PubMed Health⌕ Search

Biomedical subjects

Hans-Werner Schmidt

Publications and source records attributed to Hans-Werner Schmidt.

6 recordsLinked to original sources
PubMed2005

A new class of low-molecular-weight amphiphilic gelators.

A new powerful class of low-molecular-weight amphiphilic compounds has been synthesized and their structure-property relationships with respect to their gelation ability of organic solvents have been investigated. These compounds are able to gel organic solvents over a broad range of polarity. Especially polar solvents such as valeronitrile and gamma-butyrolactone can be gelled even at concentrations far below 1 wt %. It was found that the gelation ability of these asymmetrically substituted p-phenylendiamines depends on a well-balanced relation of the terminal head group, the units involved in hydrogen bonding (amide or urea groups), and on the length of the alkyl chain. With this class of new gelators it is possible to tailor thermal and mechanical properties in different organic solvents and open various application possibilities.

4-Butyrolactone↗
PubMed2004

Consequences of the Kramers-Kronig relations for light diffraction on thick gratings.

Diffraction of monochromatic light on a grating leads to the attenuation of the transmitted beam of diffraction order zero. In the case of a thick grating the diffraction efficiency, and hence the effective attenuation coefficient, is a fast-varying function of the Bragg mismatch angle. According to Kramers-Kronig theory, the transmitted beam encounters a phase shift that also depends on the mismatch angle. This phase shift is measured for holographic gratings in a photoaddressable block copolymer and compared with analytical calculations.

Journal Article↗
PubMed2003

Field relevance of a synergistic effect observed in the laboratory between an EBI fungicide and a chloronicotinyl insecticide in the honeybee (Apis mellifera L, Hymenoptera).

It had been found earlier that the chloronicotinyl insecticide thiacloprid (as the 480 g litre(-1) SC Calypso) poses a favourably low toxicity hazard to the honeybee, Apis mellifera L. As with pyrethroids, the metabolization of chloronicotinyl compounds involves monooxygenases, which are known to be inhibited by some ergosterol biosynthesis inhibitor (EBI) fungicides potentially co-applied with these insecticides. The potential synergistic enhancement of the toxicity of thiacloprid to honeybees when co-applied with such fungicides was therefore studied under laboratory and semi-field conditions. Fungicides of other chemical classes were also examined for synergistic potential to reveal other metabolic interactions. In the laboratory, only a slight synergistic effect was observed with the anilinopyrimidine fungicide examined, while a significant enhancement of thiacloprid toxicity to honeybees was found with EBI fungicides. In three tunnel tests conducted under different environmental conditions to simulate field exposure, no increased mortality was observed when honeybees were directly sprayed with thiacloprid (Calypso) alone or in combination with the EBI fungicide tebuconazole (250 g litre(-1) EW, Folicur). There was also no synergized reduction in the foraging intensity on the treated crop. In general, the foraging intensity decreased after thiacloprid treatment but was restored within 24-48 h. The hive vitality was not affected by either thiacloprid or its tank mix with tebuconazole. Our results suggest that, at the recommended use rates, thiacloprid poses a negligible lethal risk to honeybees when applied either alone or in tank mixes with fungicides of various chemical classes.

Animals↗
PubMed2002

Application of a new color detection based method for the fast parallel screening of DeNO(x) catalysts.

A new fast parallel detection method for stage I screening of solid catalysts has been developed. This method is based on the color change of organic dyes in the presence of either educts or reaction products in a reaction gas flow. As an example, NO decomposition and NO reduction with propylene under lean or rich conditions were studied. The presence of NO in a gas stream was detected by the color change from colorless to blue-green of filter paper impregnated with an organic dye, 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), which was placed in the gas stream after the catalyst bed. The catalyst library was made up of mixed metal oxides, synthesized by impregnation of activated carbon with metal oxide precursor solutions and subsequent combustion of the carbon matrix. Catalytic activity of these metal oxides was compared to platinum on gamma-alumina as a reference catalyst. The most active compounds were then studied in detail for their DeNO(x)properties in a high precision parallel flow test rig under a stationary and cyclic lean/reach operation. A new promising NO(x) storage catalyst was discovered.

Journal Article↗
PubMed2002

Efficient synthesis and cell-transfection properties of a new multivalent cationic lipid for nonviral gene delivery.

Lipid-mediated delivery of DNA into cells holds great promise both for gene therapy and basic research applications. This paper describes the efficient and facile synthesis and the characterization of a new multivalent cationic lipid with a double-branched headgroup structure for gene delivery applications. The synthetic scheme can be extended to give cationic lipids of different charge, spacer, or lipid chain length. The chemical and physical properties of self-assembled complexes of the cationic liposomes (CLs) with DNA give indications of why multivalent cationic lipids possess superior transfection properties. The lipid bears a headgroup with five charges in the fully protonated state, which is attached to an unsaturated double-chain hydrophobic moiety based on 3,4-dihydroxybenzoic acid. Liposomes consisting of the new multivalent lipid and the neutral lipid 1,2-dioleoyl-sn-glycerophosphatidylcholine (DOPC) were used to prepare complexes with DNA. Investigations of the structures of these complexes by optical microscopy and small-angle X-ray scattering reveal a lamellar L(alpha)(C) phase of CL-DNA complexes with the DNA molecules sandwiched between bilayers of the lipids. Experiments using plasmid DNA containing the firefly luciferase reporter gene show that these complexes efficiently transfect mammalian cells. When compared to the monovalent cationic lipid 2,3-dioleyloxypropyltrimethylammonium chloride (DOTAP), the higher charge density of the membranes of CL-DNA complexes achievable with the new multivalent lipid greatly increases transfection efficiency in the regime of small molar ratios of cationic to neutral lipid. This is desired to minimize the known toxicity effects of cationic lipids.

Animals↗