The dienophilic behavior of the sulfilimine 2, synthesized from (Z)-3-p-tolylsulfinylacrylonitrile 1, in its Diels−Alder reactions with furan and acyclic dienes has been investigated. A complete ...π-facial selectivity for 2, opposite to that observed from its precursor 1, is the main feature of all these cycloadditions. Moreover, the high exo selectivity observed in reactions of 2 with furan (not observed for 1) contrasts with the almost complete endo selectivity with other cyclic and acyclic dienes. Additionally, the opposite regioselectivities obtained for 2 with Dane's diene and 1-substituted butadienes (not observed for 1) are also noteworthy. This behavior allows dienophiles 1 and 2 to be considered as complementary precursors from a synthetic point of view.
Mule deer historic range in Mexico has declined dramatically in the last decade. Forage availability and quality at the Chihuahuan Desert may play an important role sustaining populations at the ...southern end of their current distribution. We evaluated forage availability and quality at the end of a 3-year drought at two different localities in the Chihuahuan Desert: Old Net and Pulpit, we measured plant availability and quality, diet content and calculated diet preference indices. Vegetation at Old Net consisted primarily of both succulents (47%) and trees-shrubs (42%) while Pulpit had more grasses (60%) and herbs (24%) (P < 0.005). Feces collected at the Pulpit presented a high proportion of herbs (44%), while those collected at Old Net contained more trees and shrubs (53%). Preference index suggests that mule deer prefer herbs and overlook grasses, but there is no strong selection for any particular plant. Our results suggest that forage is appropriate to sustain mule deer populations, however, we found considerable variation in both localities suggesting a patchy landscape. More information regarding forage nutritional status and diet preferences can enhance our understanding on mule deer population dynamics in the Chihuahuan Desert.
The theoretical study reported in the present work deals with chiral cyclic vinyl sulfilimines and their reactivity as dienophiles in 4 + 2 cycloaddition reactions, using B3LYP/6-31G(d)//AM1 and ...B3LYP/6-31G(d)//B3LYP/6-31G(d) model chemistries. Consideration of Lewis acid catalysis, illustrated by BF3, decreases the activation energies of the cycloaddition process while the charge transfer from the diene to the sulfilimine is augmented. The 4 + 2 cycloaddition reactions of sulfilimines with both furan and cyclopentadiene occur in the gas phase with endo stereoselectivity, which is more pronounced with the latter diene. Endo-exo energy differences in the gas phase with the B3LYP/6-31+G(d)//B3LYP/6-31+G(d), B3LYP/6-31G(d)//B3LYP/6-31G(d), and B3LYP/6-31G(d)//AM1 model chemistries are almost the same. Solvent effects are responsible for the inversion of the stereoselectivity in the reactions of sulfilimines with furan because of the great difference in the dipole moments in endo and exo approaches.
The hetero-Diels−Alder reactions of 1,2-diaza-1,3-butadiene with ethylene, methyl vinyl ether, and methyl acrylate have been investigated theoretically with the aid of density functional theory using ...the Becke3LYP/6-31G(d) computational level. In the reactions with substituted alkenes, the transition states are concerted but asynchronous; the shortest bond-forming distance involves the nonsubstituted carbon of the alkene. In agreement with the experimental results, the reaction with methyl vinyl ether proceeds with high endo stereoselectivity and with complete regioselectivity to form the 6-methoxy cycloadduct. The conformational study of the transition states shows a sharp s-trans preference. In contrast, the 4 + 2-cycloaddition of 1,2-diaza-1,3-butadiene with methyl acrylate have been found to occur with low regio- and stereoselectivity but with a s-cis preference in the transition structures.
O sedentarismo atinge aproximadamente metade da população brasileira, sendo associado a mais de 10% das mortes no Brasil. A rotina universitária pode tanto limitar como promover à prática de ...Atividades Físicas de Lazer (AFL) pela comunidade acadêmica. O objetivo geral desse estudo de caso foi relacionar o sedentarismo com as variáveis do perfil dos estudantes, mapeando os cursos e lugares onde parece existir mais predisposição ao sedentarismo na Universidade de Brasília. A metodologia se baseou no estudo de caso, por meio de inquérito que se utilizou o Questionário Internacional de Atividade Física (International Physical Activity Questionnaire- IPAQ) para estimar o sedentarismo e investigar as variáveis relacionadas aos estudantes, como câmpus de origem, área do curso (saúde, exatas ou humanas), turno do curso (diurno ou noturno), gênero e assistência oferecida pela instituição (bolsas de apoio a graduação), em uma amostra estratificada por câmpus, período do curso e gênero de 431 estudantes. Os resultados revelaram que apenas 3% dos universitários foram classificados como sedentários, enquanto 13,7% foram considerados irregularmente ativos, 45,7% e 37,6% foram classificados como ativos e muito ativos, respectivamente. Na área da Saúde, 41% são ativos e 47% muito ativos, na área de Humanas 47% são ativos e 35% muito ativos, dados próximos aos universitários de Exatas. Considera-se que a UnB vem tendo êxito no combate ao sedentarismo acadêmico por alcançar níveis de AF acima da média nacional para esta faixa etária.
A study was conducted to estimate the abundance of green iguana (Iguana iguana), to characterize and to predict appropriated habitat at the reserve of La Mancha in Veracruz, Mexico. The abundance ...density was estimated by linear transects, the characterization of the habitat was realized by quadrants in the sites where iguanas were observed. The model for habitat prediction was developed with variables of vegetation, ground, slope and saturation of humidity. In order to characterize the habitat were recorded height, density, relative frequency, basal and aerial cover of the vegetal species. The variables registered to evaluate the habitat for nesting stage were the ground type and slope. The index of habitat prediction was obtained through variables of nesting, cover and water. The population density estimated was 0.68 iguana per ha. The optimal habitat for iguana includes mangrove areas, easily flooded low forest evergreen and the median forest sub evergreen. The optimal habitat for nesting represented 0.22% of the reserve. It is concluded that 5.05% of the habitat in the studied area are optimal for the development of green iguana and that the population density if the specie is low.
Mexico's wildlife has been impacted by human land use changes and socioeconomic and political factors since before the Spanish conquest in 1521. Presently, it has been estimated that more than 60% of ...the land area has been severely degraded. Mexico ranks in the top 3 countries in biodiversity, is a plant and faunal dispersal corridor, and is a crucial element in the conservation and management of North American wildlife. Wildlife management prerogatives and regulatory powers reside in the federal government with states relegated a minimum role. The continuous shifting of federal agencies responsible for wildlife management with the concomitant lack of adequate federal funding has not permitted the establishment of a robust wildlife program. In addition, wildlife conservation has been further impacted by a failure to establish landowner incentives, power struggles over user rights, resistance to change, and lack of trust and experience in protecting and managing Mexico's wildlife. We believe future strategies for wildlife programs must take into account Mexico's highly diversified mosaic of ecosystems, cultures, socioeconomic levels, and land tenure and political systems. The private sector, along with communal properties, in cooperation with federal and municipal governments, nongovernmental organizations, corporations, and international agencies may have the greatest potential of sustainable management of Mexico's wildlife. The present federal wildlife management strategy is an initial positive effort because it promotes participatory wildlife conservation by key stakeholders. We identify the aspects of this strategy that we believe will be needed to establish a sustainable program to manage Mexico's wildlife.
El objetivo del trabajo fue evaluar la variabilidad morfológica y el crecimiento corporal de 4 poblaciones del cocodrilo de pantano (Crocodylus moreletii) que se encuentran en la Unidad de Manejo ...para la Conservación de la Vida Silvestre Cacahuatal ubicada en el estado de Veracruz, México. Se compararon 4 poblaciones: 2 poblaciones cuyos individuos nacieron en vida silvestre y 2 que nacieron en cautiverio. Los rasgos morfológicos estudiados fueron similares entre poblaciones y entre sexos. Las tasas de crecimiento corporal fueron significativamente diferentes entre poblaciones. Los individuos que nacieron en condiciones naturales crecieron más rápidamente que los nacidos en cautiverio. Se concluye que el cautiverio no parece afectar la expresión morfológica, pero sí la tasa de crecimiento corporal. Estos resultados muestran que diferentes poblaciones de C. moreletii pueden presentar un crecimiento diferencial determinado por las condiciones de cautiverio.
PDF
