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Heavy oils and extra-heavy oils (bitumens) are difficult to produce and transport due to problems associated with the aggregation of asphaltene molecules. Asphaltenes, a primary component of heavy oils and bitumens, affect the viscosity significantly. Traditional methods of viscosity reduction for heavy petroleum fluids include thermal or dilution methods. In this work, we employ an alternative method for viscosity reduction, by using functionalized molecules that could interact with the asphaltenes and change the properties of the crude oil at the molecular level, reducing viscosity. Ionic liquids, having favorable thermophysical properties such as low vapor pressure, are the functionalized molecules tested in this work. Various properties of the ionic liquids such as alkyl tail lengths (C2, C4, C6, C8, C10, and C12), counter-ion charge density (chloride, thiocyanate, and tetrafluoroborate), and type of head group (imidazolium, pyridinium, and thiazolium) are tested with a Mexican heavy oil and Canadian and Venezuelan bitumens. Small amounts of the additives (between 1 and 10 ppm), dissolved in toluene, are used. Viscosity reduction up to 35% is observed for the crude oils, with dodecylpyridinium chloride showing the maximum reduction. Various molecular interactions between the ionic liquids and the asphaltene molecules, such as aromatic, acid–base, and charge-transfer interactions, seem to hinder the asphaltene aggregate formation, which consequently reduces the viscosity. These results set the stage for further research on the viscosity reduction of heavy oil and extra-heavy oils by using functionalized molecules. [ABSTRACT FROM AUTHOR]

Abstract: Hydrotropes are amphiphilic molecules that are too small to spontaneously form equilibrium structures in aqueous solutions, but form dynamic, non-covalent assemblies, referred to as clusters. In the presence of a hydrophobic compound, these clusters seem to get stabilized leading to the formation of long-lived, highly stable mesoscopic droplets, a phenomenon that we call “mesoscale solubilization”. In this work, we focus on the unusual mesoscopic properties of aqueous solutions of a nonionic hydrotrope, namely tertiary butyl alcohol (TBA), on addition of various hydrophobic compounds. Aqueous TBA solutions, in about 3–8mol% TBA concentration range and about 0–25°C temperature range, show the presence of short-ranged (∼0.5nm), short-lived (tens of picoseconds) molecular clusters which result in anomalies of the thermodynamic properties. These clusters are transient but do not relax by diffusion, thus distinctly different from conventional concentration fluctuations. In this concentration and temperature range, upon the addition of a third (more hydrophobic) component to TBA–water solutions, long-lived mesoscopic droplets of about 100nm size are observed. In this work, we clarify the ambiguity behind the definition of solubility and elucidate the phenomenon of mesoscale solubilization. A systematic study of the macroscopic and mesoscopic phase behavior of three ternary systems TBA–water-propylene oxide, TBA–water-isobutyl alcohol, and TBA–water-cyclohexane has been carried out. We differentiate between molecular solubility, mesoscale solubilization, and macroscopic phase separation. We have confirmed that practically stable aqueous colloids can be created from small molecules, without addition of surfactants or polymers. Such kind of novel materials may find applications in the design of various processes and products, ranging from pharmaceuticals to cosmetics and agrochemicals. [Copyright &y& Elsevier]

The tumor suppressor protein, p53, utilizes multiple mechanisms to ensure faithful transmission of the genome including regulation of DNA replication, repair, and recombination. Monitoring these pathways may involve direct binding of p53 to the DNA intermediates of these processes. In this study, we generated templates resembling stalled replication forks and utilized electron microscopy to examine p53 interactions with these substrates. Our results show that p53 bound with high affinity to the junction of stalled forks, whereas two cancer-derived p53 mutants showed weak binding. Additionally, some of the templates were rearranged to form ‘chickenfoot’ structures in the presence of p53. These were mostly formed due to p53 trapping intermediates of spontaneous fork regression; however, in a small population, the protein appeared to be promoting their formation. Collectively, these results demonstrate the importance of sequence-independent binding in p53-mediated maintenance of genomic integrity. [ABSTRACT FROM AUTHOR]

Epstein-Barr virus (EBV) encodes a set of core replication factors used during lytic infection in human cells that parallels the factors used in many other systems. These include a DNA polymerase and its accessory factor, a helicase/primase, and a single strand binding protein. The EBV polymerase accessory factor has been identified as the product of the BMRF1 gene and has been shown by functional assays to increase the activity and processivity of the polymerase. Unlike other members of this class of factors, BMRF1 is also a transcription factor regulating certain EBV genes. Although several polymerase accessory factors, including eukaryotic proliferating cell nuclear antigen, Escherichia coli β protein, and T4 gene 45 protein have been shown to form oligomeric rings termed sliding clamps, nothing is known about the oligomeric state of BMRF1 or whether it forms a ring. In this work, BMRF1 was purified directly from human cells infected with an adenovirus vector expressing the BMRF1 gene product. The protein was purified to near homogeneity, and examination by negative staining electron microscopy revealed large, fiat, ring. shaped molecules with a diameter of 15.5 ± 0.8 nm and a distinct 5.3-nm diameter hole in the center. The size of these rings is consistent with an oligomer of 6 monomers, nearly twice as large as the trimetric proliferating cell nuclear antigen ring. Unlike the herpes simplex virus UL42 homologue, BMRF1 was found to self-associate in solution. These findings extend the theme of polymerase accessory factors adopting ringshaped structures and provide an example in which the ring is significantly larger than any previously described sliding clamp. [ABSTRACT FROM AUTHOR]

Claspin is an essential protein for the ATR-dependent activation of the DNA replication checkpoint response in Xenopus and human cells. Here we describe the purification and characterization of human Claspin. The protein has a ring-like structure and binds with high affinity to branched DNA molecules. These findings suggest that Claspin may be a component of the replication ensemble and plays a role in the replication checkpoint by directly associating with replication forks and with the various branched DNA structures likely to form at stalled replication forks because of DNA damage. [ABSTRACT FROM AUTHOR]