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Inelastic neutron scattering study of multimagnon states in the 1-D-ferromagnet CsNiF3

Two theoretical propositions concerning scattering from higher-order-spin-wave processes have been tested by means of neutron scattering. The so-called “second magnon” scattering could not be observed as such, and an upper limit for its intensity relative to the single-spin-wave scattering is given. Experimental evidence for the scattering from the simultaneous creation of two spin waves has been observed. The results are compared with the corresponding theories.     

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Book reviews

     

Rotational bands in the proton emitter (141)Ho

Rotational bands feeding the ground state and the isomeric state in the proton emitter (141)Ho were observed using the recoil-decay tagging method. This constitutes direct evidence that (141)Ho is deformed. A quadrupole deformation of beta(2) = 0.25(4) was deduced for the ground state from the extracted dynamic moment of inertia. Based on observed band crossings and signature splittings the 7/2(-)[523] and 1/2(+)[411] configurations were proposed for the ground state and the isomeric state, respectively. Comparison with particle-rotor calculations for beta(2) = 0.25 indicates, however, that (141)Ho may have significant hexadecapole deformation and could be triaxial in the 7/2(-)[523] ground state.     

Redox modification of proteins using sequential-parallel electrochemistry in microtiter plates

Redox modification of proteins has frequently been used to improve the electron-transfer properties in amperometric biosensors. One approach is the coordinative labelling of histidine residues with metal complexes like [Ru(bpy)2Cl2] and [Ru(bpy)2CO3]. Although the reaction depends on a variety of parameters no detailed optimisation of these modification procedures has been done, most probably due to the complexity of the parameter matrix and the expected differences for any individual protein. A multi electrode sequential analyser (MESA) system has been developed which allows one to follow in a sequential-parallel scheme a number of modification reactions by performing electrochemical measurements such as cyclic voltammetry or differential pulse voltammetry in individual wells of a conventional microtiter plate. Using this system, the ligand exchange reaction leading to the binding of the Ru-complex to histidine residues could be investigated with imidazole as a model compound. Furthermore, the selective labelling of soluble PQQ (pyrrolochinolinquinone)-dependent glucose dehydrogenase (sGDH) and glucose oxidase (GOx) with Ru complexes could be optimised and the electrochemical and biological properties of the obtained 'electroenzymes' were examined.     

16+ spin-gap isomer in 96Cd

A β-decaying high-spin isomer in (96)Cd, with a half-life T(1/2)=0.29(-0.10)(+0.11) s, has been established in a stopped beam rare isotope spectroscopic investigations at GSI (RISING) experiment. The nuclei were produced using the fragmentation of a primary beam of (124)Xe on a (9)Be target. From the half-life and the observed γ decays in the daughter nucleus, (96)Ag, we conclude that the β-decaying state is the long predicted 16(+) "spin-gap" isomer. Shell-model calculations, using the Gross-Frenkel interaction and the πν(p(1/2),g(9/2)) model space, show that the isoscalar component of the neutron-proton interaction is essential to explain the origin of the isomer. Core excitations across the N=Z=50 gaps and the Gamow-Teller strength, B(GT) distributions have been studied via large-scale shell-model calculations using the πν(g,d,s) model space to compare with the experimental B(GT) value obtained from the half-life of the isomer.     

Optimized strategies to synthesize β-cyclodextrin-oxime conjugates as a new generation of organophosphate scavengers

A new generation of organophosphate (OP) scavengers was obtained by synthesis of β-cyclodextrin-oxime derivatives 8-12. Selective monosubstitution of β-cyclodextrin was the main difficulty in order to access these compounds, because reaction onto the oligosaccharide was closely related to the nature of the incoming group. For this purpose, non-conventional activation conditions were also evaluated. Intermediates 5 and 7 were then obtained with the better yields under ultrasounds irradiation. Finally, the desired compounds 8-10 were obtained from 5-7 in high purity by desilylation using potassium fluoride. Quaternarisation of compounds 8 and 9 was carried out. OP hydrolytic activity of compounds 8-12 was evaluated against cyclosarin (GF) and VX. None of the tested compounds was active against VX, but these five cyclodextrin derivatives detoxified GF, and the most active scavengers 10 and 11 allowed an almost complete hydrolysis of GF within 10 min. Even more fascinating is the fact that compounds 9 and 10 were able to hydrolyze enantioselectively GF.     

First observation of electrorheological plasmas

We report the experimental discovery of "electrorheological (ER) complex plasmas," where the control of the interparticle interaction by an externally applied electric field is due to distortion of the Debye spheres that surround microparticles (dust) in a plasma. We show that interactions in ER plasmas under weak ac fields are mathematically equivalent to those in conventional ER fluids. Microgravity experiments, as well as molecular dynamics simulations, show a phase transition from an isotropic to an anisotropic (string) plasma state as the electric field is increased.     

Morphological instabilities of polymer crystals

We present experimental observations at comparatively low supercooling of morphology transitions from dendritic to faceted structures in polymer crystals growing in thin films of a poly-2-vinylpyridineblock-polyethyleneoxid copolymer. Our results are compared with theoretical concepts describing morphological instabilities of single crystals. Although these concepts originally were not developed for polymers, they allow to describe and interpret our experimental results quite well. In particular, the measured temperature dependence of the width W and frequency of dendritic side branches and the radius of curvature ρ of the growth tips of the crystals follow these concepts. We present preliminary evidence for the influence of polymer attachment kinetics and reorganisation processes behind the growth front. Polymer thin films provide valuable model systems for studying general concepts of crystallisation and allow to distinguish at which point the connectivity of the crystallising units within chain-like molecules starts to play a measurable role.