Physicochemical processes occurring during the formation of cellulose diacetate membranes—research of criteria for optimizing membrane performance—III. Evaporation Rate And Equilibrium Phase Separation

The kinetics of acetone evaporation from films obtained by casting solutions of cellulose diacetate-acetone-water-inorganic additive have been analysed. Three successive regimes of evaporation have been identified. The first two are exponential and end, respectively, at critical times t₁ and t₂. Casting solution compositions have been determined both at the instant of phase separation (cloud point) and upon complete gelation. Also, the period of evaporation required to produce total film opacification has been measured for certain systems. These measurements have shown that time t₁ corresponds to polymer precipitation at the film surface, and that time t₂ corresponds to complete gelation of the medium. The results illustrate the effects of film thickness, casting temperature and “swelling” or “gelling” characteristics of the inorganic additive on times t₁ and t₂.     

An artificial beta-sheet that dimerizes through parallel beta-sheet interactions

This Article introduces a simple chemical model of a beta-sheet (artificial beta-sheet) that dimerizes by parallel beta-sheet formation in chloroform solution. The artificial beta-sheet consists of two N-terminally linked peptide strands that are linked with succinic or fumaric acid and blocked along one edge with a hydrogen-bonding template composed of 5-aminoanisic acid hydrazide. The template is connected to one of the peptide strands by a turn unit composed of (S)-2-aminoadipic acid (Aaa). 1H NMR spectroscopic studies show that these artificial beta-sheets fold in CDCl3 solution to form well-defined beta-sheet structures that dimerize through parallel beta-sheet interactions. Most notably, all of these compounds show a rich network of NOEs associated with folding and dimerization. The compounds also exhibit chemical shifts and coupling constants consistent with the formation of folded dimeric beta-sheet structures. The aminoadipic acid unit shows patterns of NOEs and coupling constants consistent with a well-defined turn conformation. The present system represents a significant step toward modeling the type of parallel beta-sheet interactions that occur in protein aggregation.     

Development and application of an analytical protocol for evaluation of treatment processes for landfill leachates. II. Evaluation of leachate treatment efficiency of different steps in a constructed pilot plant

Different methods for treatment of leachate from a municipal solid waste (MSW) landfill were tested in a pilot plant. Raw leachate was pre-treated with aeration and sedimentation, followed by several parallel individual steps such as bioremediation, chemical oxidation, ozonation, and geo-bed filters. The efficiency of different treatment steps was evaluated according to one previously developed protocol, which includes measurements of several parameters such as conductivity, pH, nutrients, chloride, metals, organic compounds, and acute toxicity before and after a treatment step. The treatment steps which showed the highest efficiency towards organic pollutants in leachate were ozone treatment and chemical oxidation. The use of an adsorption filter, a geo-bed with a mixture of peat and bottom ash with ca 10% remaining carbon, also had good effects. A combination of pre-treatment and a geo-bed filter with peat and carbon ash gave the best overall treatment results when water-quality parameters such as total organic carbon and ammonia-nitrogen were also considered.     

Photoredox mediated annelation of iododifluoromethylated alcohols with 1,1-diarylethylenes

A method for the synthesis of 3,3-difluorotetrahydrofurans from iododifluoromethylated alcohols and 1,1-diarylethylenes is described. The reaction is performed under irradiation with 400?nm light emitting diodes in the presence of a cationic iridium(III) photocatalyst, [Ir(ppy)₂(dtbbpy)]PF₆, substoichiometric amounts of triphenylphosphine and sodium trifluoroacetate as a base.     

Electronic absorption spectra of heteroanalogs of substituted biphenyl

Conclusions It has been demonstrated that Dewar's rule is inapplicable to predictions of absorption band behavior for heteroanalogs of C₆E₅C₆E₄X. A different criterion is proposed, based on the distribution of electron density in the ground and excited states, through which correct predictions can be made.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1770–1772, August, 1987.