New ligands and structural insights into the catalytic asymmetric addition of organozinc reagents to ketones

The catalytic asymmetric addition of alkyl groups to ketones has received considerable attention. Outlined herein is the synthesis of two new ligands based on the C₂-symmetric 11,12-diamino-9,10-dihydro-9,10-ethanoanthracene. The scope of the new ligands has been evaluated in the catalytic asymmetric addition of diethylzinc to a variety of ketones. Enantioselectivities as high as 99% have been achieved. The structures of two of these ligands have been determined by X-ray crystallography and are compared with related structures. Additionally, the structure of a titanium complex bound to a bis(sulfonamide) diol ligand is reported.     

Morita Invariance for Infinitesimal Deformations

Algebras and Representation Theory - Let A and B be two Morita equivalent finite dimensional associative algebras over a field ��. It is well known that Hochschild cohomology is...     

Polyvinyl Alcohol–Pectin Cryogel Films for Controlled Release of Enrofloxacin

The release of enrofloxacin entrapped in polyvinyl alcohol (PVA) cryogel at pH?5.5 showed a first-order kinetic, releasing 69.7% of the antibiotic after 4.5?h at 37?°C. In order to slow down the fluoroquinolone release rate, high-methoxylated pectin was added into the cryogel (PVA?CP). A film containing 1.0% (w/v) HM pectin and 5.0???g/ml enrofloxacin released only 3.7% of the antibiotic after 4.5?h. Since the FTIR spectrum showed that most of the interactions between PVA?CP matrix and enrofloxacin were due to polar groups (carboxylate and amine), a two-layer film system was designed to modulate the releasing rate of the drug. The top film equilibrated with 0.75 or 1.5?M NaCl release up to 41.9% and 89.0% of the enrofloxacin in 4?h, respectively. The release rate of enrofloxacin was found dependent on NaCl concentration in the upper gel layer. The two-layer cryogel system showed attractive features for transcutaneous antibiotic delivery.     

Gerstenhaber Algebra Structure on the Hochschild Cohomology of Quadratic String Algebras

We describe the Gerstenhaber algebra structure on the Hochschild cohomology HH^?(A) when A is a quadratic string algebra. First we compute the Hochschild cohomology groups using Barzdell’s resolution and we describe generators of these groups. Then we construct comparison morphisms between the bar resolution and Bardzell’s resolution in order to get formulae for the cup product and the Lie bracket. We find conditions on the bound quiver associated to string algebras in order to get non-trivial structures.     

Reversible and Irreversible Tracer Dispersion in an Oscillating Flow Inside a Model Rough Fracture

We study the mixing dynamics of a dyed and a clear miscible fluid by an oscillating flow inside an Hele-Shaw cell with randomly distributed circular obstacles. A transparent setup allows us to analyze the distribution of the two fluids and the reversible and irreversible mixing components. At the lower Péclet numbers Pe (based on the averaged absolute fluid velocity), geometrical dispersion due to the disordered flow field between the obstacles is dominant: the corresponding dispersivity is constant with Pe and, at constant Pe, increases with the amplitude of the oscillations and is negligible at small ones. Compared to echo dispersion with only one injection–suction cycle, oscillating flows are shown to provide additional information when the number of oscillations and, as a result, the distance of transverse mixing are varied. Geometrical dispersion is dominant up to a limiting Pe increasing with the amplitude. At higher \({\textit{Pe}}'{\textit{s}}\), the results are similar to those of Taylor dispersion in cells with smooth walls.     

Asymmetric addition of diethylzinc to benzaldehyde catalyzed by novel chiral C2-symmetric tetrakis(sulfonamide)–titanium(IV) complexes

A series of chiral C₂-symmetric tetrakis(sulfonamides) 3a–f, 4a–f were prepared and employed as ligands for titanium(IV) complexes in the asymmetric addition of diethylzinc to benzaldehyde. The chiral secondary alcohols were obtained in high yields and in moderate enantioselectivities.     

New acyclic receptors containing pyridazine units. The influence of π-stacking on the selective transport of lipophilic phenethylamines

The synthesis of four new series of acyclic heteroaromatic receptors is described. They are built by two flexible polyether chains functionalised at their end with pyridazinone or methylpyridazine rings and connected by pyridine or benzene units. Their ability as carriers of lipophilic and hydrophilic phenethylamines and metallic cations has been evaluated. Transport rates show that, in general, these compounds are much more efficient carriers of lipophilic amines than of dopamine and Na⁺, K⁺ and Ca²⁺ ions. Their transport selectivities towards phenethylamine and homoveratrylamine are discussed on the basis of their structural features. Molecular modelling studies suggest that interaction of the aromatic moiety of the guest with the pyridazinone rings via double π-stacking, or with the pyridine ring by single π-stacking, should be responsible of their enhanced efficacy and selectivity in the transport of lipophilic phenethylamines.     

A new series of heteroaromatic receptors containing the 1,3-bis(6-oxopyridazin-1-yl)propane unit: their selective transport ability towards NH4 in relation to Na, K and Ca

The synthesis of a new series of heteroaromatic macrocycles 6-9 containing the 1,3-bis(6-oxopyridazin-1-yl)propane and pyridine units is reported. The acyclic compounds 11-15 had to be prepared as the intermediates in the synthetic sequence. Evaluation of the ionophoric properties of 6-9 and 11-15 shows that 8 and 13 behave as good ammonium ion carriers and exhibit a high selectivity for ammonium with respect to spherically symmetric metallic ions like Na⁺, K⁺, and Ca²⁺. Molecular modelling of the ammonium complexes suggests that the host's oxyimino groups play a more relevant part in effective complexation than the pyridine unit, and that the high complexating efficiency of 13 might be related to the formation of a pseudocavity by intramolecular hydrogen bonding.     

Hochschild cohomology of triangular string algebras and its ring structure

We compute the Hochschild cohomology groups HH^?(A)${\mathrm{HH}}^{?}(A)$ in case A is a triangular string algebra, and show that its ring structure is trivial.