Unexpected reactivity of trifluoromethylated olefins with indole: a mechanistic investigation

Several trifluoromethylated compounds were reacted with indole sodium salt, leading to monofluorinated compounds. The unexpected products formation was rationalized by DFT calculations.     

The Heck-Matsuda arylation of 2-hetero-substituted acrylates

The Heck-Matsuda arylation of 2-aza and 2-oxo-substituted acrylates is described. Several reaction conditions were evaluated including the influence of solvents, temperature, catalysts, and stoichiometry. While the oxygenated system was successfully arylated in benzonitrile with Pd₂(dba)₃ as catalyst, the aza-acrylate furnished methoxylated products. The methoxylated products were subjected to an elimination/reduction protocol to obtain the corresponding N,O-protected phenylalanine derivatives. A one-pot procedure for the preparation of phenylalanine derivatives from 2-aza-substituted acrylates is presented.     

Trapped instability and vortex formation by an unstable coastal current

This paper addresses the instability of a two-layer coastal current in a quasigeostrophic model; the potential vorticity (PV) structure of this current consists in two uniform cores, located at different depths, with finite width and horizontally shifted. This shift allows both barotropic and baroclinic instability for this current. The PV cores can be like-signed or opposite-signed, leading to their vertical alignment or to their hetonic coupling. These two aspects are novel compared to previous studies. For narrow vorticity cores, short waves dominate, associated with barotropic instability; for wider cores, longer waves are more unstable and are associated with baroclinic processes. Numerical experiments were performed on the f-plane with a finite-difference model. When both cores have like-signed PV, trapped instability develops during the nonlinear evolution: vertical alignment of the structures is observed. For narrow cores, short wave breaking occurs close to the coast; for wider cores, substantial turbulence results from the entrainment of ambient fluid into the coastal jet. When the two cores have opposite-signed PV, the nonlinear regimes range from short wave breaking to the ejection of dipoles or tripoles, via a regime of dipole oscillation near the wall. The Fourier analysis of the perturbed flow is appropriate to distinguish the regimes of short wave breaking, of dipole formation, and of turbulence, but not the differences between regimes involving only vortex pairs. To explain more precisely the regimes where two vortices (and their wall images) interact, a point vortex model is appropriate.     

NMR relaxation study of avocado quality

Four nuclear magnetic resonance relaxation protocols are investigated as potential candidates for off-line and on-line determination of avocado maturity. Two-dimensionalT ₁-T ₂ andT ₂-D correlation spectroscopy provides the most information but is only suitable for off-line quality control. The CPMGT ₂ spectrum gives avocado oil content but requires intensive data processing. Suppression of the tissue water signal byT ₁-Null methods is shown to be unreliable but a new, single-shot pulse sequence which uses diffusive attenuation to suppress the tissue water is shown to give a good correlation with oil content and is suitable for both off-line and on-line implementation.     

Ochratoxin A non-conventional exposure sources — A review

Ochratoxin A (OTA) is one of the most studied mycotoxins, with great public health and agroeconomic significance. The exposure of both humans and animals to this fungal toxin has been associated to food matrices since its discovery. However, according to recent reports, OTA may also represent a potential airborne hazard, in water-damaged buildings, or occupational contamination, in workplaces with high mould exposure, such as agricultural, farm and alimentary industries. Further, in addition to the conventional studied food matrices, worldwide consumed, there are increasing reports on different and less obvious sources of alimentary exposure. These include traditional and home-made food products, highly consumed by specific groups of populations that thus might be at risk. This paper aims to spotlight the current knowledge on these non-conventional OTA exposure sources.     

Medical genetics in Paraguay

Paraguay is a developing country with low levels of health coverage, with 81% of the population without health insurance, a proportion that reaches 98.1% among the poor, 93% among the rural population and 91.7% among the mainly Guarani-speaking population. The infant mortality rate is 19.4 per 1,000, although there is gross under-reporting. Maternal mortality rate is alarmingly high at 110.9 per 100,000 livebirths, reaching 420.5 in rural areas. There are only two clinical geneticists and four biochemists trained in human genetics, and virtually all genetic services in the country are concentrated in the 'Instituto de Investigaciones en Ciencias de la Salud' (IICS) from the National University. The teaching of medical genetics in medical schools is included in physiology and pathology courses, while at the postgraduate level, training in medical genetics is limited to pediatrics and gynecology. In 1999, a pilot newborn screening program was initiated to determine the frequency of congenital hypothyroidism and phenylketonuria and to provide early treatment for affected babies. Another pilot project recently launched by the Ministry of Health is the Program for the Prevention of Neural Tube Defects, mandating folic acid fortification of flour, but as of the end of 2003 it had not been implemented. Paraguay lacks adequate resources to provide accurate diagnoses and treatment of genetic conditions.     

Quaternary Stereogenic Centers through Enantioselective Heck Arylation of Acyclic Olefins with Aryldiazonium Salts: Application in a Concise Synthesis of (R)‐Verapamil

We describe herein a highly regio‐ and enantioselective Pd‐catalyzed Heck arylation of unactivated trisubstituted acyclic olefins to provide all‐carbon quaternary stereogenic centers. Chiral N,N ligands of the pyrimidine‐ and pyrazino‐oxazoline class were developed for that purpose, providing the desired products in good to high yields with enantiomeric ratios up to >99:1. Both linear and branched substituents on the olefins were well‐tolerated. The potential of this new method is demonstrated by the straightforward synthesis of several O‐methyl lactols and lactones containing quaternary stereocenters, together with a concise enantioselective total synthesis of the calcium channel blocker verapamil.     

Luminescent Di‐ and Trinuclear Boron Complexes Based on Aromatic Iminopyrrolyl Spacer Ligands: Synthesis,Characterization, and Application in OLEDs

New bis‐ and tris(iminopyrrole)‐functionalized linear (1,2‐(HNC₄H₃‐C(H)?N)₂‐C₆H₄ ( 2 ), 1,3‐(HNC₄H₃‐C(H)?N)₂‐C₆H₄ ( 3 ), 1,4‐(HNC₄H₃‐C(H)?N)₂‐C₆H₄ ( 4 ), 4,4′‐(HNC₄H₃‐C(H)?N)₂‐(C₆H₄‐C₆H₄) ( 5 ), 1,5‐(HNC₄H₃C‐(H)?N)₂‐C₁₀H₆ ( 6 ), 2,6‐(HNC₄H₃C‐(H)?N)₂‐C₁₀H₆ ( 7 ), 2,6‐(HNC₄H₃C‐(H)?N)₂‐C₁₄H₈ ( 8 )) and star‐shaped (1,3,5‐(HNC₄H₃‐C(H)?N‐1,4‐C₆H₄)₃‐C₆H₃ ( 9 )) π‐conjugated molecules were synthesized by the condensation reactions of 2‐formylpyrrole ( 1 ) with several aromatic di‐ and triamines. The corresponding linear diboron chelate complexes (Ph₂B[1,3‐bis(iminopyrrolyl)‐phenyl]BPh₂ ( 10 ), Ph₂B[1,4‐bis(iminopyrrolyl)‐phenyl]BPh₂ ( 11 ), Ph₂B[4,4′‐bis(iminopyrrolyl)‐biphenyl]BPh₂ ( 12 ), Ph₂B[1,5‐bis(iminopyrrolyl)‐naphthyl]BPh₂ ( 13 ), Ph₂B[2,6‐bis(iminopyrrolyl)‐naphthyl]BPh₂ ( 14 ), Ph₂B[2,6‐bis(iminopyrrolyl)‐anthracenyl]BPh₂ ( 15 )) and the star‐shaped triboron complex ([4′,4′′,4′′′‐tris(iminopyrrolyl)‐1,3,5‐triphenylbenzene](BPh₂)₃ ( 16 )) were obtained in moderate to good yields, by the treatment of 3 – 9 with B(C₆H₅)₃. The ligand precursors are non‐emissive, whereas most of their boron complexes are highly fluorescent; their emission color depends on the π‐conjugation length. The photophysical properties of the luminescent polyboron compounds were measured, showing good solution fluorescence quantum yields ranging from 0.15 to 0.69. DFT and time‐dependent DFT calculations confirmed that molecules 10 and 16 are blue emitters, because only one of the iminopyrrolyl groups becomes planar in the singlet excited state, whereas the second (and third) keeps the same geometry. Compound 13 , in which planarity is not achieved in any of the groups, is poorly emissive. In the other examples ( 11 , 12 , 14 , and 15 ), the LUMO is stabilized, narrowing the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO–LUMO), and the two iminopyrrolyl groups become planar, extending the size of the π‐system, to afford green to yellow emissions. Organic light‐emitting diodes (OLEDs) were fabricated by using the new polyboron complexes and their luminance was found to be in the order of 2400 cd m^?2, for single layer devices, increasing to 4400 cd m^?2 when a hole‐transporting layer is used.     

Graphene Oxide Nanosheets Modified with Single‐Domain Antibodies for Rapid and Efficient Capture of Cells

Peripheral blood can provide valuable information on an individual’s immune status. Cell‐based assays typically target leukocytes and their products. Characterization of leukocytes from whole blood requires their separation from the far more numerous red blood cells. 1 Current methods to classify leukocytes, such as recovery on antibody‐coated beads or fluorescence‐activated cell sorting require long sample preparation times and relatively large sample volumes. 2 A simple method that enables the characterization of cells from a small peripheral whole blood sample could overcome limitations of current analytical techniques. We describe the development of a simple graphene oxide surface coated with single‐domain antibody fragments. This format allows quick and efficient capture of distinct WBC subpopulations from small samples (～30 μL) of whole blood in a geometry that does not require any specialized equipment such as cell sorters or microfluidic devices.