In this work, we report for the first time the observation of naturally occurring discotic liquid-crystalline domains of ca. 100 μm in diameter in unreacted heavy fractions of petroleum. Precipitated solids from several bitumen and heavy oil samples exhibited the characteristic optical patterns of liquid crystals when observed under cross-polarized light. Samples included asphaltenes precipitated from Athabasca and Cold Lake bitumen (Canada), Maya heavy crude oil (Mexico), and Safaniya crude oil (Saudi Arabia) and a maltene fraction of Athabasca bitumen. The liquid-crystal domains appeared in asphaltene solids at ∼330 K in a nitrogen atmosphere and disappeared at ∼430 K. Upon cooling and subsequent reheating, the domains did not reappear. Liquid-crystal domains also appeared and then disappeared in the presence of toluene vapor at room temperature. Because the liquid crystals exhibit both thermotropic and lyotropic behavior, they are amphotropic. While amphotropic liquid crystals are known to arise in biological systems, the specific attributes of the liquid-crystal structures observed here are the first reported occurrence of such behavior in nature. The presence of liquid crystals in petroleum solids enriches our understanding of the complex phase and interfacial behavior of these materials and may provide new opportunities for partitioning petroleum.

The mass fraction and the properties of asphaltenes vary significantly with the n-alkane used to separate them from their parent oil and with the details of the separation procedure, such as washing steps. Measurement repeatability is challenging, with different error bounds reported within the American Society for Testing and Materials (ASTM) standards for a single operator using the same equipment and procedure vis-à-vis measurements performed by different operators in different laboratories. In this work, reversible interactions between Athabasca pentane asphaltenes and n-alkanes from pentane to hexadecane were observed using cross-polarized and visible light microscopy and were quantified using high-precision density measurements for mixtures ranging from 1000 to 8000 ppmw (from 0.8 to 6.5 g/L) and enthalpy of solution measurements for mixtures comprising from 1000 to 3500 ppmw (from 0.8 to 3 g/L) asphaltenes. The partial specific volumes of Athabasca pentane asphaltenes and the enthalpy of solution values, including a change of sign, were found to vary systematically with n-alkane carbon number. The microscopic observations revealed the formation of liquid crystals followed by isotropic liquid on the surface of the asphaltene particles. The interactions at low concentrations are consistent with n-alkane sorption by asphaltene particles, asphaltene particle swelling, and dissolution of a fraction of the asphaltenes in n-alkanes. The partial specific volume and enthalpy of solution results, simulated using a phenomenological model that includes these effects, explain the sensitivity of the repeatability of asphaltene mass fraction determinations to the details of the washing procedure applied during their preparation. Preparation techniques without washing appear to be preferred because the mass fractions of asphaltenes recovered are expected to be more repeatable and their properties are likely to be more consistent.

Naturally occurring amphotropic liquid-crystals were recently identified in unreacted hydrocarbon resources and resource fractions from around the world, including Athabasca bitumen. Liquid crystal forming constituents are present in both asphaltene and maltene fractions and appear to be an important class of materials that is missed entirely during conventional hydrocarbon characterization, i.e.: SIMDIST or SARA analysis. In this contribution, some physical properties of liquid crystals in Athabasca asphaltenes and maltenes identified using experimental methods as diverse as polarized light microscopy, differential scanning calorimetry (DSC), and mid-and near-infrared photoacoustic spectroscopy with depth profiling are reported. Liquid crystals, comprising materials with an aromaticity between that of maltenes and asphaltenes, form irreversibly on the surface of both asphaltene particles and maltene drops on heating. At higher temperatures the liquid crystals become isotropic but remain on particle surfaces. Liquid crystals do not reappear on cooling or subsequent reheating unless the samples are frozen and crushed between heating cycles. The interdependence of these phase properties on sample thermal and mechanical history may help explain unexpected and frequently deleterious surface and interfacial phenomena arising during Athabasca bitumen production and processing. ■ INTRODUCTIONLiquid-crystals were recently observed in unreacted petroleum fractions including Athabasca, Maya, and Cold Lake pentane asphaltenes, Safaniya heptane asphaltenes and a fraction of Athabasca bitumen were extracted with supercritical n-pentane (SFE6). 1 The liquid crystals form between 338 and 341 K for the pentane asphaltenes, 370 K for Safaniya heptane asphaltenes, and 316 K for SFE6. The liquid crystals disappear between 423 and 435 K for the pentane asphaltenes, 433 K for C7 Safaniya asphaltenes, and 373 K for SFE6. These materials also exhibit liquid crystalline domains in the presence of toluene vapor at room temperature. 1 Compounds that exhibit liquid crystalline properties in a defined temperature range between the melting point and the transition to the isotropic liquid state are called thermotropic. Compounds that show liquid crystalline properties by the addition of solvents are called lyotropic. For this type of liquid crystal, concentration constitutes an additional degree of freedom. Compounds that exhibit both types of behavior are termed amphotropic or amphitropic. 2 The liquid crystals observed in unreacted petroleum fractions belong to this latter group.Following these initial observations, detailed studies related to the thermophysical properties, physical structure, and chemical composition of the liquid crystals were initiated. For example, liquid crystal rich material extracted from Athabasca pentane asphaltenes comprises more than 10,000 different constituents. Their mean molecular size is smaller than asphaltenes, and they are enriched in heteroatoms relative to asphaltenes. Detailed chemical composition data...

In this study, we use some modified semiempirical quantum mechanics (SQM) methods for improving the molecular docking process. To this end, the three popular SQM Hamiltonians, PM6, PM6‐D3H4X, and PM7 are employed for geometry optimization of some binding modes of ligands docked into the human cyclin‐dependent kinase 2 (CDK2) by two widely used docking tools, AutoDock and AutoDock Vina. The results were analyzed with two different evaluation metrics: the symmetry‐corrected heavy‐atom RMSD and the fraction of recovered ligand‐protein contacts. It is shown that the evaluation of the fraction of recovered contacts is more useful to measure the similarity between two structures when interacting with a protein. It was also found that AutoDock is more successful than AutoDock Vina in producing the correct ligand poses (RMSD≤2.0 Å) and ranking of the poses. It is also demonstrated that the ligand optimization at the SQM level improves the docking results and the SQM structures have a significantly better fit to the observed crystal structures. Finally, the SQM optimizations reduce the number of close contacts in the docking poses and successfully remove most of the clash or bad contacts between ligand and protein.

A microreactor equipped with a view window and a stirrer was used to observe mesophase formation in Athabasca vacuum residue with and without catalyst. The effect of stirring on mesophase formation and its growth and coalescence was studied during the cracking of vacuum residue under hydrogen at 4.8 MPa and 440 °C. Stirring can result in a bimodal distribution of size of mesophase domains. The forced coalescence of mesophase droplets by the stirrer led to the formation of very large mesophase regions (bulk mesophase), which coexisted with a large number of small micrometer-sized mesophase domains. The addition of catalyst likely had both chemical and physical effects on the formation and growth of mesophase. The catalyst gave a delay in the onset of mesophase formation as a chemical effect and a decrease in the amount of bulk mesophase regions by suppressing the coalescence of smaller mesophase domains as a physical effect. The analysis of the resulting cokes by scanning electron microscopy (SEM) showed that catalyst particles agglomerated and stuck to the outer surface of the mesophase domains and suppressed their coalescence. The agglomeration of catalyst particles likely decreased their ability to suppress the formation of small mesophase domains, in the range of a few micrometers in size. However, catalyst was effective in suppressing the formation of bulk mesophase domains with areas over 2000 μm2. The results showed that the onset of observable mesophase initially increased with the addition of catalyst, but then decreased at higher catalyst concentrations. SEM observation confirmed that the significant agglomeration of catalyst particles at higher concentrations was likely responsible for the decreased effectiveness of the catalyst in suppressing mesophase formation.