Didodecyldimethylammonium Bromide Research Articles

High luminescence and external quantum efficiency in perovskite quantum-dots light-emitting diodes featuring bilateral affinity to silver and short alkyl ligands

Perovskite quantum dots (PeQDs) have been under commercial and functional development in recent years since they offer outstanding optoelectronic properties and solution processability. However, both insulating ligands around PeQDs and instability impair the performance of photoelectronic devices. Therefore, we introduce multi-step ligands exchange by silver (Ag)- trioctylphosphine (TOP) as short alkyl ligands to reinforce the optical properties and stability for PeQDs and successfully elevated light-emitting diodes characters. The PeQDs with Ag-TOP ligands (Ag@QD) perform higher photoluminescence quantum yield (PLQY, ~93%), higher exciton binding energy (57.6 meV) with better solvent, temperature, and ambient stability over 1 month presenting better performances on comparison with conventional di-dodecyl dimethyl ammonium bromide (DDAB) or TOP ligands. Nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and time-resolved photoluminescence (TR-PL) measurement provides clear insight on bilateral affinity in Ag@QD illustrating excellent defect passivation and appropriate steric hindrance. Furthermore, we demonstrate Ag@QD with lower turn-on voltage (~2.8 V), high electroluminescence (~3820 cd/cm−2), and high efficiency (EQE ~ 9.43%).

Stable silica coated DDAB-CsPbX3 quantum dots and their application for white light-emitting diodes

Silica-coated CsPbX3 QDs with di-dodecyl dimethyl ammonium bromide (DDAB) short chain ligand was proposed to improve its stability. Green DDAB-CsPbBr3@SiO2 QDs shows a high photoluminescence quantum yield (PL-QY) of about 80%. After SiO2 coating, the thermal and water stability of DDAB-CsPbBr3@SiO2 QDs are enhanced. In addition, red DDAB-CsPbBr1I2@SiO2 QDs with long photoluminescence lifetime and good thermal stability was also synthesized and characterized. XPS results show that Br content can be significantly increased after DDAB modification, and the longer photoluminescence lifetime of DDAB-CsPbX3@SiO2 QDs after DDAB modification indicates that DDAB can decrease the Br vacancy defects on the CsPbX3 surface. Furthermore, white light-emitting diodes (LEDs) are obtained by mixing green light DDAB-CsPbBr3@SiO2 and red light DDAB-CsPbBr1I2@SiO2 on GaN chip. The LED device exhibits bright white light emission and good electroluminescence stability with a color coordinate of (0.35, 0.348), corresponding color rendering index of 85.3 and color temperature (CCT) of 5274 K under the injection current 30 mA. The results indicate that DDAB-CsPbX3@SiO2 has potential application for the luminescent materials of the white light-emitting devices.

Human Cytochrome P450 2C9 and its Polymorphic Modifications: Electroanalysis, Catalytic Properties and Approaches to the Regulation of Enzymatic Activity

The electrochemical properties of cytochrome P450 2C9 (CYP2C9) and polymorphic modifications P450 2C9*2 (CYP2C9*2) and P450 2C9*3 (CYP2C9*3) were studied. To analyze the comparative catalytic activity, the enzymes were immobilized on electrodes modified with a membrane-like synthetic surfactant (didodecyldimethylammonium bromide (SPE/DDAB). Peaks of reduction and oxidation of the heme iron, which confirms the adequate choice of the type of modified electrode, characterize cyclic voltammograms of cytochromes P450 under anaerobic conditions. The midpoint potential, Emid, of cytochrome P450 2C9 was -0.318 ± 0.01 V, and Emid =-0.324 ± 0.01 V, and Emid = -0.318 ± 0.03 V for allelic variant 2C9*2 and allelic variant 2C9*3, respectively. In the presence of substrate diclofenac under aerobic conditions, cytochrome P450 2C9 and its polymorphic modifications P450 2C9*2 and P450 2C9*3 exhibit catalytic properties registered by increasing the catalytic current. The amplitude ratio of diclofenac/oxygen currents ((IDF/IO2, catalytic index) is 1.80 for cytochrome P450 2C9, 1.33 and 2.18 for isoforms 2C9 *2 and 2C9*3, respectively. Antioxidant medications mexidol and taurine (at a concentration of 98 μM and 100 μM, respectively) stimulated aerobic reduction of cytochromes P450 heme iron. In the presence of mexidol, an increase in the catalytic activity of cytochrome P450 2C9 in relation to diclofenac by 1.7 times is registered. Taurine, vitamin-like compound with antioxidant properties also stimulates the metabolism of diclofenac by 1.5 times.

Influence of surfactants on a pre-adsorbed cationic layer: Removal and modification

Removal of organic species from solid surfaces is a crucial process. The use of oppositely charged surfactants provides a potential method for enhanced removal. Neutron reflectometry has been used to investigate the complex behaviour of a pre-adsorbed and tenacious layer of the cationic surfactant didodecyldimethylammonium bromide (DDAB) on a mica surface, during exposure to different organic species in solution. The anionic surfactant sodium dodecylsulfate (SDS) was shown to be able to remove the cationic layer, but only if anionic micelles were present in solution. To facilitate comparison with the behaviour of a non-ionic surfactant, the direct adsorption of pentaethylene glycol monododecyl ether (C12E5) to mica was also studied; low surface coverage adsorption was seen at the critical micelle concentration and above. C12E5 was then found not to remove the cationic layer, but did include into the layer to some degree. The presence of cationic surfactant on the mica was however shown to significantly modify the adsorption behaviour of the non-ionic surfactant.

Surface Crystal Growth of Perovskite Nanocrystals via Postsynthetic Lead(II) Bromide Treatment to Increase the Colloidal Stability and Efficiency of Light-Emitting Devices.

The surface modification of metal halide perovskite nanocrystals (NCs) significantly impacts their optical properties and colloidal stability. This subsequently affects the performance of light-emitting devices (LEDs). Therefore, numerous surface passivation techniques like ligand exchange and metal halide doping have been explored to passivate the surface defects of perovskite NCs and obtain highly efficient LEDs. In this study, we demonstrated the postsynthetic metal halide doping treatment using lead(II) bromide (PbBr2) to passivate the surface defects of the CsPbBr3 NCs at a moderate reaction temperature of 80 °C. The alkyl quaternary ammonium salt, didodecyldimethylammonium bromide (DC12AB), enabled the complete dissolution of PbBr2 in a nonpolar solvent, toluene. Because of surface crystal growth, the particle sizes of the PbBr2-doped CsPbBr3 NCs were higher than those of the as-synthesized CsPbBr3 NCs. The photoluminescence quantum yield of the CsPbBr3 NCs drastically increased from 26.8 to 83.9% after the PbBr2 doping treatment. Moreover, the PbBr2-doped CsPbBr3 NCs possessed long-term colloidal stability of more than 2 months that indicates the strong bonding between the NCs and ligands. We observed that the alkyl chain length of the quaternary alkyl ammonium salts affected the luminance and device stability during operations. In this study, a promising strategy was devised to achieve highly luminescent perovskite NCs with excellent colloidal stability that can enhance the performance of LEDs.

Hydration Shell Changes in Surfactant Aggregate Transitions Revealed by Raman-MCR Spectroscopy

Hydration states of many self-assemblies directly relate to their structures and functions. Here, we use Raman multivariate curve resolution (Raman-MCR) assisted by differential scanning calorimetry and nuclear magnetic resonance to explore the hydration properties of aggregates formed by three cationic ammonium surfactants, trimethylene-1,3-bis(dodecyldimethylammonium bromide) (12-3-12(Br)2), didodecyldimethylammonium bromide (DDAB), and dodecyltrimethylammonium bromide (DTAB). For 12-3-12(Br)2, the transitions from spherical to rodlike and wormlike micelles lead to about 20% and 60% dehydration and gradually weaken water tetrahedral order and H-bond in hydration shells for both headgroup and hydrophobic chain. As to DDAB, unilamellar vesicles contain two kinds of hydration water species, but multicompartment vesicles exhibit decreased water order and weaker H-bond. DTAB only forms spherical micelles and its hydration structure is similar to that of the 12-3-12(Br)2 spherical micelles. This work provides a basis to explore the hydration states of complex biological self-assemblies.

Removal of polycyclic aromatic hydrocarbons from aqueous media using modified clinoptilolite

Carcinogenic polycyclic aromatic hydrocarbons (PAHs) are widespread in the environment. In this study, the removal of PAHs from aqueous media was assessed using samples of clinoptilolite, a natural zeolite, pre-treated with 1 mol/L of NaCl, (Na pre-treated clinoptilolite, NC). Samples (10 g) of NC were separately modified with 5, 2, 2, and 20-mmol/L solutions of cetylpyridinium chloride (CPC), didodecyldimethyl ammonium bromide (DDAB), hexadecyltrimethylammonium bromide (HDTMA), and tetramethyl ammonium chloride (TMA) surfactants as potential cost-effective adsorbents. The kinetics, optimal sorbent dosage, and competitive effects were evaluated through batch adsorption tests using deionised water spiked with five PAHs (anthracene (50 μg/L), fluoranthene (100 μg/L), fluorene (100 μg/L), phenanthrene (100 μg/L), and pyrene (100 μg/L)). The surfactant non-modified (NC) and TMA-MC (modified clinoptilolite) exhibited PAH removal of <66% from the spiked concentration in aqueous solution, while CPC-MC, DDAB-MC, and HDTMA-MC achieved removal rates of >93% for the five PAHs after 24 h at a solid:liquid ratio of 1:100. The remaining concentrations of anthracene and fluoranthene were below 3 μg/L, and that of fluorene was <6 μg/L, lower than the water quality criteria of British Columbia, Canada, for protecting aquatic life. However, HDTMA-MC retained >83% of the fluorene. Over 80% of all PAHs were absorbed within 15 min for the CPC-MC and DDAB-MC, and the maximum adsorption was reached in <2 h. Three kinetic models were applied assuming pseudo-first-order, pseudo-second-order, and intra-particle equations, and the results were well-represented by the pseudo-second-order equation. The PAH sorption results indicated that the adsorption mechanism is based on PAH hydrophobicity, and π-π electron-donor-acceptor interaction with surfactant. CPC and DDAB with two long chain hydrocarbons had more PAH adsorption than HDTMA with one, and TMA with no long chain hydrocarbons (DDAB-MC > CPC-MC > HDTMA-MC ≫ TMA-MC > NC). With a solid:liquid ratio of 1:200, over 90%, 80%, and 70% of the anthracene, fluoranthene, and pyrene were adsorbed by the CPC-MC, DDAB-MC, and HDTMA-MC, respectively.

No effect of lipoic acid on catalytic activity of cytochrome P450 3A4.

Objectives α-Lipoic acid is used as an antioxidant in multivitamin formulations to restore the normal level of intracellular glutathione after depletion caused by environmental pollutants or during physiological aging of the body, as a chelating agent, as a dietary supplement, in anti-aging compositions. Lipoic acid (LA) acts as a buffer in cancer therapy and in therapy of diseases associated with oxidative stress. The effect of LA on the catalytic functions of cytochrome P450 3A4 as the main enzyme of the biotransformation of drugs was studied. It was shown that LA in the concentration range of 50-200μM affects the stage of electron transfer (stage of cytochrome P450 3A4 heme reduction), decreasing the cathodic reduction current by an average of 20±5%. The kinetic parameters (k cat) of the N-demethylation reaction of erythromycin, the antibiotic of the macrolide group, used as a marker substrate for the comparative analysis of the catalytic activity of cytochrome P450 3A4, both in the presence of α-lipoic acid and in the cytochrome P450 3A4-erythromycin complex, amounted to comparable values of 3.5±0.9 and 3.4±0.9min-1, respectively. Based on these experimental data, we can conclude that there is no significant effect of α-lipoic acid on the catalysis of cytochrome P450 3A4. These results can be projected on the possibility of using α-lipoic acid in complex therapy without negative impact on the enzymatic cytochrome P450 system. Methods The analysis was performed in electrochemical non-invasive model systems for recording the catalytic activity of cytochrome P450 3A4, using screen-printed electrodes, modified with membranous didodecyldimethylammonium bromide. Results It was shown that LA did not affect the N-demethylation of macrolide antibiotic erythromycin. Catalytic constant (k cat) of N-demethylation of erythromycin corresponds to 3.4±0.9min-1 and in the presence of LA corresponds to 3.5±0.9min-1. Conclusions Based on the obtained experimental data, we can conclude that there is no significant effect of α-lipoic acid on individual stages and processes of catalysis of cytochrome P450 3A4. LA can be recommended for inclusion in complex therapy as an antioxidant, antitoxic and chelating compound without negative impact on the enzymatic cytochrome P450 3A4 activity of the human body.

Cytochrome P450 3A4 as a Drug Metabolizing Enzyme: the Role of Sensor System Modifications in Electocatalysis and Electroanalysis

The electroanalytical characteristics of the recombinant cytochrome P450 3A4 (CYP3A4) immobilized on the surface of screen-printed graphite electrodes modified by multi-walled carbon nanotubes (MWCNTs) have been investigated. The role and the influence of the modification of a graphite working electrode by carbon nanotubes on the electroanalytical parameters of this cytochrome have been demonstrated. The conditions for its immobilization on the obtained screen-printed graphite electrodes modified by MWCNTs have been optimized. The electrochemical parameters of the oxidation and reduction of the enzyme heme iron ion were determined: these included midpoint-potential (E0') of –0.35 ± 0.01 V (relative to the silver/silver chloride reference electrode, Ag/AgCl); the electrochemical rate constant of heterogeneous electron transfer (ks) of 0.57 ± 0.04 s–1, the amount of electroactive CYP3A4 on the modified electrode (Γ0) of (2.6 ± 0.6) × 10–10 mol/cm2. The functioning mechanism of this electrochemical sensor followed the principle of “protein film voltammetry” (i.e. voltammetry of a protein film on the electrode surface). In order to develop medical biosensors using immobilized CYP3A4 for electroanalysis of drug substances, the substrates of this hemoprotein, we performed a voltammetric study of the catalytic activity of immobilized CYP3A4. We investigated electrocatalytic properties of the recombinant CYP3A4 immobilized on modified screen-printed graphite electrode using macrolide antibiotic erythromycin as a substrate. The modification of electrodes has been shown to play a decisive role for the study of the properties of cytochromes P450 in electrochemical studies. Smart electrodes can serve as electroanalyzers for analytical purposes, as well as electrocatalysts for the study of biotransformation and metabolic processes. Electrodes modified with carbon nanomaterials are applicable for analytical purposes in the registration of hemoproteins. Electrodes modified with synthetic membrane-like compounds (for example, didodecyldimethylammonium bromide) are effective in enzyme-dependent electrocatalysis.

Effective Adsorptive Removal of Methylene Blue from Water by Didodecyldimethylammonium Bromide-Modified Brown Clay

In the present investigation, brown clay (BC) was modified with didodecyldimethylammonium bromide (DDAB) to produce a sorbent (DDAB-BC), which was characterized and applied for sorption of methylene blue (MB) from aqueous media. BC was functionalized using DDAB by cation exchange of the DDAB moiety with positive ions existing inside the interlayer spaces of the BC. X-ray diffraction (XRD) studies confirmed that the d-spacing of DDAB-BC became wider (3.39 Å) than that of BC (3.33 Å). Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were exploited to explore the functional groups and morphological structure of sorbents, respectively. The Brunauer–Emmett–Teller (BET) surface area, pore volume, and pore diameter of DDAB-BC were determined as 124.6841 m2/g, 0.316780 cm3/g, and 8.75102 nm, respectively. Batch sorption investigations were carried out to determine the optimum experimental conditions, using the one-factor one-time procedure. The sorption of MB on DDAB-BC strongly obeyed the Langmuir isotherm and agreed well with pseudo-second-order kinetics. Sorption of MB onto DDAB-BC showed maximum efficiency (∼98%) and maximum sorption capacity (∼164 mg/g) at optimal values of pertinent factors: dye concentration (100 mg/L), pH (7), and temperature (55 °C). Sorption isothermal studies predicted that removal of MB on DDAB-BC follows multilayer sorption at higher MB dye concentrations and monolayer sorption at lower MB dye concentrations.

Preparation and characterization of positively surface charged zinc oxide nanoparticles against bacterial pathogens

Solvothermal synthesis was used to investigate the formation of zinc oxide (ZnO) nanoparticles (NPs). A series of ZnO NPs was synthesized with different relative ratios of didodecyldimethylammonium bromide (DDAB) and zinc nitrate (ZN). The variation in the molarity influenced the crystallinity, size, and morphology of the obtained ZnO NPs. X-ray diffraction, Fourier-transform infrared spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and zeta potential analysis were used to study the characteristic features of the ZnO NPs. The ZnO surface charge, size, and morphological structure were highly reliant on the concentrations of DDAB and ZN. With increasing relative ratio of DDAB to ZN, the particle size of ZnO NPs decreased and the surface charge increased to higher positive value. The ZnO NPs synthesized with cationic liquid DDAB presented enhanced performance in preventing the growth of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) strains. The antibacterial activity of ZnO NPs have direct contact with the microbial cell wall resulting in destruction of bacterial cell integrity, release of antimicrobial Zn2+ ions, and induce cell death. This is due to the positively charged smaller ZnO NPs, prepared with DDAB cationic surfactant, effectively acting as an antimicrobial agent against food-borne pathogenic bacteria.

Rayleigh and Rayleigh-Debye-Gans light scattering intensities and spetroturbidimetry of dispersions of unilamellar vesicles and multilamellar liposomes

Hypothesis: Since the volume fraction of the surfactant bilayer(s), of thickness db, in a vesicle and liposome is smaller than one, the dependences of the Rayleigh (R) scattering intensity and turbidity on the particle radius a are weaker than those for a homogeneous sphere, which are proportional to a3. The dependences of the Rayleigh-Debye-Gans (RDG) scattering intensity and turbidity on a are also weaker. Work done: The dependences of the effective relative refractive index on a, db, and dw (water layer thickness) were derived. The specific Rayleigh ratio Rθ** and the specific turbidity τ** for single and independent scattering were derived analytically for R and RDG scattering. Spectroturbidimetry data at 25°C for a cationic double-chain surfactant, didodecyldimethylammonium bromide (DDAB) were compared to the turbidity predictions. Findings: For R scattering, Rθ** and τ** are proportional to a2db for vesicles, and to a3dbdw+db for liposomes. For RDG and particle radii 20–1000 nm, τ** is proportional to an, where n is 2 to 0.4 for vesicles and 2 to 1.1 for liposomes. Turbidity data for DDAB vesicles are consistent with the RDG predictions, which are also used to estimate the vesicles’ sizes. RDG applies to liposomes < 800 nm and to much larger sizes for vesicles.

Rapid sorption of fenitrothion on didodecyldimethylammonium bromide-montmorillonite organoclay followed by the degradation into less toxic 3-methyl-4-nitrophenolate

Abstract Didodecyldimethylammonium bromide (DDAB)-modified montmorillonite (MT) organoclay was used for the sorption and degradation of an organophosphate pesticide, fenitrothion, in water. The degree of sorption increased by the modification of MT with DDAB, because of the formation of hydrophobic DDAB assemblies for the sorption of hydrophobic fenitrothion. Fenitrothion ([M + 1] = 278) sorbed on the organoclay rapidly converted to the degraded product anion ([M] = 262) followed by the further degradation into 3-methyl-4-nitrophenol ([M-1] = 152). The activation energy for the first-order reaction of the primary degradation of fenitrothion (79.9 kJ mol-1) in the organoclay was lower than the value (94.1 kJ mol-1) in water. Organoclay-mediated catalytic activity expressed over a wide pH region (pH 5-9), being advantageous for the application to different wastewaters and environmental waters. Continuous sorption and degradation of fenitrothion in contaminated water was examined by using a laboratory-scale organoclay-packed column. Fenitrothion-free effluent containing its degraded product, 3-methyl-4-nitrophenol, having lower toxicity to aquatic organisms outflowed from the bottom of the column. These results strongly suggests the usefulness of DDAB-MT organoclay as a barrier material for diffusion control of organophosphate pesticides.

Effect of a Cationic Surfactant on Droplet Wetting on Superhydrophobic Surfaces.

We experimentally and theoretically examine the influence of a double-chain cationic surfactant, didodecyldimethylammonium bromide (DDAB), on the wetting states and contact angles on superhydrophobic (SH) surfaces made of hydrophobic microcylinders. We use two types of micropatterns of different surface roughness, r, and packing fraction, ϕ, and vary nine dimensionless surfactant concentrations (CS), normalized by the critical micelle concentration (CMC), in the experiments. At low CS, some of the surfactant-laden droplets are in a gas-trapping, Cassie-Baxter (CB) state on the high-roughness microstructures. In contrast, some droplets are in a complete-wetting Wenzel (W) state on the low-roughness microtextures. We found that the contact angle of CB drops can be well predicted using a thermodynamic model considering surfactant adsorption at the liquid-vapor (LV) and solid-liquid (SL) interfaces. At high CS, however, all of the DDAB drops wet in a Wenzel mode. Based on a Gibbsian thermodynamic analysis, we find that for the two types of superhydrophobic surfaces used, the Wenzel state has the lowest thermodynamic energy and thus is more favorable theoretically. The CB state, however, is metastable at low CS due to a thermodynamic energy barrier. The metastable CB wetting state becomes more stable on the SH microtextures with greater ϕ and r, in agreement with our experimental observations. Finally, we generalize this surface-energy analysis to provide useful designs of surface parameters for a DDAB-laden surfactant droplet on the SH surface with a stable and robust CB state.

Organo-montmorillonites as adsorbent materials for thiophanate-methyl removal: Adsorption-desorption studies and technological applications

Thiophanate-methyl (TM) is a fungicide widely used in post-harvest treatment of pears and apples. The wastewater of this treatment usually is discharged to the natural rivers without treatment, with the consequent concern about the contamination of these waters. The fungicide adsorption on montmorillonites (Mt) and organo-montmorillonites (organo-Mt) can be a good alternative for wastewater treatment containing fungicides, used as filtering materials or flocculants. The TM adsorption on Mt and organo-Mt samples was studied in batch and column systems. Different organo-Mt samples were obtained, by cationic exchange reaction with octadecyltrimethylammonium (ODTMA) and didodecyldimethylammonium (DDAB) bromide at different surfactant loading. The anionic nature of the TM generated a very low adsorption in raw Mt, while the organo-Mt samples showed an increase of TM adsorption with the content of the surfactant. These results suggest two different types of interactions between organo-Mt samples and TM. At low surfactant contents, the adsorption occurs predominantly through hydrophobic interactions between the TM and the surfactant. While when the surfactant content is above the CEC value, additionally stronger interactions appear across water bridges between the TM molecules and the surfactant ammonium group. The similar TM adsorption percentages attained by organo-Mt with DDAB than those with activated carbon, points out the first material as a promising adsorbent that could be used to remove TM from wastewater in batch and also as filters or flocculants.

The incorporation of cationic property and immunopotentiator in poly (lactic acid) microparticles promoted the immune response against chronic hepatitis B

Biodegradable microparticles (MPs) as vaccine adjuvants have sparked the passion of researchers in recent decades. However, it is still a huge challenge to develop an efficient vaccine delivery system to reverse chronic hepatitis B (CHB). Herein, we integrated a physiochemical merit and an immunopotentiator property in poly (lactic acid) (PLA) MPs and verified the therapeutic effect on CHB model mice. We prepared uniform MPs with insertion of cationic lipid didodecyldimethylammonium bromide (DDAB), which endowed a physiochemical merit for MPs. Such a DDAB-PLA (DP) group raised the recruitment of immune cells to the injection site along with the secretion of chemokines and pro-inflammatory cytokines, promoting the activation of antigen-presenting cells (APCs). Further combination of stimulator of interferon genes (STING) agonist 5,6-dimethylxanthenone-4-acetic acid (DMXAA) (DP-D) elevated 5.8-fold higher interferon regulatory factor 7 (IRF-7) expression compared to that for DP group. The DP group showed preferred lysosome escape advantage, which was in line with the DMXAA release behavior and the intracellular target of DMXAA. In addition, DP-D vaccine augmented the IFN-γ secreting splenocytes and motivated Th1-biased antibodies in a more efficient way than that for the DP group. In the CHB model, the MPs based vaccines achieved 50% HBsAg seroconversion rate, and HBcAg in the liver also got a reduction. DP-D produced higher amount of memory T/B cells to confer protection in a sustained manner. Present work thus provided a promising strategy, via integrating a fine-tuned physiochemical property and an immunopotentiator virtue in the MPs, which synergistically reinforced both humoral and cellular immune responses against CHB.

Effect of adsorbed polyelectrolytes on the interactions and elasticity of charged surfactant bilayers

We present studies on the structure of complexes of the cationic, bilayer-forming surfactant, didodecyldimethylammonium bromide (DDAB), and the anionic polyelectrolyte sodium polyacrylate (PAANa). In the presence of uncomplexed polyelectrolyte in the coexisting aqueous solution, these complexes are found to exhibit a swelling transition followed by a deswelling transition on increasing the salt concentration. Lamellar structures with low periodicities occur at both low and high salt concentrations, which are stabilized by polymer bridging and van der Waals attraction, respectively. The swollen complex found at intermediate salt concentrations forms the sponge phase. Our results reveal that polyelectrolyte adsorption on bilayers has a profound effect on inter-bilayer interactions. The polymer-induced interaction changes from being attractive to repulsive as the surface coverage increases on increasing the salt concentration. Our results also confirm that polymer adsorption alters the elastic moduli of the bilayer, in agreement with earlier theoretical predictions.

Biocompatible cationic solid lipid nanoparticles as adjuvants effectively improve humoral and T cell immune response of foot and mouth disease vaccines

In this work, we explored the potential of cationic solid lipid nanoparticles (cSLN) as efficient adjuvants for inactivated foot and mouth disease virus (iFMDV) vaccine. The cSLN were prepared by O/W emulsion method with Compritol 888 ATO as lipid matrix, and were modified by cationic lipid Didodecyldimethylammonium bromide (DDAB). The content of cationic lipid was optimized to produce cSLN with appropriate particle size, surface morphology, zeta potential, and polydispersity. Loading iFMDV onto cSLN by electrostatic attraction did not destruct iFMDV particle structure as measured by high performance size exclusion chromatography (HPSEC). Differential scanning fluorimetry (DSF) showed the transition temperature, Tm, related to iFMDV dissociation increased for 1.2 °C after loading on cSLN, indicating an enhanced stability of this unstable antigen. The cSLN loaded iFMDV enhanced in vitro antigen uptake and activation of bone-marrow-derived dendritic cells (BMDCs) with augmented expression of CD86, CD40, and MHC I. In animal trials, BALB/c mice were immunized with free iFMDV, antigen adjuvanted with the cSLN, and antigen adjuvanted with Montanide ISA 206 emulsion. Specific antibody titers showed cSLN could stimulate similar FMDV-specific IgG and IgG subclasses antibody level compared with the widely used ISA 206. In addition, cSLN significantly enhanced memory immune response including effector-memory T cells and central-memory T cells compared to free iFMDV antigen and antigen adjuvanted with ISA 206. Taken together the enhanced humoral and T cell immune responses and the antigen structure friendly properties, cSLN can be a potential adjuvant for iFMDV vaccines.

All-electrochemical nanocomposite two-electrode setup for quantification of drugs and study of their electrocatalytical conversion by cytochromes P450

This paper describes the electrochemical behavior and an electrooxidative method for the determination of diclofenac, DF, (2-[(2,6-dichlorophenyl)amino]benzeneaceticacid) and acetaminophen, AC, (N-acetyl-p-aminophenol). Drugs electrochemical oxidation was realized on the surface of graphite-based screen printed electrodes (SPEs) modified with a stable dispersion of multiwalled carbon nanotubes (MWCNTs) in aqueous solutions of an amphiphilic poly(1,2-butadiene)-block-poly(N,N-dimethylaminoethyl methacrylate) diblock copolymer (PB-b-PDMAEMA). The oxidation peak potentials of DF and AC were detected at + 0.53 ± 0.02 V and + 0.35 ± 0.02 V (vs. Ag/AgCl), respectively. The analytical characteristics of electro-oxidation of the drugs on the SPE/(PB-b-PDMAEMA/MWCNTs) constructs were estimated with a detection limit of 35 nM and 40 nM, and a sensitivity of 4.90 mA/M and 2.3 mA/M for DF and AC, respectively. Electro-oxidation of DF and AC was applied as analytical technique for the detection of these pharmaceuticals in their mixtures and in human serum. Further, we demonstrate an approach for the estimation of the enzymatic activity of cytochrome P450 3A4 (CYP3A4) based on the electrochemical oxidation of residual DF used as a model drug. Two separate electrochemical cells were used and each was supplied by a specific electrode. The first one was CYP-sensitive electrode, which contains CYP3A4 immobilized on didodecyldimethylammonium bromide (DDAB) as a CYP3A4 fixing matrix, while another one was our newly developed drug-sensitive electrode. Therefore, drug conversion, which takes place in the first electrochemical cell supplied by CYP-sensitive electrode, can be quantitatively monitored by drug-sensitive electrode by taking aliquots at specified time periods and assaying a residual drug concentration in the second electrochemical cell. Thus, the estimation of kinetic parameters for CYP3A4 catalysis can be carried out.

Electroanalytical and electrocatalytical characteristics of cytochrome P450 3A4 using electrodes modified with nanocomposite carbon nanomaterials

The electroanalytical characteristics of recombinant cytochrome P450 3A4 (P450 3A4) immobilized on the surface of screen-printed graphite electrodes modified with multi-walled carbon nanotubes have been studied. The role and the influence of graphite working electrode modification with carbon nanotubes on electroanalytical characteristics of cytochrome P450 3A4 have been demonstrated. The conditions for the immobilization of cytochrome P450 3A4 on the obtained screen-printed graphite electrodes modified with carbon multi-walled nanotubes have been optimized. The electrochemical parameters of the oxidation and reduction of the heme iron of the enzyme have been estimated. The midpoint potential E0' was -0.35±0.01 V vs Ag/AgCl; the calculated heterogeneous electron transfer rate constant ks, was 0.57±0.04 s-1; the amount of electroactive cytochrome P450 3A4 on the electrode Г0, was determined as (2.6±0.6)⋅10-10 mol/cm2. The functioning mechanism of P450 3A4-based electrochemical sensor followed the "protein film voltammetry". In order to develop electrochemical analysis of drugs being substrates of that hemoprotein and respective medical biosensors the voltammetric study of catalytic activity of immobilized cytochrome P450 3A4 was carried out. Electrocatalytic properties of cytochrome P450 3A4, immobilized on modified screen-printed graphite electrodes, has been investigated using erythromycin (macrolide antibiotics). It has been shown that the modification of electrodes plays a decisive role for the study of the properties of cytochromes P450 in electrochemical investigations. Smart electrodes can serve as sensors for analytical purposes, as well as electrocatalysts for the study of biotransformation processes and metabolic processes. Electrodes modified with carbon nanomaterials are applicable for analytical purposes in the registration of hemoproteins. Electrodes modified with synthetic membrane-like compounds (e.g. didodecyldimethylammonium bromide) are effective in enzyme-dependent electrocatalysis.