The Bellus-Claisen rearrangement

Among the reactions available to synthetic chemists for the construction of new C--C bonds, the Claisen rearrangement is one of the most powerful, elegant, and well-characterized methods. A genuinely new variant, the Bellus-Claisen rearrangement came to light a quarter of a century ago: The reaction of an allylic ether, thioether, or amine with a ketene leads through a [3,3] sigmatropic bond reorganization of a zwitterionic intermediate to an E unsaturated ester, thioester, or amide. When applied to cyclic allylic substrates, a ring-enlargement by four carbon atoms in one step provides medium-ring unsaturated E-configured lactones, thiolactones, and lactams. The scope of the Bellus-Claisen rearrangement and the optimum reaction conditions will be discussed in this Minireview.     

Oscillation Theorems for Neutral Differential Equations of Higher Order

In this paper we present some new oscillatory criteria for the n-th order neutral differential equations of the form The results obtained extend and improve a number of existing criteria.     

Axially polar columnar phase made of polycatenar bent-shaped molecules

The polycatenar bent-shaped molecules are able to form columnar phases with column stratum built of few molecules, arranged in coplanar or conelike geometry. In the latter case, the phase becomes axially polar, with electric spontaneous polarization reorientable in the electric field by flipping the cone axis. The phase is antiferroelectric; in the plane perpendicular to columns, the ferroelectric hexagonal order exists, but the columns are broken along the z direction and the polarization direction alternates between the blocks.     

Classification of regular maps of negative prime Euler characteristic

We give a classification of all regular maps on nonorientable surfaces with a negative odd prime Euler characteristic (equivalently, on nonorientable surfaces of genus where is an odd prime). A consequence of our classification is that there are no regular maps on nonorientable surfaces of genus where is a prime such that (mod ) and .

     

Synthesis of Substituted Salicylanilides under Microwave Irradiation

Salicylanilides were prepared in 70–95% yields in 4–8min from phenyl salicylate or phenyl 4-methoxysalicylate and substituted anilines under microwave irradiation under solvent free conditions.     

Analysis of the importance of the metallo-beta-lactamase active site loop in substrate binding and catalysis

The role of the mobile loop comprising residues 60-66 in metallo-beta-lactamases has been studied by site-directed mutagenesis, determination of kinetic parameters for six substrates and two inhibitors, pre-steady-state characterization of the interaction with chromogenic nitrocefin, and molecular modeling. The W64A mutation was performed in IMP-1 and BcII (after replacement of the BcII 60-66 peptide by that of IMP-1) and always resulted in increased K(i) and K(m) and decreased k(cat)/K(m) values, an effect reinforced by complete deletion of the loop. k(cat) values were, by contrast, much more diversely affected, indicating that the loop does not systematically favor the best relative positioning of substrate and enzyme catalytic groups. The hydrophobic nature of the ligand is also crucial to strong interactions with the loop, since imipenem was almost insensitive to loop modifications.     

DISPA method in the analysis of Mössbauer spectra of metallic glasses

A plot of the DISPersion mode of a pure, ideal Lorentzian line versus the Absorption one (DISPA plot) gives a perfect circle. Non-Lorentzian profiles distort this reference circle in an unambiguous way. A modification of the DISPA method for the lineshape analysis of Mössbauer spectra of amorphous Fe₈₃B₁₇ and Fe₄₀Ni₄₀B₂₀ pointed out convolutions of Gaussian and Lorentzian lines to be somewhat superior. Based on the previous results a construction of a hyperfine field distribution is proposed.     

Effect of Ti pretreatment on photoelectric properties of TiO2 layers prepared by plasma-anodic oxidation

Photoactive TiO₂ layers were formed by anodic oxidation of Ti in O₂ RF plasma under various conditions and Ti surface pretreatment. The photocurrent spectrum in 1M NaOH was used to calculate the quantum efficiency of the photocurrent production and the band-gap energy for indirect transitions. Photoelectrochemical properties of TiO₂ layers were studied on the decomposition of p-cresol water solution. The method of Ti surface pretreatment (mechanical polishing or chemical etching) has a decisive influence on the photoelectrochemical properties and the structure of the polycrystalline oxide, rutile, anatase or amorphous phase content.This study was supported by the Grant Agency for Sciences of Slovakia.