Hydrogen production on iron–magnesium oxide in the high-temperature water-gas shift reaction

The effect of the structure of the achiral primary amine additive on the enantioselective heterogeneous catalytic hydrogenation of (E)-2-methyl-2-butenoic acid over cinchonidine modified Pd/Al₂O₃ was studied. It was found that a variety of amines increase the enantioselectivity, which was always accompanied by decrease in the initial rate of the hydrogenations. Based on these results, the participation of the amine additive in the formation of the intermediate complex responsible for enantioselection was suggested. A decrease in the reaction temperature resulted in further increase in the optical purity of the product up to 67%, the highest value reported in the hydrogenation of unsaturated aliphatic acids in this heterogeneous catalytic system so far.     

LIMIT CYCLES OF THE GENERALIZED POLYNOMIAL LINARD DIFFERENTIAL SYSTEMS

Using the averaging theory of first and second order we study the maximum number of limit cycles of generalized Linard differential systems{x = y + εh_l~1(x) + ε~2h_l~2(x),y=-x- ε(f_n~1(x)y~(2p+1) + g_m~1(x)) + ∈~2(f_n~2(x)y~(2p+1) + g_m~2(x)),which bifurcate from the periodic orbits of the linear center x = y,y=-x,where ε is a small parameter.The polynomials h_l~1 and h_l~2 have degree l;f_n~1and f_n~2 have degree n;and g_m~1,g_m~2 have degree m.p ∈ N and[·]denotes the integer part function.     

A dimeric copper coumarin complex: synthesis and crystal structure of [{Cu(4-methyl-7-(salicylideneamino)coumarin)2}2]

A binuclear copper complex [{Cu(L)₂}₂], C₆₈H₄₈Cu₂N₄O₁₂C (where L is 4-methyl-7-(salicylideneamino)coumarin), has been synthesized and characterized using elemental analysis, molar conductance measurements, and infrared, ultraviolet and ESR spectrosopy. The molecular structure of title compound, determined by single-crystal X-ray diffraction studies, reveals that the two symmetric Cu(L)2 units are associated into a dimer by rather long Cu...O bonds. The Cu(II) ions are bridged via the phenolic oxygen of one of the monomers and have distorted trigonal bipyramidal conformation geometry. Within each monomer the two methylsubstituted coumarin skeletons are trans to one another, but adopt a parallel arrangement with respect to the other monomer. Only half of the complex molecule can be found in the asymmetric unit, Z′ = 0.5, the other half is generated by the symmetry centre.      

A New Approach to Dendrimers made from p-tert-Butyl Calix[4]arenes

A new family of hyperbranched molecules and dendrimers has been constructed from a diamide–dicalix derivative prepared from monocarbomethoxymethyl p-tert-butyl calix[4]arene and tris(2-aminoethyl)amine (‘tren’) via amide-formation reactions. The selective 1,3-di-O-functionalization of p-tert-butyl calix[4]arene moieties allows the synthesis of first- (G1) and second-generation (G2) calix-dendrimers. Replacement of the quadridentate amine by a trithia-ether-triamine-mono-ol, ’hyten’, again results in acylation of the amino groups, but with the generation of a central cavity with different complexing properties.

A new family of hyperbranched molecules and dendrimers has been constructed from a diamide–dicalix derivative prepared from monocarbomethoxymethyl p-tert-butyl calix[4]arene and tris(2-aminoethyl)amine (‘tren’) via amide-formation reactions. The selective 1,3-di-O-functionalization of p-tert-butyl calix[4]arene moieties allows the synthesis of first- (G1) and second-generation (G2) calix-dendrimers     

Antimicrobial activity and phytochemical screening of Arbutus unedo L.

In this study, antimicrobial activities of water and methanol extract, and three phenolic fractions of the roots of Arbutus unedo L. were investigated. Poor antibacterial activity against both Staphylococcus aureus and Pseudomonas aeruginosa bacteria was shown with water and methanol extract. However moderate antibacterial activity was shown by water extract and phenolic fractions against Escherichia coli and S. aureus, respectively. The phytochemical screening of roots of A. unedo revealed the presence of quinones, anthraquinones reducteurs compounds, anthocyanins, tannins and flavonoids. Quantitative analysis showed that the roots were strongly dominated by anthocyanins compounds (3.65 mg g^?1) followed by total flavonoids (0.56 mg^?1) and flavones & flavonols (0.17 mg g^?1).     

Microwave-assisted synthesis of a triazole-linked 3′-5′ dithymidine using click chemistry

Synthesis of a triazole-linked 3′-5′ thymidine dimer making use of 1,3-dipolar cycloaddition is described. The azido-precursor was obtained by regioselective chlorination of thymidine, followed by azidation. The second precursor, a propargyl derivative, was obtained by selective 3′-O-alkylation of thymidine. Two ‘click systems’ were compared to obtain the desired dimer. These reactions were performed by microwave irradiation.     

Kinetics of the alkaline hydrolysis of isatin and N-methylisatin in water and water-N,N-dimethylacetamide mixtures

The kinetics of amide bond cleavage of isatin and N-methylisatin in the presence of N,N-dimethylacetamide (DMA) was followed spectrophotometrically in the range of solvent composition (0–48.53 wt.%) and temperatures (40–70 °C) using piperidine as a nucleophile. The reaction was studied under pseudo-first-order kinetics. The rate of the reaction decreases largely with increasing organic solvent content. The thermodynamic activation parameters were calculated and discussed in terms of solvation of the activated complex. No linearity was observed between log rate constant and the reciprocal dielectric constant for the solvent used suggesting that there is a selective solvation by higher polar solvent (water). Finally, a mechanism for the ring opening for isatin and N-methylisatin was proposed.     

Synthèse et caractérisation de fluorbritholites strontiques dopées au néodyme

Strontium fluorbritholites with the general formula Sr_10-xNd_x(PO₄)_6-x(SiO₄)_xF₂ (0 ≤ x ≤ 6), were prepared by solid state reaction at temperatures between 1200 and 1400 °C. The XRD analysis showed that a pure apatitic phase was formed only for x ≤ 2.5. Above this value, there was formation of secondary phases. The variation of the lattice parameters as a function of x indicated that the formed solid solution was discontinuous on both sides of x = 3. The analysis by Raman and IR spectroscopies confirmed the incorporation of SiO₄ groups within the apatite lattice, and showed that this incorporation induced in the structure a disorder that increased with increasing content of Nd³⁺ and SiO₄⁴⁻. Optical absorption measurements showed a wide variation in the local environment of Nd³⁺ ions, corresponding to the existence of new spectroscopic sites, evidenced by a luminescence study.     

Design,synthesis of novel quinazolin-4-one derivatives and biological evaluation against human MCF-7 breast cancer cell line

A new series of 6,8-dibromo-2-(4-chlorophenyl)quinazolin-4(3H)-one derivatives VI–XIII were synthesized. Their chemical structures were confirmed by spectral and elemental analysis. The cytotoxic effect of the newly synthesized compounds was tested in vitro against human breast cancer cell line (MCF-7). Most of the tested compounds have shown promising cytotoxic activity. Compounds X and XIIIb exerted a powerful cytotoxic effect against MCF-7 with a very low IC50 (0.0015 and 0.0047 µmol/ml), while compounds VI, VII, VIII, XIIb, XI, XIIIc and IX exerted a moderate cytotoxic effect (IC50 0.01523, 0.0213, 0.031, 0.0478, 0.049, 0.068 and 0.079 µmol/ml respectively), compared to doxorubicin (0.0025 µmol/ml). Exploring their apoptotic effect; interestingly,all compounds activated apoptotic cascade in MCF-7. Compounds VI, XIIIb, XIIb, XI, XIIa, VII, V and VIII showed potent effect even much more than doxorubicin by 12.87–5.91 folds, while compounds XIIIc, IX, XIIIa, XIIc and X showed moderate increase in CASP3 activity by 4.96–3.22 folds relative to untreated cells more or less similar to doxorubicin (5.57 folds).     

Cyclability of 3‐connected graphs

A subset S of vertices of a graph G is called cyclable in G if there is in G some cycle containing all the vertices of S. We denote by α(S, G) the number of vertices of a maximum independent set of G[S]. We prove that if G is a 3‐connected graph or order n and if S is a subset of vertices such that the degree sum of any four independent vertices of S is at least n + 2α(S, G) −2, then S is cyclable. This result implies several known results on cyclability or Hamiltonicity. © 2000 John Wiley & Sons, Inc. J Graph Theory 34: 191–203, 2000