Synthesis of 4-aryl-2-pyrrolidones and beta-aryl-gamma-amino-butyric acid (GABA) analogues by Heck arylation of 3-pyrrolines with arenediazonium tetrafluoroborates. Synthesis of (+/-)-rolipram on a multigram scale and chromatographic resolution by semipreparative chiral simulated moving bed chromatography

We report herein a new, practical, and economic synthesis of the phosphodiesterase inhibitor Rolipram on a multigram scale as well as the synthesis of new 4-aryl pyrrolidones and beta-aryl-gamma-amino butyric acids (GABA derivatives) employing an efficient Heck-Matsuda arylation of 3-pyrroline with aryldiazonium tetrafluoroborates. Racemic Rolipram was resolved into its enantiomers using chiral simulated moving bed chromatography having the low-cost microcrystalline cellulose triacetate as a chiral stationary phase.     

Sol-Gel Synthesis of Nanoscaled Spinels Using Propylene Oxide as a Gelation Agent

Spinel nanoparticles of CoAl₂O₄ (blue), CoCr₂O₄ (bluish green), ZnFe₂O₄ (brown) and CuCr₂O₄ (black) were synthesized by a sol-gel route with propylene oxide as a gelation agent. This method has proven to be an effective route to synthesize mixed oxide nanoparticles, especially for that with one of metal ion having a formal charge of less than +3. Transmission electron micrographs show the small particle size (less than 60 nm) of the four pigments and their narrow particle size distributions.     

Low power laser radiation at 685 nm stimulates stem-cell proliferation rate in Dugesia tigrina during regeneration

Today’s scientific interest in tissue engineering for organ transplantations and regeneration from stem cells, allied with recent observations on biostimulation of tissues and cells by laser radiation, stands as a strong motivation for the present work, in which we examine the effects of the low power laser radiation onto planarians under regenerative process. To investigate those effects, a number of 60 amputated worms were divided in three study groups: a control group and two other groups submitted to daily 1 and 3 min long laser treatment sections at 910 W/m² power density. A 685 nm diode laser with 35 mW optical power was used. Samples were sent to histological analysis at the 4th, the 7th and the 15th days after amputation. A remarkable increase in stem cells counts for the fourth day of regeneration was observed when the regenerating worms was stimulated by the laser radiation. Our findings encourage further research works on the influence of optical radiation onto stem cells and tissue regeneration.     

Substituent effects in the migration step of the Baeyer-Villiger rearrangement. A theoretical study

Quantum mechanical calculations have been performed on the migration step of the Baeyer-Villiger (BV) rearrangements of some acetophenones, p-RC6H4COCH3 (R = CN, Cl, H, CH3, CH3O) with m-chloroperbenzoic acid. The energy barriers, charge distributions, and frontier molecular orbitals determined for the aryl migration step explain the effects of substituents on the reactivity of these ketones. A plot of the log of relative oxidation rates of the ketones versus their corresponding calculated energy barriers of the migration stage showed a downward deviation for the p-OCH3 derivative. This result is consistent with a change in the rate-determining step, from the aryl migration to the carbonyl addition, in the case of p-methoxyacetophenone, according to the suggestion that the rate-determining step of the BV oxidation can change with variations in the substituent group.     

Melting of "porous" vortex matter

Bitter decoration and magneto-optical studies reveal that in heavy-ion irradiated superconductors, a "porous" vortex matter is formed when vortices outnumber columnar defects. In this state ordered vortex crystallites are embedded in the "pores" of a rigid matrix of vortices pinned on columnar defects. The crystallites melt through a first-order transition while the matrix remains solid. The melting temperature increases with density of columnar defects and eventually turns into a continuous transition. At high temperatures a sharp kink in the melting line is found, signaling an abrupt change from crystallite melting to melting of the rigid matrix.     

Polyelectrolytes in the presence of multivalent ions: gelation versus segregation

We analyze solutions of strongly charged chains bridged by linkers such as multivalent ions. The gelation induced by the strong short range electrostatic attractions is dramatically suppressed by the long range electrostatic correlations due to the charge along the non-cross-linked monomers and ions. A modified Debye-Hückel approach of cross-linked clusters of charged chains is used to determine the mean field gelation transition self-consistently. Highly dilute polyelectrolyte solutions tend to segregate macroscopically. Semidilute solutions can form gels if the Bjerrum length l(B) and the distance between neighboring charged monomers along the chain b are both greater than the ion size a.     

Rectangular to hexagonal columnar phase transition exhibited by a biforked mesogen

We present the structural study of a biforked compound exhibiting a Col_r-Col_h phase transition. This study was performed by means of DSC, optical microscopy, X-ray diffraction, dilatometry and molecular modelling. The molecular packing within the two columnar mesophases of this compound is discussed. For the first time, it is shown that the clusters of adjacent molecules which form the elementary section of a column are tilted with respect to the columnar axis in the rectangular mesophase. From the whole set of experimental data, the number of molecules in a columnar section is found to be about 5 in the rectangular mesophase, and 4 in the hexagonal one. The transition between the two columnar mesophases is discussed with respect to its slow kinetics. Received 1st October 2002 Published online: 16 April 2003 RID="a" ID="a"e-mail: ribeiro@cii.fc.ul.pt RID="b" ID="b"UMR 7504     

Ethylene-styrene copolymerization with constrained geometry catalysts: a density functional study

A density functional theory (DFT) study of the ethylene-styrene copolymerization process with titanium-based constrained geometry catalyst (CGC) is presented. To establish the difference between simplified CGC or real CGC models, i.e., considering all ligands of the catalyst, we have performed calculations for ethylene and styrene insertions in both models. Thus, we have used two different DFT functional, BP86 and B3L YP along with two basis set, LANL 2DZ (without polarization functions) and DZVP (including polarization functions). We have noted certain differences between theoretical results published by other authors and our theoretical and experimental data.     

Charge induced pattern formation on surfaces: segregation in cylindrical micelles of cationic-anionic peptide-amphiphiles

Micelles, vesicles, and films composed of two species of incompatible heterogeneous molecules exhibit full internal segregation of the component species. This macroscopic segregation can be inhibited by oppositely charging the two different molecular species. The degree of compatibility achieved by the charges leads to either fully homogenous mixtures or to local segregation and the possible formation of regular patterns. We investigate the induction of periodic surface patterns by the presence of opposite charges in flat films and cylindrical micelles. In the strong segregation limit the incompatibility between species can be described by a line tension parameter gamma. The size of the patterns formed is of the order of a characteristic size L approximately (gamma/sigma(2))(1/2), where sigma is the surface charge density. The pattern symmetry on flat surfaces is function only of the fraction of area covered by the components, f: lamellar for 0.34相似文献   

The Local Linearization Method for Numerical Integration of Random Differential Equations

A Local Linearization (LL) method for the numerical integration of Random Differential Equations (RDE) is introduced. The classical LL approach is adapted to this type of equations, which are defined by random vector fields that are typically at most Hölder continuous with respect to the time argument. The order of strong convergence of the method is studied. It turns out that the LL method improves the order of convergence of conventional numerical methods that have been applied to RDEs. Additionally, the performance of the LL method is illustrated by means of numerical simulations, which show that it behaves well even in those equations with complicated noisy dynamics where conventional methods fail.AMS subject classification (2000) 34F05, 34K28, 60H25.H. Cruz: This work was partially supported by the Research Grant 03-059 RG/MATHS/LA from the Third World Academic of Science (TWAS).Received July 2004. Accepted October 2004. Communicated by Anders Szepessy.