Study on the Langmuir aggregation of fluorinated surfactants on protein

The microphase adsorption-spectral correction (MPASC) technique was described and applied to the study of the interactions of fluorinated surfactants such as potassium perfluorooctanesulfonate (PFOS) and potassium perfluorobutanesulfonate (PFBS) with human serum albumin (HSA). Sodium octanesulfonate (SOS) was also studied as non-fluorinated surfactant. The aggregation of PFOS, PFBS and SOS obeys the Langmuir monolayer adsorption. The results show that the adsorption ratios of surfactants to HSA are PFOS:HSA = 120:1, PFBS:HSA = 205:1 and SOS:HSA = 18:1. The adsorption constants are K_PFOS-HSA = 5.01 × 10³, K_PFBS-HSA = 9.79 × 10² and K_SOS-HSA = 4.03 × 10³. The detection limits are 2.7 mg/L for BSA using PFOS, 3.1 mg/L using PFBS and 3.1 mg/L using SOS. It was found that fluorinated surfactant exhibited stronger interaction with protein than hydrogenated one, and fluorinated surfactant with long hydrophobic chain exhibited stronger interaction with protein than that with short hydrophobic chain.     

Original fluorinated surfactants potentially non-bioaccumulable

This minireview updates non-exhaustive recent strategies of synthesis of original fluorosurfactants potentially non-bioaccumulable. Various strategies have been focused on (i) the preparation of CF₃–X–(CH₂)_n–SO₃Na (with X = O, C₆H₄O or N(CF₃) and n = 8–12), (ii) the oligomerization of hexafluoropropylene oxide (HFPO) to further synthesize oligo(HFPO)–CF(CF₃)CO–R_H (where R_H stands for an hydrophilic chain); (iii) the telomerization of vinylidene fluoride (VDF) with 1-iodopentafluoroethane or 1-iodononafluorobutane to produce C_nF_2n+1–(VDF)₂–CH₂CO₂R (n = 2 or 4, R = H or NH₄), (iv) the radical telomerization of 3,3,3-trifluoropropene (TFP) with isoperfluoropropyliodide or diethyl hydrogenophosphonate to prepare (CF₃)₂CF(TFP)_x–R_H or CF₃–CH₂–CH₂–(TFP)_y–P(O)(OH)₂, and (v) the radical cotelomerization of VDF and TFP, or their controlled radical copolymerization in the presence of (CF₃)₂CFI or a fluorinated xanthate. In most cases, the surface tensions versus the surfactant concentrations have been assessed. These above strategies led to various highly fluorinated (but yet not perfluorinated) telomers whose chemical changes enabled to obtain original surfactants as novel alternatives to perfluorooctanoic acid (PFOA), ammonium perfluorooctanoate (APFO), or perfluorooctylsulfonic acid (PFOS) regarded as bioaccumulable, persistent, and toxic.     

Mixed adsorption of fluorinated and hydrogenated surfactants

The adsorption isotherms of sodium perfluorooctanoate and sodium decyl sulfate and their 1:1 mixture on gamma-alumina are recorded by depletion-type experiments with (1)H and (19)F NMR spectroscopy as the detection tool. The isotherms of the different surfactant species, obtained with and without added salt, closely resemble each other. Salt addition changes the isotherms from stepwise to the familiar S-shaped. After having reached saturation, a further increase of surfactant concentration in the mixed system leads to decyl sulfate desorption and increased perfluorooctanoate adsorption. The (19)F chemical shift of adsorbed perfluorooctanoate suggests that, for saturated surfaces, the two sorts of adsorbed surfactants form molecularly mixed surface aggregates.     

Mixed micelles of fluorinated and hydrogenated surfactants

The model mixed surfactant system of sodium perfluorooctanoate and sodium decyl sulfate was carefully reexamined by a combination of nuclear magnetic resonance methods. Over a wide range of sample compositions, detailed (19)F and (1)H chemical shift data in combination with self-diffusion coefficients for the perfluorooctanoate and decyl sulfate ions are collected. All data are analyzed together in a framework that uses a minimal number of initial assumptions to extract the monomer concentrations of both surfactants and the micellar chemical shifts of (19)F and (1)H as a function of relative concentration. The main conclusion drawn from this analysis is that there exists neither complete demixing nor complete mixing on molecular or micellar levels. Instead, the experimental data favor a single type of micelles within which fluorinated surfactants are preferentially coordinated by fluorinated ones and hydrogenated surfactants by hydrogenated ones. The data are quantitatively interpreted in the framework of the first approximation of the regular solution theory (also called the quasi-chemical treatment) leading to an energy of mixing of omega = W/kT = 0.98 between the constituting surfactant types. These findings may help to resolve a long controversy about micellar mixing-demixing in this particular mixture and in its relatives.     

Mixtures of hydrogenated and fluorinated lactobionamide surfactants with cationic surfactants: study of hydrogenated and fluorinated chains miscibility through potentiometric techniques

The work reported herein deals with the aqueous behavior of hydrocarbon and/or fluorocarbon ionic and nonionic surfactants mixtures. These mixtures were studied using potentiometric techniques in NaBr (0.1 mol L-1) aqueous solution as well as in pure water. Mixed micelles were formed from a cationic surfactant (dodecyl or tetradecyltrimethylammonium bromide respectively called DTABr or TTABr) and neutral lactobionamide surfactants bearing a hydrogenated dodecyl chain (H12Lac) or a fluorinated chain (CF3-(CF2)5-(CH2)2- or CF3-(CF2)7-(CH2)2-). We showed that concentrations of ionic and nonionic surfactants in the monomeric form as well as the composition of the mixed micelles can be specified thanks to a potentiometric technique. The complete characterization does not request any model of micellization a priori. The activities of the micellar phase constituents, as well as the free enthalpies of mixing, were calculated. The subsequent interpretation only relies on the experimental characterization. Comparison of the behaviors of the various systems with a model derived from the regular solution theory reveals the predominant part of electrostatic interactions in the micellization phenomenon. It also appears that the energy of interaction between hydrogenated and fluorinated chains is unfavorable to mixing and is of much lower magnitude than the electric charges interactions.     

Aqueous solubilization of highly fluorinated molecules by semifluorinated surfactants

The physical and chemical properties of organic compounds are deeply affected by the introduction of fluorinated substituents. Perfluorinated and highly fluorinated organic molecules are both hydrophobic and lipophobic. This makes the recognition and the binding of fluorinated molecules extremely difficult to achieve through classical elements of molecular recognition. Here we show that semifluorinated water-soluble block copolymers can generate micellar structures having a fluorous phase-based inner core in aqueous solution. Furthermore, we show that these micelles can be used to encapsulate and bind highly fluorinated molecules through association in the internal fluorous phase (fluorophobic effect). We report that semifluorinated block copolymers can be used for the aqueous solubilization of the widely diffused gaseous anesthetic sevoflurane, thereby suggesting the possibility of the intravenous delivery of this commonly used anesthetic.     

Synthesis of novel oil-soluble fluorinated surfactants via Wittig-Horner reaction

In this paper, the synthesis and characterization of novel oil-soluble fluorinated surfactants were reported. Both Wittig and Wittig-Horner reaction were used for constructing the perfluorinated branch-chain structure, and the latter provided a better method through a three-step synthesis route which was easy worked up and low cost. The surface tension of novel products in toluene, n-hexane and nitromethane with concentrations of 0.1?mol/L, 0.05?mol/L, 0.025?mol/L, 0.0125?mol/L, 0.00625?mol/L and 0?mol/L were examined. The surface tension research of these surfactants showed that they can reduce the surface tension of organic reagents dramatically. For example, compound 1e can reduce the surface tension of nitromethane from 36.6?mN/m to 24.2?mN/m in the concentration of 0.1?mol/L, and the surface tension of toluene was reduced from 28.0?mN/m to 22.7?mN/m when the concentration of compound 1a was 0.1?mol/L.     

Synthesis and surface activities of organic solvent-soluble fluorinated surfactants

A variety of fluorinated surfactants soluble in organic solvent were prepared, including C₈F₁₇SO₂NHC_nH_2n+1 (n = 2, 4, 6, 8, 10), C₈F₁₇SO₂NHR (R = C₆H₁₁, C₆H₅), C₈F₁₇SO₂N(C_nH_2n+1)₂ (n = 1, 2, 3, 4) and C₈F₁₇SO₂NH(CH₂)_nNHO₂SC₈F₁₇ (n = 6, 10). Their surface activities in various organic solvents were determined by surface tension measurement. The results showed that these fluorinated surfactants can reduce the surface tension of both polar and non-polar organic solvents. In general, organic solvents with strong polarity or long alkyl chain are beneficial to increase the surface activity of these polar fluorinated surfactants. By comparing fluorinated surfactants with the same fluorocarbon segment and connecting group, C₈F₁₇SO₂N(C_nH_2n+1)₂ (n = 1, 2, 3, 4) showed lower surface activity in organic solvents than C₈F₁₇SO₂NHC_nH_2n+1 (n = 2, 4, 6, 8) with an equal carbon number of the solvophilic group. Through surface tension vs. concentration curves given for N-octyl perfluorooctanesulfonamide in various organic solvents, a break point like the critical micelle concentration of ordinary surfactants in aqueous solutions was observed, and the effect of the different types of organic solvents on adsorption and aggregation behavior was also studied.     

Recent advances on synthesis of potentially non-bioaccumulable fluorinated surfactants

Fluorinated surfactants are exceptional compounds that have found many applications in everyday life. This review focuses on severe issues on the toxicity, persistency and bioaccumulation of these halogenated products, especially perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), the half-lives of which are several years in human serum. After an introduction on their productions, uses and hazards, this minireview updates non-exhaustive recent strategies of synthesis of original fluorosurfactants that may be potentially non-bioaccumulable. These routes have been devoted on: (i) the preparation of CF₃-X-(CH₂)_n-SO₃Na (with X = O, C₆H₄O or N(CF₃) and n = 8–12), (ii) the use of fluorinated polyethers (achieved either by oligomerization of hexafluoropropylene oxide (HFPO) or by ring opening cationic oligomerization of fluorinated oxetanes; (iii) the telomerization of vinylidene fluoride (VDF) with 1-iodoperfluoralkanes to produce C_nF_2n + 1-(VDF)₂-CH₂CO₂R (n = 2 or 4, R = H or NH₄), (iv) the radical telomerization of 3,3,3-trifluoropropene (TFP) with isoperfluoropropyliodide to prepare (CF₃)₂CF(TFP)_x-R_H, and (v) the radical cotelomerization of VDF and TFP, or their controlled radical copolymerization in the presence of either (CF₃)₂CFI or a fluorinated xanthate. In most cases, the surface tensions versus the surfactant concentrations have been assessed. These above pathways led to various highly fluorinated (but yet not perfluorinated) telomers or cooligomers, the chemical changes of which enabled to obtain original surfactants as novel alternatives to PFOA, ammonium perfluorooctanoate (APFO), or PFOS regarded as the PCBs of the XXIst century.     

Protein-surfactant interaction: differences between fluorinated and hydrogenated surfactants

The interactions of proteins with fluorinated/hydrogenated surfactants were investigated by circular dichroism and turbidity measurement. Pairs of fluorinated and hydrogenated surfactants with similar critical micelle concentrations (cmc), including sodium perfluorooctanoate/sodium decylsulfate and lithium perfluorononanoate/sodium dodecylsulfate were compared in view of their interactions with proteins including BSA, lysozyme, β-lactoglobulin and ubiquitin. It was found that fluorinated surfactants exhibited stronger interactions with proteins than hydrogenated ones, which, however, depended on the structures of both proteins and surfactant molecules. If the proteins are very stable, or the surfactant–protein interactions are very strong, such differences between the two kinds of surfactants might be indistinguishable.     

Mixing behavior of fluorinated and hydrogenated gemini surfactants at the air-water interface

Mixing behavior of hydrogenated and fluorinated cationic gemini surfactants was studied at the air-water interface by Brewster angle microscopy and pi-A isotherm curves. In the bulk, these two molecules did not mix and showed phase separation. At the air-water interface, if a monolayer was formed by separate deposition of the two solutions, they formed separate domains, and the compression occurred in two steps: first the domains with hydrogenated gemini surfactant were compressed until they showed collapse; then the domains with fluorinated gemini surfactant were compressed. If the two solutions were mixed before the deposition, they remained mixed upon compression; on the other hand, separate domains under separate deposition were shown to mix if the subphase was heated.     

Molecular aggregates of partially fluorinated quaternary ammonium salt gemini surfactants

The size and shape of novel partially fluorinated gemini surfactant 1,2-bis[dimethyl-(3-perfluoroalkyl-2-hydroxypropyl)ammonium]ethane bromide (CnFC3-2-C3CnF, where n=4, 6, and 8) were investigated in aqueous solution by means of light scattering and transmission electron microscopy (TEM). The sizes of these molecular aggregates changed with increasing carbon number of the alkyl chain and concentration. For example, the apparent hydrodynamic radius by dynamic light scattering was 18 nm at a concentration of cmcx5 for n=4, 115 nm at the cmcx15 for n=6, and 62 nm at the cmcx30 for n=8, at 298.2 K. The shapes of CnFC3-2-C3CnF aggregates drastically changed with the alkyl chain length; the aggregates were mainly in the form of large or irregular small aggregates (n=4), string-like aggregates (n=6), and vesicles (n=8). The bromide-ion activity was measured using a bromide-ion-selective electrode to determine the degree of counterion binding to the aggregates. The degree of counterion binding to aggregate was very small compared with that in the typical hydrogenated gemini surfactants. These results indicated that the small curvature of large aggregates was not influenced by an electrostatic repulsion between the cationic head groups in the case of the bulky molecular volume of fluorinated gemini surfactants.     

Thermodynamics of micellization for partially fluorinated cationic gemini surfactants and related single-chain surfactants in aqueous solution

A series of partially fluorinated cationic gemini surfactants and their corresponding monomeric surfactants have been studied by isothermal titration microcalorimetry. The critical micelle concentration (CMC) and enthalpy of micellization (DeltaH(mic)) were obtained from calorimetric curves. The CMCs of the gemini surfactants are much lower than those of the corresponding monomeric surfactants and decrease with an increase in the number of fluorine atoms on the hydrophobic chain. The micellization of partially fluorinated cationic gemini surfactants is much more exothermic than that of the corresponding monomeric surfactants. Because of the incompatibility of hydrocarbon spacer and partially fluorinated chain, DeltaH(mic) values of the surfactants with a C6 spacer are more negative than those of the surfactants with a C12 spacer. The variations in the architecture of the fluorocarbon chain segments may be the reason of the irregularities in the change of DeltaH(mic) for the gemini surfactants. Moreover, the contribution of the enthalpy generally increases with an increase in the number of fluorine atoms.     

Segregation phenomena in micelles from mixtures of fluorinated and hydrogenated surfactants

Mixtures of hydrogenated and fluorinated surfactants are known to form either mixed or segregated micelles: the conclusions are much dependant on the precision of the experimental measurements and on the model used for interpretation. Recently, mixed surfactant solutions were probed at the micellar or molecular level by SANS, fluorescence or NMR. It leads to an intermediate structure for the mixed micelles with an intramicellar segregation of the fluorinated and hydrogenated surfactant.This intramicellar segregation was also observed in a variety of more complex systems which are rapidly surveyed in the second part.     

Determination of nucleic acid based on increased resonance light-scattering of fluorinated surfactants

Two novel surfactants perfluoroalkanesulfonyl quaternary ammonium iodides (FC134) and potassium perfluorooctanesulfonate (FC95) were successfully used as new probes for detection of DNA by resonance light-scattering (RLS) technique. Resonance light-scattering characteristics of the binding of fluorinated surfactants FC134 and FC95 to calf thymus nucleic acid (ctDNA) were studied. After DNA was added, aggregation of FC134 on the molecular surface of DNA in the pH 3.0-6.0 and aggregation of FC95 on the surface of DNA in the pH 3.5-6.0 occurred, both of which resulted in an enhanced resonance light-scattering peak at 370 nm. The intensity of resonance light-scattering was found to be proportional to the concentration of DNA. The determination limits were 3.5 and 20.0 μg L⁻¹, respectively. UV-vis spectra and IR-spectra both proved the binding of fluorinated surfactants to DNA.     

Hydrogenated/fluorinated catanionic surfactants as potential templates for nanostructure design

The structure and physicochemical properties of the nanoparticles spontaneously formed within aqueous mixtures of the hydrogenated/fluorinated catanionic surfactant cetyltrimetylammonium perfluorooctanoate in the absence of counterions as a function of its concentration are investigated by a combined experimental/computational study at room temperature. Apparent molar volumes, isentropic apparent molar compressibilities, and dynamic light scattering measurements together with transmission and cryo-scanning electron as well as confocal laser microscopy images, and computational molecular dynamics simulations indicate that a variety of structures of different sizes coexist in solution with vesicles of ～160 nm diameter. Interestingly, the obtained nanostructures were observed to self-assemble from a random distribution of monomers in a time scale easily accessible by atomistic classical molecular dynamics simulations, allowing to provide a comprehensive structural and dynamic characterization of the surfactant molecules at atomic level within the different aggregates. Overall, it is demonstrated that the use of mixed fluorinated hydrogenated surfactant systems represents an easy strategy for the design of specific nanoscale structures. The detailed structural analysis provided in the present work is expected to be useful as a reference to guide the design of new nanoparticles based on different hydrogenated/fluorinated catanionic surfactants.     

Surface properties and aggregate morphology of partially fluorinated carboxylate-type anionic gemini surfactants

Three anionic homologues of a novel partially fluorinated carboxylate-type anionic gemini surfactant, N,N′-di(3-perfluoroalkyl-2-hydroxypropyl)-N,N′-diacetic acid ethylenediamine (2 edda, where n represents the number of carbon atoms in the fluorocarbon chain (4, 6, and 8)) were synthesized. In these present gemini surfactants, the relatively small carboxylic acid moieties form hydrophilic head groups. The surface properties or structures of the aggregates of these surfactants are strongly influenced by the nonflexible fluorocarbons and small head groups; this is because these surfactants have a closely packed molecular structure. The equilibrium surface tension properties of these surfactants were measured at 298.2 K for various fluorocarbon chain lengths. The plot of the logarithm of the critical micelle concentration (cmc) against the fluorocarbon chain lengths for 2 edda (n = 4, 6, and 8) showed a minimum for n = 6. Furthermore, the lowest surface tension of 2 edda at the cmc was 16.4 mN m⁻¹. Such unique behavior has not been observed even in the other fluorinated surfactants. Changes in the shapes and sizes of these surfactant aggregate with concentration were investigated by dynamic light scattering and transmission electron microscopy (TEM). The TEM micrographs showed that in an aqueous alkali solution, 2 edda mainly formed aggregates with stringlike (n = 4), cagelike (n = 6), and distorted bilayer structures (n = 8). The morphological changes in the aggregates were affected by the molecular structure composed of nonflexible fluorocarbon chains and flexible hydrocarbon chains.     

Effect of different surfactants on colloidal and polymer properties of fluorinated acrylate latex

Fluorinated acrylate latex was successfully prepared by semi-continuous seeded emulsion polymerization of dodecafluoroheptyl methacrylate (DFMA) with butyl acrylate (BA), methyl methacrylate (MMA) initiated by potassium persulfate in the water. The resultant latexes and their films are characterized with Fourier transform infrared (FTIR) spectrometry, contact angle determinator, dynamic light scattering detector and surface tension determinator. Effect of different surfactants on colloidal and polymer properties of fluorinated acrylate latex was studied. Results show that the latex prepared with sodium dodecyl benzene sulfonate surfactant has the smallest particle size and contact angle but the moderate surface tension. The latex prepared with perfluorooctanesulfonic acid potassium surfactant has the smallest surface tension, moderate particle size but the biggest contact angle. The latex prepared with sodium 2-hydroxy-3-(methacryloyloxy) prop- ane-1-sulfonate surfactant has the biggest particle size and surface tension but moderate contact angle. In addition, the latex prepared with sodium 2-hydroxy-3-(methacryloyloxy) prop- ane-1-sulfonate has higher electrolyte stability.     

Effect of alkyl chain asymmetry on catanionic mixtures of hydrogenated and fluorinated surfactants

In this work we studied and compared the physicochemical properties of the catanionic mixtures cetyltrimethyl-ammonium bromide–sodium dodecanoate, cetyltrimethyl-ammonium bromide–sodium perfluorodacanoate, octyltrimethylammonium bromide–sodium perfluorodacanoate and cetyltrimethyl-ammonium bromide–sodium octanoate by a combination of rheological, transmission electron microscopy (TEM) and polarized optical microscopy measurements. The binary mixtures of the surfactants have been analyzed at different mixed ratios and total concentration of the mixture. Mixtures containing a perfluorinated surfactant are able to form lamellar liquid crystals and stable spontaneous vesicles. Meanwhile, system containing just hydrogenated surfactants form hexagonal phases or they are arranged in elongated aggregates.