Christophe Fajolles

Physico-chemical investigation of asymmetrical peptidolipidyl-cyclodextrins.

A new class of amphiphilic peptidolipidyl-cyclodextrins is reported. The derivatives are chiral due to the presence of an L-leucine in the spacer arm that links a saccharide moiety and a grafted, saturated hydrocarbon chain. Self-assembly properties of the peptidolipidyl-cyclodextrins are characterized by quasi-elastic light scattering, turbidity and UV-visible absorption measurements. NMR experiments give insight into the intermolecular dipolar interactions as a function of temperature and concentration. N-dodecyl-N alpha-(6 I-amidosuccinyl-6 1-deoxy-cyclomaltoheptaose)-L-leucine (1) is poorly soluble in aqueous media. N-dodecyl-N(alpha)-(6 I-amidosuccinyl-6 I-deoxy-2 I,3 I-di-O-methyl-hexakis-(2 II-VII,3 II-VII,6 II-VII-tri-O-methyl)-cyclomaltoheptaose)-L-leucine (2) is found to be more soluble and self-assembles into stable supramolecular colloidal aggregates with nanometric dimensions above a critical aggregation concentration (CAC). It has a propensity for solubilization of hydrophobic species revealing a micellar-like behavior, which is compared to that of the non-ionic detergent octyl glucoside. On the contrary, compound 1 precipitates in a crystalline phase beyond its water solubility limit, and it does not display any solubilizing capacity. The observed behavior corroborates at the molecular level with the NMR results.

[3H]RP 62203, a ligand of choice to label in vivo brain 5-HT2 receptors.

There are only a few ligands available for labelling brain receptors simply because in vivo binding requires more severe experimental conditions than in vitro binding. We now describe the in vivo binding properties of [3H]RP 62203, a new potent and selective 5-HT2 antagonist. After intravenous injection into rats, [3H]RP 62203 accumulated predominantly in brain regions containing 5-HT2 receptors, with a frontal cortex/cerebellum ratio of 6 to 7. A good correlation was obtained between the regional distribution of [3H]RP 62203 in the brain and the density of 5-HT2 receptors measured in vitro. In vivo binding of [3H] RP 62203 was saturable in the frontal cortex but not in the cerebellum. The Bmax in the frontal cortex was equal to 42.5 fmol/mg, thus in the same range as was found in vitro. The 5-HT2 selectivity was ascertained by displacement (prevention) experiments; 5-HT2 antagonists or the agonist 2,5-dimethoxy- 4-iodophenylisopropylamine could prevent specific labelling of [3H]RP 62203 only in brain regions containing 5-HT2 receptors. Interestingly, the radioactivity remaining in various brain regions after displacement with pipamperone corresponded exactly to that measured in the cerebellum, with or without pipamperone. In conclusion, [3H]RP 62203 possesses striking properties of in vivo binding which make it a suitable candidate for examining 5-HT2 receptors in human brain by positron emission tomography scanning.

Insertion properties of cholesteryl cyclodextrins in phospholipid membranes: a molecular study

Amphiphilic cyclodextrins (CDs) are good candidates to functionalize natural membranes, as well as synthetic vesicles. In this paper, we fully describe and compare the insertion properties of the permethylated mono-cholesteryl α-CD (TASC) and its mono- and di-cholesteryl β-CD analogues (TBSC and TBdSC) in dipalmitoyl-L-α-phosphatidylcholine (DPPC) mono- and bi-layers as membrane models from the macroscopic to the molecular scale. By calculating the inverse compressibility moduli and free excess Gibbs energies from the Langmuir isotherms, the influence of the CD type, CD ratio and number of cholesteryl anchors on the membrane properties have been established. TBdSC, with its two cholesteryl residues, seems to be anchored best to the membrane compared to CD derivatives with only one anchor. Furthermore, TASC appears to be more firmly inserted into the membrane than TBSC. The in-plane structure is characterized by Brewster angle microscopy (BAM) at the air–water interface and atomic force microscopy (AFM) of the mono- and bi-layers deposited on mica. Depending on the compression, full miscibility of the cholesteryl CDs and the phospholipids is observed at low surface pressures and a clear demixing tendency is apparent during compression. CD-modified bilayers are stable and are subject to a gel–liquid phase transition upon heating. Due to their bulky CD moiety, the amphiphilic CDs exhibit a distinct fluidizing effect, shifting the DPPCs gel–liquid transition. The structure of the mixed TASC/DPPC mono- and bi-layers perpendicular to the surface is investigated with Angstrom resolution by neutron reflectivity. In this way a molecular model of the insertion has been established, which suggests that the CD cavities partly protrude into the subphase, which should leave them accessible for complex formation.

Low-frequency Raman spectra of fluorobenzene in the liquid state

Abstract Low-frequency Raman spectra of liquid fluorobenzene at −15°C and 60°C are investigated. Both spectra show in the R( ν )-representation a broad band with a maximum at approximately 75 cm−1. This is assigned to librational motions. A simple model based on a damped oscillator is used to explain main features in the spectra.

Amphiphilic behavior and membrane solubility of a dicholesteryl-cyclodextrin.

Amphiphilic cyclodextrins (CDs) are good candidates to functionalize natural membranes as well as synthetic vesicles. In this paper, we provide a full description of the interfacial behavior of pure 6I,6IV-(β-cholesteryl)succinylamido-6I,6IV-(6-deoxy-per-(2,3,6-O-methyl))cycloheptaose (TBdSC) and how it inserts in dipalmitoyl-l-α-phosphatidylcholine (DPPC) monolayers as a membrane model. Langmuir isotherms of pure TBdSC suggest a reorganization upon compression, which could be clarified using X-ray reflectivity. The CD head can adjust its conformation to the available area per molecule. A compatible model involving a rotation around a horizontal axis defined by the two selectively substituted glucose units is proposed. The in-plane structure is characterized at all scales by Brewster angle microscopy (BAM) on the water surface and atomic force microscopy (AFM) on monolayers deposited on solid substrates. The same tools are used for its mixtures with DPPC. We show in particular that TBdSC seems to be soluble in the liquid-expanded DPPC. However, phase segregation occurs at higher pressure, allowing for sequentially liquid-condensed DPPC and high-pressure conformation of TBdSC. This gives rise to a remarkable contrast inversion in both imaging methods.

Membrane insertion of sliding anchored polymers

We have studied the insertion into lipid bilayers of Sliding Anchored Polymers (SAPs), a new class of macromolecules based on topological complexes between end-capped polyethylene glycol (PEG) polymers and mono-cholesteryl cyclodextrins (CD). By using Infra Red Reflection Absorption Spectroscopy (IRRAS) we demonstrate that these new sliding polymer complexes anchor well in phospholipid model membranes self-assembled from DPPC. The in-plane organization is characterized by Brewster Angle Microscopy (BAM) at the air–water interface and by Atomic Force Microscopy (AFM) for lipid monolayers and for lipid bilayers deposited on mica. Demixing between SAPs and the phospholipids is observed even at low surface pressures. Using neutron reflectivity, we show that for sufficiently high polymer densities the SAPs inserted into lipid monolayers and lipid bilayers form polymer brushes, consistent with theoretical predictions for polymers with a sliding anchor.

Amphiphilic behavior of new cholesteryl cyclodextrins: a molecular study.

Amphiphilic cyclodextrins (CDs) are good candidates to functionalize natural membranes as well as synthetic vesicles. In this paper, we describe the synthesis of the amphiphilic permethylated monocholesteryl α-CD (TASC). Its interfacial behavior is compared with that of the permethylated mono- and dicholesteryl β-CD analogues (TBSC and TBdSC). Langmuir isotherms suggest a reorganization upon compression for all compounds, which is quantified using neutron as well as X-ray reflectivity. The in-plane structure is characterized by atomic force microscopy (AFM) on monolayers deposited on solid substrates. A model involving a reorientation of the CD with respect to the interface to adjust its conformation to the available area per molecule is proposed. Although we observe for TBSC a rearrangement similar to TASC and TBdSC, it is already achieved at lower surface pressures compared with its disubstituted derivative. This specific behavior is explained by an increased structural flexibility and compressibility compared with TBdSC and TASC. The average number of water molecules per CD was determined using the neutron data and validated from X-ray data, which also allows the determination of the CDs molecular volume. The permethylated CD molecules are strongly hydrated in the film, but the α-CD analogue is less hydrated than the β-CD derivatives, and hydration decreases with compression.

Sliding tethered ligands add topological interactions to the toolbox of ligand–receptor design

Adhesion in the biological realm is mediated by specific lock-and-key interactions between ligand–receptor pairs. These complementary moieties are ubiquitously anchored to substrates by tethers that control the interaction range and the mobility of the ligands and receptors, thus tuning the kinetics and strength of the binding events. Here we add sliding anchoring to the toolbox of ligand–receptor design by developing a family of tethered ligands for which the spacer can slide at the anchoring point. Our results show that this additional sliding degree of freedom changes the nature of the adhesive contact by extending the spatial range over which binding may sustain a significant force. By introducing sliding tethered ligands with self-regulating length, this work paves the way for the development of versatile and reusable bio-adhesive substrates with potential applications for drug delivery and tissue engineering.