Fluorinated phosphocholine-based amphiphiles as components of fluorocarbon emulsions and fluorinated vesicles

Progress in the synthesis of fluorinated phosphatidylcholines for biological applications

Fluorinated phospholipids have attracted a lot of interest over the past 40 years. While mono- and polyfluorinated analogs are mostly designed to be used as ¹⁹F NMR probes, highly fluorinated phospholipids are mainly developed as drug delivery devices and oxygen carriers. This review describes their synthetic pathways, their properties and potential applications.

Supported Membranes Meet Flat Fluidics: Monitoring Dynamic Cell Adhesion on Pump-Free Microfluidics Chips Functionalized with Supported Membranes Displaying Mannose Domains

In this paper we demonstrate the combination of supported membranes and so-called flat microfluidics, which enables one to manipulate liquids on flat chip surfaces via “inverse piezoelectric effect”. Here, an alternating external electric field applied to the inter-digital transducers excites a surface acoustic wave on a piezoelectric substrate. Employing lithographic patterning of self-assembled monolayers of alkoxysilanes, we successfully confine a free-standing, hemi-cylindrical channel with the volume of merely 7 µL . The experimentally determined maximum flow velocity scales linearly with the acoustic power, suggesting that our current setup can drive liquids at the speed of up to 7 cm/s (corresponding to a shear rate of 280 s⁻¹) without applying high pressures using a fluidic pump. After the establishment of the functionalization of fluidic chip surfaces with supported membranes, we deposited asymmetric supported membranes displaying well-defined mannose domains and monitored the dynamic adhesion of E. Coli HB101 expressing mannose-binding receptors. Despite of the further technical optimization required for the quantitative analysis, the obtained results demonstrate that the combination of supported membranes and flat fluidics opens a large potential to investigate dynamic adhesion of cells on biofunctional membrane surfaces with the minimum amount of samples, without any fluidic pump.

Interactions of DPPC with semitelechelic poly(glycerol methacrylate)s with perfluoroalkyl end groups

Semitelechelic poly(glycerol methacrylate)s having a perfluoroalkyl end group (PGMA(n)-F(9)) were synthesized by ATRP. The interactions of these polymers with different degrees of polymerization with chiral or racemic dipalmitoylphosphatidylcholine (l-DPPC, d-DPPC, or rac-DPPC) monolayers at the air/water interface were studied. Langmuir trough measurements coupled with epifluorescence microscopy allowed for the observation of domain formation within the coexistence region of liquid-expanded (LE) and liquid-condensed (LC) states of DPPC in mixed DPPC-polymer films prepared by spreading a solution of both compounds in the same organic solvent (cospread films). Because of the incorporation of PGMA(n)-F(9) polymers into the LE phase and their line-active behavior, a formation of novel types of domains could be observed. During compression, a thinning out of the tips of two- to six-lobed flowerlike domain structures and consecutive spiral formation appeared for l- and d-DPPC within the two-phase coexistence region (LE/LC) of the monolayer. When rac-DPPC was used, symmetrical stripe formation was induced at the vertices of the domains and fingerprint-like structures were created by convection-inducing movements of the domains at the air/water interface. Additional investigations of the interaction of PGMA(n)-F(9) with DPPC vesicles using differential scanning calorimetry (DSC) supported the finding on the monolayer system that the incorporation of the polymers into the lipid monolayers is not solely driven by the perfluoroalkyl chain but significantly by the hydrophilic polymer part. Apparently, interactions of the PGMA chain with the lipid headgroups are important as the interactions increase with the elongation of the polymer chain, indicating that the polymer also has hydrophobic character.

Attenuating the size and molecular carrier capabilities of polyacrylate nanoparticles by a hydrophobic fluorine effect

This study investigates the effect of introducing alkyl chain fluorination on the properties of polyacrylate nanoparticles prepared in aqueous solution by emulsion polymerization. For this, 2,2,3,3,4,4,4-heptafluorobutyl acrylate (1) and methyl trifluoroacrylate (2) were tested as monomers as a means to prepare fluorinated polyacrylate nanoparticles to evaluate how side chain fluorination may affect nanoparticle size and drug carrier properties. Our results show that as fluorine content within the polyacrylate matrix increases, the size of the nanoparticle systematically diminishes, from 45 nm (for nanoparticles containing no fluoroacrylate) to ~7 nm (for nanoparticles constructed solely of fluoroacrylate). We also observe that as fluoroacrylate content and hydrophobicity increases, the nanoparticles decrease their ability to incorporate lipophilic molecules during the process of emulsification. These findings have meaningful implications in the implementation of fluorinated nanoparticles in molecular delivery.

Long Lived Microbubbles for Oxygen Delivery

Exceptionally long lived microbubbles containing a fluorocarbon as part of their filling gas have been obtained by using a fluorinated phospholipid instead of a standard phospholipid as shell component. An unexpected, strong synergistic effect between the fluorocarbon gas and the fluorinated phospholipid has been discovered. Such bubbles could be used for in vivo oxygen delivery, ultrasound contrast imaging and drug delivery.

Purification and thermal analysis of perfluoro-n-alkanoic acids

Purification of perfluoro-n-alkanoic acids (C(n)F(2n+1)COOH, n=7, 9, 11, 13, 15 and 17) was made by repeated recrystallizations from n-hexane/acetone mixed solvent, and their purity was found to be more than 99.5% by GC-MS, NMR, and elemental analysis. The thermal behaviors such as melting point and enthalpy change of fusion were investigated using differential scanning calorimetry (DSC). The melting point monotonously increased with increasing carbon number (n) of the acids, while the enthalpy change showed irregularity at n=14. The crystal structure of these acids was found to be dependent upon solvent used for recrystallization; that is, the acids recrystallized from the above solvent becomes more stable energetically, indicating their higher enthalpy change of fusion than that of the solidified acids from fused ones. The solid state was also found to vary depending upon the thermal history, indicating that a few crystal structures of the solid state are quite similar energetically. The melting points (T(m)) of perfluoro-n-alkanoic acids are higher than those of corresponding n-alkanoic acids, and the difference in T(m) increases with increasing carbon number in the acids.

Water evaporation rates across hydrophobic acid monolayers at equilibrium spreading pressure

The effect of alkanoic acid [CH(3)(CH(2))(n-2)COOH; HCn] and perfluoroalkanoic acid [CF(3)(CF(2))(n-2)COOH; FCn] monolayers on the water evaporation rate was investigated by thermogravimetry tracing the decrease in amount of water with time. The evaporation rate from the surface covered by a monolayer was measured as a function of temperature and hydrophobic chain length of the acids, where the monolayer was under an equilibrium spreading pressure. From thermal behavior of the crystallized acids, their solid states are C-type in crystalline state over the temperature range from 298.2 to 323.2 K. The dry air was flowed through a furnace tube of a thermogravimetry apparatus at the flow rate of 80 mL min(-1), where the evaporation rate becomes almost constant irrespective of the flow rate. The temperature dependence of the evaporation rate was analyzed kinetically to evaluate the activation energy and thermodynamics values for the activated complex, which demonstrated that these values were almost the same for both alkanoic acids and perfluoroalkanoic acids, although the effect of perfluoroalkanoic acids on the evaporation rate was smaller than that of corresponding hydrogenated fatty acids. The difference in the evaporation rate between FCn and HCn was examined by atomic force microscopy (AFM), Brewster angle microscopy (BAM), surface potential (DeltaV) at equilibrium spreading pressure, and Langmuir curve (pi-A isotherm), and their results were consistent and supported the difference.

Nanoscale patterning in mixed fluorocarbon-hydrocarbon phospholipid bilayers

A growing body of literature suggests that fluorocarbons can direct self-assembly within hydrocarbon environments. We report here the fabrication and characterization of supported lipid bilayers (SLBs) composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and a synthetic, fluorocarbon-functionalized analogue, 1. AFM investigation of these model membranes reveals an intricate, composition-dependent domain structure consisting of approximately 50 nm stripes interspersed between approximately 1 microm sized domains. Although DSC of 1 showed a phase transition near room temperature, DSC of DPPC:1 mixtures exhibited complex phase behavior suggesting domain segregation. Finally, temperature-dependent AFM of DPPC:1 bilayers shows that, while the stripe structures can be melted above the Tm of 1, the stripes and domains result from immiscibility of the hydrocarbon and fluorocarbon lipid gel phases. Fluorination appears to be a promising strategy for chemical self-assembly in two dimensions. In particular, because no modification is made to the lipid headgroups, it may be useful for nanopatterning biologically relevant ligands on bilayers in vitro or in living cells.

The Design and Synthesis of Highly Branched and Spherically Symmetric Fluorinated Oils and Amphiles

A new emulsifier design principle, based on concepts borrowed from protein science, is proposed. Using this principle, a class of highly branched and spherically symmetric fluorinated oils and amphiles has been designed and synthesized, for potential applications in the construction of fluorocarbon nanoparticles. The Mitsunobu reaction was employed as the key step for introducing three perfluoro-tert-butoxyl groups into pentaerythritol derivatives with excellent yields and extremely simple isolation procedures. Due to the symmetric arrangement of the fluorine atoms, each fluorinated oil or amphile molecule gives one sharp singlet (19)F NMR signal.

Properties of two-component Langmuir monolayer of single chain perfluorinated carboxylic acids with dipalmitoylphosphatidylcholine (DPPC)

The surface pressure (pi)- and the surface potential (DeltaV)-area (A) isotherms were obtained for two-component monolayers of four different perfluorocarboxylic acids (FCns; perfluorododecanoic acid: FC12, perfluorotetradecanoic acid: FC14, perfluorohexadecanoic acid: FC16, perfluorooctadecanoic acid: FC18) with dipalmitoylphosphatidylcholine (DPPC) on substrate solution of 0.15 M NaCl (pH 2.0) at 298.2 K as a function of compositions in the mixtures by employing the Wilhelmy method, the ionizing electrode method, the fluorescence microscopy, and the atomic force microscopy. The data for the two-component monolayers on these systems were analyzed in terms of the additivity rule. Assuming a regular surface mixture, the Joos equation which allows one to describe the collapse pressure of a two-component monolayer with miscible components was used to declare the miscibility of the monolayer state, and an interaction parameter and an interaction energy were calculated. The new finding was that FCns and DPPC are miscible or immiscible depending on chain length increment of fluorocarbon part. That is, FC12/DPPC monolayer was perfectly miscible, and FC14/DPPC, and FC16/DPPC (0 < or = X(FC16) < or = 0.3) monolayers were partially miscible. While FC16/DPPC (0.3 < X(FC16) < 1) and FC18/DPPC systems are immiscible in the monolayer state. Furthermore, the mean molecular area, the surface dipole moment, and the phase diagrams enabled us to estimate the molecular orientation of four different perfluorocarboxylic acids/DPPC in the two-component monolayer state. One type of phase diagrams was obtained and classified into the positive azeotropic type. The miscibility of FCns and DPPC in the monolayer was also supported by fluorescence microscopy and atomic force microscopy. FC12/DPPC, FC14/DPPC and FC16/DPPC (0 < or = X(FC16) < or = 0.3) two-component monolayers on 0.15 M NaCl (pH 2) showed that FC12, FC14 and FC16 (0 < or = X(FC16) < or = 0.3) can dissolve or partially dissolve the ordered solid DPPC domains formed upon compression. This indicates that these fluorinated amphiphiles soften or harden the lipid depending on their chain length.

Perfluoroalkylphosphocholines are poor protein-solubilizing surfactants, as tested with neutrophil plasma membranes

We have tested the membrane-protein solubilizing properties of two perfluoroalkylphosphocholines. These compounds belong to a series of fluorinated amphiphiles which are being investigated as potential stabilizing agents for a variety of fluorocarbon-based systems. We are particularly interested in cytochrome b558 from phagocytes, the redox component of NADPH oxidase. Its heavy subunit is believed to carry binding sites for NADPH and FAD. Nevertheless, when the cytochrome is purified in the presence of classical detergents, it carries no FAD. This could be due to a delipidating, denaturing effect of these detergents (octyl glucoside, Triton, etc). The first perfluoroalkyphosphocholine, C8F17(CH2)2O-P(O2-)-O(CH2)2N+(CH3)3(F8C2PC), extracted about as much protein from neutrophil plasma membranes into a 100,000 g supernatant as octyl glucoside. The second compound, C8F17(CH2)11O-P(O2-)-O(CH2)2N+(CH3)3(F8C11PC), was less efficient. We found that flavin was still protein-bound in the crude F8C2PC extract at a FAD to heme ratio of about 1, and a good NADPH oxidase activity was obtained without addition of exogenous FAD, even after dialysis or gel filtration, whereas dialysis eliminated most of the FAD from the octyl glucoside extracts. These experiments appeared to make F8C2PC an interesting membrane-solubilizing agent. Nevertheless, no protein in the F8C2PC extract could be adsorbed on the chromatographic supports normally used for purification. After dilution of the extract and addition of 15 mM octyl glucoside, some of the proteins, such as myeloperoxidase, could be adsorbed (and eluted), but not cytochrome b558. Freeze-fracture electron microscopy showed that the F8C2PC extracts contained numerous vesicles and aggregates of small shapeless particles. Higher centrifugal forces sedimented most proteins of the 100,000 g supernatant. As a check, the effect of F8C2PC was tested on sarcoplasmic reticulum vesicles, the behavior of which with respect to the usual non-denaturating detergents has been well studied. There was little, if any, solubilization. We conclude that, although supernatants of F8C2PC extracts of neutrophil membranes are optically clear, proteins are not really solubilized. This result is in keeping with the absence of lytic effects of F8C2PC on erythrocyte membranes.