Facile synthesis of @-tide beta-strand peptidomimetics: improved assembly in solution and on solid phase

The synthesis of @-tide beta-strand peptidomimetics has been improved such that oligomers now can be obtained from solution- and solid-phase synthesis protocols approaching the efficiency and flexibility of peptide chemistry. These methods enable the synthesis of @-tide oligomers with a variety of amino acids and with lengths up to 13 units. [reaction: see text]     

The quickest flow problem

Consider a network =(G, c, ) whereG=(N, A) is a directed graph andc _ij and _ij , respectively, denote the capacity and the transmission time of arc (i, j) A. The quickest flow problem is then to determine for a given value the minimum numberT() of time units that are necessary to transmit (send) units of flow in from a given sources to a given sinks.In this paper we show that the quickest flow problem is closely related to the maximum dynamic flow problem and to linear fractional programming problems. Based on these relationships we develop several polynomial algorithms and a strongly polynomial algorithm for the quickest flow problem.Finally we report computational results on the practical behaviour of our metholds. It turns out that some of them are practically very efficient and well-suited for solving large problem instances.Partial financial support by the Air Force Office of Scientific Research under grants AFOSR-89-0512 and AFOSR-90-0008 is gratefully acknowledged by the first author.     

A study on thorium levels in human femur bones

The incorporation of naturally occurring thorium isotopes in human femur bones was studied by analyzing 28 bone samples. The results show that the activity concentrations of ²³²Th and ²³⁰Th are in the range of the blank values resulting in an upper limit of theirs activity concentrations in human bones. The presence of ²²⁸Th can be attributed, on the basis of model calculations, to the radioactive decay of deposited ²²⁸Ra. We conclude that thorium is not detectably incorporated into human bones.     

Sugar–Edge Interactions in a DNA–RNA G‐Quadruplex: Evidence of Sequential C−H⋅⋅⋅O Hydrogen Bonds Contributing to RNA Quadruplex Folding

DNA G‐quadruplexes were systematically modified by single riboguanosine (rG) substitutions at anti‐dG positions. Circular dichroism and NMR experiments confirmed the conservation of the native quadruplex topology for most of the DNA–RNA hybrid structures. Changes in the C8 NMR chemical shift of guanosines following rG substitution at their 3′‐side within the quadruplex core strongly suggest the presence of C8?H???O hydrogen‐bonding interactions with the O2′ position of the C2′‐endo ribonucleotide. A geometric analysis of reported high‐resolution structures indicates that such interactions are a more general feature in RNA quadruplexes and may contribute to the observed preference for parallel topologies.     

On minimum weight pseudo-triangulations

In this note we discuss some structural properties of minimum weight pseudo-triangulations of point sets.     

Adsorption of poly(N‐ethyl‐4‐vinyl pyridinium bromide) onto langmuir‐blodgett films built up from amphiphilic polymers

The interaction of a strong cationic polyelectrolyte, poly(N‐ethyl‐4‐vinyl pyridinium bromide), with Langmuir‐Blodgett (LB) films built up from four monolayers of amphiphilic derivatives of the alternating copolymers of maleic acid and alkenes (one of the monolayers was formed by the amphiphilic copolymer containing pyrenyl groups as fluorescent labels) was examined. Transformations of absorbance spectra and quenching of fluorescence of the LB films were detected after their contact with aqueous solutions of the cationic polyelectrolyte. These changes were attributed to the adsorption of poly(N‐ethyl‐4‐vinyl pyridinium bromide) onto such films. The efficiency of this process was found to be rather sensitive to the variations in pH of the surrounding medium: adsorption of the cationic polyelectrolyte onto the LB films was pronounced in basic media while it became rather weak in acidic media.     

The Quillen categories of <Emphasis Type="Italic">p</Emphasis>-groups and coclass theory

Coclass theory can be used to define infinite families of finite p-groups of a fixed coclass. It is conjectured that the groups in one of these infinite families all have isomorphic mod-p cohomology rings. Here we prove that almost all groups in one of these infinite families have equivalent Quillen categories. We also show how the Quillen categories of the groups in an infinite family are connected to the Quillen category of their associated infinite pro-p-group of finite coclass.