mM Of SDS Research Articles

Exploiting the unique specialty of hydrazone functionality: Synthesis of a highly sensitive UV–Vis active solvatochromic probe

The unique physico-chemical attributes of the hydrazone functionality have been extensively studied for a diverse range of chemical, biological and analytical applications. The synthesis of a highly sensitive hydrazone based UV–Vis active solvatochromic probe that exhibits excellent sensitivity toward sensing of solvent polarity, microstructural changes and onset of micellization in aqueous systems was carried out. Specifically, synthesis of 2,4-dinitrophenyl-2-(2-nitrobenzylidene)hydrazone (DNPNBH), through an easy to carry, atom economical, one-pot single step approach via use of low-cost precursors viz. ortho-nitrobenzaldehyde and 2,4-dinitrophenyl hydrazine is presented. The UV–Vis absorption features of the synthesized hydrazone exhibit excellent sensitivity toward the polarity of its immediate microenvironment. The microenvironment polarity sensing potential of DNPNBH is demonstrated for some single solvent systems and DMF-Water mixture as a model binary solvent system and the results are supported by quantum mechanical calculations. Use of the DNPNBH as a probe (at concentrations many orders lower than required for conventional probes) to precisely reflect the onset of micellization and estimation of critical micelle concentration (CMC) of amphiphilic molecules (5.25 mM for SDS, 1.53 mM for CTAB and 0.055 mM for Brij56) in aqueous solutions is also demonstrated. The results clearly qualify the synthesized hydrazone as a highly sensitive UV–Vis probe that can be employed for reliable sensing of solvent polarity, composition dependence of physicochemical attributes in mixed solvent systems and the estimation of CMC of surfactant systems via spectrophotometry.

Purification and characterization of latent polyphenol oxidase from truffles (Terfezia arenaria)

The polyphenol oxidase was extracted and purified from truffles (Terfezia arenaria) and it exhibited a molecular weight of 67 kDa. The truffle PPO was able to oxidize monophenolic, o-diphenolic and triphenolic substrates. Thus, the enzyme seems to be stable under wide range of pH and temperature. Best catalytic efficiency was observed for catechol as substrate (Kcat/km; 674.2 S−1 mM−1).The effect of detergents, chaotropic agents, metal ions and eleven different inhibitors on relative activity of Truffles PPO was also investigated. A latent form of enzyme was observed and its activity was stimulated using 4 mM of SDS. Likewise, the type of inhibition and the values of KI and IC50 were reported for L-cysteine, Sodium fluoride, sodium metabisulfite and kojic acid. Besides, the effect of four concentrations of kojic acid(0.05.,0.1.,0.2 and 0.3 mM) on thermal inactivation of PPO was performed in temperature range “ 60–75° C”. The use of Kojic acid increase the rate of inactivation process and disrupt enzymatic activity. Moreover, the combined effect of temperature and kojic acid prevent from enzymatic browning reaction and maintain high antioxidant activities including ABTS scavenging activity, FRAP, and total phenolic contents.

Sensing of Micellar Microenvironment with Dual Fluorescent Probe, Triazolylpyrene (TNDMBPy)

We report a dual fluorescent triazolylpyrene ((TNDMB) Py) as an efficient fluorescent light-up probe of various micellar microenvironments. The absorption spectra of (TNDMB) Py in an aqueous solution of varying surfactant concentration, CTAB, SDS and TX-100 showed that as the surfactant concentration was increased the absorbance increased with no shift in wavelength maxima. The increase of absorbance in each surfactant solution with increase in surfactant concentration was due to the enhanced solubilization of (TNDMB) Py in surfactant solutions. Our investigations based on steady state and time resolved fluorescence techniques showed that the probe reports the microenvironment of ionic surfactant solutions (CTAB and SDS) via dual emission (LE and ICT) at low surfactant concentration. The ICT band showed a blue shifting pattern with enhanced intensity that disappeared as the concentration of surfactant increases (> 1 mM for CTAB and > 3 mM for SDS). In non-ionic surfactant (Triton X-100) solution, the fluorophore showed dual emission with dominant ICT behaviour over LE emission at low concentration (up to 0.35 mM). In reverse micelle we observed a blue shifted ICT band with no LE band with increasing molar concentration of water. We found 100 nm blue shifting when we moved from R = 0 to R = 7, where R is the molar ratio of water to TX-100 (R = [H2O]/[TX-100]). The blue shifting of ICT band is because of the movement of the probe from hydrophilic core to hydrophobic core (surface) of the reverse micelle. Thus from the steady-state fluorescence study it was observed that the ICT band of the probe, (TNDMB) Py was more influenced by the micellar environment in comparison to the LE band. This difference in behaviour of the fluorophore is probably because of varying extent of hydrophobic/hydrogen bonding interactions experienced by the probe and its relative disposition inside the various micellar nanocores.

Online Coupling of Capillary Electrophoresis with Direct Analysis in Real Time Mass Spectrometry

The online coupling of capillary electrophoresis with ambient direct analysis in real time mass spectrometry (DART-MS) was realized by a coaxial tip interface. The analytes eluted from capillary electrophoresis (CE) were directly ionized by the metastable helium flux produced by DART and transferred into MS for the detection, with which the online separation and simultaneous detection were achieved. The CE-DART-MS can tolerate higher concentrations of detergents and salts than traditional CE-electrospray ionization (ESI)-MS and avoided the difficulties of collecting CE effluent and cleaning the interface, which simplified the experimental procedures and shortened the analysis time. The performance of the technique was successfully verified by capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) using a mixture of 4-aminoantipyrine, zolmitriptan, and quinine. This online technique showed good repeatability with the relative standard deviations (RSDs; n = 5) of 0.56-1.23% for the retention times and 2.01-7.41% for the peak areas. The quantitative analysis of 4-aminoantipyrine was accomplished in the range of 0.01-0.50 mg/mL with the linear correlation coefficient of 0.9995 and limit of detection of 14.7 fmol. Compared with CE-ESI-MS, the ion suppression effects of nonvolatile salts and detergents were efficiently minimized. The signal intensity remained constant when the concentrations reached 100 mM for sodium borate and 30 mM for SDS (in 30 mM sodium borate buffer). In addition, the proposed method was successfully applied to the detection of the endogenous caffeine in Chinese white tea.

Fast investigations from biological matrices using CE – Test of a blood–brain barrier model

In order to adopt a general workflow for complex biological matrices with respect to a new blood-brain barrier (BBB) model, a micellar electrokinetic chromatography method has been developed. The cells forming the BBB have been cultivated in a special cell growth medium in which six drugs (acetaminophen, caffeine, carbamazepine, cimetidine, indometacin and propranolol) have been dissolved and tested for their penetration properties. The results showed good to very good accordance to the reference values. Samples were directly injected onto the capillary without any pretreatment (fused silica capillary, id: 50 μm, L: 48 cm, l: 40 cm). After method development, separations were carried out using a 60 mM borate buffer containing 200 mM of SDS at 30 kV, leading to an analysis time of less than 10 min. Between two runs the capillary was rinsed with a mixture of equal parts of running buffer and isopropanol (70% v/v), which proved to be very effective to remove matrix compounds. An appropriate choice of the detection wavelength (220 or 254 nm) could avoid major interferences between analytes and matrix. The typical RSD% for migration times was approximately 2%, for peak areas, it ranged from 2 to 6%, which was very well acceptable for the generic method used in this study and the low concentrations investigated. The LODs ranged from 10 to 30 ng/mL.

Protein–Surfactant Interaction: Sodium Dodecyl Sulfate-Induced Unfolding of Ribonuclease A

Protein-surfactant interaction is widely studied to understand stability and structural changes in proteins. In this Article, we have investigated SDS-induced unfolding of RNase A using absorbance, intrinsic fluorescence of the protein, anisotropy, TNS fluorescence, and near- and far-UV circular dichroism. Unfolding titration curves obtained from the absorbance and fluorescence changes were fitted into a five-state protein unfolding model by assuming formation of three intermediate states. Free energy changes and m-values of all four transitions between the native and unfolded state were evaluated. The transitions are categorized into two different regions. Region I, up to 0.5 mM of SDS, involves ionic interaction between the protein and SDS where the secondary and tertiary structure of the protein is altered to a less extent. In region II, hydrophobic interaction dominates and has two distinct transitions. The first transition arises from the aggregation of surfactant molecules around the protein hydrophobic sites. In the following transition, the micelles probably expand more, and a few more hydrophobic sites are occupied by the surfactant. In this region, the tertiary contacts are completely broken, and almost 50% of the secondary structure is lost. The aggregation of SDS around the protein starts well below the CMC. These conformational changes can be explained by the necklace and beads model, and the free energy of formation of such a complex for the RNase A-SDS system is found to be 5.2 (±1.0) kcal mol(-1). The probable interaction sites and the mechanism of unfolding have been discussed in detail.

Experimental study on micellar-enhanced ultrafiltration (MEUF) of aqueous solution and wastewater containing lead ion with mixed surfactants

We studied the performance of single and mixed surfactants for removal of Pb 2+ from aqueous solution and wastewater by MEUF. Anionic surfactant, SDS and 2 nonionic surfactants, TX-100 and NP12 were used. The experiments were carried out using a flat sheet module with polyethersulfone membrane (MWCO 10 kDa). Single surfactants, SDS gave high Pb 2+ rejections but low SDS rejections while TX-100 and NP12 showed opposite results. The use of mixed surfactants between SDS and nonionic surfactants can effectively enhance both Pb 2+ and surfactant rejections. The optimum amount of nonionic surfactants added was at mole fractions of 0.1 for both SDS/TX-100 and SDS/NP12 systems in which the highest Pb 2+ rejection can be achieved. At this mole fraction (1.37 mM) of TX-100 and NP12 with 12.3 mM of SDS, the Pb 2+ rejections were higher than 98.4%. High rejections of SDS (80%), TX-100 and NP12 (> 99%) were also obtained. The MEUF showed promising results of real wastewater tested. The analysis of transport resistances showed that polarization resistance was dominant and fouling was very low for both single and mixed surfactants. Fouling resistances of mixed surfactants were higher than that of pure SDS but lower than those of pure nonionic surfactants.

Study of Efficiencies of Selected Extractants: SDS, Iodide, Citric Acid in Soil Remediation from Lead

The effect of anionic surfactant sodium dodecyl sulphate, SDS, utilized individually and also in different combinations with the ligand iodide or citric acid, in leaching of Pb present in contaminated soils was investigated. Remediation studies were carried out at constant pH. Soil samples artificially contaminated by Pb in concentrations between 40–400 mg kg−1 with volume-to-mass (V/m) ratio of 20 mL g−1, and between 80–800 mg kg−1 with V/m of 40 mL g−1 were first treated with SDS, iodide, and citric acid individually. Remediation power of SDS did not exceed 10% at 6–100 mM concentrations. Leaching process was relatively more successful with ligands iodide (50 to 400 mM) and citric acid (2.5 to 20 mM). Desorption of Pb varied between 5 and 75% when only iodide was present in the medium, whereas the percent of desorption was between 4 and 42% in the presence of citric acid alone. Generally, desorption of Pb increased as V/m ratio increased. SDS was then paired with either one of the ligands. The combination of 400 mM iodide with 50 mM SDS having V/m ratio of 20 mL g− 1 resulted in removal of 65 to 75% Pb from the soil; whereas the percent of removal was 75–82% when V/m ratio was 40 mL g−1. The same efficiency was not observed with 100 mM SDS, in which case desorption of Pb was 50 to 65%. When citric acid was used in combination with SDS, it was found to be not as effective as iodide with respect to both V/m ratios of SDS. Highest percentage of Pb removed was 48% when 20 mM citric acid was used in combination with 50 mM of SDS with V/m ratio of 40 mL g−1. The remediation order was: SDS < citric acid < SDS+citric acid < iodide < SDS+iodide.

Application of microchip electrophoresis with electrochemical detection to environmental aldehyde monitoring

A method based on microchip electrophoresis with electrochemical detection has been developed for the simultaneous determination at trace levels of the main small-chain aldehydes (formaldehyde, acetaldehyde and 2-propenal) present in the atmosphere. Sampling was performed by forcing atmospheres through silica-gel cartridges coated with 2,4-dinitrophenylhydrazine (DNPH), where aldehydes were derivatized to form the corresponding hydrazones, which were then injected and eluted into the electrophoresis system. Factors affecting both separation and detection processes were optimized, with best performance achieved by applying a voltage of 2500 V both in the separation and in the electrokinetic injection (5 s) and using a 15 mM borate buffer (pH 9.2) added with 25 mM of SDS and 20% v/v ACN plus 10% v/v 1-propanol. Under these optimal conditions, well satisfactory resolution could be achieved, so that the analytes could be separated and detected within about 400 s, by applying a detection potential of - 1.0 V versus Ag/Ag/Cl to the glassy carbon-working electrode. The recorded peaks were characterized by both a good repeatibility (RSD <3%) and a linear dependence over a wide concentration range (2-100 microg/mL). Detection limits, estimated for a S/N of 3, equal to 9.5, 7.2 and 9.2 microM were inferred for the DNPH derivatives of formaldehyde, acetaldehyde, 2-propenal, respectively. The application of the method to aldehyde analysis in real air samples is also presented.

SPE and large‐volume sample stacking in MEKC for determination of doxycycline in biological fluids: Comparison of direct injection to SPE‐MEKC

A novel and simple method has been developed for the determination of doxycycline (DOX) in biological fluids. The method is based on SPE, large-volume sample stacking (LVSS) and MEKC with UV-DAD detection. Six SPE cartridges have been used in investigation for sample clean up and pre-concentration (Supelco LC-8, LC-18, LC-SCX, and LC-WCX, as well as Strata-X and X-C). DOX was determined on a 56 cm (effective length 50 cm) x 50 microm id fused-silica capillary. The BGE was 20 mM borate buffer, pH 9.3, containing 80 mM SDS and 7.5% v/v of methanol (30 sx50 mbar), and the temperature and voltage were 25 degrees C and 30 kV, respectively. The analytical wavelength was set at 210 nm. Under optimized conditions it is possible to determine DOX in human serum, urine, semen, tears and saliva with recovery of 97.5% (RSD 2.5%). The method was shown to be sensitive (LOD is 1 microg/L) and precise (intra-day RSD 0.2 and 2.4%; inter-days 0.4 and 3.5% for migration time and peak area, respectively). Results for developed SPE-LVSS-MEKC were compared with LVSS-MEKC method with direct sample injection. The new LVSS-MEKC method is presented as a useful technique for rapid determination without extraction procedure of DOX in human urine and serum, using 80 mM of SDS, 10% v/v of methanol and 40 mM borate buffer (pH 9.3; 30 s x 50 mbar; 25 degrees C; 30 kV; 350 nm), but not for the other biological fluids, according to lower sensitivity of the method and because of the sample composition.

Shear rheology and porous media flow of wormlike micelle solutions formed by mixtures of surfactants of opposite charge

The rheology of solutions of wormlike micelles formed by oppositely charged surfactant mixtures (cationic cetyl trimethylammonium p-toluene sulfonate, CTAT, and anionic sodium dodecyl sulfate, SDS), in the dilute and semi-dilute regimes, were studied under simple shear and porous media flows. Aqueous mixtures of CTAT and SDS formed homogeneous solutions for SDS/CTAT molar ratios below 0.12. Solutions of mixtures exhibited a strong synergistic effect in shear viscosity, especially in the semi-dilute regime with respect to wormlike micelles, reaching a four order of magnitude increase in the zero-shear rate viscosity for solutions with 20 mM CTAT. Oscillatory shear results demonstrated that the microstructure of CTAT wormlike micelles is sensitive to SDS addition. The cross-over relaxation times of wormlike micelles of 20 mM CTAT solutions increased by three orders of magnitude with the addition of up to 2 mM of SDS, and the solutions became increasingly elastic. The shear thickening process observed in shear rheology became more pronounced in porous media flow due to the formation of stronger cooperative structures induced by the extensional component of the flow.

Characterization of interactions between chitosan and an anionic surfactant.

Chitosan is a cationic biopolymer that has many potential applications in the food industry because of its unique nutritional and physiochemical properties. Many of these properties depend on its ability to interact with anionic surface-active molecules, such as phospholipids, surfactants, and bile acids. The purpose of this study was to characterize the interaction between chitosan and a model anionic surfactant (sodium dodecyl sulfate, SDS) using isothermal titration calorimetry (ITC), surfactant-selective electrode (SSE), and turbidity measurements. ITC and SSE indicated that SDS bound strongly to chitosan via a highly exothermic interaction. The turbidity measurements indicated that chitosan formed insoluble complexes with SDS that strongly scattered light. The chitosan bound approximately 4 mM of SDS per 0.1 wt % chitosan before becoming saturated with surfactant. The SDS-chitosan interaction was weakened appreciably by the presence of 100 mM NaCl, which suggested that it was electrostatic in origin. This study provides information about the origin and characteristics of molecular interactions between chitosan and anionic surface-active lipids that may be useful for the rational design of chitosan-based food ingredients with specific nutritional and functional characteristics, e.g., cholesterol lowering or fat replacement.

Chiral separation of amino acids by capillary electrophoresis with 3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate as chiral selector

3-[(3-cholamidopropyl)-dimethylammoniol-1-propane sulfonate (CHAPS) can be used as an effective chiral selector for the separation of dansyl-amino acids by capillary electrophoresis (CE). While CHAPS can serve as an chiral selector, better enantiomeric separation can be performed by using CHAPS not as the sole chiral selector but as one of a [CHAPS-SDS-cyclodextrin] three-component system. In this CHAPS-SDS-CD system, enantiomeric separations of the amino acids can be readily accomplished by judiciously adjusting the pH of the solution, concentrations of CHAPS and SDS, and the concentration and type of CD. All amino acids can be baseline resolved in less than 15 minutes with resolution as high as 2.01 at pH 6.5 with 50 mM of CHAPS and 75 mM of SDS. The resolution is also dependent on the size of the CD. Substantial increase in the resolution can be readily achieved by replacing β-CD with γ-CD. For example, theR s for Leu was increased by four-folds (from 1.65 to 6.29) while the elution time still remains as short as 20 min when β-CD was replaced by γ-CD.

Isothermal titration calorimetry study of pectin-ionic surfactant interactions.

Isothermal titration calorimetry (ITC) was used to measure enthalpy changes resulting from injection of anionic (sodium dodecyl sulfate, SDS) or cationic (dodecyl trimethylammonium bromide, DTAB) surfactants into aqueous 1 wt % pectin solutions (30, 60, or 90% methoxylated). In the absence of pectin, the critical micelle concentrations (cmc) determined by ITC were 14.7 mM for DTAB and 7.7 mM for SDS. Binding of DTAB to pectin was endothermic and was attributed to electrostatic attraction between the cationic surfactant and anionic biopolymer. Binding of SDS to pectin was exothermic and was attributed to hydrophobic interactions. Pectin reduced the cmc of SDS, probably because of long-range electrostatic repulsion between the molecules. Above a particular concentration, which depended on pectin and surfactant type, both ionic surfactants promoted pectin aggregation (monitored by turbidity increase). This study demonstrates the potential of ITC for providing valuable information about interactions between polysaccharides and amphiphiles.

High-speed chiral separations on microchip electrophoresis devices.

High-speed electrophoretic chiral separations have been successfully performed in a microfabricated device by employing cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC). Utilizing short separation channels and relatively high field strengths in combination with small volume-defined injection plugs, and operating in counter-electroosmotic flow conditions, fast and efficient separations of fluorescein insothiocyanate (FITC)-labeled amino acid enantiomers were obtained. Analysis time ranged from 75 s for the most basic amino acids to 160 s for the most acidic ones with associated efficiencies from 7000 up to 28 000 effective plates (100 000 to 395 000 plates/m). Buffer parameters were varied in order to study the effect on chiral resolution. A buffer system consisting of 100 mM borate (pH 9.4), 30 mM of SDS, and 10 mM gamma-CD as chiral selector provided adequate resolution of the majority of FITC-amino acid enantiomers tested.