Synthèse et caractérisation du phosphate de hafnium comme échangeur d'ions

The preparation, crystalline structure, properties and behaviour of the hafnium bis (monohydrogen phosphate) monohydrate as a cationic exchanger have been studied. The crystalline product has been characterized by elemental analysis, X-ray Powder patterns, thermal analysis, photoelectron spectrometry and infra red spectroscopy. A layered structure in which the hafnium and phosphorus atoms are disposed in such a way as to form zeolitic-type cavities is suggested. The reversibility of the exchange with respect to sodium ions is discussed and can be related to the water content of the exchanger.     

Acid-base chemistry of red wine: analytical multi-technique characterisation and equilibrium-based chemical modelling

In this paper an attempt is made to model the alkalimetric titration trend (pH<7) of a series of red wines on the basis of an equilibrium-based calculation involving as input the chemical equilibria of the acid-base active substances, whose analytical concentration was determined in each wine under consideration. The chemical model (14 acid-base active substances and 22 protonation equilibria were considered) has been built in reliable conditions with respect to the chemical environment of the fluids under study, in order to describe the acid-base properties at a thermodynamic level using specific professional software. In this connection, protonation constant values of the substances involved were necessary, paying attention to: solvent composition, background salt, ionic strength and temperature. A series of synthetic solutions (based on mixed ethanol/water solvents at known ionic strength) was then pH-metrically titrated (25 °C) in order to refine suitable protonation constant values.Analytical measurements of carboxylic acids, amino acids, inorganic anions and metals were executed to know the concentration of a series of acid-base active reactants (pH<7) and the ionic strength state of each wine. Finally, a comparison between the experimental trend of the alkalimetric titration of each wine and the calculated one via the chemical model tested by means of a computer-assisted simulation has been performed. As an overall check of our job, the charge balance principle was adopted. During the alkalimetric titrations of each wine conductometric detection was performed as well, with the aim of confirming the values of ionic strength calculated using both analytical and equilibrium concentrations. The agreement we found when comparing the calculated values of ionic strength with varying pH with the trend of the conductometric signal can be considered as a significant validation of the chemical model proposed. The jump from the analytical to the equilibrium composition may allow the prediction of the effect on red wines consequent to chemical actions (addition of substances) or natural phenomena.     

Soft functional polynuclear coordination compounds containing pyrimidine bridges

In this account, we describe the use of simple pyrimidine derivatives in combination with metal ions to build highly structured molecular architectures containing functional nanoenvironments, cavities and surfaces that can interact with additional species. The supramolecular structure of these systems can be rationally controlled by metal fragment geometry, reaction conditions and presence of templating agents. Thus, the use of transition metals with low coordination numbers or blocked bonding positions in combination with pyrimidines (e.g. 2-hydroxypyrimidine, 4-hydroxypyrimidine, 2,4-dihydroxypyrimidine, 2-aminopyrimidine) leads to the formation of either discrete assemblies, 1D polymers or helixes. When metal ions with higher coordination possibilities are applied instead, 2D and 3D networks are generated. Some of the assemblies built in this way possess functional cavities, pores and surfaces that can interact with additional species by means of hydrophobic, electrostatic, H-bonding interactions and coordinative bonds to give rise to recognition processes. The latter range from molecular recognition in homogeneous phase as well as clathrate formation, to heterogeneous solid-gas and solid-liquid adsorption phenomena. It should be noted that these materials are not rigid but able to undergo guest-induced reorganisation processes even in the solid state. Finally, some of these materials also combine additional interesting magneto-optical properties. Thus, dual systems can be envisaged in which two or more of these properties are present in the same material.     

Thermodynamics of beta-amyloid fibril formation

Amyloid fibers are aggregates of proteins. They are built out of a peptide called beta-amyloid (Abeta) containing between 41 and 43 residues, produced by the action of an enzyme which cleaves a much larger protein known as the amyloid precursor protein (APP). X-ray diffraction experiments have shown that these fibrils are rich in beta-structures, whereas the shape of the peptide displays an alpha-helix structure within the APP in its biologically active conformation. A realistic model of fibril formation is developed based on the 17 residues Abeta12-28 amyloid peptide, which has been shown to form fibrils structurally similar to those of the whole Abeta peptide. With the help of physical arguments and in keeping with experimental findings, the Abeta12-28 monomer is assumed to be in four possible states (i.e., native helix conformation, beta-hairpin, globular low-energy state, and unfolded state). Making use of these monomeric states, oligomers (dimers, tertramers, and octamers) were constructed. With the help of short, detailed molecular dynamics calculations of the three monomers and of a variety of oligomers, energies for these structures were obtained. Making use of these results within the framework of a simple yet realistic model to describe the entropic terms associated with the variety of amyloid conformations, a phase diagram can be calculated of the whole many-body system, leading to a thermodynamical picture in overall agreement with the experimental findings. In particular, the existence of micellar metastable states seem to be a key issue to determine the thermodynamical properties of the system.     

Toward the supramolecular structure of collagen: a molecular dynamics approach

The structure, stability, and conformational dynamics of an assembly of two pentameric bundles made of collagen-like triple helical segments are explored using 1.2 ns molecular dynamics simulations in three environments: 8.0% (v/v) formaldehyde/water solution, 1.4% (v/v) gallic acid/water solution, and pure water. Stable supramolecular arrangements, where the two collagen units are very close to each other at interacting distances, are identified via docking and energy minimization procedures. Analysis of the interaction with formaldehyde and gallic acid suggests that they perturb the protein in a similar way depending on hydrogen-bonding capability, hydrophobic association properties, and the size and concentration of the compound.     

Treatment with lignin residue

Acid hydrolysis of lignocellulose to hydrolysates intended for production of fuel ethanol results in the formation of byproducts in addition to fermentable sugars. Some of the byproducts, such as phenolic compounds and furan aldehydes, are inhibitory to the fermenting microorganism. Detoxification of the hydrolysates may be necessary for production of ethanol at a satisfactory rate and yield. The lignin residue obtained after hydrolysis is a material with hydrophobic properties that is produced in large amounts as a byproduct within an ethanol production process based on lignocellulosic raw materials. We have explored the possibility of using this lignin residue for detoxification of spruce dilute-acid hydrolysates prior to fermentation with Saccharomyces cerevisiae. Three dilute-acid hydrolysates of spruce were treated with lignin residue, which in all cases resulted in improved fermentability in terms of productivity and yield of ethanol. The effect was improved by washing the lignin before treatment, by using larger amounts of lignin in the treatment, and by performing the treatment at low temperature. Treatment with the lignin residue removed up to 53% of the phenolic compounds and up to 68% of the furan aldehydes in a spruce dilute-acid hydrolysate. A larger fraction of furfural was removed compared to the less hydrophobic 5-hydroxymethylfurfural.     

The migratory insertion of carbon monoxide and methyl isocyanide into zirconium–carbon and titanium–carbon bonds anchored to a calix[4]arene moiety: a dynamical density functional study

The energetics and reaction mechanism of the migratory insertion of carbon monoxide and methyl isocyanide into the zirconium–carbon and titanium–carbon bonds in [calix[4](OMe)₂(O)₂–M–Me₂], (M=Zr, Ti), have been investigated by combining static and dynamic density functional calculations. Two steps have been characterized: the coordination of the incoming nucleophilic moiety leading to relatively stable facial adducts; its subsequent insertion into the M–C bond, leading to ²-bound acyl or iminoacyl complexes, providing a rationale for the different behavior of CO and MeNC towards both insertion and deinsertion reactions. Our results indicate that the rate-determining step for the overall MeNC insertion into the M–C bond is its coordination to the electron-deficient metal center, with the titanium system featuring a higher energy barrier (12.7 versus 5.5 kcal mol^–1). Ab initio molecular dynamics simulations have been performed on the Zr system by means of the Car–Parrinello method, to study the hitherto inaccessible mechanistic features of the insertion reactions.Contribution to the Björn Roos Honorary Issue     

Diastereoselective reduction of enantiopure N-p-toluenesulfinyl ketimines derived from pyridyl ketones

DIBAL reduction of enantiopure N-p-toluenesulfinyl ketimines derived from 2-pyridyl ketones bearing an additional substituent on the 6-position of the pyridine ring afforded the related N-p-toluenesulfinyl amines with high yields and diastereoselectivities. The results of a number experiments exploring the conversion of a optically active 1-substituted N-toluenesulfinyl 1-(6-bromopyridin-2-yl)methylamine in a number of more complex pyridine derivatives with maintenance of the toluenesulfinyl group N-protecting group is also reported.     

Coordination frameworks containing the pyrimidin-4-olate ligand. Synthesis, thermal, magnetic, and ab initio XRPD structural characterization of nickel and zinc derivatives

Extended coordination frameworks containing the pyrimidin-4-olate ligand (4-pymo) and Zn(II) and Ni(II) metal ions have been obtained by solid state reactions and have been fully characterized by spectroscopic, thermal, and magnetic measurements and by ab initio XRPD. The reaction of ZnO and 4-Hpymo at 140 degrees C gives a solid microcrystalline phase, Zn(4-pymo)(2) (1). Its 3D framework contains Zn(II) centers linked by 4-pymo ligands acting in two different coordination modes, namely, the N,N'- and the N,O-exo-bidentate ones, which result in a pseudotetrahedral ZnN(3)O chromophore. Thermal treatment of the "molecular" Ni(4-pymo)(2)(H(2)O)(4) complex (2) above 140 degrees C gives an anhydrous amorphous material analyzing as Ni(4-pymo)(2) (3a). Further heating of this material above 388 degrees C results in the formation of the microcrystalline layered Ni(4-pymo)(2) species (3b), in which Ni(II) centers are bridged by N,O-exo-bidentate 4-pymo ligands (assisted by longer Ni.N contacts). The thermal dependence of the magnetic susceptibility has been studied for the paramagnetic species 2 and 3a. 2 shows a weak antiferromagnetic interaction [J = -0.313(5) cm(-)(1)] transmitted through the multiple H-bonding interactions between the exocyclic pyrimidine and water oxygen atoms coordinated to the metal centers. 3a behaves as a 2D Heisenberg antiferromagnet with J = -4.11(3) cm(-)(1).     

Influence of membrane surface properties on the growth of neuronal cells isolated from hippocampus

Membranes have become of great interest for tissue engineering application, since they offer the advantage of developing neuronal tissue that may be used in implantable or in vitro hybrid systems for the simulation of brain function. The behaviour of neurons isolated from the hippocampus on membranes with different surface properties was investigated.