Nanoemulsions of synthetic rhamnolipids act as plant resistance inducers without damaging plant tissues or affecting soil microbiota.

Plant pathogens and pests can cause significant losses in crop yields, affecting food security and the global economy. Many traditional chemical pesticides are used to combat these organisms. This can lead to the development of pesticide-resistant strains of pathogens/insects and negatively impact the environment. The development of new bioprotectants, which are less harmful to the environment and less likely to lead to pesticide-resistance, appears as a sustainable strategy to increase plant immunity. Natural Rhamnolipids (RL-Nat) are a class of biosurfactants with bioprotectant properties that are produced by an opportunistic human pathogen bacterium. RL-Nat can act as plant resistance inducers against a wide variety of pathogens. Recently, a series of bioinspired synthetic mono-RLs produced by green chemistry were also reported as phytoprotectants. Here, we explored their capacity to generate novel colloidal systems that might be used to encapsulate bioactive hydrophobic compounds to enhance their performance as plant bioprotectants. The synthetic mono-RLs showed good surfactant properties and emulsification power providing stable nanoemulsions capable of acting as bio-carriers with good wettability. Synthetic RLs-stabilized nanoemulsions were more effective than RLs suspensions at inducing plant immunity, without causing deleterious effects. These nanoemulsions were innocuous to native substrate microbiota and beneficial soil-borne microbes, making them promising safe bio-carriers for crop protection.

Self-assembled nanostructures of L-ascorbic acid alkyl esters support monomeric amphotericin B.

HYPOTHESIS: Amphotericin B (AmB) is a highly effective antimicrobial, with broad antimycotic and antiparasitic effect. However, AmB poor water-solubilisation and aggregation tendency limits its use for topical applications. We studied the capacity of nanostructures formed by alkyl esters of L-ascorbic acid (ASCn) to solubilise AmB and tested the relationship between the prevalence of the monomeric form of AmB and its effectiveness as antimicrobial agent. EXPERIMENTS: We developed self-assembled nanostructures formed by the commercial compound, palmitoyl ascorbic acid, as well as the shorter chained myristoyl and lauroyl ascorbic acid. AmB loaded ASCn nanostructures were studied by a combination of spectroscopic techniques, together with particle analysis, differential scanning calorimetry, microbiological tests, and Langmuir monolayer visualisation. FINDINGS: We found no direct relation between the antimicrobial capacity and the prevalence of the monomeric form of the drug. However, the later was related to chemical stability and colloidal robustness. Nanostructures formed by ASC16 in its anionic state provide an appropriate environment for AmB in its monomeric form, maintaining its antimicrobial capacity. Langmuir film visualisation supports spectrophotometric evidence, indicating that ASC16 allows the in-plane solubilisation of AmB. Coagels formed by ASC16 appear as promising for carrying AmB for dermal delivery.

Liposome Fusion Mediated by Hydrophobic Magnetic Nanoparticles Stabilized with Oleic Acid and Modulated by an External Magnetic Field.

Membrane fusion is considered relevant in countless scientific areas and biotechnological processes, ranging from vital life events to biomedicine, pharmaceuticals, and materials engineering, among others. In this study, we employed hydrophobic oleic acid (OA)-coated magnetite (Fe3O4) nanoparticles (MNP-OA) as a platform to induce the fusion of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine liposomes [large unilamellar vesicles (LUVs)] in a colloidal dispersion. This fusion was monitored through dynamic light scattering, turbidimetry, and fluorescence assay using the well-known Tb/dipicolinic acid (DPA) complex formation assay. MNP-OA have shown to be able to induce fusion with the mixing of liposomal inner content with direct dependence on the nanoparticle concentration added to the LUVs. Moreover, changes in the permeability of the liposome bilayer, upon the addition of MNP-OA to liposomes, were evaluated by studying the leakage of carboxyfluorescein and of the co-encapsulated Tb/DPA complex. These assays allowed us to determine that MNP-OA did not significantly modify liposome permeability during the fusion process. Transmission electron microscopy and confocal microscopy revealed that MNP-OA remained embedded in the lipid bilayer without producing membrane rupture, liposome deformation, or destruction. In addition, we evaluated the effect of applying a low-intensity magnetic field to the LUVs/MNP-OA system and observed that the nanoparticles considerably increased their fusogenic activity under this external stimulus, as well as they are capable of responding to low magnetic fields of around 0.45 mT. These results revealed the potential of hydrophobic magnetic nanoparticles, stabilized with OA, to act as a fusogen, thus representing a valuable tool for biotechnological applications.

Complex systems that incorporate cyclodextrins to get materials for some specific applications.

Cyclodextrins (CDs) are a family of biodegradable cyclic hydrocarbons composed of α-(1,4) linked glucopyranose subunits, the more common containing 6, 7 or 8 glucose units are named α, ß and γ-cyclodextrins respectively. Since the discovery of CDs, they have attracted interest among scientists and the first studies were about the properties of the native compounds and in particular their use as catalysts of organic reactions. Characteristics features of different types of cyclodextrins stimulated investigation in different areas of research, due to its non-toxic and non-inmunogenic properties and also to the development of an improved industrial production. In this way, many materials with important properties have been developed. This mini-review will focus on chemical systems that use cyclodextrins, whatever linked covalently or mediated by the non covalent interactions, to build complex systems developed mainly during the last five years.

Hydrophobic silver nanoparticles interacting with phospholipids and stratum corneum mimic membranes in Langmuir monolayers.

The interaction of hydrophobic silver nanoparticles with different phospholipids and stratum corneum mimic (SCM) membranes is studied in Langmuir monolayers. Thus, silver nanoparticles coated with oleic acid (AgNP-OA) were synthesized, characterized and incorporated in Langmuir monolayers of single phospholipids -having different chain length, saturation degree and phase state- or of a SCM mixture. The incorporation of AgNP-OA to the lipid monolayers generated an expansion of the monolayers and a decrease of the surface compressional modulus compared to the pure lipid. X-ray photoelectron spectroscopy (XPS) suggested that the zwitterionic choline-phospholipids can be adsorbed onto the nanoparticles' surface, which is relevant considering that phospholipids are the major constituents of the cell membrane. We also studied the changes in the topography at the mesoscale level using Brewster angle microscopy. We found the most prominent changes in the lipids with liquid-condensed phase, such as SCM, showing segregation of their components. This could have major implications in the barrier function of the membrane, affecting for example the skin permeability towards hydrophobic nanoparticles. Finally, the capability of hydrophobic AgNP-OA for delivering Ag+ ions was studied in aqueous media in the absence and presence of phospholipids. In both conditions, AgNP-OA released Ag+ at reported-bactericidal concentrations, being double in the presence of phospholipids.

Cavity Orientation Regulated by Mixture Composition and Clustering of Amphiphilic Cyclodextrins in Phospholipid Monolayers.

Artificial supramolecular-hierarchical structures that emulate nature represent an overcoming alternative for the design of new drug delivery systems. Thermodynamic and topographic properties of films formed by a monoacylated amphiphilic ß-cyclodextrin (ßCD-C16) with the phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) at the air/water interface were studied. ßCD-C16 formed stable mixed films with POPC at several proportions when spread together at the air/water interface. The orientation of ßCD-C16 cavity at the interface depends on its mole fraction in the film as reveled by the analysis of partial mean molecular areas as a function of composition. Furthermore, ßCD-C16 was able to penetrate POPC preformed films in a broad range of initial surface pressures, including that near the collapse pressure of the phospholipid. These results demonstrated the strong tendency of ßCD-C16 to be inserted into this lipid matrix commonly used in liposome formulations. Topography studies show that ßCD-C16 segregate from POPC forming clusters enriched in ßCD-C16. Segregation of ßCD-C16 was especially noticeable when ßCD-C16 were incorporated by themselves into a preformed POPC matrix leading to ordered and highly birefringent structures that suggest the formation of hierarchical stacked ßCD-C16 arrangement at the interface.

Phytotoxic phenylpropanoids isolated from Ophryosporus charua (Griseb.) Hieron.

Bioguided isolation of the EtOH extract from the medicinal native plant, Ophryosporus charua, against Raphanus sativus, yielded three phenylpropanoids, charuol A [(Z)-4-((1S,2R)-3-acetoxy-1,2-dihydroxypropyl)phenyl) 2-methylbut-2-enoate], charuepoxide [(Z)-4-((2S,3R)-3-(acetoxymethyl oxiran-2-yl)phenyl) 2-methylbut-2-enoate] and charuol B [(Z)-4-((1R,2R)-3-acetoxy-1,2-dihydroxypropyl)phenyl) 2-methylbut-2-enoate]. Their structures and absolute configuration were established by extensive spectroscopic analyses. The effective concentrations for 50% inhibition of germination (ECg50) and root (ECr50) and shoot (ECs50) elongations were determined for these compounds against P. miliaceum (monocot) and Raphanus sativus (dicot). Charuol A was the most active in the inhibition of germination of P. miliaceum (ECg50 = 0.97 mM), followed by charuol B and charuepoxide, although charuol B was the most effective in regulating the root growth of P. miliaceum seedlings, with an ECr50 of 1.0 mM. Charuol A inhibited the germination of R. sativus, while its seedling development was also affected by all three compounds with different effectiveness. Charuol A was also highly effective in the 0.09-0.30 mM range against other test species such as Lactuca sativa, Eruca sativa, Allium ampeloprasum and Secale cereale.

The Rheological Properties of Lipid Monolayers Modulate the Incorporation of l-Ascorbic Acid Alkyl Esters.

In this work, we tested the hypothesis that the incorporation of amphiphilic drugs into lipid membranes may be regulated by their rheological properties. For this purpose, two members of the l-ascorbic acid alkyl esters family (ASCn) were selected, ASC16 and ASC14, which have different rheological properties when organized at the air/water interface. They are lipophilic forms of vitamin C used in topical pharmacological preparations. The effect of the phase state of the host lipid membranes on ASCn incorporation was explored using Langmuir monolayers. Films of pure lipids with known phase states have been selected, showing liquid-expanded, liquid-condensed, and solid phases as well as pure cholesterol films in liquid-ordered state. We also tested ternary and quaternary mixed films that mimic the properties of cholesterol containing membranes and of the stratum corneum. The compressibility and shear properties of those monolayers were assessed in order to define its phase character. We found that the length of the acyl chain of the ASCn compounds induces differential changes in the rheological properties of the host membrane and subtly regulates the kinetics and extent of the penetration process. The capacity for ASCn uptake was found to depend on the phase state of the host film. The increase in surface pressure resultant after amphiphile incorporation appears to be a function of the capacity of the host membrane to incorporate such amphiphile as well as the rheological response of the film. Hence, monolayers that show a solid phase state responded with a larger surface pressure increase to the incorporation of a comparable amount of amphiphile than liquid-expanded ones. The cholesterol-containing films, including the mixture that mimics stratum corneum, allowed a very scarce ASCn uptake independently of the membrane diffusional properties. This suggests an important contribution of Cho on the maintenance of the barrier function of stratum corneum.

Alkyl esters of L-ascorbic acid: Stability, surface behaviour and interaction with phospholipid monolayers.

L-ascorbic acid alkyl esters (ASCn) are molecules of pharmaceutical interest for their amphiphilic nature and proposed antioxidant power. In contrast to L-ascorbic acid, ASC(n) with different acyl chain lengths behaved stably upon oxidation and a tautomeric isomerization was observed. In Langmuir films, when the ascorbic ring has a negative charge, ASC14 and ASC16 form stable monolayers, contrary to ASC10 and ASC12. ASC16 films showed transition from liquid-expanded (LE) to liquid-condensed phase, whereas ASC14 showed only an LE phase. When ASCn are mainly neutral, ASC14 showed phase transition from LE to a crystalline phase, as previously reported for ASC16. The two-dimensional domains displayed crystal-like shapes with anisotropic optical activity when interacting with the polarized light under Brewster angle microscopy. The compounds with the longer acyl chain (ASC16, ASC14 and ASC12) exhibited good surface activity, forming Gibbs monolayers. They also were able to penetrate into phospholipid monolayers up to a critical point of 45-50 mN/m. The 1-palmitoyl-2-oleoylphosphatidylcholine/ASCn films showed LC and/or crystalline domains only for ASC16. This study provides valuable evidence regarding the stability and surface properties of this drug family, and casts light into the differential interaction of these drugs with lipid membranes, which is important for understanding its differential pharmacological activity.

Distinctive interactions of oleic acid covered magnetic nanoparticles with saturated and unsaturated phospholipids in Langmuir monolayers.

The growing number of innovations in nanomedicine and nanobiotechnology are posing new challenges in understanding the full spectrum of interactions between nanomateriales and biomolecules at nano-biointerfaces. Although considerable achievements have been accomplished by in vivo applications, many issues regarding the molecular nature of these interactions are far from being well-understood. In this work, we evaluate the interaction of hydrophobic magnetic nanoparticles (MNP) covered with a single layer of oleic acid with saturated and unsaturated phospholipids found in biomembranes through the use of Langmuir monolayers. We find distinctive interactions among the MNP with saturated and unsaturated phospholipids that are reflected by both, the compression isotherms and the surface topography of the films. The interaction between MNP and saturated lipids causes a noticeable reduction of the mean molecular area in the interfacial plane, while the interaction with unsaturated lipids promotes area expansion compared to the ideally mixed films. Moreover, when liquid expanded and liquid condensed phases of the phospholipid(s) coexist, the MNP preferably partition to the liquid-expanded phase, thus hindering the coalescence of the condensed domains with increasing surface pressure. In consequence organizational information on long-range order is attained. These results evidence the existence of a sensitive composition-dependent surface regulation given by phospholipid-nanoparticle interactions which enhance the biophysical relevance of understanding nanoparticle surface functionalization in relation to its interactions in biointerfaces constituted by defined types of biomolecules.

Inclusion of the insecticide fenitrothion in dimethylated-ß-cyclodextrin: unusual guest disorder in the solid state and efficient retardation of the hydrolysis rate of the complexed guest in alkaline solution.

An anhydrous 1:1 crystalline inclusion complex between the organophosphorus insecticide fenitrothion [O,O-dimethyl O-(3-methyl-4-nitrophenyl)phosphorothioate] and the host compound heptakis(2,6-di-O-methyl)-ß-cyclodextrin (DIMEB) was prepared and its structure elucidated by single-crystal X-ray diffraction. This revealed two independent host molecules in the asymmetric unit. In one of these, the cavity is occupied by two disordered guest components (distinguishable as rotamers with respect to the P-OAr bond) while in the other, three distinct guest components with site-occupancies 0.44, 0.29 and 0.27 appear, the last having a reversed orientation relative to all the other components. Kinetic studies of the alkaline hydrolysis of fenitrothion in the presence of DIMEB showed a remarkable reduction of 84% in the rate of this reaction relative to that for the free substrate, a value exceeding those previously attained with the native hosts, ß- and γ-cyclodextrin, and fully methylated ß-cyclodextrin.

Multivalent interaction of cyclodextrin vesicles, carbohydrate guests, and lectins: a kinetic investigation.

An artificial glycocalix self-assembles when unilamellar bilayer vesicles of amphiphilic ß-cyclodextrins are decorated with maltose- and lactose-adamantane conjugates by host-guest interactions. The maltose-decorated vesicles aggregate in the presence of lectin concanavalin A whereas the lactose-decorated vesicles aggregate in the presence of lectin peanut agglutinin. The kinetics of the orthogonal multivalent interfacial interactions present in this ternary system of vesicles, carbohydrates, and lectins were studied by time-dependent measurements of the optical density at 400 nm. The average vesicle and vesicle aggregate sizes were monitored by dynamic light scattering. The aggregation process was evaluated as a function of lectin concentration, vesicle concentration, and surface coverage of the vesicles by the carbohydrate-adamantane conjugates. The initial rate of vesicle aggregation scales linearly with the lectin as well as the cyclodextrin vesicle concentration. Furthermore, each lectin requires a characteristic critical density of carbohydrates at the vesicle surface. These observations allow a prediction of the response of the ternary supramolecular system at different concentrations of its components. Also, the effective binding site separation in a multivalent receptor such as a multiple binding site protein can be accurately determined. This methodology can be extended to multivalent noncovalent interactions in other ligand-receptor systems at interfaces.

Effect of cyclodextrins on the reactivity of fenitrothion.

The hydrolysis reaction of fenitrothion was studied in water containing 2% dioxane and in the presence of native cyclodextrins (α-, ß- and γ-CD) and two commercially available modified derivatives, namely, permethylated ß- and α-cyclodextrin (TRIMEB and TRIMEA, respectively). The kinetics of the reaction in the presence of TRIMEA could not be measured because the complex formed is insoluble and precipitated even at low concentration. On the other hand, the reaction is only weakly affected by the presence of α-CD. The hydrolysis reaction is inhibited by all the other cyclodextrins. From the kinetic data the association equilibrium constants for the formation of the 1:1 inclusion complexes were determined as 417, 511 and 99M(-1) for ß-CD, TRIMEB and γ-CD, respectively. Despite the differences in the association constants for ß- and γ-CD, the observed inhibition effect is about the same and this is due to the fact that the rate of hydrolysis in the cavity of γ-CD is smaller than that in the cavity of ß-CD. The strongest inhibitor is TRIMEB and this result is consistent with the known structure of the complex in the solid state.

Reactivity of the insecticide fenitrothion toward O and N nucleophiles.

The reactivity of Fenitrothion (1) toward several O- and N-based nucleophiles, including ambident and alpha-nucleophiles, was investigated in basic media at 25 degrees C in water containing 2% 1,4-dioxane. In the reactions with HO(-) and HOO(-) quantitative formation of 3-methyl-4-nitrophenoxide (2) was observed indicating a S(N)2(P) pathway. In the reactions with NH(2)OH, NH(2)O(-), and BuNH(2), demethylfenitrothion (4) was formed along with 2, indicating competition between the S(N)2(P) and S(N)2(C) pathways; no evidence of a S(N)Ar pathway was observed in any case. The observed rate constants were dissected into the values corresponding to the S(N)2(P) and S(N)2(C) pathways. The yield of 4 depends on the nucleophile and on the pH of the reaction, being the main product in the case of BuNH(2). With HOO(-), NH(2)OH, and NH(2)O(-) a significant alpha-effect was observed, confirming the participation of the nucleophile in the rate-limiting step of the reaction.

PM-IRRAS assessment of the compression-mediated orientation of the nanocavity of a monoacylated beta-cyclodextrin in monolayers at the air-water interface.

The structural orientation adopted along the compression-decompression isotherm by a monoacylated beta-cyclodextrin (C16-betaCD) at the air-water interface was assessed by polarization-modulation infrared reflection-adsorption spectroscopy (PM-IRRAS). The adoption of different orientations of the cyclic oligosaccharide unit, relative to the interfacial plane, was interpreted analyzing the PM-IRRAS band intensity ratios of specific vibrations corresponding to the cyclodextrin moiety as a function of the surface pressure for successive compression/decompression cycles. The spectroscopic analysis revealed that the cyclic oligosaccharide modifies its position under compression from one in which the plane of the cavity of the monoacylated beta-cyclodextrin lies almost parallel to the interface to another in which the plane of the cavity is perpendicular to the interface. Through the PM-IRRAS analysis, it was also possible to evidence the establishment of an intermolecular hydrogen bonding network that may play an important role in the dynamic properties of the monolayer packing. The hydrogen bonding network becomes more important with the increases of surface pressure, up to a molecular packing limit, and it imparts the surface properties of the film for future compression-decompression cycles.

Solid-state structures and thermal properties of inclusion complexes of the organophosphate insecticide fenitrothion with permethylated cyclodextrins.

The X-ray crystal structures and thermal stabilities of the inclusion complexes formed between the organophosphate insecticide fenitrothion [O,O-dimethyl O-(3-methyl-4-nitrophenyl) phosphorothioate] and the host compounds TRIMEA and TRIMEB (permethylated alpha- and beta-cyclodextrins, respectively) are reported. In the complex (TRIMEA)(2).fenitrothion 1, the guest phosphate ester group is disordered and the molecule is fully encapsulated within a novel TRIMEA dimer in which the secondary rims of the two host molecules are in close contact. In contrast, the complex TRIMEB.fenitrothion 2 is monomeric and the guest molecule is statistically disordered over two positions, with the phosphate group inserted in the host cavity in both cases. Thermal analysis indicated gradual and partial loss of the guest in 1 during heating between 130 degrees C and the melting point of the complex (approximately 200 degrees C), whereas complex 2 displayed significant mass loss only after fusion of the complex at 161 degrees C.

Molecular organization, structural orientation, and surface topography of monoacylated beta-cyclodextrins in monolayers at the air-aqueous interface.

The surface behavior of monoacylated beta-cyclodextrins, with hydrocarbon chains of 16, 14, and 10 carbons, has been assessed by the measurement of the surface pressure, surface (dipole) potential, optical reflectivity, and surface topography in monolayers at the air-water interface. For all the derivatives studied, the intermolecular organization adopted along compression-decompression isotherms reveals a rich variety of packing states which imply profound reorganization of the hydrophobic and hydrophilic moieties of the beta-cyclodextrin derivatives in the film, depending on the lateral surface pressure. The intermolecular arrangements are consistent with the adoption of a different and defined orientation of the cyclic oligosaccharide unit, relative to the interfacial plane and the aqueous subphase. This is different from the behavior of the per-substituted derivatives, and none of the changes exhibited by the monosubstituted forms are consistent with the oligosaccharide ring remaining in a fixed orientation along the interface when the surface pressure is varied.