N-dodecyltrimethylammonium Bromide Research Articles

Biotransformation of t-butyl phenols by micellar nanoreactors of peroxidase/ionic surfactants at mild conditions: nanobiocatalyst performance and kinetic analysis

Recently, some bulk reaction media were substituted by micellar systems. Micellar media can be created by different types of surfactants which generate micellar nanoreactors for diverse reactions. Ionic surfactants can be used as aqueous micellar systems, providing mild conditions for the specified reactions. Ionic surfactants: sodium dodecyl sulfate, sodium decyl sulfate (SDeS), sodium octyl sulfate (SOS), n-dodecyl trimethyl ammonium bromide, and cetyltrimethylammonium bromide were used to prepare aqueous micellar and entrapped peroxidase nanoreactors as biocatalysts. Oxidative coupling reactions were investigated for a series of phenolic hydrogen donors including 2-tert-butyl phenol, 4-tert-butyl phenol, and 2,4-tert-butyl phenol catalyzed by micellar nanoreactors of horseradish peroxidase (HRP) with hydrogen peroxide and/or tert-butyl peroxide as oxidants. Higher oxidation reaction rates were obtained for 2-tert-butylphenol and 4-tert-butylphenol with hydrogen peroxide in 90 mM SDeS (SDeS90) and 150 mM SOS (SOS150) nanoreactors, respectively. Among the micellar nanoreactors studied, the SDeS90 nanoreactor showed excellent protection of the enzyme against the peroxide inactivation effect. The long-term activity of the HRP/SDeS90 nanobiocatalyst was related to the gradual diffusion of peroxide into the nanoreactor. The biocatalytic kinetic parameters: V max, k cat, catalytic efficiency, and suicide-peroxide inactivation rate constants were determined for HRP/SDeS90. Reactions were carried out successfully under mild conditions in the micellar nanoreactors. Results confirmed that substituted functional groups on the benzene ring affect the oxidative reaction routes and products. Excellent protection of the enzyme, enhanced biocatalytic parameters, higher selectivity, and yield, in the peroxidative coupling of alkylphenols, reveal the high potential of such micellar nanoreactors for diverse organic synthesis and biotransformation.

Dodecyltrimethylammonium bromide-styrene microemulsion dielectric investigation in aqueous media

In this paper, we report the complex permittivity of aqueous microemulsions of N-dodecyltrimethylammonium bromide and styrene. The studies were carried out at 298.15 K while varying the styrene to surfactant concentration ratio, S0 (0.16 ≤ S0 ≤ 0.71) and the surfactant concentration, c (0.1032 ≤ c (mol·dm−3) ≤ 0.7806). The frequencies ranged from 100 MHz to 89 GHz. An analysis of a particular solution is conducted over the temperature range of 278.15–328.15 K to calculate the energy of the activation parameters. At 298.15 K, the spectra are fitted to a total of five Debye processes for concentration dependency series and three Debye processes for temperature dependence series. Br− surface and bulk diffusion surrounding the micelles best describes the two low-frequency dispersions, at 100 MHz and 0.8 GHz, respectively. These mechanisms were examined using Grosse theory. The Maxwell–Wagner relaxation process is equivalent to high-frequency micelle dispersion at 0.8 GHz. The thickness of the conducting shell of the micelle is determined by using the electrical conductivity of the particles and parameters taken from the Grosse theory, and the results are comparable to those from an examination of the Pauly and Schwan model. The Grosse model and solvent dispersion analysis were used to calculate the volume fractions of micelles. Both approaches were in agreement. The surfactant head group non-rotationally hydrates almost ∼7 ± 1 water molecules. Styrene addition allows for the non-rotationally bound accommodation of an additional ∼7 ± 1 water molecules.

Mixed micelle formation by sodium dodecylsulfate and dodecyltrimethylammonium bromide in aqueous ionic liquid media

Surfactant self-aggregation within ionic liquid (IL) - based media has been investigated to compare and contrast the role of such media with that of water. Behavior of a surfactant mixture constituting of two surfactants with oppositely charged head groups, namely anionic sodium dodecylsulfate (SDS) and cationic n-dodecyltrimethylammonium bromide (DTAB), is assessed in aqueous IL media. Contrary to what is observed in water, it is shown earlier that effective charge screening of the surfactant headgroups by IL ions in a typical IL 1-ethyl-3-methylimidazolium ethylsulfate ([C2C1im][EtSO4]) results in formation of (SDS + DTAB) mixed micelles with critical micelle concentrations (CMCs) ranging between those of SDS and DTAB, respectively. The miscibility of (SDS + DTAB) mixture in aqueous [C2C1im][EtSO4] reveals that as the content of IL [C2C1im][EtSO4] is increased, the miscibility of the surfactant mixture improves indicating increased charge screening involving ions of the IL and the surfactant headgroups. For water mole fraction (XW) ≤ 0.90, (SDS + DTAB) surfactant mixture is miscible in aqueous [C2C1im][EtSO4] system in all proportions. For 1.00 ≥ XW≥ 0.90, while synergism persists due to the presence of attractive electrostatic attraction between SDS and DTAB headgroups leading to mixture CMCs below the CMCs of SDS and DTAB, respectively, the extent of synergism diminishes with increase in IL [C2C1im][EtSO4] in the solution. For XW = 0.80, the (SDS + DTAB) mixture exhibits CMC values that are closest to the values estimated assuming ideal behavior. For 0.70 ≥ XW ≥ 0.30, the (SDS + DTAB) exhibits antagonistic trend with CMC values higher than those estimated for ideal solution; the antagonistic trend gradually decreases with increase in [C2C1im][EtSO4] and again attains close to ideal behavior in neat IL [C2C1im][EtSO4]. This trend is subsequently manifested in the composition of the mixed micelles as well as in the net interaction parameter, β. Addition of small proportion of IL to water helps in solubilization of surfactant mixture of oppositely charged surfactants due to effective charge screening of the surfactant headgroups and results in formation of mixed micelles in aqueous IL media over complete composition range.

Thermodynamics of Micellization of Ionized Surfactants: The Equivalence of Enthalpies of Micellization from Calorimetry and the Variation of Critical Micelle Points with Temperature as Exemplified for Aqueous Solutions of an Aliphatic Cationic Surfactant

There is considerable confusion on experimental and thermodynamic aspects of the formation of ionized surfactant micelles. Recent claims that the van't Hoff and calorimetric enthalpies of micellization of ionized surfactants represent different aspects of micellization are shown to be incorrect. New conductance and surface tension measurements on n-dodecyltrimethylammonium bromide (DTAB) in water and in cosolution with 0.1 M KBr over a range of temperatures are used to provide a set of critical micelle concentrations (cmc's). The molar enthalpies of micellization derived from these cmc's are compared with calorimetric enthalpies of micellization obtained from a critical survey of the literature and shown to be equivalent. This signifies that both enthalpies capture the contributions from all aspects of micellization of charged micelles. The apparent discrepancies arise from experimental problems, incorrect use of the van't Hoff equation, and failure to recognize the constraints of the Phase Rule and electroneutrality. Deficiencies in the application of the two major models of micellization, namely, the "mass-action" model and the "phase" model, are exposed. Neither model is generally valid. The van't Hoff enthalpies of micellization of DTAB in water are similar in the presence and absence of 0.1 M KBr, confirming a similar correspondence found with calorimetric enthalpies for DTAB in water and NaBr.

Solid-state synthesis and physico-chemical characterization of modified smectites using natural clays from Burkina Faso

Solid-state intercalation was applied to prepare organo-smectites using cationic surfactants and natural clays containing smectite at various surfactant/smectite ratios. The surfactants enter the interlayers of smectites causing a swelling of the clays. The used clays were collected in Siétougou and Diabari villages located in the eastern part of Burkina Faso. The solid-state intercalation was successful for all four surfactants applied, n-dodecyltrimethylammonium bromide, (n-C12H25(CH3)3NBr), n-tetradecyltrimethylammonium bromide, (n-C14H29(CH3)3NBr), n-hexadecyltrimethylammonium bromide (n-C16H33(CH3)3NBr) and di-n-dodecyldimethyl­ammonium bromide ((n-C12H25)2(CH3)2NBr) at different levels of the cation exchange capacity (CEC). The synthesized organo-smectites were characterized regarding relative density, structural and textural properties. XRPD data showed a systematic increase of the basal spacing of the unit cell of the smectite up to >38 Å at 2.0-CEC loading of the surfactant. This increase indicates that the surfactants penetrated into the smectite interlayers with the surfactants being arranged parallel to the layers at low concentrations and almost perpendicular at high ones. FTIR spectra of the organo-smectites showed a decrease in the intensities of the water bands at around 1630 cm-1 and 3400 cm-1, and new specific bands close to 2920 cm-1 and 2850 cm-1 were assigned to the asymmetric and symmetric stretching of CH2 groups of the surfactants, respectively.
 
 KEY WORDS: Smectite, Organo-smectite, Surfactant, Intercalation
 
 Bull. Chem. Soc. Ethiop. 2021, 35(1), 43-59.
 DOI: https://dx.doi.org/10.4314/bcse.v35i1.4

A case study on the partitioning of pharmaceutical compound naproxen in edible oil-water system in the presence of ionic and non-ionic surfactants

The partitioning coefficient is a physicochemical quantity which gives important information about the distribution and efficiency of bioactive compounds in various biological systems. The present work aims at detailed investigation of the partition process of drug naproxen between edible oils (olive, sunflower, sesame) and water in the presence of two differently charged surfactants consisting of SDS (sodium dodecylsulfate), DTAB (n-dodecyltrimethylammonium bromide) and non-ionic surfactant Brij 35 (polyethylene glycol dodecyl ether). The evaluation was done at atmospheric pressure and 25.0 °C by using UV–Vis spectrometric and shake-flask techniques. In this work, all the surfactants are used in a concentration below their CMC due to the turbidity that occurs in the biphasic oil-water systems in the concentrations above their CMC. The experimental results obtained indicate that the oil-water partition coefficient (Koil/w) of naproxen reduce with rising the surfactants concentration in medium irrespective of the oil employed. Moreover, these values in the surfactant media are lower in comparison with surfactant free medium. The values of standard Gibbs free energy of the transfer (ΔGw→oil∘) calculated for all binary oil-water systems have negative sign which indicates the preference of this drug for oil phase and thus spontaneous partitioning process. The surfactant effect on the partition coefficients of drug is analyzed in terms of the intermolecular interactions such as hydrogen bonding, dispersion and electrostatic forces between the drug and the surfactant.

Evaluation of a New Agent for Wettability Alteration During Enhanced Oil Recovery

Wettability alteration is an important mechanism when applying surfactants during enhanced oil recovery (EOR). Moreover, in carbonate reservoirs, the rock has more tendencies to be oil-wet than those of sandstone reservoirs. This mainly arises from the interaction amongst the carbonate surface chemistry exposed to the asphaltenic/aromatic components of crude oil. Therefore, it is of great significance to develop surfactants with high efficiency in wettability alteration of carbonate rocks. In this work, a cationic surfactant n-dodecyl trimethylammonium bromide (DTEAB), was prepared and applied in a wettability alteration experiment for the first time. Then, the critical micelle concentration and wettability properties were studied by means of electrical conductivity and sessile drop techniques, respectively. Consequently, it was observed that this surfactant can alter the wettability of Bangestan rock pellets from oil-wet to water-wet state, and the results are better than that of wettability alteration observed for Khark rock pellets. Based on this mechanism, nearby 22% Original Oil in Place (OOIP) was obtained by tertiary surfactant flood during core displacement in excess of ultimate recovery factor of secondary water injection. As a consequence, the suggested cationic surfactant in this study can be a good agent for increasing the oil recovery factors in the petroleum industry.

Nitroxyl spin probe in ionic micelles: A molecular dynamics study

The compounds containing nitroxyl radical (NO˙) are actively used as spin probes to examine colloid systems, including lipid membranes and micelles. Their electron paramagnetic resonance spectrum provides information about the composition of the medium, in particular, the content of water there. Yet, the proper treatment of the measurement results demands understanding the microscopic characteristics of the molecular probe. In the present paper, we extend our previous studies on the microscopic state of acid-base and solvatochromic probes in surfactant micelles to the field of spin probes. We report the results of molecular dynamics simulation of a common spin probe, methyl-5-doxylstearate, in micelles of anionic (sodium n-dodecyl sulfate, SDS) and cationic (n-dodecyltrimethylammonium bromide, DTAB) surfactants. The localization of the molecule within the micelles, its shape, composition of the local environment, hydration were quantified and compared with the available relevant experimental data. No significant dissimilarity was found in the characteristics of the probe molecule in both kinds of micelles. However, the characteristics of the O˙ atom carrying the unpaired electron are pronouncedly different, namely, in DTAB micelles it is less hydrated and forms less hydrogen bonds with water. Similar situation was observed for the COO group. The main reason was found to be the interactions with cationic surfactant headgroups, which screen the O˙ atom and COO group from water. These findings allowed revisit the point of view that the surface layer of DTAB micelles as a whole is less hydrated in comparison to that of the SDS ones.

Influence of the Hamaker Constant on the Value of the Critical Thickness of Foam Films

The aim of the present study was to check the influence of the Hamaker constant (A(h)) on the calculated critical thickness of foam films. It was done by a comparison between the experimental data of the critical thickness and the theoretically obtained data with different values of (A(h)), which take part in the equations of Radoev, Scheludko, Manev, and Vrij. We calculated the latter for film thicknesses from 15 to 70 nm based on several equations. We used the experimental data of hcr (average value of critical thickness and measured once, in the place of a spot appearance) for foam films stabilized by non-ionic surfactant n-dodecyl-β-D-maltoside (C12G2) or by cationic surfactant n-dodecyl trimethylammonium bromide (C12TAB), as measured by the interferometric method. The foam films were produced from solutions with surfactant concentration at CMC (Critical Micelle Concentration) in the presence of 0.1 M NaBr. For films of C12G2, the best correspondence was found between measured hcr (in the spot) and calculated ones by the RShM equation using effective A(h) (introduced by Coons et al.) or Vassilieff’s values, but with a correction for the added electrolyte. For films stabilized by C12TAB, a difference between the measured and theoretically calculated hcr was found, which was probably due to the nature of the surfactant. Nevertheless, this difference was smallest when calculated hcr values were obtained with data for Aeff (h) and Vassilieff’s A(h) constant, respectively.

Structures of Thymosin Proteins.

The thymosin proteins are all short, highly charged, intrinsically unstructured proteins under natural conditions. However, structure can be induced in many of the thymosin proteins by providing charge neutralization at low pH or by the addition of Zn(2+) ions, organic reagents such as trifluoroethanol, hexafluoropropanol, or n-dodecyltrimethylammonium bromide, or interactions with their natural binding partner proteins. The differing structures of thymosin alpha and thymosin beta proteins have been studied by circular dichroism, nuclear magnetic resonance, and crystallographic methods in order to better understand the role of these proteins. In this structural biology review the structures of prothymosin, parathymosin, thymosin alpha-1, and several beta thymosin proteins, in both native states and under secondary structure-inducing conditions are discussed.

PRECONCENTRATION OF COPPER FROM NATURAL WATER SAMPLES USING LIGAND-LESSIN SITUSURFACTANT-BASED SOLID PHASE EXTRACTION PRIOR TO FAAS DETERMINATION

In the present work, a simple and rapid ligand-less, in situ, surfactant-based solid phase extraction for the preconcentration of copper in water samples was developed. In this method, a cationic surfactant (n-dodecyltrimethylammonium bromide) was dissolved in an aqueous sample followed by the addition of an appropriate ion-pairing agent (ClO4-). Due to the interaction between the surfactant and ion-pairing agent, solid particles were formed and subsequently used for the adsorption of Cu(OH)2 and CuI. After centrifugation, the sediment was dissolved in 1.0 mL of 1 mol L-1 HNO3 in ethanol and aspirated directly into the flame atomic absorption spectrometer. In order to obtain the optimum conditions, several parameters affecting the performance of the LL-ISS-SPE, including the volumes of DTAB, KClO4, and KI, pH, and potentially interfering ions, were optimized. It was found that KI and phosphate buffer solution (pH = 9) could extract more than 95% of copper ions. The amount of copper ions in the water samples varied from 3.2 to 4.8 ng mL-1, with relative standard deviations of 98.5%-103%. The determination of copper in water samples was linear over a concentration range of 0.5-200.0 ng mL-1. The limit of detection (3Sb/m) was 0.1 ng mL-1 with an enrichment factor of 38.7. The accuracy of the developed method was verified by the determination of copper in two certified reference materials, producing satisfactory results.

Ligand-Lessin situSurfactant-Based Solid Phase Extraction for Preconcentration of Cobalt, Nickel and Zinc from Water Samples Prior to their FAAS Determination

A new simple and rapid ligand-less in situ surfactant-based solid phase extraction (LL-ISSPE) was developed for preconcentration of cobalt, nickel and zinc in water samples. In this method, a cationic surfactant containing a proper alkyl group (n-dodecyltrimethylammonium bromide) is dissolved in the aqueous sample and then a proper ion-pairing agent (ClO4−) is added. Due to the interaction between surfactant and ion-pairing agent, solid particles are formed and precipitate of the analytes was adsorbed on surface of sorbent. After centrifugation, the sediment is dissolved in 3.0 mL HNO3 in ethanol and then aspirated directly into the flame atomic absorption spectrometer. Variables affecting the extraction efficiencies such as pH, concentrations of surfactant and ion pair, CO32− amount, extraction time, time and rate of centrifuge were optimized. Detection limits for Co(II), Ni(II) and Zn(II) based on 3Sb/m were 1.0, 1.5 and 0.3 ng mL−1, respectively. The proposed method has been successfully applied for the determination of cobalt, nickel and zinc ions in real water samples.

The Species and Heme Pocket Properties of Sturgeon Hemoglobins Upon Interaction with N-dodecyl Trimethylammonium Bromide

The variations in fish hemoglobin (Hb) structures play a vital role in their respiratory performance under various environmental conditions and are impacted by their physiological properties. The major hemoglobins from two species of sturgeon were studied upon interaction with n-dodecyl trimethyl ammonium bromide (DTAB) using the UV-vis absorption, circular dichroism (CD), fluorescence spectroscopy, and oxygen affinity measurement methods as well as chemometric analysis. The UV-Vis absorption spectra between 500 and 650 nm was used to identify each species of hemoglobin, and to show that the concentration of oxyHb and metHb decreases, while that of deoxyHb increases upon interaction with DTAB. Both reduced oxyHb and oxidized hemichrome of the two Hbs were studied to obtain information about the DTAB efects on their structural features. The circular dichroism (CD) was utilized to obtain secondary structure and compactness for Hb upon interaction with DTAB. Binding of DTAB molecules induced the unfolding of Hb, and was accompanied with exposure of the heme pocket facilitating its oxidation. The differences between unfolding processes for the two Acipenser species were indicated by fluorescence spectroscopy. The chemometric analysis of Hbs was investigated upon interaction with DTAB under titration, using fluorescence spectra allowing determination of the number of components and mole fractions of the oxidized Hb. Our data showed that Acipenser persicus Hb had a more hyperchromic character, more surface area, more loosely folded structure, and therefore, exposed region of heme group compared with Acipenser stellatus oxyHb. In addition, with increasing DTAB the transition of Acipenser stellatus oxyHb to the state of hemichrome occurred at a slower speed than Acipenser persicus oxyHb, and finally more oxygen affinity and compactness. Our results suggest that these differences aroused from the inherent differences between the heme groups which fulfil a potentially important physiological role in these fish.

Ligand-less in situ surfactant-based solid phase extraction for preconcentration of silver from natural water samples prior to its determination by atomic absorption spectroscopy

A simple and rapid ligand-less in situ surfactant-based solid phase extraction method for preconcentration of silver from water samples is developed. In this method, a cationic surfactant containing a proper alkyl group (n-dodecyltrimethylammonium bromide) is dissolved in the aqueous sample and then a proper ion-pairing agent (ClO4 −) is added. Due to the interaction between surfactant and ion-pairing agent, solid particles are formed and used for adsorption of silver carbonate. After centrifugation, the sediment is dissolved in 2.0 mL 1 M HNO3 in ethanol and then aspirated directly into the flame atomic absorption spectrometer. Variables affecting the extraction efficiencies such as pH, concentrations of surfactant and CO3 2−, ion pair concentration, and extraction time, are optimized. Under such conditions, the calibration curve is linear from 3 to 700 μg L−1. Detection limit is 1.1 μg L−1 with an enrichment factor of 37. The relative standard deviation for eight replicate measurements of 100 μg L−1 is 2.1%. The method has been applied for the determination of silver in water samples.

Spectral inverse quantum (Spectral-IQ) method for modeling mesoporous systems: application on silica films by FTIR.

The present work advances the inverse quantum (IQ) structural criterion for ordering and characterizing the porosity of the mesosystems based on the recently advanced ratio of the particle-to-wave nature of quantum objects within the extended Heisenberg uncertainty relationship through employing the quantum fluctuation, both for free and observed quantum scattering information, as computed upon spectral identification of the wave-numbers specific to the maximum of absorption intensity record, and to left-, right- and full-width at the half maximum (FWHM) of the concerned bands of a given compound. It furnishes the hierarchy for classifying the mesoporous systems from more particle-related (porous, tight or ionic bindings) to more wave behavior (free or covalent bindings). This so-called spectral inverse quantum (Spectral-IQ) particle-to-wave assignment was illustrated on spectral measurement of FT-IR (bonding) bands’ assignment for samples synthesized within different basic environment and different thermal treatment on mesoporous materials obtained by sol-gel technique with n-dodecyl trimethyl ammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB) and of their combination as cosolvents. The results were analyzed in the light of the so-called residual inverse quantum information, accounting for the free binding potency of analyzed samples at drying temperature, and were checked by cross-validation with thermal decomposition techniques by endo-exo thermo correlations at a higher temperature.

Denaturation and intermediates study of two sturgeon hemoglobins by n-dodecyl trimethylammonium bromide

Varieties of hemoglobin (Hb) forms exist in fish, which are usually well adapted to the different ecological conditions or various habitats. In the current study, Hbs from two Sturgeon species of the Southern Caspian Sea Basin were purified and studied upon interaction with n-dodecyl trimethylammonium bromide (DTAB; as a cationic surfactant) by various methods including UV–visible absorption, dynamic light scattering (DLS), and ANS fluorescence spectrophotometry. The chemometric analysis of Hbs was investigated upon interaction with DTAB under titration, using UV–visible absorption spectra. The chemometric resolution techniques were used to determine the number of the components and mole fraction of the oxidized Hbs. These results provided the evidence for the existence of three different molecular components including native (N), intermediate (I) and denatured (D) in sturgeon Hbs. According to the distribution of intermediates, which were broadened in a range of DTAB concentration, the aggregation states, DLS experiments, and thermal stability (Tm obtained by differential scanning calorimetry (DSC)), the Acipenser stellatus Hb was more stable compared to Acipenser persicus Hb. These results demonstrate a significant relationship between the stability of fish Hbs and the habitat depth requirements.

Computational Analysis between two different hemoglobins from Caspian Sea sturgeons (Acipenser persicus and Acipenser stellatus) induced by n‐dodecyl trimethylammonium bromide

The multiplicity of the Hemoglobins (Hbs) of the and the A. stellatus, two species from the Caspian Sea, A.persicus was confirmed with the polyacrylamide gel electrophoresis (SDS‐PAGE), cellulose acetate electrophoresis, and isoelectric focusing (IEF) experiments. In the current study, the interaction of n‐dodecyl trimethylammonium bromide (DTAB) as a cationic surfactant under variable concentrations, with the purified dominant Hbs was investigated using UV‐visible absorption spectra and circular dichroism (CD). The chemometric resolution techniques were used to determining the number of the components and mole fraction of the oxidized Hbs. The analysis of the obtained spectral data using singular value decomposition (SVD), evolving factor analysis (EFA) and multivariate curve resolution‐alternative least square (MCR‐ALS) as well‐known chemometrical techniques, gave the evidence for the existence of four different molecular components including native (N), intermediate (I), intermediate (II) and denatured (D) in sturgeon Hbs. On the basis of the interpretation of chemometrical results, the formation of intermediate states of fish Hbs, plays an important role for regulation of the respiratory system of the fishes proportional to their habitat depths and environmental partial pressure of oxygen.

Combination of In Situ Surfactant-based Solid Phase Extraction and Central Composite Design for Preconcentration and Determination of Manganese in Food and Water Samples

A new kind of solid phase extraction (SPE), which we named in situ surfactant-based solid phase extraction (ISS-SPE), represents a simple, selective and rapid method for preconcentration and determination of manganese from food and water samples. This method has distinct advantages: extraction times are short and recoveries are high; further, we can see formation of fine particles of large specific surface and their good dispersion in the solution. In this work, a small amount of cationic surfactant, n-dodecyltrimethylammonium bromide (DTAB) was injected into the water sample containing Mn ions, which were complexed by 1-(2-pyridylazo)-2-naphthol (PAN). After shaking, a little volume of NaPF6 as an ion-pairing agent was added into the solution by a microsyringe. After preconcentration, the settled phase was dissolved in a specific volume of ethanol and then aspirated into the flame atomic absorption spectrometer by using a homemade microsample introduction system. The effective parameters such as pH, concentration of surfactant, concentration of chelating agent, concentration of ion-pairing agent and effect of salt concentration were optimized by a fractional factorial design to identify the most important parameters and their interactions, and central composite methodology was used to achieve the optimum point of effective parameters to the response. Under the optimum conditions, preconcentration of 10 ml of the sample solution permitted detection of 0.88 μg l−1 with enhancement factor of 45.6, and the relative standard deviation (RSD) for five determinations of Mn ions was 3.5%. The developed method was applied to the determination of trace manganese in various real samples with satisfactory results.

Curing Behavior and Thermal Properties of Autocatalytic Cycloaliphatic Epoxy

Cycloaliphatic epoxy resin containing hydroxyl group (DMTMP) was prepared by the transesterification between methyl-3,4-epoxycyclohexane carboxylate (MEC) and trimethylolpropane (TMP), which was then thermally cured with methylhexahydrophthalic anhydride (MHHPA). As comparison, a commercial available cycloaliphatic epoxy 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (ERL-4221) cured with the same curing agent was also investigated. The chemical structure was characterized by FT-IR and 1H-NMR. And the curing behavior and the thermal properties were studied by DSC and TGA. The DSC results showed that the DMTMP systems exhibited higher reactivity than the ERL-4221 systems due to the autocatalysis of hydroxyl group of DMTMP. While the glass temperature transitions (Tg s) of DMTMP systems were much lower than ERL-4221 systems, and the Tg s of DMTMP and ERL-4221 systems both reduced after introducing n-dodecyl trimethylammonium bromide (DTAB) as catalyst. The decomposition behavior from TGA shows that the DMTMP epoxy resins exhibited a relative slow weight decreasing tendency in comparison with ERL-4221 epoxy resins, but initial degradation temperatures of DMTMP systems were lower than ERL-4221 systems.

Luciferase and fluorescent protein as dual reporters analyzing the effect of n-dodecyltrimethylammonium bromide on the physiology of Pseudomonas putida

With the growing interest in using surfactants to improve microbial cell performance for whole-cell biocatalysis and bioremediation, understanding the interactions between surfactants and bacteria is of great importance. By using cyanine fluorescent protein (CFP) and bacterial luciferase (LUX) as dual bioreporters, the effects of n-dodecyltrimethylammonium bromide (DTAB) on the whole cells and intracellular proteins in Pseudomonas putida cultures were quantitatively and systematically studied. The dual reporter system was shown to be a useful indicator to assess the effect of DTAB treatment on whole-cell metabolic activity, membrane permeability, and cellular enzyme activity. CFP was useful to assess the leakage of intracellular enzymes and the lysis of cells and was able to reflect the activities of most cellular enzymes, while LUX reflected the permeability of cell membranes and cellular metabolic activity. The validity of CFP-LUX dual bioreporters was further confirmed by detecting changes in extracellular proteins, membrane potential, oxygen consumption rate (OUR), and intracellular catechol 2,3-dioxygenase (C23O) activity with the addition of DTAB. The dual LUX-CFP bioreporter is a useful tool for analyzing the surfactant-bacterium interactions for biotechnological applications.