Frank Sauer

Formation of hydroxymethyl hydroperoxide and formic acid in alkene ozonolysis in the presence of water vapour

Abstract Ozonolysis experiments of a series of terminal alkenes were performed to study the products formed in the presence of water vapour. Alkenes investigated were ethene, propene, isobutene and isoprene. Concentrations of the reactants were 4–6 ppmv alkene and 2 ppm ozone. The concentration of water vapour was varied from 0.5 ppmv to 17,000 ppmv. Hydroxymethyl hydroperoxide (HMHP) was found to be the sole product in the reactions of the stabilized Criegee biradical CH2OO with water vapour. The yield of HMHP relative to ozone consumption was measured to be 42% ethene, 14% propene, 13% isobutene and 30% isoprene in the presence of 9,000–18,000 ppmv H2O. HMHP was not stable under the experimental conditions and decomposed to HCOOH and water, presumably via a heterogeneous process. The atmospheric fate of HMHP and the relative rate constants of the CH2OO Criegee biradical with H2O, HCOOH and NOx are discussed.

Transcriptional control by Drosophila gap genes.

Summary The segmented body pattern along the longitudinal axis of the Drosophila embryo is established by a cascade of specific transcription factor activities. This cascade is initiated by maternal gene products that are localized at the polar regions of the egg. The initial long-range positional information of the maternal factors, which are transcription factors (or are factors which activate or localize transcription factors), is transferred through the activity of the zygotic segmentation genes. The gap genes act at the top of this regulatory hierarchy. Expression of the gap genes occurs in discrete domains along the longitudinal axis of the preblastoderm and defines specific, overlapping sets of segment primordia. Their protein products, which are DNA-binding transcription factors mostly of the zinc finger type, form broad and overlapping concentration gradients which are controlled by maternal factors and by mutual interactions between the gap genes themselves. Once established, these overlapping gap protein gradients provide spatial cues which generate the repeated pattern of the subordinate pair-rule gene expression, thereby blue-printing the pattern of segmental units in the blastoderm embryo. Our results show different strategies by which maternal gene products, in combination with various gap gene proteins, provide position-dependent sets of transcriptional activator/repressor systems which regulate the spatial pattern of specific gap gene expression. Region-specific combinations of different transcription factors that derive from localized gap gene expression eventually generate the periodic pattern of pair-rule gene expression by the direct interaction with individual cis-acting “stripe elements” of particular pair-rule gene promotors. Thus, the developmental fate of blastoderm cells is programmed according to their position within the anterior-posterior axis of the embryo: maternal transcription factors regulate the region-specific expression of first zygotic transcription factors which, by their specific and unique combinations, control subordinate zygotic transcription factors, thereby subdividing the embryo into increasingly smaller units later seen in the larva.

Determination of H2O2 and organic peroxides in cloud‐and rain‐water on the Kleiner Feldberg during FELDEX

This letter reports high-pressure liquid chromatography (HPLC) measurements of H2O2 and organic hydroperoxides in cloud- and rain-water. Observations were conducted on the Kleiner Feldberg (Germany) from late October to late November 1995, within the FELDEX-campaign. It was the first campaign ever in which organic peroxides were determined in cloud-water. H2O2 was found with concentrations of <0.008–3.19 µmol · 1−1. Hydroxymethyl hydroperoxide (HOCH2OOH, HMHP) and 1-hydroxyethyl hydroperoxide (CH3CH(OH)OOH, 1-HEHP) were observed with concentrations in the range of <0.008–1.0 µmol · 1−1 (HMHP) and <0.008–0.28 µmol · 1−1 (1-HEHP). The ratio of the sum of organic peroxides over the total amount of peroxides (H2O2+organic peroxides) was 0–81%. The concentrations of S(IV) and H2O2 in the samples were anticorrelated. The results indicate that organic peroxides, such as HMHP and 1-HEHP, should be included into modelling studies of the aqueous phase oxidation of S(IV).

Functional and conserved domains of the Drosophila transcription factor encoded by the segmentation gene knirps.

The Drosophila gap gene knirps (kni) is required for abdominal segmentation. It encodes a steroid/thyroid orphan receptor-type transcription factor which is distributed in a broad band of nuclei in the posterior region of the blastoderm. To identify essential domains of the kni protein (KNI), we cloned and sequenced the DNA encompassing the coding region of nine kni mutant alleles of different strength and kni-homologous genes of related insect species. We also examined in vitro-modified versions of KNI in various assay systems both in vitro and in tissue culture. The results show that KNI contains several functional domains which are arranged in a modular fashion. The N-terminal 185-amino-acid region which includes the DNA-binding domain and a functional nuclear location signal fails to provide kni activity to the embryo. However, a truncated KNI protein that contains additional 47 amino acids exerts rather strong kni activity which is functionally defined by a weak kni mutant phenotype of the embryo. The additional 47-amino-acid stretch includes a transcriptional repressor domain which acts in the context of a heterologous DNA-binding domain of the yeast transcriptional activator GAL4. The different domains of KNI as defined by functional studies are conserved during insect evolution.

Transcriptional cascades in Drosophila.

Genetics and molecular analyses have combined to yield insights into a functional cascade of transcription factors necessary to establish the molecular blueprint of the Drosophila body pattern in response to positional information in the egg. Recent progress in this field raises exciting questions regarding the molecular mechanisms involved, and their conservation in biological pattern-forming processes.