SYNTHESIS AND PROPERTIES OF CONDUCTING MATERIALS IN THE TiO2 - SnO2 SYSTEM

Des poudres submicroniques de TiO2 ont été synthétisées par hydrolyse ménagée de l'isopropoxyde de titane. L'influence de la concentration des réactifs a été étudiée. L'addition de Niobium conduit à des particules sphériques. D'autre part des oxydes mixtes TiO2-SnO2 ont été élaborés par l'hydrolyse d'une solution de chlorures d'étain et d'antimoine contenant une suspension de TiO2 dopé par Nb. Les solutions solides SnO2-TiO2 se forment aisément dès 1100°C mais l'incorporation des dopants spécifiques dans ces solutions est limitée. La conductibilité électrique est une fonction non-linéaire de la composition.TiO2 submicronic powders have been synthesised by controlled hydrolysis of titanium tetraisopropoxide. The influence of reagents concentration has been investigated. Additions of Niobium result in spherical particles. Mixed powders of TiO2-SnO2 have been produced by hydrolysis of SnCl4-SbCl3 solutions containing the Nb doped TiO2 particles. The SnO2-TiO2 solid solutions are easily formed from 1100°C. However, the incorporation of the specific dopants is limited. The electrical conductivity is a non-linear function of the composition

SYNTHESIS AND PROPERTIES OF CONDUCTING MATERIALS IN THE TiO2 - SnO2 SYSTEM

Des poudres submicroniques de TiO2 ont été synthétisées par hydrolyse ménagée de l'isopropoxyde de titane. L'influence de la concentration des réactifs a été étudiée. L'addition de Niobium conduit à des particules sphériques. D'autre part des oxydes mixtes TiO2-SnO2 ont été élaborés par l'hydrolyse d'une solution de chlorures d'étain et d'antimoine contenant une suspension de TiO2 dopé par Nb. Les solutions solides SnO2-TiO2 se forment aisément dès 1100°C mais l'incorporation des dopants spécifiques dans ces solutions est limitée. La conductibilité électrique est une fonction non-linéaire de la composition.TiO2 submicronic powders have been synthesised by controlled hydrolysis of titanium tetraisopropoxide. The influence of reagents concentration has been investigated. Additions of Niobium result in spherical particles. Mixed powders of TiO2-SnO2 have been produced by hydrolysis of SnCl4-SbCl3 solutions containing the Nb doped TiO2 particles. The SnO2-TiO2 solid solutions are easily formed from 1100°C. However, the incorporation of the specific dopants is limited. The electrical conductivity is a non-linear function of the composition

Induction of the 4-aminobutyrate and urea-catabolic pathways in Saccharomyces cerevisiae. Specific and common transcriptional regulators.

In the yeast Saccharomyces cerevisiae, induction of the 4-aminobutyrate-catabolic pathway by 4-aminobutyrate requires two positive regulatory factors, encoded by the UGA3 and the UGA35 genes respectively. In addition to this, expression of one gene of this pathway, namely the UGA4 gene encoding the 4-aminobutyrate-specific permease, is controlled negatively by the product of the UGA43 gene [Vissers, S. André, B. Muyldermans, F. & Grenson, M. (1989) Eur. J. Biochem. 181, 357-361]. We show here that the products of two of these regulatory genes, UGA35 and UGA43, also control the expression of the genes encoding the urea-catabolic pathway, although the 4-aminobutyrate and urea-catabolic pathways are synthesised under specific conditions and do not share any enzymatic step or metabolite: the UGA35 pathways are synthesised under specific conditions and do not share any enzymatic step or metabolite: the UGA35 gene is shown to be identical to the DURL gene which was previously identified as a positive regulatory factor of the urea-catabolic pathway; the UGA43 gene product is shown to behave like a negative regulatory factor of this pathway. In contrast to UGA35/DURL and UGA43, the positive regulatory factors encoded by the UGA3 gene and the previously identified DURM gene specifically control 4-aminobutyrate and urea catabolisms respectively. Northern hybridization experiments suggest that the UGA35/DURL and UGA43 common regulatory factors act at the transcriptional level. Our results show that the expression of two biochemically distinct nitrogenous catabolisms, as triggered by their respective inducers, seems to involve multiple regulatory factors, some of which are common to the two catabolic pathways.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

Molecular characterization of transposable-element-associated mutations that lead to constitutive l-ornithine aminotransferase expression in Saccharomyces cerevisiae

The carg B or CAR2 gene, coding for ornithine aminotransferase, was isolated by functional complementation of a carg B mutation in Saccharomyces cerevisiae. It was used as a hybridization probe to analyse RNA and chromosomal DNA from four strains bearing cis‐dominant regulatory mutations leading to constitutive, mating‐type‐dependent, ornithine aminotransferase synthesis. The four mutations appear to be insertions. Their size and restriction pattern suggested that they were transposable elements, Ty1. All were inserted in the same orientation with respect to the carg B gene. We cloned the carg B gene with its associated insertion from two constitutive mutants (carg B+Oh‐1 and carg B+Oh‐2). We determined the sequence of the carg B 5′ region from the wild‐type gene and from the two mutated genes. The DNA sequences of the extremities of the two insertions were very homologous but not identical and were similar to previously reported Ty1 element direct repeats (δ). The same five‐base‐pair sequence, ATATA, was found at both ends of both Ty1 elements, indicating that both Ty1 were transposed to the same site. This site is located 115 base pairs upstream from the putative carg B coding region. The 5′ end of carg B transcript as determined by S1 mapping was the same in the wild‐type strain and in the four mutants. The carg B transcript was not detected in the wild‐type strain grown under non‐induced conditions, while under the same conditions it was present in all four mutants. Copyright © 1987, Wiley Blackwell. All rights reservedSCOPUS: ar.jinfo:eu-repo/semantics/publishe