RESUMEN
The aromaticity of the rings of thiophene, pyrrole, furan, and benzene annelated cyclooctatetraene (COT) derivatives and of their double charged ions was studied using the graph-theoretical theory of aromaticity. On the basis of topological resonance energy, it was found that the global aromaticity is dependent upon on the arrangement of heteroatoms in the given molecule. Relative stability of these molecules when in different charged states can been explained in terms of the topological charge stabilization rule. We expect that fusing the COT ring with an increasing number of aromatic rings will lead to an increase in the aromaticity of the molecule. According to the bond resonance energy (BRE) and circuit resonance energy (CRE) indices, local antiaromaticity of the COT ring is weakened as the number of fused rings increases, and these changes play a significant role in the global aromaticity of the molecule. For some compounds, our BRE and CRE indices do not predict the same order of magnitude of the local aromatic character of certain rings that the nucleus independent chemical shift (NICS(0) and (NICS(1)) methods predict. Finally, for the available compounds, correlations between the diatropic and paratropic chemical shifts of the protons and our ring current results were analyzed and good agreement was found.
RESUMEN
All extant equid species are grouped in a single genus - Equus. Among those, ass-like equids have remained particularly unstudied and their phylogenetic relations were poorly understood, most probably because they inhabit extreme environments in remote geographic areas. To gain further insights into the evolutionary history of ass-like equids, we have used a non-invasive sampling approach to collect representative fecal samples of extant African and Asiatic ass-like equid populations across their distribution range and mitochondrial DNA (mtDNA) sequencing analyses to examine intraspecific genetic diversity and population structure, and to reconstruct phylogenetic relations among wild ass species/subspecies. Sequence analyses of 410 base pairs of the fast evolving mtDNA control region identified the Asiatic wild ass population of Kalamaili (China) as the one displaying the highest diversity among all wild ass populations. Phylogenetic analyses of complete cytochrome b sequences revealed that African and Asiatic wild asses shared a common ancestor approximately 2.3Mya and that diversification in both groups occurred much latter, probably driven by climatic events during the Pleistocene. Inferred genetic relationships among Asiatic wild ass species do not support E. kiang monophyly, highlighting the need of more extensive studies in order to clarify the taxonomic status of species/subspecies belonging to this branch of the Equus phylogeny. These results highlight the importance of re-assessing the evolutionary history of ass-like equid species, and urge to extend studies at the population level to efficiently design conservation and management actions for these threatened species.
