Group contributions to the partial molar volume of ionic organic solutes in aqueous solution

Partial molar volumes at infinite dilution in water at 25°C for more than 400 organic electrolytes (carboxylic acid and amine salts, sulfates, sulfonates, selected polyelectrolyes, aminoacids and derivatives) are described through a simple additivity scheme already adopted for non-electrolytes. Twenty-five charged groups are assigned a contribution and the partial molar volumes of more than 150 monofunctional organic ions are reproduced with a standard deviation of 0.8 cm³-mol^–1. The different volumetric behavior of hydrophobic and hydrophilic centers, either charged or uncharged, is discussed. Deviations from additivity for mono-and polyfunctional ions are analyzed in terms of (i) extension of the hydration cosphere of different polar centres; (ii) intramolecular interactions and their dependence on the nature, number and mutual separation of interacting groups.     

Solvation dynamics of Li+ and Cl- ions in liquid methanol

Car-Parrinello molecular dynamics simulations have been performed on Li(+) and Cl(-) in fully deuterated liquid methanol. The results have been compared with available experimental and theoretical data. It has been found that the lithium cation has a stable tetrahedral coordination, whereas the chloride anion presents an average coordination number of 3.56. The polarization effects induced by the ion on the solvent have been analyzed in terms of Wannier function centers. Particular attention has been devoted to the charge transfer, which is particularly important in these types of systems. Evidence for the stability of the lithium cation solvent cage also has been found in the vibrational spectra.     

Highly diastereoselective addition of nitromethane anion to chiral alpha-amidoalkylphenyl sulfones. Synthesis of optically active alpha-amino acid derivatives

Optically active syn-alpha-amidoalkylphenyl sulfones can be prepared from chiral aldehydes in anhydrous conditions using benzenesulfinic acid. These sulfones in basic conditions give N-acylimines that react with sodium methanenitronate to afford the corresponding nitro adducts with high anti diastereoselectivity. PM3 semiempirical calculations provide a rationale for the observed opposite stereoselectivity. The obtained nitro derivatives undergo a Nef reaction followed by a methylation giving optically active beta-hydroxy-alpha-amino acid and alpha,beta-diamino acid esters in good yield. These amino acid derivatives are important building blocks for the preparation of biologically active compounds.     

Electron and electrospray ionization mass spectrometry in the characterization of some 1-allyl-3-phenylaziridines

A series of cis- and trans-isomeric aziridines has been studied under electron impact (EI) and electrospray ionization (ESI) conditions. The fragmentation patterns of the examined compounds have been elucidated by means of sequential product ion fragmentation experiments (MS(n)) performed using an ion trap mass spectrometer. Particular attention has been paid to isomer characterization in these precursors of azetidinones, that in turn are precursors of new beta-lactam antibiotics.     

Synthesis and characterization ofpara- andmeta-substituted benzeneseleninato complexes of tin(II), silver(I) and iron(II)

Summary New complexes of tin(II), silver([) and iron(II) withpara- andmeta-substituted benzeneseleninic acids are reported and studied by chemical analyses, spectroscopic methods, conductivity and magnetic measurements. The complexes, of the type Sn(XC₆H₄SeO₂)₂, Ag(XC₆H₄SeO₂) and Fe(H₂O)₂(XC₆H₄SeO₂)₂, were obtained by reaction of SnCl₂, · 2 H₂O. AgNO₃ and Fe(NH₄)₂(SO₄)₂·6 H₂O with the sodium benzeneseleninates, XC₆H₄SeO₂Na (X = H.p-Cl,m-Cl,p-Br,m-Br orp-Me). The i.r. spectral data suggest that the silver and iron complexes contain RSeO ₂ ^– ligands which act as bidentates in O,O-seleninato complexes. All the iron complexes have a distorted octahedralD _4h symmetry. The number of bands in the i.r. spectra of the tin derivatives indicates that there is no equivalence in the manner in which the two seleninato ligands are bonded. We could suggest that the tin atoms are intermolecularly O.O-bonded via one RSeO ₂ ^– group, whereas the second ligand is coordinated to the metal via one oxygen atom forming polymeric -tetrahedral derivatives.     

Asymptotic behaviour of minimum problems with bilateral obstacles

Summary In this paper we study the asymptotic behaviour (as h) of the solutions of minimum problems for the functional [¦Du¦²+g(x, u)]dx with bilateral obstacles of the type _hu_h, where _h and _h are sequences of arbitrary functions fromR ⁿ into ¯R.     

The constant flow rate problem for fluids with increasing yield stress in a pipe

Experiments show that the degradation effect observed during both stirring and pipelining tests of some coal-water slurries is mainly to be ascribed to the increase of the yield stress. Regardless of the particular mathematical model adopted to investigate the dynamics of these fluids, engineering applications force us to consider the problem of how long a constant flow rate can be maintained during the pipelining process. We choose a Bingham model where the yield stress is assumed to increase with the dissipated energy as in [5]. It is first shown that the constant flow rate problem is equivalent to solving a nonlinear functional equation in the unknown pressure gradient that generalizes the classical algebraic Buckingham equation for the same problem with constant rheological parameters. By means of a fixed-point argument we also prove that the functional equation has one and only one solution which is local in time. We finally find an estimate from below of the interval of the interval of existence. Numerical results are rather good and agree with those expected from the engineering point of view.     

Existence for a doubly nonlinear Volterra equation

We consider a doubly nonlinear Volterra equation involving a nonsmooth kernel and two possibly degenerate monotone operators. By exploiting an implicit time-discretization procedure, we obtain the existence of a global strong solution and extend to the nonlocal in time situation some former results by Colli [P. Colli, On some doubly nonlinear evolution equations in Banach spaces, Japan J. Indust. Appl. Math. 9 (2) (1992) 181-203].