Paulo H. Schneider

Novel selenoesters fluorescent liquid crystalline exhibiting a rich phase polymorphism

A simple and efficient procedure for the synthesis of a new class of selenoesters 4a and 4b was developed. Polarized-light optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction showed that the selenoester 4a with a shorter alkyl chain displayed a wide nematic range (ΔT = 110.7 °C), while 4b with a longer alkyl chain possesses a rich phase polymorphism: Cr → SmI → SmC → N → I mesophase sequence during heating cycle and I → N → SmC → SmI → SmX → Cr transition on cooling. For 4b, a large temperature range (135.7 °C) from crystal to isotropic phase can be observed. In addition, UV-Vis, steady-state fluorescence emission and excitation spectra in solution were also applied in order to characterize their photophysical behaviour. Compounds 4a and 4b are fluorescent in the blue region and present a Stokes shift at around 80 nm and 39 nm in dichloromethane and dioxane, respectively.

Facile and practical enantioselective synthesis of propargylic alcohols by direct addition of alkynes to aldehydes catalyzed by chiral disulfide–oxazolidine ligands

Abstract The enantioselective alkynylation reaction of aldehydes with alkynes and diethylzinc, catalyzed by chiral disulfide–oxazolidine ligands, provides a simple, practical and inexpensive method to access chiral propargylic alcohols in good yields and satisfactory ees.

Creatine protects against the convulsive behavior and lactate production elicited by the intrastriatal injection of methylmalonate

Methylmalonic acidemias are metabolic disorders caused by a severe deficiency of methylmalonyl-CoA mutase activity, which are characterized by neurological dysfunction, including convulsions. It has been reported that the accumulating metabolite, L-methylmalonic acid (MMA), inhibits succinate dehydrogenase leading to ATP depletion in vitro, and that the intrastriatal injection of MMA induces convulsions through secondary NMDA receptor stimulation. In this study we investigated the effect of creatine (1.2, 3.6 and 12.0 mg/kg, (i.p.), [DOSAGE ERROR CORRECTED] succinate (1.5 micromol/striatum) and MK-801 (3 nmol/striatum) on the convulsions and on the striatal lactate increase induced by MMA (4.5 micromol/striatum) in rats. The effect of creatine on the striatal phosphocreatine content and on MMA-induced phosphocreatine depletion was also evaluated. Creatine, succinate and MK-801 pretreatment decreased the number and duration of convulsive episodes and the lactate increase elicited by MMA. Creatine, but not succinate, prevented the convulsions and the lactate increase induced by the direct stimulation of NMDA receptors. Acute creatine administration increased the total striatal phosphocreatine content and prevented MMA-induced phosphocreatine depletion. Our results suggest that MMA increases lactate production through secondary NMDA receptor activation, and it is proposed that the anticonvulsant effect of creatine against MMA-induced convulsions may be due to an increase in the phosphocreatine content available for metabolic purposes.

Acceleration of arylzinc formation and its enantioselective addition to aldehydes by microwave irradiation and aziridine-2-methanol catalysts.

The formation and 2-amino alcohol catalyzed addition of arylzinc reagents from and with boronic acids, respectively, is drastically accelerated to a few minutes under microwave irradiation without loss of enantioselectivity (up to 98% ee). Of the amino acid derived catalysts tested, the conformationally restricted bulky substituted aziridine-2-methanols derived from serine show the best overall performance in the formation of diarylmethanols.

A new functionalized, chiral disulfide derived from (L)-cysteine: R,R-bis[(3-benzyloxazolan-4-yl)-methane] disulfide as a catalyst in the diethylzinc addition to aldehydes

Abstract A new, easily accessible, chiral disulfide 3 was prepared from l -cysteine in a short synthetic sequence ( Scheme. 1 ) and applied successfully as a highly efficient catalyst for the enantioselective addition of diethyl zinc to aromatic and aliphatic aldehydes to afford the product alcohols in up to more than 99% ee. In contrast to the more common amino alcohols used in similar reactions, catalyst 3 does not have a protic hydrogen in the form of a free hydroxy group.

Recoverable Cu/SiO2 composite-catalysed click synthesis of 1,2,3-triazoles in water media

An eco-friendly multicomponent reaction for the synthesis of 1,2,3-triazoles using a recoverable and recyclable Cu/SiO2 composite as the catalyst is reported. The reaction proceeds by mixing the benzyl halide, sodium azide, the alkyne and the catalyst in an aqueous medium to afford the desired products in excellent yields. The heterogeneous catalytic system showed high efficiency, performing the multicomponent Huisgen reaction in a green approach based on recoverability, recyclability and avoidance of waste. Microwave irradiation was also applied, substituting for conventional heating, resulting in excellent yields of the products with a dramatic reduction in the reaction time.

Interaction between phospholipids bilayer and chitosan in liposomes investigated by 31P NMR spectroscopy

The interaction between chitosan and the polar head of phosphatidylcholine (PC) is discussed for a composite nanovesicle obtained by incorporating chitosan in the organic phase before PC self-assembling. Nanovesicles free of chitosan are studied in parallel to allow the comparison concerning modifications produced on the composite system. Zeta Potential increases in the presence of chitosan and with the increase in its concentration proving the localization of the polymer over the external surface of the vesicle as one interaction site. A (31)P resonance around 0 ppm, characteristic of the system, is reduced with addition of chitosan at 25 degrees C, indicating motional freedom reduction of the polar head phosphate group. The same resonance signal remains almost constant after increasing the temperature to 60 degrees C, suggesting that chitosan shields the phospholipids polar heads as a consequence of the electrostatic interactions leading to an increase in the thermodynamic stability of the composite.

New C2-symmetric chiral disulfide ligands derived from (R)-cysteine

Abstract Several sulfur-containing optically active C 2 -symmetrical ligands have been synthesized from ( R )-cysteine and applied successfully as chiral catalysts in the asymmetric addition of diethylzinc to aldehydes. The resulting secondary alcohols could be obtained in good yields and excellent enantiomeric excess.

Caracterização da pureza de fosfatidilcolina da soja através de RMN de ¹H e de 31P

A strategy is proposed to evaluate the purity of phosphatidylcholine from soybean lecithin, obtained by extraction or column chromatography, using the integrals ratio of 1H NMR spectra. Integrals of methylene signals, around 1.3 and 1.6 ppm, are added and divided by the integral of the choline methyl groups, around 3.3 ppm. Before purification, a ratio of 19.68±1.37 was determined. Using extraction, a ratio of 10.70±0.61 was found, while from column chromatography, a value of 2.99±0.25 was detected. 31P NMR of standard phosphatidylcholine showed signals at -0.2 and -0.9 ppm, whereas the purified one showed a single signal at -0.9 ppm.

Selenides and diselenides containing oxadiazoles: a new class of functionalised materials

A simple and efficient procedure for the synthesis of a new class of organoselenium liquid crystal compounds was developed. The coupling of aryl bromides with elemental selenium was catalysed using copper oxide nanopowder in the presence of potassium hydroxide employing dimethyl sulfoxide as the solvent. This is the first report of the synthesis and characterisation of liquid crystal-based diselenides. Their mesophases were characterised by polarising optical microscopy and differential scanning calorimetry. Compounds 1, 2 and 4b exhibited the smectic A phase. In addition, these compounds showed weak blue fluorescence in solution (λmax. em. 350–405 nm) and a Stokes shift of around 90 nm.