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61.
R. S. Corrêa S. R. Souza e Silva L. P. Duarte G. D. F. Silva L. C. A. Barbosa J. Ellena A. C. Doriguetto 《Journal of Structural Chemistry》2012,53(1):156-163
The structural study of two (C30H48O2) pentacyclic triterpene (PCTT) isomers is presented. These terpenes, known as 30-hydroxy-lup-20(29)-en-3-one (1) and (11α)-11-hydroxy-lup-20(29)-en-3-one (2), were isolated from Maytenus imbricata Mart. Ex Reissek (Celastraceae). The molecular structure of 1 and 2 differs in the position of the hydroxyl group. Both compounds crystallize in non-centrosymmetric space groups with two molecules
in the asymmetric unit. The crystal structure of 1 shows a triclinic P1 space group (a = 9.5518(1) ?, b = 9.7083(1) ?, c = 14.4696(2) ?, α = 93.832(1)°, β = 102.833(1)°, and γ = 103.307(1)°), while compound 2 crystallizes in a monoclinic P21 one (a = 13.4439(16) ?, b = 14.4463(14) ?, c = 13.5224(9) ? and β = 99.703(8)°). The two molecules independent by symmetry of 1 differ slightly due to the presence of static disorder in oxygen atoms. In addition, the intermolecular geometries of 1 and 2 were analysed, and in each isomer the crystal packing is stabilized by O-H…O intermolecular hydrogen bonds and van der Waals
forces. 相似文献
62.
63.
Mónica S. Estevão Filipe J.S. Duarte Eduarda Fernandes A. Gil Santos M. Manuel B. Marques 《Tetrahedron letters》2012,53(16):2132-2136
Several trifluoromethylated compounds were reacted with indole sodium salt, leading to monofluorinated compounds. The unexpected products formation was rationalized by DFT calculations. 相似文献
64.
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. 相似文献
65.
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. 相似文献
66.
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. 相似文献
67.
Ascurra de Duarte M 《Community genetics》2004,7(2-3):146-149
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. 相似文献
68.
Luminescent Di‐ and Trinuclear Boron Complexes Based on Aromatic Iminopyrrolyl Spacer Ligands: Synthesis,Characterization, and Application in OLEDs 下载免费PDF全文
Dr. D. Suresh Dr. Clara S. B. Gomes Patrícia S. Lopes Dr. Cláudia A. Figueira Bruno Ferreira Prof. Pedro T. Gomes Dr. Roberto E. Di Paolo Prof. António L. Maçanita Prof. M. Teresa Duarte Dr. Ana Charas Prof. Jorge Morgado Diogo Vila‐Viçosa Prof. Maria José Calhorda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(25):9133-9149
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. 相似文献
69.
70.
Computing graph separators in networks has a wide range of real-world applications. For instance, in telecommunication networks, a separator determines the capacity and brittleness of the network. In the field of graph algorithms, the computation of balanced small-sized separators is very useful, especially for divide-and-conquer algorithms. In bioinformatics and computational biology, separators are required in grid graphs providing a simplified representation of proteins. This papers presents a new heuristic algorithm based on the Variable Neighborhood Search methodology for computing vertex separators. We compare our procedure with the state-of-the-art methods. Computational results show that our procedure obtains the optimum solution in all of the small and medium instances, and high-quality results in large instances. 相似文献