Particle size distribution and ultracentrifugation experiments show control of o/w Pickering emulsion droplet size by silica content, till a regime with excess silica is reached.
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► ...Comprehensive investigation of o/w Pickering emulsions stabilized by hydrophobically modified silica particles is presented. ► Droplet size is controlled by the oil-to-silica ratio. ► Coverage of oil droplets by silica particles is not constant. ► Silica is fully adsorbed to oil droplets till saturation of the interface. ► Excess silica is observed in the aqueous phase at high silica content.
The control of droplet size and stability of oil-in-water Pickering emulsions stabilized by hydrophobized fumed silica was investigated. Three regimes were observed according to the silica content: instability at low silica content, stable emulsions with droplet size controlled by the silica content, and emulsions of constant size set by the emulsification process at high silica concentrations. The oil-to-silica ratio was the relevant parameter of the size control in the medium concentration regime. Centrifugation experiments and particle size distribution measurements gave evidence of the presence of excess silica present as dispersion in the aqueous phase in the high silica content regime. Adsorption of silica to the droplet surface did not follow adsorption equilibrium; strong adsorption prevailed. Lastly, aggregation of silica particles appeared a crucial parameter. Oil adsorption and capillary condensation of oil within the silica aggregates provided a supplementary mechanism of silica aggregation that contributed to the stability of emulsions.
X–ZnS quantum dots (QDs) are synthesized in aqueous solution by a simple aqueous chemical route where X represents 3-mercaptopropionic acid (MPA) or 3-mercapto-1-propanesulfonic acid (MPS) which are ...two well-known low cost and stable ligands. The synthesized X–ZnS QDs yielded aqueous suspensions of nanoparticles with excellent monodispersity, water solubility and fluorescence stability with a relatively high fluorescence quantum yield of 11% and 10% for MPA-ZnS QDs and MPS-ZnS QDs respectively. Under optimal conditions, the prepared X–ZnS QDs are used to detect tetracycline (TC) based on their fluorescence quenching induced by the target analyte via electrostatic interaction. The Stern–Volmer-type equation has been fitted to the quenching curve of each QDs, from which MPA-ZnS QDs has shown a larger linear range and a lower limit of detection than MPS-ZnS QDs. The fluorescence response of MPA-ZnS QDs is linearly with respect to TC concentration over a wide range from 200 nM to 6000 nM with a detection limit of 30 pM. The combination of non-toxicity, simplicity and low cost together with high analytical performance of the proposed MPA-ZnS QDs make it promising for the determination of trace TC in food products of animal origin.
•A luminescent MPA-ZnS and MPS-ZnS QDs were chemically synthetized successfully. .•The synthesized ligands-ZnS QDs exhibits excellent monodispersity with a relatively high fluorescence quantum yield .•The mechanism of sensing properties of ligands-ZnS quantum dots towards TC was discussed in details.•MPA-ZnS QDs presents better analytical performance than MPS-ZnS QDs towards TC.
Penetration of molecules and particles inside and through skin has long been well documented but it now merits renewed attention as a result of new areas of concern such as transdermal therapies, ...safety of cosmetic products, penetration of environmental compounds and skin decontamination.
The topic is complex as skin structure is heterogeneous and because there are a number of penetration routes through the stratum corneum barrier: the intercellular, intracellular and follicular pathways. Recent advances in the study of penetration mechanisms deal with the control of the intercellular penetration route by the crystalline state of lipids, and the penetration through skin appendages (the follicular pathway) that appears to contribute much more than was previously thought.
Applications dependent on skin penetration that have received special attention include transdermal delivery of nano- and microparticles by hair follicles, targeting of the skin immune system in order to develop new vaccination strategies, and problems relating to the risk assessment of nanoparticles and skin decontamination.
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► Skin penetration through Stratum corneum is controlled by lipids crystalline state. ► Penetration enhancers alter crystalline phases of Stratum corneum lipids. ► Hair follicle is the predominant skin penetration pathway of nano- and microparticles. ► Drugs that penetrate skin by intercellular pathway significantly enter hair follicles. ► Nano- and microparticles allow targeting the skin immune system.
•Skin irritancy of surfactants is related to their physico-chemical properties.•Surfactants can be split into two well-separated classes: toxic and mild.•Ionic surfactants can be mild; non-ionic ...surfactants can be toxic.•The order parameter is a universal molecular descriptor of surfactants.
The skin toxicity of four ionic surfactants and fourteen non-ionic surfactants was investigated so as to disclose structure/toxicity relationships. The skin toxicity was assessed by means of four in vitro assays, MTT and LDH test of cell viability, and detection of the inflammation markers IL-1α and IL-8. Several descriptors of the physicochemical properties of the surfactants were measured in order to find out those molecular descriptors that correlate with the toxicity measured on skin. Principal component analysis and analysis of the matrix of Pearson's correlation coefficients were used for the search of the molecular descriptors having the highest relevance. There was a definite difference between ionic and non-ionic surfactants. Ionic surfactants are the most toxic if they are soluble in water. Crystalline ionic surfactants of low solubility show low toxicity. The sign of the charge, anionic or cationic, does not matter. The value of the CMC that has been put forward as a highly relevant parameter does not account for the full skin toxicities observed; the CMC of non-ionic surfactants is not a parameter of relevance. For non-ionic surfactants, the nature of the chemical bond linking the polar head group and the alkyl chain has a significant impact on skin toxicity; PEG ethers appear more toxic than PEG esters. The results revealed the mildness of polyoxyethylene sorbitan esters whatever be their alkyl chain length. On the other hand, for sucrose ester surfactants, C12 alkyl length resulted in the greatest skin toxicity. Since the molecular parameters of ionic, non-ionic, water-soluble and crystalline surfactants are different, a universal parameter was introduced, the order parameter describing the orientation ordering of surfactant molecules at interfaces. The highly ordered organization of crystalline surfactants associated with their low solubility in water makes them very low-irritant surfactants.
Surfactant-free emulsions stabilized by solid particles (Pickering emulsions) have been evaluated in the terms of skin absorption of lipophilic drugs. The behavior of three formulations: a ...surfactant-based emulsion, a Pickering emulsion stabilized by silica particles and a solution in triglyceride oil, were compared in order to assess the effect of the surface coating of Pickering emulsions as new dosage forms for topical application. Such comparative investigation was performed
in vitro on excised pig skin in Franz diffusion cells with
all-trans retinol as model lipophilic drug. Surfactant-based (classical, CE) and Pickering (PE) oil-in-water emulsions containing retinol were prepared with the same chemical composition (except the stabilizing agent: surfactant or silica particles), the same droplet size and the same viscosity. No permeation through the skin sample was observed after 24
h exposure because of the high lipophilic character of retinol. Penetration of retinol was 5-fold larger for both CE and PE than for the solution in triglyceride. The distribution of retinol inside the skin layers depended significantly on the emulsions type: the classical emulsion allowed easy diffusion through the
stratum corneum, so that large amounts reached the viable epidermis and dermis. Conversely, high storage of retinol inside the
stratum corneum was favored by the Pickering emulsion. The retinol content in
stratum corneum evaluated by skin stripping, demonstrated the increased retinol accumulation from PE. Therefore Pickering emulsions are new drug penetration vehicles with specific behavior; they are well-suited either for targeting the
stratum corneum or aimed at slow release of drug from
stratum corneum used as a reservoir to the deeper layers of skin.
Owing to the demand for chemical analysis of low concentrations of the Brilliant Green (BG) dye released into the environment, molecularly imprinted polymer (MIP) materials have been investigated for ...their use in SPME preconcentration devices. Thin coatings of MIP on solid supports allow fast adsorption of the analyte and higher selectivity of adsorption. Biosourced fibers of
Posidonia oceanica
(Pos) were taken as a the solid support to which a thin film of MIP was chemically attached. The material synthesis involved two steps: chemical grafting of methacrylate groups onto Pos by a silane coupling, and copolymerization with the free functional monomer and cross-linker in the presence of BG. Polymerization of the functional monomers methacrylic acid and acrylamide yielded the materials PosMAA@MIP and PosAA@MIP respectively. The strength of their interaction with BG and the stoichiometry of the pre-polymerization complex were assessed by
1
H NMR experiments in DMSO-
d
6
solution. Characterization by IR spectroscopy and thermogravimetric analysis validated the successful syntheses. The points of zero charge were at pH 3.31 and 4.50 for PosMAA@MIP and PosAA@MIP, respectively, influencing the optimal adsorption of BG at pH 4. Kinetic studies revealed the rapid adsorption of more than 90% of the BG within 20 min. All MIPs exhibited higher adsorption capacity for BG compared to non-imprinted materials. PosAA@MIP showed the highest adsorption efficiency and selectivity, with an imprinting factor of 1.9. The thermodynamics of adsorption was studied by fitting the Langmuir–Volmer and Volmer models to the experimental data, from which the selective adsorption capacities of BG on PosMAA@MIP and PosAA@MIP were 289 and 313 µmol·g
−1
, respectively. Additionally, PosAA@MIP exhibited higher extraction efficiency for BG than for its metabolites eosin and methylene blue, underscoring its superior ability to selectively capture target molecules.
In this paper, a novel kind of microcapsules containing 2-ethoxynaphtalene (neroline) was successfully synthesized into polyurethane shells through the interfacial polycondensation of β-cyclodextrin ...with 4,4’-methylene (bisphenyl isocyanate) (MDI) in direct emulsion. The IR spectroscopy was used, on the one hand to confirm the success of polymerization reaction leading to the polyurethane shell formation, but on the other hand to check the encapsulation efficiency of fragrance that accounts for 40%. Microcapsules’ spherical shape and particle size distributions were revealed by means of optical microscopy, scanning electron microscopy (SEM) observation, and small-angle light scattering measurement. The impregnation of neroline-loaded microcapsules on polyamide knitted fabric was tested as an application method at a yield of around 74%. Adhesion of synthesized microcapsules to textile materials was evaluated through microscopic observations. The durability of the impregnation effect was tested by SEM and UV-visible spectroscopy. Washing fastness test of the impregnated polyamide knitting proved that the loaded microparticles retained their efficiency after more than 35 washing cycles.
The skin absorption from Pickering emulsions as a new dosage form was investigated for the first time. Pickering emulsions are stabilized by adsorbed solid particles instead of emulsifier molecules. ...They are promising dosage forms that significantly differ from classical emulsions within several features. The skin permeation of a hydrophilic model penetrant (caffeine) was investigated from a w/o Pickering emulsion and compared to a w/o classical emulsion stabilized with an emulsifier. Both emulsions had the same composition and physicochemical properties in order to focus on the effect of the interfacial layer on the drug release and skin absorption processes. The highest permeation rates were obtained from the Pickering emulsion with a pseudo-steady state flux of 25μgcm−2h−1, threefold higher than from a classical emulsion (9.7μgcm−2h−1). After 24h exposure, caffeine was mostly in the receptor fluid and in the dermis; cumulated amounts of caffeine were higher for the Pickering emulsion. Several physicochemical phenomena were investigated for clearing up the mechanisms of enhanced permeation from the Pickering emulsion. Among them, higher adhesion of Pickering emulsion droplets to skin surface was disclosed. The transport of caffeine adsorbed on silica particles was also considered relevant since skin stripping showed that aggregates of silica particles entered deeply the stratum corneum.
Gadolinium is extensively used in pharmaceuticals and is very toxic, so its sensitive detection is mandatory. This work presents the elaboration of a gadolinium chemical sensor based on ...2-methylpyridine-substituted cyclam thin films, deposited on gold electrodes, using electrochemical impedance spectroscopy (EIS). The 2-methylpyridine-substituted cyclam (bis-N-MPyC) was synthesized in three steps, including the protection of cyclam by the formation of its CH
-bridged aminal derivative; the product was characterized by liquid
H and
C NMR spectroscopy. Spin-coated thin films of bis-N-MPyC on gold wafers were characterized by means of infrared spectroscopy in ATR (Attenuated Total Reflectance) mode, contact angle measurements and atomic force microscopy. The impedimetric chemical sensor was studied in the presence of increasing concentrations of lanthanides (Gd
, Eu
, Tb
, Dy
). Nyquist plots were fitted with an equivalent electrical circuit including two RC circuits in series corresponding to the bis-N-MPyC film and its interface with the electrolyte. The main parameter that varies with gadolinium concentration is the resistance of the film/electrolyte interface (
), correlated to the rate of exchange between the proton and the lanthanide ion. Based on this parameter, the detection limit obtained is 35 pM. The bis-N-MPyC modified gold electrode was tested for the detection of gadolinium in spiked diluted negative urine control samples.
1,3,5-tricyclohexyl-1,3,5-triazinane-2,4,6-trione (
TCy-TAZTO
) was obtained with high chemoselectivity and excellent yield, through an efficient and simple cyclotrimerization of ...isocyanatocyclohexane, performed at room temperature and under mild reaction condition. The newly synthesized
TCy-TAZTO
was characterized with FT-IR,
1
H, and
13
C NMR spectra. Single-crystal X-ray diffraction was used to investigate its molecular structure. The Hirshfeld surface, curvedness, shape index, and 2D-fingerprint plots were used to evaluate various intermolecular interactions within the crystal structure. DFT calculations, intrinsic reaction coordinate (IRC), Wiberg bond index, and FOMs computational studies were performed to get more insights into the stability and the reaction mechanism. Furthermore, the molecular docking of the
TCy-TAZTO
was studied against different proteins to investigate the efficacy against selected drug targets of platelet aggregation, blood coagulation, antithrombotic, and anti HIV-1 disease.
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