Alcindo A. Dos Santos

Helical Poly(phenylacetylene) Bearing Chiral and Achiral Imidazolidinone-Based Pendants that Catalyze Asymmetric Reactions due to Catalytically Active Achiral Pendants Assisted by Macromolecular Helicity

A series of optically active helical copolymers of phenylacetylenes are prepared by the rhodium-catalyzed copolymerization of the imidazolidinone-linked, catalytically active achiral phenylacetylenes and catalytically inactive chiral phenylacetylenes. The obtained chiral/achiral copolymers exhibit an induced circular dichroism in the UV-vis regions of the copolymer backbones resulting from a preferred-handed helical conformation biased by the chiral imidazolidinone units incorporated in the copolymers. The copolymers are found to catalyze the asymmetric Diels-Alder reaction and produce the products with a moderate enantioselectivity in spite of the fact that the catalytically active units of the copolymers are achiral, indicating that the observed enantioselectivity totally originates from the helical chirality dynamically induced by the optically active, but catalytically inactive imidazolidinone units incorporated in the copolymers.

Novel nanocomposites based on a strawberry-like gold- coated magnetite (Fe@Au) for protein separation in multiple myeloma serum samples

A new process to produce magnetite partially coated with strawberry-like gold nanoparticles in aqueous media is reported. The fast response to magnetic fields and optical properties of gold nanoparticle-based colloidal systems are the two main advantages of this new Fe@Au nanomaterial. These advantages allow for the use of this new colloidal nanomaterial for various purposes in proteomics and biomedicine, as proteins can bind to the surface, and the surface can also be functionalized. As proof-of-concept, the new Fe@Au nanoparticles have been assessed in biomarker discovery as a tool for pre-concentration and separation of proteins from complex proteomes. To this end, sera from healthy people were compared with sera from patients diagnosed with multiple myeloma. The application of this new Fe@Au nanomaterial combined with mass spectrometry has allowed for the identification of 53 proteins, and it has also shown that the heat shock protein HSP75 and the plasma protease C1 inhibitor are potential biomarkers for diagnostics and control of multiple myeloma progression.

A recoverable Pd nanocatalyst for selective semi-hydrogenation of alkynes: hydrogenation of benzyl-propargylamines as a challenging model

We describe a recyclable heterogeneous palladium nanocatalyst for the selective hydrogenation of alkynes to alkenes. The catalyst was prepared through the decomposition of the organometallic precursor Pd2(dba)3 over a magnetic support, obtaining well-dispersed Pd nanoparticles that formed exclusively on the support surface, with average diameter of 3.5 ± 0.8 nm. The catalytic activity was investigated in the hydrogenation reactions of alkenes and alkynes, and the chemo- and stereoselectivity were evaluated in the hydrogenation of benzyl-propargylamines. The catalyst is highly selective in performing semi-hydrogenation reactions under mild conditions and short reaction times, with good overall yields. Furthermore, it can be easily recovered and recycled, with no leaching of palladium detected, and activities and selectivity retained over multiple reaction cycles.

Organotellurides as Precursors of Reactive Organometallics

Reaction of organotellurides with easily available organometallics leads to a fast and clean tellurium/metal exchange reaction, allowing the preparation of a range of functionalized organometallics with C-sp 3 , C-sp 2 , and C-sp hybridization carbanionic centers. Some synthetic applications of the tellurium/metal exchange reactions are discussed.

New-coated fluorescent silver nanoparticles with a fluorescein thiol esther derivative: fluorescent enhancement upon interaction with heavy metal ions

Abstract A new fluorescein thiol esther derivative L was successfully synthesized and fully characterized. The interaction of compound L with spherical silver nanoparticles (AgNPs) was explored in toluene, through the exchange of the tetraoctylammonium bromated (TOAB) molecules stabilizing the silver nanoparticle surface (AgNPs@TOAB). A new hybrid system AgNPs@L was obtained in which an intense metal-enhancement fluorescence phenomenon takes place. The behaviour of the new-coated AgNPs@L system was explored in the presence of silent toxic metal ions, such as Hg2+, Pb2+ and Tl+ in organic phase. Surprisingly, system AgNPs@L reveals to be sensitive to Hg2+ ions over the other heavy metal ions studied.

Reactive organometallics from organotellurides: application in organic synthesis

In this paper the preparation of reactive organometallics starting from organotellurides is reviewed. The application of the reactive organometallics prepared in this way in the synthesis of bioactive compounds is commented.

beta-butyltellanyl carbonyl compounds: a useful source of masked metal homoenolates

Secondary higher order cyanocuprates and lithium homoenolates, were efficiently generated from b-butyltellanylketals and reacted with benzaldehyde and 2-cyclohexen-1-one.

A one-pot glycerol-based additive-blended ethyl biodiesel production: A green process

N-methyl-2-pyrrolidonium methyl sulfonate, a Brønsted acid ionic liquid, promoted the transesterification of soybean oil with ethanol giving a high quality fatty acid ethyl ester. At the end of the reaction, after distillation of excess of ethanol, spontaneous phase separation took place. While the clear upper phase corresponded to the ethyl ester, the lower phase was composed of a mixture of glycerol byproduct and the catalyst. By addition of a stoichiometric amount of appropriated reagents to the resulting mixture, a new ionic liquid-catalyzed process allows the conversion of the glycerol into less polar derivatives, and consequent migration to the ethyl esters phase. This work demonstrated that emulsion, phase separation and contamination problems were completely avoided and the glycerol could be incorporated into the biodiesel as additives in a single step. The whole process involves two renewable starting materials, ethanol and vegetable oil, allowing a total green additive-blended biodiesel production process.

Solvent-free catalysed synthesis of tetrahydropyran odorants: the role of SiO

An efficient, green and solvent-free catalysed Prins-cyclization reaction based on the simple grinding of an aldehyde and a homoallylic alcohol in the presence of catalytic amount of p-TSA on silica gel is reported. By this protocol were synthesized tetrahydropyran odorants including commercial Florol® and Clarycet®, in one and two steps respectively.

Antioxidant effect of functionalized alkyl-organotellurides: a study in vitro

We evaluated the in vitro antioxidant effect of alkyl-organotellurides A–D on lipid peroxidation and protein carbonylation in rat liver homogenates. The thiol oxidase and thiol peroxidase-like activities of compounds were investigated. δ-Aminolevulinic acid dehydratase (δ-ALA-D) activity was determined in rat liver homogenates. Compounds A–D protected against lipid peroxidation induced by Fe2+/EDTA and sodium nitroprusside (SNP). According to the confidence limits of the IC50 values of compounds A–D, the IC50 values for organotellurides followed the order: C (0.30 µM) ≤ B (0.40 µM) < D (0.68 µM) < A (2.90 µM), for Fe2+/EDTA, and B (0.21 µM) ≤ C (0.33 µM) ≤ D (0.43 µM) < A (1.21 µM) for SNP-induced lipid peroxidation. Compounds A–D reduced protein carbonyl content to control levels. The results demonstrated an inverse correlation between thiol oxidase and δ-ALA-D activities. This study supports an antioxidant effect of organotellurides A–D on rat liver.