Physicochemical properties of nevirapine-loaded solid lipid nanoparticles and nanostructured lipid carriers

Solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) coated with human serum albumin (HSA) were fabricated for formulating nevirapine (NVP). Here, NLCs contained low-melting-point oleic acid (OA) in the internal lipid phase. The results revealed that the two nanoparticles were uniformly distributed with the average diameter ranging from 145 to 180 nm. The surface HSA neutralized the positive charge of dimethyldioctadecyl ammonium bromide (DODAB) on SLNs and NLCs and reduced their zeta potential. In a fixed ratio of solid lipids, SLNs entrapped more NVP than NLCs. The incorporation of OA also reduced the thermal resistance of NLCs and accelerated the release of NVP from the nanocarriers. When incubated with DODAB-stabilized SLNs, the viability of human brain-microvascular endothelial cells (HBMECs) reduced. However, the surface HSA increased the viability of HBMECs about 10% when the concentration of SLNs was higher than 0.8 mg/mL. HSA-grafted SLNs and NLCs can be effective formulations in the delivery of NVP for viral therapy.     

Tryptanthrin-loaded nanoparticles for delivery into cultured human breast cancer cells, MCF7: the effects of solid lipid/liquid lipid ratios in the inner core

Tryptanthrin is an ancient medicine which recently was also found to have a function of downregulating multidrug resistance (MDR). However, tryptanthrin is insoluble in water, which limits its availability for delivery into cancer cells. There is a need to improve delivery systems to increase the inhibition of MDR. The aim of this study was to employ nanoparticles encapsulating tryptanthrin to improve the delivery and promote the sustained release of this drug. The approach was to encapsulate tryptanthrin in various nanoparticles, including solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), and lipid emulsions (LEs). We compared the particle size and zeta potential of these nanoparticles, and evaluated the partitioning behavior of tryptanthrin in them. We also determined the release kinetics of tryptanthrin from these nanoparticles. Moreover, cellular cytotoxicity toward and uptake of tryptanthrin-loaded nanoparticles by human breast cancer cells were determined. We found that the mean particle size of NLCs was lower, and the partition coefficient was higher than those of SLNs, and an increased tryptanthrin release rate was found with the NLC delivery system. NLCs achieved the sustained release of tryptanthrin without an initial burst. In particular, the NLC-C formulation, composed of a mixture of Compritol and squalene as the core materials, showed the highest release rate and cytotoxic effect. Confocal laser scanning microscopic images confirmed drug internalization into cells which enhanced the endocytosis of the particles. These results suggested that NLCs can potentially be exploited as a drug carrier for topical or intravenous use in the future.     

Influence of lipid content and dilution on properties and stability of nanostructured lipid carriers (NLCs) prepared from rambutan (Nephelium lappaceum L.) kernel fat and evaluation of their β-carotene loading capacity

Abstract

The effects of lipid content and dilution on the properties and stability of nanostructured lipid carriers (NLCs) prepared from rambutan (Nephelium lappaceum L.) kernel fat were investigated. The β-carotene-loading capacity of the NLCs was also evaluated. NLCs containing various lipid phase concentrations (5, 10, and 15?wt%) were prepared using Tween 80 as the emulsifier with a lipid to emulsifier weight ratio of 1:0.2. The results showed that an increase in the lipid content up to 15?wt% had no effect on the zeta-potential, particle size and polydispersity index but resulted in a higher particle density. All samples showed no phase separation during storage at 25?°C for 28?days; however, the relative recrystallization index (RRI) increased. Dilution of concentrated NLC (15?wt%) to a lower lipid content (5 and 10?wt%) produced no differences in the particle characteristics and stability during storage. NLCs loaded with β-carotene at different concentrations (0, 0.5, and 1?wt% of the lipid phase) exhibited desirable characteristics and had high encapsulation efficiency (～97%) over 28?days of storage. These results demonstrated that NLC prepared from rambutan kernel fat can be used to entrap lipophilic bioactive components which could be used as ingredients in functional food products.     

The contrasting kinetics of peroxidation of vitamin E-containing phospholipid unilamellar vesicles and human low-density lipoprotein

It is well established that alpha-tocopherol, TocH, is an outstanding lipid-soluble, peroxyl radical trapping antioxidant in homogeneous systems. It is also well established that TocH functions as a prooxidant in human low-density lipoprotein, LDL, subjected to attack by peroxyl radicals generated in the aqueous phase by, for example, thermal decomposition of the azo compound, ABAP. This tocopherol-mediated peroxidation, TMP, of LDL involves a three-step chain reaction, one step being hydrogen atom abstraction from the LDL lipids by the tocopheroxyl radical, Toc*. The occurrence of TMP has been attributed to three factors, (i) translocation by TocH of radical character from the aqueous phase into LDL lipid, (ii) isolation of the water-insoluble Toc* in the LDL particle in which it is formed for times sufficient to permit it to react with the lipid, and (iii) the small lipid volume of LDL which ensures that no particle can contain more than a single radical for a significant length of time. This consensus view of TMP implies that it should occur in any TocH-containing dispersion of small lipid particles. However, the present examination of the kinetics of the ABAP-initiated peroxidation of small unilamellar vesicles, SUVs, made from palmitoyllinoleoylphosphatidylcholine and cholesterol with a composition designed to mimic the surface coat of LDL, has shown that TocH functions as an antioxidant in such systems and that TMP does not occur under conditions where it would have occurred if the particles had been LDL. Several possible reasons for the kinetic differences between SUVs and LDL have been considered and ruled out by experiment. It is concluded that TMP can occur in LDL because these particles contain a lipid core in which the Toc* radical "hides" for much of its lifetime well away from the peroxyl radicals in the aqueous phase. In contrast, because SUVs have no lipid core, the Toc(*) radical is always "exposed" and available to aqueous peroxyl radicals with which it reacts rapidly and is destroyed before it can abstract a hydrogen atom from the lipid.     

Colloidal particles as elastic triads in nematic liquid crystals

ABSTRACT

In this short review we summarise already published results to manifest very important role of high order elastic terms in the formation of colloidal structures in nematic liquid crystals (NLC). We reveal that every colloidal particle in nematics can be effectively represented as a triad of nonzero elastic moments. Usually colloidal particles in NLCs are treated with their elastic dipole and/or quadrupole moments only. But we demonstrate that octupole, hexadecapole and even 64-pole moments play an important role as well and determine parameters of different 1D, 2D and even 3D colloidal crystals in NLCs. In general the triad of the first three nonzero elastic moments can describe almost all colloidal structures observed so far. Dipole particles should be considered as hard spheroids with a triad of the dipole, quadrupole and octupole moments. Quadrupole particles should be treated as hard spheres with a triad of quadrupole, hexadecapole and 64-pole elastic moments

PACS numbers: 61.30.Dk, 82.70.Dd, 64.70.M?     

Perspectives and Prospective on Solid Lipid Nanoparticles as Drug Delivery Systems

Combating multiple drug resistance necessitates the delivery of drug molecules at the cellular level. Novel drug delivery formulations have made it possible to improve the therapeutic effects of drugs and have opened up new possibilities for research. Solid lipid nanoparticles (SLNs), a class of colloidal drug carriers made of lipids, have emerged as potentially effective drug delivery systems. The use of SLNs is associated with numerous advantages such as low toxicity, high bioavailability of drugs, versatility in the incorporation of hydrophilic and lipophilic drugs, and the potential for production of large quantities of the carrier systems. The SLNs and nanostructured lipid carriers (NLCs) are the two most frequently used types of nanoparticles. These types of nanoparticles can be adjusted to deliver medications in specific dosages to specific tissues, while minimizing leakage and binding to non-target tissues.     

Formulating fluticasone propionate in novel PEG-containing nanostructured lipid carriers (PEG-NLC)

The aim of this study was to develop nanostructured lipid carriers (NLC) for topical delivery of fluticasone propionate (FP) with the aim to further improve the safety profile and decrease the adverse-side effects commonly reported in topical corticotherapy. NLC are colloidal drug-carriers consisting of a blend of a solid lipid and a small amount of liquid lipid since these carriers have proved to be effective in epidermal targeting in particular of glucocorticoids. NLC consisting of glyceryl palmito-stearate, and PEG-containing medium chain triglycerides mixture, stabilised by polysorbate 80 and soybean phosphatidylcholine were prepared. A mean particle size between 380 and 408 nm and entrapment efficacy of 95% were obtained for FP-loaded NLC. The crystallinity and polymorphic phase behaviour of FP-free and FP-loaded NLC were examined by differential scanning calorimetry and wide angle X-ray diffraction. Results revealed a low-crystalline structure and confirmed the incorporation of FP into the particles. The suitability of PEG-containing liquid lipids to form the lipid matrix of NLC was also confirmed.     

Photostability enhancement by encapsulation of α-tocopherol into lipid-based nanoparticles loaded with a UV filter

The aim of this study was to develop some sunscreen formulations able to maintain their photoprotection when exposed to UV radiation. In this context, the influence of the antioxidant α-tocopherol on the photostability of lipid-based nanoparticles, namely solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs), encapsulated with a UVA filter, has been investigated. The nanoparticles co-encapsulated with both actives exhibited dimensions smaller than 200 nm and zeta potentials of –45 mV. The photoprotection of the creams based on lipid nanoparticles was evaluated in terms of two protection factors, SPF and erythemal UVA–PF. By exposing the creams to UV radiation, it was observed that tocopherol results in obtaining quite stable formulations, but it does not improve the overall photoprotection much. However, by adding the antioxidant to the formulation confers a double action: protection of the skin against reactive oxygen species and the photostabilization of the UVA filter into lipid nanoparticles.     

How lipid unsaturation, peroxyl radical partitioning, and chromanol lipophilic tail affect the antioxidant activity of α-tocopherol: direct visualization via high-throughput fluorescence studies conducted with fluorogenic α-tocopherol analogues

The preparation of two highly sensitive fluorogenic α-tocopherol (TOH) analogues which undergo >30-fold fluorescence intensity enhancement upon reaction with peroxyl radicals is reported. The probes consist of a chromanol moiety coupled to the meso position of a BODIPY fluorophore, where the use of a methylene linker (BODIPY-2,2,5,7,8-pentamethyl-6-hydroxy-chroman adduct, H(2)B-PMHC) vs an ester linker (meso-methanoyl BODIPY-6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid, H(2)B-TOH) enables tuning their reactivity toward H-atom abstraction by peroxyl radicals. The development of a high-throughput fluorescence assay for monitoring kinetics of peroxyl radical reactions in liposomes is subsequently described where the evolution of the fluorescence intensity over time provides a rapid, facile method to conduct competitive kinetic studies in the presence of TOH and its analogues. A quantitative treatment is formulated for the temporal evolution of the intensity in terms of relative rate constants of H-atom abstraction (k(inh)) from the various tocopherol analogues. Combined, the new probes, the fluorescence assay, and the data analysis provide a new method to obtain, in a rapid, parallel format, relative antioxidant activities in phospholipid membranes. The method is exemplified with four chromanol-based antioxidant compounds differing in their aliphatic tails (TOH, PMHC, H(2)B-PMHC, and H(2)B-TOH). Studies were conducted in six different liposome solutions prepared from poly- and mono-unsaturated and saturated (fluid vs gel phase) lipids in the presence of either hydrophilic or lipophilic peroxyl radicals. A number of key insights into the chemistry of the TOH antioxidants in lipid membranes are provided: (1) The relative antioxidant activities of chromanols in homogeneous solution, arising from their inherent chemical reactivity, readily translate to the microheterogeneous environment at the water/lipid interface; thus similar values for k(inh)(H(2)B-PMHC)/k(inh)(H(2)B-TOH) in the range of 2-3 are recorded both in homogeneous solution and in liposome suspensions with hydrophilic or lipophilic peroxyl radicals. (2) The relative antioxidant activity between tocopherol analogues with the same inherent chemical reactivity but bearing short (PMHC) or long (TOH) aliphatic tails, k(inh)(PMHC)/k(inh)(TOH), is ~8 in the presence of hydrophilic peroxyl radicals, regardless of the nature of the lipid membrane into which they are embedded. (3) Antioxidants embedded in saturated lipids do not efficiently scavenge hydrophilic peroxyl radicals; under these conditions wastage reactions among peroxyl radicals become important, and this translates into larger times for antioxidant consumption. (4) Lipophilic peroxyl radicals show reduced discrimination between antioxidants bearing long and short aliphatic tails, with k(inh)(PMHC)/k(inh)(TOH) in the range of 3-4 for most lipid membranes. (5) Lipophilic peroxyl radicals are scavenged with the same efficiency by all four antioxidants studied, regardless of the nature of their aliphatic tail or the lipid membrane into which they are embedded. These data underpin the key role the lipid environment plays in modulating the rate of reaction of antioxidants characterized by similar inherent chemical reactivity (arising from a conserved chromanol moiety) but differing in their membrane mobility (structural differences in the lipophilic tail). Altogether, a novel, facile method of study, new insights, and a quantitative understanding on the critical role of lipid diversity in modulating antioxidant activity in the lipid milieu are reported.     

Nanostructured lipid carriers based suppository for enhanced rectal absorption of ondansetron: In vitro and in vivo evaluations

The current research aimed to fabricate ondansetron nanostructured lipid carriers (OND-NLCs) and incorporate them into a suppository base to manage chemotherapy-induced vomiting and nausea, which offer the advantage of both rapid onset and prolonged release. NLCs were fabricated by adopting the solvent diffusion method. The binary lipid mixture of oleic acid (liquid lipid) and lauric acid (solid lipid) were prepared in distinct ratios. The NLCs were characterized concerning the surface charge, size, drug encapsulation efficiency, and surface morphology. In addition, the influence of surfactant, co-surfactant, and lipid on entrapment efficiency and particle size was investigated. Phosphate buffer having pH 7.4 is used for evaluating in vitro drug release by utilizing a dialysis membrane. Various kinetics models were used to estimate the drug release kinetics of fabricated nanostructured lipid carriers. The particle size of the NLCs was calculated between 101 and 378 nm with negative zeta potential on the NLC’s surface. The entrapment efficiency was found between 68 and 87%. Scanning Electron Microscopic analysis showed the spherical shape of nanostructured lipid carriers. The dissolution profile of the ondansetron-loaded NLC suppository depicts biphasic behavior of firstly burst release then slow release was observed. The diffusion controlled release was evident from kinetic modeling. The succeeding step comprehended the fabrication and characterization of NLC-based suppositories utilizing NLC formulations that demonstrated the combined advantage of rapid onset, prolonged release, and better in vivo bioavailability as compared to control suppository.     

The Elucidation of Peroxyl Radical Reactions in Aqueous Solution with the Help of Radiation-Chemical Methods

Whenever free radicals are formed, independent of whether this occurs thermally, is induced by UV or ionizing irradiation, or takes place in redox reactions, they are converted rapidly into the corresponding peroxyl radicals in the presence of oxygen. Peroxyl radical reactions in aqueous environments are observed not only in aquatic systems (e.g., rivers, lakes and oceans) but also in the living cell and to a considerable degree even in the atmosphere (in water droplets). The peroxyl radical chemistry occurring in this medium is often very different from that observed in the gas phase or in organic solvents. In spite of the great importance of these reactions in medicine (for example in anti-cancer irradiation therapy and ischaemia) there have been comparatively few studies of peroxyl reactions in aqueous media. Radiation-chemical techniques such as pulse radiolysis offer the best means for carrying out such studies, so that it is not surprising that the majority of the information available in this area has been obtained with the help of radiation-chemical methods. The radiation chemistry of water can be con trolled in such a manner that the main products are ^˙OH radicals (90 % yield), which react with substrate molecules to give substrate radicals and in the presence of oxygen to give substrate peroxyl radicals. The experimental conditions can also be varied in such a way that HO/O radicals can be formed in 100 % yield and caused to react with substrates. We therefore have a simple access to these intermediates, which are extremely important in biological systems. A detailed product analysis, supported by kinetic studies carried out with the help of pulse radiolysis, has been used to clarify the chemistry of a series of peroxyl radicals, so that sufficient material is now available to justify a review of the variety of the peroxyl radical reactions studied by means of radiation-chemical methods. A more general survey of the physical properties of the peroxyl radicals and their unimolecular and bimolecular reactions will be followed by a discussion of selected examples of various classes of substance. Because of the great biological importance of radical-induced DNA damage this area will also be treated briefly.     

Theoretical calculations of carbon-oxygen bond dissociation enthalpies of peroxyl radicals formed in the autoxidation of lipids

Theoretical calculations were carried out to provide a framework for understanding the free radical oxidation of unsaturated lipids. The carbon[bond]hydrogen bond dissociation enthalpies (BDEs) of organic model compounds and oxidizable lipids (R[bond]H) and the carbon[bond]oxygen bond dissociation enthalpies of peroxyl radical intermediates (R[bond]OO*) have been calculated. The carbon[bond]hydrogen BDEs correlate with the rate constant for propagation of free radical autoxidation, and the carbon[bond]oxygen BDEs of peroxyl radicals correlate with rate constants for beta-fragmentation of these intermediates. Oxygen addition to intermediate carbon radicals apparently occurs preferentially at centers having the highest spin density. The calculated spin distribution therefore provides guidance about the partitioning of oxygen to delocalized carbon radicals. Where the C[bond]H BDEs are a function of the extent of conjugation in the parent lipid and the stability of the carbon radical derived therefrom, C[bond]OO* BDEs are also affected by hyperconjugation. This gives way to different rates of beta-fragmentation of peroxyl radicals formed from oxygen addition at different sites along the same delocalized radical. We have also studied by both theory and experiment the propensity for benzylic radicals to undergo oxygen addition at their ortho and para carbons which, combined, possess an equivalent unpaired electron spin density as the benzylic position itself. We find that the intermediate peroxyl radicals in these cases have negative C[bond]OO* BDEs and, thus, have rate constants for beta-fragmentation that exceed the diffusion-controlled limit for the reaction of a carbon-centered radical with oxygen.     

Lipid-Based Nanostructures for the Delivery of Natural Antimicrobials

Encapsulation can be a suitable strategy to protect natural antimicrobial substances against some harsh conditions of processing and storage and to provide efficient formulations for antimicrobial delivery. Lipid-based nanostructures, including liposomes, solid lipid nanoparticles (SLNs), and nanostructured lipid nanocarriers (NLCs), are valuable systems for the delivery and controlled release of natural antimicrobial substances. These nanostructures have been used as carriers for bacteriocins and other antimicrobial peptides, antimicrobial enzymes, essential oils, and antimicrobial phytochemicals. Most studies are conducted with liposomes, although the potential of SLNs and NLCs as antimicrobial nanocarriers is not yet fully established. Some studies reveal that lipid-based formulations can be used for co-encapsulation of natural antimicrobials, improving their potential to control microbial pathogens.     

Coencapsulation of Butyl‐Methoxydibenzoylmethane and Octocrylene into Lipid Nanocarriers: UV Performance,Photostability and in vitro Release

The coencapsulation of two UV filters, butyl‐methoxydibenzoylmethane (BMDBM) and octocrylene (OCT), into lipid nanocarriers was explored to develop stable cosmetic formulations with broad‐spectrum photoprotection and slow release properties. Different types of nanocarriers in various concentrations of the two UV filters were tested to find the combination with the best absorption and release properties. Solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) have been the two types of lipid nanocarriers used. The NLCs were based on either medium chain triglycerides (MCT) or squalene (Sq). The following physicochemical properties of the nanocarriers have been evaluated: particle size, morphology, zeta potential (ZP), entrapment efficiency, loading capacity, and thermal behavior. The nanocarriers have been formulated into creams containing low amounts of UV filters (2.5% BMDBM and 1% OCT). The best photoprotection results were obtained with the cream based on NLCs prepared with MCT, having a sun protection factor (SPF) of 17.2 and an erythemal UVA protection factor (EUVA–PF) of 50.8. The photostability of the encapsulated BMDBM filter was confirmed by subjecting the nanocarriers‐based creams to in vitro irradiation. The prolonged UV‐protection efficacy was coupled with a slow in vitro release of the synthetic UV filters, which followed the Higuchi release model.     

Amino-substituted amphiphilic calixarenes: self-assembly and interactions with DNA

The amphiphilic 5,11,17,23-tetramino-25,26,27,28-tetradodecyloxycalix[4]arene is shown to self-assemble as stable and well-defined Langmuir monolayers at the air-water interface. The effect of the presence of DNA in the subphase reveals interactions taking place at the interface between the positively charged surface and the negatively charged DNA, causing an expansion of the monolayers and a phase transition from a liquid-condensed to a liquid-expanded phase; a slight decrease in the stability of the monolayers is also observed. The title compound is shown to self-assemble, with the absence of a cosurfactant, as stable colloidal suspensions. Photon correlation spectroscopy, zeta-potential measurements, and atomic force microscopy reveal that these colloidal suspensions present a monodisperse size distribution and are composed of positively charged solid lipid nanoparticles (SLNs), with an average hydrodynamic diameter of 190 nm and a surface potential of +13.2 mV. The interaction of these SLNs with double-stranded DNA is demonstrated.     

A Mini-Review on Solid Lipid Nanoparticles and Nanostructured Lipid Carriers: Topical Delivery of Phytochemicals for the Treatment of Acne Vulgaris

Acne vulgaris (acne) is one of the most common dermatological problems affecting adolescents and young adults. Although acne may not lead to serious medical complications, its psychosocial effects are tremendous and scientifically proven. The first-line treatment for acne is topical medications composed of synthetic compounds, which usually cause skin irritation, dryness and itch. Therefore, naturally occurring constituents from plants (phytochemicals), which are generally regarded as safe, have received much attention as an alternative source of treatment. However, the degradation of phytochemicals under high temperature, light and oxygen, and their poor penetration across the skin barrier limit their application in dermatology. Encapsulation in lipid nanoparticles is one of the strategies commonly used to deliver drugs and phytochemicals because it allows appropriate concentrations of these substances to be delivered to the site of action with minimal side effects. Solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) are promising delivery systems developed from the combination of lipid and emulsifier. They have numerous advantages that include biocompatibility and biodegradability of lipid materials, enhancement of drug solubility and stability, ease of modulation of drug release, ease of scale-up, feasibility of incorporation of both hydrophilic and lipophilic drugs and occlusive moisturization, which make them very attractive carriers for delivery of bioactive compounds for treating skin ailments such as acne. In this review, the concepts of SLNs and NLCs, methods of preparation, characterization, and their application in the encapsulation of anti-acne phytochemicals will be discussed.     

Polymeric encapsulated membrane for optrodes

Highly efficient and simple reagent immobilisation procedure for an optrode membrane has been developed. The preparation procedure combines two well-known physical immobilisation procedures, viz. adsorption and encapsulation techniques, applied sequentially which, in turn, produce a combined optical sensing layer. The sensitive polymeric encapsulated membrane (PEM) contains the polymeric resin, which can adsorb a large amount of indicator dye, encapsulated within porous polymeric structure. The procedure has been tested in the preparation of a pH sensor.     

Chain-breaking antioxidant activity of phosphite esters

The inhibition of the autoxidation of hydrocarbons and polypropylene by aliphatic, aromatic, sterically hindered and cyclic phosphites has been studied by means of volumetric and ³¹P-NMR techniques. The antioxidant activity of phosphites depends on the rate of their reactions with peroxyl radicals and on the way they react with alkoxyl radicals. Only those phosphites which react by substitution to give free aryloxyl radicals are effective as chain-breaking antioxidants.The reaction modes of various phosphites with various peroxyl and alkoxyl radicals have been studied in some model reactions and the relationship between structure, reaction mechanism and antioxidant activity has been elucidated.     

Nanostructured Lipid Carriers (NLC) for Biologically Active Green Tea and Fennel Natural Oils Delivery: Larvicidal and Adulticidal Activities against Culex pipiens

(1) Background: The control of mosquitoes with essential oils is a growing demand. (2) Methods: This study evaluated the novel larvicidal and adulticidal activity of fennel and green tea oils and their nanostructured lipid carriers (NLC) against Culex pipiens (C. pipiens) in the laboratory, field conditions and evaluated their effect against non-target organisms. SLN type II nanoformulations were synthesized and characterized using dynamic light scattering (DLS), zeta potential and transmission electron microscope. (3) Results: The synthesized NLCs showed spherical shaped, homogenous, narrow, and monomodal particle size distribution. The mortality percent (MO%) post-treatment (PT) with 2000 ppm for 24 h with fennel oil and NLC fennel (NLC-F) reached 85% (LC₅₀ = 643.81 ppm) and 100% (LC₅₀ = 251.71), whereas MO% for green tea oil and NLC green tea (NLC-GT) were 80% (LC₅₀ = 746.52 ppm) and 100% (LC₅₀ = 278.63 ppm), respectively. Field trial data showed that the larval reduction percent of fennel oil and NLC-F reached 89.8% and 97.4%, 24 h PT and the reduction percent of green tea oil and NLC-GT reached 89% and 93%, 24 h PT with persistence reached 8 and 7 days, for NLC-F and NLC-GT, respectively. The adulticidal effects showed that NLC-F and NLC-GT (100% mortality) were more effective than fennel and green tea oils (90.0% and 83.33%), with 24 h PT, respectively. Moreover, their reduction of adult density after spraying with LC₉₅ X2 for 15 min, with fennel oil, NLC-F, and green tea oil, NLC-GT were 83.6%, 100%, 79.1%, and 100%, respectively, with persistence (>50%) lasting for three days. The predation rate of the mosquitofish, Gambusia affinis, and the bug, Sphaerodema urinator, was not affected in both oil and its NLC, while the predation rate of the beetle, Cybister tripunctatus increased (66% and 68.3%) by green tea oil and NLC-GT, respectively. (4) Conclusions: NLCs nanoformulation encapsulated essential oils was prepared successfully with unique properties of size, morphology, and stability. In vitro larvicidal and adulticidal effects against C. pipiens supported with field evaluations have been performed using essential oils and their nanoformulations. The biological evaluation of nanoformulations manifested potential results toward both larvicidal and adulticidal compared to the essential oils themselves, especially NLC encapsulated fennel oil which had promising larvicidal and adulticidal activity.     

Mechanism of action of sensors for reactive oxygen species based on fluorescein-phenol coupling: the case of 2-[6-(4'-hydroxy)phenoxy-3H-xanthen-3-on-9-yl]benzoic acid

We demonstrate the ability of a sensor containing a tethered fluorescein-phenol structure to react with peroxyl radicals and with an oxidizing agent such as potassium ferricyanide. This latter reaction yields the corresponding peroxyl radical as observed by EPR analysis. We propose that the reaction of the sensor with peroxyl and alkoxyl radicals is also initiated by the formation of the phenoxyl radicals, which is followed by radical-radical reactions and product hydrolysis responsible for the release of fluorescein. The proposed mechanism is based on results obtained by laser flash photolysis, HPLC and EPR studies of the reaction of peroxyl and alkoxyl radicals with 4-phenoxylphenol, a molecule used to mimic the behavior of the sensor.