N-alkyltrimethylammonium Bromides Research Articles

Alkyl chain length and headgroup dependent stability and agglomeration properties of surfactant-assisted colloidal selenium nanoparticles

In this study, we have systematically investigated and reported the growth, stability, and aggregation properties of selenium nanoparticles (Se NPs) in the presence of surfactant systems comprising different head groups and alkyl chain lengths. Here, the n-alkyl sulfates (C10-C14) and n-alkyl trimethylammonium bromides (C12-C18) were used as the anionic and cationic surfactants. The obtained results showed that the shortening in the alkyl chain length both in anionic and cationic groups does not affect the Se NPs morphologically, however it leads to a gradual increase in their mean sizes. It was also found that the surfactants having a cationic head group pave the way for forming the bigger NPs compared to the anionic ones. In addition, especially in the cationic group, the NPs were found to be in an increasing aggregation tendency with decreasing number of carbon atoms in the chain length. On the other hand, it was observed that the absorbance tends to decrease with time both in the anionic and cationic systems. The rate of decrease in the absorbance within the time revealed that the elongation in the alkyl chain length gives rise to a more stable nanoparticle solution for both surfactant systems. Furthermore, the results revealed that the surfactants having an anionic head group kept the Se NPs more stable in their solutions as compared to cationic ones. The scanning electron microscopy images corresponding to absorption measurements taken for certain days suggested that the formation of aggregated structures, which increase along with time in the nanoparticle solution, is responsible for the accelerated decrease in the absorbance as the tail length decreases.

Control of ZIF-7-III aspect ratio using water-in-oil microemulsion

Zeolitic imidazolate framework-7-III (ZIF-7-III), a well-known metal–organic framework (MOF), has attracted attention as gas separation membrane material. For practical realization, it is necessary to adjust the aspect ratio of ZIF-7-III particles because it can affect the gas separation performance. In this study, we demonstrate the control of the aspect ratio by changing the synthesis condition using microemulsion prepared from n-alkyltrimethylammonium bromide as a surfactant, 1-hexanol as a co-surfactant, heptane as a continuous phase, and water as a dispersed phase. When cetyltrimethylammonium bromide (CTAB) was used as surfactant, ZIF-7-III particles with particle sizes of 10–20 μm were prepared by changing the water and CTAB concentration. In synthesis using four types of surfactants, the particle size of the resultant ZIF-7-III particles increased from 7 μm to 26 μm, and the aspect ratio increased from 4.9 to 11 with an increase in the hydrophobic chain length from C12 to C18. The control of the morphology is attributed to the adsorption of surfactants on hydrophobic (001) facets of ZIF-7-III, which is currently hypothesized to be monolayer or bilayer. The supply of the reactants could be hindered further with the increase of the hydrophobic chain length of the surfactants in either cases. ZIF-7-III particles obtained in this study can be exfoliated into nanosheets, which will accelerate the development of ZIF-7-III-based molecular–sieve gas separation membranes.

Self-Propelled Water Drops on Bare Glass Substrates in Air: Fast, Controllable, and Easy Transport Powered by Surfactants.

Self-propelled drops are capable of motion without external intervention. As such, they constitute attractive entities for fundamental investigations in active soft matter, hydrodynamics, and surface sciences, as well as promising systems for autonomous microfluidic operations. In contrast with most of the examples relying on organic drops or specifically treated substrates, here we describe the first system of nonreactive water drops in air that can propel themselves on a commercially available ordinary glass substrate that was used as received. This is achieved by exploiting the dynamic adsorption behavior of common n-alkyltrimethylammonium bromide (CnTAB) surfactants added to the drop. We precisely analyze the drop motion for a broad series of surfactants carrying n = 6 to 18 carbon atoms in their tail and establish how the motion characteristics (speed, probability of motion) are tuned by both the hydrophobicity and the concentration of the surfactant. We show that motion occurs regardless of the n value but only in a specific concentration range with a maximum speed at around one tenth of the critical micelle concentration (CMC/10) for most of the tested surfactants. Surfactants of intermediate hydrophobicity are shown to be the best candidates to power drops that can move at a high speed (1-10 cm s-1), the optimal performance being reached with [C12TAB] = 800 μM. We propose a mechanism where the motion originates from the anisotropic wettability of the substrate created by the electrostatic adsorption of surfactants beneath the moving drop. Simply drawing lines with a marker pen allows us to create guiding paths for drop motion and to achieve operations such as complex trajectory control, programmed drop fusion, drop refilling, as well as drop moving vertically against gravity. This work revisits the role of surfactants in dynamic wetting and self-propelled motion as well as brings an original strategy to build the future of microfluidics with lower-cost, simpler, and more autonomous portable devices that could be made available to everyone and everywhere.

Insights on the structure of caseinate particles based on surfactants-induced dissociation

Caseinate is derived from casein, the major protein in milk, and forms aggregates in aqueous solution. Here, the internal structure of caseinate particles based on dissociation induced by the different alkyl chain n-alkyl trimethylammonium bromides (CnTAB, n = 10, 12, 14, 16) was investigated by the combination of calorimetric, spectral, scattering and electron microscopic techniques. The results suggested the hydrophobic environment of, at least, Trp, Tyr, Phe, Leu and Ala residues in caseinate increased with increasing the chain length of CnTAB. The dissociation of caseinate aggregates induced by CnTAB was possibly due to the binding of ammonium bromide groups of CnTAB with opposite charged κ-casein via electrostatic interactions, as well as the binding of CnTAB alkyl chain with the P,Q-rich portion of calcium-sensitive caseins (αs1-,αs2-and β-casein) which provided more energetically favorable non-covalent interactions, such as hydrogen bonding and hydrophobic interactions. These interactions resulted in the disruption of backbone-to-backbone interactions of caseins and thus the dissociation of the caseinate aggregates into smaller caseinate clusters. When 10 mM EDTA was added, the size distribution of caseinate-CnTAB complexes exhibited a greater extent of disruption due to the depletion of calcium ions in the caseinate aggregate, suggesting that the binding of CnTAB with casein may not disrupt the phosphate centers on caseins. According to molecular dynamics (MD) simulations, the “necklace and bead” structure of αs1-casein-CnTAB and the binding number increased with increasing the alkyl chain of CnTAB, providing more hydrophilic headgroups and electrostatic repulsion for αs1-casein-CnTAB complex. Electron microscopy images showed that, upon addition of CnTAB, caseinate nanoparticles lost their initial morphology dissociating into smaller caseinate aggregates with diameters ranging from ~30 to ~100 nm. The caseinate aggregates were made of amorphous denser clusters with a diameter of ~10 nm, and the distance between the clusters was observed as ~20–30 nm. This work provides molecular insights into the structure of caseinate particles by exploiting surfactants-induced dissociation.

Micellization and Interaction of Cationic Surfactants with Different Hydrophobic Group in Polar Organic Solvent

Surfactants are amphiphilic compounds that are widely used in various technological fields and biological systems. In many of these applications, mixtures of amphiphiles in organic solvents are employed for better performance The work aims at establishing the extent of ideality or otherwise in the mixed micelles of n-alkyl trimethylammonium bromide, (n = 14 and 16 for TTABr and CTABr respectively), in water (AQ) and water-monoethanolamine (AQ-MEA) at different mole fractions (0.1 to 0.6) and temperatures by Conductance measurement.: The values of the critical micelle concentration (Cmx) obtained in AQ, and AQ-MEA were lower than that obtained assuming an ideal mixing system. Substantial deviation from ideality was observed in the presence of AQ-MEA at all temperatures, suggestive of more favourable association of the surfactants in MEA solvent. The composition (χ₁) of the mixed micelles obtained in the context of Rubingh’s model showed that the micelles of CTABr were dominant, and the values of the interaction parameters (β_mx) were negative in AQ and AQ-MEA media with more synergistic interaction in the latter case at 0.1:0.9 mole fraction ratio at a particular temperature. The values of the activity coefficients (f_TTABr, f_CTABr) were below unity, and the evaluation of the energetics of micellization showed that the process was spontaneous and feasible.

Effects of alkyl chain length on synergetic interaction and micelle formation between a homologous series of n-alkyltrimethylammonium bromides and amphiphilic drug propranolol hydrochloride

The aggregation behavior of a homologous series of n-alkyltrimethylammonium bromides (CnH2n+1TAB; n = 12, 14, and 16) in the presence of amphiphilic drug propranolol hydrochloride (PPL) in aqueous solutions were studied using conductometric technique. The critical micelle concentrations (CMCs) were determined for pure PPL and surfactant as well as mixed micelles [surfactant(1)/PPL(2)] using the Carpena method. Various physicochemical parameters such as ideal CMC (CMCid), degree of counter-ion binding (α), micellar mole fractions of surfactant (X1m and X1id), interaction parameter (βm), the activity coefficients of components (f1m and f2m), standard Gibbs free energy of micellization (ΔGmic0) and the excess free energy of micellization (GmicE) values have been calculated and compared in detail using Clint's and Rubingh's theories. The activity coefficients of surfactant and PPL are less than 1 (f1m < 1 and f2m < 1) and the values of βm are negative in all mixtures, which indicates the synergistic interaction between surfactant and PPL. Also, the results show that the synergistic effects of mixed micelles strongly depend on the chain length of cationic surfactant, and the values of interaction parameter increase with increasing the alkyl chain length of surfactant. Of the several interactive interactions, it seems hydrophobic interaction is the most dominant interaction between the molecules of the mixed systems among all observed interactive interactions in this study.

Understanding the structure and dynamics of cationic surfactants from studies of pure solid phases.

A homologous series of n-alkyl trimethylammonium bromide surfactants, H(CH2)nN+(CH3)3 Br-, from C10TAB to C18TAB have been studied systematically in the bulk over a wide range of temperatures. Common features in the structures are identified, with packing dominated by the co-ordination of the cationic head groups with bromide anions and interdigitation of the hydrocarbon chains. This arrangement provides an explanation for the thin adsorbed bilayers that have been observed at various hydrophilic surfaces from aqueous solutions in previous studies. The molecular volumes and arrangement are comparable with structures of a number of different self-assembled amphiphiles. For these surfactants with bromide counter-ions, formation of crystal hydrates was not observed. The alkyl chains are highly mobile and at high temperatures a plastic phase is found for all materials with a transition enthalpy that is similar to the melting enthalpy of many long alkyl chains. Other unexpected phase transitions depend more markedly on the hydrocarbon chain length and evidently depend on delicate balances of the various contributions to the free energy.

Concentration at the Minimum Bubble Velocity (CMV) for Various Types of Flotation Frothers

This paper presents the determination of a concentration at the minimum bubble velocity (CMV) for different types of frothers, such as straight and branched alkyl chain aliphatic alcohols, 1,ω-diols, poly(propylene glycol) and poly(ethylene glycol) alkyl ethers, n-alkyltrimethylammonium bromides, commercial frothers and others. The values of terminal rise bubble velocity were reviewed from the experimental data published in the literature for two different types of columns, i.e., a short PAS (used in Polish Academy of Sciences) of height (35 cm) and a long McGill of height (350 cm). The obtained empirical equation is universal and allows one to rapidly and accurately determine the CMV for all surfactants. The proposed empirical model can also be used to predict the terminal bubble velocity–frother concentration curve by knowing the maximum and minimum terminal velocities, as well as the values of CMV. Assessment and usefulness of frother characterization parameters (i.e., concentration at the minimum bubble velocity (CMV), dynamic frothability index (DFI) and critical coalescence concentration (CCC)) were shown in the flotation of coal.

Size control of surfactant vesicles made by a mixture of cationic surfactants and organic derivatives.

Spontaneous size-controllable vesicles that are prepared by a mixture of surfactants with different alkyl chain lengths (n-alkyltrimethylammonium bromide, C(n)TAB) and an organic derivative (5-methyl salicylic acid, 5mS) in aqueous solution have been investigated. When the organic derivative 5mS is mixed with the C(n)TAB surfactants in aqueous solution, the surfactant vesicles are spontaneously formed above a certain 5mS concentration. Small angle neutron scattering reveals that the core radius of surfactant vesicles is clearly increased from ca. 31 nm to ca. 97 nm with the alkyl chain length of surfactants while the bilayer thickness of the vesicles is nearly constant. The structure of surfactant vesicles maintains against temperature change ranging from 30 degrees C to 45 degrees C, showing no structural change. These results can provide thermally stable surfactant vesicles with various sizes and constant bilayer thickness that may possess a different permeability and may allow the surfactant vesicle to be used in gene or drug delivery for a variety of goods.

The molecular structures, vibrational spectroscopies (FT-IR and Raman) and quantum chemical calculations of n-alkyltrimethylammonium bromides

The FT-IR and micro-Raman spectra of three n-alkyltrimethylammonium bromides (dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and hexadecyl(cetyl)trimethylammonium bromide (CTAB)) in powder form were recorded in the regions 4000–550 cm−1 and 3200–300 cm−1, respectively. The optimized geometries and vibrational frequencies of DTAB, TTAB and CTAB have been carried out with ab initio Hartree-Fock (HF) and density functional theory method B3LYP calculations with the 6–31 G (d, p) basis set in the ground state. The comparison of the observed fundamental vibrational frequencies and calculated results for the fundamental vibrational frequencies of DTAB, TTAB and CTAB indicate that the scaled B3LYP method is superior compared to the scaled HF method.

Inclusional association as studied by the drying dissipative structure. Part 3. Drying pattern of aqueous mixtures of β-cyclodextrin and n-alkyltrimethylammonium bromide

Macroscopic and microscopic drying patterns were observed on a cover glass and a watch glass during the course of dryness of aqueous mixtures of β-cyclodextrin (βCD) with n-alkyltrimethylammonium bromide (alkyl: n-decyl, n-dodecyl, n-tetradecyl, and n-hexadecyl). Macroscopic patterns of the broad rings and the spoke lines appeared. The inclusional association constants of βCD with the cationic surfactants were determined from the bent points in the curves of the drying broad-ring size vs. surfactant concentration when a finite amount of cyclodextrin presents. The short and thick rod-like microscopic drying patterns were observed for the inclusional complexes.

Inclusional association as studied by the drying dissipative structure. Part 2. Drying pattern of n-alkyltrimethylammonium bromide

Macro- and microscopic drying patterns were observed on a cover glass and a watch glass during the course of dryness of aqueous solutions of a series of n-alkyltrimethylammonium bromides (alkyl: n-decyl, n-dodecyl, n-tetradecyl, and n-hexadecyl). The broad rings formed at the outside edges of the macroscopic patterns. Size of the initial liquid on the substrates, d i, that of the final broad ring, d f, and the ratio, d f/d i, changed as the surfactant concentration changed, and there appeared a bending point in each curve, which was found to correspond to the critical micelle concentration (cmc) of the surfactant. The cmc values evaluated from the d i, d f, and d f/d i values agreed well with the reference values reported previously. Cooperative drying processes of the convection, sedimentation, and solidification were supported. Microscopic drying patterns such as rod-like, dendritic, and granule-like patterns were observed, and they changed as a function of the carbon number of the alkyl groups, surfactant concentration, and the distance from the center of the pattern.

Thermodynamics of formation of β-cyclodextrin inclusion complexes with four series of surfactant homologs

We report on a titration microcalorimetric study of the formation of β-cyclodextrin inclusion complexes with the members of series of anionic, cationic, and nonionic surfactant homologs containing even numbers of carbon atoms in the alkyl chains. n-Alkyltrimethylammonium bromides (CxTAB, x = 6–16), sodium n-alkyl sulfates (SCxS, x = 6–12), sodium n-alkanesulfonates (SCxSN, x = 6–12), and N,N-dimethylalkylamine-N-oxides (DCxAO, x = 8–12) were selected for use. The stoichiometry, the binding constant, and the changes in enthalpy, entropy, and Gibbs free energy of the complexation reactions were determined at 298 K. It was found in each case that the complexation is favored by both the enthalpy and the entropy changes and that the thermodynamics of the process is affected far more strongly by the length of the alkyl chain than by the nature of the headgroup.

Synergism in mixtures of n-octyl-β-d-thioglucoside and different n-alkyltrimethylammonium bromides: effect of the alkyl chain length

Mixtures of n-octyl-β-d-thioglucoside with three different n-alkyltrimethylammonium bromides (n = 12 (DTAB), 14 (TTAB), and 16 (CTAB)) have been studied by using fluorescence spectroscopic techniques. The critical micelle concentration values of pure and mixed systems were determined by the pyrene 1:3 ratio method. The experimental results were treated by using thermodynamic mixing approaches based on the pseudophase separation model. It was found that all the mixed systems show a negative deviation from ideal behavior, more pronounced as the larger the alkyl tail of the co-surfactant. It was also observed that the three mixed systems fulfill the conditions of synergism, this behavior being also dependent on the alkyl chain length. By using the static quenching method, the mean micellar aggregation numbers of mixed micelles were obtained. In all the cases, it was observed that the aggregation number is initially reduced with the participation of the cationic surfactant, remaining almost constant and close to the aggregation number of the pure cationic micelles. The local viscosity of pure and mixed micelles was examined by the photophysical response of the hydrophobic probe coumarin 6 solubilized in the micellar medium. It was found that the participation of the ionic component induces the formation of a less ordered structure than that of pure nonionic micelles. This effect being less pronounced as the chain hydrocarbon length of the co-surfactant increases.

Antimicrobial activity of n-alkyltrimethylammonium bromides: influence of specific growth rate and nutrient limitation.

The antimicrobial activity of an homologous series of n-alkyltrimethylammonium bromides has been assessed towards Escherichia coli grown at a variety of specific growth rates and under various conditions of nutrient limitation. For each individual set of growth conditions activity was parabolically related to the n-alkyl chain length of the compounds and thus to compound lipophilicity (log P). The compound that showed optimal activity and thereby optimal lipophilicity (log Po) changed according to growth rate and nutrient limitation. Such changes are related to variations in the gross cell envelope composition of the cultures (phospholipid, lipopolysaccharide, neutral lipids, proteins). The data therefore support the hypothesis that changes in growth rate and nutrient limitation alter the overall lipophilicity of the cell envelope and thereby the optimal value of log P for compounds to traverse it. Additionally, the data suggest that for the compounds examined, the neutral acidic:neutral phospholipid ratios of the cell envelope, also influence the permeation of it.

Physicochemical studies on ion-pair amphiphiles: Solution and interfacial behaviour of systems derived from sodium dodecylsulfate and n-alkyltrimethylammonium bromide homologues

Bulk and interfacial properties of ion-pair amphiphiles (IPA), formed between sodium dodecylsulfate (SDS) and n-alkyltrimethylammonium bromide homologues (C n TAB; n = 10, 12, 14, 16, and 18), have been investigated. Different phases and aggregated states, formed in the ternary combinations of CnTAB/SDS/H2O, have been identified and described. Equimolar mixture of IPAs in water yielded precipitates, in the form of coacervates. Aqueous solubility of isolated coacervates in presence and absence of additives like cholesterol and bile salts have been examined. The isolated coacervates have been characterized by 1H NMR, FTIR, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and polarization microscopic measurements. The coacervates have appeared in the shape of needle and complex flower-like aggregates. Surface pressure (π)-area (A) isotherm of the coacervates at the air/water interface have been constructed and compared with the lipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). Morphologies of the IPA monolayers at different surface pressures have been also examined by epifluorescence microscopy. The compressed interfacial monolayers have produced spherical (both regular and irregular) and fern-leaf like domains.

14N and 81Br Quadrupolar Nuclei as Sensitive NMR Probes of n-Alkyltrimethylammonium Bromide Crystal Structures. An Experimental and Theoretical Study

This is the first time a comprehensive study has been carried out on n-alkyltrimethylammonium bromide salts using (14)N and (81)Br solid state NMR, X-ray diffraction, and theoretical calculations. The investigation represents a necessary step toward further (14)N and (81)Br NMR characterization of the environment of cationic and anionic groups in materials, accounting for the amphiphilic properties of cationic surfactants. The NMR spectra of five C(x)H(2x+1)(CH(3))(3)N(+)Br(-) polycrystalline samples with different n-alkyl chain lengths (x = 1, 12, 14, 16, 18) were recorded and modeled. The (14)N and (81)Br quadrupolar coupling interaction parameters (C(Q), eta(Q)) were also estimated from spectrum modeling and from computer simulation. The obtained results were discussed in depth making use of the experimental and reoptimized crystal structures. In the study, both (14)N and (81)Br nuclei were found to be sensitive probes for small structural variations. The parameters which influence the NMR properties the most are mobility, deviation of C-N-C bond angles from T(d) angles, and variations in r(N-Br) distances.

Interaction of cellulase with cationic surfactants: Using surfactant membrane selective electrodes and fluorescence spectroscopy

The interaction of cationic surfactants, n-alkyl trimethyl ammonium bromides (C n TAB, n = 12 and 14), with cellulase from Aspergillus niger has been investigated at 25 °C and various pH, using C n TAB-membrane selective electrodes as a simple, fast, cheap and accurate technique and fluorescence spectroscopy. The regions of C 1 (the surfactant concentration at which binding is initiated) and C 2 (enzyme saturated by surfactant) were determined using potentiometric measurements. The obtained binding isotherms have been analyzed using Scatchard plot and binding capacity concept. The results were interpreted on the basis of nature of forces which interfered in the interaction and represent two binding sets system for all of the studied conditions. Hill equation parameters have been estimated and used for calculation of intrinsic Gibbs free energy that decreases with extension of binding. The effect of C n TAB binding on cellulase intrinsic fluorescence spectra was also examined. A biphasic behavior was observed for quenching process of endoglucanase by C n TAB that confirms the results of binding studies correspond to the existence of two types of binding sites for C n TAB on cellulase.

Removal of Eriochrome Blue Black R from wastewater using micellar-enhanced ultrafiltration

Micellar-enhanced ultrafiltration (MEUF) represents a potentially attractive tool for the removal of different contaminants from wastewater. In this study, MEUF was carried out to investigate the retention of Eriochrome Blue Black R (EBBR), an anionic dye, from aqueous stream. N-Alkyltrimethylammonium bromide i.e. dodecyltrimethylammonium bromide (C 12TAB), tetradecyltrimethylammonium bromide (C 14TAB), cetyl-trimethylammonium bromide (C 16TAB) and octadecyltrimethylammonium bromide (C 18TAB) were taken as cationic surfactants, and NaCl, Na 2SO 4, Na 2HPO 4 as electrolytes. A hydrophilic membrane made of cellulose (molecular weight cut-off 10 000 Da) was used in a cross-flow ultrafiltration unit. The removal of EBBR was studied as a function of dye and surfactant concentrations, ionic strength, transmembrane pressure and pH. The MEUF experiments showed that the highest dye rejection was about 99% for the used range of dye and surfactant concentrations. This retention depended slightly on dye and surfactant concentrations, ionic strength, pH and transmembrane pressure. However, permeate flux changed significantly with those parameters due mainly to concentration polarisation and osmotic pressure.

Photophysical Changes of Pyranine Induced by Surfactants: Evidence of Premicellar Aggregates

We studied photophysical changes of pyranine in different surfactant environments using spectrophotometry, steady-state fluorescence, and time-resolved fluorescence lifetime. The effect of surfactants on such properties varied as a function of the surfactant charge. Whereas anionic surfactants did not show any kind of interaction, the nonionic surfactant Triton X-100 produced spectral changes in the dye, as a consequence of the shift of equilibrium between its excited species. In the case of fluorescence, these changes allowed the critical micellar concentration of the surfactant to be determined. However, the most important features were obtained from the interaction with cationic surfactants of the n-alkyl trimethylammonium bromides. Such interactions enabled the formation of premicellar aggregates to be determined. In addition, three or four critical concentrations could be defined, which were dependent on the length of the hydrocarbon chain. One of these was the critical micellar concentration of the surfactant. The remaining two or three were in the very dilute concentration domain from which several types of premicellar aggregates are formed. However, the interaction with dodecyltrimethylammonium bromide at submicellar concentrations evidenced a quenching effect of a different nature (either static or combined), depending on the surfactant concentration. By deconvoluting the overall pyranine fluorescence emission spectrum into a sum of overlapping Lorentzian-Gaussian functions, the principal microenvironments of the pyranine molecules can be ascertained. Fluorescence data are consistent with the location of pyranine in a variety of sites, including partitioning that may be influenced by electrostatic and pi-cation interactions in aqueous micelles.