Effect Of Solvent Mixtures Research Articles

Small aggregates of benzoporphyrin molecules observed in water–organic solvent mixtures

AbstractBenzoporphyrins, chlorin‐type compounds, are efficient new drugs in photodynamic therapy. In this work, some aspects of the benzoporphyrin‐1,3‐diene dimethyl ester (DiesterB) aggregation were investigated in water–organic solvent mixtures, using visible spectrophotometry. The effects of solvent mixtures, water with acetonitrile, dioxane, methanol and ethanol, were compared taking the calculated aggregation equilibrium constant (K) and the aggregation number. The K dependence on temperature, DiesterB concentration and water content suggest that, in water with acetonitrile, the predominant species is a dimer, whereas in dioxane, methanol and ethanol systems, there are multiple equilibria, with a pre‐equilibrium between the monomer and dimer (small amount), followed by trimer formation. Not only the solvent polarity but also the nature of the organic solvent are important for the aggregation process, driving the aggregate size and the magnitude of the equilibrium constant. Copyright © 2004 John Wiley & Sons, Ltd.

Effects of Solvent Mixtures on Dispersion of Lanthanum‐Modified Lead Zirconate Titanate Tape Casting Slurries

The effects of xylenes/ethanol solvent mixtures on lanthanum‐modified lead zirconate titanate (PLZT) nonaqueous suspensions were investigated by measuring sediment height, viscosity, and adsorption of dispersant. Well‐dispersed colloidal suspensions were obtained in xylene‐rich solvents with a minimum amount of menhaden fish oil as a dispersant. It was also shown that adsorption of dispersant on particle surfaces strongly depends on selection of solvent(s). The ratio of solvent mixture affects PLZT solids content of unfired tapes, in which using insufficient as well as excess dispersant could decrease the packing density of particles. Solubility of other organic additives, such as binder, was also considered when selecting a xylene/ethanol ratio.

Transfer Gibbs energies for ClO3–, BrO3–, IO3–, ClO4–and IO4–anions for water–methanol and water–propan-2-ol mixtures: some quantum-chemical aspects of ionic solvation

The transfer Gibbs energies, ΔtrsGo, of KClO3, KBrO3, KIO3, KClO4, KIO4 and the corresponding caesium salts have been obtained through gravimetric measurements of the solubility in aqueous mixtures with methanol (MeOH) and propan-2-ol (PriOH) at 298.2 K. In addition, the solubility of Ph4P(pic)(pic = picrate anion) as well as K(pic) and KBPh4 and the corresponding caesium salts are reported in these mixtures at 298.2 K. Single-ion values of ΔtrsGo have been calculated using the tetraphenylphosphonium tetraphenylborate (TPTB) assumption. The semiempirical quantum-chemical AM1 method was used for calculations of interaction energy of BPh4– and Ph4P+ with a series of five solvent molecules and energy demands associated with a deformation of these ions. Trends observed for ΔtrsGo are discussed in terms of specific ion–solvent interactions and the structural effect of solvent mixtures.

Problems in Assessing the Risks of Mixtures of Contaminants in Drinking Water

In conducting risk assessments on drinking water contaminants, the U.S. Environmental Protection Agency (EPA) attempts to evaluate all available toxicity data to develop Health Advisory (HA) and Maximum Contaminant Level Goal (MCLG) values. The EPA often has grappled with the issues surrounding the toxicity of chemical mixtures, including radioactive contaminants, nitrate/nitrite, and trihalomethanes (THMs). In evaluating the toxicity of chemical mixtures, the EPA's immediate concern is whether the individual HA values and MCLGs are protecting public health when multiple contaminants are present in drinking water. Potential toxic interactions between drinking water contaminants are difficult to predict because experimental studies are generally performed only at high doses relative to environmental levels. Although the contamination of drinking water involves mixtures of contaminants, drinking water regulations are generally based on an assessment of the risks of individual contaminants. This paper discusses three issues of major concern to the EPA: the synergistic effects of solvent mixtures, vehicle effects in laboratory studies, and setting standards for essential trace nutrients where the absorption and/or toxicity are affected by an individual's nutritional status or other dietary components.