Butter, Speisefette und ?le

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Allgemeine Bestandteile der Nahrungs- und Genu?mittel

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Allgemeine analytische Methoden und Apparate

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Wein

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Studies of the esterification of dextran: routes to bioactive polymers and graft copolymers

Problems associated with the esterification of dextran as a means of coupling bioactive molecules or introduction of functionality suitable for graft polymerization are considered. In particular, the importance of eliminating side-reactions which incorporate into dextran unwanted residues, e.g. groups containing nitrogen, is emphasized and practical techniques for minimizing this are described. We have developed a formamide-based solvent suitable for esterification with the aid of dicyclohexyl carbodiimide (DCC) and carbonyl di-imidazole (CDI) as coupling agents. The preferred catalyst is p-pyrrolidinopyridine. CDI has the advantage of enabling dimethylsulphoxide to be used as solvent for dextran and other hydroxylic polymers without inducing oxidation of hydroxyl groups. This coupling agent is flexible and offers a choice of two routes to esterification, each having its merits. We have optimized conditions for coupling by use of butyric acid as model. Esterification of dextran has been employed in the preparation of soluble bioactive macromolecules by coupling the anti-platelet agent (I) and also in the synthesis of graft copolymers via introduction of 2-bromopropionate groups. Crosslinking of dextran and the polymerization of dipyridamole have been effected by use of CDI.     

The mechanisms of collisional activation of ions in mass spectrometry

This article is a review of the mechanisms responsible for collisional activation of ions in mass spectrometers. Part I gives a general introduction to the processes occurring when a projectile ion and neutral target collide. The theoretical background to the physical phenomena of curve‐crossing excitation (for electronic and vibrational excitation), impulsive collisions (for direct translational to vibrational energy transfer), and the formation of long‐lived collision intermediates is presented. Part II highlights the experimental and computational investigations that have been made into collisional activation for four experimental conditions: high (>100 eV) and intermediate (1–100 eV) center‐of‐mass collision energies, slow heating collisions (multiple low‐energy collisions) and collisions with surfaces. The emphasis in this section is on the derived post‐collision internal energy distributions that have been found to be typical for projectile ions undergoing collisions in these regimes. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 28:608–639, 2009     

Mehle und Backwaren

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