Stability of triazophos in self-nanoemulsifying pesticide delivery system

Formation of nano-emulsions has been studied in the system water/nonylphenol polyoxyethylene ether (S₁)/triazophos or water/nonylphenol polyoxyethylene ether/N-octyl-2-pyrrolidone (S₂)/triazophos at 25 °C by low-energy emulsification methods: stepwise addition of water to a solution of the surfactant in oil. Nano-emulsions’ high kinetic stability has been obtained at oil weight fractions lower than 0.25 or 0.20 for the two systems respectively. Phase behavior studies have revealed that compositions giving rise to nano-emulsions consist of Om (isotropic liquid phase), Wm (O/W micro-emulsion), La (lamellar liquid crystalline), and O (oil) phases, at equilibrium. Droplet sizes of the nano-emulsions were measured by dynamic light scattering (DLS), and mean sizes are within the typical droplet radius of nano-emulsion except for low-dilution-fold; the higher the water concentration, the higher the size. The hydrolysis of triazophos was studied in buffered solutions with pH 5, 7 and 9, the results showed that triazophos is relatively stable in acidic and neutral solutions and easily hydrolyzed in basic solutions. Furthermore, the research indicated triazophos can be protected from hydrolysis by incorporating into nano-emulsion system. The effect of surfactant on the hydrolysis inhibition of triazophos in the basic condition is more prominent than that in acidic condition.     

Larvicide Activity on Aedes aegypti of Essential Oil Nanoemulsion from the Protium heptaphyllum Resin

The aim of this work was to prepare a nanoemulsion containing the essential oil of Protium heptaphyllum resin and to evaluate the larvicidal activity and the residual larvicidal effect against Aedes aegypti. The essential oil was identified by gas chromatography coupled to a mass spectrometer, and the nanoemulsions were prepared using a low-energy method and characterized by photon correlation spectroscopy. The results indicated the major constituents as p-cimene (27.70%) and α-Pinene (22.31%). Nanoemulsions had kinetic stability and a monomodal distribution in a hydrophilic-lipophilic balance of 14 with particle diameters of 115.56 ± 1.68 nn and zeta potential of −29.63 ± 3.46 mV. The nanoemulsion showed larvicidal action with LC₅₀ = 2.91 µg∙mL⁻¹ and residual larvicidal effect for 72 h after application to A. aegypti larvae. Consequently, the nanobiotechnological product derived from the essential oil of P. heptaphyllum resin could be used against infectious disease vectors.     

Comparative efficacy of Eucalyptus globulus (Labill) hydrodistilled essential oil and temephos as mosquito larvicide

Abstract

In this study Eucalyptus globulus essential oil was tested on major mosquito species and toxicity was compared with temephos. Mortality was calculated after 24?h and 48?h post treatment. In 24?h treatment essential oil show strong larvicidal activity with LC₅₀ and LC₉₀ values were 30.198ppm, 103.389ppm for Anopheles stephensi, 13.578ppm, 106.755ppm for Aedes aegypti; and, 7.469ppm, 32.454ppm for Culex quinquefasciatus and 48?h post treatment LC₅₀ and LC₉₀ values were, 12.576, 49.380ppm for Anopheles stephensi, 7.926, 34.470ppm for Aedes aegypti and 4.408, 21.048ppm for Culex quinquefasciatus. Chemical composition of essential oil using GC-MS and FT-IR analysis shows the presence of 1,8-cineol, (71.7%); α-pinene, (9.14%) as a major compounds. Our findings suggest that essential oil from Eucalyptus globulus leaves can be used for control of mosquito larvae.     

Green synthesis of para-Menthane-3,8-diol from Eucalyptus citriodora: Application for repellent products

A simple and efficient method was developed for the synthesis of para-Menthane-3,8-diol (PMD), a well-known repellent active against mosquitoes, from Eucalyptus citriodora essential oil by a treatment of citric acid in a biphasic medium (H₂O/essential oil). The E. citriodora contains as main component (+)-citronellal (74% in the present case), which cyclises (Prins reaction) to form cis/trans PMD isomers. As an example, an emulsion containing an aqueous solution of 7% citric acid and E. citriodora oil at 50°, conducted after 15 h stirring to 82% conversion of (+)-citronellal with a selectivity of 80% with the remaining presence of monoterpenes and sesquiterpenes in the medium. Investigations of lasting protection on human volunteers are carried out using a cage test bioassay protocol and Aedes aegypti mosquitoes. At 20% in ⁱPrOH, the new reaction mixture showed a complete protection of 303 min compared to 22 min with the pure essential oil. The modified oil was compared with N,N-diethyl-m-methylbenzamide (DEET), the most popular active used in repellent formulations. Thermogravimetric analyses (TGA) of E. citriodora, the modified oil, PMD, DEET, and (+)-citronellal were performed and showed a slow evaporation rate for PMD and DEET as well as for the modified oil, which may explain their long lasting protection action.     

A Low Energy Approach for the Preparation of Nano-Emulsions with a High Citral-Content Essential Oil

Pectis elongata is found in the northern and northeastern regions of Brazil. It is considered a lemongrass due to its citric scent. The remarkable citral content and the wide antimicrobial properties and bioactive features of this terpene make this essential oil (EO) eligible for several industrial purposes, especially in cosmetics and phytotherapics. However, to address the problems regarding citral solubility, nano-emulsification is considered a promising strategy thanks to its improved dispersability. Thus, in this paper we propose a low-energy approach for the development of citral-based nano-emulsions prepared with P. elongata EO. The plant was hydrodistillated to produce the EO, which was characterized with a gas chromatograph coupled to mass spectrometry. The nano-emulsion prepared by a non-heated water titrating (low-energy) method was composed of 5% (w/w) EO, 5% (w/w) non-ionic surfactants and 90% (w/w) deionized water and was analyzed by dynamic light scattering. Levels of citral of around 90% (neral:geranial—4:5) were detected in the EO and no major alteration in the ratio of citral was observed after the nano-emulsification. The nano-emulsion was stable until the 14th day (size around 115 nm and polydispersity index around 0.2) and no major alteration in droplet size was observed within 30 days of storage. Understanding the droplet size distribution as a function of time and correlating it to concepts of compositional ripening, as opposing forces to the conventional Ostwald ripening destabilization mechanism, may open interesting approaches for further industrial application of novel, low-energy, ecofriendly approaches to high citral essential oil-based nano-emulsions based on lemongrass plants.     

Larvicidal activity of plant extracts from Colombian North Coast against Aedes aegypti L. mosquito larvae

The Aedes aegypti L. mosquito is considered the most important vector of arboviruses in the world. Insecticide-resistant phenomenon is a difficult barrier to overcome for government health entities around the planet. This problem forces to increase the concentrations of insecticides in the environment causing environmental pollution and health threat to human beings. Plants have been used to combat pests for centuries and are an eco-friendly source for the search for molecules with larvicidal activity. In this work, 65 ethanol-soluble extracts from 56 plants of the Colombian Caribbean region were evaluated as potential larvicides against Aedes aegypti mosquito, as well as, for their toxic effects on non-target organism. A high larvicidal activity was found for 16 ethanol extracts, however, the most potent activity against the larvae was obtained for the five plant extracts corresponding to the seeds of Annona squamosa L., Annona cherimolia L., Annona muricata L., Tabernaemontana cymosa Jacq. and Mammea americana L., with LC₅₀ value of 58.44, 65.10, 84.92, 25.02 and 38.58 ppm, respectively. T. cymosa seeds extract was selected for bio-guided fractionation due to the high larvicidal activity showed. Through chromatographic techniques and Nuclear Magnetic Resonance (NMR), five indole alkaloids were isolated and characterized from T. cymosa active fraction; among them, voacangine showed activity with a LC₅₀ of 5.13 ppm indicating a high larvicidal potency besides low toxicity against model organism Caenorhabditis elegans. We also report a new indole alkaloid from T. cymosa. Our study demonstrated the potential of the Colombian Caribbean flora as a host of bioactive plants against important vectors such as the A. aegypti mosquito with potential use in controlled environments.     

Modification of the stability of oil-in-water nano-emulsions by polymers with different structures

The effect of polymers (hydrolyzed polyacrylamide (HPAM) and hydrophobically modified polyacrylamide (HMPAM)) on the stability of oil-in-water nano-emulsions has been studied in paraffin oil/Span 20-Tween 20/water systems by method of phase inversion composition (PIC). The stabilization of nano-emulsions was investigated by visual observation and the change of water content induced by centrifugation. Droplet size distributions of nano-emulsions were obtained by a laser-scanner particle size distribution analyzer. The interfacial tension and charge of nano-emulsions were obtained by interfacial tension and zeta potential measurements. All the results indicate that the droplet size can be decreased by the addition of HMPAM, while almost no change could be observed when the HPAM was added. Meanwhile, HMPAM has a better effect on the stabilization of nano-emulsions than HPAM. It may conclude that the HMPAM molecules adsorbed at the oil/water interface of the nano-emulsion droplets. Therefore, the stability of nano-emulsion with the addition of HMPAM is based on both an associative thickening mechanism caused by the alkyl chains of HMPAM molecules and the adsorption of HMPAM at the oil/water interface, which can form a solid film to prevent the Ostwald ripening of nano-emulsion droplets.     

Effect of diutan microbial polysaccharide on the stability and rheological properties of O/W nanoemulsions formed with a blend of Span20-Tween20

The stability and rheological behavior of oil-in-water (O/W) nano-emulsions formed with a blend of Span20-Tween20 have been studied with and without diutan microbial polysaccharide. It is found that there exist thresholds for the water content and emulsifier to obtain stable nano-emulsions using the emulsion inversion phase (EIP) method. The viscosity of the nano-emulsion is proportional to the emulsifier content and inversely proportional to the water content. High emulsifier content is not conducive to the thermal stability of the nano-emulsion. The addition of diutan gum with negative charge into the nano-emulsions increases the electrostatic repulsion between droplets and makes the droplet size smaller and more unifom, slowing down the coalescence and Ostwald ripening of the nano-emulsions. Due to the association of the diutan gum double helix, a three-dimensional network structure is formed in the continuous phase of nano-emulsions, which improves the stability of nano-emulsions and is also the main factor giving the nano-emulsion high viscoelasticity at high temperature. This study offers new insight into the nano-emulsion containing microbial polysaccharide and may serve as a guideline for practical applications of new nano-emulsion systems.     

Insecticidal and Attractant Activities of Magnolia citrata Leaf Essential Oil against Two Major Pests from Diptera: Aedes aegypti (Culicidae) and Ceratitis capitata (Tephritidae)

In this study, Magnolia citrata Noot and Chalermglin (Magnoliaceae) essential oil (MCEO) was evaluated for insecticidal activity against the yellow fever mosquito Aedes aegypti and attractant activity for the Mediterranean fruit fly Ceratitis capitata. The leaves of Magnolia citrata (Giổi chanh) were collected from northwestern Vietnam, and the water-distilled MCEO was analyzed by gas-chromatography and mass spectrometry (GC-MS). The major constituents of MCEO were identified as linalool 19%, geranial 16%, citronellal 14%, neral 14%, and sabinene 12%. MCEO showed 100% mortality at 1 μg/μL against 1st instar larvae of Ae. aegypti (Orlando strain, ORL), and the oil exhibited 54% (ORL) and 68% (Puerto Rico strain) mortality at 5 μg/mosquito against Ae. aegypti adult females. Initial screens showed that MCEO had weak insecticidal activity compared to the positive control permethrin. In bioassays with sterile male C. capitata, MCEO exhibited moderately strong attraction, comparable to that observed with a positive control, Tetradenia riparia essential oil (TREO). Herein, the insecticidal and attractant activities of MCEO are reported for the first time.     

Preparation of water-in-diesel oil nano-emulsion using nonionic surfactants with enhanced stability and flow properties

Formation of water-in-diesel oil (w/o) nano-emulsion has been achieved by a low-energy emulsification method by stabilizing a new combination of nonionic sorbitan esters surfactants, that is PEG20-sorbitan monostearate and sorbitan monooleate in mixed proportions. Different combinations of the surfactants (T6?+?S8) have been tested and the best possible combination of mixed surfactants is found at a surfactants ratio of 35:65 (wt/wt) for T6:S8 at hydrophile–lipophile balance (HLB)?=?8.01, which resulted in smaller droplet size of 44.87?nm. A phase diagram study is performed to identify the zones of formation of transparent, translucent, and opaque emulsions (44?nm??27?m³?·?s^?1. Comparison of Ostwald ripening rate with other sets of surfactants obtained by different authors showed the lowest rate among them, indicative of enhanced stability. A rheological study of the tested set of nano-emulsions depicts the Newtonian behavior (1.0371?≤?n?≤?1.0826) over a wider range of shear rates (10–1000?s^?1) at different temperatures (25–40°C).     

Formation of water-in-oil (W/O) nano-emulsions in a water/mixed non-ionic surfactant/oil systems prepared by a low-energy emulsification method

W/O nano-emulsion formation by a low-energy emulsification method is described for the first time. The nano-emulsions have been formed in water/mixed Cremophor EL:Cremophor WO7 surfactant/isopropyl myristate systems at Cremophor EL:Cremophor WO7 ratios between 1:2 and 1:9, by slow addition of isopropyl myristate to surfactant/water mixtures. Phase behaviour studies have showed that the compositions giving rise to W/O nano-emulsions belong to multiphase regions, one of the phases being a lamellar liquid crystalline phase. The droplet size of the nano-emulsions at a fixed oil concentration of 85% and mixed surfactants/water ratio of 70/30 ranged from 60 to 160 nm as Cremophor EL:Cremophor WO7 ratio increased from 1:8 to 1:2. These nano-emulsions showed high kinetic stability. No phase separation was observed during 5 months in nano-emulsions of the water/Cremophor EL:Cremophor WO7 1:8/isopropyl myristate system with 85% oil concentration, although droplet size experienced an increase with time.     

Insecticidal potential of Ocimum canum plant extracts against Anopheles stephensi,Aedes aegypti and Culex quinquefasciatus larval and adult mosquitoes (Diptera: Culicidae)

Mosquitoes have developed resistance to various synthetic insecticides, making their control increasingly difficult. Insecticides of botanical origin may serve as suitable natural control. This study evaluates the toxic potential of Ocimum canum (Sims) leaf extract and powder against Anopheles stephensi (Liston), Aedes aegypti (Lin) and Culex quinquefasciatus (Say) larval and adult mosquitoes. Larval mortality was observed after 24 h recovery period and adult smoke toxicity observed for 40 min duration at 10 min interval. Methanol extract of O. canum showed highest larval mortality against the larvae of C. quinquefasciatus LC₅₀ = 28.3225, LC₉₀ = 44.1150; Ae. aegypti LC₅₀ = 43.327, LC₉₀ = 61.249; and An. stephensi LC₅₀ = 30.2001, LC₉₀ = 48.2866 ppm. The smoke toxicities were 93% mortality in C. quinquefasciatus, 74% in Ae. aegypti and 79% in An. stephensi adults, respectively, whereas 100% mortality was recorded in the commercial mosquito control. Our results suggest that O. canum leaf extract and powder are natural insecticide, and ideal eco friendly approach for mosquito control.     

Spontaneous Formation of Nano-Emulsions Containing Task-Special Ionic Liquid and CO2 Capture in this Nano-Emulsions System

Nano-emulsions containing task-special ionic liquid ([NH₂ebim][PF₆]) were prepared by spontaneous emulsification. The stability of nano-emulsions was investigated by analysis of droplet size. The microstructure of the mixed solvent including the Triton X-100, n-butanol, and [NH₂ebim][PF₆] was demonstrated based on macular dynamic simulation. The results indicate that nano-emulsions are relatively stable to the droplet growth at static storage, but unstable under high centrifugal force. Simulation results from the macular dynamic calculation show that [NH₂ebim][PF₆] locates in the hydrophobic layer of Triton X-100 and n-butanol, which is available for enhancing CO₂ mass transfer in an absorption process. Nano-emulsions were used as the absorbent to absorb CO₂ in absorption experiments, and the absorption rates were investigated. The results show that nano-emulsion containing [NH₂ebim][PF₆] can enhance CO₂ absorption rate compared to the system that pure water was used as the absorbent. The reason is attributed to the reversible chemical reaction between [NH₂ebim][PF₆] and CO₂ on the interface of oil and water, which decreases the concentration of CO₂ in the bulk so as to increase the mass transfer driving force between gas and liquid. Therefore, the chemical reaction on the interface of oil and water promotes the absorption process.     

Synthesis, structural and larvicidal studies of some triorganotin 2-(p-chlorophenyl)-3-methylbutyrates

A series of triorganotin 2-(p-chlorophenyl)-3-methylbutyrates, (R₃SnO₂CCH(CH(CH₃)₂)C₆H₄Cl-4), where R = methyl, ethyl, n-propyl, n-butyl, phenyl and cyclo-hexyl, have been synthesized. Elemental analyses, Mössbauer, Infrared and NMR spectroscopies have been used to characterize their structures. Based on the spectroscopic results, all the complexes with the exception of the tricyclohexyl compound were found to be five-coordinated in the solid state while the tricyclohexyltin derivative was determined to be four-coordinated. Structural assignments based on spectroscopic data are supported by the crystallographic results of four of the triorganotin butyrates (trimethyl-, tri-n-propyl-, tri-n-butyl- and tricyclohexyltin 2-(p-chlorophenyl)-3-methylbutyrate). Multinuclear NMR spectroscopy studies indicated that all the complexes were tetrahedral in solution. Larvicidal activities of the complexes were evaluated against the 2nd instar stage of the Anopheles stephensi, Aedes aegypti and Culex pipiens quinquefasciatus mosquitoes. The toxicity data indicate that there does not appear to be any significant differences of the compounds towards the different mosquito species based on their averaged toxicity values. In addition, the toxicity of the triorganotin compounds towards the mosquito larvae was concluded to be dependent on both the compound and the species of mosquito larvae.     

Larvicidal Activity of Cinnamic Acid Derivatives: Investigating Alternative Products for Aedes aegypti L. Control

The mosquito Aedes aegypti transmits the virus that causes dengue, yellow fever, Zika and Chikungunya viruses, and in several regions of the planet represents a vector of great clinical importance. In terms of mortality and morbidity, infections caused by Ae. aegypti are among the most serious arthropod transmitted viral diseases. The present study investigated the larvicidal potential of seventeen cinnamic acid derivatives against fourth stage Ae. aegypti larvae. The larvicide assays were performed using larval mortality rates to determine lethal concentration (LC₅₀). Compounds containing the medium alkyl chains butyl cinnamate (7) and pentyl cinnamate (8) presented excellent larvicidal activity with LC₅₀ values of around 0.21–0.17 mM, respectively. While among the derivatives with aryl substituents, the best LC₅₀ result was 0.55 mM for benzyl cinnamate (13). The tested derivatives were natural compounds and in pharmacology and antiparasitic studies, many have been evaluated using biological models for environmental and toxicological safety. Molecular modeling analyses suggest that the larvicidal activity of these compounds might be due to a multi-target mechanism of action involving inhibition of a carbonic anhydrase (CA), a histone deacetylase (HDAC2), and two sodium-dependent cation-chloride co-transporters (CCC2 e CCC3).     

Analysis of the Essential Oil of Elsholtzia ciliate Aerial Parts and Its Insecticidal Activities against Liposcelis bostrychophila

Water‐distilled essential oil from Elsholtzia ciliate (Labiatae) aerial parts at flowering stage was analyzed by gas chromatography/mass spectrometry (GC/MS). Thirty‐six compounds, accounting for 98.3% of the total oil content, were identified, and the main components of the essential oil were dehydroelsholtzia ketone (26.5%), (R)‐carvone (16.6%), elsholtzia ketone (14.6%), and D ‐limonene (4.1%). The essential oil contained higher amounts of monoterpenoids (83.4%) than of sesquiternoids (8.3%). Bioactivity‐directed chromatographic separation of the essential oil on repeated silica gel columns led to the isolation of three monoterpenoids. The essential oil possessed fumigant toxicity against the booklice (Liposcelis bostrychophila) with an LC₅₀ value of 475.2 μg/l, while the isolated constituents, (R)‐carvone, dehydroelsholtzia ketone, and elsholtzia ketone had LC₅₀ values of 417.4, 658.2, and 547.3 μg/l, respectively. The essential oil also exhibited contact toxicity against L. bostrychophila with an LC₅₀ value of 145.5 μg/cm². (R)‐Carvone, dehydroelsholtzia ketone, and elsholtzia ketone exhibited acute toxicity against the booklice with LC₅₀ values of 57.0, 151.5, and 194.1 μg/cm², respectively. The results indicated that the essential oil and the isolated constituents have potential for the development into natural insecticides/fumigants for the control of insects in stored grains.     

Nano-emulsions: New applications and optimization of their preparation

Nano-emulsions, as non-equilibrium systems, present characteristics and properties which depend not only on composition but also on the preparation method. Although interest in nano-emulsions was developed since about 20 years ago, mainly for nanoparticle preparation, it is in the last years that direct applications of nano-emulsions in consumer products are being developed, mainly in pharmacy and cosmetics. These recent applications have made that studies on optimization methods for nano-emulsion preparation be a requirement. This review is focused on the most recent literature on developments of nano-emulsions as final application products and on the optimization of their preparation.     

Phase behavior and nano-emulsion formation by the phase inversion temperature method

Formation of oil-in-water nano-emulsions has been studied in the water/C12E4/isohexadecane system by the phase inversion temperature emulsification method. Emulsification started at the corresponding hydrophilic-lipophilic balance temperature, and then the samples were quickly cooled to 25 degrees C. The influence of phase behavior on nano-emulsion droplet size and stability has been studied. Droplet size was determined by dynamic light scattering, and nano-emulsion stability was assessed, measuring the variation of droplet size as a function of time. The results obtained showed that the smallest droplet sizes were produced in samples where the emulsification started in a bicontinuous microemulsion (D) phase region or in a two-phase region consisting of a microemulsion (D) and a liquid crystalline phase (L(alpha)). Although the breakdown process of nano-emulsions could be attributed to the oil transference from the smaller to the bigger droplets, the increase in instability found with the increase in surfactant concentration may be related to the higher surfactant excess, favoring the oil micellar transport between the emulsion droplets.     

Properties of water-in-oil (W/O) nano-emulsions prepared by a low-energy emulsification method

Properties of water-in-oil (W/O) nano-emulsion formed by a low-energy emulsification method are described in this work. Nano-emulsions have been formed in water/mixed non-ionic surfactant/decane. Several mixtures of Span 20, Span 80, Tween 20 and Tween 80 were studied. Phase behavior studies and stability studies allowed to determine zones where nano-emulsions can be formed. Bluish and transparent W/O nano-emulsion with droplet sizes as low as 30 nm was formed. Nano-emulsion droplet size was measured by Dynamic Light Scattering. Nano-emulsions stability was studied by multiple light scattering and by dynamic light scattering. The results showed the evolution with time of the average radius droplet. The nano-emulsions prepared showed high kinetic stability for weeks, without phase separation, sedimentation or creaming. Nevertheless, their droplet size increased slightly over time. Stability studies show that nano-emulsion breakdown could be attributed to Ostwald ripening and coalescence mechanism, depending on the water concentration.     

Novel Acetogenins from the Leaves of Annona purpurea

The CH₂Cl₂ extract of the leaves Annona purpurea L. (Annonaceae) showed strong brine shrimp toxicity and pronounced activity against larvae of the yellow-fever mosquito Aedes aegypti. Activity-directed fractionation of the extract by a combination of column chromatography on silica gel, filtration, and high-pressure liquid chromatography led to the isolation of acetogenins 1–6 as the main active principles. The structures of two novel acetogenins named purpureacin 1( 5 ) and purpureacin 2 (6) were elucidated by spectroscopic analysis (UV, EI- and DCI-MS, EI-MS of Me₃Si derivatives,¹H- and ¹³C-NMR). The configuration of 5 and 6 was not established due to the limited sample amount. Compounds 3–6 also showed antifungal activity against Candida albicans, and 5 was slightly active against Bacillus subtilis.