Synthesis and characterization of α,α'-bis(aminomethyl)oligothiophenes and their related compounds

We have synthesized and characterized a series of novel compounds of α,α'-bis(arninomethyl)oligothiophenes and their related compounds whose degree of polymerization spans two (dimer) to five (pentamer). The compounds presented in our studies are α,α'-bis[(2,2,5,5-tetramethyl-1-aza-2,5-disilacyclopenthyl)methyl]oligothiophene, α,α'-bis(aminomethyl)oligothiophene dihydrochloride and α,α'-bis(aminomethyl)oligothiophene. These compounds exhibit desired chemical activity while maintaining controllable electronic properties. The synthetic processes of the oligothiophenes are as follows: 2-aminomethylthiophene is first ‘protected’ and the thiophene rings are coupled using standard Grignard methods. The protected groups are removed at the final stage of the reaction. The compounds show unique properties; for example α,α'-bis(aminomethyl)oligothiophene dihydrochloride is soluble in water. The results of electronic spectra and titration are also presented.     

Enzymatic screening of microalgae as a potential source of natural antioxidants

Extracts of over 100 species of microalgae both from nature and from laboratory cultures were screened for antioxidant activity. As an assay for antioxidant function, we examined the inhibition of the activity of two oxidizing enzymes, lipoxygenase and tyrosinase. Water, ethanol, and methanol extracts of microalgae were used for the assay. It was found that lipoxygenase and tyrosinase activities were inhibited by the extract of several microalgae. Our results suggest that these species of microalgae have useful antioxidant activity, and they will be further examined for potential biotechnological exploitation. The aim of our screening was to identify potential sources of natural antioxidant compounds, which if found to be sufficiently potent and nontoxic, might eventually replace the chemicals that are currently used as food additives and cosmetics, in order to prevent food spoilage and their oxidation.     

Preparation,properties, andin vitro thrombogenic characterization of urokinase-collagen membrane

Urokinase (EC 3.4.4.a) was immobilized on collagen membrane. The urokinase-collagen membrane gave a flat pH profile from 7.5 to 9.5. It was more stable against heat than native urokinase. Furthermore, the stability of urokinase in the pH range of 7.0-8.8 was increased with immobilization. The collagen fibril network might stabilize urokinase. The diffusion coefficients of urea, uric acid, and creatinine through the urokinase-collagen membrane were in the range of 2.5-4.5 x 10^-7 cm³/sec. The diffusion coefficients decreased to the range of 6.9-8.2 x 10^-8 cm²/sec when fibrin clot was formed on the membranein vitro. Immobilized urokinase activates plasmin which lyzes fibrin clot. Therefore, fibrin clot formed on the membrane could be lyzed during prolonged incubation at 37°C and the diffusion coefficients restored to the initial values. The fibrin clot formedin vivo may be lyzed with immobilized urokinase.     

An amperometric sensor for carbon dioxide based on immobilized bacteria utilizing carbon dioxide

A biosensor consisting of a CO₂-utilizing autotrophic bacterium (strain S-17, Pseudomonas type) and an oxygen-sensing electrode was constructed for the amperometric determination of CO₂. The correlation between current decrease and CO₂ concentration was linear in the range 5–200 mg l^?1 CO₂. The optimum temperature and pH for operation of the biosensor were 30°C and 5.5, respectively. The sensor did not respond to other volatile compounds except for acetic acid. The sensor could be operated continuously for about a month.     

Microbial detection of toxic compounds utilizing recombinant DNA technology and bioluminescence

A microbial sensing system was developed utilizing recombinant DNA technology for the determination of environmental pollutants. The emission of light in Escherichia coli was achieved by cloning the genes encoding luciferase from firefly and by injection of the luminescence substrate luciferin. A good correlation was observed between increased luminescence and the concentration of luciferin. Measurement of environmental pollutants was based on the decrease of in vivo luminescence intensity emitted by recombinant E. coli, which was affected by cell metabolic inactivator. Environmental pollutants such as sodium azide and fluoroacetic acid, which are components of ATP-inhibiting pesticides, and antibiotics were detected at or below the μg ml^?1 level by this system by measurement of the decrease in in vivo luminescence.     

Recent trends of biosensors in Japan

Remarkable progress has been made in the development of bioelectrochemical sensors, and various kinds of biosensors have been developed and applied in analytical chemistry. Many of these enzyme, microbial, and immunosensors have been recently developed in Japan and in this paper, recent trends in Japanese biosensor development are described.     

Immobilization of AMP-deaminase in acrylamide-glycidylmethacrylate copolymer

The enzyme AMP-deaminase was entrapped in an acrylamide-glycidylmethacrylate copolymer. No leakage of AMP-deaminase was observed from the copolymer. The optimum pH of native AMP-deaminase was 5.6. The pH was displaced to 5.0 with immobilization in the copolymer. The immobilized AMP-deaminase column maintained more than 95% of initial activity after 10 days of operation.     

Ammonium ion sensor based on immobilized nitrifying bacteria and a cation-exchange membrane

The ammonium ion sensor is based on nitrifying bacteria isolated from activated sludge. The sensor comprises a cation-exchange membrane, an alkaline solution layer (pH 10), a gas-permeable membrane, an immobilized microbial membrane, and an oxygen electrode. This novel combination provides accurate amperometric determinations of ammonium ions in aqueous solutions within 7 min in the range 10^-4– 4.5 × 10^-2 M. Volatile amines or other ions do not interfere. The relative error is within 4% and the sensor can be used continually for more than 10 days.