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H Huth

Publications and source records attributed to H Huth.

14 recordsLinked to original sources
PubMed2005

Pattern formation in thin polystyrene films induced by an enhanced mobility in ambient air.

Thin polystyrene films (prepared in a sandwich geometry between two aluminum electrodes) develop a characteristic pattern in ambient air when kept above the glass-transition temperature, whereas they remain unchanged in vacuum or in a pure nitrogen atmosphere. Measurements by broadband dielectric spectroscopy, capacitive dilatometry, and AC calorimetry reveal that the pattern formation is initiated in ambient air by an increase in the average relaxation rate of the dynamic glass transition, which results in a corresponding reduction of the glass-transition temperature. Infrared measurements evidence that this is caused by a shift of the molecular weight distribution to lower values as a consequence of oxygen-induced chain scissions.

Journal Article↗
PubMed2005

Molecular dynamics of hyperbranched polyesters in the confinement of thin films.

Broadband Dielectric Spectroscopy is employed to investigate the molecular dynamics in thin films of hyperbranched polyesters (type AB(1)B(2), with -OH and -OCOCH(3) as terminal groups). Three relaxation processes are detected: alpha, beta and gamma. While the latter two are not influenced by the confinement, a pronounced effect is observed on the alpha relaxation: with decreasing film thickness the slower relaxation modes of the dynamic glass transition are gradually suppressed, resulting in an increase of the average relaxation rate and in a linear decrease of the dielectric strength. This is attributed to an immobilization in confinement of the polymeric segments located at the periphery of the hyperbranched macromolecular structures.

Journal Article↗
PubMed1984

The synthesis of 15N- and deuterium-substituted, spin-labeled analogues of NAD+ and their use in EPR studies of dehydrogenases.

Two spin-labeled analogues of NAD+ were synthesized with an 15N and perdeuterated nitroxide radical, 4-amino-2,2,6,6-[2H17, 15N]tetramethylpiperidone-1-oxyl, which was attached to either the C-6 or C-8 position of the purine ring. The EPR spectra of these derivatives exhibit an approx. 6-fold increase in sensitivity compared with the corresponding 14N, protonated analogues due to a decrease in both the number of nuclear manifolds (from three to two) and the linewidth. The enhanced spectral resolution obtained with (2H17, 15N)spin-labeled-NAD+ analogues has facilitated simulation of the EPR lineshape of the nucleotide bound to lactate dehydrogenase (L-lactate:NAD+ oxidoreductase, EC 1.1.1.27). The spin-label moiety exhibits highly constrained motion indicative of a single environment. The motion of the spin label does not reflect the overall motion of the enzyme; rather, it is characteristic of some limited mobility relative to the lactate dehydrogenase. By contrast, the spin label on the membrane-bound enzyme, D-beta-hydroxybutyrate dehydrogenase (D-beta-hydroxybutyrate:NAD+ oxidoreductase, EC 1.1.1.30), is completely immobilized and exhibits two distinct spectral components for spin-labeled NAD+, which appear to differ in the polarity of the environment of the nitroxide.

Electron Spin Resonance Spectroscopy↗
PubMed1983

[Anti-epileptic agents during pregnancy. A prospective study on the course of pregnancy, malformations and child development].

In a prospective controlled study 70 children of females with epilepsy and on anticonvulsant medication during pregnancy were investigated. It was shown that epileptic females had stillbirths more frequently than expected. After delivery particularly children on phenobarbitone are sedated. Due to weak suckling this may lead to inadequate food intake. Withdrawal symptoms manifest in affected children as hyperexcitability lasting for weeks. Children of epileptic women on medication are generally smaller, of lower weight and have smaller heads than children from all control groups. Ingestion of more than one anticonvulsant leads to an even more pronounced reduction of infantile body measurements below the expected mean value. Small malformations are observed more frequently after intrauterine exposition to anticonvulsants than in the control groups. Ingestion of more than one anticonvulsant leads to an increase of the number of small malformations in the child than after single drug therapy. Children of epileptic parents are affected more frequently by large malformations than children of nonepileptic parents.

Abnormalities, Drug-Induced↗
PubMed1981

Characterization of the receptor subtype involved in alpha-adrenoceptor-mediated modulation of serotonin release from rat brain cortex slices.

Rat brain cortex slices preincubated with 3H-5-hydroxytryptamine and superfused with physiological salt solution were stimulated electrically at a frequency of 3 Hz. 1. The electrically evoked 3H-overflow was decreased by clonidine, noradrenaline and B-HT 920 in a concentration-dependent manner (negative logarithms of the IC30 values: 6.66, 6.55 and 4.40, respectively) 2. Phenylephrine 10-5 M (which increased basal 3H-efflux) and methoxamine 10-4 M decreased the impulse-evoked 3H-overflow by less than 25% whereas lower concentrations were ineffective. 3. Yohimbine produced a shift to the right of the concentration-response curves of noradrenaline (apparent pA2: 6.93) and clonidine (apparent pA2: 7.06) for their inhibitory effects on evoked 3H-overflow. Rauwolscine also shifted the concentration-response curve of noradrenaline to the right (apparent pA2: 7.29), whereas prazosin (10-6 and 3.2 x 10-6 M) was ineffective in this respect. These results suggest that the alpha-adrenoceptors on the serotoninergic nerve fibres belong to the alpha2-subtype.

Adrenergic alpha-Agonists↗
PubMed1981

Semi-reversible cross-linking. Synthesis and application of a novel heterobifunctional reagent.

The synthesis of a novel heterobifunctional cross-linking reagent, 3-(4-azido-2-nitrobenzoylseleno)propionic acid is described. The selenol ester function serves as a selective and reversible thiol reagent. Cross-linking is carried out photochemically via nitrene generation. The reagent is well suited for the identification of the environment of a defined cysteine residue according to the principle of semi-reversible cross-linking (Trommer, W.E., Friebel, K., Kiltz, H.-H. & Kolkenbrock. H. (1977) Adv. Exp. Med. Biol. 86A, 187-195). Cleavage of the thiol ester bond (the first anchor point) can be achieved by a variety of labels carrying an amino function thus giving rise to labelled amino acids or proteins in a distance of about 0.7 nm from the known cysteine residue. Optimal conditions were determined by reaction of 3-(4-azido-2-nitrobenzoylseleno)propionic acid and of its unsubstituted analog with glutathione and N alpha-benzoylglycyllysine. Nucleosidetriphosphate-adenylate kinase from pig muscle was chosen as an example to demonstrate the usefulness of the reagent. 14C-labelled aminobutyric acid was applied to cleave the thiol ester bond between the reagent and cysteine-25 leading to labelling of the N-terminal arginine peptide.

Adenylate Kinase↗
PubMed1980

Alpha-adrenoceptor-mediated modulation of 5-hydroxytryptamine release from rat brain cortex slices.

Slices of rat brain cortex preincubated with 3H-5-hydroxytryptamine were superfused with physiological salt solution and stimulated electrically, or they were superfused with Ca2+-free solution containing 25 mM K+ and stimulated by introduction of 1.3 mM CaCl2 for 2 min. 1. The electrically evoked 3H overflow was decreased by noradrenaline and increased by phentolamine in a concentration-dependent manner. 2. Phentolamine caused a parallel shift to the right of the concentration-response curve of noradrenaline for its inhibitory effect on impulse-evoked 3H overflow; by contrast, it left the inhibitory effect of unlabelled 5-hydroxytryptamine on the electrically evoked 3H overflow unaffected. 3. Propranolol did not alter the inhibitory effect of noradrenaline on impulse-induced 3H overflow. 4. The increasing effect of phentolamine on the electrically evoked 3H overflow was not modified by paroxetine. 5. Cocaine (at a concentration which almost completely blocks the uptake of 3H-noradrenaline but only partially that of 3H-5-hydroxytryptamine into cortex slices) decreased impulse-evoked 3H overflow. This effect was abolished by phentolamine. 6. In the presence of tetrodotoxin throughout superfusion, the Ca2+-evoked 3H-overflow from slices superfused with Ca2+-free solution was inhibited by noradrenaline and increased by phentolamine. These findings suggest that the terminal serotoninergic fibers of rat brain cortex possess alpha-adrenoceptors, activation of which by exogenous or endogenous noradrenaline leads to inhibition of the release of 5-hydroxytryptamine.

Animals↗
PubMed1979

The nature of the substrate inhibition in lactate dehydrogenases as studied by a spin-labeled derivative of NAD.

The formation of the ternary complex of lactate dehydrogenase (L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) from pig heart and skeletal muscle with the adduct of pyruvate to NAD", spin-labeled at N6 was studied by ultraviolet spectroscopy and ESR techniques. According to ultraviolet measurements we found identical binding characteristics for the natural coenzyme and its spin-labeled analog. The rate by which the ESR signal of free spin-labeled NAD+ decreased upon addition of pyruvate to the binary complexes was substantially different in the two isozymes. With the heart type an initial drop followed by a further linear decrease, zero order in the enzyme and coenzyme concentration was observed. In case of the skeletal muscle isozyme no immediate reaction and a first order process occurred. The initial reaction can be attributed to a non-covalent enzyme/spin-labeled NAD+/pyruvate complex with a dissociation constant for pyruvate of 11 +/- 1 mM, thus explaining the well-known substrate inhibition in the heart isozyme above 2 mM pyruvate. The further reaction is then determined by the buffer dependent enolization of pyruvate. In the muscle isozyme formation of the covalent adduct is not assisted by prior binding of pyruvate in a non-covalent ternary complex and therefore the rate depends on the binary complex concentration.

Animals↗