The binding of cadmium, zinc, lead, and mercury ions by the tripeptide glutathione has been investigated by carbon-13 magnetic resonance spectroscopy. Binding to the potential coordination sites was monitored as a function of solution conditions by observing the chemical shifts of the carbon atoms of glutathione. The results indicate that each of these metal ions binds to the potential coordination sites of glutathione with a high degree of specificity, with the actual sites involved in metal binding being dependent on the metal ion and the solution pD, with the exception of mercury which binds only to the sulfhydryl group at a mercury to glutathione ratio up to 0.5. At a metal to glutathione ratio of 0.5, Cd2+ and Zn2+ bind to both the sulfhydryl group and the amino group, the extent of binding to the two different sites being a function of pD, while Pb2+ binds only to the sulfhydryl group. Some binding of the glutamyl and glycyl carboxylic acid groups to cadmium, zinc, and lead was detected in certain pH regions. The chemical shift data for the carbonyl carbons of the two peptide linkages suggest zinc-promoted ionization of the peptide protons with subsequent binding of zinc to the ionized peptide nitrogen at pD greater than 10.5, while no evidence for this metal-promoted reaction was observed in the cadmium, lead, and mercury complexes. The results are discussed in terms of the possible structures of the complexes.

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The object of this work was to determine whether new information could be obtained by using gel permeation chromatography (GPC) to fractionate asphaltene samples prior to analysis. In particular, GPC elution profiles, elemental analyses, molecular weights by vapor pressure osmometry (VPO), and boiling point distributions of the asphaltenes isolated from the original Athabasca bitumen feed (Feed) and from its total liquid product (TLP) after visbreaking were compared. The analyses showed that for GPC run using chloroform, fractionation was based on size where elemental analyses and boiling point distributions indicated that the earlier eluting fractions were not aggregates of later eluting fractions. The largest TLP asphaltene species were slightly smaller in size (by GPC and VPO) to those in the Feed asphaltenes; the smallest TLP asphaltene species were smaller than those isolated from the Feed asphaltenes and contained material with an initial boiling point of 340 °C despite both vacuum distillation (524 °C cutpoint) and pentane extraction being used during asphaltene preparation. For comparable molecular sizes by GPC and VPO, the TLP asphaltene fractions had lower H/C ratios and so were more aromatic and consisted of higher boiling material than the Feed asphaltene fractions. VPO results and elemental analysis trends confirmed that pentane extraction leaves behind molecules (asphaltenes) on the basis of some combination of size, aromatic content, and polarity. The significance of the various fractions of asphaltene species isolated remains to be evaluated in terms of their contributions to bitumen and heavy oil behavior during both production and thermal processing.

Summary Asphaltene deposition in the near-wellbore region can block pore throats, change wettability characteristics and relative-permeability relationships, and therefore, reduce oil production. Conventional aromatic solvents (e.g., toluene, xylene) alone or in combination with various dispersants are used to remove asphaltene damage from the near-wellbore region. However, these aromatic solvents are expensive and are not environmentally friendly. The objective of this work was to systematically evaluate the asphaltene-solvating power of various non conventional solvents, including deasphalted oil, using a light-scattering technique. Experimental results suggest that deasphalted oil is a strong asphaltene solvent presumably because of its native resin and aromatic contents. Addition of asphaltene dispersants also increases the solubilizing power of the deasphalted oil. Furthermore, various refinery and heavy oil upgrader streams show strong ability to solubilize asphaltenes. Introduction Asphaltenes are defined as the n-pentane insoluble fraction of crude oil. They are polar molecules that aggregate together through aromatic - orbital association, hydrogen bonding and acid-base interactions. These asphaltene molecules also contain some heteroaromatics (aromatics with nitrogen, sulphur, and oxygen atoms included in the structure). They exist as platelets and are maintained in suspension by maltenes and resins. The growth of the aggregates is limited by the association of asphaltenes with resins in solution. The molecular weight of these aggregates can grow to several hundred thousand grams per mole. Asphaltene-solubility modelling studies based on the principle of colloidal suspension have been reported in the literature. In several cases, molecular theory has also been used to predict the dynamics of asphaltene flocculation.