A reverse micelle-mediated dispersive liquid-liquid microextraction coupled to high-performance liquid chromatography for the simultaneous determination of agomelatine and venlafaxine in pharmaceuticals and human plasma

An eco-friendly dispersive liquid-liquid microextraction mediated with a reverse micelle and coupled to an HPLC-DAD was developed for the simultaneous determination of venlafaxine and agomelatine in dosage forms and human plasma. All the parameters affecting the extraction efficiencies of both drugs were investigated and optimized. Under the optimal conditions, an effective analytes' preconcentration with enrichment factors (EFs) up to 72 was achieved. The linearity of the method was established over the concentration range of 0.50-70.0 and 3.0-100.0 ng/mL for venlafaxine and agomelatine, respectively with good correlation coefficients > 0.998. The method exhibited low detection limits in the range of 0.15-0.89 ng/mL and excellent precisions expressed in %RSD < 3% with average recoveries between 95.0 to 101.0%. The proposed method was employed to analyze the targeted analytes in dosage forms and human plasma samples with favorable characteristics like excellent enrichment, high sensitivity, great accuracy, and high precision. Finally, the greenness of the developed method was assessed using three distinct metric tools, confirming the greenness of the proposed method. The findings of this research could have more general implications for the extraction of other analytes from various matrices.

Nanostructured Colloidal Solutions of Malachite Green Formulated: Nonlinear Optical Properties and Simulation

Malachite green (MG) is a dye that has been presented to use as photosensitizers for photodynamic therapy (PDT). Nonlinear absorption coefficient (β) and nonlinear refractive index (n₂) of MG formulations with micelles and its encapsulation are studied aiming PDT. Encapsulation of MG was prepared by the mixture of water droplet in the continuous phase of oil, stabilized with surfactant. MG interacts with micelles and reverses micelle (RM), and the results are related to the size and concentration of micelles, RM, surfactant charge types. At low capsule size, the 1/β linearly increases by the increase of volume fraction of water droplet, while, an exponential behavior was observed in the higher capsule size.

Modifying the proton transfer of 3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazole by water, confinement and confined water

The effect of water, confinement and confined water on the proton transfer of 3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazole (bis-HPTA) was investigated. Water alters the proton transfer process. At higher pH, an anion is formed in water and it undergoes intermolecular proton transfer and forms a keto tautomer. Confinement of molecule in β-cyclodextrin affects the intramolecular proton transfer. It also prevents the intermolecular proton transfer of the anionic form. In reverse micelle, the molecule resides in the interfacial region and interacts with bound water. The intermolecular hydrogen bond of the surfactants opens the intramolecular hydrogen bond in the weaker β-ring of bis-HPTA. It led to single tautomer emission from bis-HPTA. An increase in water amount enhances the relative amount of trans-enol, but predominantly tautomer emission is observed.

Insight into the stability of protein in confined environment through analyzing the structure of water by temperature-dependent near-infrared spectroscopy

To understand the stability of protein in confined environment, the near-infrared (NIR) spectra of aqueous solutions and reverse micelles (RMs) containing bovine serum albumin (BSA), human serum albumin (HSA) and ovalbumin (OVA) were measured at different temperature. With the resolution enhanced spectra calculated by continuous wavelet transform (CWT), the intensity change of the α-helix band at 4617 cm^-1 with temperature shows a clear denaturation of the protein in aqueous solution but not in RMs. The effect of the confined environment on the stability of the proteins is indicated. More importantly, the intensity change of the spectral bands of water around 6956 and 6842 cm^-1 provide an evidence for the denaturation, suggesting that water can be a probe exhibiting the structural change of proteins. Furthermore, comparing the spectral features of different water structures obtained by principal component analysis (PCA) from the spectra of RM with and without BSA, it is demonstrated that the bridging water connecting NH in protein and SO in the inner surface of RM may be the reason for the stabilization.

Photocatalytic performance and interaction mechanism of reverse micelle synthesized Cu-TiO2 nanomaterials towards levofloxacin under visible LED light

The degradation performance of Cu-TiO₂ nanomaterials towards levofloxacin (LFX) antibiotic was investigated under an environmentally benign visible LED light source. Cu-TiO₂ nanomaterials were prepared using the reverse micelle sol-gel method with different copper content ranging from 0.25 to 1.0 wt% concerning titania. Characterization of Cu-TiO₂ samples was performed by XRD, TEM, UV-Vis, BET, ICP-MS, FTIR and XPS techniques. 0.5 wt% Cu-TiO₂ showed crystallite size below 6 nm, surface area (69.85 m²/g) and significant visible light absorption capacity. Both Cu¹⁺ and Cu²⁺ are formed in lower Cu-doped TiO₂ samples, whereas only Cu²⁺ is present in higher Cu-doped TiO₂ samples as evident in XPS analysis. 0.5 wt% Cu-TiO₂ has shown the optimum photocatalytic degradation of 75.5% under 6 h. of a visible light source. FTIR analysis of LFX adsorbed Cu-TiO₂ materials indicated the pollutant-catalyst interaction, where the declining trend was observed in photocatalytic degradation efficiency for higher Cu-doped TiO₂ samples due to copper-LFX complex formation. Copper-LFX complexes are formed due to the presence of Cu²⁺ in higher Cu-doped TiO₂ nanomaterials, which might have hindered the photocatalytic activity under visible light. Effects of initial pollutant concentration, catalyst loading and visible light intensity on the degradation of LFX are studied. Photocatalytic degradation pathways of LFX using best performing Cu-TiO₂ material were also proposed based on the LC-MS analysis.

Enhanced Hydrodynamic Radius of AOT/n-heptane/Water Reverse Micellar System Through Altered Electrostatic Interactions and Molecular Self-Assemblies

We have demonstrated a unique approach to alter the aqueous pool size of an AOT/n-heptane/water reverse micellar system. A positively charged dye Rhodamine B (RhB) and negatively charged Rose Bengal (RB) were incorporated in the reverse micellar pool to investigate the effect of electrostatic interactions and stacking effects among the dye molecules on the AOT/n-heptane/water interface. Dynamic light scattering revealed increase in reverse micellar pool size in presence of positively charged dye aggregates at the oil-water interface. However, less expansion was observed in presence of negatively charged dye aggregates (RB). This confirms the role of electrostatic interaction in modulating the hydrodynamic radius. A head-to-tail type of stacking of RhB molecules at the interface favors this expansion. The differences in stacking of the two dyes inside the reverse micelles and their torsional mobility indicated the role of the reverse micellar interface and H-bonding ability of the microenvironment on dye aggregation. Conductivity measurements demonstrated a significant drop in percolation temperature of the reverse micellar system in presence of dye aggregates. This confirms the effect of dye aggregation and electrostatic interaction on such expansion. This strategy can be exploited for solubilizing greater amounts and a wider variety of drug molecules in microemulsions.

Reversed lipid micellar hollow-fiber liquid-phase microextraction of rotigotine in rat plasma

A hollow fiber liquid phase microextraction (HF-LPME) based on a reversed lipid micelle as the extraction phase was proposed and combined with high performance liquid chromatography (HPLC) for the determination of rotigotine in biological matrix. In the proposed procedure, pieces of hollow fibers were fastened on a magnetic stir bar using a thread to provide better precision. Rotigotine was extracted from 5 mL of diluted plasma sample phase with pH 6 into reversed lipid micelle (5 mmol/L of dipalmitoyl phosphatidyl choline in n-octanol/water) impregnated in both the wall pores and the lumen of the hollow fiber. After the extraction at 900 rpm and room temperature for 30 min, the acceptor phase of reversed lipid micelle was collected for HPLC analysis. Various parameters affecting the extraction efficiency, such as type of surfactant and organic solvent, surfactant concentration, sample phase pH, salt amount, extraction time, stirring rate, and dilution factor of the plasma sample, were investigated and optimized. Furthermore, the formed reversed lipid micelle was characterized by fluorescence method. Under the optimal conditions, the linear range of rotigotine was between 2 ng/mL and 100 ng/mL with determination coefficient (r²) ≥ 0.9913. It is shown from results of method validation that the satisfactory accuracy (the relative errors between -8.5% and 3.3%), precision (the relative standard deviations from 3.8% to 8.9%), stability and matrix effect were obtained. The enrichment factor (EF) of the reversed lipid micelle-based HF-LPME for rotigotine reached 126. And the feasibility of the proposed method was confirmed by the application to the pharmacokinetic study of rotigotine in rat plasma.

Predicting the size of salt-containing aqueous Na-AOT reverse micellar water-in-oil microemulsions with consideration for specific ion effects

HYPOTHESIS

Reverse micellar solutions are thermodynamically stable systems in which surfactant molecules surround water droplets within a continuous organic phase. Among their many applications, they can be used for the synthesis of nanoparticles of controlled agglomeration. Here, we consider the role specific ion effects play in reverse micelle size reduction.

EXPERIMENTS

Dynamic light scattering measurements and the Gouy-Chapman electrical double layer model were combined to study water/AOT/isooctane reverse micellar systems (w_o = 10). Linear relationships between the solvodynamic diameter (D) of reverse micelles containing various concentrations of FeSO₄, Mg(NO₃)₂, CuCl₂, Al(NO₃)₃, Fe(NO₃)₃, Y(NO₃)₃, NaBH₄, ZrOCl₂, and NH₄OH, and their calculated Debye screening lengths, κ^-1, were observed with decreasing D and increasing salt concentration (c).

FINDINGS

By comparing the linear fits for reverse micelle size as a function of c^-1/2, we determined the size can be described as a function of the Debye screening length, cation valency (z), and specific anion hydrated radius (r_an), where D = 3.1z κ^-1 + b_i, and b_i is linearly related to r_an. Our model accurately predicts reverse micelle sizes with the addition of monovalent, divalent, and trivalent salts for which the primary hydrolyzed cation species has a charge that is equal to the cation valency.

Determination of teicoplanin in human plasma by reverse micelle mediated dispersive liquid-liquid microextraction with high performance liquid chromatography

A reverse micelle mediated dispersive liquid-liquid microextraction (RM-DLLME) combined with high performance liquid chromatography-ultraviolet detector (HPLC-UV) was developed for extraction and determination of 5 A₂ components of teicoplanin (TA_2-1, TA_2-2, TA_2-3, TA_2-4, TA_2-5) in human plasma, and the mechanism of RM-DLLME was analysed and explored. In this method, 80 µL of the reverse micelle solution of cetylpyridinium chloride/n-hexanol (15 mmol/L) was used as the extraction solvent for the separation, extraction and enrichment of the teicoplanin in plasma sample. All factors affecting the extraction efficiencies of the target analytes, such as the amounts of acetonitrile and chloroform, the type and volume of reverse micelle solution, pH and volume of sample phase, dispersant, salt addition, extraction mode and time, centrifugation rate and time, were investigated and optimized. Under the optimum conditions, the 5 A₂ components of teicoplanin achieved effective enrichment with the enrichment factors of 228-347 and obtained good linearity in the range of 0.8375-100.5 µg/mL with correlation coefficients higher than 0.9960. The limits of detection were ranged between 0.5025-3.015 µg/mL. Relative standard deviation values of the method precisions were lower than 10.6% and the average recoveries were in the range of 82.7-111.3%. The determination results of the method were demonstrated with favorable characteristics, such as high enrichment, good selectivity and sensitivity, satisfactory precision and accuracy, and this method could be employed to analysis of the teicoplanin in human plasma samples.

Critical kinetic parameters and rate constants representing lipid peroxidation as affected by temperature

This study aimed to comparatively investigate the temperature effect on the kinetic parameters and rate constants representing lipid hydroperoxides (LOOH) formation and decomposition during initiation and propagation peroxidations. The initiation phase was characterized by induction period IP, overall initiation rate constant k_IP, initiation oxidizability O_i, and the critical reverse micelle concentration of LOOH, CMC_L. The propagation phase was characterized by its duration t_p, the maximum rate of LOOH accumulation R_max, maximum LOOH concentration [LOOH]_max, propagation oxidizability R_n, composite rate constant k_c, and LOOH decomposition rate constant k_d. O_i and R_n indicated relatively high dependencies on temperature, respectively. Among the rate constants, k_d better highlighted oxidizabilities as affected by temperature. The oxidizabilities had good correspondences with the Arrhenius kinetic (A and E_a) and Eyring thermodynamic (ΔS⁺⁺ and ΔH⁺⁺) parameters. The most endergonic reactions (ΔG⁺⁺>0) were LOOH decompositions, followed by LOOH formations during the propagation and initiation phases, respectively.

Enhancing enrichment ability of ZIF-8 mixed matrix membrane microextraction by reverse micelle strategy for analysis of multiple ionizable bioactive components in biological samples

Recent research aimed at the design of mixed-matrix membrane (MMM) to be used for microextraction emphasized on membrane extraction phase with high surface area and porosity. This study explored the influence that surfactants have on MMM extraction efficiency for the first time. The zeolitic imidazolate framework 8-based MMM (ZIF-8-MMM) was synthesized by in situ self-assembly of ZIF-8 on the inner wall of a hollow fiber membrane with the aim of fabricating a microextraction device. By prompting the encapsulation of ionizable analytes in the polar core of reverse micelles, the presence of surfactants in extraction solvent assisted the dissolution of analytes in the fiber membrane lumen and enhanced their adsorption onto ZIF-8. Notably, hereby a microextraction method based on the novel ZIF-8-MMM-reverse micelle (ZIF-8-MMM-RM) system was developed and employed for the extraction and quantitation of two alkaloids (berberine and jatrorrhizine) and two flavonoids (wogonin and wogonoside) in biological samples. The main factors affecting microextraction performance, identity of the extraction solvent, surfactant concentration, sample solution pH and extraction time, were investigated in detail. The method showed good linearity (r² > 0.99) and repeatability (RSD < 10%), low limits of detection (0.10-0.31 ng mL^-1) and high relative recoveries (90.03-98.84%). The enrichment factor values ranged between 48.47 and 54.96. Reverse micelle formation prompted by surfactant addition was demonstrated to effectively assist the extraction of multiple ionizable analytes from biological samples, resulting in a marked improvement of ZIF-8-MMM extraction performance.

The Influence of Anionic, Cationic Surfactant and AOT/Water/Heptane Reverse Micelle on Photophysical Properties of Crocin: Compare with RPMI Effect

Encapsulation of crocin (CN), having large nonlinear optical (NLO) properties, can be utilized in studies of photodynamic therapy (PDT). For this purpose, photo-physical and NLO properties of CN encapsulation with and without cell culture medium (CCM) were investigated. As well, nonlinear absorption (NLA) coefficient and nonlinear refractive (NLR) indices were found to be 10^-7 (cm W^-1) and 10^-12 (cm² W^-1); respectively. The results revealed that NLO properties of CN had changed through its dipole moment. Reflecting on the theory of Bilot and Kawski, it was evidenced that the dipole moment of CN could change with a nano-droplet size. Furthermore, it was demonstrated that RPMI-1640 as a growth medium had failed to change NLO properties of CN encapsulated in nano-droplet. Accordingly, the encapsulated CN in nano-droplet in the form of a photosensitizer (PS) was suggested as a good candidate to examine PDT under in-vitro conditions.

Correlation of micellar aggregation - complexation regimes to discern stability of micellar structure and nano-encapsulation

HYPOTHESIS

The physico-chemical mechanisms associated reverse micelle based encapsulation processes deserve investigation owing to the direct correlation between stability of micellar structure and nano encapsulation. The presence of core nanoparticles is expected to influence the stability of micellar structure when the concentrations of surfactant and particle concentration are varied. Hence, it should be possible to define the micellar aggregation - complexation regimes and systematic measurements have robust implications for nano encapsulation.

EXPERIMENTS

Reverse micelle systems stabilized by non-ionic surfactant are formulated with the presence of core nanoparticles. Micellar aggregation and complexation processes are analyzed in two different oil phase (n-hexane and n-butanol). The regimes are probed by measuring average hydrodynamic diameter of reverse micelle, optical transmittance and specific conductivity. Shell encapsulation experiments are performed in aggregation and complexation regimes.

FINDINGS

When the concentration of surfactant increases, reverse micelle size increases (to dia ∼ 200 nm). This is a reversal of the otherwise reported trend wherein the core is absent. Breakdown of stable reverse micellar structure obstructs shell coating and this is a first attempt to analyze micellar aggregation - complexation regimes with the presence of core. Reverse micelle breakage or complexation is to be completely avoided to achieve core@shell nanoparticles.

One-step synthesis of cellooligomer-conjugated gold nanoparticles in a water-in-oil emulsion system and their application in biological sensing

Monodisperse gold nanoparticles (GNPs) were synthesized in a water-in-oil emulsion system (reverse micelles) composed of 80% N-methylmorpholine N-oxide (NMMO)/20% H₂O and dodecane, stabilized with an anionic surfactant: bis(2-ethylhexyl)sulfosuccinate sodium salt. Cellooligomers with a degree of polymerization of 6 or 15 (βGlc6 or βGlc15, respectively), which were labeled at each reducing end group with thiosemicarbazide (TSC) and dissolved in the aqueous NMMO phase, were successfully conjugated to the surfaces of GNPs in situ during spontaneous NMMO-mediated gold reduction. As-synthesized βGlc6-GNPs and βGlc15-GNPs had average diameters of 11.3 ± 2.1 and 10.5 ± 0.7 nm, respectively, while their surface sugar densities were 0.21 and 0.51 chains nm^-2, respectively. Concanavalin A (ConA), a lectin that recognizes non-reducing end groups of glucose residues, aggregated with βGlc15-GNPs with higher sensitivity than it did with βGlc6-GNPs, possibly as a result of the sugar density on the GNP surfaces. The aggregates were rapidly re-suspended by adding methyl-β-d-glucopyranoside as a binding inhibitor. Other lectins and proteins showed no interaction with βGlc-GNPs. Therefore, clustering of glucose non-reducing ends on the GNP surfaces via strong intermolecular association of cellooligomers, possibly led to high affinity for ConA. This facile synthesis route to structural carbohydrate-decorated GNPs has potential applications in carbohydrate-nanometal conjugate nano-biosensor development.

Water loading driven size, shape, and composition of cetyltrimethylammonium/hexanol/pentane reverse micelles

Cetyltrimethylammonium bromide (CTAB)/hexanol reverse micelles have found a variety of applications that demand control over physical parameters. Water content or loading is among the most basic tunable components and is the major driver of the physical properties of these systems. This study uses small-angle scattering with contrast variation to characterize these systems as a function of water loading. The scattering data were analyzed with a variety of approaches, resulting in converging physical specifications. Equations that describe basic physical parameters were determined that allow for characterization and manipulation of the CTAB/hexanol reverse micelle surfactant system. The shape of the reverse micelles was revealed to be slightly ellipsoidal and varies slightly through the water loading range. The surfactant shell is shown to contain a higher fraction of hexanol upon addition of water. Analysis reveals that the size, shape, and surfactant/cosurfactant composition are directly tunable by variation of the water content and that these properties are consequences of the balance of forces present in the reverse micelles.

Ultrasonically formation of supramolecular based ultrasound energy assisted solidification of floating organic drop microextraction for preconcentration of methadone in human plasma and saliva samples prior to gas chromatography-mass spectrometry

In this work, an ultrasonic-assisted supramolecular based on solidification of floating organic drop microextraction (UA-SM-SFO-ME) was developed as a green method for preconcentration of methadone prior to gas chromatography-mass spectrometry (GC-MS). The supramolecular solvent aggregates containing reverse micelles of 1-dodecanol in tetrahydrofuran (THF) were formed by ultrasonication that subsequently dispersed in the sample solution. Ultrasonic waves caused the fast formation of supramolecular solvent aggregates. In this work, ultrasonication was used in two phases: First phase, the formation of reverse micelles and the second phase, the dispersion of supramolecular solvent in the sample solution. Actually, ultrasonication was basic of this presented work. In order to provide the highest extraction efficiency, the influence of various parameters on the method performance (supramolecular solvent type and volume, disperser solvent condition, pH, extraction time and salt concentration) was investigated. Based on the obtained optimum conditions, the limits of detection (LODs) and the limits of quantitation (LOQs) were obtained 0.5-1.2 µg L^-1 and 1.2-2.5 µg L^-1 with preconcentration factors in the range of 182-191, in water and biological samples, respectively. Subsequently, the method was assessed for preconcentration of the methadone in human plasma and saliva samples.

Toward comprehensive measurement of protein hydration dynamics: Facilitation of NMR-based methods by reverse micelle encapsulation

Protein-water interactions are a fundamental determinant of protein structure and function. Despite their importance, the molecular details of water orientations and dynamics near protein surfaces remain poorly understood, largely due to the difficulty of measuring local water mobility near the protein in a site-resolved fashion. Solution NMR-based measurement of water mobility via the nuclear Overhauser effect was presented as a method for performing comprehensive, site-resolved measurements of water dynamics many years ago. Though this approach yielded extensive insight on the dynamics and locations of waters buried within proteins, its promise for measuring surface hydration dynamics was impeded by various technical barriers. Over the past several years, however, this approach has been pursued anew with the aid of reverse micelle encapsulation of proteins of interest. The confined environment of the reverse micelle resolves many of these barriers and permits site-resolved measurement of relative water dynamics across much of the protein surface. Here, the development of this strategy for measuring hydration dynamics is reviewed with particular focus on the important remaining challenges to its widespread application.

Rose Bengal attached and dextran coated gadolinium oxide nanoparticles for potential diagnostic imaging applications

We report here, reverse micelle mediated synthesis of multifunctional dextran (dex) coated Gd₂O₃ nanoparticles (NPs) carrying rose bengal (RB) dye for magnetic resonance and optical imaging. The diameter of these RB attached dex coated Gd₂O₃ NPs (Gd-dex-RB NPs) was found to be ~17 nm as measured by TEM. NMR line broadening effect on the surrounding water protons affirmed the paramagnetic nature of these NPs. Optical properties of Gd-dex-RB NPs were validated by UV-Vis and fluorescence spectroscopy. Time dependent release profile of RB from NPs at two different pH of 7.4 and 5.0 revealed that these NPs behave as slow releasing system. In-vitro study revealed that NPs are efficiently taken up by cells and show optical activity in cellular environment. In vitro cell viability (SRB) assay was performed on cancerous (A-549, U-87) and normal (HEK-293) cell lines, showed the absence of cytotoxic effect of Gd-dex-RB NPs. Therefore, such multifunctional NPs can be efficiently used for bio-imaging and optical tracking.

PEG coated and doxorubicin loaded multimodal Gadolinium oxide nanoparticles for simultaneous drug delivery and imaging applications

We report water-in-oil microemulsion mediated synthesis of PEG¹ coated Gd₂O₃ NPs² loaded with fluorescent anti-cancer drug dox³ for synchronous drug delivery, optical and MR⁴ imaging applications. These PEG covered Gd₂O₃ NPs loaded with dox (Gd-PEG-dox NPs) were found to possess spherical morphology with 13nm size as measured from TEM and the hydrodynamic diameter comes out to be 37nm as determined from DLS. Fluorescence spectra and fluorescence microscopy images confirmed optical activity of the NPs. The paramagnetic nature of NPs was affirmed by NMR line broadening effect on the spectrum of surrounding water protons. Therefore, these particles can be efficiently used as CA⁵ in MR imaging. In vitro analysis showed significant cellular uptake of particles by A-549 cells. A pH dependent drug release pattern was observed for the NPs. Cell viability assay performed on A-549, PANC-1 and U-87 cancerous cell lines revealed that Gd-PEG-dox NPs are cytotoxic. On the basis of these observations, it can be concluded that these multi-modal paramagnetic NPs promise potential cancer therapy along with optical and MR imaging applications.

Micellization in vegetable oils: A structural characterisation

The solubilisation of polar and polyphenol antioxidant in vegetable oils was studied. It was shown that the use of a polyglyceryl-3-diisostearate (PG3DS), a bio-sourced emulsifier well known in cosmetics, increases the yield of solubilisation thanks to some aggregation properties analysed using x-ray scattering technique. We show indeed that PG3DS forms reverse aggregates with a critical concentration that depends on the oil polarity. PG3DS reverse aggregates are elongated with a polar core and cannot be really swollen by addition of water. This supramolecular organisation allows however an efficient solubilisation of polar antioxidants in vegetable oils.

Reverse micellar extraction of bromelain from pineapple peel--Effect of surfactant structure

Pineapple peel is generally disposed or used as compost. This study was focused on extracting bromelain from pineapple peel by using reverse micelles. It was found that gemini surfactant C12-8-C12·2Br (octamethylene-α,ω-bis(dimethyldodecylammonium bromide)) showed distinctive advantage over its monomeric counterpart DTAB (dodecyl trimethyl ammonium bromide); under optimized condition, the bromelain extracted with C12-8-C12·2Br reverse micelle had an activity recovery of 163% and a purification fold of 3.3, while when using DTAB reverse micelle, the activity recovery was 95% and the purification fold was 1.7. Therefore, the spacer of gemini surfactant should play a positive role in bromelain extraction and may suggest the potential of gemini surfactant in protein separation since it has been so far rarely used in relative experiments or technologies.

Water-in-oil microemulsion doped with gold nanoparticle decorated single walled carbon nanotube: scaffold for enhancing lipase activity

The present work reports the development of water-in-oil (w/o) microemulsion doped with newly designed nanocomposite comprising of gold nanoparticle (GNP) decorated single walled carbon nanotube (SWNT). This nanocomposite included cationic reverse micelle was used to boost the catalytic activity of a surface-active enzyme, Chromobacterium viscosum lipase (CV lipase). SWNT was non-covalently dispersed using cetyltrimethylammonium bromide (CTAB), cetylalaninetrimethylammonium chloride (CATAC) while GNP was synthesized by reduction of HAuCl4 with reducing/stabilizing agent trisodium citrate. Counterion exchange between cationic SWNT dispersing agent and anionic capping agent of GNP led to the formation of GNP decorated SWNT (SWNT-GNP) nanocomposite. This newly developed SWNT-GNP included CTAB reverse micelle was characterized by several microscopic and spectroscopic techniques. Interfacially located SWNT-GNP included w/o microemulsion (confirmed from biphasic and fluorescence experiment) was used as a proficient host for enhancing the catalytic activity of lipase. Lipase activity within this self-assembled soft nanocomposite improved up to 3.9-fold (second order rate constant, k2=1694±16 cm(3) g(-1) s(-1)) compared to standard CTAB reverse micelle (k2=433±7 cm(3) g(-1) s(-1)). In case of cetyltripropyl ammonium bromide (CTPAB) based reverse micelle, the observed lipase activity improved to k2=2036±11 cm(3) g(-1) s(-1) in the presence of SWNT-GNP composite. Notably, this catalytic activity of lipase within SWNT-GNP included reverse micelle was till date the highest activity found in any w/o microemulsion. The attainment of flexibility in enzyme conformation at the augmented interface was verified using circular dichroism (CD) spectroscopy.

Protein and water confined in nanometer-scale reverse micelles studied by near infrared, terahertz, and ultrafast visible spectroscopies

Protein-containing reverse (PCR) micelles are suitable systems to study the properties of proteins and waters in a cell-like environment. A model for determining the structural parameters of PCR micelles, such as the aqueous cavity size and molecule number of water within the reverse micelle, is presented. The model is based on an important hypothesis that the structural parameters of the protein-unfilled reverse micelle do not change after solubilization of protein. I describe a procedure using near infrared spectroscopy of OH stretching vibration band of water to verify the hypothesis. Further, the terahertz (THz) absorption spectrum of myoglobin is derived from THz time-domain spectroscopy of the PCR micellar solution, and the states of waters in reverse micelles with and without protein are discussed on the basis of the structural parameters. The last topic is on internal dynamics of PCR micelles on timescales from femtoseconds to nanoseconds studied by femtosecond time-resolved fluorescence spectroscopy.