Herbicidal Ionic Liquids Research Articles

Fabrication of ionic liquid self-assemblies based on dicamba with improved herbicidal activity and reduced environmental risks

The off-target loss of pesticide formulations caused by volatilization and leaching has reduced effective utilization and increased risks to the ecological environment and human health. Self-assembly of pesticides has been widely concerned due to the improved bioactivity and environmental compatibility. Herbicidal ionic liquids (HILs) could effectively decrease off-target loss and increase efficacy and environmental safety by improving the physicochemical properties of herbicides. Herein, HILs were prepared by pairing dicamba with quaternary ammonium salts containing different alkyl chain lengths and aromatic groups and subsequently self-assembled into spherical nanoparticles (HIL NPs) via electrostatic interaction and hydrophobic effect. Compared with dicamba, the obtained HIL NPs with an average particle size of 6–55 nm exhibited improved physicochemical properties, including high zeta potential values (+20.3 to +27.8 mV), low volatilization rate (2.4–3.9 %) and surface tension (22.83–33.07 mN m−1), decreased contact angle (32.25–41.55°) and leaching potential (76.2–86.5 %), and high soil adsorption (12.1–23.8 %), suggesting low risks to the environment. The control efficacy against Amaranthus retroflexus of HIL3 NPs pairing dicamba with octadecyl-trimethyl ammonium chloride was better than that of dicamba sodium salt at different concentrations. Therefore, the ionic liquid self-assembly developed by a facile and green preparation approach to reduce the volatility and leaching of pesticides would have enormous potential in sustainable agriculture.

Cations impact the biodegradation of iodosulfuron-methyl herbicidal ionic liquids by fungi

ABSTRACT In the framework of this study, six fungal isolates which demonstrated a high capability for biodegrading iodosulphuron-methyl sodium as well as herbicidal ionic liquids based on this herbicide were isolated from different soil samples. The isolates were identified based on the ITS region, whereas biodegradation residues were determined based on LC-MS/MS. Depending on the isolate, the half-lives values of the biodegraded herbicide or herbicidal ionic liquid ranged significantly from just 1.25 days to more than 40 days. The research findings unveiled that the structure of cations is a central limiting factor affecting fungal growth and herbicide transformation in case of ionic liquids. The length of the alkyl chain has been identified as the primary driver of herbicide toxicity, emphasizing the importance of structural factors in herbicide design. In cases when dodecyl(2-hydroxyethyl)dimethyl cation was used, its biodegradation ranged from 0 to approx. 20% and the biodegradability of the iodosulfuron-methyl was notably limited for the majority of the studied isolates. This knowledge provides guidance for development and selection of herbicides with reduced environmental impact. This study highlights the ecological importance of soil fungi, their potential role in herbicide biodegradation, the influence of cations on fungal growth and herbicide transformation, and the structural factors governing herbicide toxicity. Further research in these areas may lead to more efficient and environmentally friendly approaches to herbicide management.

Ecotoxicity studies reveal that organic cations in dicamba-derived ionic liquids can pose a greater environmental risk than the herbicide itself

The following research provides novel and relevant insights into potential environmental consequences of combination of various organic cations with commercial systemic herbicide (dicamba), in accordance with a ‘herbicidal ionic liquids’ (HILs) strategy. Toxicity assays of five dicamba-based HILs comprising different hydrophobic and hydrophilic cations, namely choline [CHOL][DIC], ethyl betainate [BETC2][DIC], decyl betainate [BETC10][DIC], hexadecyl betainate [BETC16][DIC] and didecyldimethylammonium [DDA][DIC]), have been tested towards bacteria (Pseudomonas putida, Escherichia coli, Bacillus subtilis), algae (Chlorella vulgaris), fresh and marine water crustaceans (Daphnia magna, Artemia franciscana). The structure of respective substituents in the cation emerged as a decisive determinant of toxicity in the case of tested species. In consequence, small ions of natural origin ([CHOL] and [BETC2]) demonstrated toxicity numerous orders of magnitude lower compared to fully synthetic [DDA]. These results emphasize the role of cations' hydrophobicity, as well as origin, in the observed acute toxic effect. Time-dependent toxicity assays also indicated that betaine-type cations comprising an ester bond can rapidly transform into less harmful substances, which can generally result in a reduction in toxicity by even several orders of magnitude. Nonetheless, these findings challenge the concept of ionic liquids with herbicidal activity and give apparent parallels to adjuvant-dependent toxicity issues recently noted in typical herbicidal formulations.

Herbicidal ionic liquids containing double or triple anions as a new potential tool for weed control including herbicide-resistant biotypes

Herbicides are commonly used in modern agriculture for the control of unwanted plants. Contemporary expectations regarding agrochemicals emphasize the need to ensure high effectiveness and reduce side effects. Multicomponent herbicidal ionic liquids possess these features. In planning the syntheses of herbicidal ionic liquids (HILs), we took into account ensuring high activity against weeds using reduced doses of active substances and the problem of controlling herbicide-resistant weeds.Eight new double-anion and eight new triple-anion HILs were synthesized. All obtained HILs contained methyl dodecylbetainate cation and herbicidal anions belonging to both sulfonylurea and auxin-like groups of active substances in a single compound. The new HILs were tested under greenhouse and field conditions and they showed excellent efficacy against target dicotyledonous weeds. Some compounds showed very good surface properties, which are desirable for foliar application to plants. Moreover, HILs with three herbicidal anions (iodosulfuron or metsulfuron + 2,4-D + clopyralid) were very effective against cornflower biotype resistant to acetolactate synthase inhibitors.Our research indicate that herbicidal ionic liquids containing a cation of natural origin and herbicidal anions characterized by a different mode of action in a single compound are a potential new tool for weed management. The use of multicomponent herbicidal ionic liquids enables effective weed control with lower doses of the active ingredient.

2,4-D versus 2,4-D based ionic liquids: Effect of cation on herbicide biodegradation, tfdA genes abundance and microbiome changes during soil bioaugmentation.

The commercial formulations of herbicides rely on surfactants which increase the efficiency of active substance. Herbicidal ionic liquids (ILs), in which cationic surfactants are combined with herbicidal anions, allow for additives’ reduction and ensure very good herbicide performance with lower doses. We aimed to test the impact of synthetic and natural cations on biological degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). Although primary biodegradation was high, the mineralization in agricultural soil indicated incomplete conversion of ILs to CO2. Even the introduction of naturally-derived cations resulted in an increase in the herbicide’s half-lives – from 32 days for [Na][2,4-D] to 120 days for [Chol][2,4-D] and 300 days for the synthetic tetramethylammonium derivative [TMA][2,4-D]. Bioaugmentation with 2,4-D-degrading strains improves the herbicides’ degradation, which was reflected by higher abundance of tfdA genes. Microbial community analysis confirmed that hydrophobic cationic surfactants, even those based on natural compounds, played a negative role on microbial biodiversity. Our study provides a valuable indication for further research related to the production of a new generation of environmentally friendly compounds. Moreover, the results shed a new light on the ionic liquids as independent mixtures of ions in the environment, as opposed to treating them as new type of environmental pollutants.

Synthesis and Surface Properties of Piperidinium-Based Herbicidal Ionic Liquids as a Potential Tool for Weed Control

A series of piperidinium-based herbicidal ionic liquids (HILs) were synthesized and investigated. The designed HILs, obtained with high yields, consisted of cation 1-alkyl-1-methylpiperidinium with surface activity and a commercially available herbicidal anion: (3,6-dichloro-2-methoxy)benzoates (dicamba). The above-mentioned compounds were characterized in terms of surface activity and phytotoxicity. Preliminary results were obtained at higher wettability for all HILs when compared to the wettability of commercial Dicash, with HIL having 18 atoms in the carbon chain being the best effectiveness in wetting surfaces (weeds and crop leaves), whereby a drop of HILs with short alkyl chains (C8-C10) could not slide down a leaf. Our findings present that wettability or mobility of HILs drops varied depending on the plant species. Moreover, in this study, by zeta potential and atomic force microscopy measurements, we provide conclusive evidence to demonstrate that alkyl chain elongation plays a significant role in the evolution of surface properties of HILs.

Antimicrobial and Virucidal Potential of Morpholinium-Based Ionic Liquids.

Witnessed by the ongoing spread of antimicrobial resistant bacteria as well as the recent global pandemic of the SARS-CoV-2 virus, the development of new disinfection strategies is of great importance, and novel substance classes as effective antimicrobials and virucides are urgently needed. Ionic liquids (ILs), low-melting salts, have been already recognized as efficient antimicrobial agents with prospects for antiviral potential. In this study, we examined the antiviral activity of 12 morpholinium based herbicidal ionic liquids with a tripartite test system, including enzyme inhibition tests, virucidal activity determination against five model viruses and activity against five bacterial species. The antimicrobial and enzymatic tests confirmed that the inhibiting activity of ILs corresponds with the number of long alkyl side chains and that [Dec2Mor]+ based ILs are promising candidates as novel antimicrobials. The virucidal tests showed that ILs antiviral activity depends on the type and structure of the virus, revealing enveloped Phi6 phage as highly susceptible to the ILs action, while the non-enveloped phages PRD1 and MS2 proved completely resistant to ionic liquids. Furthermore, a comparison of results obtained for P100 and P001 phages demonstrated for the first time that the susceptibility of viruses to ionic liquids can be dependent on differences in the phage tail structure.

Glyphosate versus glyphosate based ionic liquids: Effect of cation on glyphosate biodegradation, soxA and phnJ genes abundance and microbial populations changes during soil bioaugmentation

The applicability of herbicidal ionic liquids (HILs) as an alternative form of herbicides is currently evaluated. Yet, the available research is lacking information on the behaviour of herbicidal ionic liquids upon addition to the environment, i.e., if cations and anions act as separate moieties or remain an ionic salt. Hence, we tested degradation of five HILs with the glyphosate anion, their bioavailability in soil, toxicity towards microorganisms, impact on the biodiversity and the abundance of phnJ and soxA genes. The cations were proven to be slightly or moderately toxic. The properties of cations determined the properties of the whole formulation, which might suggest that cations and anion act as the independent mixture of ions. The mineralisation efficiencies were in the range of 15–53%; however, in the case of cations (except non-toxic choline), only 13–20% were bioavailable for degradation. The hydrophobic cations were proven to be highly sorbed, while the anion was readily available for microbial degradation regardless of its counterion. The approach to enrich test samples with isolated microorganisms specialised in glyphosate degradation resulted in higher degradation efficiencies, yet not high enough to mitigate the negative impact of cations. In addition, increased activity of enzymes participating in glyphosate degradation was observed. In the view of obtained results, the use of cationic surfactants in HILs structure is not recommended, as sorption was shown to be determining factor in HILs degradation efficiency. Moreover, obtained results indicate that corresponding ions in HILs might act as separate moieties in the environment.

Can ionic liquids exist in the soil environment? Effect of quaternary ammonium cations on glyphosate sorption, mobility and toxicity in the selected herbicidal ionic liquids

Ionic liquids (ILs) are described as low-impact green chemicals in which the cation can influence the properties of the anion through ion pair formation. We decided to see how stable ILs are in the soil environment. Herbicidal ILs consisting of hydrophilic glyphosate [Glyph] paired with hydrophilic choline [Chol], hydrophobic C12 alkyl modified choline [C12Chol] and hydrophobic quaternary ammonium cation [C16TMA] were synthesized. The calculated interaction energies between ions (75.9–88.9 kcal/mol) were typical for ILs. The results showed independent sorption of cations and anions and no statistical effect of cations on anion sorption. Hydrophobic [C16TMA], [C12Chol] cations followed 99 % adsorption, and hydrophilic [Chol] revealed 42–45 % adsorption. The Freundlich constants were [C16TMA] Kf≈4000 > [C12Chol] Kf≈3000 > [Chol] Kf≈3 (mg1-1/n L1/ng-1). The preferential sorption of hydrophobic cations was also visible during leaching experiments and resembles the behavior of cationic surfactants. [Glyph] sorption was higher in organic-rich agricultural soil (approx. 45 %) compared to reference OECD soil (30 %), and the Kf values were constant, regardless of the presence of cations. The lack of ionic pair integrity was also visualized by the toxicity and phytotoxicity results. In the soil environment, ILs are a mixture of independent cations and anions rather than a novel emerging contaminant.

Effect of Cation Sorption on 2,4-D Mobility of Herbicidal Ionic Liquids in Agricultural Soil Combined with Diversity of the Bacterial Community

Effect of Cation Sorption on 2,4-D Mobility of Herbicidal Ionic Liquids in Agricultural Soil Combined with Diversity of the Bacterial Community

Evaluation of the influence of different cations on the mobility and performance of dicamba-based ionic liquids

Herbicidal ionic liquids are considered as an alternative to commercial crop protection products, however current research is mainly concerned with their physicochemical properties and biological activity. In our study, we decided to comprehensively evaluate the fate of selected herbicidal ionic liquids after they enter the soil environment through comprehensive sorption, mobility and leaching studies. The studies were carried out for two herbicidal ionic liquids containing cation: betaine or choline and anion dicamba. The phytotoxicity studies conducted indicate a protective effect of betaine and choline cations for root growth of monocotyledonous plants, thus offsetting the toxic effects of dicamba anion present in the soil. Moreover, the analyzed herbicidal ionic liquids do not show any toxic effect on soil microorganisms. The results also indicate that in the soil profile the hydrophilic betaine cation is not sorbed and moves quickly through the soil profile. The choline cation, on the other hand, is sorbed about 40% (depending on the soils), but is leached. On the other hand, the analysis of sorption and mobility of the dicamba anion, from the HILs, did not show significant differences to the migration of dicamba anion from the sodium form. Our results give a first insight into the fate of ionic liquids in the environment indicating that the cations and anions act as independent chemical molecules when entering the soil ecosystems.

Surface activity and phytotoxicity of morpholinium herbicidal ionic liquids

The use of efficient synthesis methods to obtain novel herbicidal ionic liquids (HILs) with biological activity is extremely important because it can eliminate certain negative environmental impacts. The authors of this work succeeded in the experiment, which resulted in the synthesis of 18 novel ionic liquids with high yields. Furthermore, a number of physicochemical and biological properties have been investigated, including surface activity, thermal analysis, and phytotoxicity. In addition, it was proven that morpholinium ionic liquids with phenoxyacid anions were more effective against cress than HILs previously studied in the literature. To the best of our knowledge, this is the first report of surface-active ionic liquids with herbicidal anions where leaf surfaces were used for analysis. An important aspect of this work was to compare the wettability of the surfaces of wheat leaves and weeds. Moreover, it was shown that using paraffin as a reference surface was not sufficient to describe the wetting properties of HILs. The research reported here proved that morpholinium ionic liquids were effective in wetting weed surfaces while they do not adversely affect wheat leaf surfaces. Our results could be significant for meeting the environmental challenges and agricultural demands of the future.

Dicationic Herbicidal Ionic Liquids Comprising Two Active Ingredients Exhibiting Different Modes of Action.

In the framework of this study, dicationic herbicidal ionic liquids (HILs) containing tetramethylene-1,4-bis(decyldimethylammonium) and dodecylmethylene-1,12-bis(decyldimethylammonium), including two different herbicidal anions exhibiting different modes of action, were synthesized and characterized. One herbicide incorporated into the HILs was a tribenuron-methyl belonging to ALS inhibitors, while the second herbicidal anion was a synthetic auxin that acts as a growth regulator, namely 2,4-dichlorophenoxyacetate (2,4-D), 2-(2,4-dichlorophenoxy)propionate, (2,4-DP), 2,4,5-trichlorophenoxyacetate (2,4,5-T), 4-chloro-2-methylphenoxyacetiate (MCPA), 2-(4-chloro-2-methylphenoxy)propionate (MCPP), and 4-chlorophenoxyacetate (4-CPA). The obtained products were found to be unstable and decomposed, which can be attributed to the presence of an additional methyl group within the sulfonylurea bridge of the tribenuron-methyl. The synthesized HILs exhibited good affinity with polar and semipolar solvents, with ethyl acetate and hexane as the only solvents that did not dissolve the HILs. Greenhouse tests demonstrated that most of the obtained HILs were more effective than the reference herbicide containing tribenuron-methyl. The length of the alkyl chain in the cation also influenced the effectiveness of the HILs. Better effects were observed for dodecylmethylene-1,12-bis(decyldimethylammonium) cations compared to tetramethylene-1,4-bis(decyldimethylammonium). Therefore, the novel dicatonic HILs showed to integrate the advent of the combination of the different herbicides into a single molecule, enhance herbicidal efficacy, and reduce the risk of weed resistance due to the various modes of action of the applied treatment.

Evaluation of Mobility and Sorption of Model Herbicidal Ionic Liquids with Dicamba Anion in Soil Matrix

Evaluation of Mobility and Sorption of Model Herbicidal Ionic Liquids with Dicamba Anion in Soil Matrix

Synthesis and characterization of herbicidal ionic liquids based on (4-chloro-2-methylphenoxy)acetate and phenoxyethylammonium

Ten ionic liquids containing the (4-chloro-2-methylphenoxy)acetate (MCPA) anion and domiphen derived phenoxyethylammonium cation were synthesized. The obtained compounds differed in terms of the substitution of the phenoxyethylammonium group in the ring (the presence of a methyl group in the meta or para positions and the presence of chlorine in the para position) as well as the length of the alkyl chain (from hexyl to tetradecyl). The basic physicochemical properties of the obtained ionic liquids (solubility and thermal stability) were characterized and their structures were confirmed. The herbicidal activity of the compounds was tested under greenhouse conditions using cornflower (Centaurea cyanus L.) as the test plant.

Confusing Ions on Purpose: How Many Parent Acid Molecules Can Be Incorporated in a Herbicidal Ionic Liquid?

To expand the application range of herbicidal ionic liquids (HILs), we attempted to increase the amount of the systemic herbicide dicamba in its HILs through the formation of neither purely ionic n...

Novel esterquat-based herbicidal ionic liquids incorporating MCPA and MCPP for simultaneous stimulation of maize growth and fighting cornflower

Modern agricultural practices are often based on the use of mixtures of specific herbicides to achieve efficient crop protection. The major drawbacks of commercial herbicidal formulations include the necessity to incorporate toxic surfactants and high volatility of active substances. Transformation of herbicides into herbicidal ionic liquids (HILs) seems to be a promising alternative which allows to almost completely reduce volatility due to ionic interactions. In the scope of this research, we transformed (2-methyl-4-chlorophenoxy)acetic acid (MCPA) into a quaternary ester (esterquat) with the use of derivatives of 2-dimethylaminoethanol. The obtained esterquats were later coupled with (±)−2-(4-chloro-2-methylphenoxy)propionic acid (MCPP) in the form of an anion. The combination of MCPA and MCPA is commonly applied in the UK, EU countries and also in the USA to increase the spectrum of targeted weed species. In the framework of this study, novel HILs with an esterquat moiety incorporating a long alkyl chain (C8, C9, C10, C11, C12, C14) were prepared and characterized in terms of basic physicochemical properties (solubility and volatility) as well as biodegradability. Their phytotoxicity was assessed towards cornflower (Centaurea cyanus) as a model weed and maize (Zea mays) as a crop plant. The presence of the esterquat cation contributed to satisfactory solubility in water and other low polar solvents, which eliminates the need to add exogenous adjuvants. Further experiments indicated that the tested HILs stimulated the germination stage of maize and maintained high herbicidal activity towards cornflower. No significant differences in terms of properties were observed in case of HILs which included alkyl substituents with an odd number of carbon atoms. Future studies should be focused on structural modifications in order to improve the biodegradability as well as field studies for evaluation of commercial applications.

Iodosulfuron-Methyl-Based Herbicidal Ionic Liquids Comprising Alkyl Betainate Cation as Novel Active Ingredients with Reduced Environmental Impact and Excellent Efficacy.

A new family of bio-based herbicidal ionic liquids (HILs) has been synthesized starting from the renewable resource glycine betaine (a derivative of natural amino acids). After esterification, the obtained alkyl betainate bromides containing straight alkyl chains varying from ethyl to octadecyl were combined with a herbicidal anion from the sulfonylurea group (iodosulfuron-methyl). The melting points of the iodosulfuron-methyl-based salts were in a range from 51 to 99 °C, which allows their classification as ionic liquids (ILs). In addition, the new HILs exhibited good affinity for polar and semipolar organic solvents, such as DMSO, methanol, acetonitrile, acetone, and chloroform, while the presence of bulky organic cations reduced their solubility in water. The synthesized products turned out to be stable during storage at 25 °C for over 6 months; however, at 75 °C they underwent fast, progressive degradation and released volatile byproducts. The values of the logarithm of the octanol–water partition coefficient of ILs with alkyls longer than hexyl occurred in the “safe zone” (between 0 and 3); hence, the risk of their migration into groundwater after application or the possibility of their bioaccumulation in the environment is lower in comparison with the currently available commercial form (iodosulfuron-methyl sodium salt). Greenhouse studies confirmed a very high herbicidal efficacy for the obtained salts toward tested plants of oilseed rape, indicating that they may become an attractive replacement for the currently available sulfonylurea-based formulations.

Synthesis and efficacy of herbicidal ionic liquids with chlorsulfuron as the anion

AbstractIn the framework of this research, four new herbicidal ionic liquids (HILs) comprising chlorsulfuron as the anion were synthesized and characterized. The new salts with chlorsulfuron contained the following cations: tetramethylammonium, didecyldimethylammonium, benzyltrimethylammonium and cholinium. All products were obtained with high yields exceeding 90% via acid–base reaction or ion exchange reaction, by the use of environment-friendly solvents. The structures of all synthesized HILs were confirmed by FT-IR, 1H NMR and 13C NMR analyses. Their efficacy against weeds has been studied under field conditions in fiber flax. All HILs showed herbicidal activity but efficiency was highly dependent on the type of cation and weed species. There were no statistically significant differences in the effectiveness of HILs toward common lambsquarters compared to the reference herbicide, except for salt with cholinium cation that showed significantly lower efficiency. As regards barnyard grass control, all HILs exhibited significantly lower efficacy than that of the reference herbicide, except for didecyldimethylammonium salt that showed similar activity. The synthesized products did not cause damage to flax plants. The obtained results confirmed that the herbicidal effectiveness of the active ingredient (chlorsulfuron) in the form of an ionic liquid can be adjusted by the selection of an appropriate cation in the synthesis.

Synthesis and Characterization of Double-Salt Herbicidal Ionic Liquids Comprising both 4-Chloro-2-methylphenoxyacetate and trans-Cinnamate Anions.

The synthesis and characteristics are presented of novel double-salt herbicidal ionic liquids (DSHILs) that contain 4-chloro-2-methylphenoxyacetate and trans-cinnamate anions. In the designed synthesis, an anion of natural origin and a herbicidal anion were combined with an amphiphilic bisammonium cation to obtain new DSHILs with high herbicidal activity while high biocompatibility is maintained. The NMR and HRMS spectral analysis confirmed that the target structures were formed. Furthermore, HPLC analyses indicated that, as assumed, both anions were present in equimolar amounts. Experiments regarding the herbicidal effectiveness confirmed that the synthesized DSHILs exhibited high biological activity. The solutions of DSHILs applied during greenhouse studies were characterized by a low contact angle (approx. 55-67°) and surface tension (approx. 32-35 mN m-1 ), which facilitated the contact of the active substance with the plant surface and penetration of the herbicide into the plant tissues.