Anionic SDS Research Articles

Robust antifouling Poly(ionic liquid)s membrane with cyclodextrin skeleton for separation of oil/water emulsions

Membrane fouling remains a persistent and arduous challenge in the industrial treatment of different surfactants-stabilized oily wastewater. Constructing a robust antifouling and sustainable hydration coating on the membrane surface to efficiently repel oils or surfactants is a critical requirement. Herein, cyclodextrin-based poly(ionic liquid)s (PILs) coatings are cross-linked via the co-deposition on poly(vinylidene fluoride) (PVDF) of quaternized heptkis(6-deoxy-6-vinylimidazolium)-β-cyclodextrin (CD-Vi) derivatives as skeleton and acrylic acid (AA) monomers, and following one-step free radical photopolymerization. Combining with the strong hydration of the CD-based PILs coating, the resultant membrane exhibits fabulous superhydrophilicity and underwater superoleophobicity, oil repulsion, and self-cleaning capability. It demonstrates robust mechanical durability and chemical stability in harsh environments without losing its superhydrophilicity. Besides, the PIL-CD/AA coating can separate various surfactant-free and different surfactants (cationic CTAB, anionic SDS, and nonionic TWEEN 80) stabilized oil / water emulsions. During the long-term cycle operations, it also realizes stable recyclability with a series of permeation fluxes as high as removal efficiencies (>99.6 %) after 20 cycles for surfactant-free cyclohexane-in-water emulsion and 10 cycles for CTAB-stabilized isooctane-in-water emulsion.

Effect of fluorocarbons and inorganic salts on wetting and foaming characteristics of hydrocarbon surfactants

To improve the wetting and foaming properties of anionic SDS foam on coal dust, we experimentally investigated the effects of short-chain fluorocarbon surfactant FS-50 and inorganic salt NaCl on the wetting and foaming properties of SDS foam and the synergistic effect of the mixed system. The experimental results show that SDS and FS-50 can effectively improve the wetting properties of coal dust in a concentration of 0.05–0.16 wt% and a ratio of 3:1–1:2. In the mixed system, SDS provides sufficient hydrophilic base, FS-50 can effectively reduce the surface tension and have a certain agglomeration effect on coal dust to accelerate the settlement of coal dust and improve the wetting properties of coal dust. When the mixed ratio is lower than 1:1, the foaming volume and foam half-life of the surfactant solution are significantly reduced. The number of SDS molecules at the solution gas-liquid interface is reduced due to electronegative repulsion, and the FS-50 replenishes to the liquid surface faster due to stronger hydrophobicity, and it is difficult to form hydrogen bonds with water molecules, which reduces the foam stability. Low concentrations of inorganic salts can significantly improve the wetting performance of the SDS/FS-50 mixed system to coal dust, and high concentrations will reduce the foam stability of the mixed system.

Enhanced washing of polycyclic aromatic hydrocarbons from contaminated soils by the empowered surfactant properties of de novo O-alkylated humic matter

Aqueous solutions of humic acid (HA) derivatized by a catalyzed O-alkylation reaction with methyl, pentyl, and benzyl groups at 40, 60, and 80% of total HA acidity were used to wash off polycyclic aromatic hydrocarbons (PAHs) from two contaminated soils. The enhanced surfactant properties enabled the alkylated HA to remove phenanthrene, anthracene, fluoranthene, and pyrene from both soils more extensively than the original unmodified HA, the 60% benzylation generally showing the greatest soil washing efficiency. For both soils, all alkylated HA revealed greater PAH removals than Triton X-100 nonionic surfactant, while the benzylated and methylated HA nearly and fully matched pollutants release by the anionic SDS in the coarse- and fine-textured soils, respectively. A consecutive second washing with 60% benzylated HA removed additional PAHs, in respect to the first washing, from the coarser-textured soil, except for fluoranthene, while removal from the finer-textured soil incremented even more for all PAHs. These findings indicate that the enhanced hydrophobicity obtained by a simple and unexpensive chemical derivatization of a natural humic surfactant can be usefully exploited in the washing of polluted soils, without being toxic to the soil biota and by potentially promoting the subsequent bio-attenuation of organic pollutants.

Evaluation of haemolymph phenoloxidase activity from the grub of Zophobas morio as a predictor of immune response.

In insects, enzyme phenoloxidase plays a critical role in cuticular sclerotisation and defensive functions. In the present investigation, haemolymph phenoloxidase activity from the grub of Zophobas morio was attempted to evaluate as a reliable predictor of insect's immunological response. Among the various substrates tested, L-DOPA was chosen as an appropriate substrate due to its high oxidation. The optimum pH and temperature for haemolymph PO activity was found to be 8 and 30°C, respectively. The optimum substrate concentration of L-DOPA was found to be 7.5mM for subsequent PO enzymatic characterisation. Among the various chemical inhibitors and copper chelators, PO activity was significantly reduced in the case of PMSF and thiourea. Preincubation of haemolymph with non-self-molecules showed enhancement of PO activity in the case of LPS from Serratia marcescens. In addition, exogenous proteases like α-chymotrypsin enhanced the PO activity of haemolymph and an increase in PO activity was demonstrated when haemolymph was preincubated with the anionic detergent, SDS and cationic detergent, cetyl pyridium chloride. Alteration of PO activity was observed under agonising conditions of starvation, ligation and microplastics injection at different time intervals. Interestingly, there were no correlation between PO and insect defence under live challenge of microbes. SDS protein profile revealed a significant increase in the 85kDa and 55kDa polypeptides in all the experiments over control after 24h, 48h and 96h. Mass spectrophotometric analysis of the polypeptides revealed their homology to antimicrobial peptides for 55kDa protein and 85kDa protein. A significant increase in 85kDa polypeptide was observed in the haemolymph of the grubs after 72h in the case of starved and microplastics injected groups only. These results demonstrated that PO may not be a reliable benchmark of immunological response in this insect.

Perturbation of surfactant-induced amyloids by abolishing electrostatic interactions

Protein amyloid fibrils are supramolecular homopolymers that play a role in numerous biological processes and illnesses. The link between type 2 diabetes and insulin-induced amyloidosis has prompted much research on the production of insulin amyloid fibrils. Many in vitro investigations have shown that insulin can turn into amyloid fibrils under certain conditions. Insulin was used as a model protein in this study to determine the role of electrostatic interactions in surfactant-induced amyloids. Our results showed that SDS-induced amyloid formation was nucleation-independent at pH 2.0, and the solubilization was also instantaneous upon electrostatic interaction disruption. Far UV circular dichroism (CD), turbidity, Rayleigh light scattering (RLS), thioflavin T (ThT), and transmission electron microscopy (TEM) imaging showed the attainment of the different structural forms of insulin due to varying degrees of electrostatic interactions between the anionic surfactant (SDS) and the cationic to the anionic state of insulin. Treatment of SDS with the cationic state of insulin strongly induces amyloid-like aggregate while anionic state insulin reverts to native-like alpha-helical structures. In all samples, SDS concentration remained unchanged. Thus, hydrophobicity remained constant; only the electrostatic interaction between anionic SDS and cationic insulin was abolished as pH increased.

Reversible Electronic Patterning of a Dynamically Responsive Hydrogel Medium

AbstractA dynamically responsive hydrogel medium is prepared from two self‐assembling components, a polysaccharide (chitosan) and a surfactant (sodium dodecyl sulfate; SDS). It is shown that this medium can be patterned using an electrode “pen” to reconfigure supramolecular structure: cathodic writing induces neutral chitosan chains to form a crystalline network, while anodic writing generates cationic chitosan chains that electrostatically crosslink with anionic SDS micelles. Both supramolecular structures are re‐configurable and each is stabilized by structure‐induced shifts in chitosan's pKa, thus electronically written patterns can be erased, new patterns can be written, and patterns can be written in three dimensions. Further, it is shown that NaCl‐induced morphological transitions of the SDS micelles allow patterns to be reversibly concealed or revealed. To demonstrate the versatility of this medium for information storage, a quick response (QR) code is electronically written and it is shown that this code can be recognized by a standard cellphone app. This QR code can be concealed by making the medium opaque (i.e., by obscuring the pattern) or by making the pattern evanescent (i.e., by making pattern invisible). Overall, this work demonstrates that a dynamically responsive medium composed of simple, safe and sustainable components can be reversibly patterned with spatial and quantitative control using top‐down electronic inputs.

Preparation of Water-Based Alkyl Ketene Dimer (AKD) Nanoparticles and Their Use in Superhydrophobic Treatments of Value-Added Teakwood Products

A process for preparing emulsions of alkyl ketene dimer (AKD) nanoparticles via a nanoemulsion template (emulsion/evaporation) method has been developed. The effects of types and contents of stabilizing agents, i.e., anionic (sodium dodecyl sulfate, SDS), cationic (cetyltrimethylammonium bromide, CTAB), amphoteric (phosphatidylcholine, PC), and polymeric (poly(vinyl alcohol), PVA), on the colloidal stability and hydrodynamic size of the AKD nanoparticles are investigated. The use of 0.1 wt % anionic SDS as a stabilizer generates nanoparticles with high stability and the smallest average size of 148 ± 5 nm. The environmentally friendly water-based emulsion prepared without halogenated compounds and harsh organic solvents is then applied to enhance the hydrophobicity of teakwood products by a simple dipping process. The properties and structures of the resulting treated woods are examined by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM), and water contact angle (WCA) measurements. The treated woods show superhydrophobicity with a WCA value of 150 ± 2°, as the emulsion generates a hydrophobic layer covering the wood surfaces due to the β-ketoester bond formation and the arrangement of AKD hydrophobic tails. The nanosized nanoparticles can penetrate the dense structure of the teakwood and form similar bonding for up to a 0.8 mm depth, generating a protective water-repellent layer in the wood structure. The emulsion has high potential for use in the commercial production of value-added teakwood products, with excellent water-resistant properties and high dimensional instability, without altering their physical appearances.

Influence of seawater on interfacial Properties, foam performance and aggregation behaviour of Fluorocarbon/Hydrocarbon surfactant mixtures

In this work, the influence of seawater on interfacial properties, foam performance and aggregation behaviour of fluorocarbon/hydrocarbon surfactant mixtures was systematically investigated. Two model foaming solutions containing different surfactants (nonionic APG, anionic SDS, and amphoteric FS-50) were prepared by deionized water and seawater, respectively. Multi-scale methods including surface tension measurements, foam ageing tests and cryogenic-transmission electron microscopy (cryo-TEM) were used. The results show that the addition of seawater reduces the equilibrium surface tension, foaming ability and adsorption kinetics of SDS/FS-50 mixtures. Among the counterions in seawater, Na+ can lower the surface tension and slightly improve the foaming ability, while the presence of Ca2+, Mg2+ and K+ allows the formation of surfactant precipitate to weaken the foaming ability of the solution. It turns out that seawater has dual effects on foam stability and the defoaming/stabilizing effects of seawater are related to ionic surfactant concentrations. Besides, it is confirmed that the spontaneous transition from single-lamellar vesicle to rod-like micelle occurs after mixing FS-50 with SDS in the deionized water, while only multi-lamellar vesicles and surfactant crystals can be observed in the seawater. The aggregation behaviour strongly affects solution viscosity as well as foam performance. At high SDS concentrations, the surfactant precipitate/aggregate can inhibit the liquid drainage process and improve foam stability.

Molecular Insight into Dye-Surfactant Interaction at Premicellar Concentrations: A Combined Two-Photon Absorption and Molecular Dynamics Simulation Study.

Both electrostatic and hydrophobic interactions play pivotal roles in ligand-surfactant binding interaction, especially for ionic surfactants. While much studies have been reported in the micellar region, less attention has been paid on such interactions at a low (premicellar) surfactant concentration. We here study the interaction between the cationic dye rhodamine 6G (R6G) with surfactants of different charge types: anionic SDS, cationic CTAB, and nonionic Tx 100 using absorption and emission spectroscopy. We identify that R6G forms dimeric aggregates at a premicellar concentration of SDS. Formation of aggregates is also confirmed from classical simulation measurements. CTAB and Tx 100 do not form any such aggregate, presumably owing to unfavorable electrostatic interactions. For a molecular-level understanding, we perform two-photon absorption (TPA) spectroscopy for the same systems. TPA allows us to calculate the two-photon absorption cross section and subsequently the change in the dipole moment (Δμ) between ground and excited states of the dye. We calculate the Δμ and observe that it passes through a maximum at a surfactant concentration half of the critical micelle concentration of SDS. This observation imparts support to earlier quantum mechanical calculation, which infers deviation from the parallel orientation of the dye during surfactant-induced aggregation. We extended our measurements and varied the carbon chain length of the anionic surfactant, and we found that all of them exhibit a maximum in Δμ, while their relative magnitude is dependent on the surfactant carbon chain length.

Multi-Step Synthesis, Photophysical and Physicochemical Properties of Novel Push- π -Pull AADC Chromophores

Coumarin based heterocyclic chalcone (E)-3-(3-(1-allyl-1H-indol-3-yl) acryloyl)-7-(diethylamino)-2H-chromen-2-one (AADC) was synthesized by the multi-steps synthesis. The structure of the AADC was established by the spectroscopic technics and purity of the AADC was confirmed by the elemental analysis. Physicochemical parameters of the AADC in ten different solvents such as molar absorption coefficient, transition dipole moments, stokes shift, oscillator strength and fluorescence quantum yield were calculated. Interaction of the AADC chromophore with cationic CATB and anionic SDS surfactants were determined by using the fluorescence spectroscopy techniques. It was observed that band fluorescence spectrum intensity increases with increasing the concentration of the surfactants. This suggests that strong interaction occurs between AADC with surfactants and this interaction arise from electrostatic forces. So, AADC chromophore could be used as analysis to define the CMC of the surfactants.

Detection of superoxide radical in all biological systems by Thin Layer Chromatography

The study presents a new method that detects O2•−, via quantification of 2-hydroxyethidium (2-ΟΗ-Ε+) as low as ∼30 fmoles by High-Performance Thin Layer Chromatography (HPTLC). The method isolates 2-ΟΗ-Ε+ after its extraction by the anionic detergent SDS (at 18-fold higher than its CMC) together with certain organic/inorganic reagents, and its HPTLC-separation from di-ethidium (di-Ε+) and ethidium (Ε+). Quantification of 2-OH-E+ is based on its ex/em maxima at 290/540 nm, and of di-E+ and E+ at 295/545 nm. The major innovations of the present method are the development of protocols for (i) efficient extraction (by SDS) and (ii) sensitive quantification (by HPTLC) for 2-OH-E+ (as well as di-E+ and E+) from most biological systems (animals, plants, cells, subcellular compartments, fluids). The method extracts 2-ΟΗ-Ε+ (by neutralizing the strong binding between its quaternary N+ and negatively charged sites on phospholipids, DNA etc) together with free HE, while protects both from biological oxidases, and also extracts/quantifies total proteins (hydrophilic and hydrophobic) for expressing O2•− levels per protein quantity. The method also uses SDS (at 80-fold lower than its CMC) to extract/remove/wash 2-ΟΗ-Ε+ from cell/organelle exterior membrane sites, for more accurate internal content quantification. The new method is applied on indicative biological systems: (1) artificially stressed (mouse organs and liver mitochondria and nuclei, ±exposed to paraquat, a known O2•− generator), and (2) physiologically stressed (cauliflower plant, exposed to light/dark).

Multi-step Synthesis, Characterization and Photophysical Investigation of Novel Biologically Active Heterocyclic Chalcone (AECO).

Novel alkylated heterocyclic chalcone (E)-1-(2-(allyloxy)phenyl)-3-(9-ethyl-9H-carbazol-3-yl)prop-2-en-1-one (AECO) with extended π-bond was prepared by the multi-steps synthesis. The structure of the AECO was established by the spectroscopic technics and purity of the compound was confirmed by the elemental analysis. Physicochemical parameters of the AECO such as molar absorption coefficient, transition dipole moments, stokes shift, oscillator strength and fluorescence quantum yield were calculated in ten various solvents on the basis of polarity of the solvents to see the effect of the solvent with AECO. Interaction of the AECO chromophore with cationic CTAB and anionic SDS surfactants were determined by using the fluorescence spectroscopy techniques. The intensity of the florescence spectrum increase with increasing the concentrations of surfactants. This suggests that strong interaction occurs between AECO with surfactants and this interaction arise from electrostatic forces. So, AECO chromophore could be used as analysis to define the Critical Micelle Concentration (CMC) of the surfactants. In addition the in-vitro antibacterial active of novel heterocyclic chalcone agents four bacteria's strain were evaluated and result showed AECO is beater antibacterial agent against Gram-Negative Bacteria (E. coli and S. flexneri) as compare to the Gram Negative Bacteria with respected to the standard drug Tetracycline.

Interfacial complexation of a neutral amphiphilic ‘tardigrade’ co-polymer with a cationic surfactant: Transition from synergy to competition

HypothesisNeutral amphiphilic PEG-g-PVAc co-polymer (a “tardigrade” polymer consisting of a hydrophilic polyethylene glycol, PEG, backbone with hydrophobic polyvinyl acetate, PVAc, grafts) can form complexes at the air–water interface with cationic dodecyltrimethylammonium bromide (DTAB) via self-assembly. Compared to anionic SDS, cationic DTAB headgroups are expected to interact strongly with the negatively charged OH– groups from the partial dissociation of the PVAc grafts. We anticipate a transition from synergistic to competitive behaviour, which is expected to be dependent on the surfactant structural characteristics and concentration. ExperimentsDTAB/PEG-g-PVAc mixtures were investigated using a combination of dynamic and equilibrium surface tension measurements, neutron reflectivity (NR) at the air–water interface, and foaming tests. We varied the concentrations of both the DTAB (0.05 to 5 critical micelle concentration, cmc) and that of PEG-g-PVAc (0.2 and 2 critical aggregation concentration, cac). FindingsOur results show that the interfacial interactions between DTAB and PEG-g-PVAc were both synergistic and antagonistic, depending sensitively on the surfactant concentration. At DTAB concentrations below its cmc, a pronounced cooperative adsorption behaviour was likely driven by the hydrophobic interactions between the DTAB tail and the PVAc grafts and the attraction between the DTAB headgroups and the partially dissociated –O- groups in the partially hydrolysed PVAc grafts, forming a mixed layer. This synergistic adsorption behaviour transitioned to a competitive adsorption behaviour at DTAB concentrations above its cmc, leading to polymer-surfactant partition, forming a “hanging” polymer layer underlying a surfactant monolayer at the interface. We postulate that DTAB/PEG-g-PVAc complexation in the bulk contributed to partial depletion of the mixture from the interface. We therefore consider this polymer/surfactant system to be a moderately interacting system at the air–water interface. No discernible differences in the foaming behaviour were observed between the DTAB/PEG-g-PVAc systems and the pure surfactant. Our results suggest that surfactant headgroup characteristics (particularly charges) were crucial in determining the structure and composition of polymer-surfactant complexes at the air–water interface, as well as the foamability and foam stability, whilst the coexistence of the synergistic and competitive adsorption behaviour is attributed to the unique architecture of the tardigrade polymer with amphiphilicity and partial charge, facilitating different surfactant-polymer interactions at different DTAB concentrations.

Preparation of 9,10-Bis(Phenylethynyl)anthracene and 1-Chloro-9,10-Bis(Phenylethynyl)anthracene nanoparticles using the laser processing in liquids: Influence of the surfactants on the optical properties

Laser processing of 9,10-bis(phenylethynyl)anthracene (BPEA) and 1-chloro-9,10-bis(phenylethynyl)anthracene (CBPEA) in the surfactant solutions of anionic SDS, cationic CTAB, and amphiphilic surfactants of HDDSA and TDDHSA were performed using the second-harmonic (532 nm) of pulsed Nd:YAG lasers. Using the present laser processing techniques, the generation of BPEA and CBPEA nanoparticles was succeeded for the first time. The optical properties of BPEA and CBPEA nanoparticles prepared by the laser processing techniques were measured and compared with the previous work prepared by the precipitation method. The pH dependence of the absorption spectra of BPEA and CBPEA obtained by the laser processing in the amphiphilic surfactants was also investigated and the results for such pH dependence of the absorption spectra were also reported.

Effects of Different Surfactant Charges on the Formation of Gold Nanoparticles by the LASiS Method.

The laser ablation synthesis in solution (LASiS) method has been widely utilized due to its significant prospects in laser microprocessing of nanomaterials. In this study, the LASiS method with the addition of different surfactant charges (cationic CTAB, nonionic TX-100, and anionic SDS) was used to produce Au NPs. An Nd:YAG laser system at 532 nm excitation with some synthetic parameters, including different laser fluences, ablation times, and surfactant concentrations was performed. The obtained Au NPs were characterized by UV-Vis spectroscopy, transmission electron microscopy, and zeta potential analyzer. The Au NPs exhibited the maximum absorption peak at around 520 nm for all samples. The color of Au NPs was changed from red to reddish by increasing the laser fluence. The surfactant charges also played different roles in the Au NPs’ growth during the synthesis process. The average sizes of Au NPs were found to be 8.5 nm, 5.5 nm, and 15.5 nm with the medium containing CTAB, TX-100, and SDS, respectively. Besides, the different surfactant charges induced different performances to protect Au NPs from agglomeration. Overall, the SDS and CTAB surfactants exhibited higher stability of the Au NPs compared to the Au NPs with TX-100 surfactant.

Influence of surfactants with different ionic character on the structure of poly(acrylic acid) adsorption layer on the activated biocarbons surface – electrokinetic and stability studies

Two samples of activated biocarbons obtained from corncobs and peanut shells precursors were applied for poly(acrylic acid) – PAA macromolecules adsorption from the aqueous solutions containing surfactants with different ionic character (non-ionic Triton X-100, cationic CTAB and anionic SDS). The effects of biocarbon structure, solution pH and surfactant type were examined. The structure of PAA adsorption layer without and with surfactant molecules on the activated carbons surface was described based on the adsorption, electrokinetic and stability results obtained from the spectrophotometric experiments, potentiometric titrations, electrophoretic mobility measurements and stability tests. It was shown that the presence of surfactant influences significantly the adsorption affinity of PAA macromolecules for the micro/mesoporous biocarbons and causes changes in both solid suspensions stability.

Micellar and Transition Metal Ion Catalysed Oxidation of Pentanol in Aqueous Medium

Abstract Micelles and 4d- or 5d-transition metal ions have been proved to be effective catalysts for the oxidation of 1-pentanol by Ce(IV) in aqueous medium under pseudo 1st order reaction conditions at 258C. Although cationic micelles show a speed retarding effect, anionic SDS micelles accelerate the reaction rate. The Ir(III) and Ru(III) catalysed reactions show shorter half-lives at micromolar concentration. Active Ce(IV) species are also identified and an explanation of the different catalytic activities of metal ions and micelles is presented. The accumulation of the substrate in the Stern-layer of the SDS micelles is detected. The reaction product is confirmed by melting point analysis, a 2,4-DNP test, and by IR and NMR studies.

Chemical equilibria of Eosin Y and its synthetic ester derivatives in non-ionic and ionic micellar environments

Eosin (EOS) and its synthetic ester derivatives have adequate properties to be employed as histological markers for and as drugs for photodynamic therapy. However, they present a very complex protolytic and tautomeric equilibrium that reflects on their photophysical properties. Hence their biomedical applications are strongly affected by the medium's pH, charge and hydrophobicity. In this study, we evaluated the effects of two neutral (Pluronic® F-127 and P-123) and two ionic (anionic SDS and cationic CTAB) surfactant micelles as a simple membrane model on the protolytic/tautomeric equilibrium of EOS and its ester derivative dyes. Multivariate analysis based on Q-Imbrie's factor and the K-matrix method on the electronic absorption spectroscopy data in different pH conditions allowed for the understanding of the complex protolytic/tautomeric equilibrium, and the influence of medium microenvironment on the EOS dyes at each pH. Our results demonstrated that, when close to physiological pH (~7.4), and electrostatic attraction towards cationic surfaces favor dyes locating close to the micelle's (biomembrane model) interface, where their biomedical applications are favored. Therefore, the analysis in different environments shows that the interactions of EOS and its derivatives with biomembranes can be modulated based on the hydrophobicity of the xanthene derivative and the cell membrane charge.

Overexpression and refolding of human Cyclin D3. A reliable method or not?

Cyclin D3 is a regulatory protein associated in a variety of human tumors. Despite several studies involving Cyclin D1 and D2, there are few articles that investigate the role of Cyclin D3. Therefore, this study aimed to produce and characterize Cyclin D3 using the Escherichia coli expression system and a protein refolding protocol. The anionic detergent SDS was used to solubilize the protein, then the solution were kept at 4 °C to precipitate SDS. After removing the precipitate by centrifugation, the supernatant was applied to the Ni-NTA column to purify His- tagged Cyclin D3. The recombinant protein shown to be refolded in a denaturation study by fluorescence spectroscopy at increasing concentrations of guanidine hydrochloride. The protein secondary structure, evaluated by circular dichroism, is composed of 39 % α helix and 15 % β-strands. In addition, the study aimed to validate the refolding protocol used to obtain Cyclin D3 from E. coli inclusion bodies.

Comparison of the retention of basic compounds in anionic and cationic microemulsion electrokinetic chromatographic systems

Retention of ionizable bases in microemulsion electrokinetic chromatography (MEEKC) has been studied using two different systems with anionic and cationic microemulsions. Microemulsion pseudostationary phase is composed of heptane (oil), 1-butanol (cosurfactant) and sodium dodecyl sulfate (SDS, anionic system) or tetradecyltrimethylammonium bromide (TTAB, cationic system) as surfactant.In contrast with micellar electrokinetic chromatography (MEKC) where the retention of neutral compounds is very different in the two micellar pseudostationary phases (SDS and TTAB, respectively); in MEEKC, neutral compounds present very similar retention factor (k) values in SDS and TTAB microemulsion pseudostationary phases.However, the k vs. pH profiles of protonable bases are very different in the two MEEKC systems. In TTAB system, retention increases with pH because of neutralization of the protonated base and partition of the unionized form into the microemulsion. However, a reversed trend is observed in SDS system. Retention decreases with pH because of the formation of an ionic pair between the protonated base and the anionic SDS, much more retained than the unionized base.Thus, it is demonstrated that the two systems behave very similar in the retention of neutral bases, but completely different for retention of protonated bases.