Buchbesprechungen

Ohne Zusammenfassung     

Trennung des Galliums von dreiwertigem Eisen mittels Ionenaustausches

Zusammenfassung Es wurde eine einfache, quantitative Trennung von Mikrogrammmengen Gallium von der bis zum Tausendfachen betragenden Menge Eisen durch Ionenaustausch-Chromatographie am stark basischen Anionenaustauscher Amberlite I. R. A.-400 ausgearbeitet. Die Methode beruht auf der unterschiedlichen Stabilität und Wanderungsgeschwindigkeit der Bhodanidkomplexe dieser Elemente bei ihrer Elution mit 0,1-n Salzsäure, wobei das Gallium vor dem Eisen ins Eluat übergeht.

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Summary A new method was developed for a simple quantitative separation of microgram quantities of gallium from amounts of iron a thousand times as great. The method is based on ion exchange chromatography on strongly basic anion exchanger Amberlite I. R. A.-400. The basis of the method is the divergent stability and migration velocity of the thiocyanate complexes of these elements when eluted with 0.1 N hydrochloric acid. The gallium precedes the iron in the eluate.

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Résumé Mise au point d'une séparation simple et quantitative de masses de gallium de l'ordre de grandeur du microgramme de masses de fer pouvant être mille fois plus élevées, par chromatographie par échange d'ions. On emploie à cette fin un échangeur d'anions fortement basique: l'amberlite I. R. A.-400. Le principe de la méthode repose sur les différences de stabilité et de vitesse de migration des suifocyanures complexes de ces éléments lors de leur élution par l'acide chlorhydrique 0, l N: le gallium passe en effet dans l'éluat avant le fer.

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Herrn Prof. Dr.Robert Strebinger zum 70. Geburtstag gewidmet.     

The effect of macromolecular architecture in nanomaterials: a comparison of site isolation in porphyrin core dendrimers and their isomeric linear analogues

The influence of macromolecular architecture on the physical properties of polymeric materials has been studied by comparing poly(benzyl ether) dendrons with their exact linear analogues. The results clearly confirm the anticipation that dendrimers are unique when compared to other architectures. Physical properties, from hydrodynamic volume to crystallinity, were shown to be different, and in a comparative study of core encapsulation in macromolecules of different architecture, energy transduction from the polymer backbone to a porphyrin core was shown to be different for dendrimers as compared to that of isomeric four- or eight-arm star polymers. Fluorescence excitation revealed strong, morphology dependent intramolecular energy transfer in the three macromolecular isomers investigated. Even at high generations, the dendrimers exhibited the most efficient energy transfer, thereby indicating that the dendritic architecture affords superior site isolation to the central porphyrin it surrounds.     

A new perspective on beta-sheet structures using vibrational Raman optical activity: from poly(L-lysine) to the prion protein

The vibrational Raman optical activity (ROA) spectrum of a polypeptide in a model beta-sheet conformation, that of poly(l-lysine), was measured for the first time, and the alpha-helix --> beta-sheet transition monitored as a function of temperature in H(2)O and D(2)O. Although no significant population of a disordered backbone state was detected at intermediate temperatures, some side chain bands not present in either the alpha-helix or beta-sheet state were observed. The observation of ROA bands in the extended amide III region assigned to beta-turns suggests that, under our experimental conditions, beta-sheet poly(L-lysine) contains up-and-down antiparallel beta-sheets based on the hairpin motif. The ROA spectrum of beta-sheet poly(L-lysine) was compared with ROA data on a number of native proteins containing different types of beta-sheet. Amide I and amide II ROA band patterns observed in beta-sheet poly(L-lysine) are different from those observed in typical beta-sheet proteins and may be characteristic of an extended flat multistranded beta-sheet, which is unlike the more irregular and twisted beta-sheet found in most proteins. However, a reduced isoform of the truncated ovine prion protein PrP(94-233) that is rich in beta-sheet shows amide I and amide II ROA bands similar to those of beta-sheet poly(L-lysine), which suggests that the C-terminal domain of the prion protein is able to support unusually flat beta-sheets. A principal component analysis (PCA) that identifies protein structural types from ROA band patterns provides a useful representation of the structural relationships among the polypeptide and protein states considered in the study.     

A study of alpha-helix hydration in polypeptides, proteins, and viruses using vibrational raman optical activity

A vibrational Raman optical activity (ROA) study, supplemented by protein X-ray crystal structure data, of alpha-helices in polypeptides, proteins, and viruses has suggested that ROA bands in the extended amide III spectral region may be used to distinguish between two types of right-handed alpha-helix. One type, associated with a positive ROA band at approximately 1300 cm(-1), dominates in hydrophobic environments and appears to be unhydrated; the other, associated with a positive ROA band at approximately 1340 cm(-1), dominates in hydrophilic environments and appears to be hydrated. Evidence is presented to support the hypothesis that unhydrated alpha-helix corresponds to the canonical conformation alpha(c) and hydrated alpha-helix to a more open conformation alpha(o) stabilized by hydrogen bonding of a water molecule or a hydrophilic side chain to the peptide carbonyl. Alpha-helical poly(L-lysine) and poly(L-ornithine) in aqueous solution and poly(L-alanine) in dichloracetic acid display both bands, but alpha-helical poly(l-glutamic acid) in aqueous solution and poly(gamma-benzyl L-glutamate) in CHCl(3) display only the approximately 1340 cm(-1) band and so may exist purely as alpha(o) due to enhanced stabilization of this conformation by particular side chain characteristics. The ROA spectrum of poly(beta-benzyl L-aspartate) in CHCl(3) reveals that it exists in a single left-handed alpha-helical state more analogous to alpha(o) than to alpha(c).