Eric Da Silva

Para-acyl-calix-arene based solid lipid nanoparticles (SLNs): a detailed study of preparation and stability parameters

The preparation and stability parameters of para-acyl-calix[4]arene based solid lipid nanoparticles (SLNs) have been investigated. Atomic force microscopy (AFM) and photon correlation spectroscopy (PCS) show a mean particle size of 130 nm. In terms of preparation parameters, using the solvent displacement method, the nature and the volume of the organic solvent, the concentration of the amphiphile and the presence of a co-surfactant in the organic phase have been shown to affect significantly the size of the produced SLNs. In contrast, the stirring speed, the viscosity and the acidity of the aqueous phase and the amphiphile hydrophobic chain length have been shown to have no effect. In terms of stability parameters, the ionic strength has been shown to affect the short-time SLN stability depending on both the anion and the cation studied, with sodium sulphate causing precipitation. Ultrasonic, ultraviolet or microwave treatments of the SLN suspensions have no effect on the size of the SLNs. The study of the effects of short time thermal treatment revealed that the SLNs are not affected by one freezing-defreezing cycle and are stable at 100 degrees C in suspension. It is difficult to reconstitute the SLN suspensions after freeze-drying. Finally, the temporal stability of these suspensions in water has been shown to be superior to 1 year. The long-term temporal stability of suspensions stored in saline solution has been investigated. It has been demonstrated that the most destabilising effects arise from the presence in the storage suspension of sulphate ions.1H NMR, X-ray powder diffraction (XPD) and AFM have also been carried out on the calix-arene based SLNs and demonstrate the presence of a semi-organised matrix structure for the SLNs.

Synthesis and complexation properties towards amino acids of mono-substituted p-sulphonato-calix-[n]-arenes

Abstract A series of mono-hydroxy functionalised calix-[ n ]-arenes, and p -sulphonato-calix-[ n ]-arenes where n =4, 6 and 8, have been synthesised, with the pendant functions being ethoxycarbonyl methoxy group, 2-carboxy methoxy group, 2-amido methoxy group or 2-amino ethoxy group. With calix-[4]-arene and calix-[6]-arenes the compounds are obtained in good yield by treatment of the relevant p -H-calix-[ n ]-arene with a suitable metal carbonate, as a weak base, in the presence of one equivalent of the corresponding alkyl bromide. However in the case of calix-[8]-arene, the extremely low solubility of p -H-calix-[8]-arene prevented its use and p - t Bu-calix-[8]-arene was used in the monosubstitution reactions. The corresponding sulphonate derivatives were prepared in the case of the 2-carboxy methoxy group, 2-amido methoxy group and 2-amino ethoxy group systems, either by sulphonation of the para -H derivatives or by ipso -sulphonation of the tert -butyl derivatives. The complexation properties of the water-soluble p -sulphonato-derivatives with regard to 11 amino acids have been studied by 1 H NMR titration experiments. The obtained association constants show a 1:1 stoichiometry. The presence of a pendant group at the lower rim of calix strongly modifies the observed association constant as compared to the parent p -sulphonato-calix-[ n ]-arenes. While generally, the cationic amino acids lysine and arginine bind strongly to all the derivatives, the binding of other amino acids is dependant on the nature of the pendant functions, in particular pendant arm-lateral chain function leads to strong binding with aspartic acid, serine and tryptophan.

A First Approach to the Study of Calixarene Solid Lipid Nanoparticle (SLN) Toxicity

The haemolytic effects of a series of amphiphilic calix-arene derived Solid LipidNanoparticles (SLNs) have been measured on human erythrocytes. The effectsof both the hydrophobic chain length and the nature of the polar head-groups on theamphiphilic calix[4]arene have been investigated. For all systems, no haemolyticeffects are observed.

A new packing motif for para-sulfonatocalix[4]arene: the solid state structure of the para-sulfonatocalix[4]arene D-arginine complex

The solid-state structure of the complex of para-sulfonatocalix[4]arene with d-arginine, contains a water channel diagonal to a zigzag bilayer of the host, within the bilayer six crystallographically independent molecules of arginine are present, four being included in the calix cavities.

The Use of Electrospray Mass Spectrometry (ES/MS) for the Differential Detection of Some Steroids as Calix-[n]-arene Sulphonate Complexes

Non-covalent inclusion complexes formed between three p-sulphonato-calix-[n]-arenes (1 n = 4, 2 n = 6 and 3 n = 8) and three steroids (progesterone, testosterone and oestradiol) have been studied by electrospray mass spectrometry (ES/MS). Mass spectrometric titration experiments have demonstrated differences with regard to selectivity of each p-sulphonato-calix-[n]-arene against the steroids. p-sulphonato-calix-[8]-arene interacts more strongly with oestradiol and p-sulphonato-calix-[6]-arene with progesterone. Studies in which different orifice voltages were applied show that all oestradiol complexes are reduced in signal intensity at 50 V as compared to 20 V, whereas the intensities observed for the testosterone and progesterone complexes do not vary with voltage. Competition experiments confirm the selectivity of the complexation.

Crystal engineering of a calix-arene dimer embedded in a hydrophobic cavity formed by a diammonium host matrix

Abstract The crystal structure of the 2:1 1,6-diamino-hexane: para-H-calix-4-arene-25,27-di-phosphonate complex shows a designed encapsulation of a calix-arene dimer within a three-dimensional matrix formed by the diamine molecules, the slight mismatch in the length of the diamine molecules compared to the size of the calix-arene molecule is compensated by chain folding in the diamine

The structure of a self-assembled calixarene aqua-channel system

The crystal structure of the complex 12.calix-[4]-arene dihydroxyphosphonic acid, 12.propane diammonium, 12.ethanol and 40.water molecules is based on dimeric units of the calix, assembled via trigonal units into a hexameric tube of 15 A radius and 16 A depth, further assemby via spanning propane diammonium cations and ethanol molecules forms a channel (40 A), selectively containing all the water molecules.

Synthesis and solid-State structures of mono-Functionalised para-H-Calix-[6]-arenes

Abstract A high yield synthetic route to mono-alkylated calix-[6]-arenes and the crystal structure of two of these molecules, 37,38,39,40,41-pentahydroxy-37-(2-cyano-methyloxy)-calix-[6]-arene and 37,38,39,40,41-pentahydroxy-37-(2-carboxy-methyloxy)-calix-[6]-arene are described.

A deep tetranuclear metallo-cavitand with bis(aryl) palladium bridges

A neutral metallo-cavitand based on cis bis-perhaloaryl Pd(II) bridges co-ordinated at the corners of a deep calix[4]arene. Both the metallo-cavitand and its inclusion complexes with other calix[4]arenes were investigated by means of (1)H and (19)F NMR experiments.