Molecular Interactions between Asphaltene and Surfactants in a Hydrocarbon Solvent: Application to Asphaltene Dispersion

Heavy oil and bitumen supply the vast majority of energy resources in Canada. Different methods can be implemented to produce oil from such unconventional resources. Surfactants are employed as an additive to water/steam to improve an injected fluid’s effectiveness and enhance oil recovery. One of the main fractions in bitumen is asphaltene, which is a non-symmetrical molecule. Studies of interactions between surfactants, anionic, and non-anionic, and asphaltene have been very limited in the literature. In this paper, we employed molecular dynamics (MD) simulation to theoretically focus on the interactions between surfactant molecules and different types of asphaltene molecules observed in real oil sands. Both non-anionic and anionic surfactants showed promising results in terms of dispersant efficiency; however, their performance depends on the asphaltene architecture. Moreover, a hydrogen/carbon (H/C) ratio of asphaltenes plays an inevitable role in asphaltene aggregation behavior. A higher H/C ratio resulted in decreasing asphaltene aggregation tendency. The results of these studies will give a deep understanding of the interactions between asphaltene and surfactant molecules.

Tris(4-methoxyphenyl)stibine

The C 3-symmetrical molecule, tris(4-methoxyphenyl)stibine, C21H21O3Sb, crystallizes with one third of the molecule in the asymmetric unit. Bond lengths and angles of the Sb—C bonds lie in between those of the isostructural homologues C21H21O3Bi and C21H21O3As. The formation of dimers via six weak C—H...π interactions is considered.

Dipositronium and other Two-Positronium Compounds

Dipositronium, Ps2, was recently prepared [1]. This is significant because: • It is the first laboratory observation of a molecule that contains more than one positron; • It is the most symmetrical molecule possible; • It is the most non-rigid (floppiest) molecule possible; • The interval between the theoretical establishment of its existence [2] and its laboratory observation [1] is inordinately long – 60 years; and • An extension of the technology developed for the Ps2 observation may soon lead to an observation of the Bose-Einstein condensation of positronium and the development of a gamma ray laser. We briefly discuss the symmetry of Ps2 and how an understanding of it will underlie its characterization in the future. Ps2O and CPs2 might be the next two-positron compounds to be prepared and characterized in the laboratory. A discussion of the contrasting eigenstates of these two molecules is given. An understanding of these states is required in order to identify them.

Formation of the Human Fibrinogen Subclass Fib420: Disulfide Bonds and Glycosylation in Its Unique (EChain) Domains

COS cell transfection has been used to monitor the assembly and secretion of fibrinogen molecules, both those of the subclass containing the novel E chain and those of the more abundant subclass whose  chains lack E’s globular C-terminus. That region, referred to as the EC domain, is closely related to the ends of β and γ chains of fibrinogen (βC and γC). Transfection of COS cells with E, β, and γ cDNAs alone results in secretion of the symmetrical molecule (Eβγ)2, also known as Fib420. Cotransfection with cDNA for the shorter  chain yielded secretion of both (βγ)2 and (Eβγ)2 but no mixed molecules of the structure E(βγ)2. Exploiting the COS cells’ fidelity with regard to Fib420 production, identification was made of the highly conserved Asn667 as the sole site of N-linked glycosylation in the E chain. No evidence from Cys → Ser replacements was found for interchain disulfide bridges involving the four cysteines of the EC domain. However, for fibrinogen secretion, the E, β, and γ subunits do exhibit different requirements for integrity of the two intradomain disulfide bridges located at homologous positions in their respective C-termini, indicating dissimilar structural roles in the process of fibrinogen assembly. © 1998 by The American Society of Hematology.

Formation of the Human Fibrinogen Subclass Fib420: Disulfide Bonds and Glycosylation in Its Unique (EChain) Domains

COS cell transfection has been used to monitor the assembly and secretion of fibrinogen molecules, both those of the subclass containing the novel E chain and those of the more abundant subclass whose  chains lack E’s globular C-terminus. That region, referred to as the EC domain, is closely related to the ends of β and γ chains of fibrinogen (βC and γC). Transfection of COS cells with E, β, and γ cDNAs alone results in secretion of the symmetrical molecule (Eβγ)2, also known as Fib420. Cotransfection with cDNA for the shorter  chain yielded secretion of both (βγ)2 and (Eβγ)2 but no mixed molecules of the structure E(βγ)2. Exploiting the COS cells’ fidelity with regard to Fib420 production, identification was made of the highly conserved Asn667 as the sole site of N-linked glycosylation in the E chain. No evidence from Cys → Ser replacements was found for interchain disulfide bridges involving the four cysteines of the EC domain. However, for fibrinogen secretion, the E, β, and γ subunits do exhibit different requirements for integrity of the two intradomain disulfide bridges located at homologous positions in their respective C-termini, indicating dissimilar structural roles in the process of fibrinogen assembly. © 1998 by The American Society of Hematology.

The Symmetrical Structure of Structural Maintenance of Chromosomes (SMC) and MukB Proteins: Long, Antiparallel Coiled Coils, Folded at a Flexible Hinge

Structural maintenance of chromosomes (SMC) proteins function in chromosome condensation and several other aspects of DNA processing. They are large proteins characterized by an NH2-terminal nucleotide triphosphate (NTP)-binding domain, two long segments of coiled coil separated by a hinge, and a COOH-terminal domain. Here, we have visualized by EM the SMC protein from Bacillus subtilis (BsSMC) and MukB from Escherichia coli, which we argue is a divergent SMC protein. Both BsSMC and MukB show two thin rods with globular domains at the ends emerging from the hinge. The hinge appears to be quite flexible: the arms can open up to 180°, separating the terminal domains by 100 nm, or close to near 0°, bringing the terminal globular domains together. A surprising observation is that the ∼300–amino acid–long coiled coils are in an antiparallel arrangement. Known coiled coils are almost all parallel, and the longest antiparallel coiled coils known previously are 35–45 amino acids long. This antiparallel arrangement produces a symmetrical molecule with both an NH2- and a COOH-terminal domain at each end. The SMC molecule therefore has two complete and identical functional domains at the ends of the long arms. The bifunctional symmetry and a possible scissoring action at the hinge should provide unique biomechanical properties to the SMC proteins.