Surface and bulk interactions of ionic and nonionic surfactants

Behavior of Triterpenoid Saponin Ginsenoside Rh2 in Ordered and Disordered Phases in Model Membranes Consisting of Sphingomyelin, Phosphatidylcholine, and Cholesterol

The ginsenoside Rh2 (Rh2) is a saponin of medicinal ginseng, and it has attracted much attention for its pharmacological activities. In this study, we investigated the interaction of Rh2 with biological membranes using model membranes. We examined the effects of various lipids on the membrane-disrupting activity of Rh2 and found that cholesterol and sphingomyelin (SM) had no significant effect. Furthermore, the effects of Rh2 on acyl chain packing (DPH anisotropy) and water molecule permeability (GP₃₄₀ values) did not differ significantly between bilayers containing SM and saturated phosphatidylcholine. These results suggest that the formation of the liquid-ordered (Lo) phase affects the behavior of Rh2 in the membrane rather than a specific interaction of Rh2 with a particular lipid. We investigated the effects of Rh2 on the Lo and liquid-disordered (Ld) phases using surface tension measurements and fluorescence experiments. In the surface tension-area isotherms, we compared the monolayers of the Ld and Lo lipid compositions and found that Rh2 is abundantly bound to both monolayers, with the amount being greater in the Ld phase than in the Lo phase. In addition, the hydration state of the bilayers, mainly consisting of the Lo or Ld phase, showed that Rh2 tends to bind to the surface of the bilayer in both phases. At higher concentrations, Rh2 tends to bind more abundantly to the relatively shallow interior of the Ld phase than the Lo phase. The phase-dependent membrane behavior of Rh2 is probably due to the phase-selective affinity and binding mode of Rh2.

Investigation of micellar and interfacial phenomenon of amitriptyline hydrochloride with cationic ester-bonded gemini surfactant mixture in different solvent media

Herein, the interaction among the antidepressant drug amitriptyline hydrochloride (AMT) and a green gemini surfactant, ethane-1, 2-diyl bis(N,N-dimethyl-N-tetradecylammoniumacetoxy) dichloride (14-E2-14), via numerous techniques such as tensiometry, fluorimetry, FT-IR and UV-visible spectroscopy in three different media (aqueous 0.050 mol·kg^-1 NaCl, 0.50 and 1.0 mol·kg^-1 urea) were investigated. AMT is used to treat mental illness or mood problems, such as depression. The aggregation of biologically active ingredients can enhance the bioavailability of hydrophobic drugs. A significant interaction between AMT and 14-E2-14 was detected by tensiometric study as the critical micelle concentration (cmc) of AMT+14-E2-14 is reduced upon an increase of mole fraction (α₁) of 14-E2-14. The decrease in cmc indicates the nonideality of studied mixtures of different compositions. Although, employed drug AMT is freely soluble in the aqueous and non-aqueous system but is not hydrophobic enough to act as its carrier. Instead, gemini surfactant formed spherical micelles in an aqueous system and their high solubilization capability, as well as their relatively lower cmc value, makes them highly stable in vivo. The cmc values of AMT+14-E-14 mixtures in all cases were further decreased and increased in NaCl and urea solutions respectively as compared with the aqueous system. Numerous micellar, interfacial, and thermodynamic parameters have been measured by applying various theoretical models. The obtained changes in the physicochemical assets of AMT upon adding of 14-E2-14 are likely to enhance the industrial and pharmaceutical applications of gemini surfactants. The negative interaction parameters (β^m and β^σ), indicate synergistic attraction is occurring in the mixed systems. The aggregation number (N_agg), Stern–Volmer constant (K_sv), etc. are attained through the fluorescence method, also supporting the attractive interaction behavior of AMT+14-E2-14 mixtures in all solvents. The N_agg was found to increase in the salt solution and decrease in the urea system compared with the aqueous solution. FT-IR and UV-visible analysis also depict the interaction between the constituent alike tensiometry and fluorimetry methods. The results suggested that gemini surfactants may serve as a capable drug delivery agent for antidepressants, improving their bioavailability.

Properties of Binary Mixture of Cetyl Diphenyl Ether Disulfonate and Linear Alkylbenzene Sulfonate

The surface properties of the binary mixture of cetyl diphenyl ether disulfonate (C16-MADS) and linear alkylbenzene sulfonate (LAS) have been investigated by salinity and hardness tolerance, equilibrium surface tension, wettability, foam and emulsification measurements. The results show that with increasing mass ratio of LAS in the C16-MADS/LAS mixed system, the ability to reduce the surface tension of the solution is improved. The wetting performance is also improved. The critical micelle concentration (CMC) values are increased first, then decreased, and are higher than the ideal CMC values, which indicates that there is an antagonistic effect that is not conducive to the formation of mixed micelles between C16-MADS and LAS. In addition, the C16-MADS/LAS system improves the hard water resistance of LAS and reduces the foam properties of LAS.

Aggregation and interfacial phenomenon of amphiphilic drug under the influence of pharmaceutical excipients (green/biocompatible gemini surfactant)

In the current study, we have examined the interaction amongst an antidepressant drug amitriptyline hydrochloride (AMH) and ethane-1, 2-diyl bis(N,N-dimethyl-N-cetylammoniumacetoxy) dichloride (16-E2-16, a green gemini surfactant) through tensiometric and fluorimetric techniques in aqueous/electrolyte/urea solutions. Significant variations are observed in the various evaluated parameters in the present study. Gemini 16-E2-16 has outstanding surface properties along with a much lower cmc value, demonstrating very little toxicity as well as considerable antimicrobial activity. The cmc values of mixtures decrease through increase in mole fraction (α₁) of 16-E2-16, which specifies the nonideality of the solution mixtures, along with demonstrating the occurrence of mixed micellization too. Negative β^Rub values signify on the whole attractive force of interaction between constituents of mixed micelles. Owing to the incidence of electrolyte NaCl (50 mmol.kg^–1), lowering of the micelles’ surface charge happens, resulting in aggregation taking place at lower concentration while the presence of urea (NH₂CONH₂) halts micellization taking place, which means the cmc value increases in the attendance of urea. The ΔGmo values for all systems were negative along with the presence of electrolyte/urea. The excess free energy (G_ex) of studied mixed systems was also estimated and found to be negative for all the systems. Using the fluorescence quenching method, the micelle aggregation number (N_agg) was evaluated and it was found that the contribution of gemini surfactant was always more than that of the AMH and their value enhances in the existence of electrolyte while decreasing in the attendance of NH₂CONH₂ in the system. In addition, other fluorescence parameters such as micropolarity (I₁/I₃), dielectric constant (D_exp) as well as Stern–Volmer binding constants (K_sv) of mixed systems were evaluated and the results showed the synergistic performance of the AMH + 16-E2-16 mixtures. Along with tensiometric and fluorimetric techniques, FT-IR spectroscopy was also engaged to reveal the interaction among constituents.

Interaction between a Nonsteroidal Anti-inflammatory Drug (Ibuprofen) and an Anionic Surfactant (AOT) and Effects of Salt (NaI) and Hydrotrope (4-4-4)

Ibuprofen (IBF), 2-(4-isobutylphenyl) propionic acid, is a surface-active, common nonsteroidal anti-inflammatory drug (NSAID), and it possesses a high critical micelle concentration (cmc) compared to that of conventional surfactants. The interactions of this common NSAID with an anionic surfactant, sodium octyl sulfosuccinate, were studied by tensiometric, fluorimetric, and calorimetric measurements to investigate this system as a possible model drug-delivery system for an NSAID like IBF, particularly in a high-dose regime for IBF. The interactions between the drug and the surfactant were modeled using a regular solution theory approach in the presence and absence of a model electrolyte (sodium iodide) and a novel nonaromatic, gemini hydrotrope, tetramethylene-1,4-bis( N, N-dimethyl- N-butylammonium)bromide (4-4-4). Both the simple and the hydrotropic electrolyte were shown to have an effect on the solution properties (aggregation parameters, interfacial properties, and thermodynamics of aggregate formation) of the drug-surfactant mixtures and on the interaction between the drug and the surfactant. Surface charges of all self-assembled systems were estimated from ζ-potential measurements, whereas density functional theory calculations showed the interaction energy comparison among all of the binary and ternary combinations. All of these results were interpreted in terms of how altering the subtle balance of hydrophobic and electrostatic forces can significantly improve the ability of these self-assembled systems to transport drug molecules.

Fluorescence studies on the aggregation behaviors of collagen modified with NHS-activated poly(γ-glutamic acid)

The poly(γ-glutamic acid)-NHS (γ-PGA-NHS) esters were used to endow collagen with both of excellent water-solubility and thermal stability via cross-linking reaction between γ-PGA-NHS and collagen. In the present work, the effect of γ-PGA-NHS on the aggregation of collagen molecules was studied by fluorescence techniques. The fluorescence emission spectra of pyrene in collagen solutions and the intrinsic fluorescence emission spectra of collagen suggested different effects of γ-PGA-NHS on collagen molecules: inhibiting aggregation below critical aggregation concentration (CAC) and promoting aggregation above CAC. The two-dimensional (2D) fluorescence correlation spectra indicated that the intermolecular hydrogen bonding and cross-linking between γ-PGA-NHS and collagen would influence the aggregation of collagen molecules. By the ultra-sensitive differential scanning calorimeter (VP-DSC), it was found that the main denaturational transition temperature (T_m2) of modified collagen increased, while its calorimetric enthalpy changes (ΔH₂) decreased compared to those of native collagen, further indicating that the modification of γ-PGA-NHS influenced the aggregation of collagen molecules. The study provide useful information for the utilizing and or the processing of water-soluble collagen in aqueous solution in the fields such as cosmetics, health care products, tissue engineering and biomedical materials, etc.

A novel combined chemical kinetic and trapping method for probing the relationships between chemical reactivity and interfacial H2O, Br- and H+ ion molarities in CTAB/C12E6 mixed micelles

A delicate balance-of-forces governs the interactions responsible for surfactant self-assembly and chemical reactivity within them. Chemical reactions in micellar media generally occur in the interfacial region of micelles that is a complex mixture of: water, headgroups, counterions, co-ions, acids or bases, organic solvents, and the reactants themselves. We have carried out a detailed study of a complex chemical reaction in mixed CTAB/C₁₂E₆ micelles by using the chemical kinetic (CK) and chemical trapping (CT) methods. The results provide a detailed quantitative treatment of the reaction of the anion of the antioxidant t-butylhydroquinone, TBHQ^-, with 4-hexadecylbenzenediazonium, 16-ArN₂⁺, within the interfacial region of the mixed micelles in the C₁₂E₆ mole fraction range of 0 to 1 at three different total surfactant concentrations. CK experiments showed that this reaction is monophasic in C₁₂E₆ micelles, but biphasic in mixed micelles. The results were fully consistent with a complex mechanism in which TBHQ^- reacts with 16-ArN₂⁺ to give a transient diazoether intermediate that competitively breaks down into products and or reverts to starting materials. The kinetics are the same in mixed micelles of CTAB/C₁₂E₆ (grow) and CTAB/C₁₂E₈ (don't grow) showing that the rates only depend on micelle composition, not shape. CT results provided estimates of interfacial molarities of H₂O are approximately constant at ca. 39 and Br^- decreases from ca. 2.75 to 0.05 moles per liter of interfacial volume as C₁₂E₆ mole fraction increases from 0 to 1. Combined CK/CT results provided values for interfacial pH, ranging from ca. 4.25 in cationic micelles to 1.5 in nonionic micelles despite a constant bulk pH of 1.5 and the TBHQ interfacial pK_a = 3.8 at all C₁₂E₆ molar fractions. In totality, these results yielded an extraordinary amount of quantitative information about the relationships between the chemical reactivity and interfacial compositions of the mixed micelles.

PPh4Cl in aqueous solution – the aggregation behavior of an antagonistic salt

The aggregation behavior of the antagonistic salt PPh₄Cl was investigated. This salt was found to be an excellent hydrotrope which does not aggregate in binary aqueous solutions or in a ternary one, upon the addition of the exemplary hydrophobic molecule DR-13.

Immunogenicity of Recombinant Human Interferon Beta-1b in Immune-Tolerant Transgenic Mice Corresponds with the Biophysical Characteristics of Aggregates

Determining to what extent biophysical characteristics of aggregates affect immunogenicity of therapeutic interferon beta-1b. Three recombinant human interferon beta-1b (rhIFNβ-1b) samples with different levels of aggregates generated by copper oxidation, thermal stress, or left untreated, as well as Avonex(®) drug substance and Betaferon(®) drug product, were injected intraperitoneally in nontransgenic and interferon beta transgenic FVB/N mice 5 times per week for 3 weeks. Antibodies against interferon beta were measured using enzyme-linked immunosorbent assay. UV and fluorescence spectroscopy, dynamic light scattering, size exclusion chromatography, reversed-phase high-performance liquid chromatography (RP-HPLC), fluid imaging microscopy, and resonant mass measurement, as well as sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting, were used to characterize and quantitate aggregates in the 3 rhIFNβ preparations, to correlate biophysical characteristics with immunogenicity. In immune-tolerant interferon beta transgenic FVB/N mice, Betaferon drug product showed the highest immunogenicity, while Avonex drug substance showed the lowest level of immunogenicity. Of the 3 forms of rhIFNβ-1b, copper-oxidized rhIFNβ-1b showed lower immunogenicity than thermally stressed rhIFNβ-1b, despite containing larger aggregates. Both copper-oxidized rhIFNβ-1b and thermally stressed rhIFNβ-1b exhibited changes in protein structure as shown using fluorescence spectroscopy and RP-HPLC. Nontransgenic, nonimmune-tolerant FVB/N mice generated high antibody titers against all interferon beta samples tested. The level of immunogenicity and the breaking of tolerance in FVB/N transgenic mice are not only related to the level of aggregation but also depend on the size and structure of the aggregates.

Synthesis of Amphiphilic Naturally-Derived Oligosaccharide-block-Wax Oligomers and Their Self-Assembly

Self-assembly characteristics of amphiphilic macromolecules into micelles, nanoparticles and vesicles has been of fundamental interest for many applications including designed nanoscale therapeutic delivery systems and enzymatic reactors. In this work, a class of amphiphilic block oligomers was synthesized from naturally occurring oligosaccharides and aliphatic alcohol precursors, which are all currently prominent in the pharmaceutical, food, and supplement industries. These block oligomer materials were synthesized by functionalization of the precursor materials followed by subsequent coupling by azide-alkyne cycloaddition and their bulk self-assembly was investigated after solvent vapor annealing. Self-assembly of the amphiphilic materials into liposomes in aqueous solution was also investigated after preparing solutions using a nanoprecipitation method. Encapsulation of hydrophobic components was demonstrated and verified using dynamic light scattering, transmission electron microscopy, and fluorescence spectroscopy experiments.

Identification and molecular interpretation of the effects of drug incorporation on the self-emulsification process using spectroscopic, micropolarimetric and microscopic measurements

Addition of a drug to a self-emulsifying drug delivery system (SEDDS) can affect the emulsification process after administration, leading to variation in the emulsion droplet size formed and potentially its clinical behavior (Mercuri et al., Pharm. Res., 2011, 28, 1540-1551). However, the mechanisms involved and, in particular, the location of the drug within the system are poorly understood. Here, we have investigated the location of a model drug, ibuprofen, in the emulsions formed from a simple anhydrous SEDDS (soybean oil, Tween 80 and Span 80), using a range of physical characterization techniques. (1)H NMR studies showed an interaction between the drug and the polyoxyethylene chains of the surfactant Tween 80. Micropolarity assessment of the emulsion droplet interfacial region, using the chemical probes pyrene and Reichardt's dye, confirmed this interaction, and suggested that the drug was altering the microenvironment around the surfactants, and hence the behavior of the SEDDS with water during emulsification. Both dielectric spectroscopy and polarized light microscopy highlighted the differential behavior with water of placebo and drug-loaded SEDDS, also seen in the initial visual observational studies on the emulsification performance of the SEDDS. (1)H NMR studies with three other NSAIDs indicate that this effect is not confined to ibuprofen alone. The study has therefore indicated that the drug's influence on the emulsification process may be related to interactions within the microenvironment of the surfactant layer. Furthermore, such interactions may be usefully identified and characterized using a combination of micropolarity, spectroscopic and microscopic methods.