Effects of magnetic atoms on the properties of ternary superconductors

Conclusion It is noteworthy that while only two classes of systems (the Chevrel phases and the rare-earth rhodium borides) have so far received extensive study, nonetheless a great many new phenomena have been encountered. This, however, should only be considered the beginning of a new and potentially very rich field, especially if one considers the vast number of possibilities of ternary compounds that can be produced. To take only one other example, recent work has shown that the compound Sc₂Fe₃Si₅ is superconducting with a superconducting transition of 4.5 K (29). This at first may appear surprising since ever in the Chevrel phase materials, the addition of Fe atoms is detrimental to superconductivity. However, recent Mossbauer effect experiments (29) have shown that the Fe in this material is not magnetic, having a magnetic moment of less than 0.03 µ_B. These silicides have also been made with rare-earth ions in place of the Sc(²⁸). The compounds show magnetic transitions and are currently under investigation. Several other interesting systems have been synthesized, and it appears that many more will be coming in the near future. The results reported above have shown the utility of hyperfine data in clarifying many of the new phenomena that occur, and it should be expected that as this new field grouws, these kinds of measurements will continue to play an active role (30).     

1,2,4-Triazoles—XXXI: Photodimerization of s-triazoleo[4,3-a]pyridines: formation of cyclobutane dimers

Irradiation of several methyl substituted s-triazolo[4,3-a]-pyridines and 3-hydroxy-s-triazolo[4,3-a]pyridines with UV light gave thermally labile cyclobutane photodimers by dimerization of the 5,6-double bond in one molecule with the 7,8-double bond in another.     

β-d-Xylosidase from Selenomonas ruminantium of glycoside hydrolase family 43

Beta-D-xylosidase from the ruminal anaerobic bacterium, Selenomonas ruminantium (SXA), catalyzes hydrolysis of beta-1,4-xylooligosacharides and has potential utility in saccharification processes. The enzyme, heterologously produced in Escherichia coli and purified to homogeneity, has an isoelectric point of approx 4.4, an intact N terminus, and a Stokes radius that defines a homotetramer. SXA denatures between pH 4.0 and 4.3 at 25 degrees C and between 50 and 60 degrees C at pH 5.3. Following heat or acid treatment, partially inactivated SXA exhibits lower k(cat) values, but similar K(m) values as untreated SXA. D-glucose and D-xylose protect SXA from inactivation at high temperature and low pH.     

pH-responsive aggregates from double hydrophilic block copolymers carrying zwitterionic groups. Encapsulation of antiparasitic compounds for the treatment of leishmaniasis

A series of well-defined poly[(ethylene oxide)-b-2-(dimethylamino)ethyl methacrylate] (PEO-b-PDMAEMA) diblock copolymers were synthesized by atom transfer radical polymerization (ATRP) techniques. Post-polymerization reactions were performed to transform a portion of the tertiary amine groups of the PDMAEpsilonMA into phosphorozwitterions. The aggregation behavior of the prepared zwitterionic block copolymers was investigated by static and dynamic light scattering techniques at 25 and 37 degrees C, in weakly basic and acidic aqueous solutions. Antiparasitic drugs used for the treatment of Leishmania were incorporated into the copolymer aggregates. The effect of the solution pH, the zwitterion content, temperature, and the quantity of the incorporated drug on the aggregation behavior of the copolymers was tested.     

Interaction between explosive and analyte layers in explosive matrix-assisted plasma desorption mass spectrometry

An HMX/insulin two-layer system was chosen as a model for further investigation of the matrix properties of explosive materials for protein analytes in plasma desorption mass spectrometry. The dependencies of the molecular ion yield and average charge state as a function of the analyte thickness were studied. An increase in the charge state of multiply protonated molecular species was confirmed as the major matrix effect, with the average charge state z at the smallest thickness studied being higher than in matrix-assisted laser desorption/ionization and closer to the value obtained in electrospray ionization under standard acidic conditions. Observed charge state distributions are significantly narrower than the corresponding Poisson distributions, which suggests that the protonation of insulin is limited in plasma desorption by the number of basic sites in the molecule, similar to electrospray ionization. Both the curve displaying total molecular ion yield and the one showing the total charge (proton) yield as a function of the insulin thickness have maxima at a thickness different from an insulin monolayer. These observations diminish the significance of a matrix/analyte interface mechanism for the explosive matrix assistance. Instead, a mechanism related to the chemical energy release during conversion of the explosive after the ion impact is proposed. As additional mechanisms, enhanced protonation of the analyte through collisions with products of the explosive decay is considered, as well as electron scavenging by other products, which leads to a higher survival probability of positively charged protein molecular ions. Copyright 1999 John Wiley & Sons, Ltd.     

Preparation of nanocrystalline metal hydrides by ball milling

The diffusion of hydrogen into metals during ball milling has been investigated. A system is described that enables the milling to be done under approximately constant hydrogen pressure and allows for the continuous measurement of the quantity of hydrogen absorbed. This method has been used to prepare nanocrystalline hydrides of a variety of early transition metals and alloys. X-ray diffraction studies are used to identify phases present before and after milling and the width of diffraction peaks is used to estimate average grain size. Changes in the microstructure of Fe-containing samples during hydrogen absorption have been investigated by Mössbauer effect. Studies of the influence of milling conditions and the effect of milling time are also presented.