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Vancomycin as a chiral selector in capillary electrophoresis: an appraisal of advantages and limitations

The properties of the macrocyclic antibiotic vancomycin, used as a chiral selector, were studied with aminoquinolycarbamate derivatives of amino acids, containing sulfur and selenium, as well as with other organic ions. Vancomycin combines the ability to resolve fully ionized anionic enantiomers, typical of proteins, with excellent separation efficiency, exceeding that of cyclodextrins. It allows better than baseline chiral separations of several anionic analytes within 3-5 min. The resolving power of vancomycin results from its great skill in discriminating enantiomers rather than from high affinities to the separated enantiomers. The association constants of vancomycin are of the same order of magnitude, 10(2) L/mol, as that found for beta-cyclodextrin (beta-CD). The difference in association constants of separated cystine enantiomers with vancomycin, 2 x 10(2) L/mol, is one order of magnitude higher than that of enantiomers separated with beta-CD. Analytically convenient mobility differences up to 1-2 x 10(9) m2V-1s-1, with only one of the enantiomers appreciably decelerated, are obtained at submillimolar vancomycin concentrations. Typical separation efficiencies are close to 250,000 theoretical plates per meter of capillary. Deceleration of various organic ions by millimolar vancomycin implies that chiral separations with vancomycin need not be restricted to carboxylic acids. The vancomycin-analyte interactions are strongly affected by the chemical composition and concentration of the buffer. An additional experimental variable, highly effective in manipulating the separation selectivity of analytes, is the buffer pH.     

Persisting deficits in rats "recovered" from transections of fibers which enter or leave hypothalamus laterally.

In a study with 36 female albino Sprague-Dawley rats, parasagittal knife cuts along the lateral border of the hypothalamus which transected most of the fibers that enter or leave the hypothalamus laterally reproduced the full spectrum of effects on food intake seen after lateral hypothalamic lesions. Ss were aphagic and adipsic for weeks or months and remained unresponsive to physiological signals that normally regulate feeding and drinking, even after voluntary ingestive behavior returned. Ss did not respond to insulin or 2-deoxy-D-glucose treatments (which decrease blood sugar or glucose utilization) and showed only a small increase in intake when exposed to low environmental temperatures. Food consumption appeared to be governed primarily by the palatability of the diet. Ss also did not respond to NaCl or polyethylene glycol treatments (which result in cellular dehydration or extracellular hypovolemia) and returned to a state of adipsia when food was removed. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dämpfen von Rundholz.—Erste Mitteilung: Papierchromatographische Untersuchungen an Dämpfkondensaten von Rotbuche

Ohne Zusammenfassung Mitteilung aus dem Forschungsinstitut für Holzwerkstoffe und Holzleime.     

Step-growth polymerization and ‘click’ chemistry: The oldest polymers rejuvenated

Since its discovery in 2001, copper catalyzed azide-alkyne ‘click’ chemistry has been extensively used in polymer chemistry to modify polymeric materials and create advanced polymer structures by efficient coupling reactions. Surprisingly, the contribution of this Huisgen cycloaddition reaction to industrially important commodity polymers, prepared by step-growth polymerization, was not existing until recently. Nevertheless, since many decades academic and industrial research was focused on finding attractive synthetic pathways to introduce large contents of different reactive functional groups in several polymer classes such as polyesters and polyurethanes. Because of the high tolerance of azide-alkyne coupling reactions to a wide variety of functional groups and to extreme reaction conditions often used in step-growth polymerizations, the straightforward synthesis of alkyne-containing building blocks created an ideal platform to modify and broaden the physico-chemical properties of step-growth polymers by choosing readily available low and high molecular weight azide components. This feature article provides a comprehensive review covering the strategies toward ‘click’-functionalization of several classes of industrially important step-growth polymers.     

A study of the microstructural evolution during selective laser melting of Ti–6Al–4V

Selective laser melting (SLM) is an additive manufacturing technique in which functional, complex parts can be created directly by selectively melting layers of powder. This process is characterized by highly localized high heat inputs during very short interaction times and will therefore significantly affect the microstructure. In this research, the development of the microstructure of the Ti–6Al–4V alloy processed by SLM and the influence of the scanning parameters and scanning strategy on this microstructure are studied by light optical microscopy. The martensitic phase is present, and due to the occurrence of epitaxial growth, elongated grains emerge. The direction of these grains is directly related to the process parameters. At high heat inputs it was also found that the intermetallic phase Ti₃Al is precipitated during the process.     

Control of human aggression: A comparative perspective.

Recent animal research has demonstrated that humans are not a uniquely aggressive species and that even in so-called violence-prone animals, aggression is always an optional strategy. Although some form of intraspecific aggression exists in every vertebrate species studied thus far, it is also true that all organisms have coevolved equally potent inhibitory mechanisms that enable them to use an aggressive strategy selectively or to suppress aggression when it is in their interest to do so. Parallel studies of aggression in children, assaultive adults, and even entire societies have suggested that humans are exquisitely sensitive to subtle social controls that could be used to reduce the frequency of individual acts of violence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)