Florent Perret

Biochemistry of the para-sulfonato-calix[n]arenes

The biochemistry of the para-sulfonato-calix[n]arenes has shown rapid development during the past ten years, the highly diverse biomedical applications of these molecules now include anti-viral, anti-thrombotic activities, enzyme blocking and protein complexation. The future is even more promising as para-sulfonato-calix[n]arenes have, now, been shown to have potential in the diagnosis of prion-based diseases. Their innocuous nature, as far as is known at present, may open up their future use in medications.

Calix[n]arenes as Protein Sensors

The use of calix[n]arene derivatives for the sensing of proteins is described. Initially the properties of the calix[n]arenes are described. In order to better understand how the calix[n]arenes may be used for protein sensors, a detailed survey of the interactions between the molecules and amino acids and peptide is presented. The known complexes between proteins and various calix[n]arene derivatives is described and the biological activity of the molecules summarised. The use of calix[n]arenes as protein sensors observed by Schrader using amphiphilic calix[n]arenes shows that these molecules may allow nanomolar sensing. The major section of the work deals with the development of a para-sulfonato-calix[n]arene-based system for the prion protein responsible for bovine spongiform encephalitis and variant-Creutzfeldt–Jacobs disease(v-CJD) in humans. Initially, the development of the test was based on a Western Blot detection, however, the need for large scale testing after the discovery that blood transfusion may lead to infection with v-CJD led to the transfer of the technology to an ELISA-based test.

Design, synthesis, and in vitro evaluation of new amphiphilic cyclodextrin-based nanoparticles for the incorporation and controlled release of acyclovir

Acyclovir possesses low solubility in water and in lipid bilayers, so that its dosage forms do not allow suitable drug levels at target sites following oral, local, or parenteral administration. In order to improve this lack of solubility, new cyclodextrin-based amphiphilic derivatives have been designed to form nanoparticles, allowing the efficient encapsulation of this hydrophobic antiviral agent. The present work first describes the synthesis and characterization of five new O-2,O-3 permethylated O-6 alkylthio- and perfluoroalkyl-propanethio-amphiphilic β-cyclodextrins. These derivatives have been obtained with good overall yields. The capacity of these molecules to form nanoparticles in water and to encapsulate acyclovir has then been studied. The nanoparticles prepared from the new β-cyclodextrin derivatives have been characterized by dynamic light scattering and have an average size of 120nm for the fluorinated derivatives and 220nm for the hydrogenated analogs. They all allowed high loading and sustained release of acyclovir.

Conformational extremes in the supramolecular assemblies of para-sulfonato-calix[8]arene

Two complex solid state structures of para-sulfonato-calix[8]arene are described, showing extremes in the macrocyclic conformation; one is planar and nearly circular, the other an inverted double cone. The differences in the molecular conformations lead to highly different packing arrangements in the structures.

Geometrical and inclusion considerations in the formation of hexagonal nanotubes of calix[4]arene di-methoxycarbonyl methyl ester and acid

The crystal structures of calix[4]arene di-methoxycarbonyl-methyl ester and carboxylic acid have been resolved. Interestingly, the packing for both molecules is in the form of crystal symmetry defined hexagonal helical nanotube architecture, but with the methyl ester derivative showing an extended form of the helix with regard to that formed by the carboxylic acid derivative. The addition of one carbon in the ester group leads to inclusion of the ethyl ester within a neighbouring calixarene cavity, and in consequence the packing becomes radically different.

Use of streptomycin for precipitation and detection of proteinase K resistant prion protein (PrPsc) in biological samples

The ability of streptomycin to form multimolecular aggregates with pathogenic prion proteins and their recovery by precipitation via a low-speed centrifugation step has been demonstrated; these novel properties of streptomycin make it a useful substance that increases the sensitivity of laboratory diagnostic techniques for prion infections in man and animals.

Thermodynamics of the Complexation of the p-Sulfonatocalix[4]arene with Simple Model Guests in Water: a Microcalorimetric Study

The formation of supramolecular complexes in water involves interactions of various types which are not always easy to identify, especially when complicated species are involved. A complete thermodynamic characterization of the binding process, which includes the enthalpies and entropies of complexation, is obviously one of the key elements in identifying the stabilizing factors and in understanding how the host and guest assemble. In order to thermodynamically characterize typical interactions of various types, we have thus undertaken a microcalorimetric study of the complexation of p-sulfonatocalixarenes with simple guests bearing different functional groups. Association constants, free energies, enthalpies and entropies for the complexation of the p-sulfonatocalix[4]arene with normal alcohols, alkylammonium, carboxylate and guanidinium ions in water, at pH 7.5 and 298.15 K, are reported. The properties for the binding of lysine and arginine, which bear similar functional groups, are also given. The comparison of the thermodynamic behaviour of these different guests allows the driving factors to be identified. This may constitute a starting point for the understanding of the recognition of more complicated guests.

A comparative study of the determination of the stability constants of inclusion complexes of p-sulfonatocalix[4]arene with amino acids by RP-HPLC and 1H NMR

Reversed-phase high-performance liquid chromatography (Separon SGX C 18, UV detection at 254 nm and acetonitrile–water–trifluoroacetic acid (70∶30∶0.5, v/v), and methanol–water–trifluoroacetic acid (3∶97∶0.5, v/v) as mobile phases) was applied to the study of the host–guest complexation of p-sulfonatocalix[4]arene (SC[4]A) with amino acids as guests in the mobile phase. It was established that the formation of the inclusion complexes results in changes in the retention times of the amino acids. Stability constants of the complexes were determined. The variations in stability constants may be explained in terms of the various interactions (ion-pairing, hydrophobic, aromatic–aromatic and electrostatic interactions) that may occur between a given amino acid and SC[4]A. For the amino acids aspartic acid and proline the association constants were also derived from 1H NMR experiments.

Solid state structures of the complexes between the antiseptic chlorhexidine and three anionic derivatives of calix[4]arene

The solid state structures of the complexes between antiseptic chlorhexidine and three anionic calix[4]arene derivatives are described. Each of the three calixarenes shows typical self-organisation in the solid-state that will further impose a specific complexation of the active molecule in the co-crystal.

Enhanced detection of the pathogenic prion protein by its supramolecular association with para -sulfonato -calix[n]arene derivatives

The supramolecular interaction between the pathogenic form of the prion protein and derivatives of the para-sulfonato-calix[n]arenes has been demonstrated and two putative binding sites determined; this interaction leads to an amplification of the Western Blot immunological detection of the prion protein by the SAF84 antibody.