Phytotoxicity of new furan-derived aminophosphonic acids, N -Aryl furaldimines and 5-nitrofuraldimine

Article abstract of DOI:10.1021/jf402401z

The aim of this work was to synthesize selected furaldimines and their aminophosphonic derivatives and evaluation the phytotoxicity of new obtained products according to OECD 208 Guideline. Four Schiff bases, N-furfurylidene-p-anisidine (1a), N-furfurylid

Full text of DOI:10.1021/jf402401z

Article
pubs.acs.org/JAFC
Phytotoxicity of New Furan-derived Aminophosphonic Acids, N‑Aryl
Furaldimines and 5‑Nitrofuraldimine
Agnieszka Matusiak,† Jarosław Lewkowski,*,† Piotr Rychter,*,‡ and Robert Biczak‡
†Department of Organic Chemistry, Faculty of Chemistry, University of Łod
́
z, Tamka 12, 91-403 Łodz, Poland
́
́
́
‡Institute of Chemistry, Environmental Protection and Biotechnology, Jan Długosz University in Częstochowa, 42-200 Częstochowa,
13/15 Armii Krajowej Av., Poland
S
* Supporting Information
ABSTRACT: The aim of this work was to synthesize selected furaldimines and their aminophosphonic derivatives and
evaluation the phytotoxicity of new obtained products according to OECD 208 Guideline. Four Schiff bases, N-furfurylidene-p-
anisidine (1a), N-furfurylidene-p-toluidine (1b), N-furfurylidene-benzhydrylamine (1c), and N-(2-nitrofurfurylidene)-p-toluidine
(1d) were synthesized and three new furan-derived N-substituted aminomethylphosphonic acids, namely: 2-furyl N-(p-
methoxyphenyl)-aminomethylphosphonic acid (2a), 2-furyl N-(p-methylphenyl)-aminomethylphosphonic acid (2b) and 2-furyl
N-(diphenylmethyl)-aminomethylphosphonic acid (2c) were synthesized by the addition of in situ generated bis-(trimethylsilyl)
phosphite to azomethine bond of corresponding Schiff bases 1a−c. Three Schiff bases 1a−b and 1d as well as all three
aminophosphonic acids 2a−c were analyzed in regard with their phytotoxicity toward two plants, radish (Raphanus sativus) and
oat (Avena sativa).
It has been found that tested N-furfurylidene-p-anisidine (1a), N-(2-nitrofurfurylidene)-p-toluidine (1d) and aminophosphonic
acids 2a−c are toxic for selected plants. N-furfurylidene-p-toluidine (1b) did not show any ecotoxicological impact in used plant
growth test.
KEYWORDS: furfuraldimines, 5-nitrofurfuraldimine, Schiff bases, aminophosphonic acids, phytotoxicity test, environmental protection,
ecotoxicology, OECD standard
etc.) became generally less popular due to adverse effects, it is
to stress that nifurtimox, apart from benznidazole is a second
effective drug for treatment of Trypanosoma cruzi or
Trypanosoma brucei infections (Chagas disease and sleeping
sickness).9 It is then obvious that studies on antimicrobial
properties on 5-nitrofurfural Schiff bases are being performed,
as this group is structurally similar to microbiologically active 5-
nitrofurfural hydrazones.
INTRODUCTION
■
It is well-known that aminophosphonic systems are highly
biologically active compounds especially being inhibitors of
various enzymes.1,2 Aminophosphonates has been also attracted
much as pesticides with potential application in agrochemistry
and their synthesis and assessment of aminophosphates
bioactivity in plants has been already reported.3−5
Nowadays there is a great problem associated with the
application of conventional pesticides or fertilizers causing
undesirable side effect after application. The presence of
pesticides soil, water, and air has raised concerns for the
protection of the natural environment. Unfortunately, only a
part of the applied amount of pesticide reach their targets,
therefore, the excess amount of these agrochemicals is
distributed into the environment. Therefore, over the last
decades, much effort has been put into the research of novel,
intelligent crop protection chemicals in order to reduce their
environmental impact.
On the other hand, furans play their important biological
function and it does not seem strange that there were many
successful attempts to construct drugs bearing furyl moiety. It is
to mention here cefuroxime, the cephalosporin antibiotics or a
histamine H2-receptor antagonist-ranitidine. But the largest and
most common group of drugs bearing a furan moiety derives
from 5-nitrofurfural. Their action is based on the redox
enzymatic reaction of nitrofurfural, which is reduced by
nitroreductase enzymes to an active radical reacting with
nucleic acids and proteins.6−8 Although nitrofurfural-deriving
antimicrobial chemotherapeutics (nitrofurantoin, nifuroxazide
Recently, aminophosphonates bearing furan and N-methoxy-
or N-methylphenyl moieties have been found to have important
in vitro action toward various types of cancer such as human
leukemia cells or squamous esophageal cancer cells.10,11 These
reports demonstrated also cytotoxic properties of their parent
2-furaldimines.
Boduszek’s studies12 revealed that the tripeptide bearing
furylaminophosphonic moiety is the irreversible inhibitor of
chymotrypsin, human neutrophilic elastase and pig pancreas
elestase. Moreover, biological studies of diphenyl (2-furyl)-N-
benzylaminomethyl-phosphonate demonstrated its herbicidal
action inhibiting the root growth of Lepidium sativum or Cumus
sativus.12
Having in mind that furan-derived aminophosphonic
compounds as well as their parent imines demonstrate the
general biological activity, we decided to investigate, what will
Received: March 11, 2013
Revised: July 17, 2013
Accepted: July 19, 2013
Published: July 19, 2013
© 2013 American Chemical Society
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Journal of Agricultural and Food Chemistry
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concentrated under reduced pressure and the residue was dissolved in
dry methanol and it was stirred for 30−45 min until precipitation of a
solid, which was filtered off and collected. In a case, if the solid did not
precipitated, 10−20 mL of propylene oxide was added and the mixture
was refrigerated for 3−7 days and the solid precipitate was collected by
filtration.
be their action on plant growth. Therefore, objectives of this
study were to evaluate the phytotoxicity of three biologically
active10,11 furaldimines: N-furfurylidene-p-anisidine (1a), N-
furfurylidene-p-toluidine (1b), and N-(2-nitrofurfurylidene)-p-
toluidine (1d) and three newly synthesized aminophosphonic
acids bearing furan moiety, namely: 2-furyl N-(p-
methoxyphenyl)aminomethylphosphonic acid (2a), 2-furyl N-
(p-methylphenyl)-aminomethylphosphonic acid (2b), and 2-
furyl N-(diphenylmethyl)-aminomethylphosphonic acid (2c)
toward Raphanus sativus (radish) and Avena sativa (oat). The
phytotoxicity evaluation was performed using OECD 208,
Terrestrial Plant Growth Test, as its application to the
polymeric degradation products or ionic liquids has been
successfully reported in literature.13,14
(2-Furyl)-N-(4-methoxyphenyl)aminomethylphosphonic Acid
1
(2a). Yield: 0.49 g (69%); Mp: 177−180 °C. H NMR (600 MHz,
DMSO−D6): δ 7.52 (d, J = 1.8 Hz, H5fur, 1H); 6.74 (d, J = 9.0 Hz, p-
C6H4, 2H); 6.68 (d, J = 9.0 Hz, p-C6H4, 2H); 6.35 (dd, J = 1.8 and 3.2
Hz, H4fur, 1H); 6.32 (d, J = 3.2 Hz, H3fur, 1H); 4.63 (d, 2JPH = 20.0 Hz,
CHP, 1H); 3.62 (s, OCH3, 3H). 13C NMR (250 MHz, DMSO−D6): δ
152.67 (Carom); 151.96 (Carom); 142.32 (d, 3JCP = 3.5 Hz, Cfur); 141.95
2
(d, JCP = 23.0 Hz, Cfur); 114.95 (Carom); 114.83 (Carom); 110.84 (d,
4
5JCP = 2.9 Hz, Cfur); 108.01 (d, JCP = 9.7 Hz, Cfur); 55.73 (OCH3);
51.69 (d, 1JCP = 153.5 Hz, C−P). 31P NMR (243 MHz, DMSO−D6):
δ 15.85. Elem. anal. Calctd. for C12H14NO5P: C, 50.89; H, 4.98; N,
4.95. Found: C, 50.69; H, 4.97; N, 5.07.
The study of phytotoxicity was not performed for the Schiff
base 1c, because this compound is not known to be biologically
active and therefore it was out of our interest in the structural
and functional point of view.
(2-Furyl)-N-(4-methylphenyl)aminomethylphosphonic Acid (2b).
Yield: 0.47 g (70%); Mp: 120−125 °C. 1H NMR (600 MHz, DMSO−
D6): δ 7.52 (m, H5fur, 1H); 6.86 and 6.62 (AA′XX′ system, 3J = 8.4, 4J
= 1.8 Hz, p-C6H4, 2H); 6.35 (m, H4fur, 1H); 6.32 (m, H3fur, 1H); 4.35
MATERIALS AND METHODS
■
2
(d, JPH = 24.0 Hz, CHP, 1H); 2.15 (s, CH3, 3H). 13C NMR (250
Materials and Chemicals. All solvents (POCh, Poland) were
routinely distilled and dried prior to use. Amines, diethyl phosphite,
and furfural (Aldrich, Poland) were used as received. NMR spectra
were recorded on a Bruker Avance III 600 MHz operating at 600 MHz
(1H NMR) and 243 MHz (31P NMR). TMS was used as the internal
MHz, DMSO−D6): δ 152.52 (Carom); 145.61 (d, 2JCP = 21.6 Hz, Cfur);
142.35 (d, 3JCP = 3.5 Hz, Cfur); 129.61 (Carom); 125.86 (Carom); 113.89
(Carom); 110.84 (d, 5JCP = 2.9 Hz, Cfur); 108.03 (d, 4JCP = 9.6 Hz, Cfur);
51.07 (d, 1JCP = 153.5 Hz, C−P); 20.50 (CH3). 31P NMR (243 MHz,
DMSO−D6): δ 15.76. Elem. anal. Calctd. for C12H14NO4P•2/3H2O:
C, 51.62; H, 5.53; N, 5.02. Found: C, 51.59; H, 5.49; N, 4.96.
(2-Furyl)-N-(diphenylmethyl)aminomethylphosphonic Acid (2c).
Yield: 0.55 g (64%); Mp: 138−140 °C. 1H NMR (600 MHz, DMSO−
D6): δ 7.61−7.59 (d, J = 1.8 Hz, H5fur, 1H); 7.45−7.41 (m, PhH, 2H);
7.33−7.31 (m, PhH, 4H); 7.30−7.27 (m, PhH, 2H); 7.25−7.19 (m,
PhH, 2H); 6.44 (dd, J = 1.8 and 3.6 Hz, H4fur, 1H); 6.29−6.28 (m,
1
standard for H NMR and phosphoric acid was used as the external
standard for 31P NMR. Elemental analyses were carried out at the
Centre for Molecular and Macromolecular Science of the Polish
́
́
Academy of Science in Łodz, Poland.
Synthesis of Schiff Bases 1a−d. Furfural derivative (2.5 mmol)
was dissolved in methanol (15 mL) and to this solution, amine (2.5
mmol) was added. The mixture was stirred at room temperature for 24
h, then solvent was evaporated and residue dried on vacuum to obtain
pure Schiff base 1a−d:
H3fur, 1H); 4.75 (s, CH, 1H); 3.73 (d, 2JPH = 20.0 Hz, CHP, 1H). 13
C
NMR (250 MHz, DMSO−D6): δ 152.34 (Cfur); 144.62 (Carom);
3
5
142.81 (d, JCP = 39.8 Hz, Cfur); 128.90 (d, JCP = 15.0 Hz, Carom);
N-Furfurylidene-p-anisidine (1a). Quantitative yield (0.50 g), mp =
127.78 (Carom); 127.52 (d, 6JCP = 4.5 Hz, Carom); 110.96 (Cfur); 108.41
60−64 °C, 68−70 °C.15 1H NMR (CDCl3, 600 MHz): δ 8.30 (s,
(d, 4JCP = 6.0 Hz, Cfur); 64.42 (d, 3JCP = 14.1 Hz, CH); 53.35 (d, 1JCP
=
CHN, 1H), 7.59 (d, J = 1.8 Hz, H5fur, 1H), 7.25 (d, J = 9.0 Hz, p-
154.5 Hz, C−P). 31P NMR (243 MHz, DMSO−D6): δ 16.40. Elem.
anal. Calctd. for C18H18NO4P: C, 62.97; H, 5.28; N, 4.08. Found: C,
62.82; H, 5.39; N, 4.33.
fur
C6H4, 2H), 6.92 (d, J = 9.0 Hz, p-C6H4, 2H), 6.91 (d, J = 3.6 Hz, H3
,
1H), 6.54 (dd, J = 3.6 and 1.8 Hz, H3fur, 1H), 3.82 (s, OCH3, 3H).
N-Furfurylidene-p-toluidine (1b). Quantitative yield (0.46 g), mp =
35−38 °C, 41−42 °C.10 1H NMR (CDCl3, 600 MHz): δ 8.30 (s,
CHN, 1H), 7.59 (d, J = 1.8 Hz, H5fur, 1H), 7.19−7.15 (AA′BB′
system, J = 9.0 Hz, p-C6H4, 4H), 6.92 (d, J = 3.6 Hz, H3fur, 1H), 6.54
(dd, J = 3.6 and 1.8 Hz, H3fur, 1H), 2.36 (s, CH3, 3H).
Evaluation of Potential Toxicity of New Synthesized
Compounds. The plant growth test was performed under laboratory
conditions by adapting the OECD 208 Terrestrial Plants Growth Test
and the PN-ISO 11269−2:2001 International Standard for furan-
derived aminophosphonic acids 2a−c, N-aryl furaldimines 1a−b and
5-nitrofuraldimine 1d, using oat (Avena sativa) as a monocotyledonous
plant and common radish (Raphanus sativus L. subvar. radicula Pers.), a
dicotyledonous plant.18,19
N-Furfurylidene-benzhydrylamine (1c). Quantitative yield (0.65
g), mp = 104−105 °C, 105−106 °C.16 1H NMR (CDCl3, 600 MHz):
δ 8.19 (s, CHN, 1H), 7.53 (d, J = 1.8 Hz, H5fur, 1H), 7.36−7.34 (m,
C6H5, 4H), 7.32−7.29 (m, C6H5, 4H), 7.24−7.22 (m, C6H5, 2H), 6.81
fur
(dd, J = 3.6 and 0.6 Hz, H3fur, 1H), 6.47 (dd, J = 3.6 and 1.8 Hz, H3
1H), 5.58 (s, CH, 1H).
,
According to mentioned above standards the plant growth test of
synthesized samples was carried out in sandy soil characterized with
parameters as follows: granulometric composition of soil −80% sand,
12% dust and loam, organic carbon content of approximately 0.9%,
pH(KCl) equal to 5.8 and moisture ranged from 15 to 18%.
To prepare the test, pots made from polypropylene (diameter of 90
mm and capacity 300 cm3) were filled, with the control soil and with
the soil with the test furaldiminines and their aminophosphonic
derivatives added at a specific concentration. Twenty identical seeds of
each of the selected plant species, originating from the same source,
were sown into the soil. Plants were grown for 14 days under
controlled conditions maintaining constant humidity, light intensity
(7000 lx), and temperature, 20 2 °C. After that time, seedlings were
counted and the dry and fresh weight of the plants above the soil
surface was determined. After that time, seedlings were counted and
the dry and fresh parts of the plants above the soil was weight.
The performed plant growth test comprised two testing steps: a
preliminary test and a final, particular test. According to PN-ISO
11269−2:2001 standard, the preliminary test was carried out to
determine the range of concentrations of compounds affecting the soil
N-(2-Nitrofurfurylidene)-p-toluidine (1d). Quantitative yield (0.57
g), mp = 131−133 °C, 130−130.5 °C.17 1H NMR (CDCl3, 600
fur
MHz): δ 8.41 (s, CHN, 1H); 7.42 (dd, J = 4.2 and 0.6 Hz, H3
,
1H); 7.24−7.20 (m, AA′BB′ system, p-C6H4, 4H); 7.17 (dd, J = 4.2
and 0.6 Hz, H4fur, 1H); 2.39 (s, CH3, 3H).
General Procedure for Preparation of Aminophosphonic
Acids 2a−c. Furfural (2.5 mmol, 0.24 g) was dissolved in methanol
(15 mL) and to this solution, amine (2.5 mmol) was added. The
mixture was stirred at room temperature for 24 h, and obtained imine
was used for further conversion without being isolated. To confirm
completion of the reaction, 1 mL sample was taken, evaproated and
1
dissolved in CDCl3 and H NMR spectrum was recorded.
Diethyl phosphite (2.5 mmol) was dissolved in dry dichloro-
methane (10 mL) and to this solution bromotrimethylsilane (6.8
mmol, 0.9 mL) was added dropwise for 10−15 min. The mixture was
stirred for 1 h at room temperature, a solution of an appropiate imine
(2.5 mmol) in dry dichloromethane (10 mL) was added and the
mixture was refluxed for 4 h. Then, the reaction mixture was
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Scheme 1. Synthesis of Schiff Bases 1a−d and Acids 2a−c
Figure 1. Changes of fresh weight value of oat and radish sprouts in toxicity test for aminophosphonic derivatives (aminophosphonic acids 2a-c).
quality, therefore prepared samples were introduced to the soil at the
following concentrations: 0 mg (control), and 1 mg, 10 mg, 100 mg,
and 1000 mg/kg of soil dry weight.
In the final test, concentrations were arranged in a geometric
progression with a factor of 2, starting from the lowest concentration
that reduces the germination and growth of plants.
In the experiment for aminophosphonic derivatives (2a-c), this
concentration was found to be 1000 mg of the tested compound per 1
kg of soil; therefore, concentrations of 200 mg, 400 mg, and 800 mg/
kg of soil dry weight were used in the final tests.
In preliminary test, the toxic concentration of compound 1a was
found to be 100 mg per kg of dry weight of soil, with this respect, the
concentrations 20 mg, 40 mg, and 80 mg/kg of soil dry weight,
respectively, were used in the final tests.
In case of the compound 1d, the mentioned concentration equals
10 mg/kg of soil, hence the concentrations 2, 4, and 6 mg/kg of soil
dry weight has been prepared.
The aminophosphonic derivatives (2a−c) were introduced to the
soil in the form of water solutions. The compounds (1a−b, 1d) were
dissolved in acetone, poured into the pots filled with 70 g of sand and
mixed together. After total evaporation of used solvent, the sand with a
tested compound was thoroughly mixed with 180g of soil. The final
test for compound 1b was not necessary to be made, because no
toxicity in preliminary test has been demonstrated.
Evaluation of phytotoxicity of tested substances at applied
concentrations was performed by comparison of the germination
and (dry and fresh) weight of control plant sprouts (seedlings) with
germination and (dry and fresh) of plants sprouts grown in the soil
contaminated with appropriate amounts of the tested compounds.
The dry weight of the tested plants was determined after drying at
75 °C until constant weight was achieved.
The visual assessment was carried out by digital photography;
pictures were analyzed in the point of view of any type of damage to
the test species, such as growth inhibition, chlorosis and necrosis of
growing plants. Tests for each sample were carried out in triplicate.
Evaluation of the significance of the obtained results was performed
using an analysis of variance (Fisher-Snedecor’s F test), whereas the
least significant difference (LSD0.95) values were calculated using
Tukey’s test.
Taking into account obtained results, the magnitudes of the LOEC
(the lowest observed effect concentration)the lowest concentration
causing observable effects in the form of a reduction in growth and
germination compared with the controland the NOEC (no observed
effect concentration)−the highest concentration not causing observable,
toxic effectswere also determined.
RESULTS AND DISCUSSION
■
Synthesis of Studied Schiff Bases 1a−d and Amino-
phosphonic Acids 2a−c. Schiff bases 1a−d were synthesized
following the previously published procedure by simple mixing
furfural with appropriate amine in methanol and stirring them
at room temperature for 24 h.20 This procedure gave imines
1a−d in quantitative yield. Their identity was confirmed by
1
melting point measurement and H NMR spectral data, which
were compared with literature data.10,15−17 The 1H NMR
spectra showed the diagnostic singlet of a proton of the
azomethine group (CHN) and signals of furan protons.
Aminophosphonic acids 2a−c were synthesized by the
addition of bis-(trimethylsilyl) phosphite to the azomethine
bond of corresponding Schiff bases 1a−c. Bis-(trimethylsilyl)
phosphite has been prepared in situ by the reaction of diethyl
phosphite with bromotrimethylsilane in dichloromethane,21
and its reaction with previously prepared Schiff bases 1a−c was
carried out in dichloromethane. The conversion was monitored
by means of 31P NMR and when the reaction was complete, it
was quenched by methanolysis. After addition of propylene
oxide, resulting acids 2a−c were obtained in 60−70% yields.
(Scheme 1) Their identity has been verified by means of the
1
1H, 13C, and 31P NMR spectroscopy. The H NMR spectra of
acids 2a−c showed diagnostic signals typical for amino-
phosphonic acids, such as a doublet of a HCP group and
typical for 2-substituted furans, that is, two doublets of H5 and
H3 and a doublet of doublets of H4. 13C NMR spectra of acids
2a−c showed a diagnostic doublet at around 50 ppm having a
coupling constant oscillating around 150 Hz corresponding to a
CP bond, which is also typical for aminophosphonic acids.
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Their purity was confirmed by the elemental analysis and
melting point measurements.
between N-furfurylidene-p-toluidine (1b) and N-furfurylidene-
p-anisidine (1a) is the substituent of the phenyl moiety, that is,
the methyl and methoksy group, respectively, which points out
to the methoxy moiety to play a key role in toxicity effect
against tested plants (see SI Figure S1).
Taking into account results obtained during plant growth test
for the 5-nitrofuraldimine 1d (Table 1), the concentration of 10
mg/kg dry weight of soil was toxic for both plants decreasing a
fresh weight of emerged sprouts, (see SI Tables S3 and S4).
Visual evaluation of a plant growth test for compound 1d is
presented in SI Figure S2.
Based on data collected in Table 1, inhibitory effect of
compound 1a on oat fresh matter (crop) at concentration of
100 mg/kg soil was found to be 25%, while for higher
concentration, (1000 mg/kg of soil) inhibition has reached
34%. Its inhibitory effect on radish at concentration level 70,
100, and 1000 mg per kg of soil reached 30, 48, and 100%,
respectively. 5-Nitrofuraldimine 1d revealed to be even more
toxic than the imine 1a for both tested plants. In case of oat,
essential inhibition was observed at concentrations 100 and
1000 mg·kg of soil reaching 63 and 95%, respectively. 5-
Nitrofuraldimine 1d was completely toxic for the radish at
concentration of 100 and 1000 mg/kg of soil and inhibitory
effect has reached 100%. From among both tested plants, the
radish revealed to be more sensitive against tested compounds
1a and 1d.
Final Test of Phytotoxicity of Imines 1a, 1d and
Aminophosphonic Acids 2a−c. Based on results obtained in
a preliminary plant growth test for all used compounds,
according to the PN-ISO 11269−2:2001 standard, only the
imine 1b did not require any additional final test, because at the
highest applied concentration, this compound was found to be
toxic neither for monocotyledonous nor for dicotyledonous
plants.
Preliminary Test of Phytotoxicity Evaluation for
Compounds 1a−b, 1d and 2a−c. Schiff bases were reported
to be investigated in soil, for example, for their effect on
nitrification inhibition22 and applied conditions were similar to
conditions used for our studies. Authors22 did not report any
symptom of problems with their stability, therefore the tested
Schiff bases were a priori considered to be stable under
conditions of the described experiment.
Preliminary tests for aminophosphonic acids 2a−b, in
concentrations up to 100 mg/kg of dry weight soil did not
reveal any significant, negative effect on the germination and
growth of tested plants. The first negative effect of used
aminophosphonic acids 2a−b was noticed at the concentration
1000 mg/kg of dry weight of soil (Figure 1) and, in the highest
applied concentration (1000 mg/kg), they were totally toxic for
both radish and oat seeds, and no germination have been
observed (except for the very slight germination of oat in a test
with compound 2b).
Assessment of the toxicity of aminophosphonic acid 2c for
oat have shown statistically insignificant influence on the
germination and growth of this plant. It is slightly toxic for
radish causing a drop in the fresh weight of sprouts below 90%.
(Figure 1)
Values obtained for the preliminary plant growth test for the
furaldimine 1b and the visual examination of tested plants (see
Supporting Information (SI) Figure S1) have not shown any
significant, negative effect on the germination and growth of
both tested plants even in concentration 1000 mg/kg of dry
weight soil, so the Schiff base 1b is not toxic for any of them.
The first negative symptom of N-furfurylidene-p-anisidine
(1a) such as drop of crop fresh weight (g/pot), has been
observed for both tested plants at the concentration 100 mg/kg
of dry weight of soil (Table 1). At the highest concentration of
As mentioned in the Materials and Methods section, the
concentrations at the final test were prepared in a geometric
progression with a factor of 2, starting from the lowest
concentration that reduces the crop, germination or plant
growth. With this respect, for aminophosphonic acids 2a−c,
this concentration was found to be 1000 mg of the test
compound per 1 kg of soil; therefore, concentrations used in
the final tests were 200 mg, 400 mg, and 800 mg/kg of soil dry
weight. In case of the N-(2-nitrofurfurylidene)-p-toluidine (1d),
the lowest toxic concentration was found to be 10 mg/kg of
soil, hence, its concentrations used for a final test were 2, 4, and
8 mg/kg of soil dry weight.
Table 1. Mean Values of Crop of N-Furfurylidene-p-
anisidine (1a) and N-(2-nitrofurfurylidene)-p-toluidine (1d)
a
versus Control (%)
concentration (mg/kg d.m. of soil)
tested
compound
plant
8
10
20
40
80
100 1000
1a
oat
nd
91
104
13.0
115
6.3
107
4.8
97
75
66
SD
4.2
110
1.6
5.9
70
4.8
52
0.1
radish
SD
nd
101
3.3
8.0
3.9
Increasing the concentration of compounds 2a−c (only for
radish) from 200 to 800 mg/kg of the soil dry weight resulted
in a systematic decrease in the crop fresh weight of total sprouts
and the crop fresh weight per plant as well as a large increase in
dry weight, both for oat and for common radish (Figure 1).
Basing on the results obtained for compounds 2a and 2b in
the final test, the NOEC, that is, the highest concentration of
the tested compound causing no significant decrease in the
plant germination and growth, was estimated to be 100 mg/kg
of the soil dry weight, whereas the LOEC (the lowest
concentration causing a reduction in plant growth/germina-
tion) was 200 mg of the respective substance per kilogram of
the soil dry weight. NOEC and LOEC values for amino-
phosphonic acid 2c were determined only for radish and were
400 and 800 mg per kg soil dry weight. As for N-furfurylidene-
p-anisidine (1a), the NOEC values for oat and radish were 80
1d
oat
105
2.7
82
nd
nd
nd
nd
nd
nd
37
5
SD
4.6
77
1.7
2.1
radish
SD
107
5.7
12.6
a
SD, standard deviation; nd, not determined. Underlined data indicate
values of NOEC and LOEC of tested compounds.
N-furfurylidene-p-anisidine, radish was found to be more
sensitive plant, as no germination of seedlings has been
observed (see SI Tables S1 and S2, Figure S1), while a drop in
the fresh weight of oat sprouts of approximately 35% as
compared to control plants was observed. The toxicity impact
was strictly dependent on concentration of applied compound,
the higher concentration, the stronger inhibition of growth has
occurred. It is to point out that the sole structural difference
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and 40 mg/per kg of dry weight of soil, while the LOEC values,
100 and 80 mg/kg of dry weight of soil, respectively.
In the final test of nitrofuraldimine 1d, for all used
concentrations ranged between 2 and 8 mg per kilogram of
the soil dry weight, the value of crop fresh and dry weight as
well as germination of oat and radish was above 90% as
compared to the control plant. NOEC and LOEC values of this
compound were determined to be 8 and 10 mg/kg of soil dry
weight, respectively, for both plants. They are presented in
Table 2.
investigation of any new synthesized furaldimines and their
aminophosphonic derivatives.
The case of N-(2-nitrofurfurylidene)-p-toluidine 1d is of
different significance, as this Schiff base 1d is highly phytotoxic.
Therefore, derivatives of 5-nitrofurfural, which are known to
have antibacterial and antiprotozoal properties, can logically be
suspected to be strongly phytotoxic too. Therefore, it is to
stress that any wastes containing 5-nitrofurfural-deriving
antibacterial and antiprotozoal drugs must be handled carefully
because they can be very hazardous for plants. However, the
problem is still on study and the further investigations of these
family of compounds from the public health and environmental
protection point of view are required.
Table 2. Values of No Observed Effect Concentration
(NOEC) and Lowest Observed Effect Concentration
(LOEC) for All Tested Compounds (in mg/kg of Dry
Weight of soil)
ASSOCIATED CONTENT
* Supporting Information
Additional information as noted in the text. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
NOEC
LOEC
compound
oat
80
radish
40
oat
radish
80
1a
1b
1d
2a
2b
2c
100
AUTHOR INFORMATION
Corresponding Author
*E-mail: jlewkow@uni.lodz.pl.
■
8
8
10
10
100
100
100
100
400
200
200
200
200
800
Notes
The authors declare no competing financial interest.
REFERENCES
■
Investigated compounds 1a, 1d, and 2a−c were toxic toward
selected plants and the results obtained from the preliminary
plant growth tests were confirmed by independently performed
final tests. The progressive inhibition of germination and
reduction of fresh/dry weight of plants depended on the
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