Electronic structure and molecular design of simplified polyimide systems

The electronic structures of newly designed polyimide systems (ethenetetracarboxylic 1,2:1,2-dianhydride-diaminoethyne (PI-A) and ethenetetracarboxylic 1,1:2,2-dianhydride-diaminoethyne(PI-B)) are studied in detail with respect to their optimized geometries on the basis of the one-dimensional tight-binding self-consistent field crystal-orbital method. The computational results have revealed that PI-B shows intriguing properties such as a very small band gap and a wide bandwidth near the frontier level, compared with PI-A and other polyimides. Since PI-B would be a promising candidate for a new electric conducting material, a reaction diagram for this polymer is also proposed.Also affiliated to Central Research Laboratories, Matsushita Electric Industrial Co., Moriguchi 570, Japan.     

Morphology,physics, chemistry and biology of Lake Rara in West Nepal

A survey of oligotrophic Lake Rara, the biggest lake in Nepal, was carried out from 1982 till 1984. Mean depth is 100 m, and maximum depth is 167 m. The surface area covers 9.8 km², and the lake contains 0.98 km³ volume of water. Transparency was about 16 m, photoquantum yield decreased exponentially with depth below 5 m, and the extinction coefficient was 8.3 × 10⁻². The concentration of Chl.-a was in the range of 0.06–0.46 mg m⁻³, and total nitrogen was 18–30 μg 1⁻¹. The whole water column was well oxygenated. Primary productivity was extremely low. It has more than 30 inflowing brooks and one outlet. The water quality of the brooks changes drastically with their location. The pH, electrical conductivity, and EDTA hardness in the waters from a landslide area were high. In the waters from a rich pine forest they were extremely low. The zooplankton consisted of two species of protozoa, five species of rotifers, two species of Cladocera, and two species of Copepoda. The zooplankton density range was 6200–16200 individuals m⁻³. The minimum was on November 11th, 1983 and the maximum on August 19th, 1983.     

Nonselective Incorporation into Sporangium of Either “Older” or “Younger” Chromosome of the Vegetative Cell During Sporulation in Bacillus cereus

Employing Bacillus cereus strain 2, we examined the fate of two chromosomes contained in vegetative cells in the course of sporulation. Cytological observations and quantitative estimation of deoxyribonucleic acid (DNA) confirmed the earlier observations that, during the course of sporulation, one of two chromosomes of the vegetative cell was incorporated into the sporangium and the other disappeared into the medium as the result of cell lysis. Log-phase cells, labeled completely with thymine-2-(14)C in the presence of deoxyadenosine, were cultured in the "cold" glucose-glutamate-glycine-salts medium, and culture samples, taken at intervals at successive generations, were subjected to sporulation in glutamate-salts medium. The percentage of radioactivity in the spores separated from each culture remained almost unchanged at nearly 50% and was independent of the number of generations of the preceding culture in the "cold" medium. This suggests that the selective incorporation into the sporangium of either the "older" or "younger" chromosome of a vegetative cell does not occur in the course of spore formation. Some examples of the selective and nonselective behavior of DNA molecules in cellular events in microorganisms are cited.     

RecA, Tus protein and constitutive stable DNA replication inEscherichia coli rnhA mutants

Constitutive stable DNA replication (cSDR), which uniquely occurs inEscherichia coli rnhA mutants deficient in ribonuclease HI activity, requires RecA function. TherecA428 mutation, which inactivates the recombinase activity but imparts a constitutive coprotease activity, blocks cSDR inrnhA mutants. The result indicates that the recombinase activity of RecA, which promotes homologous pairing and strand exchange, is essential for cSDR. Despite the requirement for RecA recombinase activity, mutations inrecB, recD, recJ, ruvA andruvC neither inhibit nor stimulate cSDR. It was proposed that the property of RecA essential for homologous pairing and strand exchange is uniquely required for initiation of cSDR inrnhA mutants without involving the homologous recombination process. The possibility that RecA protein is necessary to counteract the action of Tus protein, a contra-helicase which stalls replication forks in theter region of the chromosome, was ruled out because introduction of thetus : :kan mutation, which inactivates Tus protein, did not alleviate the RecA requirement for cSDR.     

Electronic structures of donor-acceptor polymers based on polythiophene,polyfuran and polypyrrole

Theoretical results on the geometric and electronic structures of some donor-acceptor polymers based on polythiophene (X=S), polyfuran (X=O) and polypyrrole (X=NH) were obtained, using a one-dimensional tight-binding self-consistent field crystal-orbital (SCF-CO) method at the MNDO-AM1 level of approximation. The repeat unit of these polymers consits of a bithiophene, furan or bipyrrole unit bridged by an electron-accepting group or. The optimized geometries of the polymers show a strong dependence on the nature of the electron donating group X. All the polymers studied are predicted to have band gap values ranging between 1 eV and 2 eV. An analysis of their -bond order data and of the patterns of their frontier orbitals shows they have benzenoid-like electronic structures.     

Tryptophan hydroxylase system in brain tissue slices assayed by high-performance liquid chromatography

A new method was developed to study the unsupplemented tryptophan hydroxylase system in brain tissue slices from the raphe nuclei of the rat by high-performance liquid chromatography (HPLC) with fluorescence detection. Tryptophan hydroxylase activity was measured by determining 5-hydroxytryptophan (5-HTP) accumulation in raphe nuclei slices containing all of the enzyme system (the hydroxylase, tetrahydrobiopterin, and dihydropteridine reductase) in the presence of NSD-1055 (an inhibitor of aromatic l-amino acid decarboxylase). An optimum temperature was observed at 25°C and the reaction progressed linearly for 60 min. The hydroxylation of tryptophan was maximal by the addition of 0.2 mM tryptophan in the medium. A maximum 1.5-fold activation was shown at 0.2 mM 6-methyltetrahydropterin in the presence of 10 mM dithiothreitol. Dithiothreitol alone did not affect the activity. A 1.5-fold activation was observed when incubation was carried out under gas phase of 95% oxygen and 5% CO₂ instead of air. The activity was inhibited by 75% at 10^?4 M p-chlorophenylalanine. Both A-23187, a calcium ionophore, and dibutyryl cyclic AMP (DBc-AMP) stimulated the hydroxylation of tryptophan. The activation by A-23187 plus DBc-AMP was more than additive, suggesting the two activating mechanisms by Ca²⁺ and cyclic AMP may be operating synergistically.     

Hückel framework study on the superconducting vibronic interaction in (AB) N chains

Superconducting vibronic interaction in the vibronic superconductivity motif has been studied in the Hückel framework for (AB) _N chain systems. Within the on-site and nearest-neighbor approximation a new vibronic constant, /L, has been introduced, of which the importance has been discussed. The effect of the vibronic operator, , has also been studied. It is also concluded that the size-dependence of the superconducting vibronic interaction also exists in the (AB) _N chain systems.On leave from the Changchun Institute of Applied Chemistry, Academia Sinica, Changchun, P. R. China, as an STA fellowship awardee hosted by the Institute of Physical and Chemical Research of Japan.     

Characterization of the replication of Escherichia coli DNA in the absence of protein synthesis: Stable DNA replication

After inhibiting DNA synthesis in Escherichia coli, repeated cycles of chromosome replication can occur in the absence of protein synthesis. This “stable” replication requires the products of all of the known dna genes.Stable replication results from inhibiting DNA synthesis by treatment with naladixic acid, cytosine arabinoside or hydroxyurea; or by placing dnaB, dnaE or dnaG mutants at non-permissive temperatures. It also follows a “shift-up” into rich medium in which RNA and protein are synthesized more rapidly than DNA. Paradoxically, stable replication is induced also by treatment with concentrations of streptolydigin which do not inhibit DNA replication but temporarily and partially inhibit RNA and protein synthesis. During all of these treatments, some protein synthesis must occur.Stable replication is not immediately expressed after a short period of thymine starvation or streptolydigin treatment, but requires a subsequent period of protein synthesis. Once established, however, the stable replication state is permanent and will persist in the absence of protein synthesis or during normal growth.After stable replication has been determined by a period of DNA inhibition, it is possible to inactivate replication by heating dnaA, B, C, E and G temperature-sensitive mutants. However, resynthesis of these gene products in the presence of thymine and at the permissive temperature restores stable replication activity. Since restoration of activity can occur under normal growth conditions which do not induce stable replication, it was concluded that the dnaA, B, C, E and G gene products do not directly determine the stabilized character of the replication fork.A model is presented which attempts to explain the ability of different treatments to induce stable replication.