Bioherbicidal Ionic Liquids - ACS Sustainable Chemistry

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Bio herbicidal ionic liquids Juliusz Pernak, Kamil Czerniak, Micha# Niemczak, Lukasz Lawniczak, Damian Krystian Kaczmarek, Andrzej Borkowski, and Tadeusz Praczyk ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04382 • Publication Date (Web): 12 Dec 2017 Downloaded from http://pubs.acs.org on December 14, 2017

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ACS Sustainable Chemistry & Engineering

Bio herbicidal ionic liquids *,a

Juliusz Pernak , Kamil Czerniaka, Michał Niemczaka, Łukasz Ławniczaka, Damian Krystian Kaczmareka, Andrzej Borkowskib, Tadeusz Praczykc a

Department of Chemical Technology, Poznan University of Technology, ul. Berdychowo 4,

60-965 Poznan, Poland b

Faculty of Geology, University of Warsaw, ul. Żwirki i Wigury 93, 02-089 Warsaw, Poland;

c

Institute of Plant Protection - National Research Institute, ul. W. Węgorka 20, 60-318

Poznan, Poland *

[email protected]

Abstract This study presents the properties of a new group of ILs based on various cations and pelargonic acid, a natural non-selective herbicide. The obtained bio-ILs were obtained with high yield (>92%) using a metathesis reaction or neutralisation of quaternary ammonium hydroxides and characterized in terms of physicochemical properties. Tests under greenhouse conditions confirmed the superior herbicidal activity of ILs compared to pure pelargonic acid, especially against white mustard (5- to 10-fold higher efficacy of ILs). Further studies under field

conditions

revealed

that

tetrabutylammonium,

benzalkonium

and

oleyltrimethylammonium pelargonates exhibited the highest efficiency (50.5, 49.5 and 46.7%, respectively) at an approx. 3-fold lower dose of pelargonic acid (2.72 kg per 1 ha) compared to that used in commercial products (8-11 kg per 1 ha). This allows to classify the synthesized ILs as bio herbicidal ionic liquids (bio-HILs). In addition to bio-HILs, two new auxins were also obtained. Evaluation of antimicrobial activity indicated that the most potent effect was observed in case salts with oleyltrimethylammonium and tallowtrimethylammonium cations (MIC, MBC and MFC values lower by two orders of magnitude compared to pelargonic acid). The fundamental influence of the cation was also observed during biodegradability assay, as the results varied from 0 to 85% (the highest biodegradability was observed in case of dodecylbetainium and tetrabutylammonium pelargonates). The computational data suggested that biodegradation efficiency seems to be influenced by the interactions between the cation and the anion. The performed toxicity tests allowed to classify the obtained bioHILs as category V (di(hydrogenated tallow)dimethylammonium pelargonate) or category IV compounds against rats.

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Keywords: antimicrobial activity; biodegradation; herbicidal ionic liquids; pelargonic acid; toxicity.

Introduction

The presence of weeds negatively affects the crops by significant reduction of their yield as well as quality. Due to this reason, weed control has become a major challenge for all production systems. The most common method of crop protection against undesired vegetation is based on the use of plant protection products called herbicides. Despite the significant progress made after decades of synthetic herbicide usage in reducing their negative impact on the environment and human health, the risks associated with their application still persist. This problem is indicated by current legislation applicable in the territory of the European Union, in particular Directive 2009/128/EC as well as Regulation (EC) No 1107/2009 of the European Parliament and of the Council of 21 October 2009. These documents specify that substances should only be used in plant protection products when they do not have any adverse effects on human or animal health or any unacceptable effects on the environment. Presently, there is a strong need for the development of environmentally friendly herbicides which would be safer for animal and human health. This goal may be achieved by utilization of naturally occurring substances.1 Natural products are particularly attractive as substrates because they occupy a wider space and exhibit greater structural diversity compared to traditional synthetic compounds.2 Selected fatty acids, such as pelargonic acid (PA) and oleic acid, proved to be effective nonselective herbicides against a wide spectrum of annual weed species. Pelargonic acid, also known as nonanoic acid, is classified as a herbicide and plant growth regulator, whereas oleic acid is classified as a herbicide, insecticide and fungicide.3 In general, fatty acids are very common natural substances which are known to be rapidly biodegradable in soil and exhibit low toxicity.2,4 It is considered that the middle-chain fatty acids, especially from C9 to C11, cause damage to the plant cell membrane system, induce electrolyte leakage from the cells, and ultimately promote rapid necrosis. Their action is associated with the attack on the bimolecular lipid membranes of plant cells, which destabilizes the membrane structure and causes a “burn-down” effect in plant tissues.1,5 Furthermore, the phytotoxicity also results from intercalation of such fatty acids into photosynthetic cell plasma membranes and thylakoids, which leads to displacement of free chlorophyll pigments. Once light-sensitized, hyper reactive oxygen species are 2 ACS Paragon Plus Environment

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produced, which can initiate lipid membrane peroxidation. Both effects cause irreversible cell damage and plant death.6-8 Pelargonic acid (PA) is an organic carboxylic acid which possesses 9 carbon atoms linked together by saturated bonds. PA is a naturally occurring compound found in the flowers of Pelargonium roseum. PA has been reported to be nontoxic to mammalian models in diet at doses up to 1500 mg/kg/ day, which may explain its widespread, naturally occurring pathway. Moreover, according to risk assessment guidance (US EPA 1992), PA is only slightly toxic to aquatic organisms such as zebrafish or fathead minnow.6 Therefore, this compound is commonly used in many countries as a non-selective herbicide against grasses, vines and many annual plants and perennials, including moss, bushes and trees suckers.4,7,9,10 In order to improve the effectiveness of PA, new formulations have been developed. They involve the PA in the form of esters, thioesters, amides or ammonium salts mixed with other herbicides such as glyphosate7,11-13 or sulfonylureas.14 As a result, PA mixed with glyphosate was successfully applied as an alternative to paraquat dichloride for the preparation of firebreak tracer lines at South Africa.11 However, extensive studies revealed that the addition of PA to glyphosate did not improve glyphosate absorption or translocation, or synergize its activity against trumpet creeper compared to glyphosate alone.13 Similar effect was noted for a mixture of PA and glufosinate in case of several weed species, such as lambsquarters.7,15 Inhibitors of enzymes involved in the biosynthesis of essential plant nutrients can cause irreparable damage to plants. Due to this, Nudelman et al. synthesized analogues of the 7-keto-8-aminopelargonic acid (KAPA) and 7,8-diaminopelargonic acid (DAPA) involved in the biosynthetic pathway of biotin, which presented high potential as herbicides toward thale cress. This discovery may open a new approach to the design of new bioherbicides based on PA derivatives.2,16 Middle-chain fatty acids and their derivatives, applied at the appropriate dosage, might be useful against a number of bacterial and fungal infections in or on plant tissues. It has been confirmed that pelargonic acid in the form of esters, thioesters, amides as well as sodium, potassium or mono-, di- or trialkylammonium salts effectively suppresses many pathogens of plants, such as fungi belonging to the Penicillium, Monilinia, Allernaria or Aspergillus genus, and bacteria belonging to the Bacillus, Pseudomonas or Erwinia genus.17,18 Herbicidal ionic liquids (HILs) are chemical compounds with a melting point below the temperature of 100 ºC which exhibit herbicidal activity.19-22 The first publication regarding HILs in 2011 showed that it is possible to obtain a new type of herbicide, which exhibits increased biological activity and multifunctional properties.19 This provided the 3 ACS Paragon Plus Environment


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opportunity to produce novel, effective formulations based on currently manufactured herbicides, such as halogenated derivatives of phenoxyacetic acid (2,4-D,22,23 MCPA,21 MCPB24 and MCPP25) or dicamba,20,26,27 clopyralid,21 fomesafen,28 bentazon,29 glyphosate30,31 and sulfonylurea (metsulfuron methyl).32 In addition to ILs with single herbicidal function,1929

some HILs may simultaneously act as a herbicide and a growth regulator33 or fungicide,34

protecting the crops and allowing to increase their productivity. HILs derived from renewable sources based on betaine and carnitine,35 D-glucose36 and choline37 were described recently. The reduced volatility of HILs eliminates the problem of contamination via air emissions as well as minimizes the risk of poisoning by pesticide vapours.20 Moreover, the selection of appropriate counterions allows to obtain HILs with preferred properties such as low acute toxicity,19 reduced soil and groundwater mobility21,28 or ready or inherent biodegradability.3840

A recent trend in the synthesis of ILs is focused on the utilization of ions fully derived from naturally occurring substances in order to obtain “bio-based ionic liquids”.41,42 An example of this approach includes the use of choline acetate as an alternative to imidazolium-based ILs for pre-treatment of biomass43,44 or synthesis of choline carboxylates as a biodegradable surfactant.45,46 This strategy often allows to design products characterized by high efficacy as well as low environmental impact47 which are attractive alternatives to conventional ILs (based on synthetic compounds). The synthesis of HILs which would incorporate the pelargonic acid as an anion and a cation of natural origin fits the concept of bio-based ILs and additionally corresponds well with the principles of Green Chemistry. In case of agriculturalbased ILs studies are conducted with regard to chemical modification of plant resistance inducer, benzo[1,2,3]thiadiazole-7-carboxylate (BTH)48-51 or novel antifungal agents.52 The objective of this work was to prepare new ILs which could act as effective and eco-friendly non-selective herbicides. In order to achieve this goal, the pelargonate anion has been combined with popular, cheap and commercially available ammonium cations. In addition to the synthesis of novel pelargonate-based ILs, this study also characterizes their physicochemical properties, biodegradability and herbicidal efficacy.

Result and discussion ILs containing an anion derived from pelargonic acid were obtained by the two methods shown in Scheme 1. The methods used for synthesis and purification of all the obtained ILs as well as the NMR data are described in the Supporting Information (Experimental section, pages S1-S4). The main sources of a cation in the synthesis were 4 ACS Paragon Plus Environment

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commercially available quaternary ammonium salts. The first group of precursors were salts containing

small

cations

of

natural

origin

(choline

chloride).

In

addition,

diallildimethylammonium (2) and tetrabutylammonium (3) cations were also used. The second group included precursors containing a long alkyl chain in the structure of the cation (e.g.

di(hydrogenated

tallow)dimethylammonium,

oleyltrimethylammonium,

di(tallowoyloxyethyl)-dimethylammonium or bis(2-hydroxyethyl)methyloleylammonium). Overall, fourteen salts were obtained in the framework of this study. The results of the synthesis are shown in Table 1. Most of the described compounds were synthesized for the first

time.

ILs

with

didecyldimehylammonium

(14),

benzalkonium

(8)

and

hexadecyltrimethylammonium (5) cations and the pelargonate anion are compounds which exhibit a deterrent activity and were described previously.53 Moreover, the IL with the choline cation (1) has been used in the preparation of biocompatible transparent films based on chitosan.54 Compounds 2, 4, and 13 were synthesized by an anion exchange reaction (metathesis reaction) using potassium salts of pelargonic acid (method I). For the rest of ILs, neutralization reaction between quaternary ammonium hydroxide and pelargonic acid was applied (method II). Commercial hydroxides (cholinium and tetrabutylammonium) were used in the preparations of compounds 1 and 3. The yield of the synthesis ranged from 93 to 99%. Most of the obtained salts were waxes except for the ILs containing the tetrabutylammonium cation. Compound 3 was a liquid at ambient temperature and its physicochemical characteristics are shown in the supporting information (Fig. S1-S3).

Scheme 1 The synthetic methods of preparation of pelargonate ILs.

Table 1 Characterization of synthesized ammonium ILs.



Yield

State at

(%)

25 ºC

II

99

wax

I

96

wax

II

99

liquida

I

95

wax

C16H33

II

98

wax

CH3

C18H37

II

97

wax

CH3

C22H45

II

98

wax

II

99

wax

oleylb

II

96

wax

tallowc

II

97

wax

II

93

wax

oleylb

II

97

wax

CH3

CH3

I

93

wax

CH3

CH3

II

96

wax

ILs

R1

R2

R3

1

CH3

CH3

CH3

2

CH3

CH3

3

C4H9

C4 H 9

C4H9

4

CH3

C12H25

CH3

5

CH3

CH3

CH3

6

CH3

CH3

7

CH3

CH3

8

CH3

9

CH3

CH3

CH3

10

CH3

CH3

CH3

11

CH3

CH3

12

CH3

13

14 a

Page 6 of 32

C12H25 – 40% C16H33 – 60%

R4

C4 H 9

CH3

hydrogenated tallow

d

C10H21

hydrogenated tallowd

C10H21

Method

-1

physicochemical properties at 20 ºC – viscosity: 3.67 Pa s, density: 0.90 g mL , refractive

index: 1.46, boleyl - mixture of saturated (18%) or unsaturated (82%) alkyl substituents - C12 – 5%, C14 – 1%, C16 – 14%, C18 – 80%, in Arquad O-50 and Ethoquad O-12 cations, ctallow mixture of saturated (53%) or unsaturated (47%) alkyl substituents - C12 – 1%, C14 – 4%, C16 – 31%, C18 – 64% in Arquad T-50 and Armosoft DEQ cations, dhydrogenated tallow - mixture of saturated (97%) or unsaturated (3%) alkyl substituents - C12 – 1%, C14 – 4%, C16 – 31%, C18 – 64% in Arquad 2HT. 6 ACS Paragon Plus Environment

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Unfortunately, the combination of a pelargonate anion with two amino acid-like cations occurring naturally in living organisms, betaine and carnitine, was not successful. During the anion exchange reaction, the proton transfer decomposed the obtained ILs to zwitterions, PA and potassium chloride (Scheme 2). The liquid phase separated from both products was identified as PA through 1H and 13C NMR, IR and analysis of refractive index at 20 °C. Such phenomenon was probably caused by a substantially higher binding strength between hydrogen and oxygen in the carboxyl group of PA, due to its higher value of pKa (4.9555) in comparison to both hydrochlorides (2.2656 for betaine hydrochloride and 3.8056 for carnitine hydrochloride, respectively).

Scheme 2 The proton transfer in the synthesis of betainium and carnitinium pelargonates.

Table 2. Physicochemical properties of the synthesized ILs. Tga

T mb

T cc

Tonset5%d

Tonsete

(ºC)

(ºC)

(ºC)

(ºC)

(ºC)

1

-27

2

19

186

210

2

-

-2

1

150

178

3

-53

-

-

153

178

4

33

70

74

146

226

5f

20

96

93

193

231

6

24

62

45

171

200

7

-

57

39

173

231

8f

-

-6

-12

175

243

9

-

19

24

175

219

10

-

8

29

178

212

11

-

36

38

172

262

12

1

56

68

196

238

13

-21

22

34

156

252

14f

-

33

18

180

260

ILs



a

Page 8 of 32

Tg – glass transition temperature; bTm – melting point; cTc – crystallization temperature;

d

Tonset5% – decomposition temperature of 5% sample; eTonset – decomposition temperature of

50% sample; f values taken from53.

Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) data for the ILs are presented in Table 2. The methodology of these analyses described in the Supporting Information (Thermal analysis, page S4). Among all synthesized compounds, one salt comprising tetrabutylammonium cation (3) exhibited only a glass transition temperature. Therefore, neither melting nor crystallization event were observed for this salt. Furthermore, the observed values of melting point for other pelargonates were in range from -6 ºC for 8 with the benzalkonium cation to 96 ºC for 5 with the hexadecyltrimethylammonium cation, which allow to classify all the obtained salts into the group of ILs. The lowest melting point temperatures were observed for ILs containing smaller cations, such as choline (1) diallyldimethylammonium (2) as well as the cation with benzyl substituent attached to nitrogen atom (8). Moreover, salts with dialkyldimethylammonium cation (11 and 14) melted at lower temperatures in comparison to alkyltrimethylammonium pelargonates (5-7). The differences between the crystallization temperatures of the synthesized ILs were significant and ranged from -12 ºC for 8 to 93 ºC for 5. The results indicate that the presence of only one saturated straight long alkyl chain in the cation increased this parameter and the addition of other substituents (alkyl (11, 14), benzyl (8), carboxymethyl (4) or hydroxyethyl (1, 12)) lowered the values of Tc. The glass transition temperatures were noted only for six ILs (1, 3-6, 12, 13) and varied from -53 °C for 3 to 33 ºC for 4. However, the results were diverse and did not show a clear effect of the alkyl chain length on this parameter. The obtained values of thermal stability analysis allow to divide the synthesized ILs into two groups. The first group applies to ILs characterized by decomposition temperatures of 5% sample below 160 ºC. This group includes ILs comprising shorter alkyl substituents (2, 3) or carboxyl/ester group (4, 13). The second group involves IL with choline cation (1) and ILs containing at least a single long alkyl chain attached to the nitrogen atom (5-12, 14), which possessed Tonset5% values in range 170-200 ºC. The lowest decomposition temperature Tonset5% (146 ºC) was observed for 4 with N-dodecylbetainium cation, whereas the highest stability (Tonset5% = 196 ºC) was noted for bis(2-hydroxyethyl)methyloleylammonium pelargonate (12). The collected results demonstrate that thermal stability appears to be poorly related with the length of alkyl substituents among ILs form the second group. Therefore, the


Page 9 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


differences

in

Tonset5%

between

alkyltrimethylammonium

(5-7,

9,

10)

and

dialkyldimethylammonium (11 and 14) pelargonates were lower than 30 ºC. The increase in length of the alkyl chain also enhanced the decomposition temperatures (Tonset) of the obtained ILs. Hence, only 2 and 3 were characterized by Tonset below 200 ºC. According to values presented in Table 2, ILs with benzalkonium (8) and bis(2-hydroxyethyl)methyloleylammonium (12) cations possessed higher temperatures of decomposition in comparison to alkyltrimethylammonium pelargonates (5-7, 9, 10). Among all the synthesized ILs, salts comprising the dialkyldimethylammonium cation (11, 13, 14) exhibited the highest thermal stability which exceeded 250 ºC. Slightly lower thermal stability (Tonset5% = 187 ºC; Tonset = 248 ºC) was noted for other, recently described didecyldimethylammonium undecylate, which brings a conclusion that the alkyl chain elongation in the anion does not improve the thermal stability of such ILs either. Furthermore, there are also some reports which indicate that decomposition temperatures may be mainly independent of the alkyl chain length in some ammonium or imidazolium ILs.57-60

Table 3. Solubility of the synthesized ILs at 20 ºC. Solvent ILs

A

B

C

D

E

F

G

H

I

J

1

+

+

+

+

+

+

-

+

-

-

2

+

+

+

+

+

+

-

+

-

-

3

+

+

+

+

+

+

+

+

+

-

4

-

+

+

-

+

+

-

-

-

-

+

+

+

±

±

+

±

+

±

-

6

-

+

±

±

+

+

-

+

+

-

7

-

+

±

±

+

+

-

+

+

-

±

+

+

±

±

+

±

+

±

-

9

-

+

±

±

+

+

-

+

+

±

10

-

+

+

-

±

+

-

+

+

-

11

-

+

-

-

±

+

±

+

+

+

12

-

+

±

-

±

+

±

+

+

-

13

-

+

±

+

+

+

+

+

+

+

14a

±

+

-

-

-

+

-

±

±

-

5

8

a

a



Page 10 of 32

A – water, B – methanol, C – DMSO, D – acetonitrile, E – acetone, F – 2-propanol, G – ethyl acetate, H – chloroform, I – toluene, J – hexane; Solubility test: “+”– complete solubility (0.1 g in 1 mL of solvent); “±”– limited solubility (0.1 g in 3 mL of solvent); “-”– insoluble.

a

results taken from53. The solubility properties of the pelargonic ILs (Table 3) were tested according to the modified method described by Vogel61 in ten solvents, varying from high to low polarity. The description of the performed test is available in the Supporting Information (Solubility, pages S4−S5). All the obtained ILs exhibited excellent solubility in short-chain alcohols such as methanol and 2-propanol. On the other hand, most of the synthesized compounds showed a lack of water solubility due to high hydrophobicity of the pelargonate anion and utilized cations. Good solubility in water primarily characterized ILs 1-3 containing small, polar cations and compounds 5, 8 and 14. Moreover, the presence of two long alkyl chains in the structure of the cation caused a reduction of solubility in DMSO. Surprisingly, almost all ILs were soluble in non-polar toluene, except salts 1, 2 and 4. In addition, the compound 4 containing N-dodecylbetainium cation was also insoluble in ethyl acetate and chloroform. Solubility in hexane was observed only for ILs 9, 11 and 13. The methodology of test regarding the herbicidal activity of the studied ILs under greenhouse and field conditions are described in the Supporting Information (Herbicidal activity, pages S5). Preliminary tests with two ILs 12 and 14 and three plant species (cornflower, winter wheat and white mustard) showed that PA itself had poor performance against the tested plants but its IL forms exhibited higher herbicidal activity. Moreover, the type of cation used in the synthesis was a key factor affecting this activity. In some cases, the IL form provided even ten times higher reduction of fresh weight of tested plants compared to the parent form (Table 4). PA is known as a contact, non-selective herbicide for annual weeds. It does not translocate to plant tissues but causes burndown of plant parts that have been covered with the spray solution.62 ILs based on PA retain the same mode of action and provide analogous visible effects as was presented in Fig. 1.

Table 4. Efficacy of PA and its ILs forms. Fresh weight reduction [%]

Treatment cornflower

winter wheat

white mustard


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12

37

5

16

14

53

29

33

PA

14

18

3

Figure 1. Herbicidal efficacy of spray solution of oleyltrimethylammonium pelargonate (IL 9) toward plants of winter oilseed rape in comparison to control.

Further research was focused on the selection of the best cation for synthesis of effective ILs with pelargonate anion including cations of natural origin, such as choline. The herbicidal efficacy of the synthesized ILs was evaluated under greenhouse conditions using two plant species. For ILs 2, 9-12 and 13 the plants of winter oilseed rape (Brassica napus L.) were employed (Fig. 2), while ILs 1, 3-8 and 14 were tested using common lambsquarters (Chenopodium album L.) plants (Fig. 3).



Page 12 of 32

Figure 2. Herbicidal activity of synthesized ILs (1,2,9-13) against oilseed rape plants.

Figure 3. Herbicidal activity of synthesized ILs (1,3,8-14) against common lambsquarters plants.

In general, the herbicidal activity of the tested ILs was very diverse. ILs 3, 8 and 9 were the most effective in reducing the growth of tested plants and showed an efficacy of 50.5, 49.5 and 46.7%, respectively. ILs 1, 6 and 7 showed no phytotoxic effects towards the tested plants. These results indicate that the properly selected cation has a very significant effect on the biological activity of ILs based on PA. ILs 2-4, 8, 9-14 may be classified as herbicidally active novel HILs. Among this group six compounds comprise a cation of natural origin, namely 4 (alkyl derivative of betaine) and 9-13 (AkzoNobel products including cations with long alkyl chains based on fatty acids, such as Arquad O-50, T-50 and 2HT, Ethoquad O-12 and Armosoft DEQ). The determined herbicidal activity was not high due to the low dosage of the used PA equal to 2.72 kg per 1 ha. The commercial effect is achieved by increasing the dosage to the level used in commercial preparations (8-11 kg per 1 ha, as in case of the Beloukha 680 EC commercial product). PA and 2,4-D are classified as herbicides and plant growth regulators, however they work differently after introduction to the IL structure with the choline cation. Choline pelargonate (1) is an auxin, whereas cholinium 2,4-dichlorophenoxyacetate37 is a commercial herbicide. A new natural auxin, cholinium pelargonate, has been obtained. The influence of the alkyl chain length on the herbicidal activity is visible in case of ILs 5, 6 and 7 presented in 12 ACS Paragon Plus Environment

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Fig. 3. The synthetic alkyltrimethyl cation is distinguished by a the amount of carbon atoms in the alkyl chain, namely 16, 18 and 22. IL 5 with 16 carbon atoms displayed low herbicidal activity, IL 6 with 18 carbon atoms was virtually non-active, whereas IL 7 with 22 carbon atoms is an auxin with efficacy comparable to IL 1. Bio herbicidal ionic liquids with the pelargonate anion are characterized by a lower activity in weed control compared to the previously described herbicidal ionic liquids due to the fact that they do not contain an active ingredient typical for commercial herbicides, such as HILs with a glyphosate anion.30,31 Hence, it is necessary to use higher doses compared to other herbicides. An important advantage of the synthesized ILs is their very rapid action in treated plants, and therefore the symptoms of damage are visible just after several hours following their application. The synthesized ILs, with the exception of two highly hydrophobic ILs 6 and 7, were tested for antibacterial and antifungal activity. A description of the performed tests is available in the Supporting Information (Antimicrobial properties, pages S5−S6). Both the MIC as well as MBC/MFC values were determined. The obtained differences between the obtained MIC and MBC/MFC values were marginal. The conducted antimicrobial activity tests suggest that the best overall results were obtained for HILs 9 and 10 (Table 5). These HILs were characterized by very low MIC and MBC values (both 5.6

5.6

>5.6

2.8

5.6

0.3

0.7

4

0.3

2.6

1.3

>5.2

5.2

>5.2

0.6

0.6

5

Bioherbicidal Ionic Liquids - ACS Sustainable Chemistry

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