Rapid and quantitative determination of critical micelle concentration by automatic continuous mixing and static light scattering

Efficiency of single pharmaceutical surfactants to mimic intestinal biorelevant media solubilization and dissolution of etravirine: Comparison of intrinsic and film dissolution models

We understand that quality control dissolution media may best anticipate in vivo product performance by mimicking in vivo media, but preferably involve at most a single pharmaceutical surfactant for routine laboratory use. The objective here was to estimate the concentrations of six pharmaceutical surfactants to mimic etravirine solubility and intrinsic dissolution rate, as well as dissolution rate from a film model, in each Fed State Simulated Intestinal Fluid Version 2 (FeSSIF-V2) and Fasted State Simulated Intestinal Fluid Version 2 (FaSSIF-V2). Solubility studies and colloid sizing measurements were conducted. Results indicate that all six surfactants were more efficient than FeSSIF-V2 or FaSSIF-V2 at solubilizing drug, and also exhibited higher micelle diffusivities than FeSSIF-V2 and FaSSIF-V2 mixed-micelles. The rank-order potency (on mM basis) of the six pharmaceutical surfactants to mimic etravirine solubility in each FeSSIF-V2 and FaSSIF-V2 was: polysorbate 80 (PS80) > polysorbate 20 (PS20) > polyoxyethylene(23) lauryl ether (POE23) > POE10 > hexadecyltrimethylammonium bromide (HEX) > sodium lauryl sulfate (SLS). This rank-order potency was almost the same to mimic drug dissolution rate into each FeSSIF-V2 and FaSSIF-V2, except POE10 > POE23. For the most potent surfactant, PS80, 0.461 mM and 0.140 mM PS80 was estimated to mimic etravirine's solubility and dissolution rate into FeSSIF-V2, respectively, using the intrinsic dissolution model. The low PS80 concentration to mimic dissolution rate reflects the relatively high diffusivity of PS80 micelles, compared to FeSSIF-V2 mixed-micelle diffusivity, which was the case for all six pharmaceutical surfactants. Results are also presented in terms of a film dissolution model for surfactant-mediated dissolution, where dissolution enhancement was less than that in the intrinsic dissolution model, and the film model required lower surfactant concentration than in intrinsic dissolution model to mimic FeSSIF-V2-enhanced dissolution. Findings have promised to identify single pharmaceutical surfactant concentrations that mimic key performance attributes of biorelevant media.

Application of Alcohols to Inhibit the Formation of Ca(II) Dodecyl Sulfate Precipitate in Aqueous Solutions

The presence of alkaline earth cations, in particular, Ca2+ and Mg2+ ions in brine, causes undesired effects in solutions containing anionic surfactants because of precipitate formation. In the present study, an anionic surfactant, sodium dodecyl sulfate (SDS), was investigated, focusing on the determination of various properties (surface tension, critical micelle concentration, micelle size, turbidity) in the presence of alcohols and, in particular, the inhibition of the precipitation of SDS with calcium ions. The calcium ions were added to the surfactant in increasing concentrations (3.0-10.0 g/L), and short-carbon-chain alcohols (methanol, ethanol, n-propanol and n-butanol) were used to shift the onset of precipitate formation. The critical micelle concentration (CMC) of SDS in the presence of alcohols was also determined. It was established that among these alcohols, methanol and ethanol did not exert significant effects on the solubility of the Ca(DS)2 precipitate, while n-propanol and n-butanol were found to be much more efficient inhibitors. In addition, all the alcohols in the applied concentration range (up to 20 V/V%) were found to decrease the critical micelle concentration of SDS.

A novel theoretical strategy for predicting dissolution kinetics and mechanisms of pharmaceuticals in complex biorelevant media

The influence mechanism of biorelevant media on the dissolution of active pharmaceutical ingredients (APIs) is the key to their formulation design. The dissolution kinetics of naproxen (NAP) and indomethacin (IND) in biorelevant media was systematically investigated. The dissolution mechanism was analyzed by chemical potential gradient model to explore the influence of surfactant type, pH and ionic strength. Hexadecyl trimethyl ammonium bromide (CTAB) is superior to sodium dodecyl sulfate (SDS) in promoting the dissolution of NAP and IND by increasing the solubility and accelerating the surface reaction processes. The electrostatic repulsion between SDS and NAP and IND with the same negative charge facilitates the diffusion of API, while the mutual attraction between CTAB and NAP and IND is not conducive to diffusion. High pH was favorable for the dissolution of acidic NAP and IND, as the simultaneous increase in solubility, surface reaction constant, and diffusion constant. High ionic strength was beneficial for the surface reaction of NAP and IND, but hindered their diffusion. It was shown that the modeling results were in conformity with the in vitro experimental data. These results are expected to provide theoretical supports for the design of biorelevant media and pharmaceutical formulations in the pharmaceutical development.

Polyethylenimine/cGAMP Nanocomplexes for STING-Mediated Cancer Immunotherapy: Formulation and Characterization Using Orthogonal Techniques

Cyclic GMP-AMP (cGAMP) has lately been extensively investigated in cancer immunotherapy due its activation of the innate immunity stimulation of interferon genes (STING) pathway within antigen presenting cells (APC) leading to an increase in tumor specific CD8+ T cells. As negatively charged dinucleotides are prone to enzymatic degradation before being taken up by APC, there is a need for an appropriate carrier. Therefore, polyethylenimine (PEI), a gold standard for oligonucleotide delivery, was selected. Molecular weight, type of PEI and N/P ratio between PEI/cGAMP were investigated in terms of toxicity, efficacy and physicochemical properties of the nanocomplexes (NCs) such as size, zeta potential and shape. Due to lack of nano-medicine regulations and the need for a case-by case assessment, here we examine these parameters by several orthogonal methods, such as dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and online asymmetric flow field flow fractionation (AF4) connected to DLS. N/P ratio of 2/1 ratio using linear PEI 25 kDa resulted in larger, positively charged particles of elongated shape, which were shown to have the best toxicity/efficacy ratio among different PEIs and ratios tested.

Multistep Micellization of Standard Surfactants Evidenced by Second Harmonic Scattering

Processes involving in solution a reduced number of molecules are difficult to identify and characterize. Here, we show that micellization of standard surfactants, namely sodium dodecyl sulfate and trimethyl tetradecyl ammonium bromide, two nonefficient compounds for quadratic nonlinear optics, can be investigated by second harmonic scattering (SHS). In particular, the formation of aggregates at concentrations smaller than the critical micellar concentration is evidenced through a nonmonotonic behavior of the SHS intensity as a function of the surfactant concentration. A simple model based on chemical equilibria between monomers and micelles is proposed to account for the experimental observations. Signature of long-range molecular orientation correlation is revealed by polarization resolved experiments and is discussed regarding micellization and charge-induced effects.

Abnormal behaviors in the calibration curves of liquid chromatography-tandem mass spectrometry occurring in the quantitative analysis of surfactants near critical micelle concentrations

Surfactants, including quaternary ammonium compounds, are widely used in daily life as part of consumer chemical products and, more recently, in the shale oil industry. Because of their unique amphiphilic properties, surfactants form micelles at concentrations above a certain threshold known as the critical micelle concentration (CMC). A previous electrospray ionization mass spectrometry studies conducted by Siuzdak et al. and others presented indirect evidence regarding micelle formation. Herein, we have used liquid chromatography-tandem mass spectrometry to explore how such micelle formations affect the quantitative analysis of surfactants. Results reveal abnormal behaviors in the calibration plots of a few selected anionic and cationic surfactants, such as sodium decyl sulfate (SDeS), sodium dodecyl sulfate (SDS), myristyltrimethylammonium bromide (MTAB), and benzyldimethyloctadecylammonium chloride (BAC-18). At concentrations close to the respective CMCs of these surfactants, the calibration plot for MTAB flattened, whereas the slopes of the calibration plots for SDeS, SDS, and BAC-18 suddenly changed. These abnormal behaviors can be related to micelle formation. From a practical perspective, the above observations suggest that in the quantitative analysis of surfactants, high micelle concentrations close to the CMC should be avoided to obtain accurate surfactant measurements.

Advanced nanomedicine characterization by DLS and AF4-UV-MALS: Application to a HIV nanovaccine

Nanoformulations are complex systems where physicochemical properties determine their therapeutic efficacy and safety. In the case of nanovaccines, particle size and shape play a crucial role on the immune response generated. Furthermore, the antigen's integrity is also a key aspect to control when producing a nanovaccine. The determination of all those physicochemical properties is still an analytical challenge and the lack of well-established methods hinders the access of new therapeutics to the market. In this work, robust methods for the characterization of a novel HIV nanoparticle-based vaccine produced in good manufacturing practice (GMPs)-like environment were developed. With slightly polydisperse particles (< 0.2) close to 180 nm of size, batch-mode Dynamic Light Scattering (DLS) was validated to be used as a quality control technique in the pilot production plant. In addition, a high size resolution method using Asymmetrical Flow Field Flow Fractionation (AF4) demonstrated its ability to determine not only size and size distribution but also shape modification across the size and accurate quantification of the free active ingredient. Results showed a monomodal distribution of particles from 60 to 700 nm, most of them (> 90%) with size lower than 250 nm, consistent with more traditional techniques, and revealed a slight change in the structure of the particles induced by the presence of the antigen. Finally, a batch to batch variability lower than 20% was obtained by both DLS and AF4 methods indicating that preparation method was highly reproducible.

Naphthalimide-Based Fluorophore for Soft Anionic Interface Monitoring

A naphthalimide-based low-molecular-mass fluorophore (NA) was designed and synthesized by introducing an azetidine unit onto the aromatic ring of the compound as an electron-donating structure, and a hydrophilic (2-(2-aminoethyl-amino)ethanol) moiety into the "N-imide site" of the core structure. UV-vis absorption and fluorescence measurements revealed that the fluorophore is soluble in water and shows a fluorescent quantum yield of ∼20% and lifetime of ∼3.7 ns in the solvent within a wide pH range. Moreover, the fluorescence emission and anisotropy of the fluorophore as produced are both dependent upon the viscosity and polarity of the medium. Further studies demonstrated that NA can be used as a selective probe to monitor the aggregation of anionic surfactants owing to its accumulation onto the anionic surfaces of the aggregates as formed. Inspired by the discovery, NA was successfully applied for detection of cell membranes and E. coli via monitoring of their negatively charged surfaces, which is important for fast checking of biological contamination of water. Importantly, all the tests could be performed in a visualized manner. We believe that the new, low-molecular-mass fluorophore as created may find applications in chemical and biochemical sensing and imaging.

Living cationic ring-opening polymerization of 2-ethyl-2-oxazoline following sustainable concepts: microwave-assisted and droplet-based millifluidic processes in an ionic liquid medium

The synthesis of poly(2-ethyl-2-oxazoline) has been developed in an ionic liquid and performed with microwave-assisted or droplet-based millifluidic processes.

Light scattering from hydrophobe-uptake spherical micelles near the critical micelle concentration

We have investigated aqueous micellar solutions of mixtures of a surfactant (dodecylpyridinium chloride) and a hydrophobe (1-dodecanol) near the critical micelle concentration (cmc), using simultaneous static and dynamic light scattering measurements. The static light scattering intensity for the aqueous solutions was separated into fast and slow relaxation components using dynamic light scattering results. The slow relaxation component gave us the information about the large scattering component. It turned out from this component that the amount of large colloidal particles of the hydrophobe was very tiny in the solution and hardly affects the association-dissociation equilibrium of the hydrophobe-uptake micelle. The free surfactant molecule and the hydrophobe-uptake spherical micelle in the solutions belong to the fast relaxation component. We have characterized the spherical micelle and also analyzed the association-dissociation equilibrium of the hydrophobe-uptake micelle up to near the cmc, using this scattering component extracted.

Saponins: a renewable and biodegradable surfactant from its microwave-assisted extraction to the synthesis of monodisperse lattices

Synthetic surfactants are widely used in emulsion polymerization, but it is increasingly desirable to replace them with naturally derived molecules with a reduced environmental burden. This study demonstrates the use of saponins as biodegradable and renewable surfactants for emulsion polymerization. This chemical has been extracted from soapnuts by microwave assisted extraction and characterized in terms of surfactant properties prior to emulsion polymerization. The results in terms of particle size distribution and morphology control have been compared to those obtained with classical nonionic (NP40) or anionic (SDS) industrial surfactants. Microwave-extracted saponins were able to lead to latexes as stable as standard PS latex, as shown by the CMC and CCC measurements. The saponin-stabilized PS particles have been characterized in terms of particle size and distribution by Dynamic Light Scattering and Asymmetrical Flow Field Flow Fractionation. Monomodal and monodispersed particles ranging from 250 to 480 nm in terms of diameter with a particle size distribution below 1.03 have been synthesized.

Enhanced surfactant supramicellar assembly by hydrophobic dopants

The light scattering peak (LS peak) near the surfactant critical micelle concentration (cmc) demonstrates that low hydrophobic dopant levels can cause supramolecular assembly of surfactants into metastable structures much more massive than dopant-free micelles. These supramicellar assemblies (SA) exist over the entire LS peak region, which extends from above the cmc down to well below the cmc. Dodecanol (D) was the dopant, and sodium dodecyl sulfate (SDS) and dodecyl trimethyl ammonium bromide (DTABr) were the surfactants in this work. Well above the cmc dopant is solubilized by micelles. The SA appear above the cmc, dependent on dopant level and solution ionic strength, as seen by an abrupt increase in LS. Hence, the micelles do not simply release their hydrophobic payload at the cmc; rather, the dopant causes a morphological change from normal micelles above the LS peak concentration regime into SA as the LS regime is entered from above the cmc. Below the cmc the LS peak has a cutoff concentration corresponding to the solubility limit of dodecanol in water, which can be termed a "critical supramicellar assembly concentration" (csac). A three-component model is proposed that self-consistently yields maximum micellar dopant loading, SA mass, and dopant solubility in solution. The constancy of SA molar mass under widely different ionic strength and dopant levels conditions is surprising and not currently understood.

A model for monomer and micellar concentrations in surfactant solutions: application to conductivity, NMR, diffusion, and surface tension data

An empirical model for the concentrations of monomeric and micellized surfactants in solution is presented as a consistent approach for the quantitative analysis of data obtained with different experimental techniques from surfactant solutions. The concentration model provides an objective definition of the critical micelle concentration (cmc) and yields precise and well defined values of derived physical parameters. The use of a general concentration model eliminates subjective graphical procedures, reduces methodological differences, and thus allows one to compare directly the results of different techniques or to perform global fits. The application and validity of the model are demonstrated with electrical conductivity, surface tension, NMR chemical shift, and self-diffusion coefficient data for the surfactants SDS, CTAB, DTAB, and LAS. In all cases, the derived models yield excellent fits of the data. It is also shown that there is no need to assume the existence of different premicellar species in order to explain the chemical shifts and self-diffusion coefficients of SDS as claimed recently by some authors.

Multi-wall carbon nanotube aqueous dispersion monitoring by using A4F-UV-MALS

In this work, the potentiality of asymmetrical flow field-flow fractionation (A4F) hyphenated to UV detector and multi-angle light scattering (MALS) was investigated for accurately determining multi-walled carbon nanotube (MWCNT) length and its corresponding dispersion state in aqueous medium. Fractionation key parameters were studied to obtain a method robust enough for heterogeneous sample characterization. The main A4F conditions were 10(-5) mL min(-1) NH(4)NO(3), elution flow of 1 mL min(-1), and cross flow of 2 mL min(-1). The recovery was found to be (94 ± 2)%. Online MALS analysis of eluted MWCNT suspension was performed to obtain length distribution. The length measurements were performed with a 4% relative standard deviation, and the length values were shown to be in accordance with expected ones. The capabilities of A4F-UV-MALS to size characterize various MWCNT samples and differentiate them according to their manufacturing process were evaluated by monitoring ball-milled MWCNT and MWCNT dispersions. The corresponding length distributions were found to be over 150-650 and 150-1,156 nm, respectively. A4F-UV-MALS was also used to evaluate MWCNT dispersion state in aqueous medium according to the surfactant concentration and sonication energy involved in the preparation of the dispersions. More especially, the presence or absence of aggregates, number and size of different populations, as well as size distributions were determined. A sodium dodecyl sulfate concentration of 15 to 30 mmol L(-1) and a sonication energy ranged over 20-30 kJ allow obtaining an optimal MWCNT dispersion. It is especially valuable for studying nanomaterials and checking their manufacturing processes, size characterization being always of high importance.

A facile surfactant critical micelle concentration determination

Liquid surface curvature variations in microplate wells due to different liquid surface tension cause significant signal change in spectroscopic measurement using a plate reader with a vertical detecting light beam. The signals have been quantitated and used to develop a method for facile surfactant critical micelle concentration determination.

Rapid determination of surfactant critical micelle concentration in aqueous solutions using fiber-optic refractive index sensing

We describe a simple and rapid method for determining the critical micelle concentration (CMC) of surfactants from fiber-optic measurements of refractive index. The refractive index of an aqueous surfactant solution was monitored as the surfactant concentration was increased using an automated dispensing system. On reaching the surfactant's CMC value, an abrupt change was observed in the rate of increase of the refractive index with increasing concentration. The measurement system provides rapid semiautomatic data collection and analysis, increasing the precision, sensitivity, and range of applicability of the technique while substantially decreasing the amount of manual intervention required. Measurements of CMC for sodium dodecyl sulfate (8.10mM), cetyltrimethylammonium chloride (1.58mM), and Triton X-100 (0.21mM) were in excellent agreement with values previously reported in the literature. The method is applicable to cationic, anionic, and nonionic surfactants, and it offers a facile, in situ, and sensitive means of detecting micelle formation over a broad range of CMC values larger than 10(-1)mM.