Search results for "TYR"

1991

Telechelic α,ω-macrozwitterions — narrowly distributed polystyrene chains oppositely charged at each end — were synthesized via anionic polymerization using direct functionalization with the initiator and the termination agent. The resulting products were purified (zwitterion content ≥ 0,95) and characterized with gel permeation chromatography, viscometry, static and dynamic light scattering and small-angle neutron scattering. In unpolar solvents as toluene, the polymeric zwitterions form clusters with molecular weights depending on concentration. In the dilute case, the clusters are relatively small and consist of approximately 8 zwitterions. The structure of these clusters is discussed by…

Measurement of Protein Synthesis: In Vitro Comparison of 68Ga-DOTA-Puromycin, [3H]Tyrosine, and 2-Fluoro-[3H]tyrosine

2012

Aim: Puromycin has played an important role in our understanding of the eukaryotic ribosome and protein synthesis. It has been known for more than 40 years that this antibiotic is a universal protein synthesis inhibitor that acts as a structural analog of an aminoacyl-transfer RNA (aa-tRNA) in eukaryotic ribosomes. Due to the role of enzymes and their synthesis in situations of need (DNA damage, e.g., after chemo- or radiation therapy), determination of protein synthesis is important for control of antitumor therapy, to enhance long-term survival of tumor patients, and to minimize side-effects of therapy. Multiple attempts to reach this goal have been made through the last decades, mostly u…

Nachweis und chemische umsetzungen von endgruppen in polystyrolen

1955

Bei der Losungspolymerisation van Styrol mit dem Eisen-Redox-System Brombenzoylperoxyd/Fe/Benzoin werden Brombenzoesaure-Ester-Gruppen in das Makromolekul eingebaut; diese lassen sich quantitativ verseifcn. Dabei entstehen Polymere mit alkoholischen Endgruppen; diese konnen mit Dichlorphenylisocyanat umgesetzt und quantitativ bestimmt werden. Mit Brombenzopersaure/Fe/Benzoin erhaltene Polystyrole enthalten keine Brombenzoesaure-Esterendgruppen sondern alkoholische Endgruppen, die ebenfalls mit Dichlorphenylisocyanat umgesetzt wurden. Die alkoholischen und esterartjgen Endgruppen lassen sich ultrarotspektroskopisch nachweisen. In the solutionpolymerisation of styrene with the iron-redox-syst…

1979

The thermal degradation behavior of head-to-head (H-H) and head-to-tail (H-T) polystyrenes and poly(vinylcyclohexane)s has been investigated by direct pyrolysis in a mass spectrometer. Both H-H and H-T isomers show only small differences in their initial temperatures of decomposition but remarkably different degradation processes. Whereas H-T polystyrene decomposes in accordance with earlier investigations mainly by a radicalic depolymerization into the monomer and yields only a small amount of dimer and trimer, the H-H polystyrene shows no unzipping and only a statistic degradation into oligomeric styrenes. The formation of stilbene is a diagnostic reaction of H-H polystyrene. The pyrolysi…

RELAXATION METHODS FOR STUDYING MACROMOLECULAR MOTION IN THE BULK

1982

Abstract Macromolecular motion in amorphous and partially crystalline polymers is discussed in the light of recent relaxation experiments with particular emphasis on NMR methods. Polystyrene and polyethylene serve as pertinent examples where a considerable amount of new experimental data provides a bysis for better understanding molecular processes below and above the glass transition, and in the melt.

Über die stereospezifische polymerisation von styrol mit natriumorganischen verbindungen

1958

Es wird uber die Herstellung von kristallisierbaren Polystyrolen durch Polymerisation von Styrol mit natriumorganischen Verbindungen bei niedrigen Temperaturen berichtet. Anteile der Polymeren sind rontgenkristallin und haben Schmelzpunkte von uber 200°C. Dieser kristallisierbare Anteil nimmt mit fallender Polymerisationstemperatur zu. Bei konstanter Polymerisationtemperatur fallen die Viskositatszahlen der Polymeren mit steigender Katalysatorkonzentration. It is reported on the preparation of cristallizable polystyrenes by means of polymerisation of styrene with sodiumorganic compounds under low temperatures. X-ray diffraction shows the cristallinity of the polymers having melting points o…

1990

Taking into account the dependency on molar mass of the viscometric interaction parameter B, the modified Stockmayer-Fixman-Burchard equation ([η]/M1/2) = KΘ + C″ · A2 · M1/2 is obtained. It relates the intrinsic viscosity, [η], to the second virial coefficient, A2, and to the unperturbed dimensions parameter, KΘ, with C″ being a constant. Hereupon, KΘ can be determined from [η] and A2 data of any binary (solvent/polymer) and/or ternary (solvent 1/solvent 2/polymer) system, BPS and/or TPS. Because of the scarcity of reliable sets of [η] and A2 values mostly for TPS, the application of the above equation to obtain KΘ coefficients rests limited. This limitation can be surmounted by an A2 eval…

1972

The determination of reactivity ratios is simplified by using an excess of one monomer (M1) at a time large enough that the copolymers will have a very small content of the other monomer (M2). In this case chain propagation takes place almost exclusively by addition to polymer radicals with a terminal M1-unit (P) and monomer consumption by propagation of P may be neglected. One reactivity ratio (r1) is obtained from monomer conversions by means of a simple integrated equation which is valid up to high conversions. A calculation is proposed in order to account for the neglected propagation via P. The other reactivity ratio (r2) is obtained from copolymerizations with excess M2. As the new me…

Über polymerisationen mit hilfe von redox-systemen

1951

Bei der durch Eisen-Redox-Systeme ausgelosten Polymerisation von Styrol und von Dimethylbutadien -2.3 wird die peroxydische Komponente (Diacylperoxyd) in die Makromolekule eingebaut. Es wird gezeigt, das bei der Polymerisation des Styrols mit Dibrombenzoylperoxyd-Eisenbenzoat-Benzoin die Zahl der eingebauten, markierten Endgruppen die gleiche ist wie bei der peroxydischen Polymerisation mit Di-Brombenzoylperoxyd. Dies spricht dafur, das auch die peroxydische Polymerisation durch Radikale ausgelost wird, die bei einer Redox-Reaktion zwischen Peroxyd und Monomerem entstehen. Fur das polymere Dimethylbutadien wurde nachgewiesen, das alle markierten Endgruppen, die bei der eisen-redox-katalysie…

UV-photometrische analyse kationisch erzeugter polystyrole, 1. Nachweis des covalenten einbaus von acylresten aus aromatischen acylperchloraten

1983

Polymerization of styrene was found not to take place with 4-phenylazobenzoyl perchlorate in benzene solution. 4-Biphenylcarbonyl perchlorate, however, initiates styrene polymerization under the same conditions leading to a product not containing acyl groups as indicated by UV spectroscopic analysis. 4-Phenylazobenzoyl, 2-naphthoyl, and 9,10-dioxo-2-anthracenecarbonyl perchlorate (6b, 7b, and 8b), prepared form silver perchlorate and the corresponding acyl chlorides 6a, 7a, and 8a in styrene, were found to initiate the polymerization of styrene under anhydrous conditions at −25°C in the dark. By UV spectroscopy it could be shown that the resulting polymers contain covalently bound acyl grou…