Charged Cetyltrimethylammonium Bromide Research Articles

Highly thermally conductive PVDF-based composites with well-dispersed carbon nanotubes/graphene-Ag 3D interconnected frame via electrostatic self-assembly

Polyvinylidene fluoride (PVDF) is a thermoplastic polymer known for its superior chemical and thermal stability and good mechanical properties. However, the application of polymers in heat transfer is limited by their inherent poor thermal conductivity (λ). This study uses electrostatic self-assembly between negatively charged Graphene-Silver (GNs-Ag) and positively charged cetyltrimethylammonium bromide (CTAB)-functionalized multiwall carbon nanotubes (fMWCNTs) to construct a unique three-dimensional (3D) structure in PVDF. AgNPs are uniformly loaded on graphene nanosheets, and the well-dispersed fMWCNTs act as bridges connecting adjacent AgNPs and GNs, forming a more efficient heat transfer pathway, thereby obtaining polymer nanocomposites with higher λ. The λ of GNs-Ag/fMWCNTs/PVDF composites reaches 9.24 W/(m·K) with 25 wt% of GNs-Ag/fMWCNTs fillers, which is 3495 % higher than that of pure PVDF. Additionally, the mechanical properties and electrical conductivity and electromagnetic interference shielding effectiveness of the GNs-Ag/fMWCNTs/PVDF composites are also markedly enhanced.

Synthesis of a novel next-generation positively charged polymer and its in-situ grafting into thin film composite membranes to enhance the performance for desalination

High efficiency of the polyamide membranes can be achieved by rationally tailoring the active layer, which empowers the membrane with better anti-fouling characteristics, high flux, and separation efficiencies. Herein, a next-generation anti-fouling positively charged copolymer of diallyldimethylammonium chloride (DADMAC) and N1, N1-diallyldodecane-1,12-diammonium chloride (DADAC) was synthesized and thoroughly characterized by TGA, FTIR, proton (1H) and the carbon (13C) NMR. The synthesized poly(DADMAC-co-DADAC), after conversion to poly(DADMAC-co-DADA) having free NH2 group, was in-Situ grafted while forming the active layer due to its rationally designed anchoring points of NH2 group. The in-Situ grafting resulted in a cross-linked polyamide active layer containing positively charged brushes of poly (DADMAC-co-DADA) at regular intervals. The AFM analysis has shown that the polyamide layer's surface roughness increased with the poly-(DADMAC-co-DADA) grafting concentration, which positively impacts the membranes' flux. When exposed to the water, the grafted poly-(DADMAC-co-DADA) expanded and spread a positively quaternary ammonium network on the membrane surface, effectively repelling the cations. The introduced membrane has shown high performance compared to the pristine polyamide membrane. The functionalized membranes have displayed a 3.5 times flux for 2000 ppm of NaCl while maintaining a good rejection at 93.1%. The anti-fouling behavior of the membranes was evaluated against the model positively charged CTAB (cetyltrimethylammonium bromide) foulants (2000 ppm). Poly- (DADMAC-co-DADA) grafted membranes have shown a high anti-fouling tendency. After 600 min (10 h) of continuous operation, the flux declined less than 15%, whereas the pristine polyamide membrane lost 99%. The poly-(DADMAC-co-DADA) grafted membranes recovered more than 93% of their maximum flux. Thus, the in-Situ grafting of positively charged polymer is a possible opportunity to develop the next generation of high-performance polyamide membranes.

Magnetically Controlled 3D Cartilage Regeneration.

The cartilage regeneration field has not yet overcome the issue of effective "shaping": growing regenerated cartilage in the desired shape, and maintaining that shape, is problematic. This study reports on a new method of cartilage regeneration in which the cartilage is shaped in three dimensions. Since cartilage is composed only of cartilage cells and an abundant extracellular matrix with no blood circulation, once it is damaged, the lack of nutrient supply means that it is difficult to repair. Scaffold-free cell sheet technology plays an important role in cartilage regeneration, avoiding inflammation and immune response caused by scaffold materials. However, cartilage regenerated from the cell sheet needs to be sculpted and shaped before it can be used for cartilage defect transplantation. In this study, we used a new ultra-strong magnetic-responsive Fe3O4 nanoparticle (MNP) to shape the cartilage in vitro. Super-magnetic Fe3O4 microspheres are manufactured by co-assembling negatively charged Cetyltrimethylammonium bromide (CTAB) and positively charged Fe3+ under solvothermal conditions. The Fe3O4 MNPs are swallowed by chondrocytes, and the MNP-labeled chondrocytes are acted upon by the magnetic field. The predetermined magnetic force makes the tissues coalesce to form a multilayer cell sheet with a predetermined shape. The shaped cartilage tissue is regenerated in the transplanted body, and the nano magnetic control particles do not affect cell viability. The nanoparticles in this study improve the efficiency of cell interaction through super-magnetic modification, and to a certain extent change the way the cells absorb magnetic iron nanoparticles. This phenomenon allows a more orderly and compact alignment of the cartilage cell extracellular matrix, promotes ECM precipitation and cartilage tissue maturation, and improves the efficiency of cartilage regeneration. The magnetic bionic structure, which contains specific magnetic particle-labeled cells, is deposited layer by layer to generate a three-dimensional structure with repair function, and further induce the production of cartilage. This study describes a new method for the regeneration of tissue engineered cartilage which has broad application prospects in regenerative medicine.

Highly Altered State of Proton Transport in Acid Pools in Charged Reverse Micelles.

Transport mechanisms of solvated protons of 1 M HCl acid pools, confined within reverse micelles (RMs) containing the negatively charged surfactant sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) or the positively charged cetyltrimethylammonium bromide (CTABr), are analyzed with reactive force field simulations to interpret dynamical signatures from TeraHertz absorption and dielectric relaxation spectroscopy. We find that the forward proton hopping events for NaAOT are further suppressed compared to a nonionic RM, while the Grotthuss mechanism ceases altogether for CTABr. We attribute the sluggish proton dynamics for both charged RMs as due to headgroup and counterion charges that expel hydronium and chloride ions from the interface and into the bulk interior, thereby increasing the pH of the acid pools relative to the nonionic RM. For charged NaAOT and CTABr RMs, the localization of hydronium near a counterion or conjugate base reduces the Eigen and Zundel configurations that enable forward hopping. Thus, localized oscillatory hopping dominates, an effect that is most extreme for CTABr in which the proton residence time increases dramatically such that even oscillatory hopping is slow.

Electrostatic molecular effect of differently charged surfactants on the solubilization capacity and physicochemical properties of salt-caged nanosuspensions containing pH-dependent and poorly water-soluble rebamipide

In this study, the electrostatic molecular effect of differently charged surfactants on the solubilization capacity and physicochemical properties of salt-caged nanosuspensions (NSPs) containing poorly water-soluble drug was investigated. Anionic rebamipide (RBM) was chosen as a model drug because of its poor water solubility in low pH condition and ionizable acidic forms. Negatively charged sodium lauryl sulfate (SLS) and positively charged cetyltrimethylammonium bromide (CTAB) were selected as surfactants for the preparation of NSPs or in the dissolution medium. Salt-caged NSPs surrounded by NaCl were prepared by the HCl-NaOH neutralization method in the presence of poloxamer 407. Interestingly, the addition of positively charged CTAB in the preparation process or the dissolution media could interfere with the solubilization capacity of salt-caged NSPs containing a negatively charged drug via intermolecular electrostatic attraction. In the presence of positively charged CTAB, the salt-caged NSP was disordered in structure via electrostatic attractive interaction with partially ionizable anionic RBM resulting in changes in the physicochemical properties of the salt-caged NSP such as low drug content, increased particle size, decreased dissolution rate, and the formation of water-insoluble precipitates with rough and irregular crystals. This inhibitory effect of CTAB on the dissolution rate of pure RBM and the salt-caged NSP in pH 6.8 intestinal fluid was pronounced in a concentration-dependent manner mainly owing to the formation of precipitates, so-called poorly soluble complexes. When the salt-caged NSP (F1) was dissolved in DW containing CTAB, the dissolution rate decreased more significantly, dissolving less than 20% within 2 h. Depending on the surfactant charges, the charge density and the initial potential were varied during the dissolution of NSPs in deionized water (DW). In contrast, the negatively charged SLS did not significantly change the physicochemical properties of the salt-caged NSP. For example, the dissolution rate of the salt-caged NSP containing SLS in DW or pH 1.2 gastric fluid remained over 90% for 2 h. Surfactants for the formulation or dissolution media should be chosen carefully because of their effect on the physicochemical properties and solubilization capacity of salt-caged NSPs containing poorly water-soluble and ionizable drugs via electrostatic molecular interactions.

Kinetic and Mechanistic Insight into the Surfactant-Induced Aggregation of Gold Nanoparticles and Their Catalytic Efficacy: Importance of Surface Restructuring.

Understanding the fundamental interactions between plasmonic metal nanoparticles (MNPs) and small molecules is of utmost importance in various applications such as catalysis, sensing, drug delivery, optoelectronics, and surface-enhanced Raman spectroscopy. Herein, we have investigated the early stage of the aggregation pathway of citrate-stabilized Au NPs with surfactants and explored their catalytic efficacy. Our findings reveal that (17 ± 2)-nm-sized citrate-stabilized Au NPs undergo concentration and time-dependent aggregation with positively charged cetyltrimethylammonium bromide (CTAB). Kinetic analyses revealed the presence of two distinct kinds of aggregates, namely, smaller clusters and a larger branched network of Au nanochains. At longer times and in the presence of higher concentrations of CTAB, these branched networks of Au nanochains transform into dense compact globular aggregates. The catalytic efficacy of Au NPs, branched Au nanochains, and dense compact aggregates has been explored with respect to the reductive hydrogenation of 4-nitophenol in the presence of excess NaBH4. Our study revealed that the catalytic rate decreases in the order of Au NPs > branched Au nanochains > compact aggregates. Interestingly, pre-equilibrating different Au NP samples with excess NaBH4 prior to the onset of the reaction results in similar catalytic activity irrespective of the aggregation state of Au NPs. This observation has been explained by considering efficient surface restructuring via ligand exchange with H- ions and the subsequent disruption of CTAB-induced aggregates of Au NPs. Moreover, the aggregated Au NPs can be recycled over several consecutive cycles for the reductive hydrogenation of 4-NP upon ligand exchange with H- ions. Taken together, our present study highlights the early-stage aggregation kinetics of Au NPs with CTAB surfactants and demonstrates the importance of the surface restructuring of Au NPs on their catalytic efficacy.

Carboxyl-functionalized mesoporous silica nanoparticles for the controlled delivery of poorly water-soluble non-steroidal anti-inflammatory drugs

The purpose of this study was to investigate the delivery of poorly water-soluble non-steroidal anti-inflammatory drugs (NSAIDs) by carboxyl-functionalized mesoporous silica nanoparticles (MSN-COOH) with high specific surface area (SBET). In this study, MSN-COOH was prepared by collaborative self-assembly using cetyltrimethylammonium bromide (CTAB) as template and hydrolysis (3-triethoxyl-propyl) succinic anhydride (TESPSA) as co-structure auxiliary directing agent (CSDA). The drug delivery systems were constructed with NSAIDs including Nimesulide (NMS) and Indomethacin (IMC) as model drugs. Moreover, the characterization techniques, hemolysis and bio-adsorption testes, in vitro drug release and in vivo biological studies of MSN-COOH were also carried out. The characterization results showed that MSN-COOH is spheres with clearly visible irregular honeycomb nanopores and rough surface (SBET: 1257 m2/g, pore volume (VP): 1.17 cm3/g). After loading NMS/IMC into MSN-COOH with high drug loading efficiency (NMS: 98.7 and IMC: 98.2%), most crystalline NMS and IMC converted to amorphous phase confirmed using differential scanning calorimeter (DSC) and X-ray power diffraction (XRD) analysis. Meanwhile, MSN-COOH significantly increased the dissolution of NMS and IMC compared with non-functionalized mesoporous silica nanoparticles (MSN), which was also confirmed by wettability experiments. The results of in vivo biological effects showed that MSN-COOH had higher bioavailability of NMS and IMC than MSN, and exerted strong anti-inflammatory effects by delivering more NMS and IMC in vivo. Statement of significanceThis study successfully prepared MSNs-COOH (mesoporous silica nanoparticles modified with negatively charged carboxyl groups on the surface and in the pores) with high specific surface area and pore volume by using the negatively charged carboxyl group (hyd-TESPSA) and the positively charged CTAB self-assembled through electrostatic attraction under alkaline conditions. The drug delivery systems were constructed with Nimesulide (NMS) and Indomethacin (IMC) as model drugs. The results showed MSNs-COOH had high drug loading capacity and also exhibited good in vitro drug release properties. Interestingly, NMS loaded MSNs-COOH also had a potential pH responsive release effect. In vivo biological studies revealed that NMS/IMC loaded MSNs-COOH could evidently improve the bioavailability and played the strong anti-inflammatory effects.

Easily modified barium phosphate composites for effective removal of methyl blue from solution

In this work, barium phosphate composites were easily modified by changing the reactants and surfactants to be barium sodium phosphate (NaBaPO4), barium phosphate (Ba3(PO4)2), barium hydroxyl phosphate (Ba5(PO4)3OH), and barium hydrogen phosphate (BaHPO4) (denoted NBP, BP, BPO, and BHP, respectively) using a one-step hydrothermal method. Positively charged cetyl trimethyl ammonium bromide (CTAB) on phosphate composites can slightly increase their removal capacities for methyl blue (MB) though it had no obvious effects on the composition and crystal type of materials. Dye removal experiments were carried out in a batch system to optimize operation variables such as solution pH, temperature, adsorbent dosage, contact time, and initial dye concentration. The kinetic behavior of all the materials agreed well with the pseudo-second-order model. The isothermal data of NBP and BPO fitted to the Langmuir model while Freundlich model was better to describe the isothermal data of BP and BHP. The removal capability for MB solution followed an order of NBP (249.6 ± 6.0 mg/g) > BP (226.0 ± 6.0 mg/g) > BPO (162.5 ± 5.0 mg/g) > BHP (85.84 ± 4.0 mg/g). NBP is most suitable for MB removal because of its high alkalinity: (1) The obvious increase of pH from 6.03 ± 0.10 to 12.26 ± 0.20 after adding NBP in solution can lead to improved decolorization of MB solution. (2) Strong Lewis acid base interaction between cations (Ba2+/Na+) in NBP and –SO3- in MB as well as the hydrogen bonding between PO43- in NBP and N–H or C–H in MB contributed to the high removal capacity of NBP.

Time dependent physicochemical changes of SDS-CTAB interacted self assembled vesicles: Ostwald ripening effect

It is found that oppositely charged surfactants SDS (sodium dodecyl sulfate) and CTAB (cetyltrimethylammonium bromide) at low concentrations (< critical micelle concentration or CMC) interact, and form self-assemblies (vesicles) in aqueous medium. Physicochemical characterization of the assemblies has been studied and reported. It has been found that the characteristic properties of these assemblies change with time. Investigations on the time dependent changes of such vesicles have been monitored over a period of three months. The properties studied were, turbidity, surface tension, conductance, size and shape, ζ-potential, fluorescence anisotropy and quenching of photosensitive dyes in them, thermodynamics of formation as well as toxicity. The surfactants (well below their CMCs) were mixed in different proportions making the final concentration of all at 0.6 mM. They were kept at temperature 303 K, and examined at different times (on the day of mixing, and subsequently after 10, 30, 60, and 90 days). It is known that by the phenomenon of Ostwald Ripening (OR) process, morphological changes in colloidal solution takes place; larger particles grow in size with time at the expense of smaller particles.We studied the OR effect on the physicochemical properties of the growing SDS-CTAB interacted vesicles in aqueous medium. Results and their documentations are herein presented. Such an elaborate study of vesicles with reference to OR process as per our knowledge was not done in the past.

Reciprocal effects of multi-walled carbon nanotubes and oppositely charged surfactants in bulk water and at interfaces

In this work we made the complementary use of nuclear magnetic resonance spectroscopy, dynamic light scattering, electric conductivity and surface tension methods to study the micellization of cationic surfactants cetyl trimethylammonium bromide (CTAB) and dodecyltrimethylammonium bromide (DTAB), as well as anionic surfactant sodium dodecyl sulfate (SDS) in the presence of multi-walled carbon nanotubes (CNT). It was shown that the CNTs is effectively dispersed in water medium due to the adsorption of surfactant ions at CNT surface. The NMR spectral analysis (chemical shifts and line broadening) specified that surfactants interact with CNTs surface both by alkyl chains and by charged head groups. For cationic CTAB and DTAB this interaction occurs mainly through methylene (CH2)n groups of alkyl radicals, at the same time, the anionic SDS interacts with the CNTs surface by terminal methyl groups (CH3). Interaction specificity of cationic and anionic surfactants leads to their different structural organization to CNT surface. Experimental observations make it possible to propose the model where the attraction of cationic DTAB and CTAB positively charged head groups with negatively charged CNT surface results to the orientation of cationic surfactants along CNT surface. In contrast to positively charged DTAB and CTAB the repulsion of SDS with negatively charged head group from CNT surface and contacted SDS terminal groups results in the normal orientation of anionic surfactant to CNT surface. The consistency of proposed orientation model arrived from conductivity study of surfactant-CNT dispersions. According to conductivity data, the non-micellized cationic surfactants follow complete dissociation in the presence of CNT no matter are they free or bound to CNT. On the contrary the absence of complete dissociation of anionic surfactant in the pre-micellar systems may be the result of SDS ordering on CNT surface and forming the charged surface with double electric layer binding the portion of counter-ions.

Rationally designed functionalized black phosphorus nanosheets as new fire hazard suppression material for polylactic acid

The black phosphorus (BP) nanosheets were firstly obtained by the modified lithium ion intercalation method and then functionalized by cetyl-trimethyl ammonium bromide (CTAB). Owing to the electrostatic interactions, the positively charged CTAB was successfully loaded onto the surface of negatively charged exfoliated BP and the BP-CTAB hybrids were finally obtained. It is found that BP-CTAB hybrids exhibits superior promotion effect on fire safety of Polylactic acid (PLA), which can be attributed to its typical layered structure, abundant phosphorus and good dispersion in matrix. Compared with neat PLA, the peak heat release rate (PHRR) of PLA composite with 2 wt% BP-CTAB decreases by 38.8%. Under the same loading of 2 wt%, the PLA/BP-CTAB2.0 shows better flame retardancy than PLA composites with BP or red phosphorus (RP). Moreover, the time to peak heat release rate (TPHRR) of PLA/BP-CTAB2.0 is postponed from 157 to 200 s. Derived from the uniform dispersion of BP-CTAB, the tensile strength of PLA composites are also improved. Meanwhile, the air stability of BP-CTAB in polymer is investigated. It is observed that the Ag1/Ag2 value of BP-CTAB only decreases from 0.57 to 0.54 even after immersion in water for one month, which can be ascribed to the double coating of polymer matrix and CTAB. This work enriches the method of exfoliating BP, and first explores the influence of BP on the flame retardant and mechanical properties of PLA.

ZSM-5@MCM-41 composite porous materials with a core-shell structure: Adjustment of mesoporous orientation basing on interfacial electrostatic interactions and their application in selective aromatics transport

A series of hierarchically porous materials with core-shell structures have been successfully fabricated through a modified Stöber method. The interfacial growth of mesoporous silica with adjustable mesochannel orientation on the surface of ZSM-5 nanocrystal results in the formation of a core-shell structure. The zeta potentials of ZSM-5 nanocrystals have been carefully adjusted through interfacial assembly with a certain amount of anionic surfactants, thus inducing different electrostatic interactions with positively charged cetyltrimethylammonium bromide micelles. The alignment of the outer silicate mesopores around the ZSM-5 nanocrystals transforms from parallel into vertical relative to the zeolite surface, so that the orientation effect of interfacial interactions is experimentally confirmed to be effective in the epitaxial growth of mesoporous shell on the surface of nano-zeolite. The adsorption capacities of the composite porous materials have been dramatically improved after the epitaxial growth of mesoporous shells. Moreover, the materials demonstrate different diffusion efficiencies for organic molecules on the basis of their mesochannel alignments.

Quartz Crystal Microbalance Detection of Poly(ADP-ribose) Polymerase-1 Based on Gold Nanorods Signal Amplification.

Recent findings have thrust poly(ADP-ribose) polymerase-1 (PARP-1) into the limelight as a potential biomarker and chemotherapeutic target for cancer. Thus, a sensitive method for detection of PARP-1 is necessary for early diagnosis of cancer and drug development. However, the poor electrochemical and optical activity of PARP-1 and its product poly(ADP-ribose) (PAR) prompted researchers to develop more methods. Here, we developed an efficient method for the determination of PARP-1 by using quartz crystal microbalance (QCM) because it is mass-sensitive. Once activated by the specific DNA, PARP-1 cleaves nicotinamideadenine dinucleotide (NAD+) into nicotinamide and ADP-ribose to synthesize a hyperbranched poly(ADP-ribose) polymer. Although QCM is mass-sensitive, it is not sensitive enough to discern PAR effectively. So, positively charged cetyltrimethylammonium bromide (CTAB)-coated gold nanorods (GNRs) were introduced to increase the frequency change significantly because of the strong electrostatic interaction between them with negatively charged PAR. PARP-1 ranging from 0.06 to 3 nM can be facilely detected with a low detection limit of 0.04 nM. The strategy has been used to evaluate PARP-1 inhibitors and to detect PARP-1 activity in real cancer cells lysate with satisfactory results, indicating that it was a promising candidate for clinical diagnosis and drug screening in the future.

Modulation of Surface-Catalyzed Secondary Nucleation during Amyloid Fibrillation of Hen Egg White Lysozyme by Two Common Surfactants.

Amyloid fibrillation by hen egg white lysozyme (HEWL) under the influences of two common surfactants, sodium dodecyl sulfate (SDS) and Triton X-100 (TX-100), was investigated with atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. Detailed AFM investigations indicated that both SDS and TX-100 were able to induce some significant morphological changes of HEWL amyloid fibrils. Both SDS and TX-100 could induce a morphological change which was characterized with alternating fibril regions with increased thicknesses along the fibril axis. In addition, TX-100 was also able to induce a morphological change which was characterized with fibril branching. In contrast, the positively charged cetyltrimethylammonium bromide displayed no such effect as compared with the negatively charged SDS and the nonionic TX-100. These intriguing modulation effects of SDS and TX-100 on amyloid fibrillation were hypothesized to be due to surfactant-induced surface-catalyzed secondary nucleation owing to the noncovalent interaction between the surfactants and HEWL. The proposed hypothesis was further supported by FTIR spectroscopic investigation, which demonstrated the formation of a SDS-amyloid fibril complex and TX-100-amyloid fibril complex. Detailed FTIR analysis suggested that the tail group of SDS associated with amyloid fibrils is more disordered similar to that of SDS in aqueous solution, while the headgroup of SDS appears to interact with amyloid fibrils strongly similar to that of SDS in the solid state, and the ether groups of TX-100 associated with amyloid fibrils experienced a different microenvironment as compared with that of neat TX-100. Additional control experiments with FTIR spectroscopy revealed that the interactions of SDS/TX-100 with HEWL amyloid fibrils were different from those of SDS/TX-100 with HEWL amorphous aggregates. In addition, the β-sheet structures of the HEWL amyloid fibrils were found to be increased due to the influences of SDS and TX-100. Our work provides new insight into the modulation effects of surfactants on amyloid fibrillation.

Detection of Malachite Green using a colorimetric aptasensor based on the inhibition of the peroxidase-like activity of gold nanoparticles by cetyltrimethylammonium ions.

A specific and sensitive colorimetric aptasensor is described for the determination of Malachite Green (MG). It is exploiting the inhibition of the peroxidase-like activity of gold nanoparticles (AuNPs). The AuNPs act as enzyme mimics that catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to yield a dark blue solution. The catalytic activity is inhibited by hexadecyl trimethyl ammonium ion, specifically by cetyltrimethylammonium bromide (CTAB), which causes the aggregation of AuNPs. If a (negatively charged) RNA-aptamer against MG is added, it binds to the positively charged CTAB and prevents aggregation. This enhances the enzyme mimicking activity of the AuNPs and leads to the formation of a dark blue solution. However, in the presence of MG, the aptamer binds to MG, and leads to the aggregation of AuNPs again. The aggregated AuNPs possess a light blue color. A colorimetric method (best performed at 650nm) was work out that can detect MG in a concentration range from 10 to 500nmolL-1. The detection limit based on 3σ/k criterion is 1.8nmolL-1. The assay is highly specific and accurate. Recoveries from spiked real samples (aquaculture water) ranged from 80% to 120%. Graphical abstract Based on the inhibition of cetyltrimethyal ammonium ion and the enhancement of RNA-aptamer, the differences of the peroxidase-like activities of AuNPs can be greatly enlarged with and without MG, by which a colorimetric aptasensor can be constructed for the detection of Malachite Green (MG).

Photophysical and photodynamic properties of Pyronin Y in micellar media at different temperatures.

In this study, photophysics and photodynamical properties of Pyronin Y (PyY) in different liquid media were investigated. Interactions of PyY, which is a positively charged pigment compound pertaining to the xanthene derivatives with surfactants possessing distinct charges, were determined by using the molecular absorption and fluorescence spectroscopy techniques. It was observed that band intensities of absorption and fluorescence spectra belonging to PyY increase in proportion to the water when compared to three micelle systems, cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and Triton X-100 (TX-100). This suggests that interactions in micelle systems are different from those in deionized water, and solvation and surface interactions modify. It is determined that the strongest interaction occurs between PyY dye and SDS, anionic surfactant, and this interaction arises from the electrostatic forces. Calculated photophysical parameters indicated that the microenvironment of PyY in SDS micelle is different to that of other systems. In temperature studies, it was reported that increasing the temperature of the samples increased non-radiative transitions. Steady-state fluorescence anisotropy values were calculated by using fluorescence intensities of PyY compound in pre-micellar, micellar and post-micellar systems. Once the PyY fluorescence probe is added to the surfactant containing solutions below the critical micelle concentrations, the measured anisotropy values were found to be low because the probe remains in the deionized water phase. When the surfactant concentration of the medium becomes closer to the critical micelle concentrations, the steady-state anisotropy value prominently increases. This is because of the restrictions on the rotational diffusion of the probe in micellar solution. It is observed that positively charged PyY shows a higher affinity to the negatively charged SDS compared with the positively charged CTAB and neutral TX-100 surfactants. This can be explained by Coulombic interactions.

Effects of Cetyltrimethylammonium Bromide and Heptane on the Surface Properties and CO2 Adsorption of Zeolite NaX

Zeolite X was synthesized by the gelation method for use as a CO2 adsorbent. The zeolite was prepared from a sodium silicate solution and Al(OH)3 as silicon and aluminum source, respectively. The effects of cetyltrimethylammonium bromide (CTAB) and heptane addition on surface properties, morphology, and CO2 adsorption capacities were investigated. The CO2 adsorption capacity of the synthesized zeolite with the addition of CTAB and heptane increased as demonstrated by the higher CO2 uptake (3.00 mmol/g), which was due to the higher surface area and pore volume. Interaction between CTAB micelles and sodium cations with aluminosilicate anions led to an increase in the nucleation rate and smaller crystalline sizes. The addition of heptane resulted in higher positively charged CTAB micelles and improved the affinity between the micelles and aluminosilicate anions.

Surface Enhanced Visible Light Photocurrent and Switching Behavior of Metal Oxide Semiconductor Electrodes Modified with Plasmonic Nanoparticles

Hematite (α-Fe2O3) is a promising photocatalyst for solar water splitting because of its favorable band gap of 2.2 eV, low cost, and abundance in nature. Surface plasmon-enhanced light absorption for photoelectrochemical water splitting at α-Fe2O3thin film electrode modified with Au nanoparticles (NPs) or nanorods (NRs) is described. About 3 times higher light absorption and photocurrent enhancement are obtained from thin hematite films containing Au NPs than with pristine hematite films. The plasmonic enhancement increases with the amount of Au NPs for the same thickness of hematite. Thickness-dependent study of photoactivity indicates a higher enhancement in hematite thin films compared to thicker films due to reduced charge transport distance and optimal local field enhancement effect. Such enhancement can be obtained by self-assembling Au NRs onto a hematite thin film electrode using electrostatic force between their positively charged cetyltrimethylammonium bromide (CTAB) layer and negatively charged hematite surface functionalized with poly(4-styrenesulfonate). The photoelectrochemical reaction of the plasmon active substrate for water oxidation reaction is performed and compared at various hematite layer thicknesses. When the α-Fe2O3 electrode is biased at a small potential +0.2 V (vs Ag/AgCl), the photocurrent of water oxidation is reduced because of increased recombination of holes and electrons at the surface of the Au NRs. When the bias potential is increased to +0.5 V (vs Ag/AgCl), a plasmon enhancement of the photoelectrochemical reaction of water oxidation at wavelengths near the plasmon resonance condition is observed at the α-Fe2O3 thin film electrodes accompanying a dramatic increase in the background current. The significant increase in photocurrent in the region of surface plasmon absorption is attributed to the enhanced visible light absorption of α-Fe2O3 in the presence of the plasmon active Au NPs and NRs.

Cetyltrimethylammonium bromide assisted self-assembly of phosphotungstic acid on graphene oxide nanosheets for selective determination of tryptophan

A one-step method was developed to prepare cetyltrimethylammonium bromide (CTAB) and phosphotungstic acid (PTA)-modified graphene oxide (GO) (PTA/CTAB/GO). In a system containing CTAB, GO, and PTA, negatively charged GO forms stable complex with positively charged CTAB, which assembled on the GO nanosheet surface. And then, with CTAB molecules as the molecular linker, PTA was loaded on CTAB/GO hybrid by electrostatic interaction. The PTA/CTAB/GO was characterized with Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) and subsequently used in the construction of tryptophan (Trp) sensor. Compared with the CTAB/GO, PTA/CTAB/GO exhibits better electrocatalytic activity towards the oxidation of Trp, which is attributed to the synergistic effect of PTA and GO. The differential pulse voltammetry (DPV) curve of Trp at PTA/CTAB/GO/glassy carbon electrode (GCE) exhibited two linear dynamic ranges with a detection limit of 0.02 μM (S/N = 3). In addition, the proposed sensor is successfully employed to detect Trp in the real samples with satisfactory results.

Interaction Study and Reactivity of Zr(IV) -Substituted Wells-Dawson Polyoxometalate towards Hydrolysis of Peptide Bonds in Surfactant Solutions.

The interaction between the 1:2 Zr(IV) :Wells-Dawson complex, K15 H[Zr(α2 -P2 W17 O61 )2] (1), and a range of surfactants was studied in detail with the aim of developing metal-substituted POMs as potential artificial proteases for membrane proteins. The surfactants include the positively charged cetyl(trimethyl)ammonium bromide (CTAB), the negatively charged sodium dodecyl sulfate (SDS), the neutral Triton X-100 (TX-100), and zwitterionic 3-[dodecyl(dimethyl)ammonio]-1-propanesulfonate (Zw3-13) and 3-[dimethyl(3-{[(3α,5β,7α,12α)-3,7,12-trihydroxy-24-oxocholan-24-yl]amino}propyl)ammonio]-1-propanesulfonate (CHAPS). A combination of multinuclear (1)H, (13)C, and (31) P NMR spectroscopy, (1)H diffusion-ordered NMR spectroscopy ((1)H DOSY), and nuclear Overhauser effect spectroscopy (NOESY) was used to examine the interaction between 1 and each surfactant on the molecular level. Cationic surfactant CTAB caused precipitation of 1 due to strong electrostatic interactions, while the anionic SDS and neutral TX-100 surfactants did not exhibit any interaction at neutral pD. (1)H DOSY NMR spectroscopy indicated an interaction between 1 and zwitterionic surfactants Zw3-12 and CHAPS, which occurs via the positively charged ammonium group in the surfactant molecule. In the presence of anionic, neutral, and zwitterionic surfactants, 1 preserves its catalytic activity towards the hydrolysis of the peptide bond in the dipeptide glycyl-l-histidine (GH). The fastest hydrolysis was observed at pD 7.0 and could be rationalized by taking into account pD-dependent speciation of 1 and coordination properties of GH.