The proposition of the hypothesis-relating structure with properties of asphaltenes is a very important endeavor.
In view of their complexity, being an intricate mixture of high-molecular-mass compounds, experimental and
theoretical procedures must be designed to check whether the structures proposed are consistent with expected
and found behavior. During recent years, a structural characteristic of asphaltene, whereby the several polycyclic
systems present in them are joined by flexible aliphatic chains, has been proposed by several authors. For
simplicity, we will refer to this as the rosary-type structure. In this paper, using both reported as well as new
experimental and theoretical results, an attempt is made to show how asphaltene properties, such as molecular-mass distribution, molecular fragmentation, solubility, adsorption, trapping of molecules, solvent swelling,
and aging, could be accounted for in terms of the above rosary-type structures.
Drug-resistance dissemination by horizontal gene transfer remains poorly understood at the cellular scale. Using live-cell microscopy, we reveal the dynamics of resistance acquisition by transfer of the Escherichia coli fertility factor–conjugation plasmid encoding the tetracycline-efflux pump TetA. The entry of the single-stranded DNA plasmid into the recipient cell is rapidly followed by complementary-strand synthesis, plasmid-gene expression, and production of TetA. In the presence of translation-inhibiting antibiotics, resistance acquisition depends on the AcrAB-TolC multidrug efflux pump, because it reduces tetracycline concentrations in the cell. Protein synthesis can thus persist and TetA expression can be initiated immediately after plasmid acquisition. AcrAB-TolC efflux activity can also preserve resistance acquisition by plasmid transfer in the presence of antibiotics with other modes of action.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.