Thiourea-linked upper rim calix[4]arene neoglycoconjugates: synthesis,conformations and binding properties

The thiourea group has been exploited to link two or four carbohydrate units at the upper rim of tetrapropoxycalix[4]arene derivatives in the cone conformation. Two synthetic methodologies were used, the first one consisting of the condensation of di- and tetraminocalix[4]arenes with the isothiocyanate of monosaccharides in dry CH2Cl2 at room temperature and the second one exploiting the condensation of an aminolactoside with a calixarene isothiocyanate. The first method allows the glycoconjugates to be obtained in 75-80% overall yields. The disfunctionalized derivatives exist in a closed flattened cone conformation in CDCl3 and CD3OD due to the formation of intramolecular hydrogen bonds involving the thiourea groups which are broken in DMSO-d6 to give an open flattened cone conformation. The thiourea groups act not only as linkers but also as binding units for anionic substrates as evidenced by solution 1H NMR and ESI-MS experiments. Turbidimetric analysis indicates that the tetraglucoside and tetragalactoside clusters give specific interactions with Concanavalin A (Con A) and peanut lectin (PNA), respectively. Both features show that the neoglycoconjugates could also be used as site specific molecular delivery systems.     

Perfluoropolyether-Silica Hybrids: Preparation and Surface Characterization

,-Triethoxysilane terminated perfluoropolyether-polycaprolactone block copolymers, TXCL(x)Si, were synthesised, characterised and subsequently reacted with tetraethoxysilane to prepare transparent organic-inorganic hybrid materials by using the sol–gel process. Surface characterization was carried out through contact angle measurements. All the materials investigated (independently on both the reaction time of the sol–gel reaction before coating application and the bulk organic-inorganic ratio) showed a strong hydrophobic character when compared with non-fluorinated and fully inorganic control materials. The highest water contact angles were obtained when TXCL(x)Si oligomer used for the preparation of the hybrid contained short hydrogenated polycaprolactone segments. In all cases, the surface tension values indicated that the very surface at the air-coating interface showed almost completely perfluoropolyether segments.     

A theoretical study of the nitrogen—graphite system

The chemisorption of atomic and molecular nitrogen on the basal plane of graphite has been studied by both semiempirical and non-empirical Hartree—Fock methods employing finite cluster models.

Geometric and energetic parameters obtained by semiempirical and non-empirical methods are generally in good agreement. Among the different chemisorption sites considered, nitrogen atoms are found to prefer a two-fold coordination site, and only in this case has any evidence been found for an exothermic process. No evidence of dissociative chemisorption has been found in the case of molecular nitrogen, whose preferred orientation changes from nearly vertical to nearly horizontal on approaching the surface. Molecular adsorption is strongly endothermic at the Hartree—Fock level, so that the only possible interaction occurs through dispersion forces, which are not taken into account in our computations, but can be well represented by model potentials.     

K s →π+π−γ: a laboratory for meson dynamics

We discuss the decayK _{s +–} in the framework of chiral perturbation theory. The direct emission in this decay can be an useful test of meson dynamics.     

Reactions of the unsaturated anion [Re3H4(CO)10]− with car☐ylic acids and x-ray characterization of the anions [Re3H3(CO)10(μ-O2CR)]− (R = H,CF3)

The novel anions [Re₃H₃(CO)₁₀(μ-O₂CR)]^? (R = H, CH₃, CF₃), obtained by reaction of [Re₃H₄(CO)₁₀]^? with the corresponding car?ylic acids, have been characterized by IR and NMR spectra and by X-ray analysis of the formate and trifluoroacetate derivatives. They contain a triangle of rhenium atoms, with the car?ylate group diaxially bridging on the shorter ReRe edge.     

A detailed analysis of the polarographic behaviour of methylene blue in phosphate buffer on mercury

Polarographic current-potential characteristics and current-time curves for the reduction of methylene blue (MB) to methylene blue leucoform (MBL) in a pH 7.9 aqueous phosphate buffer have been examined in detail over a wide concentration range. It has thus been shown that the so called “normal” or “main” reduction wave of MB actually consists of two separate steps, the former with a half-wave potential practically coinciding with the formal potential E₀=?0.250 V/SCE of the MB/MBL couple and the latter with a half-wave potential of about ?0.310 V/SCE. As soon as the well-known MB adsorption prewave has attained its maximum height (which occurs at a MB bulk concentration c₀^*?5×10^?5M), a further slight increase in c₀^* causes the appearance of the wave with E_1/2=?0.310 V. The height of the linear potential-sweep voltammetric peak corresponding to the latter wave increases proportionally to the sweep rate, thus revealing the “adsorption” nature of this wave. A comparison with a previous chronocoulometric investigation of the MB/MBL system has permitted us to conclude that the wave with E_1/2=?0.310 V is due to reduction of the MB molecules which, after having reached the surface of the dropping electrode by diffusion, are adsorbed at the top of the adsorbed monolayer of MBL in direct contact with the electrode and remain in this adsorbed state after reduction. For c₀^*>7×10^?5M the wave with E_1/2?E₀=?0.250 V starts to develop. This wave is due to the electroformation of MBL molecules which diffuse back into the solution. The shape of polarographic current-potential characteristics and current-time curves has been accounted for semiquantitatively through an approximate solution of the corresponding diffusional problem.     

Carbon-13 NMR study of 1-methyl-3-phenyl-4-diazo-5-benzoylamidopyrazole and other model pyrazole compounds

A ¹³C nmr study of a diazo, of two diazonium salts and of some other model pyrazole compounds is reported. It is found that the C-4 diazo carbon is more shielded than the normal sp² pyrazole hybridized carbon, while its diazonium salt is more deshielded. The electron density on the C-4 of the diazopyrazole is probably due to the positive charge on the terminal nitrogen. Thus the ¹³C chemical shift values allowed us to understand the chemical behaviour of a compound of potential antitumor activity.     

Synthesis and characterization of a new benzofulvene polymer showing a thermoreversible polymerization behavior

A new polymer based on a functionalized benzofulvene moiety has been synthesized by spontaneous polymerization of the monomer in the solid state. This polymer shows a very high molar mass, high solubility in the most common organic solvents, and thermoreversible polymerization properties. An interesting application in synthesis is reported.     

Ring B functionalization of scalarane sesterterpenes by radical relay halogenation

The functionalization of the B-ring of the scalarane framework has been achieved for the first time by a radical relay halogenation (RRH) synthetic method. The known scalaranic methyl ester, which was prepared by a procedure with an overall yield higher than those reported in the literature, has been used as the starting substrate. Some theoretical considerations explaining the course of RRH reaction are also presented.