A capillary electrophoresis study on the influence of beta-cyclodextrin on the critical micelle concentration of sodium dodecyl sulfate

Simultaneous Separation and Determination of Nine Active Ingredients in Sanyetangzhiqing by Cyclodextrin-Modified Micellar Electrokinetic Capillary Electrophoresis-Diode Array Detector

A simple and sensitive strategy using cyclodextrin-modified micellar electrokinetic chromatography with diode array detector was developed and applied for the simultaneous separation and determination of nine components in Sanyetangzhiqing (SYTZQ), a hypoglycemic and hypolipidemic agent. Several important parameters affecting separation performance were evaluated and optimized using single variable methods. Under the optimal conditions, baseline separation of the nine components, including four flavonoids (hyperoside, isoquercitrin, quercetin-3-O-glucuronoside, and astragalin), four phenolic acids (chlorogenic acid, rosmarinic acid, salvianolic acid B, and lithospermic acid), and a monoterpenoids (paeoniflorin), were achieved in less than 16 min. The correlation coefficients of the calibration curves were over 0.9996 for all the analytes. Intraday and interday precisions ranged from 0.4% to 4.8% and 1.7% to 5.0%, respectively. Recoveries of analytes varied from 95.3% to 105%. Validation results as well as the application to analyse SYTZQ samples demonstrated the applicability of the proposed method and thus provided an effective tool for the quality control of SYTZQ. Moreover, with the advantages of short time consuming, low energy consumption, high efficiency, and low cost, this method has laid a foundation for the determination and quality evaluation of multicomponents in Chinese herbal compounds.

Simultaneous determination of mitotane, its metabolite, and five steroid hormones in urine samples by capillary electrophoresis using β-CD2 SDS1 complexes as hydrophobic compounds solubilizers

Mitotane is a cytotoxic drug used in the treatment of inoperable adrenocortical carcinoma, it inhibits steroidogenesis as well, and therefore monitoring the level of steroid hormones in patients treated with mitotane is a crucial point of therapy. Hence, we have developed a simple, fast, and efficient electrophoretic method combined with reverse polarity sweeping as online preconcentration technique and dispersive liquid-liquid microextraction for the simultaneous determination of mitotane, its main metabolite DDA, and five steroid hormones (progesterone, testosterone, epitestosterone, cortisol, and corticosterone) in urine samples. In addition, a new sample matrix consisting of β-CD₂ SDS₁ complexes for a high hydrophobic compounds solubilization was developed. Approach based on the application of β-cyclodextrin and SDS complex of a ratio 2:1 allowed for hydrodynamic injection into the capillary of a solution containing both mitotane and other analytes. The detection limits of the analytes for the reverse polarity sweeping-dispersive liquid-liquid microextraction method were found to be in the range of 1.5-3 ng/mL, which were approximately 1000 times lower than in the conventional hydrodynamic injection (5 s, 0.5 psi) without any preconcentration procedure. All analytes were completely resolved in less than 13 min by uncoated silica capillary with an inner diameter of 75 μm (ID) × 60 cm. Electrophoretic separation was performed in reverse polarity with a voltage of -25 kV with a background electrolyte (BGE) consisting of 100 mM SDS, 25% ACN, 25 mM phosphate buffer (pH 2.5), and 7 mM β-cyclodextrin.

Controlled Formation of Hydrated Micelles by the Intervention of Cyclodextrins

The interaction between surfactants and cyclodextrins (CDs) is well known. Studies have focused mainly on destruction of micelles with CDs to release the encapsulated drugs. However, less emphasis has been given on understanding the formation of micelles with the CD encapsulated surfactants. We have used fluorescence spectroscopy to study the impact of CDs on micelles using a fluorophore that has been tactically designed as a reporter. This molecule has a pyrene moiety on one end and a cationic head group on the other so that the orientation of the compound can be prefixed on micelle formation in aqueous environment. We have observed that the CD encapsulated surfactants can form "hydrated micelles" that allow extensive penetration of water molecules toward the core. The mechanism for such a process involves inclusion of the hydrophobic surfactant tails within the CD core and participation of these inclusion complexes in micelle formation. The process could be controlled by tuning the concentration of CD. The degree of hydration varies as the micelles get more opened up due to the residence of the CDs inside them.

Optimization of the cydex blue assay: A one-step colorimetric protein assay using cyclodextrins and compatible with detergents and reducers

Sodium dodecyl sulfate electrophoresis (SDS) is a protein separation technique widely used, for example, prior to immunoblotting. Samples are usually prepared in a buffer containing both high concentrations of reducers and high concentrations of SDS. This conjunction renders the samples incompatible with common protein assays. By chelating the SDS, cyclodextrins make the use of simple, dye-based colorimetric assays possible. In this paper, we describe the optimization of the assay, focussing on the cyclodextrin/SDS ratio and the use of commercial assay reagents. The adaptation of the assay to a microplate format and using other detergent-containing conventional extraction buffers is also described.

A single step protein assay that is both detergent and reducer compatible: The cydex blue assay

Determination of protein concentration is often an absolute prerequisite in preparing samples for biochemical and proteomic analyses. However, current protein assay methods are not compatible with both reducers and detergents, which are however present simultaneously in most denaturing extraction buffers used in proteomics and electrophoresis, and in particular in SDS electrophoresis. It was found that inclusion of cyclodextrins in a Coomassie blue-based assay made it compatible with detergents, as cyclodextrins complex detergents in a 1:1 molecular ratio. As this type of assay is intrinsically resistant to reducers, a single-step assay that is both detergent and reducer compatible was developed. Depending on the type and concentration of detergents present in the sample buffer, either beta-cyclodextrin or alpha-cyclodextrin can be used, the former being able to complex a wider range of detergents and the latter being able to complex higher amounts of detergents due to its greater solubility in water. Cyclodextrins are used at final concentrations of 2-10 mg/mL in the assay mix. This typically allows to measure samples containing as little as 0.1 mg/mL protein, in the presence of up to 2% detergent and reducers such as 5% mercaptoethanol or 50 mM DTT in a single step with a simple spectrophotometric assay.

Cyclodextrins and surfactants in aqueous solution above the critical micelle concentration: where are the cyclodextrins located?

Cyclodextrins (CDs) are known to bind surfactant molecules below the surfactant critical micelle concentration (CMC); however, interactions of CDs with surfactant micelles (above the CMC) are not well understood. In particular, direct structural evidence of the location of CDs in the different subphases found in micellar solutions is lacking. We have utilized small-angle neutron scattering (SANS) with contrast matching to probe the localization of α-cyclodextrin (α-CD) and 2-hydroxypropyl-β-cyclodextrin (HPβ-CD) in sodium dodecyl sulfate (SDS) micelles in aqueous (D2O) solutions. SANS data from solutions containing either hydrogenated or deuterated surfactants were analyzed by considering three different scenarios pertaining to the localization of cyclodextrin, either all in solution or some in the micelle shell or some in the micelle core, and were simultaneously fitted using the core-shell prolate ellipsoid form factor and the Hansen-Hayter-based structure factor. The scenario that considered a fraction of CD to localize in the micelle core well described the SANS data from both hydrogenated and deuterated SDS-CD-D2O solutions, while the other two scenarios did not. Among the various structural and interaction parameters obtained from this analysis, it emerged that the micelle core consisted of up to ∼10% HPβ-CD or ∼16% α-CD with respect to the total number of molecules (surfactants and CDs) present in the micelle at 25 mM SDS, and up to 14% HPβ-CD or 28% α-CD at 50 mM SDS. This is the first study that provides direct evidence on the location of cyclodextrin in the core of surfactant micelles. An improved understanding of CD interactions with surfactants and lipids would enable better strategies for drug encapsulation and delivery with CDs.

Differentiation of enantiomers by capillary electrophoresis

Capillary electrophoresis (CE) has matured to one of the major liquid phase enantiodifferentiation techniques since the first report in 1985. This can be primarily attributed to the flexibility as well as the various modes available including electrokinetic chromatography (EKC), micellar electrokinetic chromatography (MEKC), and microemulsion electrokinetic chromatography (MEEKC). In contrast to chromatographic techniques, the chiral selector is mobile in the background electrolyte. Furthermore, a large variety of chiral selectors are available that can be easily combined in the same separation system. In addition, the migration order of the enantiomers can be adjusted by a number of approaches. In CE enantiodifferentiations the separation principle is comparable to chromatography while the principle of the movement of the analytes in the capillary is based on electrophoretic phenomena. The present chapter will focus on mechanistic aspects of CE enantioseparations including enantiomer migration order and the current understanding of selector-selectand structures. Selected examples of the basic enantioseparation modes EKC, MEKC, and MEEKC will be discussed.

CE frontal analysis employing contactless conductivity detection for determination of CMCs of non-UV absorbing charged surfactants

Micellar systems composed of surfactants are used extensively in academia and industry for many different applications. In this work a highly versatile CE method for determination of CMCs of charged surfactants has been developed. In the case of positively charged surfactants a coating procedure of the fused-silica capillary was used, whereas negatively charged surfactants were analyzed using uncoated capillaries. The CE method is based on frontal analysis (FA) employing use of contactless conductivity and UV detection. The main advantages of the method are that it can be used for non-UV absorbing surfactants without introducing marker compounds which previously has been found to affect CMCs, requires very limited sample volume and is easily implemented and automated using standard CE equipment. The fact that counterions and different aggregated states are separated allows a detailed characterization of the micelle systems using the developed method. In the case of UV absorbing surfactants similar results were obtained employing contactless conductivity and UV detection. Finally, CMCs obtained using conductometry gave similar results as compared to the developed CE-FA procedure.

Chemometric studies of lysozyme upon interaction with sodium dodecyl sulfate and β-cyclodextrin

The interaction of hen egg-white lysozyme with sodium n-dodecyl sulfate (SDS) as an anionic surfactant was investigated by UV-vis spectrophotometry at different pHs at 25 degrees C using HCl/glycine and NaOH/glycine for acidic and basic pH ranges, respectively. Analysis of the spectral data using chemometric method gave the evidence for the existence of intermediate components during the cited interaction. Results also indicated a connection between turbidity of the protein solution upon interaction with SDS and distribution of our newly found intermediates. As intermediates are important in aggregation of proteins, beta-cyclodextrin was employed as an anti-aggregation agent and the results obtained for the lysozyme-SDS-beta-cyclodextrin ternary system were compared with those obtained in the absence of beta-cyclodextrin on distribution and mole fraction of intermediates with. It is also shown that as the distribution of intermediates broadens in a range of SDS concentrations, the turbidity and aggregation state of solution are reduced.

The application of cyclodextrins in textile area

The application of Cyclodextrins for textiles was reviewed in this paper. Cyclodextrins are crystalline, water soluble, cyclic, non-reducing oligosaccharides consisting of six, seven, or eight glucopyranose units. Cyclodextrins are known as products which are able to form inclusion complexes. The ability of Cyclodextrins to form inclusion complexes can be used, e.g., to remove malodor from textile materials, etc. Furthermore, some modifications of the parent Cyclodextrins are possible. The derivatives can be reactive (e.g. cyclodextrin with a monochlorotriazinyl group), more hydrophilic (by means of hydrophilic side groups, such as hydroxypropyl and hydroxyethyl), less hydrophilic (by means of lipophilic side groups, such as ethylhexyl glycidyl) or ionic (by means of ionic side groups, such as hydroxypropyl trimethyl ammonium chloride).The methods for treating textiles are thus quite simple. The method using anchor-bearing Cyclodextrins is especially useful, since no fixation agent is needed, enabling they use of conventional textile treatment techniques and equipment. Furthermore, this method has virtually no limitations with respect to the textile materials that can be used.

Simultaneous determination of allantoin, choline and L-arginine in Rhizoma Dioscoreae by capillary electrophoresis

A rapid, easy and reproducible capillary electrophoresis (CE) method for the simultaneous determination of allantoin, choline and arginine in Rhizoma Dioscoreae was developed first time. Under the optimum condition, the three analytes could be well separated within 5 min in a 70 cm (60 cm effective length) x 75 microm i.d. capillary. The relative standard deviations for both migration time and peak height were less than 3.20%. The linear response range was 5.0-150, 0.9-100 and 1.0-200 microg/ml for arginine, choline and allantoin, respectively. The detection limit of three components was 2.0, 0.4 and 0.5 microg/ml for arginine, choline and allantoin, respectively. Contents of arginine, choline and allantoin in the crude drug of Rhizoma Dioscoreae could be easily determined by the proposed method with satisfactory results.

Determination of critical micelle concentration of surfactants by capillary electrophoresis

Capillary electrophoresis (CE) has been proven to be a convenient and useful technique for the determination of the critical micelle concentration (CMC) of a surfactant in an electrophoretic system under operating conditions. In this review, methodological approaches to the determination of the CMC of surfactants by CE technique are described. The practical requirements for making such measurements and the CMC values of surfactants determined by CE methods are presented. In addition, difficulties and uncertainty, as well as misconceptions that may arise in the CMC determination are discussed.

Combined effect of SLS and (SBE)7M-β-CD on the solubilization of NSC-639829

Complexation and micellization are two effective ways of solubilizing drugs. In this study, the combined effect of surfactant and complexant on the solubilization of a poorly water soluble compound (NSC-639829) is investigated. With increasing concentration of sodium lauryl sulphate (SLS) in solutions of fixed concentration of (SBE)(7M)-beta-CD, the total solubility of the drug decreases linearly, reaches a minimum and then increases linearly. At each minimum, the molar ratio of SLS to (SBE)(7M)-beta-CD is close to unity. The above observation is attributed to the fact that the surfactant molecule competes with the drug to "fit" in the non-polar cyclodextrin cavity. The surfactant depletes cyclodextrin to form a 1:1 complex. Once the concentration of free SLS reaches the CMC, it starts forming micelles and hence, solubilizes the drug. A slight decrease of the solubilizing power is noticed in the presence of SLS/(SBE)(7M)-beta-CD complex. The combined use of two solubilizing agents, a surfactant and a complexant, results in a much lower solubility than when either one is used alone at the same concentration. The surfactant molecule acts as a competitive inhibitor in the solubilization of the drug by the complexant. Similarly the complexant "pulls" the surfactant out of solution, making it unavailable for solubilizing the drug.

Separation and migration behavior of structurally related phenothiazines in cyclodextrin-modified capillary zone electrophoresis

The influences of buffer pH and the concentration of beta-cyclodextrins (beta-CDs) on the separation and migration behavior of 13 structurally related phenothiazines in CD-modified capillary zone electrophoresis (CD-CZE) using a phosphate background electrolyte at low pH were investigated. We focused on the separation of these phenothiazines, including the enantiomers of chiral analytes, with the use of beta-CD and hydroxypropyl-beta-CD (HP-beta-CD) as electrolyte modifiers or chiral selectors at concentrations less than 8 mM. The results indicate that the interactions of phenothiazines with beta-CDs are very strong and that effective separations of 13 analytes can be achieved with addition of 0.3 mM beta-CD or 0.5 mM HP-beta-CD in a phosphate buffer at pH 3.0. Binding constants of phenothiazines to beta-CDs were evaluated for a better understanding of the interactions of phenothiazines with beta-CDs.