Synthesis of Novel Chiral Diol Ligands for the Enantioselective Reactions

The chiral diols ((,(,((,((-Tetraaryl-1,3-dioxolane-4,5-dimethanols) have been used for the formation of cyclic titanates and similar derivatives of Mg, Al and Zr. These complexes of oxophilic metal centers were employed in catalytic and stiochiometric enantioselective reactions such as enantioselective addition reactions of carbon-centered nucleophiles to aldehydes1, [2+2] cycloadditions2, and Diels-Alder reactions3. So far, the two hydrogen atoms of all this type of diols are in trans form…     

Heterodinuclear Ln[bond]Na complexes with an asymmetrical macrocyclic compartmental Schiff base

Heterodinuclear lanthanide(III)-sodium(I) complexes [LnNa(L)(Cl)(2)(CH(3)OH)] (Ln=La[bond]Nd, Sm[bond]Lu), where H(2)L is a [1+1] asymmetric compartmental macrocyclic ligand containing a N(3)O(2) Schiff base and a O(3)O(2) crown-ether-like coordination site, have been prepared and characterized by IR, (1)H, (13)C, and (23)Na NMR spectroscopy, mass spectrometry, and electron microscopy. In the solid state, the lanthanide(III) ions coordinate the Schiff-base N(3)O(2) site, and the sodium ion occupies the O(3)O(2) crownlike cavity, as shown by the X-ray crystal structures of the Nd, Eu, Gd, and Yb derivatives. In these complexes, the lanthanide(III) ion is coordinated by two chlorine atoms in the trans position and by three nitrogen and two negatively charged phenol oxygen atoms of the Schiff base, and the ion is heptacoordinated with a pentagonal bipyramidal geometry. The sodium ion is coordinated by three etheric oxygen atoms and the two phenolic oxygens that act as a bridge. A methanol molecule is also coordinated in the apical position of the resulting pentagonal pyramidal polyhedron. A detailed (1)H and (13)C NMR study was carried out in CD(3)OD for both diamagnetic and paramagnetic heterodinuclear complexes [LnNa(L)(Cl)(2)(CH(3)OH)]. The complexes are also isostructural in solution, and their structures parallel those found in the solid state. Moreover, some significative distances determined in the solid state and in solution are comparable. Finally, the potential use of these complexes as molecular probes for the selective recognition of specific metal ions has been tested. In particular, their ability to act as shift reagents and the selectivity of the O(3)O(2) site towards Li(+), Ca(2+), and K(+) were investigated by (23)Na NMR spectroscopy.     

A novel approach to consolidation of historical limestone: the calcium alkoxides

Potential utilization of calcium alkoxides as stone consolidants was considered. Reaction of Ca(OCH₃)₂, Ca(OCH₂CH₃)₂(CH₃CH₂OH)₄ and Ca[OCH(CH₃)₂]₂ with the atmosphere in different experimental conditions was studied. The reaction produced CaCO₃ and two different pathways seem to be involved, the first taking place through CO₂ insertion into the Ca–O bond of Ca(OR)₂ species with formation of an alkylcarbonate derivative, subsequently transformed into CaCO₃ through ROH elimination; the second takes place through hydrolysis of Ca(OR)₂ to Ca(OH)₂, which is then carbonated to CaCO₃. The vaterite/calcite ratios found in the final CaCO₃ vary considerably with the experimental conditions adopted. Investigations demonstrated the potentiality of Ca(OCH₃)₂ to act as a stone consolidant. In fact, impregnation of a porous substrate, simulating the deteriorated stone, with a methanol solution of Ca(OCH₃)₂, produced a crystalline vaterite film, which gradually filled all the pores and cavities of substrate and seems to fulfil the necessary requirements for a consolidant. Copyright © 2008 John Wiley & Sons, Ltd.     

On the electric current from electrodes in a magnetized semiconductor film

The problem on the electric current from electrodes in a magnetizedsemiconductor film is reduced to the skew derivative problemfor the Laplace equation outside cuts in a plane. The problemfor the Laplace equation is studied under different conditionsat infinity, which have a certain physical meaning. With thehelp of potential theory, the skew derivative problem is reducedto a Fredholm integral equation of the second kind, which isuniquely solvable. The Neumann problem for the Laplace equationin the exterior of cuts in a plane is a particular case of ourproblem.     

Mass spectrometric investigation of some macrocyclic and macroacyclic compartmental schiff bases

The mass spectrometric behaviour of four macroacyclic and five macrocyclic Schiff bases using two ionization methods (electron impact and fast atom bombardment) was studied in detail with the aid of mass-analysed ion kinetic energy (MIKE) spectrometry. It was possible to propose a common electron impact-induced decomposition pattern for the acyclic compounds, whereas for the cyclic compounds, analysed by fast atom bombardment, peculiar fragmentation routes occurred, which were strongly dependent on the macrocyclic structure and on the different side-chains.     

Evaluation of polymers for conservation treatments of outdoor exposed stone monuments. Part I: Photo-oxidative weathering

The commercial acrylic polymers, Paraloid B72 and Paraloid B67, and a silicon-based product, Dri-Film 104, commonly used as water repellents/consolidants in the restoration of stone artefacts, have been tested to evaluate their performances when submitted to ageing, simulating the outdoor conditions of treated stone. After full characterization, the three polymers were applied as thin films on slides, as thick film on petri dishes and on marble by brush or by imbibition and the resulting samples were submitted to photo-oxidative weathering (λ = 340 nm). The weathering evolution was checked by ultrasonic and colorimetric measurements and by FT-IR, NMR and SEC determinations. Removability tests were also performed. All the polymers underwent irreversible modifications with reduction of their conservative properties, colour change and, above all, impossibility of their complete removal.     

A new approach to reduction of the Neumann problem in acoustic scattering to a non-hypersingular integral equation

The Neumann problem for the propagative Helmholtz equation inthe exterior of several bodies (obstacles) is studied in twoand three dimensions by a special modification of the boundaryintegral equation method. This modification can be called the'method of interior boundaries', because additional boundariesare introduced inside scattering bodies. The solution of theproblem is obtained in the form of a single layer potentialon the whole boundary. The density in the potential satisfiesthe uniquely solvable Fredholm equation of the second kind andcan be computed by standard codes. In fact our method holdsfor any positive wave numbers.