Search results for "Mono"
showing 10 items of 6843 documents
Ylide als polymerisationsinitiatoren. I. Salzhaltige und salzfreie phosphoniumylide
1972
Phosphorylide, R3PCHX und R3PCH2·LiBr, konnen eine anionische Polymerisation von Vinylmonomeren starten. Dabei werden im Falle des Methacrylnitrils und des Methylmethacrylats die Ylide als Endgruppen in die Polymeren eingebaut. Bei den salzfreien Yliden hangt die Startwirksamkeit von der Basizitat des Ylidcarbanions ab, die Struktur dieser Ylide hat aber keinen mesbaren Einflus auf das Molekulargewicht und die Taktizitat der entstehenden Polymeren. Im Gegensatz dazu wird bei der Initiierung mit den salzhaltigen Yliden auch die Taktizitat der Polymeren von den Substituenten der Phosphorylide beeinflust. Phosphorous ylids, R3PCHX and R3PCH2·LiBr, are able to start an anionic polymerization of…
Über umsetzungen an poly-p-lithiumstyrol. 4. Mitt. Darstellung carbonylgruppenhaltiger derivate des polystyrols
1961
In Fortsetzung fruherer Arbeiten wird die Reaktivitat von Poly-p-lithiumstyrol gegenuber solchen Agenzien gepruft, die zur Bildung von carbonylgruppenhaltigen Verbindungen fuhren. Wahrend bei der Umsetzung mit Orthoameisensaureester nur vernetzte Polymere entstechen, last sich mit Dimethylformamid ein losliches Derivat des Polystyrols herstellen das p-standige Formylgruppen tragt. Die Reaktion mit Nitrilen liefert polymere Ketone; mit Acetophenon entsteht Poly-p-vinylacetophenon, das mit dem aus dem Monomeren durch Polymerisation erhaltenen Produkt verglichen wird. Mit Benzonitril erhalt man Poly-p-vinylbenzophenon. Die polymeren Ketone konnen in die Oxime ubergefuhrt werden, deren Sticksto…
Über die cyclopolymerisation einiger bis-(N-vinyl)-verbindungen
1966
Durch Umsetzung von Vinylisocyanat mitAthylenglykol, Butandiol-1,4, Hexandiol-1,6, Octandiol-1,8, Brenzcatechin, Resorcin, Hydrochinon, cis- und trans-Chinit sowie Piperazin wurden die entsprechenden Bis-(N-vinyl)-Verbindungen hergestellt. Diese Monomeren werden unter gleichen Bedingungen radikalisch polymerisiert. Der Gehalt an seitenstandigen N-Vinylgruppen ergibt sich aus der bei saurer Hydrolyse gebildeten Menge Acetaldehyd. Der auf 0% Umsatz berechnete Doppelbindungsgehalt und damit der Cyclisierungsgrad hangt von der Struktur der Monomeren ab. Die Ergebnisse stimmen uberein mit der Ringbildungstendenz bei niedermolekularen Verbindungen (z. B. Ansaverbindungen) und werden an Hand von M…
Carbohydrates from Chemical Pulps: Characterization by Capillary Zone Electrophoresis
2006
Capillary zone electrophoresis (CZE) is one of the novel separation techniques, being applicable, for example, to virtually all important biomass-derived monosaccharides. However, in spite of this fact the utilization of this technique in the pulp and paper industry is currently rather limited. In this chapter practical guidance and some application examples are given to show how carbohydrate material (polysaccharides, oligosaccharides, and neutral and acidic monosaccharides) in pulps and spent liquors can be analyzed by CZE. Emphasis is placed on sample preparation and separation conditions including comparison with other separation methods, such as gas chromatography (GC) and high-perform…
Polymer Retention Mechanism in GPC on Active Gels
1980
Abstract The elution behaviour of low molecular weight polystyrene (PS) down to the monomer on spherosil gel in several eluents has been studied. In the medium range of molecular weights the elution behaviour is similar to that followed by high molecular weight PS, the differences in elution volumes among different eluents increasing monotonically with decreasing molecular weight and partition rather than adsorption probably being responsible for the shifts in retention volumes. However, at the total permeation limit, the situation is alike to that found in liquid-solid chromatography, the elution volumes of solutes with molecular sizes very close to that of styrene being determined by solv…
Metabolic Inactivation of Reactive Metabolites
1978
ABSTRACT Many compounds which are not electrophilically reactive as such are transformed by mammalian enzymes to reactive metabolites which are, in many cases, responsible for cytotoxic, mutagenic and/or carcinogenic effects of the compounds in question. The essential role of activating systems in this situation has become common knowledge during the last decade. However, many reactive metabolites are also subject to inactivation by mammalian enzymes. This important parameter is frequently not taken into account. Compounds possessing aromatic or olefinic moieties are very widely occurring and activation of these often proceeds via an electrophilically reactive epoxide. This may be transform…
Synthesis of Protected Enantiopure Erythrulose Derivatives
1996
D- and l-Erythrulose derivatives 2–6 bearing protective O-silyl and O-benzyl groups in various positions were synthesized in enantiopure form from l-ascorbic acid, D-isoascorbic acid, and D-glucose.
Infiuence of Foreign Compounds on Formation and Disposition of Reactive Metabolites
2008
Many toxic compounds are unreactive and need biotransformation in order to exert their toxic effects. Several enzymes control the formation or disposition of reactive metabolites. Especially well studied is the group of enzymes responsible for the control of reactive epoxides. Such epoxides may bind spontaneously to DNA, RNA and protein. These alterations of critical cellular macromolecules may disturb the normal biochemistry of the cell and lead to cytotoxic, allergenic, mutagenic and carcinogenic effects. Whether these effects will be manifested depends on the chemical reactivity as well as on other properties (geometry, lipophilicity) of the epoxide in question. Enzymes controlling the c…
Metabolism of Chemical Carcinogens
1989
Most chemical carcinogens are chemically unreactive per se and need metabolic activation to the ultimate carcinogenic species. The enzyme pattern responsible for the generation and disposition of reactive metabolites constitutes one important early contribution to the control of chemical carcinogenesis. Especially well studied is the group of enzymes responsible for the control of reactive epoxides. Many natural as well as manmade foreign compounds, including pharmaceuticals, possess olefinic or aromatic double bonds. Such compounds can be transformed to epoxides by microsomal monooxygenases present in many mammalian organs. By virtue of their electrophilic reactivity such epoxides may spon…
Dihydrodiol Dehydrogenase: An Important Enzyme in Dihydrodiol-Epoxide Pathway — Mediated Benzo(A)Pyrene Mutagenicity
1978
Benzo(a)pyrene is metabolized to two major groups of mutagenically reactive metabolites: Monofunctional epoxides and dihydrodiol-epoxides. Various monooxygenase forms catalyze the various pathways at very different rates. In metabolic situations where the contribution by dihydrodiol-epoxides is small, epoxide hydratase represents a very efficient protective system. However, in situations where the mutagenic effect is predominately due to dihydrodiol-epoxide, the effect of epoxide hydratase is complicated and weak. We have now obtained evidence that a dihydrodiol dehydrogenase represents an efficient protective system in the latter situation. The enyzme was purified to homogeneity and the pu…