Françoise Giulieri

The Incorporation of Indigo Molecules in Sepiolite Tunnels

Evidence for access of molecules the size of acetone or pyridine to the intracrystalline tunnels of nanofibre clay (sepiolite) has indicated formation of a new type of organic-inorganic nanocomposites. However, the introduction of larger molecules has been a recurring problem. It is now agreed that for indigo, the molecules are located on the external surface and at the ends of the fibres, thus blocking access to internal tunnels. We claim, however, that it is possible for indigo molecules to access the internal channels of sepiolite. FTIR and XRD analyses have provided evidence for folding of the sepiolite structure preheated at high temperature (above 350 degrees C). By comparison, we have shown that for indigo/sepiolite mixtures treated in the same conditions, no change in the crystalline structure of the sepiolite is observed, and that blue samples, related to Maya blue, with indigo molecules incorporated deeply enough into sepiolite to prevent folding of the tunnels, can be obtained. NMR, FTIR and thermal analysis confirm the interaction of indigo with the water coordinated to magnesium(II) and located inside the internal and external channels of sepiolite. Two other hypotheses are excluded; we show both that zeolitic water is not blocked in the tunnels by indigo, and that if thermal decomposition products of indigo can be formed, they are in a minority.

MICELLIZATION AND ADSORPTION OF FLUORINATED AMPHIPHILES : QUESTIONING THE 1 CF2 1.5 CH2 RULE

Great caution must be exercised when applying the 1 CF2≈1.5 CH2“rule” for surfactants: when grafted to a fluorinated chain, a hydrocarbon chain does not fully participate in micellization and adsorption processes, so these are controlled primarily by the length of the -CF2- chain. It is proposed that the hydrocarbon spacer adopts a folded conformation as a result of the difference in cross-sections between fluorocarbon and hydrocarbon chains.

Tubular microstructures made from nonchiral single-chain fluorinated amphiphiles: Impact of the structure of the hydrophobic chain on the rolling-up of bilayer membrane

The nonchiral, single-chain fluorinated amphiphiles derived from dimorpholinophosphate, C(n)F(2n+1)(CH(2))(m)OP(O)[N(CH(2)CH(2))(2)O](2) (FnCmDMPs), form hollow tubular bilayer-based self-assemblies when dispersed in water, ethanol/water mixtures, and dimethylformamide. The fluorinated tubules are highly stable and sturdy. Upon heating, they transform reversibly into giant multilamellar vesicles. Uncommon U-shaped and V-shaped coiled membranes were obtained from mixtures of FnCmDMPs. Depending on conditions, fluorinated tubules can evolve with time into collapsed flattened crystallized needles. The successive steps involved in the formation and evolution of these tubules were identified, and the specific features of fluorinated chains that are relevant to membrane coiling and tubule formation are discussed.

Can the formation of vesicles from single-chain perfluoroalkylated amphiphiles be predicted?

Abstract The formation of vesicles from single-chain perfluoroalkylated amphiphiles was recently reported. We wanted to know whether this aggregation behaviour, which is unusual for single-chain surfactants, was predictable using the amphiphile self-organization model described by J. Israelachvili, D.J. Mitchell and B.W. Ninham, J. Chem. Soc., Faraday Trans. 2, 72 (1976) 1525–1568. The pertinent surface-activity data and geometrical characteristics needed to calculate the packing parameter P were determined for two single-chain perfluoroalkylated amphiphiles (a neutral phosphoramidate and a zwitterionic phosphocholine derivative) and for their hydrogenated analogues. It was found that the polar-head surface area remained identical for fluorinated and hydrogenated amphiphiles while, as expected, the hydrophobic chain volume of the former was significantly larger. The structures predicted from these results are vesicles in the case of the perfluoroalkylated amphiphiles ( P =0.7) and micelles in the case of their hydrogenated analogues ( P =0.5), in agreement with our previously reported experimental results. The formation of vesicles instead of micelles from F-alkylated single-chain amphiphiles can thus be explained by their truncated-cone geometry. It is also suggested that the bulkiness of the fluorinated chains brings them closer together, thus increasing lateral hydrophobic interactions.

Supramolecular assemblies from single-chain perfluoroalkylated phosphorylated amphiphiles

Abstract We report here that a diversity of organized supramolecular systems of various shapes and structures, including vesicles, fibers and globules, can be formed from dispersions of single-chain perfluoroalkylated phosphocholine derivatives and dimorpholinophosphoramidates. The formation of these various aggregates can be controlled by regulating the amount of energy provided to the system. This highly versatile aggregation behavior of the fluorinated amphiphiles is in marked contrast to that of the hydrogenated analogs which only form micelles. The fluorinated aggregates have been characterized by transmission electron microscopy after freeze-fracture or negative staining and by optical microscopy. Their size has been assessed by laser light scattering spectroscopy.

Impact of the structure of phospholipid dispersions on the stability of fluorocarbon/phospholipid emulsions for biomedical uses

Abstract The preparation of injectable fluorocarbon emulsions includes the dispersion of the phospholipids in the aqueous phase, then the admixing of the fluorocarbon to produce a crude premix; emulsification is then achieved using a high pressure mechanical procedure, followed by final heat-sterilization. In this work we report that, depending on the procedure used and energy applied, the dispersions of phospholipids consist of poorly organized unclosed “pre-liposomes”, multilamellar vesicles (MLV), or small unilamellar vesicles (SUV). This has a significant impact on the stability of the final fluorocarbon emulsions (90% (w/v) concentration), those prepared from “pre-liposomes” being more stable than those prepared from MLV or SUV. The first emulsion is shown to contain less fluorocarbon-free phospholipid vesicles than the other two. These free vesicles have previously been reported to have a detrimental effect on the stability of concentrated fluorocarbon emulsions.

Impact of the Spacer on the Condensing Effect of Fluorinated Chains Investigated by Grazing Incidence X-ray Diffraction on Ultrathin Langmuir Monolayers

Langmuir monolayers of double perfluoroalkyl(alkyl) chain amphiphiles fitted with a monomorpholinophosphate polar head, [C(n)F(2n+1)(CH(2))(m)O](2)P(O)[N(CH(2)CH(2))(2)O] (di(FnHm)MP with n = 6, 8, or 9; and m = 1 or 2), were investigated by surface pressure (π)/molecular area (A(0)) compression isotherms for temperatures ranging from 15 to 50 °C, and by grazing-incidence X-ray diffraction (GIXD) at 25 °C. Ultrathin monolayers were obtained for these short surfactants. Though the hydrocarbon spacer is short, it has a remarkable impact on the monolayers organization. At 25 °C, whereas di(F8H2)MP monolayer presents a liquid expanded (LE)/liquid condensed (LC) transition, simply replacing one CH(2) by a CF(2) in the latter compounds structure at constant chain length, i.e. shortening the spacer from 2 to 1 CH(2) (as in di(F9H1)MP), suppresses the LE phase. At 25°, GIXD established that for both di(F8H2)MP and di(F9H1)MP, the chains form an hexagonal lattice in the LC phase. The collective tilt of the two compounds is close to zero. The lattice of the dense phase can be compressed, as assessed by the continuous linear decrease of the d spacing with increasing pressure. This indicates that the azimuthal distribution of the molecular tilts is progressively reduced upon compression. The d value for di(F9H1)MP is significantly lower than that of di(F8H2)MP, providing evidence for strong condensing effect of the fluorinated chains. Molecular areas were determined directly from the compression curves and also from the X-ray data, the latter allowing reconstruction of the compression isotherms. The calculated lattice compressibilities are ~30% and 50% of the macroscopic compressibilities for di(F9H1)MP and di(F8H2)MP, respectively. Comparison with the experimentally determined isotherms shows that the monolayer of di(F9H1)MP is more stable than that of di(F8H2)MP. The enthalpies and entropies determined for di(F9H1)MP and di(F8H2)MP, derived from the Clausius-Clapeyron equation, confirm that the observed transitions are both of the LE/LC type, although the triple point temperatures are strikingly different (27 °C vs -18 °C); this large difference further illustrates the stabilizing effect of the fluorinated chains. Disorder is hindered by the fluorinated chains and facilitated by a hydrocarbon spacer when larger than 1 CH(2).

Indigo/sepiolite nanohybrids: stability of natural pigments inspired by Maya blue

Maya blue is formed from insertion of indigo into palygorskite and sepiolite. Sepiolite and palygorskite are porous fibrous clays. Controlling the insertion, location and organisation of organic molecules in the cavities of nanotubes associated with the release or stability of these molecules is a crucial challenge in the evolution towards unusual properties in nanotechnologies. We validate simple FTIR analyses able to determine the location of indigo in or outside the pores of the fibres. Then, we compare the stability of indigo/palygorskite and indigo/sepiolite systems obtained from similar formulations. The heating treatment is stopped when all indigo is complexed with the clay. We show that in these conditions indigo/palygorskite is more stable than indigo/sepiolite. The formation of stable pigment is more complicated for indigo–sepiolite than for indigo–palygorskite.

Microtubules from Fluorinated Phosphorylated Amphiphiles in Aqueous/Alcoholic and Non-Aqueous Solvents

Abstract Phospholipids are known to self-organize into bilayer membranes and liposomes. Recently, much attention has also been focussed on highly ordered cylindrical, bilayer-based hollow microstructures usually called tubules, that form, for example, from diacetylenic phosphatidylcholines [1]. However, despite the potential of these new supramolecular architectures in both fundamental and applied area, only few tubule-forming surfactants have been reported yet. We have shown that the driving force required to form and stabilize coiled membranes in water can be brought by fitting amphiphiles with a single fluorinated chain, without need for rigid segments, hydrogen bonding between polar head or chiral centers [2,3].

Enhanced Proclivity to Self-Aggregation of Phosphorus-Based Amphiphiles when Perfluoroalkylated : The (Perfluoroalkyl)Alkyl Dimorpholinophosphates

Abstract Dimorpholinophosphates 1, with a single perfluoroalkyl chain, self-aggregate when dispersed in water to give tubular structures which reversibly transform into giant vesicles when heated. Compounds 1 also allow the preparation of stable reverse water-in-fluorocarbon emulsions destined to pulmonary drug delivery. None of this could be achieved with non-fluorinated analogs.