Stability Of Surfactants Research Articles

Investigating the role of cholesterol in the formation of non-ionic surfactant based bilayer vesicles: Thermal analysis and molecular dynamics

The aim of this research was to investigate the molecular interactions occurring in the formulation of non-ionic surfactant based vesicles composed monopalmitoyl glycerol (MPG), cholesterol (Chol) and dicetyl phosphate (DCP). In the formulation of these vesicles, the thermodynamic attributes and surfactant interactions based on molecular dynamics, Langmuir monolayer studies, differential scanning calorimetry (DSC), hot stage microscopy and thermogravimetric analysis (TGA) were investigated. Initially the melting points of the components individually, and combined at a 5:4:1 MPG:Chol:DCP weight ratio, were investigated; the results show that lower (90 °C) than previously reported (120-140 °C) temperatures could be adopted to produce molten surfactants for the production of niosomes. This was advantageous for surfactant stability; whilst TGA studies show that the individual components were stable to above 200 °C, the 5:4:1 MPG:Chol:DCP mixture show ∼2% surfactant degradation at 140 °C, compared to 0.01% was measured at 90 °C. Niosomes formed at this lower temperature offered comparable characteristics to vesicles prepared using higher temperatures commonly reported in literature. In the formation of niosome vesicles, cholesterol also played a key role. Langmuir monolayer studies demonstrated that intercalation of cholesterol in the monolayer did not occur in the MPG:Chol:DCP (5:4:1 weight ratio) mixture. This suggests cholesterol may support bilayer assembly, with molecular simulation studies also demonstrating that vesicles cannot be built without the addition of cholesterol, with higher concentrations of cholesterol (5:4:1 vs 5:2:1, MPG:Chol:DCP) decreasing the time required for niosome assembly.

Optimization of Extraction of Novel Pectinase Enzyme Discovered in Red Pitaya (Hylocereus polyrhizus) Peel

Plant peels could be a potential source of novel pectinases for use in various industrial applications due to their broad substrate specificity with high stability under extreme conditions. Therefore, the extraction conditions of a novel pectinase enzyme from pitaya peel was optimized in this study. The effect of extraction variables, namely buffer to sample ratio (2:1 to 8:1, X1), extraction temperature (−15 to +25 °C, X2) and buffer pH (4.0 to 12.0, X3) on specific activity, temperature stability, storage stability and surfactant agent stability of pectinase from pitaya peel was investigated. The study demonstrated that the optimum conditions for the extraction of pectinase from pitaya sources could improve the enzymatic characteristics of the enzyme and protect its activity and stability during the extraction procedure. The optimum extraction conditions cause the pectinase to achieve high specific activity (15.31 U/mg), temperature stability (78%), storage stability (88%) and surfactant agent stability (83%). The most desirable conditions to achieve the highest activity and stability of pectinase enzyme from pitaya peel were the use of 5:1 buffer to sample ratio at 5 °C and pH 8.0.

Effect of aqueous pH and electrolyte concentration on structure, stability and flow behavior of non-ionic surfactant based solid lipid nanoparticles

The effects of pH and electrolyte concentration on the structure evolution, polymorphism, flow behavior and stability of solid lipid nanoparticles (SLNs), stabilized by the food-grade non-ionic surfactant Tween 80, were investigated. Development of a lipid crystal was governed by thermodynamically stable β- and β′-subunits and relative crystallinity decreased with increasing pH and electrolyte concentration. Aqueous stability and dispersibility increased with increasing pH and decreased with increasing electrolyte concentration. Flow behavior of the SLNs suspension was affected by the electrolyte concentration. However, the pH of the aqueous surfactant medium has not shown any effect on the flow behavior. From the results, it is clear that the pH and electrolyte concentration are among the potential factors which determines the stability and release properties of entrapped materials from SLNs.

An improved whitecap timescale for sea spray aerosol production flux modeling using the discrete whitecap method

AbstractThe discrete whitecap method (DWM) to model the sea spray aerosol (SSA) production flux explicitly requires a whitecap timescale, which up to now has only considered a whitecap decay timescale, τdecay. A reevaluation of the DWM suggests that the whitecap timescale should account for the total whitecap lifetime (τwcap), which consists of both the formation timescale (τform) and the decay timescale (timescale definitions are given in the text). Here values of τform for 552 oceanic whitecaps measured at the Martha's Vineyard Coastal Observatory on the east coast of the USA are presented, and added to the corresponding values of τdecay to form 552 whitecap timescales. For the majority of whitecaps, τform makes up about 20–25% of τwcap, but this can be as large as 70% depending on the value of τdecay. Furthermore, an area‐weighted mean whitecap timescale for use in the DWM (τDWM) is defined that encompasses the variable nature of individual whitecap lifetimes within a given time period, and is calculated to be 5.3 s for this entire data set. This value is combined with previously published whitecap coverage parameterizations and estimates of SSA particle production per whitecap area to form a size‐resolved SSA production flux parameterization (dF(r80)/dlog10r80). This parameterization yields integrated sea‐salt mass fluxes that are largely within the range of uncertainty of recent measurements over the size range 0.029 µm < r80 < 0.580 µm. Physical factors controlling whitecap lifetime such as bubble plume lifetime and surfactant stabilization are discussed in the context of SSA production from whitecaps.

Antiretroviral Solid Drug Nanoparticles with Enhanced Oral Bioavailability: Production, Characterization, and In Vitro–In Vivo Correlation

Nanomedicine strategies have produced many commercial products. However, no orally dosed HIV nanomedicines are available clinically to patients. Although nanosuspensions of drug particles have demonstrated many benefits, experimentally achieving >25 wt% of drug relative to stabilizers is highly challenging. In this study, the emulsion-templated freeze-drying technique for nanoparticles formation is applied for the first time to optimize a nanodispersion of the leading non-nucleoside reverse transcriptase inhibitor efavirenz, using clinically acceptable polymers and surfactants. Dry monoliths containing solid drug nanoparticles with extremely high drug loading (70 wt% relative to polymer and surfactant stabilizers) are stable for several months and reconstitute in aqueous media to provide nanodispersions with z-average diameters of 300 nm. The solid drug nanoparticles exhibit reduced cytoxicity and increased in vitro transport through model gut epithelium. In vivo studies confirm bioavailability benefits with an approximately four-fold higher pharmacokinetic exposure after oral administration to rodents, and predictive modeling suggests dose reduction with the new formulation may be possible.

Research on the Performance of Polyether-Modified Trisiloxane Surfactant

The surface tension, CMC, HLB, emulsifying ability and hydrolytic stability of the polyether-modified trisiloxane surfactants were tested. The hydrolytic stability of different products was compared.

Thermal Reduction of Graphene Oxide in Organic Solvents for Producing Colloidal Suspensions of Reduced Graphene Oxide Sheets

A new method for preparing graphene colloidal suspension is studied by thermal reducing graphene oxide in N-methylpyrrolidone (NMP) and γ-Butyrolactone (GBL) at 200°. Without assistance of polymeric or surfactant stabilizers, thermal reduction and dispersion of reduced graphene sheets are performed in one pot, and stable suspensions are confirmed by transmission electron microscope (TEM) and atomic force microscope (AFM) technic. Experimental results such as thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Raman indicate bulk cleavage of oxygen-containing functional groups and restoration of graphite structure on reduced graphene oxide sheets. The study contributes to the preparation of graphene-based nanocomposites using this quick and low-cost processing technique.

English

The aim of this work was to improve the in vitro dissolution of simvastatin through development of self-nanoemulsifying tablets. Various modified oils, surfactant and co-surfactant mixtures were used to prepare different self-nanoemulsifying drug delivery systems (SNEDDS) whose composition was optimized using drug-solubility, ternary phase diagram, system stability and droplet size distribution studies. Optimized SNEDDSs, with acceptable surfactant ratio, stability and particle size (nano-range) upon dilution with simulated gastric fluid (SGF, pH 1.2) under gentle agitation conditions, were loaded onto microcrystalline cellulose and nano-size colloidal silicon dioxide powders using loading factor (Lf) = 0.2 and excipient ratio (R) = 20. Prepared powders were compressed into tablets and the in vitroperformance of the prepared self-nanoemulsifying tablets was investigated. Results revealed that systems with 10% relatively polar oils (C8), 60% Cremophore® RH 40 (surfactant), and 30% Transcutol® HP (co-surfactant), acquired good self-nanoemulsification properties either in liquid or tableted forms. Prepared self-nanoemulsifying tablets demonstrated significantly higher dissolution rates, compared to direct compression tablets (DCT) and marketed tablet (Zocor®). In conclusion, self-nanoemulsifying tablets were able to introduce simvastatin successfully in a unique immediate-release solid dosage form.   Key words: Simvastatin, self-nanoemulsifying tablets, self-nanoemulsifying drug delivery systems (SNEDDS), droplet size.

A single mutation within a Ca2 + binding loop increases proteolytic activity, thermal stability, and surfactant stability

We improved the enzymatic properties of the oxidatively stable alkaline serine protease KP-43 through protein engineering to make it more suitable for use in laundry detergents. To enhance proteolytic activity, the gene encoding KP-43 was mutagenized by error-prone PCR. Screening identified a Tyr195Cys mutant enzyme that exhibited increased specific activity toward casein between pH 7 and 11. At pH 10, the mutant displayed 1.3-fold higher specific activity for casein compared to the wild-type enzyme, but the activity of the mutant was essentially unchanged toward several synthetic peptides. Furthermore, the Tyr195Cys mutation significantly increased thermal stability and surfactant stability of the enzyme under oxidizing conditions. Examination of the crystal structure of KP-43 revealed that Tyr195 is a solvent exposed residue that forms part of a flexible loop that binds a Ca2+ ion. This residue lies 15–20Å away from the residues comprising the catalytic triad of the enzyme. These results suggest that the substitution at position 195 does not alter the structure of the active center, but instead may affect a substrate–enzyme interaction. We propose that the Tyr195Cys mutation enhances the interaction with Ca2+ and affects the packing of the Ca2+ binding loop, consequently increasing protein stability. The simultaneously increased proteolytic activity, thermal stability, and surfactant stability of the Tyr195Cys mutant enzyme make the protein an ideal candidate for laundry detergent application.

Polysorbate 20 vesicles as oral delivery system: In vitro characterization

Non-phospholipid vesicles made with non-ionic surfactants represent a promising alternative to the more widely studied liposomes. The main aim of the present work is to evaluate if vesicles of polysorbate 20 may be used as delivery systems for oral administration of drugs. Then in vitro stability and mucoadhesion studies in simulated gastrointestinal fluids were carried out. The colloidal stability of the surfactant vesicles was determined by size and fluorescence-dequenching assay, while their mucoadhesive properties were evaluated by light-scattering and protein assay. The results of in vitro stability demonstrated that the pHs and enzymes (pepsin and/or pancreatin) of the gastrointestinal fluids had not influence on surfactant vesicle stability. However, in presence of bile salts the nanosize vesicles showed a release of fluorescent marker (about 11% at 2h and 28% at 4h), whereas they were stable in size as confirmed by the light scattering experiments.Finally, the in vitro mucoadhesive experiments showed that the capacity of nanovesicles to adsorb mucin was higher at neutral pH than at acidic pH. As a conclusion of these preliminary studies, the surfactant vesicles could be considered a versatile tool for the oral delivery of drugs with poor stability in gastrointestinal tract and low permeability. Nevertheless, further work is required in order to examine the interaction with and/or the transport route through the epithelial cells of the gastrointestinal wall.

Surfactant-mediated low-temperature synthesis of phase pure multiply twinned copper nanoparticles under non-inert condition via thermal decomposition of copper malonate

Multiply twinned phase pure copper nanoparticles were successfully synthesized without any inert gas protection via a low-temperature thermal decomposition of a new precursor copper malonate, [CuCH2C2O4]·2H2O in the presence of surfactant stabilizers oleylamine (C18H35NH2) and triphenylphosphine ((C6H5)3P). The synthesized nanoparticles were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), FT-IR and UV–vis spectroscopy. Freshly prepared copper nanoparticles showed surface plasmon resonance (SPR) around 574nm. TEM studies revealed a five-fold multiply twinned morphology of decahedral shape for the copper nanoparticles. Powder XRD pattern furnished evidence for a face-centered cubic crystal structure of pure metallic copper having an average crystallite size of about 35nm.

First Examples of Hybrids Based on Graphene and a Ring‐Shaped Macrocyclic Polyoxometalate: Synthesis, Characterization, and Properties

AbstractThis work introduces facile synthetic methods of two new classes of green materials based on graphene (G) and the macrocyclic polyoxometalate [H7P8W48O184]33– (P8W48) alone or assembled with an imidazolium‐based poly(ionic liquid) (PIL). The polyoxometalate serves as both an efficient graphite oxide reductant and a stabilizer. Owing to the strong adsorption of P8W48 on the resulting G sheets, water‐dispersible P8W48@G hybrids were obtained without the need for surfactant or polymeric stabilizers. The P8W48@G hybrids were characterized by X‐ray photoelectron spectroscopy, Raman spectroscopy, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, and cyclic voltammetry. The presence of G in these hybrids induces an outstanding enhancement in the electrochemical properties of P8W48 in comparison with those observed with glassy carbon. Moreover, P8W48@G‐ and P8W48@PIL‐G‐based electrodes exhibit remarkable stability during prolonged potential cycling in various aqueous electrolytes. To the best of our knowledge, these are the first examples of successful syntheses of a high nuclearity polyoxometalate and graphene assemblies that might facilitate photoelectrocatalysis of multielectronic reactions.

양이온성 계면활성제 거품 지속성 증진방법 연구

This study tried to find a suitable method for enhancing the foam stability of cationic surfactants that normally generate less foam or no foam. Several trials were made to enhance the foam stability: addition of anionic surfactant, colloids and polymer. Cationic starch (CA-ST) did not form foam at all, while the foam stability of two other cationic surfactant also showed low levels; methyl triethanol ammonium methyl sulfate distearyl ester (CEQ90) for 46 sec. and Cetyl trimethyl ammonium chloride (CM29) for 31 seconds. Foam stability of cationic surfactants were significantly affected by addition of anionic surfactant, sodium dodecyl sulfate (SDS). Foam stability of CA-ST was significantly enhanced by addition of SDS, while those of CEQ90 and CM29 were decreased. Addition of colloids (SiO2, kaolin) and polyvinyl alcohol (PVA) enhanced foam stabilities of CEQ90 and CM29. However, CA-ST did not form foam even in the presence of colloids or PVA. Effect of simultaneous addition of colloids and anionic surfactant on foam stability of cationic surfactant showed that foam stability of cationic surfactant was more influenced by addition of anionic surfactant than colloids. Effect of simultaneous addition of PVA and anionic surfactant on the foam stability of cationic surfactant also showed that presence of anionic surfactant significantly affect the foam stability of cationic surfactant. Foam stability of CA-ST was greatly increased to 8,780 seconds by addition of SDS 0.14% and PVA 2.5%. The foam stability of CA-ST was 8 times higher than CEQ 90. This study suggested that cationic surfactants not forming foam can generate foam by addition of anionic surfactant and its stability can be additionally increased by addition of colloids and PVA. The study results showed that enhancement in foam stability of cationic surfactant was prominently affected by the concentration of anionic surfactant added.

Surfactant-controlled low-temperature thermal decomposition route to monodispersed phase pure tricobalt tetraoxide nanoparticles

A low-temperature synthesis of tricobalt tetraoxide, Co3O4 nanoparticles was accomplished via thermal decomposition of a new precursor cobalt malonate, [CoCH2C2O4]· 2H2O in presence of surfactant stabilizers oleylamine (C18H35NH2) and triphenylphosphine ((C6H5)3P). The synthesized nanoparticles were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), FT-IR and Raman spectroscopy. Powder XRD pattern furnished evidence for a face-centered cubic structure of Co3O4 with average crystallite size of about 10nm. TEM studies revealed Co3O4 nanoparticles to be monodispersed, mostly cubic having sizes 4–12nm. Electron diffraction pattern indicates polycrystalline nature of the synthesized material. Raman spectrum showed four characteristic peaks of Co3O4 which further affirmed the phasic purity of the material.

Surfactant mediated low temperature thermal decomposition route to zinc oxide nanocrystals

Zinc oxide nanocrystals were synthesized via thermal decomposition of a new precursor zinc malonate, [ZnCH2C2O4]·2H2O in the presence of surfactant stabilizers oleylamine (C18H35NH2) and triphenylphosphine ((C6H5)3P). The nanocrystals were characterized by X-ray diffraction, transmission electron microscopy, FT-IR and UV–visible spectroscopy. XRD pattern showed a hexagonal wurtzite structure of ZnO having average crystallite size of about 22nm. The TEM image showed the nanocrystallites constituting the flower-like pattern to be of 25–55nm sizes. The band gap luminescence was observed at 354nm (∼3.50eV) alongwith defect related blue emission at 450nm (∼2.75eV).

Facile Photoreduction of Graphene Oxide by an NAD(P)H Model: Hantzsch 1,4-Dihydropyridine

To make "clean" reduced GO sheets in high quality and in large scale, a natural reduced nicotinamine adenine dinucleotide NAD(P)H model, Hantzsch 1,4-dihydropyridine (HEH), is used as a mild organic photoreductant in this work. Benefiting from the intense absorption of HEH in the range of 300-420 nm, the graphene oxide (GO) can be readily reduced by HEH under UV light irradiation (λ > 320 nm) to afford single or few-layer reduced graphene oxide at room temperature. Studies on reduction extent reveal that both irradiation time and concentration ratio of HEH to GO are important for effective reduction of GO under UV light. The as-prepared photochemically reduced graphene oxide (PRGO) dispersion is stable without the need for any polymeric or surfactant stabilizers. Simply by extraction treatment, the "clean" PRGO sheets can be obtained in large quantities, and its conductivity approaches to 4680 S·m(-1) that is the highest value reported by photochemical approaches so far.

Preparation of Novel Gemini Quaternary Ammonium Salt Cationic Surfactant

In order to obtain some novel cationic surfactants with high surface activity, n-octadecyldimethylamine and epichlorohydrin were used to synthesize 2-hydroxy-1, 3-dis (chloride octadecyl dimethyl ammonium) propane, which was a kind of gemini quaternary ammonium salt. N-octadecyldimethylamine and epichlorohydrin were used to prepare active epoxy intermediate glycidyloctadecyldimethyl ammonium chlorided, and then glycidyloctadecyldimethyl ammonium chlorided was reacted with octadecyldimethyl amine hydrochloride to synthesize the gemini cationic surfactant. FTIR and 1H NMR were used to represent structure of the gemini cationic surfactant. The interface characteristics were studied in detail. The critical micellar concentration (CMC) was determined by surface tension test to obtain the values of CMC and surface tension at CMC. The foam ability and foam stability of the gemini cationic surfactant were also discussed through contrast octadecyltrimethyl ammonium chloride and cetyltrimethyl ammonium chloride.

Nonionic Surfactant and Interfacial Structure Impact Crystallinity and Stability of β-Carotene Loaded Lipid Nanodispersions

The stability, crystallization, and melting behavior of canola stearin (CaSt) solid lipid nanoparticle dispersions (SLN) and canola oil-in-water emulsions (COE) with 10 wt % Poloxamer 188 (P188) or Tween 20 (T20) with and without 0.1 wt % β-carotene (BC) were investigated. Particles or droplets with diameters in the range of 115 nm were formed and stable for up to 90 days at 4 or 20 °C. Polymorphism was affected by surfactant type; that is, only β versus both β' and β were observed for the P188 and T20 SLN, respectively. According to Cryo-TEM, the emulsions and SLN were spherical versus platelet-like structures, respectively, with differences observed between SLN with P188 or T20. More surfactant was interfacially adsorbed in the SLN versus COE. Incorporation of BC at 0.1 wt % had no impact on SLN or COE size, polymorphism, or melting behavior. Less BC degradation was observed for the SLN versus COE and during storage at 4 versus 20 °C (p < 0.05).

Effect of lateral heterogeneity in mixed surfactant-stabilized interfaces on the oxidation of unsaturated lipids in oil-in-water emulsions

The development of lipid oxidation in oil-in-water (O/W) emulsions is widely influenced by the properties of the interfacial layer, which separates the oil and water phases. In this work, the effect of the structure of the interface on the oxidative stability of surfactant stabilized O/W emulsions was investigated. Emulsions were prepared with either single Tween 20 or Tween 20/co-surfactant mixtures in limiting amounts. The co-surfactants, Span 20 and monolauroyl glycerol have the same hydrophobic tail as Tween 20 but differ by the size and composition of their polar headgroup. Metal-initiated lipid oxidation, monitored through the measurement of oxygen uptake, formation of conjugated dienes and volatile compounds, developed more rapidly in the emulsions stabilized by the surfactant mixture than in the single Tween 20-stabilized emulsion. The reconstitution of Tween 20/co-surfactant films at the air–water interface and their surface-pressure isotherms highlighted that, contrary to single Tween 20 molecules, Tween 20/co-surfactant mixtures exhibited an heterogeneous distribution within the interfacial layer, offering probably easier access of water-soluble pro-oxidants to the oil phase. These observations provide direct information about the link between the homogeneity of the interface layer and the oxidative stability of emulsions.

Microwave- and Nitronium Ion-Enabled Rapid and Direct Production of Highly Conductive Low-Oxygen Graphene

Currently the preferred method for large-scale production of solution-processable graphene is via a nonconductive graphene oxide (GO) pathway, which uncontrollably cuts sheets into small pieces and/or introduces nanometer-sized holes in the basal plane. These structural changes significantly decrease some of graphene's remarkable electrical and mechanical properties. Here, we report an unprecedented fast and scalable approach to avoid these problems and directly produce large, highly conductive graphene sheets. This approach intentionally excludes KMnO(4) from Hummers' methods and exploits aromatic oxidation by nitronium ions combined with the unique properties of microwave heating. This combination promotes rapid and simultaneous oxidation of multiple non-neighboring carbon atoms across an entire graphene sheet, thereby producing only a minimum concentration of oxygen moieties sufficient to enable the separation of graphene sheets. Thus, separated graphene sheets, which are referred to as microwave-enabled low-oxygen graphene, are thermally stable and highly conductive without requiring further reduction. Even in the absence of polymeric or surfactant stabilizers, concentrated dispersions of graphene with clean and well-separated graphene sheets can be obtained in both aqueous and organic solvents. This rapid and scalable approach produces high-quality graphene sheets of low oxygen content, enabling a broad spectrum of applications via low-cost solution processing.