization
with DCA to yield ILs 13–15. The nal salts were puried by
extraction of DCA with excess diethyl ether and isolated by
evaporation in yields of over 90%. The above synthetic strategy
could provide an economic, efficient and easy-to-operate
approach for producing ammonium dichloroacetates on
a large scale. It should be stressed that the second method
trough acid–base reactions of ammonium hydroxides and DCA,
not metathesis of ammonium hydroxides halides with sodium
salts of DCA, proved to be efficient at minimizing the separation
difficulties of KBr. Moreover, this method has been used in the
preparation of HILs based on dicamba acid or glyphosate
acid.8,9
NMR analysis conrmed the formation of salts (Fig. S1–S30,
ESI†). In the 1H NMR spectra (in DMSO-d6), the acidic proton of
DCA at 12.48 ppm completely disappeared, and new charac-
teristic signals of protonated 1ꢀ–3ꢀ ammonium cations in ILs 1–
9 were observed as a broad singlet at 5.65–9.98 ppm. In the 13
C
NMR spectra, the chemical signal assigned to the carboxyl of the
dichlorocetate anion appeared at approximately 165 ppm. The
results demonstrated that the proton was successfully trans-
ferred from DCA to the amines, which implied that the newly
prepared ILs were ionic salts rather than either the mixture of
acid and base or amides.
These salts were isolated as either a viscous liquid or a low
ꢀ
melting point solid with the melting points below 100 C, and
hence were classied as ionic liquids, with one exception where
IL 2 had a higher melting point above 100 ꢀC. They were all
nonvolatile, soluble in polar organic solvents, i.e., water,
methanol, dimethylsulfoxide, acetonitrile, acetone, and iso-
propanol, and insoluble in toluene or diethyl ether except ILs
13–15, which were partially soluble (Table S1, ESI†). Good water
solubility is vital to increasing the uptake of ILs by plants
through preventing crystallization, slowing drying and pro-
longing spray retention in liquid for absorption,35 which further
improve the ultimate herbicidal activity.
2.2 Surface activity
The surface tension of aqueous solutions of ILs was measured
by the platinum ring method at 298 K. All ILs reduced the
surface tension of aqueous solutions (Fig. 1 and S31†). Partic-
ularly, only three salts, ILs 13–15, were found to self-assemble
into micelles (Fig. 1). This was related to the chemical struc-
ture. Due to both the long hydrophobic alkyl chains, and
hydrophilic 4ꢀ ammonium and hydroxylethyl groups were
Scheme 1 Structures of ammonium cations used and the synthetic
routes of ammonium dichloroacetates ILs.
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Fig.
1 Surface tension (g[mN m
ꢁ1]) data vs. the logarithm of
Fig. 2 Influence of the alkyl chain length (R) in the cation on the
logarithm of cmc.
concentration (C mg Lꢁ1) isotherms measured at 298 K for aqueous
solutions of ILs 13–15. The position of the cmc is indicated.
and postemergence treatments under greenhouse conditions –
an important consideration in herbicide development. The
selected weed species include one grass E. indica and ve
broadleaf weeds A. retroexus, E. prostrata, X. sibiricum, C. album
and S. nigrum, which have become major problematic weeds in
the cotton elds in Northern China.
present in the cations, and ILs 13–15 therefore had an amphi-
philic nature. In contrast, others (ILs 1–12) which lack long alkyl
chains and did not form micelles, and just behaved as simple
salts.36 For ILs 13–15, the critical micelle concentration (cmc,
a breakpoint in the surface tension g–log C plots) values were
found to range from 2.43 to 6.87 mmol Lꢁ1 (Table 1), closer to
that of new 4ꢀ ammonium surfactants N-alkyl-N,N-2-dihydrox-
yethyl-N-methylammonium bromides (CnDHAB, n ¼ 12, 14 or
16).37 Additionally, as the alkyl chain in the hydrophobic portion
was linearly elongated from 12 to 16, the cmc was decreased
from 6.87 mmol Lꢁ1 for IL 13 to 12.43 mmol Lꢁ1 for IL 15. The
relationship between log cmc and the alkyl chain length, pre-
sented in Fig. 2, followed the Stauff–Klevens rule.38 The surface
tension at cmc (gcmc) was also decreased, which is consistent
with the cmc decreasing in the same order.
The lower the cmc or gcmc value, the higher surface activity.
These values for ILs 13–15 were markedly lower than those of
alkyltrimethylammonium chloride ((CnTMA)Cl, n ¼ 12, 14 or
16), which are well known as agricultural wetting agents for
regulating the properties of herbicidal spray solution, such as
the wettability, spreadability and permeability,39 thus demon-
strating that ILs 13–15 were superior to these agents. Never-
theless, two exible hydroxylethyl groups can easily interact
with plant membranes through hydrogen bonding or electro-
static interaction, enabling their permeabilization.
The results of the greenhouse studies are summarized in
Table S2.† All ILs tested showed no pre emergence herbicidal
activities, even at concentrations up to 15 mg mLꢁ1, in that the
weed seeds germinated and grew normally to the water control.
However, when post emergence was applied, differential
herbicidal activities were observed for the ILs. Among them, ILs
13–15 showed a complete post emergence herbicidal activity
against ve broadleaf weeds, and only a slight activity against
grass E. indica, whereas other salts (ILs 1–12) had either limited
or no herbicidal effect, and even had growth promoting effect
towards weeds at the highest concentration (e.g., ILs 8, 10 and
11). It illustrated that the herbicidal activity was closely asso-
ciated with alkyl chains length and the degree of substitution of
the ammonium cation. Apparently, the long alkyl chain
substituents attached on the 4ꢀ ammonium cations, as in ILs
13–15, seemed to signicantly affect the herbicidal activity,
mainly due to their higher surface effect. Long chain in ILs 13–
15 can enhance their wetting, spreading or permeating abilities
by lowering the surface tension, which allow more absorption
by weed plants, potentially disrupting the plant membranes and
causing stronger herbicidal effects. This hypothesis was sup-
ported by the facts of those long-chained HILs.7–18
2.3 Herbicidal activity
In addition, some differences in the herbicidal selectivity by
ILs 13–15 between two weed species was also observed, which
2.3.1 Preliminary of herbicidal potential study. Initially,
the herbicidal potential of ILs was assessed by standard pre-
Table 1 Surface properties of ILs 13–15 in aqueous solution at 298 K
gcmc (mN mꢁ1
)
Gmaxa (mmol mꢁ2
)
Aminb (nm2)
pC20
Tcmc (mN mꢁ1
)
c
IL
cmc (mM)
13
14
15
6.46
3.92
2.35
32.46
31.11
28.66
1.30
1.33
1.34
1.279
1.243
1.238
3.04
3.37
3.84
39.84
41.19
43.64
a
b
Gmax – maximum adsorption. Amin – minimum area per surfactant molecule at the air–water interface were calculated by using the Gibbs
absorption equation. c pC20 – efficiency of surface adsorption on an air–water interface.
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was dependent on both the leaf surface differences40,41 and the nature. The herbicidal enhancement was indeed achieved by
hydrophilic nature for ILs 13–15 with HLB values in the range of ILs 13–15 by using the HIL strategy. It was concluded that the
8.14–9.56. Since grass E. indica exhibited hydrophobicity with structural conversion of DCA into an ionic salt form leads to the
a greater epicuticular wax deposition 0.5 mm thick,42 the large enhancement of herbicidal activity, which might be a conse-
and isolated drops were formed and rolled off the leave surface quence of the synergistic effect of structural factors per se, e.g.,
aer spraying, thereby leading to less of such salts being surface activity, solubility, and stability. Depending on their
absorbed. This might be the reason why E. indica was more stable ionic structures, ILs 13–15 possess a requisite stability to
tolerant to ILs 13–15.
undergo less photolysis, thus leading to a high photochemical
2.3.2 Further herbicidal activity study. In a preliminary stability. Moreover, no amide formation was observed aer
screening of the herbicidal potential of ILs, only ILs 13–15 three months of storage in an ambient light at room tempera-
completely controlled the broadleaf weeds but could not ture for ILs 13–15. It was also demonstrated that no reduction in
successfully control the grass weed when post emergence was herbicidal activity was observed under the same conditions.
applied, whereas others were not highly active. Therefore, ILs
Furthermore, ILs 13–15 took a shorter time than DCA to
13–15 were chosen for further post emergence activity against reach a maximal efficiency, e.g., at 7.5 mg mLꢁ1 during the rst
some broadleaf weeds, including C. album, S. nigrum and X. 7 days aer spraying (Fig. 4), again likely due to structural
sibiricum, using DCA as a positive control.
factors that promote the rates of cuticular penetration and/or
It was shown that ILs 13–15 exhibited clear concentration- uptake of these active salts.35,44 In addition, ILs 13–15 had
dependent herbicidal effects, which was enhanced with an a quicker response than glyphosate (isopropylamine salt),
increasing IL concentration from 1.25 to 15 mg mLꢁ1 (Table 2 which belongs to systemic herbicides.4 For glyphosate treat-
and Fig. S32–S43†). Aer spray application, they caused the ment with the same time period, there was no clear herbicidal
weed seedlings to become yellow, stunt, fold, wither, and effect on weeds (data were not shown).
eventually led to weed death. These symptoms of toxicity
became more severe when the concentration was applied above 2.4 Crop selectivity
2.5 mg mLꢁ1. To quantify the herbicidal efficacies, the EC50
ILs 13–15 were also tested for phytotoxicity effects on the growth
of cotton plants (Zhongmiansuo 79) under greenhouse condi-
values were calculated aer 21 days of spraying. The EC50 values
of ILs 13–15 were in the range of 1.74–2.95 mg mLꢁ1 for C.
tions. The results showed that when ILs 13–15 were applied at
album, 2.46–4.40 mg mLꢁ1 for S. nigrum, and 1.12–2.66 mg
the highest concentration of 15 mg mLꢁ1, they damaged the
mLꢁ1 for X. sibiricum. In either case, the EC50 values increased
growth of cotton and caused relatively severe phytotoxicity
effects (stalk browning, leaf burning, necrosis, wilting). At lower
concentrations, the slightly injured cotton can recover from the
linearly with extending alkyl chain lengths (Fig. 3), meaning
that elongation of the alkyl chain decreased the herbicidal
activity. Since the larger steric hindrance from a longer alkyl
initial injury during the growth. Moreover, the selectivity index
chain prevents penetration across cuticular membranes,43 the
(SI) values of ILs 13–15 between cotton plants and three
broadleaf weeds were identied. The SI values of ILs 13–15
ranged from 0.443 to 3.67 (Fig. 5). The more SI increases above
herbicidal activity is decreased as a result.
Signicantly, the EC50 values for ILs 13–15 were 1.7–10.8
folds of magnitude below those of the anionic precursor DCA
1, the more selective the herbicide is between the crop and the
(Table 2), which proved to be less active due to its photolysis
weeds, and An SI above 2 means that an herbicide could safely
Table 2 Comparison of the postemergence herbicidal activity of ILs 13–15 versus DCA against some broadleaf weeds in the greenhouse
Fresh weight inhibitiona (%) at 21 days aer spraying
b
Broadleaf
weeds
EC50 (95% CL) (mg
Compd. 1.25 (mg mLꢁ1) 2.5 (mg mLꢁ1
)
5 (mg mLꢁ1
)
7.5 (mg mLꢁ1
)
10 (mg mLꢁ1) 15 (mg mLꢁ1) mLꢁ1
)
C. album
IL 13
IL 14
IL 15
DCA
IL 13
IL 14
IL 15
DCA
IL 13
IL 14
IL 15
DCA
34.80 ꢂ 2.34a 65.68 ꢂ 2.30a 90.23 ꢂ 1.48a 99.49 ꢂ 0.87a
100 ꢂ 0a
100 ꢂ 0a
1.74 (1.32–2.14)
2.22 (1.58–2.87)
2.95 (3.137–3.50)
27.43 ꢂ 5.28 ab 47.63 ꢂ 4.52b 84.41 ꢂ 1.10b 96.77 ꢂ 2.79a 99.74 ꢂ 0.44a 100 ꢂ 0a
16.76 ꢂ 5.43bc 39.29 ꢂ 2.31c 67.56 ꢂ 2.22c 89.69 ꢂ 3.63b 98.11 ꢂ 3.26a 100 ꢂ 0a
8.23 ꢂ 2.32c 19.53 ꢂ 2.95d 38.44 ꢂ 2.16d 62.11 ꢂ 2.25c 86.78 ꢂ 2.72b 99.74 ꢂ 0.44a 5.08 (3.32–7.12)
S. nigrum
X. sibiricum
24.73 ꢂ 5.46a 42.89 ꢂ 3.90a 74.29 ꢂ 6.85a 98.75 ꢂ 6.85a 99.89 ꢂ 0.18a 100 ꢂ 0a
10.7 ꢂ 1.71b 35.7 ꢂ 3.75 ab 68.49 ꢂ 2.08a 92.22 ꢂ 4.15a 99.84 ꢂ 0.27a 100 ꢂ 0a
2.46 (1.41–3.57)
3.13 (2.36–3.94)
4.40 (2.36–6.61)
2.21 ꢂ 1.11b 28.82 ꢂ 1.99b 40.60 ꢂ 2.56b 76.9 ꢂ 1.19b 99.65 ꢂ 0.59a 100 ꢂ 0a
7.58 ꢂ 1.29b 15.24 ꢂ 2.28c 27.21 ꢂ 2.18c 37.00 ꢂ 4.24c
41.10 ꢂ 7.04a 76.20 ꢂ 1.48a 96.94 ꢂ 2.65a 100 ꢂ 0a
41.5 ꢂ 4.89b 72.95 ꢂ 5.52b 10.00 (7.51–15.71)
100 ꢂ 0a
100 ꢂ 0a
100 ꢂ 0a
1.12 (0.75–1.59)
2.16 (4.54–2.74)
2.66 (2.09–3.24)
23.7 ꢂ 3.15b 54.65 ꢂ 5.13b 97.67 ꢂ 4.02a 98.8 ꢂ 2.07 ab 100 ꢂ 0a
19.5 ꢂ 2.90b 41.22 ꢂ 3.13c 76.09 ꢂ 1.41b 92.9 ꢂ 1.18b 98.69 ꢂ 2.25a 100 ꢂ 0a
ꢁ10.5 ꢂ 5.53c
4.66 ꢂ 3.47d 13.32 ꢂ 2.81c 24.89 ꢂ 4.33c
41.8 ꢂ 3.96b 58.56 ꢂ 2.38b 12.46 (11.06–14.61)
a
All data represent mean ꢂ SD values, n ¼ 3. The small letters were signicant differences (P < 0.05) according to Tukey's multiple post hoc test by
ANOVA. b EC50 was the 50% inhibition in fresh weight of target weeds.
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Fig. 3 (A, C and E) The image of the response of C. album, S. nigrum and X. sibiricum after different treatments at 7.5 mg mLꢁ1. (B, D and F) Fresh
weight inhibition rates of different treatments to C. album, S. nigrum and X. sibiricum after 2, 4, 7 days spraying, respectively. The small letters
were significant differences (P < 0.05), n ¼ 3.
be used in a crop.45 It was noted that only IL 13 was safe for Furthermore, IL 13 was also safer than DCA, because the SI
cotton against these broadleaf weeds when applied post- values of which were just in the range of 0.16–0.863.
emergence, with favorable SI values above 2. In addition, the SI
values of IL 13 were generally higher than that of IL 14 and IL 15;
3 The herbicidal mechanism study
it indicated that IL 13 was safer than IL 14 and IL 15.
Here, to elucidate the mechanism of action of IL 13 in PS II, Chl
a uorescence induction curve OJIP46 of C. album was studied,
using water as a control (Fig. 6). The DCA- and IL 13 treated
leaves exhibited different induction curves compared to control.
At DCA treatment for 24 h, a slight rise in uorescence during
the rst OJ phase was detected, because the electron transport
from QA to QB was partially blocked by DCA resulting in a small
amount of QAꢁ accumulation.47 Whereas, IL 13 treatment
decreased the uorescence intensity of polyphaser (J–I–P). At IP
phase, the intensity of IL 13-treated leaves was much lower than
that of water-treated leaves. It suggested that IL 13 caused the PS
II center damage leading to decreased excitation energy transfer
from the antenna to the reaction center.48 The damage to PS II
center can be detected from the decreases in maximal PS II
quantum yield Fv/Fm and the performance index PIabs. The
values of Fv/Fm and PIabs of IL 13-treated leaves were decreased
Fig. 4 Influence of the alkyl chain length (R) in the cation on EC50
values.
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size of was blocked.49 Additionally, the damage of PS II structure
and function also led to a characteristic rise of Fo,50,51 the value
of which was increased by 12.9% relative to control. These
results suggested that IL 13 was possibly a novel PS II inhibitor
by interrupting electron transport between QA and QB, which
can cause the death of weed plants. Furthermore, most uo-
rescence parameters of IL 13 were lower than the DCA treat-
ment, which consisted with the enhanced herbicidal activity of
IL 13 when compared to DCA.
4 Conclusions
Fig. 5 Selectivity index expressed as the ratio of the EC10 value for
HIL strategy can be used for designing novel ammonium
dichloroacetates ILs, which combine dichlorocetate anion with
ammonium cations. The results demonstrated that ionic
structure strong inuenced the solubility and stability of ILs.
Notably, three salts ILs 13–15 with longer alkyl chains preserved
the surface activity of the cations, thus enhanced post-
emergence herbicidal activity against some broadleaf weeds
and accelerated weed death than DCA. Moreover, the further
crop safety experiment indicated IL 13 had better safety for
cotton in controlling some broadleaf weeds. Chlorophyll
a uorescence measurements indicated that the action mech-
anism of IL 13 seemed to inhibit electron transport between QA
and QB of PS II. To our knowledge, this is the rst example of
ammonium dichloroacetates, which shows herbicidal activity
against broadleaf weeds in agriculture.
cotton and the EC90 value for weeds.
Fig. 6 Effects of IL 13 and DCA on the chlorophyll fluorescence
induction curves of a dark-adapted C. album leaf.
5 Experimental section
5.1 Materials and methods
Methanol, acetonitrile, acetone, isopropanol, and dimethyl
sulfoxide (DMSO), toluene, diethyl ether, and potassium
hydroxide were of analytical grade and purchased from Energy
Chemical Co., Ltd. (Shanghai, China). The above agents were
used without further distillation. Dichloroacetic acid (CAS no.
79-43-6), 1-bromododecane (CAS no. 143-15-7), 1-bromote-
tradecane (CAS no. 112-71-0), 1-bromohexadecane (CAS no. 112-
82-3) and hydroxylalkylamines were purchased from Energy
Chemicals (Shanghai, China). Glyphosate isopropylamine salt
(purity 62%, aqueous solution) was obtained from Lier Chem-
ical Co., Ltd (Sichuan, China). N-Alkyl-N,N-2-dihydroxyethyl-N-
methylammonium bromide (CnDHAB, n ¼ 12, 14 and 16) were
synthesized according to reported procedures described in the
literature.45 Methyl sulfoxide-d6 with a deuteration degree of
99.8% for NMR spectra was obtained from J & K Scientic Co.,
Ltd. (Beijing, China).
by 18% and 70%, respectively. In the radar plot (Fig. 7), IL 13
caused the decreases in TR0/RC, ET0/RC, RE0/RC, associated to
the decrease of 4po, jEo and 4Eo, which resulted in the decrease
of PIabs. A further conrmation of PS II center damage is the
reduction in the area size above the uorescence curve between
Fo and Fm. The area size was decreased by 38.7% compared to
control, indicating that the electron transfer to quinone pool
1
The H, 13C NMR spectra were recorded with a Bruker 400
spectrometer (Bruker, Germany) at 400 and 100 MHz, respec-
tively. Chemical shis (d) are reported relative to the residual
solvent resonances of methyl sulfoxide-d6.
5.2 Synthesis of ammonium dichloroacetates ILs 1–15
Fieen ammonium dichloroacetates ILs were synthesized
through acid–base neutralization but in two different synthetic
routes.
Fig. 7 Radar plot graphs showing the effects of IL 13 on some chlo-
rophyll a fluorescence parameter calculated from OJIP curve.
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+
OH), 5.97 (s, 1H, CHCl), 8.99 (s, br, 2H, NH2 ); 13C NMR (100
MHz, DMSO-d6) d (ppm) ¼ 32.71 (CH3), 50.56 (CH2), 56.47
(CH2), 70.47 (CHCl2), 166.45 (COOꢁ).
5.2.1 Route I (preparation of ILs 1–12). Hydroxylalkyl-
amines (0.01 mol) dissolved in methanol (20 mL) was added to
a round-bottom ask equipped with a magnetic stirrer. Next,
0.011 mol of dichloroacetic acid was added dropwise and the
mixture was stirred at room temperature for 24 h. Methanol was
removed via rotary evaporation, and the desirable product was
thoroughly washed with diethyl ether and nally dried under
5.3.6 IL 6. Yield: 98%; light yellow liquid; 1H NMR (400
MHz, DMSO-d6) d (ppm) ¼ 0.87 (t, 3H, 3JH–H ¼ 8.0 Hz, CH3), 1.31
(sext, 2H, CH2), 1.57 (m, 2H, CH2), 2.85 (m, 2H, CH2), 2.94 (t, 2H,
3JH–H ¼ 4.0 Hz, C2), 3.63 (t, 2H, 3JH–H ¼ 8.0 Hz, CH2), 5.40 (s, br,
1H, OH), 5.93 (s, 1H, CHCl), 8.45 (s, br, 2H, NH2+); 13C NMR (100
MHz, DMSO-d6) d (ppm) ¼ 13.55 (CH3), 19.35 (CH2), 27.40
(CH2), 46.59 (CH2), 48.90 (CH2), 56.47 (CH2), 70.51 (CHCl2),
165.43 (COOꢁ).
ꢀ
a reduced pressure at 50 C for 24 h.
5.2.2 Route II (preparation of ILs 13–15). A total of 0.01 mol
of quaternary ammonium bromide was rst dissolved in
methanol and a stoichiometric amount of saturated methanol
solution of potassium hydroxide was added. The anion
exchange progress was monitored with the addition of an
AgNO3 solution. Upon completing the substitution of bromide
via hydroxide, no AgBr precipitation could be found. The by-
product (KBr) was precipitated and separated via ltration
through a sintered glass lter (Synthware Co., Ltd, Beijing,
China). Then, the lter (quaternary ammonium hydroxide) was
transferred to a round-bottom ask equipped with a magnetic
stirrer and was neutralized with dichloroacetic acid at a 1 : 1.1
molar ratio. The mixture was stirred at room temperature for
another 24 h. Methanol was removed via rotary evaporation,
followed by adding diethyl ether to the residue. Aer removing
the solvents by evaporation, the desirable product was obtained
5.3.7 IL 7. Yield: 93%; light yellow liquid; 1H NMR (400
MHz, DMSO-d6) d (ppm) ¼ 1.08 (dd, 6H, 3JH–H ¼ 8.0 Hz, 4.0 Hz,
CH3), 2.76 (m, 4H, CH2), 2.96 (m, 2H, CH2), 3.95 (m, 2H, CH),
5.25 (s, br, 2H, OH), 5.97 (s, 1H, CHCl), 8.63 (s, br, 2H, NH2+);
13C NMR (100 MHz, DMSO-d6) d (ppm) ¼ 21.18 (CH3), 53.68
(CH2), 62.03 (CH), 70.52 (CHCl2), 165.46 (COOꢁ).
5.3.8 IL 8. Yield: 99%; light yellow liquid; 1H NMR (400
MHz, DMSO-d6) d (ppm) ¼ 2.80 (s, 3H, CH3), 3.19 (t, 4H, 3JH–H
¼
3
8.0 Hz, CH2), 3.73 (t, 4H, JH–H ¼ 8.0 Hz, CH2), 4.23 (s, br, 2H,
OH), 6.02 (s, 1H, CCl), 9.98 (s, br, 1H, NH+); 13C NMR (100 MHz,
DMSO-d6) d (ppm) ¼ 40.56 (CH3), 55.43 (CH2), 57.49 (CH2),
70.13 (CHCl2), 166.03 (COOꢁ).
5.3.9 IL 9. Yield: 94%; light yellow liquid; 1H NMR (400
MHz, DMSO-d6) d (ppm) ¼ 1.16 (t, 6H, 3JH–H ¼ 8.0 Hz, CH3), 3.06
ꢀ
and nally dried under a reduced pressure at 50 C for 24 h.
3
3
(t, 6H, JH–H ¼ 8.0 Hz, CH2), 3.70 (t, 6H, JH–H ¼ 8.0 Hz, CH2),
5.65 (s, br, 2H, OH, NH+), 5.98 (s, 1H, CHCl2); 13C NMR (100
MHz, DMSO-d6) d (ppm) ¼ 8.84 (CH3), 46.92 (CH2), 53.18 (CH2),
5.3 Physicochemical data
5.3.1 IL 1. Yield: 98%; light yellow solid; mp: 68.0–68.8 ꢀC; 55.93 (CH2), 70.44 (CHCl2), 166.32 (COOꢁ).
1H NMR (400 MHz, DMSO-d6) d (ppm) ¼ 2.84 (t, 2H, JH–H
¼
5.3.10 IL 10. Yield: 92%; white solid; mp: 67.4 ꢀC; 1H NMR
3
8.0 Hz, CH2), 3.57 (t, 2H, JH–H ¼ 8.0 Hz, CH2), 5.30 (s, br, 1H, (400 MHz, DMSO-d6) d (ppm) ¼ 3.09 (t, 6H, 3JH–H ¼ 4.0 Hz, CH2),
3
OH), 5.91 (s, 1H, CHCl), 7.98 (s, br, 3H, NH3 ); 13C NMR (100 3.66 (t, 6H, 3JH–H ¼ 4.0 Hz, CH2), 5.26 (s, br, 3H, OH), 5.95 (s, 1H,
+
MHz, DMSO-d6) d (ppm) ¼ 41.28 (CH2), 57.65 (CH2), 70.84 CHCl); 13C NMR (100 MHz, DMSO-d6) d (ppm) ¼ 55.81 (CH2),
(CHCl2), 165.50 (COOꢁ).
56.43 (CH2), 70.70 (CHCl2), 165.63 (COOꢁ).
1
5.3.2 IL 2. Yield: 95%; white solid; mp: 109.8–110.8 ꢀC; H
5.3.11 IL 11. Yield: 90%; light yellow solid; mp: 63.8–
3
1
ꢀ
NMR (400 MHz, DMSO-d6) d (ppm) ¼ 1.08 (d, 3H, JH–H
¼
68.0 C; H NMR (400 MHz, DMSO-d6) d (ppm) ¼ 1.08 (d, 9H,
4.0 Hz, CH3), 2.60 (m, 1H, CH2), 2.82 (dd, 1H, JH–H ¼ 8.0 Hz, 3JH–H ¼ 8.0 Hz, CH3), 3.12 (m, 6H, CH2), 4.06 (m, 3H, CH), 4.68
3
4.0 Hz, CH2), 3.82 (m, 1H, CH), 5.44 (s, br, 1H, OH), 5.94 (s, 1H, (s, br, 3H, OH), 6.05 (s, 1H, CHCl); 13C NMR (100 MHz, DMSO-
+
CHCl), 8.08 (s, br, 3H, NH3 ); 13C NMR (100 MHz, DMSO-d6) d6) d (ppm) ¼ 20.91 (CH3), 21.41 (CH3), 21.60 (CH3), 60.14 (CH),
d (ppm) ¼ 20.97 (CH3), 45.66 (CH2), 63.14 (CH), 70.83 (CHCl2), 60.81 (CH), 61.15(CH2), 61.83 (CH2), 69.99 (CHCl2), 165.59
165.50 (COOꢁ).
(COOꢁ).
5.3.3 IL 3. Yield: 97%; light yellow liquid; 1H NMR (400
5.3.12 IL 12. Yield: 90%; yellow liquid; 1H NMR (400 MHz,
MHz, DMSO-d6) d (ppm) ¼ 1.69 (quint, 2H, 3JH–H ¼ 8.0 Hz, CH2), DMSO-d6) d (ppm) ¼ 3.12 (s, 9H, CH3), 3.06 (t, 2H, JH–H
¼
3
3
3
2.84 (t, 2H, JH–H ¼ 8.0 Hz, CH2), 3.47 (t, 2H, JH–H ¼ 8.0 Hz, 4.0 Hz, CH2), 3.82 (m, 2H, CH2), 5.92 (s, br, 1H, OH), 5.85 (s, 1H,
CH2), 4.84 (s, br, 1H, OH), 5.90 (s, 1H, CHCl), 7.95 (s, br, 3H, CHCl); 13C NMR (100 MHz, DMSO-d6) d (ppm) ¼ 38.89 (CH3),
+
NH3 ); 13C NMR (100 MHz, DMSO-d6) d (ppm) ¼ 30.17 (CH2), 55.43 (CH2), 57.49 (CH2), 70.13 (CHCl2), 166.03 (COOꢁ).
36.64 (CH2), 57.93 (CH2), 71.00 (CHCl2), 165.09 (COOꢁ).
5.3.13 IL 13. Yield: 94%; white solid; mp: 38.9 ꢀC; 1H NMR
5.3.4 IL 4. Yield: 97%; light yellow liquid; 1H NMR (400 (400 MHz, DMSO-d6) d (ppm) ¼ 0.84 (t, 3H, 3JH–H ¼ 8.0 Hz, CH3),
MHz, DMSO-d6) d (ppm) ¼ 2.96 (t, 2H, 3JH–H ¼ 4.0 Hz, CH2), 3.45 1.23 (m, 16H, CH2), 1.66 (m, 2H, CH2), 3.08 (s, 3H, CH3), 3.39
3
3
(t, 2H, JH–H ¼ 4.0 Hz, CH2), 3.51 (t, 2H, JH–H ¼ 8.0 Hz, CH2), (m, 4H, CH2), 3.43 (m, 4H, CH2), 3.81 (m, 4H, CH2), 5.67 (s, br,
3.59 (t, 2H, 3JH–H ¼ 8.0 Hz, CH2), 5.92 (s, 1H, CHCl), 7.19 (s, br, 2H, OH), 5.83 (s, 1H, CHCl); 13C NMR (100 MHz, DMSO-d6)
3H, NH3+); 13C NMR (100 MHz, DMSO-d6) d (ppm) ¼ 38.74 d (ppm) ¼ 14.05 (CH3), 21.66 (CH2), 22.19 (CH2), 25.88 (CH2),
(CH2), 60.17 (CH2), 66.67 (CH2), 70.81 (CH2), 72.26 (CHCl2), 28.60 (CH2), 28.80 (CH2), 28.92 (CH2), 29.02 (CH2), 29.10 (CH2),
165.57 (COOꢁ).
31.38 (CH2), 49.05 (CH3), 54.83 (CH2), 58.87 (CH2), 59.92 (CH2),
5.3.5 IL 5. Yield: 96%; light yellow liquid; 1H NMR (400 62.45 (CH2), 63.25 (CH2), 71.41 (CHCl2), 164.43 (COOꢁ).
1
MHz, DMSO-d6) d (ppm) ¼ 2.54 (s, 3H, CH3), 2.95 (t, 2H, 3JH–H
¼
5.3.14 IL 14. Yield: 93%; white solid; mp: 52.3–53.6 ꢀC; H
8.0 Hz, CH2), 3.63 (t, 2H, JH–H ¼ 8.0 Hz, CH2), 5.48 (s, br, 1H, NMR (400 MHz, DMSO-d6) d (ppm) ¼ 0.85 (t, 3H, 3JH–H ¼ 8.0 Hz,
3
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CH3), 1.23 (m, 20H, CH2), 1.66 (m, 2H, CH2), 3.07 (s, 3H, CH3),
Each salt was rst dissolved in ethanol, and then diluted
3.40 (s, 8H, CH2), 3.81 (m, 4H, CH2), 5.43 (s, br, 2H, OH), 5.80 (s, with deionized water containing 0.1% Tween 80 to form an
1H, CHCl); 13C NMR (100 MHz, DMSO-d6) d (ppm) ¼ 14.04 emulsiable solution in different concentrations from 1.25 to
(CH3), 21.64 (CH2), 22.17 (CH2), 25.86 (CH2), 28.58 (CH2), 28.78 15 mg mLꢁ1. In greenhouse tests, the solutions were sprayed
(CH2), 28.89 (CH2), 29.01 (CH2), 29.08 (CH2), 29.13 (CH2), 31.36 using a laboratory spray bottle. There were three replicates for
(CH2), 49.02 (CH3), 54.82 (CH2), 58.54 (CH2), 59.65 (CH2), 62.43 each treatment. A mixture of the same amount of deionized
(CH2), 63.22 (CH2), 71.57 (CHCl2), 164.04 (COOꢁ).
water, ethanol plus Tween 80 was used as a blank control.
1
5.3.15 IL 15. Yield: 90%; white solid; mp: 80.9–81.8 ꢀC; H Dichloroacetic acid was applied as a positive control.
NMR (400 MHz, DMSO-d6) d (ppm) ¼ 0.85 (t, 3H, 3JH–H ¼ 8.0 Hz,
5.6.2 Pre emergence tests. Loamy sand in plastic pots (5 cm
CH3), 1.23 (m, 26H, CH2), 1.66 (m, 2H, CH2), 3.07 (s, 3H, CH3), depth) was wetted with water, and ten sprouting seeds of the
3.37 (s, 4H, CH2), 3.43 (m, 4H, CH2), 3.80 (m, 4H, CH2), 5.40 (s, weeds were planted in earth (0.6 cm depth) in a greenhouse at
br, 2H, OH), 5.82 (s, 1H, CHCl); 13C NMR (100 MHz, DMSO-d6) a temperature of 25 ꢀC, a relative humidity of 60%, and
d (ppm) ¼ 20.82 (CH3), 21.38 (CH2), 21.56 (CH2), 60.33 (CH3), a photoperiod (day/night hours) of 16/8. 2 mL of emulsiable
61.06 (CH2), 61.40 (CH2), 62.00 (CH2), 70.47 (CHCl2), 165.28 solution of each salt was applied directly to the surface of the
(COOꢁ).
soil using a laboratory spray bottle. Then the pots were placed in
a greenhouse, being watered daily.
5.4 Solubilities
5.6.3 Post emergence tests. Aer emergence, for the grass
species 10 plants were grown per pot, but for the larger broad-
leaf weed species, 3–5 plants were grown in each pot. The
seedlings of the weeds at the 4–6 leaf stage were sprayed with
the tested salts at different concentrations from 1.25 to 15 mg
mLꢁ1. Subsequently, the weeds were returned to the green-
house, being watered daily. Their responses to the individual
treatments were recorded at 2, 4, 7, 11, 14, and 21 days aer
application.
Dichloroacetic acid was applied as a positive control. A
similar set of experiments was conducted.
5.6.4 Data collection. Aer 21 days of treatment, the aerial
parts of the weeds were harvested and the fresh weights were
recorded. The herbicidal efficacies were measured from the
fresh weights.
The solubilities of the ILs in eight representative solvents were
determined according to the protocols in Vogel's Textbook of
Practical Organic Chemistry.52 The solvents were selected for
analyses and arranged in decreasing order of Snyder polarity
index: water, 9.0; methanol, 6.6; DMSO, 6.5; acetonitrile, 6.2;
acetone, 5.1; isopropanol, 4.3; diethyl ether, 2.8; and toluene,
2.3. A 0.1 g sample of each salt was added to a certain volume of
the solvent. Based on the volume of the solvent used, three types
of behaviors were recorded: ‘soluble’ applies to compounds that
dissolved in 1 mL of solvent, ‘limited solubility’ applies to
compounds that dissolved in 3 mL of solvent, and ‘not soluble’
applies to compounds that did not dissolve in 3 mL of solvent.
ꢀ
The treatments were performed at 25 C.
The fresh weight inhibition rates relative to the water blank
control was then calculated using the following formula (eqn
(1)):
5.5 Surface tension measurement
The surface tension measurements were measured with the
platinum ring method using a ZF-2 tensiometer at 298 ꢂ 0.2 K.
The tensiometer was calibrated against ultrapure water, which
was generally 72.00 ꢂ 0.50 mN mꢁ1. The IL solutions in
Fresh weight inhibition rate (%) ¼ (1 ꢁ T/C) ꢃ 100
(1)
different concentrations were freshly prepared using ultrapure where T is the average fresh weight in the treatment, and C is
water. The platinum ring was thoroughly cleaned and dried the average fresh weight in the blank control.
before each measurement. Then the platinum ring was dipped
to the solutions at a slow speed and stopped when the surface
5.7 Crop selectivity
tension values remained unchanged, indicating that equilib-
The cotton seeds (Gossypium hirsutum L.) were planted in plastic
rium had been reached. In all cases, ve successive measure-
pots (5 cm depth) and grown in a greenhouse at a temperature
ments were performed, and the standard deviation did not
ꢀ
of 25 C, a relative humidity of 60%, and a photoperiod (day/
exceed 0.20 mN mꢁ1
.
night hours) of 16/8. When the cottons reached the 4–6 true
leaf stage, crop safety experiments were conducted at the same
concentrations ranging from 1.25 to 15 mg mLꢁ1. Aer 21 days
of treatment, the fresh weight inhibition rates of the cottons
were then calculated by using the above formula.
5.6 Herbicidal activity assays of ILs 1–15
5.6.1 Weed species and preparation of the IL solutions.
Herbicidal activity was evaluated against both grass and
broadleaf weeds grown in greenhouses: Eleusine indica (L.)
Gaertn., Amaranthus retroexus L., Eclipta prostrata, Xanthium
sibiricum Patr, Chenopodium album L. and Solanum nigrum L.
5.8 Statistical analysis
The weed seeds were collected from the experimental farm of Data analyses were conducted using the statistical analysis
the Institute of Cotton Research of the Chinese Academy of soware (SPSS, Standard Version 16.0, SPSS Inc., USA). The
Agricultural Sciences (CAAS), PR China. These species are concentration at which 50% inhibition EC50 or 90% inhibition
malignant weeds that have become problematic in the cotton EC90 and its 95% condence intervals (weeds), as well as 10%
elds in Northern China.
inhibition EC10 (cotton) were calculated by probit analyses
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based on the logarithm of the concentration versus the percent
inhibition. All quantitative data were presented as the mean ꢂ
SD of at least three independent experiments using the Tukey's
multiple post hoc test. P < 0.05 was considered as a statistically
signicant difference.
M. P. Mokoena, A. O. Olaniran and J. R. Shi, Plant Pathol.,
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EC90(weeds)
where EC90 equals a 90% effect on the weeds and EC10 equals
a 10% effect on the crop, respectively.
The more SI increases above 2, the more selective IL becomes
in the crop species.
´
´
´
´
5 F. Orellana-Garcıa, M. A. Alvarez, V. Lopez-Ramon, J. Rivera-
´
Utrilla, M. Sanchez-Polo and A. J. Mota, Chem. Eng. J., 2014,
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5.9 Chlorophyll uorescence determination
´
6 C. Delye, M. Jasieniuk and V. L. Corre, Trends Genet., 2013,
Chlorophyll uorescence determination was assessed 24 h aer
spray application of IL 13. Prior to the measurements, C. album
was kept in the dark for 15 min, then the leaves were excited by
saturating red light pulse (3000 mmol mꢁ2 sꢁ1) from three light-
emitting diodes (650 nm). The pulse duration was 1 s. Chloro-
29, 649.
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phyll
a uorescence induction curves (OJIP curves) were
measured with a Handy-PEA chlorophyll uorometer (Plant
Efficiency Analyzer, Hansatech, King's Lynn, UK). The JIP-test was
used to analyze each chlorophyll a uorescence parameter. It
provided information about biophysical properties of the
photosynthetic energy conversion and transport of electrons.46–51
Some uorescence parameters were highlighted: (a) area: total
complementary area between Fo and Fm (reecting the size of the
plastoquinone pool); where Fo is minimal uorescence when PSII
RCs are all open, Fm: maximal uorescence when PSII RCs are all
closed; (b) the specic energy uxes per reaction center RC for
absorbance (ABS/RC), for transport (ET0/RC), for trapping TR0/RC
and for reduction (RE0/RC); (c) the phenomenological energy
uxes per excited cross section for absorbance (ABS/CSm), for
transport (ETo/CSm), for trapping (TRo/CSm) and for reduction
(RE0/CSm); (d) the performance index: PIABS ¼ (RC/ABS) ꢃ (4po/(1
ꢁ 4po)) ꢃ (jEo/(1 ꢁ jEo)), where, RC is for reaction center; ABS is
for absorption ux; 4po is the maximum yield of primary
photochemistry (4po ¼ TR0/ABS) and jEo is the probability that
a trapped exciton moves an electron into the electron transport
chain beyond QA (jEo ¼ ET0/TR0).
9 J. Pernak, M. Niemczak, R. Giszter, J. L. Shamshina,
G. Gurau, O. A. Cojocaru, T. Praczyk, K. Marcinkowska and
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13 G. Tang, B. T. Wang, G. L. Ding, W. B. Zhang, Y. Liang,
C. Fan, H. Q. Dong, J. L. Yang, D. D. Kong and Y. S. Cao,
Sci. Total Environ., 2018, 616–617, 128.
14 P. Bałczewski, R. Biczak, M. Turek, B. Pawłowska,
´
˙
E. Rozycka-Sokołowska, B. Marciniak, M. Deska and
J. Skalik, Ecotoxicol. Environ. Saf., 2018, 163, 408.
15 M. Niemczak, R. Giszter, K. Czerniak, K. Marcinkowska and
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G. Głowacki, T. Praczyk, K. Marcinkowska and
R. D. Rogers, J. Agric. Food Chem., 2015, 63, 3357.
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Conflicts of interest
There are no conicts to declare.
Acknowledgements
´
18 A. Syguda, A. Gielnik, A. Borkowski, M. Wozniak-
Karczewska, A. Parus, A. Piechalak, A. Olejnik, R. Marecik,
Ł. Ławniczak and Ł. Chrzanowski, New J. Chem., 2018, 42,
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This study was supported by the Cotton Industrial Technology
System of China (grant number CARS-15-20), the National Key
Research and Development Plan of China (grant number
2016YFD0200700), and the National Natural Science Founda-
tion of China (grant number 31801751).
19 A. Syguda, K. Marcinkowska and K. Materna, RSC Adv., 2016,
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20 H. Choudhary, J. Pernak, J. L. Shamshina, M. Niemczak,
R. Giszter, Ł. Chrzanowski, T. Praczyk, K. Marcinkowska,
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Notes and references
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