Pesquisa | SciELO

Asphaltene aggregation mechanism is still a nebulous and controversial issue. Many authors argue that the aggregation of its components is due to π-stacking interactions, nonetheless, alkyl chains, heteroatoms, and even acidic groups are also constituents of asphaltenes and can play an important role in the chemistry of asphaltene. Excimers from pyrene are easily detected by fluorescence and were used in the current study to probe the effect of the side chain on the π-stacking capacity of pyrene. Pyrene was acylated with acyl chains varying from two to twelve carbon atoms, and the effect of the variation of the acyl chain length on excimer formation was followed by fluorescence emission spectroscopy. The results revealed that as the side chain grows from two to twelve carbon atoms the excimer/monomer ratio decreases and the excimer heat of formation drops from ΔH = -6.00 to -1.29 kcal mol-1. Further, the crystal structure of octanoyl pyrene (PC8) indicates that in the crystal structure, the aromatic moiety faces the acyl chain. This result was corroborated by density functional theory (DFT) calculations. Finally, the results were compared with two different asphaltenes and indicate that π-stacking cannot be assumed as the main driving force for asphaltene aggregation.

ABSTRACT The limited temporal completeness and taxonomic accuracy of species lists, made available in a traditional manner in scientific publications, has always represented a problem. These lists are invariably limited to a few taxonomic groups and do not represent up-to-date knowledge of all species and classifications. In this context, the Brazilian megadiverse fauna is no exception, and the Catálogo Taxonômico da Fauna do Brasil (CTFB) (http://fauna.jbrj.gov.br/), made public in 2015, represents a database on biodiversity anchored on a list of valid and expertly recognized scientific names of animals in Brazil. The CTFB is updated in near real time by a team of more than 800 specialists. By January 1, 2024, the CTFB compiled 133,691 nominal species, with 125,138 that were considered valid. Most of the valid species were arthropods (82.3%, with more than 102,000 species) and chordates (7.69%, with over 11,000 species). These taxa were followed by a cluster composed of Mollusca (3,567 species), Platyhelminthes (2,292 species), Annelida (1,833 species), and Nematoda (1,447 species). All remaining groups had less than 1,000 species reported in Brazil, with Cnidaria (831 species), Porifera (628 species), Rotifera (606 species), and Bryozoa (520 species) representing those with more than 500 species. Analysis of the CTFB database can facilitate and direct efforts towards the discovery of new species in Brazil, but it is also fundamental in providing the best available list of valid nominal species to users, including those in science, health, conservation efforts, and any initiative involving animals. The importance of the CTFB is evidenced by the elevated number of citations in the scientific literature in diverse areas of biology, law, anthropology, education, forensic science, and veterinary science, among others.

Abstract Dams are one of the main threats to Neotropical potamodromous fish, causing blockages of migratory routes and loss of breeding areas in an increasing number of drainage systems. In this scenario, current data argue that the maintenance of free-flowing tributaries along fragmented watersheds would be an important strategy to the migratory fish conservation, both in panmixia situations and in scenarios with different coexisting stocks, as already reported for Prochilodus lineatus. This study analyzed microsatellite loci and mitochondrial haplotypes in samples of P. lineatus obtained in different years along the Cinzas River basin, as well as in the Capivara Reservoir (largest Reservoir in the Paranapanema main channel, upper Paraná River) and in the Tibagi River, all connected by free stretches, aiming to investigate the contributions of the Cinzas River basin to the population dynamics of migratory fish in the Capivara reservoir region. Both markers detected high genetic diversity levels and indicated different genetic stocks of P. lineatus along the Cinzas River basin, suggesting some temporal genetic structuring, as well as the mixture of these stocks in the sample from the Capivara reservoir and from other points, corroborating the relationships among stocks in this reservoir and its tributaries.

Resumo Barragens são umas das principais ameaças para peixes potamódromos Neotropicais, causando bloqueios de rotas migratórias e perdas de áreas de reprodução em um número crescente de sistemas de drenagem. Neste cenário, dados atuais defendem que a manutenção de tributários de fluxo livre em bacias hidrográficas fragmentadas seria uma importante estratégia na conservação de peixes migradores, tanto em situações de panmixia quanto em cenários com diferentes estoques coexistindo, tal como já relatado para Prochilodus lineatus. Este estudo analisou locos microssatélites e haplótipos mitocondriais em amostras de P. lineatus obtidas em diferentes anos ao longo da bacia do rio das Cinzas, no reservatório de Capivara (maior reservatório na calha principal do rio Paranapanema, alto rio Paraná) e no rio Tibagi, todos conectados por trechos livres, visando investigar as contribuições da bacia do rio das Cinzas na dinâmica populacional de peixes migradores na região do reservatório de Capivara. Ambos os marcadores detectaram altos níveis de diversidade genética e indicaram diferentes estoques de P. lineatus ao longo da bacia do rio das Cinzas, sugerindo alguma estruturação genética temporal, bem como a mistura destes estoques na amostra do reservatório de Capivara e de outros pontos, corroborando as relações de estoques neste reservatório e seus tributários.

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