SDS System Research Articles

Preconcentration of 3-nitrotyrosine in urine by transient isotachophoresis in MEKC

Transient isotachophoresis (tITP), usually performed in CZE, is a useful on-line sample preconcentration technique for high saline samples. However, only a few papers have applied tITP in MEKC especially SDS system. This study compared tITP in MEKC with that in CZE for 3-nitro-tyrosine (NT) analysis in urine. No sample clean-up was required. Self-stacking occurred simultaneously as chloride in urine acted as a leading ion. HEPES–Tris buffer at pH 8.2 was used as a terminating electrolyte and separation buffer. UV detection wavelength was set at 426nm. Experiments showed that tITP in MEKC exhibited much higher peak efficiency (up to 1000000), and improved 4-fold sensitivity, compared with those by tITP in CZE. The limit of detection was 0.07μM for 3-nitrotyrosine in urine.

Diffusion NMR study of complex formation in membrane-associated peptides

Pulsed-field-gradient nuclear magnetic resonance (PFG-NMR) is used to obtain the true hydrodynamic size of complexes of peptides with sodium dodecyl sulfate SDS micelles. The peptide used in this study is a 19-residue antimicrobial peptide, GAD-2. Two smaller dipeptides, alanine-glycine (Ala-Gly) and tyrosine-leucine (Tyr-Leu), are used for comparison. We use PFG-NMR to simultaneously measure diffusion coefficients of both peptide and surfactant. These two inputs, as a function of SDS concentration, are then fit to a simple two species model that neglects hydrodynamic interactions between complexes. From this we obtain the fraction of free SDS, and the hydrodynamic size of complexes in a GAD-2-SDS system as a function of SDS concentration. These results are compared to those for smaller dipeptides and for peptide-free solutions. At low SDS concentrations ([SDS] ≤ 25 mM), the results self-consistently point to a GAD-2-SDS complex of fixed hydrodynamic size R = (5.5 ± 0.3) nm. At intermediate SDS concentrations (25 mM < [SDS] < 60 mM), the apparent size of a GAD-2-SDS complex shows almost a factor of two increase without a significant change in surfactant-to-peptide ratio within a complex, most likely implying an increase in the number of peptides in a complex. For peptide-free solutions, the self-diffusion coefficients of SDS with and without buffer are significantly different at low SDS concentrations but merge above [SDS] = 60 mM. We find that in order to obtain unambiguous information about the hydrodynamic size of a peptide-surfactant complex from diffusion measurements, experiments must be carried out at or below [SDS] = 25 mM.

Interaction between Zwitterionic Surface Activity Ionic Liquid and Anionic Surfactant: Na+-Driven Wormlike Micelles

The physicochemical properties of the mixed zwitterionic surface activity ionic liquid/anionic surfactant (N-alkyl-N'-carboxymethyl imidazolium inner salts/sodium dodecyl sulfate, [N-C(12), N'-CO(2)-Im]/SDS) at various molar ratios (R(1) = C([N-C(12),N'-CO(2)-Im])/(C([N-C(12),N'-CO(2)-Im]) + C(SDS)) were investigated by surface tension and steady-state fluorescence measurements. The results show that the mixed [N-C(12), N'-CO(2)-Im]/SDS system has a much lower cmc value and higher surface activity than individual surfactant. Compared with the mixed zwitterionic betaine surfactant/SDS system, the mixture studied exhibits a stronger synergism, i.e., more negative interaction parameters (β(m) and β(σ)). Through addition of NaCl, the wormlike micelles (WMs) could be formed in a [N-C(12), N'-CO(2)-Im]/SDS system. Steady and dynamic rheology was employed to characterize the WMs with different surfactant ratio (R(1)), NaCl concentration, and temperature. An optimal composition, viz., C(T) = 60 mM, R(1) = 0.45, and C(NaCl) = 0.10 M, was detected to form the strongest and longest wormlike micelles. Compared with the WMs formed by a traditional zwitterionic C(12) betaine/anionic surfactant mixture (e.g., laurylamidopropyl betaine/SDS), the WMs studied have a stronger network structure, which is expected to have potential applications in some fields, such as in nanomaterials synthesis, personal care products, and flooding liquid for tertiary oil recovery.

Optimal Control for a Family of Systems in Novel State Derivative Space Form with Experiment in a Double Inverted Pendulum System

Optimal control for a family of systems in novel state derivative space form, abbreviated as SDS systems in this study, is proposed. The first step in deriving optimal control laws for SDS systems is to form an augmented cost functional. It turns out that novel differential Lagrange multipliers must be used to adjoin SDS system constraints (namely, the dynamical equations of the control system) to the integrand of the original cost functional which is a function of state derivatives. This not only eases our derivation but also makes our derivation parallel to that for systems in standard state space form. We will show via a real electric circuit that optimal control for a class of descriptor systems with impulse modes can easily be carried out using our design method. It will be shown that linear quadratic regulator (LQR) design for linear time-invariant SDS systems using state derivative feedback can be obtained via an algebraic Riccati equation. Furthermore, this optimal state derivative feedback may also be implemented using an equivalent state feedback. This is useful in real situations when only states but not the state derivatives are available for measurement. The LQR design for a double inverted pendulum system is implemented to illustrate the use of our method.

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.

Simultaneous removal of cadmium ions and phenol with MEUF using SDS and mixed surfactants

Micellar-enhanced ultrafiltration (MEUF) is a promising technology to remove metal ions and organic contaminants simultaneously from wastewater. A laboratory experiment was conducted to evaluate the efficiency of a MEUF operation for the removal of Cd2+ and phenol using pure SDS and mixed surfactants (Triton X-100/SDS). In pure SDS system, with the increase of the feed SDS concentration, a significant rise in Cd2+ rejection was obtained, which peaked at 97.0% with initial SDS concentration being 8.0mM. Nevertheless, the phenol rejections only kept moderately increasing from 14.5% to 40.0%. In mixed Triton X-100/SDS system, the rejections of Cd2+ and phenol were both enhanced by the moderate addition of nonionic surfactant for the same total feed surfactant concentration as the pure SDS system. With the increase of the molar ratios of Triton X-100 to SDS (α), Cd2+ rejection increased slightly with α ranging from 0 to 0.8, and peaked at 91.3%. And the phenol rejection kept increasing from 27.7% to 42.4% when α was less than 1.0 followed by slight decrease to 40.2% at α=1.5. Moreover, the SDS dosage and the surfactant(s) concentration in permeate were reduced efficiently. The permeate flux of MEUF with mixed surfactants was lower than that with pure SDS.

UV-absorption and fluorimetric methods for the determination of alprazolam in pharmaceutical formulation

The development of UV and fluorescence spectrophotometric methods for the quantitative determination of alprazolam in dosage forms using As(III)−SDS system. The two simple and sensitive, spectrophotometric and spectrofluorimetric methods were developed for the determination of alprazolam (ALP) in tablets. These methods are based on formation of ALP−As(III) complex in the presence of SDS. The UV-spectrum of 30% methanolic solution of ALP (5×10−5M) at pH 6.5 (Mclivaine buffer) was run between 200 and 380nm. The absorption spectrum of ALP exhibits two peaks with a λmax. at 255nm and a weak band at 325nm. When the spectra of the drug were run at varying pH in the region 200–380nm, one isosbestic point at 290nm was observed, which indicated the presence of two ionic conditions in solution. The complex exhibited an absorption maximum at 265nm and emission peak at 520nm with respect to the excitation wavelength of 325nm. The spectrophotometric method was found to be linear in 8.0–17.0μgml−1 range with detection limit of 13.520μgml−1, while 0.05–9.5μgml−1 range was with detection limit of 1.048×10−2μgml−1 by spectrofluorimetric method. The mean percentage recovery of the added quantity was found to be 99.54 (spectrophotometric method) and 100.22 (spectrofluorimetric method) and the %RSD are lower than 0.478 and 0.296 determined spectrophotomerically and spectrofluorimtrically, respectively. This indicates that the proposed method is accurate. The apparent ionization constant of ALP was found to be 9.29. The spectra, experimental conditions were set followed by determination stoichiometry, stability constant and thermodynamic parameters of the As(III), Co(II), Ni(II), and Zn(II) complexes with ALP at pH 6.5. The proposed methods have been successfully applied to the assay of ALP in tablets and the results were statistically evaluated.

A pair of regio-isomeric compounds acting as molecular logic gates with different functions

Regioisomers 6a and 6b display different spectral properties towards pH and surfactant concentration. For compound 6a, an obvious color change from yellow to red and significant fluorescence quenching were observed upon addition of acid, whereas large enhancements in emission and absorption intensities of 6b were found with decreasing pH value. CTAB and Triton X-100 enhanced the fluorescence intensity of both dyes. Small amount of SDS (less than its cmc) quenched, while large amount of SDS ([SDS] > cmc) recovered the fluorescence of 6a and 6b. 6a and 6b can execute different Boolean operations: much more logic functions can be implemented with 6a in SDS system, while half addition can be realized with 6b when both inputs are SDS.

SDS: A Scalable Data Services System in Data Grid

It is very complex and of low efficiency for grid users to access heterogeneous diverse data resources distributed over the whole wide area network. Data Grid has denoted a network of storage resources, from archival systems, to caches, to databases, that are linked across a distributed network. And it should provide integrated, scalable data services which implement more wide range of transparent access to data resources in Data Grid, such as location transparency, time transparency. In this paper, we describe a SDS system which can implement integrated, scalable data services. We have implemented one of the important building blocks for SDS is the server called DSB which can provide integrated data services. The DSB bases on cluster and agent technologies. Agent-based DSB can cleverly prefetch required data, replicate them among DSBs. Each DSB based on cluster implements a single entry and a virtual integrated storage system in a data domain. As far as whole SDS, Multiple DSBs are formed cluster data services, which are scalable, and provide a single entry for all data grid users, and provide a virtual integrated mass storage system, and hide distributed heterogeneous low-level data resources, and insure load balance of each server. SDS architecture supporting these various scenarios, are also described.

STIM1- and Orai1-dependent Store-operated Calcium Entry Regulates Human Myoblast Differentiation

Our previous work on human myoblasts suggested that a hyperpolarization followed by a rise in [Ca(2+)](in) involving store-operated Ca(2+) entry (SOCE) channels induced myoblast differentiation. Advances in the understanding of the SOCE pathway led us to examine more precisely its role in post-natal human myoblast differentiation. We found that SOCE orchestrated by STIM1, the endoplasmic reticulum Ca(2+) sensor activating Orai Ca(2+) channels, is crucial. Silencing STIM1, Orai1, or Orai3 reduced SOCE amplitude and myoblast differentiation, whereas Orai2 knockdown had no effect. Conversely, overexpression of STIM1 with Orai1 increased SOCE and accelerated myoblast differentiation. STIM1 or Orai1 silencing decreased resting [Ca(2+)](in) and intracellular Ca(2+) store content, but correction of these parameters did not rescue myoblast differentiation. Remarkably, SOCE amplitude correlated linearly with the expression of two early markers of myoblast differentiation, MEF2 and myogenin, regardless of the STIM or Orai isoform that was silenced. Unexpectedly, we found that the hyperpolarization also depends on SOCE, placing SOCE upstream of K(+) channel activation in the signaling cascade that controls myoblast differentiation. These findings indicate that STIM1 and Orai1 are key molecules for the induction of human myoblast differentiation.

Human liver dihydrodiol dehydrogenase 1‐catalyzed reaction generating 9α,11β‐prostaglandin F2 from prostaglandin D2 followed by micellar electrokinetic chromatography

An enzyme reaction converting prostaglandin D2 (PGD2) into 9alpha,11beta-prostaglandin F2 (9alpha,11beta-PGF2) by a human liver-originated recombinant dihydrodiol dehydrogenase 1 (DD1) has been studied using CE. Four prostaglandins, viz. PGD2, 9alpha,11beta-PGF2, PGE2, and PGF2a (see Fig. 1, the latter two major PGs are possibly coexisting compounds in the assay mixtures), were completely separated by using SDS or PEG as buffer additives. Because analysis times in the SDS system were shorter than in the PEG system, SDS was employed in measurements of the enzyme activity of DD1. The pH dependence and the reaction temperature dependence of enzyme activity have been studied. The present method enabled us to detect all of the participants in the enzyme reaction: PGD2, 9alpha,11beta-PGF2, nicotinamide adenine dinucleotide phosphate (NADPH), and NADP+. Thus, direct, comprehensive, and reliable analysis of the enzyme reaction becomes possible. Enzyme activity has hitherto been estimated indirectly from the decrease of fluorescence derived from NADPH as an index of progress of the enzyme reactions in batch methods employed in conventional studies. In addition, the low sample consumption characteristic of CE should be a significant advantage of the present method in characterization of less commonly available enzymes such as the recombinant species used in this work.

On-line micellar-enhanced spectrofluorimetric determination of rhodamine dye in cosmetics

A simple FI-fluorimetric analytical methodology for the continuous and sequential determination of rhodamine B (RhB) in cosmetic products has been developed and evaluated in terms of sensibility and selectivity. The influence of several surfactant solutions on RhB fluorescence signal has been studied; particular attention was paid in the aggregation behavior of RhB–SDS system. Linear response has been obtained in the range of 1.6 × 10 −9 and 1 × 10 −6 mol L −1, with a detection limit of 5 × 10 −10 mol L −1. The novel technique provides a simple dissolution of sample, on-line filtration with sampling rate higher than 100 samples h −1 and has been satisfactorily applied to the RhB determination in commercial lipsticks.

Effect of the Chain-Length Compatibility of Surfactants and Mechanical Properties of Mixed Micelles on Surfaces

Force/distance curves for silicon nitride tip/flat silica or alumina coated by a layer of mixed micelles of cationic/anionic surfactant are measured by using AFM. Mixtures of SDS/C(n)TAB (with molecular ratios of 3:1 and 20:1) and C(n)TAB/SDS (with molecular ratio of 85:15) were used for alumina and silica substrates, respectively. The number of carbon atoms per C(n)TAB molecule, n, was in the range of 8 to 16. On the basis of the force/distance curves, the elastic modulus, E, and yield strength, Y, of surface micelles are calculated. It is shown that in surfactant mixtures containing SDS the maximal repulsive force (the barrier F(bar)) at which the tip punctured the micelles, as well as the magnitudes of E and Y, attained the maximal values for C(12)TAB ( i.e., when the hydrocarbon chain lengths of two oppositely charged surfactants are the same). Obviously, it can be related to the highest density structure of these micelles. Note that the literature data for the surface micelles from pure C(n)TAB solutions demonstrate a monotonic dependence of F(bar), E, and Y on n in the range of n = 8-16, whereas the oppositely charged mixed surfactant systems yield much higher values of F(bar), E, and Y than does an equivalent chain length from the homologue series plots. The results obtained for mechanical characteristics of mixed micelles at the surface are compared with the results for the relaxation time, tau(2), that characterizes the lifetime (and therefore structure) of the bulk micelles. Both the dependence of F(bar), E, and Y on n for the surface mixed micelles and tau(2) on n for the bulk mixed micelles demonstrate a maximum at n = 12 for the C(n)TAB + SDS system. This correlation between properties of the surface and bulk micelles suggests that the mechanical properties of the surface micelles are largely determined by the interactions between surfactant molecules with surfactant-substrate interactions playing a secondary role.

The influence of ascorbic acid on the rheological properties of the microemulsion region of the SDS/pentanol/water system

The rheological properties of the microemulsion region of the SDS, pentanol, and water micellar system have been studied experimentally. The W/O and O/W microemulsions behave as typical Newtonian fluids: viscosity remains constant independent of the shear rate. For the bicontinuous system the shear-thinning effect is observed. The addition of ascorbic acid to the system caused a microemulsion viscosity increase, which was the highest in the bicontinuous region and at the lowest temperature.

HCl‐Catalyzed Stereoselective Mannich Reaction in H2O—SDS System.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Adsorption kinetics of surfactant mixtures from micellar solutions as studied by maximum bubble pressure technique

The adsorption kinetics of micellar solutions of anionic/cationic SDS/DATB mixtures with mixing ratios of 10/1 and 10/2, respectively, are studied experimentally by means of the maximum bubble pressure method. For long adsorption times the adsorption of the highly surface-active anionic/cationic complex leads to a decrease of dynamic surface tension in comparison to the single SDS system. However, the situation is the reverse for short adsorption times where the dynamic surface tension is increased by addition of the cationic surfactant, although the overall concentration is increased. This unexpected behavior is explained by partial solubilization of free SDS molecules into micelles formed by SDS/DTAB complexes. With increasing overall concentration, when eventually the CMC of SDS is reached, the anionic/cationic complex itself is solubilized by SDS micelles. Finally, no complex micelles, which for their part can solubilize an excess of SDS molecules, are present. Hence, the dynamic properties of the solution are no longer influenced by the depletion of SDS molecules and the mixture tends to behave like a pure SDS solution.

Detection of HBV DNA using real time analysis.

Isolation of HBV DNA was performed using the MagnaPure LC isolation station (Roche Applied Science, Penzberg, Germany), with a modified protocol HBV-02 to perform a proteinase K digestion initially. DNA was concentrated fourfold. Amplification was performed in a 50 ul reaction mixture, containing 20 ul isolated DNA, 2× TaqMan universal MasterMix (Applied BioSystems). After an incubation step of 2 min at 50 °C to inactivate possible contaminating amplicons using uracyl N -glycosylase, an incubation of 10 min at 95 °C activated AmpliTaq Gold polymerase. The PCR cycling program consists of 50 two step cycles of 15 s at 95 °C and 60 s at 60 °C. All reactions were performed in an 7700 SDS system (Applied BioSystems). * Corresponding author. Tel.: +31-10-463-3431; fax: +3110-463-3441 E-mail address: niesters@viro.fgg.eur.nl (H.G.M. Niesters).

The Scalar Field Equation in Schwarzschild–de Sitter Space

The scalar wave equation between the inner and the outer horizon in the Schwarzschild–de Sitter geometry is solved numerically, and the spatial variations of the field amplitude, as well as of the potential, are shown graphically. By generalizing the "tortoise" coordinate x known from Schwarzschild theory to the SdS system we first transfer the wave equation to a convenient form in which the potential V is written as a function of x. We then show how a useful "tangent" approximation can be introduced which leads to a simple, analytically invertible, relation between x and the radius r. We concentrate on two limiting cases. The first case is when the two horizons are close to each other, the so-called Nariai black hole, and the second case is when the horizons are far apart. Reflection and transmission coefficients are worked out on the basis of a replacement of the real barrier V(x) by a square barrier.

Molecular dynamics simulation of adrenocorticotropin (1-10) peptide in a solvated dodecylphosphocholine micelle.

Adrenocorticotropin (ACTH) (1-10), an adrenocorticotropin hormone fragment, has been studied by molecular dynamics (MD) simulation in an NPT ensemble in an explicit dodecylphosphocholine (DPC) micelle. Two starting configurations of the peptide/micelle system, corresponding to the insertion and surface-binding modes, were used. A common equilibrated configuration, in which the peptide lies parallel to the micellar surface, was reached from both simulations. In the initial part of the simulations, distance restraints derived from NMR nuclear Overhauser enhancements were incorporated before the peptide reached an equilibrium configuration with respect to the micelle. Analyses of the trajectories from the subsequent free (unrestrained) MD simulation showed that ACTH (1-10) does not conform strictly to a helical structure. The loss of the helical structure is due to decreased intramolecular hydrogen bonding accompanied by an increase of hydrogen bonding between the amide protons of the peptide and the micellar head groups. However, the extent of the latter interaction is less pronounced than in the negatively charged SDS micelle. The final structure enhances the amphipathic nature of the peptide, facilitating better interactions at the water-hydrophobic interface. The primary hydrophobic interactions with the micelle came from the side chains of Met4, Phe7, and Trp9. All peptide bonds were either hydrated or were involved in intramolecular hydrogen bonding. The interactions with the DPC micelle, the conformation of the bound peptide, and the dynamics of the peptide, as revealed by the time correlation functions of the N-H bonds, were compared with those of the ACTH (1-10)/SDS system studied previously by MD simulations.

Excited State Proton Transfer as a Probe for Polymer−Surfactant Interaction

Interaction between the polymer, poly(vinylpyrrolidone) (PVP) and an anionic surfactant (sodium dodecyl sulfate, SDS) has been studied using excited-state proton transfer (ESPT) of 1-naphthol as a probe. In aqueous solution, the ESPT process of 1-naphthol is very fast and occurs in ∼35 ps. The kinetics of the ESPT process remains unchanged on addition of 4 mg PVP per mL. However, on addition of SDS, in the presence of PVP, the ESPT process of 1-naphthol is retarded dramatically. Compared to ordinary water, the intensity of the emission of the neutral form of 1-naphthol (at 360 nm) is enhanced ∼200 times in the presence of PVP (4 mg per mL) and 15 mM SDS. In the PVP−SDS complex, the anion emission of 1-naphthol shows a rise time of 1.6 ns and a decay of lifetime 13 ns, while the neutral emission (at 360 nm) exhibits a biexponential decay having components of 1.6 and 5.3 ns. This indicates the existence of two kinds of environment in the SDS−PVP aggregates. In one of them, ESPT of 1-naphthol is totally suppressed leading to a long lifetime (5.3 ns) of the neutral emission. In the other environment, ESPT occurs on a 1.6 ns time scale. The critical association concentration (CAC) of SDS for the PVP−SDS system is 10 times lower than the CMC of SDS.