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Dissociation Behavior (dissociation + behavior)

Distribution by Scientific Domains
Chemistry50%

Selected Abstracts

Influence of Grafting on the Solution Properties and the Dissociation Behavior of Ionic/Nonionic Grafted Copolymers

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2007
Jens Weber
Abstract A new synthetic approach towards grafted terpolymers based on a poly[(methyl vinyl ether)- alt -(maleic anhydride)] backbone and poly(ethylene glycol) monomethyl ether (MPEG) side chains is presented. Resulting comb polymers with controllable grafting degree still have highly reactive anhydride moieties along the polymer backbone, as proved by IR spectroscopy. Grafting degree depends on the anhydride hydroxide stoichiometric ratio. It is not influenced by the molecular weight of MPEG. An increase in the grafting degree leads to a contraction of the polymer in the solution. Evaluation of potentiometric titration data gave a deeper insight into the dissociation process. The copolymers showed a two-step dissociation behavior. No significant influence of the grafting degree on the acidic strength was observed, whilst there is a strong effect of the grafting degree on the free energy change upon neutralization ,Gel. Grafting leads to a higher change in free energy ,Gel,1 for the first step but to lower ,Gel,2 required for the second step. [source]

Fragmentation of Alkoxo(catecholato)vanadium(V) Complexes[(C6H4O2)V(OR1)(OR2)]+ in the Gas Phase

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2005
Malgorzata Kaczorowska
Abstract Electrospray ionization (ESI) mass spectrometry is used to investigate the gas-phase dissociation behavior of vanadium(V) complexes [(C6H4O2)V(OR1)(OR2)]+ containing two identical or different alkoxy groups (R1, R2 = CH3, C2H5, n -C3H7, i -C3H7 and t -C4H9) and a catecholato ligand (C6H4O2). The fragmentation reactions of the complexes are studied by collision-induced dissociation (CID) and labeling experiments. For [(C6H4O2)V(OR1)(OR2)]+ cations with alkoxo groups larger than methyl, a trend for preferential evaporation of hydrocarbon fragments is observed, followed by expulsion of neutral alcohols. Further, the CID spectra of all complexes show a signal which can be assigned to the complex [(C6H4O2)VO]+. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Influence of Grafting on the Solution Properties and the Dissociation Behavior of Ionic/Nonionic Grafted Copolymers

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2007
Jens Weber
Abstract A new synthetic approach towards grafted terpolymers based on a poly[(methyl vinyl ether)- alt -(maleic anhydride)] backbone and poly(ethylene glycol) monomethyl ether (MPEG) side chains is presented. Resulting comb polymers with controllable grafting degree still have highly reactive anhydride moieties along the polymer backbone, as proved by IR spectroscopy. Grafting degree depends on the anhydride hydroxide stoichiometric ratio. It is not influenced by the molecular weight of MPEG. An increase in the grafting degree leads to a contraction of the polymer in the solution. Evaluation of potentiometric titration data gave a deeper insight into the dissociation process. The copolymers showed a two-step dissociation behavior. No significant influence of the grafting degree on the acidic strength was observed, whilst there is a strong effect of the grafting degree on the free energy change upon neutralization ,Gel. Grafting leads to a higher change in free energy ,Gel,1 for the first step but to lower ,Gel,2 required for the second step. [source]

Electrospray ionization mass spectrometric characterization and quantitation of xanthine derivatives using isotopically labelled analogues: an application for equine doping control analysis

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2004
Mario Thevis
Isotope-dilution mass spectrometry has been employed successfully in numerous fields of analytical chemistry enabling the establishment of fast and reliable procedures. In equine sports, xanthine derivatives such as caffeine and theobromine are prohibited, and doping control laboratories analyze horse urine specimens regarding these illicit performance-enhancing drugs. Theobromine has to exceed a threshold level of 2,,g/mL, hence a robust and reliable quantitation is required. Stably deuterated theobromine and caffeine were synthesized by the reaction of xanthine or theobromine with iodomethane-d3 in the presence of N -methyl- N -trimethylsilyltrifluoroacetamide or potassium carbonate in acetonitrile, respectively. Both compounds were characterized by nuclear magnetic resonance spectroscopy and electrospray ionization tandem mass spectrometry, and a robust and fast assay for the qualitative and quantitative analysis of theobromine in equine urine samples was validated. Urine specimens were extracted by means of solid-phase extraction cartridges, and concentrated extracts were analyzed by liquid chromatography interfaced to a triple-quadrupole mass spectrometer. In addition, the dissociation behavior of deuterated analogues to caffeine and theobromine allowed proposals for fragmentation routes of xanthine derivatives after atmospheric pressure ionization and collisionally activated dissociation. Copyright © 2004 John Wiley & Sons, Ltd. [source]