14 research outputs found
Photoredox Organocatalysis for the Enantioselective Synthesis of 1,7-Dicarbonyl Compounds
We describe an asymmetric organocatalytic method to synthesize 1,7-dicarbonyl compounds containing a β-stereocenter. The chemistry relies on the formation of γ-keto radicals, generated upon oxidative ring opening of cyclobutanols mastered by an organic photoredox catalyst. These nonstabilized primary radicals are stereoselectively intercepted by an iminium ion intermediate, formed upon activation of aliphatic and aromatic enals by a chiral secondary amine catalyst. This organocatalytic photoredox method served to prepare scaffolds found in natural products and drug molecules
UV laser-induced high resolution cleaving of Si wafers for micro-nano devices and polymeric waveguide characterization
In this work we propose a method for cleaving silicon-based photonic chips by using a laser based micromachining system, consisting of a ND:YVO4laser emitting at 355 nm in nanosecond pulse regime and a micropositioning system. The laser makes grooved marks placed at the desired locations and directions where cleaves have to be initiated, and after several processing steps, a crack appears and propagate along the crystallographic planes of the silicon wafer. This allows cleavage of the chips automatically and with high positioning accuracy, and provides polished vertical facets with better quality than the obtained with other cleaving process, which eases the optical characterization of photonic devices.
This method has been found to be particularly useful when cleaving small-sized chips, where manual cleaving is hard to perform; and also for polymeric waveguides, whose facets get damaged or even destroyed with polishing or manual cleaving processing. Influence of length of the grooved line and speed of processing is studied for a variety of silicon chips. An application for cleaving and characterizing sol–gel waveguides is presented. The total amount of light coupled is higher than when using any other procedure
Phenolic and furanic compounds of Portuguese chestnut and French, American and Portuguese oak wood chips
Botanical species used on aging process must
be wisely and judiciously chosen, and for this selection, a
basic knowledge of the chemical composition of woods is
warranted. Aiming to contribute to extend the knowledge
of the chemical composition of several wood species useful
for enological purposes, we have focused our studies on
Portuguese chestnut and French, American and Portuguese
oak chips. The profile of low molecular weight phenolic
composition of these chips was achieved, using an optimized
extraction method based on pressurized liquid
extraction, followed by the quantification of phenolic acids,
phenolic aldehydes and furanic derivatives by high-performance
liquid chromatography (HPLC-DAD). The
identification of those compounds was also confirmed by
LC-DAD/ESI-MS. This study allowed the determination of
the low molecular phenolic composition of Portuguese
chestnut and French, American and Portuguese oak wood.
According to our results, the influence of the botanical
species seems to be more relevant than the geographic
origin of the wood species
Improvement of Ni phytostabilization by inoculation of Ni resistant Bacillus megaterium SR28C
The use of metal tolerant plants for the phytostabilization of metal contaminated soil is an area of
extensive research and development. In this study the effects of inoculation of Ni-resistant bacterial
strains on phytostabilization potential of various plants, including Brassica juncea, Luffa cylindrica and
Sorghum halepense, were studied. A Ni-resistant bacterial strain SR28C was isolated from a nickel rich
serpentine soil and identified as Bacillus megaterium based on the morphological features, biochemical
characteristics and partial 16S rDNA sequence analysis. The strain SR28C tolerated concentrations up to
1200 mg Ni L 1 on a LuriaeBertani (LB) agar medium. Besides, it showed high degree of resistance to
various metals (Cu, Zn, Cd, Pb and Cr) and antibiotics (ampicillin, tetracycline, streptomycin, chloramphenicol,
penicillin and kanamycin) tested. In addition, the strain bound considerable amounts of Ni in
their resting cells. Besides, the strain exhibited the plant growth promoting traits, such as solubilization
of phosphate and production of indole-3-acetic acid (IAA) in modified Pikovskayas medium and LB
medium, respectively in the absence and presence of Ni. Considering such potential, the effects of SR28C
on the growth and Ni accumulation of B. juncea, L. cylindrica and S. halepense, were assessed with
different concentrations of Ni in soil. Inoculation of SR28C stimulated the biomass of the test plants
grown in both Ni contaminated and non-contaminated soils. Further, SR28C alleviated the detrimental
effects of Ni by reducing its uptake and translocation to the plants. This study suggested that the PGPB
inoculant due to its intrinsic abilities of growth promotion and attenuation of the toxic effects of Ni could
be exploited for phytostabilization of Ni contaminated site.M. Rajkumar acknowledges the financial support received in the
form of Ramalingaswami re-entry fellowship from Department of
Biotechnology (DBT), Government of India. Y. Ma thankfully acknowledges
the Portuguese Foundation for Science and Technology
(FCT) for awarding a post-doctoral research grant (SFRH/BPD/
76028/2011)