Electrodeposition of Asphaltenes. 2. Effect of Resins and Additives

Electrodeposition of asphaltenes from oil/heptane, asphaltene/heptane, and asphaltene/heptane/additive mixtures has been investigated. Toluene, native petroleum resins, and a synthetic asphaltene dispersant, <i>p</i>-nonylphenol, were used as additives. The addition of these components led to partial dissolution of asphaltenes in heptane. The charge of asphaltenic particles was found to be negative in oil/heptane mixtures and positive in asphaltene/heptane mixtures. In asphaltene/heptane/toluene systems, the charge of the deposit varied from positive to neutral to negative, depending upon the method of preparation of the mixture and the toluene content. Introduction of petroleum resins into asphaltene/heptane mixtures resulted in neutralization of the asphaltene particle charge. The addition of <i>p</i>-nonylphenol to asphaltene suspensions in heptane did not alter the charge of asphaltene particles. Current transients recorded during electrodeposition tests indicated that the current was transported by the dissolved asphaltene fraction rather than the solid asphaltene particles and a sharp increase in conductivity was observed upon transition from systems with asphaltene deposition to systems without deposition

X‑ray Transparent Microfluidic Chip for Mesophase-Based Crystallization of Membrane Proteins and On-Chip Structure Determination

Crystallization from lipidic mesophase matrices is a promising route to diffraction-quality crystals and structures of membrane proteins. The microfluidic approach reported here eliminates two bottlenecks of the standard mesophase-based crystallization protocols: (i) manual preparation of viscous mesophases and (ii) manual harvesting of often small and fragile protein crystals. In the approach reported here, protein-loaded mesophases are formulated in an X-ray transparent microfluidic chip using only 60 nL of the protein solution per crystallization trial. The X-ray transparency of the chip enables diffraction data collection from multiple crystals residing in microfluidic wells, eliminating the normally required manual harvesting and mounting of individual crystals. We validated our approach by on-chip crystallization of photosynthetic reaction center, a membrane protein from <i>Rhodobacter sphaeroides</i>, followed by solving its structure to a resolution of 2.5 Å using X-ray diffraction data collected on-chip under ambient conditions. A moderate conformational change in hydrophilic chains of the protein was observed when comparing the on-chip, room temperature structure with known structures for which data were acquired under cryogenic conditions