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G Strobl

Publications and source records attributed to G Strobl.

At least 19 recordsLinked to original sources
PubMed2005

A thermodynamic multiphase scheme treating polymer crystallization and melting.

A comparison of transition and melting temperatures of n-alkanes with experimentally determined ticknesses and melting points of polyethylene lamellae shows that the variation of the thickness with the crystallization temperature virtually agrees with the chain length dependence of the crystalline-mesomorphic phase transition in n-alkanes. Mesomorphic polyethylene layers are stable objects up to the thickness set by this phase transition. The findings lend further support to the view that polymer crystallization generally uses a route which includes a passage via a mesomorphic phase. We construct a thermodynamic scheme dealing with the transitions between melt, mesomorphic layers and lamellar crystallites, assuming for the latter ones that they exist both in an initial "native" and a final "stabilized" form. Application of the scheme in a reconsideration and quantitative evaluation of SAXS and DSC results previously obtained for PE, sPP, iPS and P(epsilonCL) yields the equilibrium transition temperatures between the various phases, latent heats of transition and surface free energies. According to the results the mesomorphic phases are not liquid-like, but have thermodynamic properties which place them truly intermediate between melt and crystals.

Computer Simulation↗
PubMed2005

Crystallization of a poly(ethylene-co-octene): I. A precursor structure and two competing mechanisms.

Observations of a sample of poly(ethylene-co-octene)in a polarizing optical microscope reveal peculiarities in its crystallization behavior. When cooled from the melt to a fixed crystallization temperature, at first a structure of diffuse appearance with variations on the length scale of micrometers forms rapidly. The transformation into the final semi-crystalline state then proceeds in two ways, by a continuous change of the inner structure of microm-sized objects and by the growth of spherulites. Time dependent small angle and wide angle X-ray scattering experiments corroborate the occurrence of the two crystallization mechanisms. Atomic force microscopy indicates that the change of the inner structure of the preformed objects is due to an in-filling of crystallites.

Journal Article↗
PubMed2005

Crystallization of poly(ethylene-co-octene): II. Melt memory effects on first order kinetics.

Dilatometric and X-ray scattering experiments of the crystallization kinetics of a sample of poly(ethylene-co-octene) show pronounced melt memory effects, i.e., the shapes of isotherms and characteristic times vary systematically with the temperature of the melt prior to cooling to the crystallization temperature. The temperature range of the effect is limited; crystallization kinetics remains constant below a melt temperature T(m)l and above a melt temperature T(m)h and varies only in-between. Analysis shows that the melt memory effect is caused by a variation of the characteristic time of a first order crystallization process. The process can be assigned to the in-filling of crystallites into objects of a previously generated precursor structure.

Journal Article↗
PubMed2003

Characteristic variations in the effect of diluents on polymer crystallization and melting observed for a sample of poly(ethylene-co-octene).

Melting points in mixtures of a crystallizable polymer with a low-molar-mass diluent depend on both, the diluent fraction and the crystal thickness. A differentiation of the two factors can be achieved by temperature-dependent SAXS experiments. A corresponding study, complemented by DSC, dilatometry, microscopy and AFM-imaging, was carried out for mixtures of a poly(ethylene-co-octene) with n-C16H34, c-C16H32 and methyl-anthracene, respectively. All diluents lead for a constant crystal thickness to melting point depressions in agreement with Raoult's law. On the other hand, the effect of the diluents on the thickness of the crystals formed at a fixed crystallization temperature varies. While in the presence of the two alkanes thicker crystals form, no effect arises for the methyl-anthracene--as was previously found for the octene-co-units. We consider these observations as a further support for our view that polymer crystallization follows a multi-stage route which includes a passage through an intermediate mesomorphic phase. Under such conditions crystal thicknesses would only be affected if the diluent is still present in the mesomorphic phase and stay invariant if the diluent molecules are already rejected when this intermediate phase forms.

Journal Article↗
PubMed1993

Quinolone antibacterial agents: relationship between structure and in vitro inhibition of the human cytochrome P450 isoform CYP1A2.

The inhibitory effect of 44 quinolone antibacterials and derivatives (common structure, 4-oxoquinoline-3-carboxylic acid) on cytochrome P450 isoform CYP1A2 activity was tested using human liver microsomes and caffeine 3-demethylation as a specific test system for this enzyme. By direct comparison of molecules differing structurally in only one position, the following structure-activity relationships were found. 3'-Oxo derivatives had a reduced or similar activity and M1 metabolites (cleavage of piperazinyl substituent) had a greater inhibitory activity, compared with the parent molecule. Alkylation of the 7-piperazinyl substituent resulted in a reduced inhibitory potency. Naphthyridines with an unsubstituted piperazinyl group at position 7 displayed a greater inhibitory potency than did corresponding quinoline derivatives. Derivatives with a fluorine substitution at position 8 had only a minor effect. Molecular modeling studies with inhibitors and caffeine showed that it is possible to explain the potency of the quinolones to inhibit CYP1A2 on a molecular level. The keto group, the carboxylate group, and the core nitrogen at position 1 are likely to be the most important groups for binding to the active site of CYP1A2, because the molecular electrostatic potential of all inhibitors is very similar to that of caffeine in these regions. The presence of a piperazinyl substituent, however, seems to be no prerequisite for inhibitory potency. Finally, an equation to estimate the potency to inhibit CYP1A2 was developed by quantitative structure-activity relationship analysis.

4-Quinolones↗
PubMed1992

The tungsten-containing aldehyde oxidoreductase from Clostridium thermoaceticum and its complex with a viologen-accepting NADPH oxidoreductase.

Purification of aldehyde oxidoreductase from C. thermoaceticum, the first detected enzyme able to reduce reversibly non-activated carboxylic acids to the corresponding aldehydes (White, H., Strobl, G., Feicht, R. & Simon, H. (1989) Eur. J. Biochem. 184, 89-96), results in the generation of multiple forms of the enzyme. The specific activities for the viologen-mediated dehydrogenation of butyraldehyde for the two main forms of the purification procedure are 530 and 450 U/mg. Two forms of the enzyme composed of alpha,beta- and alpha,beta,gamma-subunits, can be differentiated. The latter binds to red-Sepharose and can be eluted very specifically with NADPH. In contrast to the alpha,beta-types the trimeric forms also catalyse the reversible reduction of oxidised viologen with NADPH (VAPOR activity). The dimer alpha,beta can oligomerize and the alpha,beta,gamma-trimer can easily form various oligomers or split off the gamma-subunit. The apparent molecular masses of the subunits alpha,beta and gamma are 64, 14 and 43 kDa. The alpha,beta-form reveals an apparent molecular mass of 86 kDa containing about 29 iron, 25 acid-labile sulphur, 0.8 tungsten and forms about 1 mol pterine-6-carboxylic acid by permanganate oxidation. The corresponding values of the trimer showing a mass of 300 kDa, are about 82 Fe, 54 S, 3.4 W and 2.5 pterine-6-carboxylic acid. In addition, 1.7 mol of FAD could be found which seems to be a component of the gamma-subunit. The aldehyde oxidoreductase from C. thermoaceticum and that from C. formicoaceticum (White, H., Feicht, R., Huber, C., Lottspeich, F. & Simon, H. (1991) Biol. Chem. Hoppe-Seyler 372, 999-1005) show qualitative similarities as far as the Fe, S, W and pterin content and the broad substrate specificity are concerned. However, there are also surprisingly marked differences with respect to composition and amino-acid sequence.

Aldehyde Oxidoreductases↗
PubMed1990

13C and 15N NMR studies on the interaction between 6,7-dimethyl-8-ribityllumazine and lumazine protein.

The interaction between the prosthetic group 6,7-dimethyl-8-(1'-D-ribityl)lumazine and the lumazine apoproteins from two marine bioluminescent bacteria, one from a relatively thermophilic species, Photobacterium leiognathi, and the other from a psychrophilic species, Photobacterium phosphoreum, was studied by 13C and 15N NMR using various selectively enriched derivatives. It is shown that the electron distribution in the protein-bound 6,7-dimethyl-8-ribityllumazine differs from that of free 6,7-dimethyl-8-ribityllumazine in buffer. The 13C and 15N chemical shifts indicate that the protein-bound 6,7-dimethyl-8-ribityllumazine is embedded in a polar environment and that the ring system is strongly polarized. It is concluded that the two carbonyl groups play an important role in the polarization of the molecule. The N(3)-H group is not accessible to bulk solvent. The N(8) atom is sp2 hybridized and has delta+ character. Nuclear Overhauser effect studies indicate that the 6,7-dimethyl-8-ribityllumazine ring is rigidly bound with no internal mobility. The NMR results indicate that the interaction between the ring system and the two apoproteins is almost the same.

Bacterial Proteins↗
PubMed1989

Carboxylic acid reductase: a new tungsten enzyme catalyses the reduction of non-activated carboxylic acids to aldehydes.

An enzyme which we call carboxylic acid reductase (aldehyde dehydrogenase) seems to be the first which is able to reduce non-activated carboxylic acids to aldehydes at the expense of reduced viologens. There is no further reduction of the aldehydes to the corresponding alcohols. In the presence of oxidized viologens aldehydes can be dehydrogenated to carboxylic acids roughly 20 times faster than the latter are reduced. The specific enzyme activity in crude extracts is about 100 times increased if 10 microM tungstate and a sulphur source in addition to sulphate is given to the growth medium of Clostridium thermoaceticum. Carboxylic acid reductase seems to be present in two forms. One has an apparent molecular mass of about 240 kDa and is bound to red-Sepharose, whereas, the other, a form of an apparent molecular mass of about 60 kDa, is not bound. SDS gel electrophoresis shows a higher complexity. The very labile enzyme has been enriched by a factor of about 145 by binding to octyl-Sepharose and further chromatographic separation by red-Sepharose and FPLC using Mono-Q and phenyl-Superose columns. After cell growth in the presence of [185W]tungstate, radioactivity coincides with the two forms of enzyme activity during all purification steps. This is also the case when the enzyme is electrophoretically separated on polyacrylamide slab gels.

Aldehyde Oxidoreductases↗
PubMed1980

[The diagnostic value of cranial computerized tomography in exogenous psychoses and mental disorders associated with organic disease (author's transl)].

205 patients hospitalized in a psychiatric department were subjected to cranial computerized tomography. The diagnosis on discharge according to the ICD key in each case was "psychoses or mental disorders associated with physical conditions". Pathological findings were obtained in 67.8% of the patients. In the case of space-occupying lesions the connection between psychiatric symptoms and syndromes and the underlying organic disease is obvious. Moreover, with inflammatory, vascular or traumatic diseases, a relationship to focal lesions found on the computer tomography appears likely if backed by appropriate neurological indications in the history or on clinical examinations. However, when alterations signifying diffuse brain atrophy are obtained on computer tomography any connections with psychiatric features should be very critically evaluated and, in individual cases, such connections had better not be looked for at all. Especially in cases of psychoses or mental disorders associated with physical conditions cranial computerized tomography is of high diagnostic value and the indications for its implementation in these cases should be judged very leniently.

Adult↗
PubMed1980

[Quantitative evaluation of lateral ventricle width by means of CT--values obtained from a normal population (author's transl)].

The possibilities of differentiation between a "normal" and an "enlarged" ventricular system by means of Computerized Tomography are limited. The main problems are the definition of the Normal Population and the fact that a certain methodical error in measurement is not to be avoided. On the other hand, that differentiation is essential for the diagnosis of Ventricular Enlargement, Hydrocephalus internus and Brain Atrophy. The daily practice requires a method, which allows an accurate measurement as well as a quick and simple performance. The evaluation of the width of the lateral ventricles by means of the Ventricle-Index-Quotient (VIQ) and of the Ventricle-Waist-Quotient (VTQ) is likely to meet all these requirements. The results have been obtained from the computer-tomograms of 53 men and 69 women (n = 122), aged between 15 and 80 years. A statistically significant correlation was found between the VIQ- and VTQ-values on the one hand, and the patient's ages on the other. Consequently, whether normal values or the diagnosis of brain atrophy are in question, the patient's age has always to be considered.

Adolescent↗
PubMed1978

[Indications for neuroradiological investigations using contrast media in patients with psychiatric disorders (author's transl)].

The results are presented of neuroradiological investigations using contrast media in 100 patients hospitalized in a psychiatric department. The existence of neurological disturbances or the psychoorganic syndrome, as well as the results of screening methods such as EEG and brain scan are important factors in the decision for or against the performance of cerebral angiography or pneumoencephalography. The significance of the "brain atrophy syndrome" accompanying psychotic diseases is discussed. In addition, some cases are demonstrated of organic neurological brain diseases with predominantly psychiatric features, where the diagnosis was reached on the basis of only neuroradiological methods using contrast media.

Adolescent↗
PubMed1978

[Sport and cardiac risk factors in middle age (author's transl)].

1477 employees (868 males and 609 females) were examined for cardiac risk factors. The risk factor frequency was tested in relation to the amount of physical activity. Men and women active in sports are less subject to over-weight, diabetes, high blood pressure, and pathological ECG changes than are physically inactive; males who participate in sports also smoke less. On the other hand, a connection between risk factors and different levels of physical activity on the job could not be established. The mutual relations between risk factors, physical activity, weight, and social level imply that the lower number of risk factors in those who participate in sports is due largely to their consciously healthy way of living.

Age Factors↗
PubMed1977

Reversal by physostigmine of clozapine-induced delirium.

Clozapine, a new antipsychotic drug without extrapyramidal side effects and with strong sedating potency, can produce acute symptoms of central anticholinergic toxicity. The authors report that physostigmine, a reversible anticholinesterase agent, which can pass the blood-brain barrier, was effective in reversing the clozapine-induced brain syndrome in two patients. Physostigmine also reduced one patient's tachycardia.

Adult↗
PubMed1976

Slow-drip dibenzepine infusion in depression. Proof of rapid efficacy by quantitative EEG and affect-polarity profile studies.

The efficacy of a new intensive antidepressive treatment procedure--48 h slow drip infusion with 1,440 mg dibenzepine2 and subsequent oral treatment--was investigated in endomorphous (endogenous) depressed patients. In addition to evaluations of alterations in psychopathology by clinicians, time of onset and the extent of the therapeutic effect was determined by the patients themselves using the affect-polarity profile, and by EEG power-spectral density analysis. Clinical improvement started as early as in the 3rd hour of the dibenzepine infusion and was predominantly due to an anxiolytic/sedative drug effect. The thymoleptic effect started at the end of the infusion and increased with progressing oral treatment up to the 3rd week. Neurophysiological changes were ahead of the psychopathological ones, since a statistical decrease in dominant frequency of the EEG occurred 1 h after the start of dibenzepine infusion.

Administration, Oral↗