New chiral phosphine-phosphite ligands in the enantioselective palladium-catalyzed allylic alkylation

A series of chiral phosphine-phosphite ligands 1-6 have been synthesized and used in the enantioselective palladium-catalyzed reaction of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate as nucleophile. Ligands 1a, 2, 3, 5a, 6a, and 6b have been synthesized starting from racemic tert-butylphenylphosphinoborane. The use of dynamically resolved Li phosphide (-)-sparteine provided the optically pure ligands. Crystals of the allylpalladium (6a) complex were obtained, suitable for X-ray crystal structure determination. The X-ray crystal structure of the allylpalladium (6a) complex revealed a longer palladium-carbon bond distance trans to the phosphine moiety indicating that the attack of the nucleophile takes place at the carbon trans to the phosphine moiety. This was confirmed by the fact that the phosphine moiety did not affect the enantioselectivity directly. Under mild reaction conditions, enantioselectivities up to 83% were obtained (25 degrees C) with ligand 1e. Systematic variation of the ligand bridge and the phosphite moiety showed that the configuration of the product is controlled by the atropisomerism of the biphenyl substituent at the phosphite moiety. The conformation of the biphenyl group, in turn, is controlled by the substituent at the chiral carbon in the bridge. Ligands with large bite angles yielded higher enantioselectivities.     

An analytic version of the De Rham theorem

LetV be a real analytic paracompact variety; in §1 of this paper we prove that: $$H^q (V,R) \approx \frac{{closed analytic differentiable q - forms on V}}{{exact analytic differentiable q - forms on V}}$$ Then we prove that the closed (exact) analytic differentiableq-forms onV are dense, in the Whitney topology, in the set of closed (exact) differentiableq-forms onV. We also consider the problem of extending closed (exact) analytic differentiableq-forms, defined on a subvarietyX ofV, to closed (exact) analytic forms defined onV.     

Intercalation of Benzamide into Kaolinite

Well-crystallized kaolinite (K) was initially reacted at 60 degrees C with a water/dimethylsulfoxide (DMSO) mixture and the resulting intercalation derivative (K-DMSO) was characterized by powder X-ray diffractometry (PXRD), thermal analysis (simultaneous TG and DSC), and Fourier-transformed infrared spectroscopy (FTIR). Benzamide crystals were then melted with the K-DMSO derivative at 140 degrees C for 4 days, when a gradual displacement of DMSO by benzamide was observed within the interlayer spacing of the modified kaolinite. The resulting material, after extensive washing with acetone, was characterized and compared to the results obtained previously for the K-DMSO composite. Benzamide intercalation proceeded by gradual displacement of DMSO molecules until completion. The structural stabilization of the K-BZ derivative was explained through the establishment of hydrogen bonds between the carbonyl oxygen atoms of the intercalated benzamide and aluminol groups present at the surface of the kaolinite layer. The interlamellar spacing of K-BZ was shown to be possibly occupied by benzamide molecules that were located at a 68 degrees orientation in relation to the layer surface. Unlike most intercalation molecules such as DMSO, variations in the interplanar spacing of kaolinite were consistent with the nonkeying of any other part of the molecule between the aluminosilicate interlayers. Copyright 2000 Academic Press.     

A transmission problem on a polygonal partition: regularity and shape differentiability

We consider a transmission problem on a polygonal partition for the two-dimensional conductivity equation. For suitable classes of partitions we establish the exact behaviour of the gradient of solutions in a neighbourhood of the vertexes of the partition. This allows to prove shape differentiability of solutions and to establish an explicit formula for the shape derivative.     

Minimal dissipation rate approach to correlate phase inversion data

Phase inversion refers to the phenomenon whereby a small change in operational flow conditions causes an oil-in-water dispersed flow pattern to suddenly switch to a water-in-oil flow pattern, and viceversa. This paper proposes an interpretation of phase inversion in terms of minimal dissipation rate. To this end, the dissipation rate is computed by a simple homogeneous model together with available correlations for effective viscosity in dispersed flows. It is shown that the data available in the literature can be reasonably interpreted as a manifestation of minimal dissipation rate. Furthermore, if the assumed effective viscosity correlations take into account pipe wettability, the minimal dissipation rate approach is capable to interpret also the so-called ambivalent range (hysteresis effect) and correlate the available data.     

Dipolar Rotors Orderly Aligned in Mesoporous Fluorinated Organosilica Architectures

New mesoporous covalent frameworks, based on hybrid fluorinated organosilicas, were prepared to realize a periodic architecture of fast molecular rotors containing dynamic dipoles in their structure. The mobile elements, designed on the basis of fluorinated p‐divinylbenzene moieties, were integrated into the robust covalent structure through siloxane bonds, and showed not only the rapid dynamics of the aromatic rings (ca. 10⁸ Hz at 325 K), as detected by solid‐state NMR spectroscopy, but also a dielectric response typical of a fast dipole reorientation under the stimuli of an applied electric field. Furthermore, the mesochannels are open and accessible to diffusing in gas molecules, and rotor mobility could be individually regulated by I₂ vapors. The iodine enters the channels of the periodic structure and reacts with the pivotal double bonds of the divinyl‐fluoro‐phenylene rotors, affecting their motion and the dielectric properties.     

Conformation of the tridimensional structure of 1,2,3,4,6-pentagalloyl-β-D-glucopyranose (PGG) by (1)H NMR, NOESY and theoretical study and membrane interaction in a simulated phospholipid bilayer: a first insight

1,2,3,4,6-Penta-O-galloyl-β-D-glucopyranose (PGG) is a polyphenolic compound found in substantial amounts in a number of medicinal herbs. We report (i) its conformational analysis by solution NMR and molecular dynamics calculation and (ii) theoretical study of its interaction with a model membrane bilayer. The galloyl groups B and E appear to play important roles in the interaction with the phospholipid bilayer.