Surface properties of some carotenoids spread in monolayers at the air/water interface. Experimental and computational approach

The surface pressure versus molecular area isotherms of some carotenoids: β,β-carotene-4-one (echinenone, ECH), β,β-carotene-4,4′-dione (canthaxanthin, CAN) and 4,4′-diapo-ω,ω-carotene-4,4′-dial (APO), spread at the air/water interface, are reported. A van der Waals type state equation is used to describe the high molecular area portions of the compression isotherms and interaction parameters within monolayers are derived. Quantum chemical semi-empirical SCF MO calculations (AM1 and PM3) are performed for the optimized geometries of molecules and dipole moments are calculated. Similar theoretical magnitudes are obtained by both methods. Surface properties, like collapse pressure, surface compressional modulus and interaction parameters are discussed in terms of dipole-dipole interactions, and correlations with the calculated quantities for the carotenoid molecules are analyzed. The orientation of the different carotenoid molecules in the monolayer is discussed.     

Insoluble mixed monolayers : II. Protolytic equilibria and the influence of the pH on the collapse pressure

A general thermodynamic treatment is given for the protolytic equilibria in an insoluble monolayer, containing surfactant molecules with n ionizable protons and able to accept m more protons, and being spread at the liquid/gas interface. The correlation between the pH of the subphase liquid and the collapse pressure of the monolayer is discussed. By using the approximation of perfect solutions and of binary surface systems (protonated and deprotonated molecular species of the surfactant) several methods are proposed for deriving apparent surface acidity constants from experimental collapse pressure vs pH curves, in the case of both miscible in monolayer miscible in collapsed bulk phase and miscible in monolayer immiscible in collapsed bulk phase, type systems. Some of these methods are based on a complete perfect solution approximation (CA) taking into account the molar fraction of the subphase liquid in the monolayer and the others use “surfactant” approximation (SA), neglecting this molar fraction. The methods proposed are tested on monolayers of carotenoid pigments spread at aqueous solution/air interfaces. Results obtained by the different methods are rather close to each other, but the approximation CA is better than SA. The apparent surface acidity constants of different carotenoids are compared with each other and discussed in terms of molecular structure and electronic effects.     

A graph partition problem

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Characterization of some acrylic anion-exchangers by pyrolysis-gas chromatography

Pyrolysis-gas chromatography was used in the study of the thermal behaviour of some acrylic anion-exchangers for identification of the thermal decomposition products and their percentage estimation. The acrylic anion-exchangers were prepared by aminolysis of cross-linked acrylic ester copolymer with difunctional amines. The pyrolysis-gas chromatography studies, coupled with data obtained by thermogravimetry, showed that the acrylic anion-exchangers first lose the water easily absorbed from the air, and the decomposition starts at temperatures above 100°. The great number of decomposition products identified in the pyrograms on the thermal degradation of acrylic anion-exchangers indicated a complex degradation mechanism, with important variations in the contents of the evolved amine compounds.     

Asymmetric hydroformylation of styrene catalyzed by furanoside phosphine–phosphite–Rh(I) complexes

A series of phosphine–phosphite ligands, derived from inexpensive -(+)-xylose, were tested in the Rh-catalyzed asymmetric hydroformylation of styrene. Systematic variation of the phosphite moiety revealed a remarkable effect on the selectivity of the hydroformylation catalysts. High regioselectivities for 2-phenylpropanal (up to 95%) and moderate enantioselectivity were found under mild reaction conditions (25–40°C, 25 bar of syn gas). The hydroformylation results are explained by the solution structures of the intermediate species formed under hydroformylation conditions.     

p-Benzyne derivatives that have exceptionally small singlet-triplet gaps and even a triplet ground state

In an effort to find a p-benzyne (1,4-didehydrobenzene) derivative with a triplet ground state, we have investigated tetrasubstitution by -F, -NH(2), -CH(3), and -NO(2) groups. These were predicted to reduce the singlet-triplet gap, but none led to a triplet ground state because of unexpected destabilization of one of the radical orbitals. This effect is likely the result of rehybridization of the substituted C atom, which has been observed for substituted benzene and perturbs the side sigma and sigma* orbital energies of the phenyl ring. The role of substituent rotation on the energy difference between the two nominally singly occupied orbitals (S and A) was then investigated. The energy of the A radical orbital was found to be much more sensitive to perturbations within the sigma C[bond]C framework than the S MO. Consequently, we believe that rehybridization of the ring carbons destabilizes the A radical orbital and can lead to large singlet-triplet splittings. To test this hypothesis, calculations on a p-benzyne with 2,6 substitution by oxygen were performed. Interestingly, a triplet ground state was predicted. Yet, examination of the geometry and wave function showed that 2,6-quinone p-benzyne is a very twisted molecule with a C3-C4-C5 allene linkage and a C1 triplet carbene center.     

Systematic Study of the Asymmetric Methoxycarbonylation of Styrene Catalyzed by Palladium Systems Containing Chiral Ferrocenyl Diphosphine Ligands

We present the first systematic study of the Pd‐catalyzed asymmetric methoxycarbonylation of styrene in the presence of chiral ferrocenyl phosphine ligands. The reaction conditions were optimized, and a screening of different catalyst precursors was performed. A number of 1,1′‐bis(phosphino)ferrocenes of the Mandyphos, Josiphos, Walphos, and Taniaphos types were tested in combination with [PdCl₂(NCPh)₂], in the presence of TsOH as the acid source. These systems afforded high enantioselectivities, although the regioselectivity of the reaction was found to be in favor of the (undesired) linear ester. The catalytic system made with the Josiphos ligand 1 gave rise to an enantiomeric excess (ee) of 86%.     

The mucic acid as chromogenic agent

The absorption spectra in the infrared and vis-uv regions of mucic acid were established. The analytical behavior of mucic acid as a potential chromogenic reagent for the spectrophotometric determination of trace materials was studied. Interactions with iron(III), copper(II), cobalt(II) and (III), nickel(II), vanadium(IV), and uranyl(II) in basic medium were observed.     

High frequency wave packets for the Schrödinger equation and its numerical approximations

We build Gaussian wave packets for the linear Schrödinger equation and its finite difference space semi-discretization and illustrate the lack of uniform dispersive properties of the numerical solutions as established in Ignat and Zuazua (2009) [6]. It is by now well known that bigrid algorithms provide filtering mechanisms allowing to recover the uniformity of the dispersive properties as the mesh size goes to zero. We analyze and illustrate numerically how these high frequency wave packets split and propagate under these bigrid filtering mechanisms, depending on how the fine grid/coarse grid filtering is implemented.