Comparison of the Performance of Different Bile Salts in Enantioselective Separation of Palonosetron Stereoisomers by Micellar Electrokinetic Chromatography.

Bile salts are a category of natural chiral surfactants which have ever been used as the surfactant and chiral selector for the separation of many chiral compounds by micellar electrokinetic chromatography (MEKC). In our previous works, the application of sodium cholate (SC) in the separation of four stereoisomers of palonosetron (PALO) by MEKC has been studied systematically. In this work, the parameters of other bile salts, including sodium taurocholate (STC), sodium deoxycholate (SDC), and sodium taurodeoxycholate (STDC) in the separation of PALO stereoisomers by MEKC were measured and compared with SC. It was found that all of four bile salts provide chiral recognition for both pairs of enantiomers, as well as achiral selectivity for diastereomers of different degrees. The structure of steroidal ring of bile salts has a greater impact on the separation than the structure of the side chain. The varying separation results by different bile salts were elucidated based on the measured parameters. A model to describe the contributions of the mobility difference of solutes in the aqueous phase and the selectivity of micelles to the chiral and achiral separation of stereoisomers was introduced. Additionally, a new approach to measure the mobility of micelles without enough solubility for hydrophobic markers was proposed, which is necessary for the calculation of separation parameters in MEKC. Under the guidance of derived equations, the separation by SDC and STDC was significantly improved by using lower surfactant concentrations. The complete separation of four stereoisomers was achieved in less than 3.5 min by using 4.0 mM of SDC. In addition, 30.0 mM of STC also provided the complete resolution of four stereoisomers due to the balance of different separation mechanisms. Its applicability for the analysis of a small amount of enantiomeric impurities in the presence of a high concentration of the effective ingredient was validated by a real sample.

Simultaneous separation and determination of three huperzine alkaloids in Huperzia serrata and its preparations by cyclodextrin-modified mixed micellar electrokinetic capillary chromatography.

In this study, a simple and sensitive cyclodextrin-modified mixed micellar electrokinetic capillary chromatography (CD-MEKC) method has been developed for the simultaneous separation and determination of Huperzine A (HupA), Huperzine B (HupB) and Huperzine C (HupC) in Huperzia serrata (H. serrata). The optimal conditions (pH 9.3) were composed of 10 mM sodium tetraborate solution, 40 mM sodium dodecyl sulfate (SDS), 50 mM sodium cholate (SC) and 3.0 mM mono-(6-ethylenediamine-6-deoxy)-ß-cyclodextrin (ED-ß-CD). The separation and determination process were performed on a P/ACE MDQ capillary electrophoresis system, the separation voltage was 15 kV, the temperature was 25 °C and the detection wavelength was 308 nm. Under the optimum conditions, the migration time was less than 9 min. The LOD and LOQ were between 0.38 and 0.80 µg/mL and 1.2-2.3 µg/mL, respectively. The developed method, with excellent precision and accuracy, was applied for the determination of three alkaloids in H. serrata and its formulations.

Effect of Detergents and Osmolytes on Thermal Stability of Native and Mutant Rhodobacter sphaeroides Reaction Centers.

Photosynthetic reaction center (RC) of the purple bacterium Rhodobacter sphaeroides is one of the most well-studied transmembrane pigment-protein complexes. It is a relatively stable protein with established conditions for its isolation from membranes, purification, and storage. However, it has been shown that some amino acid substitutions can affect stability of the RC, which results in a decrease of the RCs yield during its isolation and purification, disturbs spectral properties of the RCs during storage, and can lead to sample heterogeneity. To optimize conditions for studying mutant RCs, the effect of various detergents and osmolytes on thermal stability of the complex was examined. It was shown that trehalose and, to a lesser extent, sucrose, maltose, and hydroxyectoin at 1 M concentration slow down thermal denaturation of RCs. Sodium cholate was found to have significant stabilizing effect on the structure of native and genetically modified RCs. The use of sodium cholate as a detergent has several advantages and can be recommended for the storage and investigation of the unstable mutant membrane complexes of purple bacteria in long-term experiments.

Process optimization in ginseng fermentation by Monascus ruber and study on bile acid-binding ability of fermentation products in vitro.

Ginseng (Panax ginseng C. A. Meyer) is a famous Traditional Chinese Medicine, which is widely used to treat cardiovascular disease. Monascus ruber (M. ruber) is a fungus used in food and medicine fermentation, and lovastatin, its metabolite, is used extensively in the treatment of dyslipidemia. In this study, ginseng has been fermented by M. ruber, and the response surface methodology (RSM) was applied to optimize fermentation parameters to obtain optimal fermentation system, with further exploring to lipid-lowering activity of P. ginseng C. A. Meyer-M. ruber fermentation products (PM). The concentration of ginseng, temperature, and rotating speed were set as variables and the lovastatin yield was optimized by a Box-Behnken design (BBD) analyzed by RSM. The binding capacity of PM for sodium taurocholate and sodium cholate was assayed by UV spectrophotometry. The highest content of lovastatin production (85.53 µg g-1) was obtained at a ginseng concentration of 1.96%, temperature of 30.11 °C, and a rotating speed of 160.47 rpm. PM exhibited bile acid binding capacity, which was stronger than unfermented ginseng. The RSM can be used to optimize the fermentation system to obtain the best fermentation process. In addition, the fermentation of ginseng by M. ruber can enhance the lipid-lowering effect.

An efficient method to quantitatively detect competitive adsorption of DNA on single-walled carbon nanotube surfaces.

In this study, we quantitatively detected adsorption and desorption of DNA molecules that competed with sodium cholate (SC) molecules on single-walled carbon nanotubes (SWNTs) by fluorescence spectroscopy. In previous studies, competitive adsorption and/or replacement were studied based on techniques such as near-infrared (NIR) absorbance and photoluminescence (PL) spectroscopy of SWNTs. In those studies, adsorption of organic molecules was detected as spectral changes in SWNTs, but not in organic molecules. In this study, we employed fluorescent-labeled DNA (Fc-DNA) to detect competitive adsorption through quenching of fluorescent dyes that were attached to DNA molecules. Through this approach, the adsorption behaviors of DNA molecules could be directly determined. Hence, we found that Fc-DNA molecules adsorbed on SWNT surfaces that were pre-wrapped with SC when the SC concentration was reduced. However, when SC concentrations recovered after three days of incubation, detachment of Fc-DNA molecules was observed. In addition, our method could be applied to evaluate the adsorption of fluorescent dyes on SWNT surfaces instead of DNA molecules. Hence, our method is effective in studying competitive adsorption of organic molecules on SWNT surfaces. The obtained information is complementary to that obtained from NIR spectroscopy of SWNTs.

Nanodisc self-assembly is thermodynamically reversible and controllable.

Many highly ordered complex systems form by the spontaneous self-assembly of simpler subunits. An important biophysical tool that relies on self-assembly is the Nanodisc system, which finds extensive use as native-like environments for studying membrane proteins. Nanodiscs are self-assembled from detergent-solubilized mixtures of phospholipids and engineered helical proteins called membrane scaffold proteins (MSPs). Detergent removal results in the formation of nanoscale bilayers stabilized by two MSP "belts." Despite their numerous applications in biology, and contributions from many laboratories world-wide, little is known about the self-assembly process such as when the bilayer forms or when the MSP associates with lipids. We use fluorescence and optical spectroscopy to probe self-assembly at various equilibria defined by the detergent concentration. We show that the bilayer begins forming below the critical micellar concentration of the detergent (10 mM), and the association of MSP and lipids begins at lower detergent levels, showing a dependence on the concentrations of MSP and lipids. Following the dissolution process by adding detergent to purified Nanodiscs demonstrates that the self-assembly is reversible. Our data demonstrate that Nanodisc self-assembly is experimentally accessible, and that controlling the detergent concentration allows exquisite control over the self-assembly reaction. This improved understanding of self-assembly could lead to better functional incorporation of hitherto intractable membrane target proteins.

Sodium Cholate Bile Acid-Stabilized Ferumoxytol-Doxorubicin-Lipiodol Emulsion for Transcatheter Arterial Chemoembolization of Hepatocellular Carcinoma.

PURPOSE: To develop bile acid-stabilized multimodal magnetic resonance (MR) imaging and computed tomography (CT)-visible doxorubicin eluting lipiodol emulsion for transarterial chemoembolization of hepatocellular carcinoma (HCC). MATERIALS AND METHODS: Ferumoxytol, a US Food and Drug Administration-approved iron oxide nanoparticle visible under MR imaging was electrostatically complexed with doxorubicin (DOX). An amphiphilic bile acid, sodium cholate (SC), was used to form a stable dispersion of ferumoxytol-DOX complex in lipiodol emulsion. Properties of the fabricated emulsion were characterized in various component ratios. Release kinetics of DOX were evaluated for the chemoembolization applications. Finally, in vivo multimodal MR imaging/CT imaging properties and potential therapeutic effects upon intra-arterial (IA) infusion bile acid-stabilized ferumoxytol-DOX-lipiodol emulsion were evaluated in orthotopic McA-Rh7777 HCC rat models. RESULTS: DOX complexed with ferumoxytol through electrostatic interaction. Amphiphilic SC bile acid at the interface between the aqueous ferumoxytol-DOX complexes and lipiodol enabled a sustained DOX release (17.2 ± 1.6% at 24 hours) at an optimized component ratio. In McA Rh7777 rat HCC model, IA-infused emulsion showed a significant contrast around tumor in both T2-weighted MR imaging and CT images (P = .044). Hematoxylin and eosin and Prussian blue staining confirmed the local deposition of IA-infused SC bile acid-stabilized emulsion in the tumor. The deposited emulsion induced significant increases in TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) stain-positive cancer cell apoptosis compared to those in a group treated with the nonstabilized emulsion. CONCLUSIONS: SC bile acid-stabilized ferumoxytol-DOX-lipiodol emulsion demonstrated sustained drug release and multimodal MR imaging/CT imaging capabilities. The new lipiodol-based formulation may enhance the therapeutic efficacy of chemoembolization in HCC.

Preparation and evaluation of self-assembly Soluplus®-sodium cholate-phospholipid ternary mixed micelles of docetaxel.

Ternary mixed micelles constituted of Soluplus®, sodium cholate, and phospholipid were prepared as nano-delivery system of the anticancer drug, docetaxel. The formulation of docetaxel-loaded ternary mixed micelles (DTX-TMMs) with an optimized composition (Soluplus®/sodium cholate/phospholipid= 3:2:1 by weight) were obtained. The main particle size of DTX-TMMs was 76.36 ± 2.45 nm, polydispersity index (PDI) was 0.138 ± 0.039, and the zeta potential was -8.46 ± 0.55 mv. The encapsulation efficiency was 94.24 ± 4.30% and the drug loading was 1.25%. The critical micelle concentration value was used to assess the ability of carrier materials to form micelles. The results indicated that the addition of Soluplus® to sodium cholate-phospholipid mixed micelles could reduce the critical micelle concentration and improve the stability. In vitro release studies demonstrated that compared with DTX-Injection group, the DTX-TMMs presented a controlled release property of drugs. In vivo pharmacodynamics results suggested that DTX-TMMs had the most effective inhibitory effect on tumor proliferation and had good biosafety. In addition, the relative bioavailability of mixed micelles was increased by 1.36 times compared with the DTX-Injection in vivo pharmacokinetic study indicated that a better therapeutic effect could be achieved. In summary, the ternary mixed micelles prepared in this study are considered to be promising anticancer drug delivery systems.

Structural, antioxidant and adsorption properties of dietary fiber from foxtail millet (Setaria italica) bran.

BACKGROUND: Foxtail millet (Setaria italica) bran is a by-product of millet processing, rich in dietary fiber (DF) and has great application value. A comparative study was conducted to explore the differences in structural and functional properties among millet bran DF, soluble dietary fiber (SDF) and insoluble dietary fiber (IDF). RESULTS: There was a significant difference in the content of monosaccharides between SDF and IDF, in which xylose, arabinose and glucose were the main compositions. The results of scanning electron microscopy showed that DF and IDF had different forms of network structure, and SDF presented a sign of mutual adhesion. The total phenolic and flavonoid contents were 0.54 and 0.08 g kg-1 in SDF. Antioxidant activity of SDF was higher than that of IDF based on the evaluation of free radical scavenging and iron reducing capacity in vitro. Meanwhile, the glucose dialysis retardation index of IDF and SDF was 12.59% and 9.26% at 30 min, respectively. And, there was no significant difference in the adsorption capacity of glucose among different samples (P > 0.05). Furthermore, SDF had strong α-amylase inhibition (17.92% inhibition rate) and sodium cholate adsorption capacities; the adsorption amount was 16.76 g kg-1 in 2.00 g L-1 sodium cholate solution. CONCLUSION: Foxtail millet bran DF, especially SDF, has good functional properties and would be a suitable ingredient for health-beneficial food production. However, the relevant verification trials in vivo need to be carried out in the next steps. © 2019 Society of Chemical Industry.

A Multiscale Study on the Effect of Sodium Cholate on the Deformation Ability of Elastic Liposomes.

Elastic liposoxy1mes (ELs) are biocompatible bilayer vesicular systems commonly used in the transdermal delivery of drugs. Compared with conventional liposomes (CLs), the strong deformation ability conferred by edge activators (EAs) is one of the most critical properties of ELs. However, due to limited research methods, little is known about the effect of EAs on the deformation abilities of vesicles. In this study, taking sodium cholate as an example, a multiscale study was carried to study the effect of EAs on the deformability of ELs, including in vitro diffusion experiment at macroscale, "vesicle-pore" model experiment at the microscale and flat patch model experiment at the molecular scale. As a result, it was found that sodium cholate could decrease the kc of DPPC bilayer, which enabled it to remain morphologically intact during a strong deformation process. Such kind of differences on deformation ability made pogostone ELs (contain sodium cholate) present a better permeation effect compared with that of pogostone CLs. All of these provide a multiscale and thorough understanding of the effect of sodium cholate on the deformation ability of ELs.

Bile Salts Caught in the Act: From Emulsification to Nanostructural Reorganization of Lipid Self-Assemblies.

Bile salts (BSs) are important for the digestion and absorption of fats and fat-soluble vitamins in the small intestine. In this work, we scrutinized, with small-angle X-ray scattering (SAXS), the crucial functions of bile salts beyond their capacity for the interfacial stabilization of submicrometer-sized lipid particles. By studying a wide compositional range of BS-lipid dispersions using two widely applied lipids for drug-delivery systems (one a monoglyceride being stabilizer-sensitive and the other an aliphatic alcohol being relatively stabilizer-insensitive), we identified the necessary BS to lipid ratios to guarantee full emulsification. A novel ad hoc developed global small-angle-X-ray scattering analysis method revealed that the addition of BS hardly changes the bilayer thicknesses in bicontinuous phases, while significant membrane thinning is observed in the coexisting fluid lamellar phase. Furthermore, we show that a BS strongly decreases the average critical packing parameter. At increasing BS concentration, the order of phases formed is (i) the bicontinuous diamond cubic ( Pn3 m), (ii) the bicontinuous primitive cubic ( Im3 m), and (iii) the fluid lamellar phase ( Lα). These distinctive findings on BS-driven "emulsification" and "membrane curvature reduction" provide new molecular-scale insights for the understanding of the interfacial action of bile salts on lipid assemblies.

Simultaneous separation and determination of praeruptorin A, B and C by micellar electrokinetic chromatography using sodium dodecyl sulphate and sodium cholate as mixed micelles.

INTRODUCTION: Praeruptorin A, B and C are major bioactive constituents in Peucedani Radix. They display anti-inflammatory effect, anti-hypertension effect, antiplatelet aggregation, potential anti-cancer activities and so on. They are worthy of investigation as potentially novel and versatile drugs. OBJECTIVE: To develop a method using micellar electrokinetic chromatography (MEKC) for the application in simultaneously separation and determination of praeruptorin A, B and C from Peucedani Radix and its medicinal preparations. METHODS: Method optimisation was carried out by investigating influences of significant factors on the separation. The method was subjected to validation. The determination of praeruptorin A, B and C in Peucedani Radix and its drug formulations was accomplished by the developed method. RESULTS: The optimal separation condition was 20 mM borate buffer containing 40 mM sodium cholate (SC), 22 mM sodium dodecyl sulphate (SDS) and 25% (v/v) acetonitrile (pH 10.00); 15 kV of voltage; 25°C of temperature; detection at 224 nm. Under this condition, three analytes were baseline separated within 16 min. A good linearity was obtained with correlation coefficients from 0.9988 to 0.9995. The limits of detection (LODs) and limits of quantitation (LOQs) ranged from 0.50 to 0.80 µg/mL and from 1.50 to 2.50 µg/mL, respectively. The recoveries ranged between 95.3% and 103.4%. CONCLUSION: The proposed method has been successfully applied to the simultaneous determination of praeruptorin A, B and C in Peucedani Radix and its pharmaceutical preparations. Additionally, it could be a potential alternative to the quality control of Peucedani Radix.

Application of Fluorescence Emission for Characterization of Albendazole and Ricobendazole Micellar Systems: Elucidation of the Molecular Mechanism of Drug Solubilization Process.

Albendazole (ABZ) and ricobendazole (RBZ) are referred to as class II compounds in the Biopharmaceutical Classification System. These drugs exhibit poor solubility, which profoundly affects their oral bioavailability. Micellar systems are excellent pharmaceutical tools to enhance solubilization and absorption of poorly soluble compounds. Polysorbate 80 (P80), poloxamer 407 (P407), sodium cholate (Na-C), and sodium deoxycholate (Na-DC) have been selected as surfactants to study the solubilization process of these drugs. Fluorescence emission was applied in order to obtain surfactant/fluorophore (S/F) ratio, critical micellar concentration, protection efficiency of micelles, and thermodynamic parameters. Systems were characterized by their size and zeta potential. A blue shift from 350 to 345 nm was observed when ABZ was included in P80, Na-DC, and Na-C micelles, while RBZ showed a slight change in the fluorescence band. P80 showed a significant solubilization capacity: S/F values were 688 for ABZ at pH 4 and 656 for RBZ at pH 6. Additionally, P80 micellar systems presented the smallest size (10 nm) and their size was not affected by pH change. S/F ratio for bile salts was tenfold higher than for the other surfactants. Quenching plots were linear and their constant values (2.17/M for ABZ and 2.29/M for RBZ) decreased with the addition of the surfactants, indicating a protective effect of the micelles. Na-DC showed better protective efficacy for ABZ and RBZ than the other surfactants (constant values 0.54 and 1.57/M, respectively), showing the drug inclusion into the micelles. Entropic parameters were negative in agreement with micelle formation.

Assessment of the functionality and stability of detergent purified nAChR from Torpedo using lipidic matrixes and macroscopic electrophysiology.

In our previous study we examined the functionality and stability of nicotinic acetylcholine receptor (nAChR)-detergent complexes (nAChR-DCs) from affinity-purified Torpedo californica (Tc) using fluorescence recovery after photobleaching (FRAP) in Lipidic Cubic Phase (LCP) and planar lipid bilayer (PLB) recordings for phospholipid and cholesterol like detergents. In the present study we enhanced the functional characterization of nAChR-DCs by recording macroscopic ion channel currents in Xenopus oocytes using the two electrode voltage clamp (TEVC). The use of TEVC allows for the recording of macroscopic currents elicited by agonist activation of nAChR-DCs that assemble in the oocyte plasma membrane. Furthermore, we examined the stability of nAChR-DCs, which is obligatory for the nAChR crystallization, using a 30 day FRAP assay in LCP for each detergent. The present results indicate a marked difference in the fractional fluorescence recovery (ΔFFR) within the same detergent family during the 30 day period assayed. Within the cholesterol analog family, sodium cholate and CHAPSO displayed a minimum ΔFFR and a mobile fraction (MF) over 80%. In contrast, CHAPS and BigCHAP showed a marked decay in both the mobile fraction and diffusion coefficient. nAChR-DCs containing phospholipid analog detergents with an alkylphosphocholine (FC) and lysofoscholine (LFC) of 16 carbon chains (FC-16, LFC-16) were more effective in maintaining a mobile fraction of over 80% compared to their counterparts with shorter acyl chain (C12, C14). The significant differences in macroscopic current amplitudes, activation and desensitization rates among the different nAChR-DCs evaluated in the present study allow to dissect which detergent preserves both, agonist activation and ion channel function. Functionality assays using TEVC demonstrated that LFC16, LFC14, and cholate were the most effective detergents in preserving macroscopic ion channel function, however, the nAChR-cholate complex display a significant delay in the ACh-induce channel activation. In summary, these results suggest that the physical properties of the lipid analog detergents (headgroup and acyl chain length) are the most effective in maintaining both the stability and functionality of the nAChR in the detergent solubilized complex.

Direct Measurement of the Thermodynamics of Chiral Recognition in Bile Salt Micelles.

Isothermal titration calorimetry (ITC) is shown to be a sensitive reporter of bile salt micellization and chiral recognition. Detailed ITC characterization of bile micelle formation as well as the chiral recognition capabilities of sodium cholate (NaC), deoxycholate (NaDC), and taurodeoxycholate (NaTDC) micelle systems are reported. The ΔH(demic) of these bile salt micelle systems is directly observable and is strongly temperature-dependent, allowing also for the determination of ΔCp(demic). Using the pseudo-phase separation model, ΔG(demic) and TΔS(demic) were also calculated. Chirally selective guest-host binding of model racemic compounds 1,1'-bi-2-napthol (BN) and 1,1'-binaphthyl-2,2'-diylhydrogenphosphate (BNDHP) to bile salt micelles was then investigated. The S-isomer was shown to bind more tightly to the bile salt micelles in all cases. A model was developed that allows for the quantitative determination of the enthalpic difference in binding affinity that corresponds to chiral selectivity, which is on the order of 1 kJ mol(-1).

Laccase bioelectrocatalyst at a steroid-type biosurfactant-modified carbon nanotube interface.

Achieving oxygen reduction at high positive potentials with fast heterogeneous electron transfer is desirable for the biocathode of fuel cells based on enzymes. Here, we present an effective interface for obtaining direct electron transfer from a laccase (Lac)-based cathode for O2 reduction, starting from a potential very close to the redox equilibrium potential of the oxygen/water couple. The interface between Lac and single-walled carbon nanotubes was improved by modification with the steroid biosurfactant sodium cholate. The heterogeneous electron-transfer rate between the type-1 Cu site of Lac and the modified electrode was determined to be 3000 s(-1). The electron-transfer rate was sensitive to the side chain of the steroid biosurfactant, and the rate decreased more than 10-fold when sodium deoxycholate was used as the side chain.

Separation mechanisms for palonosetron stereoisomers at different chiral selector concentrations in MEKC.

The separation mechanisms for palonosetron (PALO) stereoisomers in MEKC using sodium cholate (SC) as surfactant and chiral selector have been studied, in a wide range of concentrations below and above the CMC. It was found that SC micelles only provide chirally selective recognition for 3a carbon chiral center in PALO molecules. The resolution of the configurations of 2 carbon chiral center is achieved by the difference of mobility in continuous phase. A schematic diagram depicting the separation mechanisms and the corresponding migration orders among all of four stereoisomers was proposed based on the measured separation parameters. A MEKC method to achieve the complete separation of four stereoisomers in very short time using a very low chiral selector concentration, instead of high concentrations generally considered, was developed based on the understanding of the mechanisms.

Vesicle solubilization by bile salts: comparison of macroscopic theory and simulation.

Lipid metabolism is accompanied by the solubilization of lipid bilayer membranes by bile salts. We use Brownian dynamics simulations to study the solubilization of model membranes and vesicles by sodium cholate. The solubilization pathways of small and large vesicles are found to be different. Both results for small and large vesicles can be compared with predictions of a macroscopic theoretical description. The line tension of bilayer edges is an important parameter in the solubilization process. We propose a simple method to determine the line tension by analyzing the shape fluctuations of planar membrane patches. Macroscopic mechanical models provide a reasonable explanation for processes observed when a spherical vesicle consisting of lipids and adsorbed bile salt molecules is transformed into mixed lipid-bile salt micelles.

Hydrophobicity is the governing factor in the interaction of human serum albumin with bile salts.

The present study demonstrates a detailed characterization of the interaction of a series of bile salts, sodium deoxycholate (NaDC), sodium cholate (NaC), and sodium taurocholate (NaTC), with a model transport protein, human serum albumin (HSA). Here, steady-state and time-resolved fluorescence spectroscopic techniques have been used to characterize the interaction of the bile salts with HSA. The binding isotherms constructed from steady-state fluorescence intensity measurements demonstrate that the interaction of the bile salts with HSA can be characterized by three distinct regions, which were also successfully reproduced from the significant variation of the emission wavelength (λ(em)) of the intrinsic tryptophan (Trp) moiety of HSA. The time-resolved fluorescence decay behavior of the Trp residue of HSA was also found to corroborate the steady-state results. The effect of interaction with the bile salts on the native conformation of the protein has been explored in a circular dichroism (CD) study, which reveals a decrease in α-helicity of HSA induced by the bile salts. In accordance with this, the esterase activity of the protein-bile salt aggregates is found to be reduced in comparison to that of the native protein. Our results exclusively highlight the fact that it is the hydrophobic character of the bile salt that governs the extent of interaction with the protein. Isothermal titration calorimetry (ITC) and molecular docking studies further substantiate our other experimental findings.

Adsorption of phenanthrene on multilayer graphene as affected by surfactant and exfoliation.

Surfactant mediated exfoliation of multilayer graphene and its effects on phenanthrene adsorption were investigated using a passive dosing technique. In the absence of surfactant (sodium cholate, NaC), multilayer graphene had higher adsorption capacity for phenanthrene than carbon nanotube and graphite due to the higher surface area and micropore volume. The observed desorption hysteresis is likely caused by the formation of closed interstitial spaces through folding and rearrangement of graphene sheets. In the presence of NaC (both 100 and 8000 mg/L), phenanthrene adsorption on graphene was decreased due to the direct competition of NaC molecules on the graphene surface. With the aid of sonication, multilayer graphene sheets were exfoliated by NaC, leading to better dispersion. The degree of dispersion depended on the graphene-NaC ratio in aqueous solution rather than critical micelle concentration of NaC, and the good dispersion occurred after reaching adsorption saturation of NaC molecules on graphene sheets. In addition, exfoliation weakened the competition between phenanthrene and NaC and enhanced the adsorption capacity of graphene for phenanthrene due to exposed new sites. The findings on exfoliation of graphene sheets and related adsorption properties highlight not only the potential applications of multilayer graphene as efficient adsorbent but also its possible environmental risk.