Application of chiral dipyridylmethane ligands in the enantioselective palladium-catalyzed allylic alkylation

New chiral C₁-symmetric dipyridylmethane ligands have been prepared from naturally occurring monoterpenes according to a method based on two consecutive constructions of the pyridine rings. These ligands have been assessed in the enantioselective palladium catalyzed allylic alkylation of 1,3-diphenylprop-2-enyl acetate with dimethylmalonate. Enantioselectivity up to 68% ee has been obtained.     

Liquid—liquid extraction of metal ions by the sulfide podand 1,12-di-2-thienyl-2,5,8,11-tetrathiadodecane

The sulfide podand (an open-chain neutral mutlidentate ligand with six sulfur donor atoms) 1,12-di-2-thienyl-2,5,8,11-tetrathiadodecane (TTD) was synthesized. Its extracting properties were examined with 1,2-dichloroethane and 4-methylpentan-2-one as solvents. The reagent showed high selectivity for silver(I) and copper(I) ions; mercury(II) was extracted (ca. 97%) under certain conditions. Extraction of silver(I) was studied in detail with ^110mAg tracer. Log D values ?2 were obtained for the range from pH 6 (with perchlorate as counter-ion) to 2 M perchloric acid or 6 M nitric acid. The ratio of Ag:TTD in the complex was 1:1. Silver could be back-extracted with 4–6 M hydrochloric acid.     

Structure-property correlations in polypropylene from metallocene catalysts: stereodefective, regioregular isotactic polypropylene

A series of MAO-activated C(1)-symmetric indenyl-ansa-dithienocyclopentadienyl-based zirconocenes have been used to produce isotactic polypropylenes of medium to high molecular weights, of different degrees of stereoregularity, and free from regioerrors. The effect of the presence of rr defects on the polymorphic behavior and mechanical properties of polypropylene is analyzed. The presence of rr defects induces crystallization of gamma form and of disordered modifications intermediate between alpha and gamma forms. A linear relationship between the amount of gamma form and the average length of isotactic sequences has been found. Samples with low concentration of rr defects, up to 3-4%, present high melting temperatures, in the range 160-130 degrees C, and behave as stiff-plastic materials; sample with higher rr content, in the range 4-6% and melting temperatures around 115-120 degrees C are highly flexible thermoplastic materials, and, finally, samples with concentration of rr defects in the range 7-11% and melting temperatures in the range 80-110 degrees C are thermoplastic elastomers with high strength. The fine-tuning of the chain microstructure, achieved by a tailored design of new metallocene catalysts, has allowed production of new polypropylenes having desired properties, intermediate between those of stiff plastic and elastomeric materials.     

Moisture-triggered 1,3,5-triazine-based Cu(II) molecular switch: a combined X-ray single-crystal and powder diffraction study

A solvothermal synthetic procedure has been exploited to prepare the new [Cu(3)L(NO(3))(6)](n) coordination polymer (1) by reaction of the polydentate N,N'-{2,4-di-[(di-pyridin-2-yl)amine]-1,3,5-triazine}ethylenediamine ligand (opytrizediam L) with copper(II) nitrate. 1 has been structurally characterized by means of the conventional X-ray single-crystal diffraction technique. It crystallizes in the monoclinic C2/c space group with a = 16.830(3), b = 20.701(4), c = 18.170(4) Angstroms, beta = 113.26(3) degrees, V = 5816(2) Angstroms(3), Z = 4. 1 consists of trinuclear Cu(3)L(NO(3))(5) units connected by means of a nitrato-O,O' bridge. The resulting chains are involved in weak interchain head-to-tail pi-pi stacking interactions. In the presence of moisture, 1 is readily converted into the hydrated [Cu(3)L(NO(3))(5)](NO(3)).H(2)O form (2). This second phase, monoclinic P2(1)/c, consists of isolated [Cu(3)L(NO(3))(5)](+) and (NO(3))(-) ions which accommodate water molecules in the crystal lattice. These subtle chemical and structural modifications accompanying the moisture-triggered 1-to-2 transformation have been demonstrated through a X-ray powder diffraction study. A thermodiffractometric analysis has evidenced that this solid-to-solid transformation is fully reversible, i.e., thermally induced dehydration of 2 restores 1. The analysis of the temperature dependence of the magnetic susceptibility for 2 has revealed very weak ferromagnetic interactions, consistent with the large Cu...Cu separation (ca. 7.5 Angstroms) in the trinuclear units.     

A combined computational and experimental study of polynuclear Ru-TPPZ complexes: insight into the electronic and optical properties of coordination polymers

We report a combined experimental and computational study of polynuclear [Ru(n)(TPPZ)(n)(+1)](2)(n)(+) complexes, of interest in the field of photoactive polymers. The complexes with n = 1, 2, 3 and n > 5 have been synthesized and spectroscopically characterized. A red-shift of the visible band maximum from 2.59 to 2.03 eV is observed going from the monomer to the longer oligomeric species (n > 5). To characterize the geometries, electronic structure, and excited states of these complexes, density functional theory (DFT) and time-dependent DFT calculations on the [Ru(n)(TPPZ)(n)(+1)](2)(n)(+) series with n = 1-4 in solution have been performed. The agreement between experimental and calculated spectra is good, both in terms of absorption maximum energies and relative intensities for different values of n. For all the investigated complexes, we assign the main band in the visible region as a metal-to-metal plus ligand charge transfer (MMLCT) transition. The resulting excited states are delocalized throughout the entire complexes, as they originate from a superposition of pi(TPPZ)-t(2g)(Ru) states. The low-energy shoulder of the main visible absorption band, present in the experimental spectra for n > 1, is proposed to arise from spin-forbidden singlet-triplet transitions of similar MMLCT character, consistent with the observed enhancement of this feature in the spectra of the corresponding Os oligomers.     

Surface chemistry study of RuO2/IrO2/TiO2 mixed-oxide electrodes

DSA metal oxide electrodes such as the RuO(2)/IrO(2)/TiO(2) mixed system are widely studied for their excellent electrocatalytic activity. In order to understand their catalytic properties, the comprehension of the surface chemistry involved during electrochemical treatments is crucial. With this aim, RuO(2)/IrO(2)/TiO(2) mixed-oxide electrodes having various noble metal contents were studied by means of secondary ion mass spectrometry (SIMS). In particular, cathodic and anodic polarization and O(2) evolution reactions were carried out to test the electrode behaviour and SIMS analyses were performed after all these treatments. In this way, surface changes induced by electrochemical treatments and depending on electrode composition were widely investigated by SIMS, revealing, for example, the presence of hydration or preferential dissolution phenomena induced by electrochemical processing.     

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.     

Über die Anwendbarkeit konsistometrischer Messungen beim Studium binärer Systeme

Zusammenfassung Mit einem modifiziertenHöppler-Konsistometer verfolgten wir die Temperaturabhängigkeit der Stempelsenkung bei verschiedenen Zusammensetzungen in den Systemen NaNO₃–KNO₃ und ZnSO₄–KCl. Die Ergebnisse zeigen, daß man auf Grund solcher Messungen Aussagen über die Form der Zustandsdiagramme machen kann. Außerdem ergänzen die Messungen im System ZnSO₄–KCl die Literaturangaben.Mit 8 Abbildungen     

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.     

Binding to DPF-motif by the POB1 EH domain is responsible for POB1-Eps15 interaction

Background  

Eps15 homology (EH) domains are protein interaction modules binding to peptides containing Asn-Pro-Phe (NPF) motifs and mediating critical events during endocytosis and signal transduction. The EH domain of POB1 associates with Eps15, a protein characterized by a striking string of DPF triplets, 15 in human and 13 in mouse Eps15, at the C-terminus and lacking the typical EH-binding NPF motif.