Surfactant Cetyltrimethylammonium Bromide Research Articles

Shaping Block Copolymer Microparticles by Positively Charged Polymeric Nanoparticles.

Shape-transforming block copolymer (BCP) microparticles have attracted extensive attention due to their promising applications in nanotechnology, biomedicines, interfacial science, and other fields. As their performance is highly associated to their shape and structure, it is very important to realize the precise control of particle shape. In this report, a method is proposed to regulate the shape and structure of polystyrene-b-polydimethoxysiloxane (PS-b-PDMS) microparticles by using positively charged core-crosslinked nanoparticles (CNPs) as a cosurfactant, combining with cationic surfactant cetyltrimethylammonium bromide (CTAB). The electrostatic repulsive interactions between CNPs and CTAB dominate the shape of PS-b-PDMS particles. Upon introducing NaCl, the electrostatic repulsion is reduced, resulting in the reshape of PS-b-PDMS particles from striped Janus ellipsoids to onion-like microspheres at a critical concentration of NaCl (cNaCl ). Interestingly, it is found that the critical cNaCl first increases then reaches a plateau, with the increase in the crosslinking degree of the CNPs. The work provides a simple strategy to tailor the morphology of BCPs by manipulating the electrostatic interaction.

Interactions between amino acids and a cationic surfactant in binary solvent system

The interaction of the cationic surfactant cetyltrimethylammonium bromide (CTAB) with amino acids (Lysine and Serine) in water and binary solvent combinations (Water-Ethyl Acetate) was studied conductometrically in this work. Solution formation method was used to study the effect of different parameters on interactions. Measured specific data were used to calculate the effect of temperature and concentration of added amino acids on the micellization of surfactant. Thermodynamic parameters for micellization i.e., Gibb's energy (ΔGm), and enthalpy (ΔHm), and entropy (ΔSm) have also been determined in presence of amino acids (Serine and Lysine). Results revealed that an increase in the concentration of added amino acids and binary solvent mixture (Ethyl Acetate-Water) causes an increase in critical micelle concentration (CMC) of CTAB where CMC of CTAB decreases with increasing temperature due to a decrease in hydrophobicity of molecules.

Hydrothermal synthesized delafossite CuGaO2 as an electrocatalyst for water oxidation

Hydrogen production from water splitting provides an effective method to alleviate the ever-growing global energy crisis. In this work, delafossite CuGaO2 (CGO) crystal was synthesized through hydrothermal routes with Cu(NO3)2·3H2O and Ga(NO3)3·xH2O used as reactants. The addition of cetyltrimethylammonium bromide (CTAB) was found to play an important role in modifying the morphology of CuGaO2 (CGO-CTAB). With the addition of CTAB, the morphology of CGO-CTAB samples changed from irregular flake to typical hexagonal sheet microstructure, with an average size of 1–2 μm and a thickness of around 100 nm. Furthermore, the electrocatalytic activity of CGO-CTAB crystals for oxygen evolution reaction (OER) was also studied and compared with that of CGO crystals. CGO-CTAB samples exhibited better activity than CGO. An overpotential of 391.5 mV was shown to be able to generate a current density of 10 mA/cm2. The as-prepared samples also demonstrate good stability for water oxidation and relatively fast OER kinetics with a Tafel slope of 56.4 mV/dec. This work highlights the significant role of modification of CTAB surfactants in preparing CGO related crystals, and the introduction of CTAB was found to help to improve their electrocatalytic activity for OER.Graphical abstract

First electrochemical study of a potent antifungal drug caspofungin: Application to its enhanced voltammetric sensing based on the performance of boron-doped diamond electrode in CTAB-mediated measurements

This present study describes the first electrochemical investigation of caspofungin, which is a semisynthetic echinocandin class of antifungal drug. For this purpose, an electrochemically pretreated (anodically and subsequently cathodically) boron-doped diamond (BDD) electrode was used. The cyclic voltammetric scans showed a single oxidation step that is irreversible and controlled by a dual mechanism of adsorption and diffusion. For the optimization of experimental conditions, the influence of the electrode pretreatment, pH of the supporting electrolyte, concentration of cationic surfactant cetyltrimethylammonium bromide (CTAB), accumulation variables, and instrumental parameters was examined on the current response of caspofungin. The improved sensitivity of the voltammetric measurements was observed due to the synergistic effect of CTAB on the adsorption capacity of BDD electrode in alkaline pH conditions. Employing square-wave adsorptive stripping voltammetry (using open-circuit accumulation for 60 s), the oxidation signal at around +0.45 V allowed to the determination of caspofungin in Britton-Robinson buffer at pH 11.0 containing 1 × 10−4 M CTAB. The process could be used in the concentration range from 2.06 × 10−7 to 1.03 × 10−5 M (from 0.25 to 12.5 μg mL−1 as acetate salt) with a detection limit of 5.27 × 10−8 M (0.064 μg mL−1 as acetate salt). A technique developed here was used successfully to determine caspofungin concentration in commercial parenteral dosage formulations.

Bentonite functionalized with amine groups by the sol-gel route as efficient adsorbent of rhodamine-B and nickel (II)

Environmental issues caused by population growth and increased industrial activity have become the object of criticism and discussion. This study evaluates how efficiently surfactant-modified bentonite bearing amine groups removes the metal nickel(II) and the dye rhodamine-B (RB) from wastewaters. First, hybrid inorganic-organic materials were obtained by intercalation of a bentonite (Bent) with the surfactant cetyltrimethylammonium bromide (CTA), followed by functionalization with [N-3 (trimethoxysilyl)propyl] ethylenediamine (DAPTMS) by the sol–gel process. Then, the resulting materials were characterized by X-ray diffraction, infrared absorption spectroscopy, thermal analysis, specific surface area analysis, Small-Angle X-ray Scattering, and pHPZC and tested as adsorbents of Ni(II) or RB by the batch method. X-ray diffraction confirmed that the Bent interlayer space expanded after intercalation with CTA —the basal space varied from 1.3 nm in Bent to 1.8 nm in Bent-CTA and to 1.6 nm in Bent-CTA-DAPTMS. Infrared absorption spectroscopy attested that Bent-CTA-DAPTMS contained organosilane and surfactant: the spectra displayed bands at 2925, 2853, 1470 cm−1, assigned to the CH2, CH3, and NH2 groups, respectively. The batch adsorption equilibrium experiments revealed that Bent and Bent-CTA-DAPTMS had higher adsorptive capacity for Ni(II) (qt = 65.77 mg g−1) and RB (qt = 0.98 mg g−1), respectively. The use of nonlinear equation models revealed that Ni(II) or RB adsorption onto the investigated materials followed pseudo-second-order kinetics, thereby confirming the high affinity between adsorbent and contaminants.

Naked-Eye Detection of 3-Nitro-1,2,4-triazole-5-one at Sub-Femtomolar Levels with Melamine and Unlabeled Au Nanoparticles

In this paper, a simple and rapid nanosensing assay was developed for 3-nitro-1,2,4-triazole-5-one (NTO) exploiting target-directed adsorption by unlabeled gold nanoparticles (AuNPs) and competitive supramolecular association of NTO with melamine (MEL). While AuNPs aggregated in the presence of MEL with a color change from red to blue, AuNPs remained dispersed and retained their original plasmonic red color with the addition of NTO, owing to the hydrogen bonding affinity of the NTO triazole ring to MEL. The concentration of NTO leading to color change could be determined with the naked-eye even at the sub-femtomolar level. Analytical results showed that the absorption ratio (A520nm/A630nm) varied linearly with the logarithm of NTO concentration in the range of 3.08 × 10–16 to 3.08 × 10–12 mol L–1 with a correlation coefficient of 0.9994. The synthesized and resultant AuNPs (in the presence of NTO and/or MEL) were characterized using ultraviolet–visible spectrophotometry, scanning transmission electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, and ζ-potential measurements. Possible interferences of various energetic substances in synthetic mixtures containing 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitrophenol, hexahydro-1,3,5-trinitro-1,3,5-triazine, and ammonium nitrate, of possible camouflage materials used in passenger belongings such as cationic surfactants (cetyltrimethylammonium bromide and cetylpyridinium chloride), d-(+)-glucose as a representative sugar, acetylsalicylic acid- and paracetamol-based painkiller drugs, and of commonly found soil ions (Cl–, NO3–, SO42–, Ca2+, Mg2+, CuII, FeII/III, and AgI) were also examined. In addition, recovery of NTO was successfully performed from NTO-based melt-cast formulations consisting of mixtures of TNT and NTO. The proposed method was statistically validated against a reference liquid chromatography–tandem mass spectrometry method applied to NTO standards, NTO-contaminated soil, and loam samples.

Effects of CTAB and SDS on the nucleation and growth of MnO2 and Ag-doped MnO2 nanoparticles formation

Permanganate (MnO4−) redox reaction with cysteine and sodium borohydride (NaBH4) were studied spectrophotometrically in absence and presence of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulphate (SDS) surfactants. Water soluble dark brown color MnO2 was formed as the stable product with CTAB and SDS. Absorbance of MnO4− at 526 nm increases with CTAB concentrations. The order of mixing of CTAB and reducing agents (cysteine and NaBH4) have significant effect on the redox reactions of MnO4−. The MnO4− purple color was not decolorized in a reaction system containing CTAB + MnO4− + NaBH4. These observations can be rationalized due to the strong MnO4− and BH4− electrostatic interactions with the ionized CTAB. Such type of observations were not noticed with SDS. Cationic and anionic head groups of CTAB and SDS were responsible to the incorporation as well as exclusion of MnO4−, cysteine, and BH4− from the Stern-layer of both micelles. Ag-Doped MnO2 was prepared using seedless and seed growth methods with SDS and CTAB. Morphology of MnO2 and Ag-Doped MnO2 were determined with SEM, EDX, XRD, and FTIR.

Synthesis of two-dimensional WS2/nickel nanocomposites via electroforming for high-performance micro/nano mould tools

To reduce the adhesion and friction between polymer and mould surfaces during polymeric micro/nano structures replication, we have used tungsten disulfide (WS2) nanosheets to fabricate high-performance nickel/WS2 nanocomposite mould using electroforming. However, the aggregation of WS2 nanosheets in the electroforming solution is a critical issue that influences the mechanical and tribological properties of the mould. In this study, we first propose a new strategy of combining anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetyltrimethylammonium bromide (CTAB) to achieve uniform dispersion and incorporation of WS2 nanosheets in the electroformed nickel mould. Our results indicate that appropriately designing the structure of CTAB-SDS complex can achieve a stable WS2 dispersion, contributing to the uniform co-deposition of WS2 nanosheets into nickel mould. The combination of high concentration of CTAB and SDS (1.0 g/L CTAB and 1.0 g/L SDS) significantly improved the dispersibility and incorporation of WS2 into the nickel matrix, compared to individual SDS or CTAB. Consequently, the maximum hardness enhanced by 350% from 284 HV for pure nickel to 1280 HV for nickel/WS2 nanocomposite mould, along with the coefficient of friction (COF) against the polymethyl methacrylate (PMMA) pin reducing from 0.75 to 0.31. It is also found that CTAB promotes particle encapsulation while SDS improves the particle dispersion but cannot control the particle incorporation. The surface wettability of nickel/WS2 mould altered to hydrophobicity from hydrophilicity of nickel mould, where the adhesion-induced wear caused by polymer pin significantly reduced. Moreover, the surface roughness did not change much with the incorporation of WS2 into the mould, which is acceptable for mould applications. Finally, the nickel/WS2 nanocomposite mould was successfully fabricated via electroforming and its self-lubricating properties was validated by micro hot embossing PMMA microfluidic chips with good surface quality.

Study of interaction between cationic surfactant (CTAB) and ascorbic acid/ascorbic acids derivatives by tensiometric and spectroscopic methods

The interactions between the cationic surfactant-cetyltrimethylammonium bromide (CTAB) and ascorbic acid and its derivatives in an aqueous media were investigated by using tensiometric and spectroscopic methods. On the basis of the surface tension isotherms, the values of the critical micelle concentration were determined also the adsorption parameters (the Gibbs free energy of adsorption, the surface excess at the saturated interface, the minimum molecular area in the adsorption layer at the saturated interface) were calculated using the Szyszkowski equation. The charged pseudophase model was adopted for define the Gibbs free energy of micellization. The infrared analysis (FTIR) contributed to the estimation of the possibility of the existence of interactions prevailing in the analyzed systems. The effect of CTAB-ascorbic acid/ascorbic acid derivatives interactions on their antioxidant activity was analyzed. Sets of ascorbic acid, 3-O-ethyl ascorbic acid and ascorbyl glucoside solutions differing in CTAB concentration were prepared. For the total antioxidant capacity determination, the Ferric Reducing Antioxidant Power (FRAP) assay and 1,1-diphenyl-2-picrylhydrazyl (DPPH•) assay were used. The results obtained for CTAB - ascorbic acid/ascorbic acid derivatives systems were compared with the ones obtained for pure antioxidants.

Eco-Friendly Synthesis of Silver Nanoparticles Using Pulsed Plasma in Liquid: Effect of Surfactants

Silver (Ag) nanoparticles were successfully prepared by using the in-liquid pulsed plasma technique. This method is based on a low voltage, pulsed spark discharge in a dielectric liquid. We explore the effect of the protecting ligands, specifically Cetyl Trimethylammonium Bromide (CTAB), Polyvinylpyrrolidone (PVP), and Sodium n-Dodecyl Sulphate (SDS), used as surfactant materials to prevent nanoparticle aggregation. The X-Ray Diffraction (XRD) patterns of the samples confirm the face-centered cubic crystalline structure of Ag nanoparticles with the presence of Ag2O skin. Scanning Transmission Electron Microscopy (STEM) reveals that spherically shaped Ag nanoparticles with a diameter of 2.2 ± 0.8 nm were synthesised in aqueous solution with PVP surfactant. Similarly, silver nanoparticles with a peak diameter of 1.9 ± 0.4 nm were obtained with SDS surfactant. A broad size distribution was found in the case of CTAB surfactant.

Doxazosin adsorption in natural, expanded, and organophilized vermiculite-rich clays

Vermiculite clays are adsorbent materials that have good chemical adsorption capacity, which makes them applicable in the removal of drugs from aqueous solutions. Their lamellar structure can be easily expanded and organophilized. To assess the efficacy and environmentally-tolerant capacity of the adsorption method, the organophilized vermiculite clay was compared to both natural and expanded vermiculite clays. To prepare the organophilized clays, a natural clay sample was expanded at 900 °C. The expanded clay was thus treated by immersion in a 1.0 M NaCl solution and organophilized using a cetyltrimethylammonium bromide (CTMA-Br) surfactant, for 24 h at 50 °C. Natural, expanded, and organophilized samples were characterized using the techniques of XRD, FTIR, TG/DSC, and SEM to observe structural changes after expansion and organophilization. These characterizations indicated that there was an increase in the interlamellar space of the expanded and organophilized sample. In addition, a study of the point of zero charge was performed to determine the surface changes of the samples and the amount of doxazosin adsorption in the samples was determined by the time adsorption test. Further, the organophilized sample showed potential adsorption of the drug doxazosin and high performance in relation to the expanded and natural samples.

The Role of the Presence of Aliphatic Alcohols on the Formation of Wormlike Micelle of Anionic-Cationic Surfactants Mixture

Thermodynamically controlled supramolecular gel or aggregate is commonly resulted from the formation of one-dimensional micelles through specific self-assembling of amphiphilic molecules. This phenomenon is commonly referred to as the formation of worm- or thread-like micelle which is still considered as quite complicated and obscure. This, in spite of the recent physical insight for interpreting this phenomenon, is referred to as the critical intermolecular forces (CIF) of which still needs further support. Therefore, attention by scientists in this field should be given in order to make this transition phenomenon clear. In this work, investigations concerning the effect of addition of aliphatic alcohols with different chain lengths of even carbon numbers (ethanol, 1-butanol, 1-hexanol, 1-octanol and 1-decanol), at different concentrations (0.002-0.040 M), and temperatures on the formation of wormlike micelle for the mixture of anionic sodium dodecylsulfate (SDS) and cationic cetyltrimethylammonium bromide (CTAB) surfactants were carried out. The formation of these one dimensional micelles were practically detected by following the sharp change of physical properties through the presence of a remarkable high viscosity peak. The results indicate there is no linear or systematic relationship between the effects of the presence of these alcohols with their chain lengths. It has been found that the presence of aliphatic alcohols causes a positive effect on the formation of one dimensional micelles. The ability of the transition from spherical to wormlike micelles increases with increasing their concentrations of alcohols except for that of 1-octanol. The obtained achievements were explained in terms of CIF theory which then offered a reasonable support to this theory. It was concluded that alcohols particularly ethanol and 1-octanol can be employed as adjustment reagents for controlling required viscosity of threadlike micelles.

Effect of CTAB on the healing of concrete cracks repaired by electrodeposition and the durability of repaired concrete

In this study, the surfactant cetyltrimethylammonium bromide (CTAB) was doped in an electrolyte solution to improve the healing effect of concrete cracks repaired by electrodeposition. The effect of the CTAB dosage (0.25%, 0.50%, 1.00%, 1.50%, 2.00%) on the healing of concrete cracks was investigated, as well as the durability of repaired mortar specimens. Under the current dosage range, the experimental results demonstrated that the healing effect of concrete cracks peaks at 1.00% CTAB dosage. Nevertheless, the extra more addition of CTAB could weaken the healing effect. In terms of the specimens repaired in electrolyte solution containing 1.00% CTAB, the steel-mortar adhesive strength, chloride ion resistance and corrosion resistance of steel were significantly enhanced compared with those of specimens repaired by electrodeposits without CTAB. Additionally, instead of influencing the composition of electrodeposits ZnO (formed in ZnSO4 solution) and Mg(OH)2 (formed in MgSO4 solution)), the different CTAB dosages could lead to diverse morphology of electrodeposits and different porosity of specimens.

Differential surface partitioning for an ultrasensitive solid-state SERS sensor and its application to food colorant analysis

Solid-state SERS sensors are desirable point-of-care tools due to their portability. However, the level of SERS sensitivity achieved in liquid phase is rarely duplicated in the solid phase. We report herein the fabrication of a SERS sensor using alumina beads as the solid support and demonstrate its high SERS sensitivity with the model analyte 4-aminophenyl disulfide (4-APDS). The key to sensitivity is a hydrophilic-hydrophobic surface gradient constructed by sequentially coating with the surfactant cetyltrimethylammonium bromide and fluorous 1H,1H,2H,2H-perfluorooctyltriethoxysilane. The surface gradient, together with chloride etching, allows the detection of 4-APDS at the low concentration of 10−15 M. The practicality of the sensor beads is evidenced by successfully tracking the SERS fingerprints of five food colorant standards in the SERS spectra of a popular candy product. These SERS sensor beads are easy to prepare, convenient to use, and highly responsive as a SERS platform for the analysis of colorants.

PHOTOPHYSICAL ASPECTS OF POLARITY SENSITIVE FLUOROPHORE IN CATIONIC REVERSE MICELLES

In recent years, the field of reverse micelles has witnessed a significant growth of interest, partly due to the finding that proteins, other biopolymers, and even bacterial cells can be solubilized in the reverse micellar systems. Among surfactants capable of forming water in oil microemulsion, the cationic surfactant cetyltrimethylammonium bromide (CTAB) has received particular attention because of its ability to solubilize relatively large amount of water in a variety of hydrophobic organic solvents. Due to versatile photochemical and photophysical properties of Ru(II) complexes, Ru(II)- phenanthroline and its derivatives were used in this present work to form CTAB cationic reverse micelles and studied to characterise their photophysical properties such as absorption, emission and excited state life time. The findings from the spectral data observed in the present study proves that the excited state properties of Ru(II)-phenanthroline complexes are dramatically altered in the presence of reverse micelle. Specifically reverse micelle encapsulation of [Ru(dpphen)3]2+ complex in restricted environment causes blue shift in the emission maximum as well as have longer radiative lifetime. The blue shift in the emission maximum in the case of [Ru(dpphen)3]2+ indicates that the probes are near the water in oil reverse micellar interface, tightly bound and are not displaced towards the water pool of the micelle even at the highest water loading W0=50, which reveals the increased hydrophobicity. This highest fluorescence lifetime can serve as an excellent indicator to point out the location of the probe in a microheterogeneous system/environment.

STATIONARY AND ULTRASONIC NANOPARTICLE ASSEMBLY ON NOTABLE SURFACES

Frequently used wettable (SiO[Formula: see text] and nonwettable highly oriented pyrolytic graphite (HOPG) surfaces have been investigated for the deposition and shape separation of gold nanorods and rod–sphere mixture using the droplet evaporation method. In this paper, we explore and compare the resulting assembly using immovable and ultrasonic systems. On HOPG, stable evaporation produces monolayer arrays of gold nanorods on the terraces whereas aligned arrays of nanorods at the step-edges of HOPG. However, isolated large islands of nanorods on the terraces of HOPG and aligned nanorods at the step-edges become chaotic under the ultrasonic deposition. Also besides gold nanorods, excess cetyltrimethylammonium bromide (CTAB) molecules in suspension are deposited on the terraces in the form of mono- and multilayers revealed by an atomic force microscope (AFM). Both stable as well as ultrasonic vibration techniques were employed on the rod–sphere mixture over the SiO2 substrate. Stable drying of a droplet showed order arrays of gold nanorods separated from nanospheres everywhere in the coffee-stain ring. The fascinating assembly has been observed for such suspension deposits obtained under ultrasonic vibrations. Aligned arrays of nanorods covered with CTAB surfactants have been sterically as well as osmotically depleted first nearly all CTAB-coated nanospheres and then self-assembled them with the similar geometries within the coffee-stain ring on the SiO2 surface. The same separation effect has been observed within the initial pinning as well as everywhere over the terraces of the HOPG.

In-situ fabrication of surfactant modified CNT-based novel bio-composite and its performance evaluation for simultaneous removal of anionic dyes: Optimization by Box-Behnken design

• CTAB modified Saccharum munja containing 1% CNT bio-composite was fabricated. • Anionic dyes were removed effectively from single and multi-component systems. • RSM with Box-Behnken design was used for the optimization. • Regeneration of the bio-composite was studied up to 5 cycles. The simultaneous and efficient removal of anionic dyes at neutral pH is a challenging task and is thus attracting considerable attention to remediate wastewater. Herein, cetyltrimethylammonium bromide (CTAB) surfactant was used for the modification of Saccharum munja based bio-composite containing 1% functionalized carbon nanotube (CNT). The as-synthesized bio-composite was characterized and used to study the affinity and efficacy towards the removal of Coomassie Brilliant Blue R-250 (BB), Reactive Red 35 (RR) and Reactive Orange 107 (RO) dyes from the single and multi-component systems. Response surface methodology (RSM), with Box–Behnken design matrix was successfully employed for the optimization of operating parameters i.e., pH, adsorbent dosage and initial concentration of dyes. The proposed models were significant as per the analysis of variance (ANOVA) statistical analysis. Furthermore, the experimental data were well fitted with the pseudo-2nd-order kinetic model and the Langmuir isotherm model with a very high monolayer adsorption capacity for the single-component system, i.e., 1179.39, 109.41 and 22.14 mg/g for BB, RR and RO dyes respectively at neutral pH conditions. The interactive effects between dye molecules in binary and ternary systems were studied using the extended Langmuir model, which revealed competitive as well as synergistic behavior of dyes. Interestingly, the observed affinity trend, BB > RR > RO was explained on the basis of the proposed adsorption mechanism. Regeneration of the exhausted bio-composite depicted excellent reusability even after five adsorption-desorption cycles, which makes CTAB modified SM + CNT a promising candidate adsorbent for treating simulated dyeing effluents and the whole process is cyclic and eco-friendly.

Radical Anions and Dianions of Naphthalenediimides Generated within Layer-by-Layer Zirconium Phosphonate Thin Films.

Chemical reduction of N,N'-bis(2-phosphonoethyl)-1,4,5,8-naphthalenediimide (PNDI) with the reducing agent sodium dithionite gave stable colored reduced species, both in homogeneous solutions and in self-assembled thin films. When colorless PNDI aqueous solutions were titrated with the reducing agent, stepwise reduction was observed, giving first the radical anion (PNDI-•) and then the dianion (PNDI2-) species, which were detected by UV-visible-NIR spectroscopy, allowing the unambiguous determination of absorption maxima and molar absorptivities for each species. The radical anion PNDI-• was found to form π-dimers in water, but monomeric PNDI-• was formed in the presence of the cationic surfactant cetyltrimethylammonium bromide, indicating association with the micelles. Thin films of PNDI with 25 layers were grown by the zirconium phosphonate method on quartz substrates. Reduction of the films with sodium dithionite also produced radical anions and dianions of PNDI. However, reduction in the films was much slower than in solution, evidencing the compactness of the films. Moreover, reduction in the films did not proceed to completion, even with excess of the reducing agent, which can be attributed to the repulsion of negative charges within the film.

Methodological approaches to assessing the toxicity of compounds by changing the behavioral response of soil oligochaetes

The methodological aspects of assessing the toxicity of surface-active substances (SAS) by changing the behavioral response of avoiding the substrate by earthworms Eisenia fetida andrei Bouche, 1972 were studied. The conditions for biotesting were selected, under which the method is more sensitive to the tested pollutants. In this method, 30 worms. placed in a Petri dish with a substrate unfavorable for worms (dry sand). Around it, Petri dishes with test samples of moistened sand contaminated with individual toxicants in various concentrations and their mixtures were placed radially. A control sample (wet sand) was also placed among the prototypes. When the worms selected the most favorable of the tested contaminated substrate samples, their movement from dry sand was observed. After 4 h from the start of the experiment, the number of worms in each of the compartments was counted. The toxic effect of the cationic surfactant cetyltrimethylammonium bromide (CTAB) was manifested when its content in the soil sample was from 0.001 g / kg; nonionic surfactant Tween-80 – from 1 ml / kg; anionic surfactant sodium lauryl sulfate – from 20 mg / kg.

Improved membrane permeability with cetyltrimethylammonium bromide (CTAB) addition for enhanced bidirectional transport of substrate and electron shuttles

The effects of membrane permeability on extracellular electron transfer (EET) and performance of microbial fuel cell (MFC) need to be explored. In this work, cetyltrimethylammonium bromide (CTAB) was chosen to enhance the current generation and bidirectional transport of substrate and electron shuttles by tailoring the cell membrane permeability. Specifically, the peak currents of biofilms treated with CTAB especially at 200 μM were obviously higher than the control biofilm with no CTAB, and the riboflavin mediated electron transfer was promoted prominently. Biomass and viability analyses showed that an appropriate concentration of CTAB had almost no adverse effect on the cell viability of biofilm and could increase the biomass of biofilm. Measurements of the extracellular activity of alkaline phosphatase and UV–vis absorption confirmed the increased membrane permeability and the promoted efficiency of substrates transported into cells. This contribution paves the key step for facilitating EET process by adjusting membrane permeability through CTAB or other surfactants addition.