New Analogs of Polyamine Toxins from Spiders and Wasps: Liquid Phase Fragment Synthesis and Evaluation of Antiproliferative Activity

Polyamine toxins (PATs) are conjugates of polyamines (PAs) with lipophilic carboxylic acids, which have been recently shown to present antiproliferative activity. Ten analogs of the spider PATs Agel 416, HO-416b, and JSTX-3 and the wasp PAT PhTX-433 were synthesized with changes in the lipophilic head group and/or the PA chain, and their antiproliferative activity was evaluated on MCF-7 and MDA-MB-231 breast cancer cells, using Agel 416 and HO-416b as reference compounds. All five analogs of PhTX-433 were of very low activity on both cell lines, whereas the two analogs of JSTX-3 were highly active only on the MCF-7 cell line with IC₅₀ values of 2.63–2.81 μΜ. Of the remaining three Agel 416 or HO-416b analogs, only the one with the spermidine chain was highly active on both cells with IC₅₀ values of 3.15–12.6 μM. The two most potent compounds in this series, Agel 416 and HO-416b, with IC₅₀ values of 0.09–3.98 μΜ for both cell lines, were found to have a very weak cytotoxic effect on the MCF-12A normal breast cells. The present study points out that the structure of both the head group and the PA chain determine the strength of the antiproliferative activity of PATs and their selectivity towards different cells.     

Single-Step Hydrolysis and Derivatization of Homocysteine Thiolactone Using Zone Fluidics: Simultaneous Analysis of Mixtures with Homocysteine Following Separation by Fluorosurfactant-Modified Gold Nanoparticles

Herein, we report a new automated flow method based on zone fluidics for the simultaneous determination of homocysteine and homocysteine thiolactone using fluorimetric detection (λ_ext = 370 nm/λ_em = 480 nm). Homocysteine thiolactone is hydrolyzed on-line in alkaline medium (1 mol L⁻¹ NaOH) to yield homocysteine, followed by reaction with o-phthalaldehyde in a single step. Derivatization is rapid without the need of elevated temperatures and stopped-flow steps, while specificity is achieved through a unique reaction mechanism in the absence of nucleophilic compounds. Mixtures of the analytes can be analyzed quantitatively after specific separation with fluorosurfactant-capped gold nanoparticles that are selectively aggregated by homocysteine, leaving the thiolactone analogue in solution. As low as 100 nmol L⁻¹ of the analyte(s) can be quantified in aqueous solutions, while concentrations > 2 μmol L⁻¹ can be analyzed in artificial and real urine matrix following 20-fold dilution. The percent recoveries ranged between 87 and 119%.     

Smectic Mesophases from Dihydroxy Derivatives of Quaternary Alkylammonium Salts

Long alkyl-chain quaternary ammonium salts bearing two hydroxyethyl groups at the polar head group form smectic A mesophases at high temperatures and ordered smectic T mesophases of tetragonal symmetry at lower temperatures. The latter phase resembles a supermolecular grid (figure); it is formed by a hydrogen-bonding network between the hydroxy groups themselves on the one hand, and between the hydroxy groups and the bromide anions on the other, which is perfectly congruous with the tetragonal packing of the quaternary ammonium groups.     

Dynamic scheduling in multiclass queueing networks: Stability under discrete-review policies

This paper describes a family of discrete-review policies for scheduling open multiclass queueing networks. Each of the policies in the family is derived from what we call a dynamic reward function: such a function associates with each queue length vector q and each job class k a positive value r _k (q), which is treated as a reward rate for time devoted to processing class k jobs. Assuming that each station has a traffic intensity parameter less than one, all policies in the family considered are shown to be stable. In such a policy, system status is reviewed at discrete points in time, and at each such point the controller formulates a processing plan for the next review period, based on the queue length vector observed. Stability is proved by combining elementary large deviations theory with an analysis of an associated fluid control problem. These results are extended to systems with class dependent setup times as well as systems with alternate routing and admission control capabilities. This revised version was published online in June 2006 with corrections to the Cover Date.     

Study of polystyrene-poly(tert-butyl acrylate) heteroarm star copolymers in dilute solutions

Heteroarm star copolymers with polystyrene and poly(tert-butyl acrylate) arms are studied in dilute solutions by means of viscometry and static light scattering. In a weakly selective solvent a segregated-nonsegregated conformational transition is observed induced by temperature change. In a strongly selective solvent association phenomena take place and the heteroarm star molecules form multimolecular micelles.     

Design of “smart” segmented polymers by incorporating random copolymers as building blocks

This article is dealing with the design of novel segmented polymers comprising homopolymer and random copolymer building blocks designated as block-random. This type of polymeric materials can be prepared through macromolecular engineering by using controlled polymerization methods. By replacing a homopolymer block with a random one, in block copolymer topologies, further tuning of the copolymer properties can be achieved. The present article highlights the recent developments on block-random segmented macromolecules, bearing building blocks of tunable properties (e.g. thermo-sensitivity (LCST), hydrophobicity) and exhibiting responsive behavior in aqueous environments. Furthermore, preliminary novel results regarding pH-sensitive segmented macromolecules of various topologies, bearing random polyampholyte blocks among others, are also demonstrated and discussed.     

Light and heavy dansyl reporter groups in food chemistry: amino acid assay in beverages

5‐Dimethylamino‐1‐sulfonyl naphthalene (DNS, commonly referred as dansyl) is a functionality, bearing well‐established properties in directing the fragmentation, by mass spectrometry (MS), of the corresponding ionized sulfonylated derivatives. This property is shared also by its labeled analogs. The use of d₀/d₆ DNS derivatives is now exploited in the application of the well‐established isotope dilution mass spectrometric approach in the assay of complex mixtures. A new method for the quantitation of amino acids (AAs) in beverages is therefore presented, which relies on liquid chromatographic separation of their N‐dansylated derivatives followed by comparative electrospray tandem MS/MS of the d₀/d₆ isobaric mixtures. Labeled and unlabeled DNS derivatives of the selected AAs are readily available by microwave‐assisted synthetic protocols. The novelty of the method is represented by the use of heavy and light DNS‐isotopologue providing suitable reporter groups. Multiple‐reaction monitoring has been applied in the assay of AAs in wine, pineapple juice and bergamot juice with good‐to‐excellent results as proved by both relative standard deviation, lower than 15%, and by the accuracy values in the range 90–110%. Copyright © 2012 John Wiley & Sons, Ltd.     

Invariant measures for skew products and uniformly distributed sequences

??Almost all?? sequences (r ₁, . . . , r _n , . . . ) of positive integers have the following ??universal?? property: Whenever (X,???) is a Borel probability compact metric space, and ?? ₁, ?? ₂, . . . , ?? _n , . . . a sequence of commuting measure preserving continuous maps on (X,???), such that the action (by composition) on (X,???) of the semigroup with generators ?? ₁, . . . ,?? _n , . . . is uniquely ergodic and equicontinuous, then for every ${x \in X}$ the sequence w ₁,w ₂, . . . , w _n , . . . where $$w_n:=\varPhi_{r_n}(\varPhi_{r_{n-1}}(\ldots(\varPhi_{r_2}(\varPhi_{r_1}(x)))\ldots))$$ is uniformly distributed for???. This is a contribution to Problem 116 of Schreier and Ulam in the Scottish Book.     

Surface tension-induced gel fracture. Part 1. Fracture of agar gels

This work involves an experimental investigation of the spreading of liquids on gel layers in the presence of surfactants. Of primary interest is the instability that accompanies the cracking of gels through the deposition and subsequent spreading of a drop of surfactant solution on their surfaces. This instability manifests itself via the shaping of crack-like spreading "arms", in formations that resemble starbursts. The main aim of this study is to elucidate the complex interactions between spreading surfactants and underlying gels and to achieve a fundamental understanding of the mechanism behind the observed phenomenon of the cracking pattern formation. By spreading SDS and Silwet L-77 surfactant solutions on the surfaces of agar gels, the different ways that system parameters such as the surfactant chemistry and concentration and the gel strength can affect the morphology and dynamics of the starburst patterns are explored. The crack propagation dynamics is fitted to a power law by measuring the temporal evolution of the length of the spreading arms that form each one of the observed patterns. The values of the exponent of the power law are within the predicted limits for Marangoni-driven spreading on thick layers. Therefore, Marangoni stresses, induced by surface tension gradients between the spreading surfactant and the underlying gel layer, are identified to be the main driving force behind these phenomena, whereas gravitational forces were also found to play an important role. A mechanism that involves the "unzipping" of the gel in a manner perpendicular to the direction of the largest surface tension gradient is proposed. This mechanism highlights the important role of the width of the arms in the process; it is demonstrated that a cracking pattern is formed only within the experimental conditions that allow S/Δw to be greater than G', where S is the spreading coefficient, Δw is the change in the width of the crack, and G' is the storage modulus of the substrate.     

Cognitive styles,task presentation mode and mathematical performance

This paper reports the outcomes of an empirical study undertaken to investigate the relationship of prospective teachers’ cognitive styles and levels of performance in measurement and spatial tasks. A total of 116 prospective kindergarten school teachers were tested using the VICS and the extended CSA-WA tests (Peterson 2005) in order to place them along the Verbal/Imagery and the Wholistic/Analytic cognitive style continua. The same prospective teachers were also administered a mathematical test with 6 measurement and 6 spatial tasks. The results suggest that there were no significant differences between Verbalisers-Imagers and Wholistic-Analytic prospective teachers in their performance on the spatial pictorial and textual tasks, and on the measurement textual tasks. However, there were differences between Verbalisers-Imagers and Wholistic-Analytic prospective teachers in their performance on the measurement pictorial tasks. This difference was attributed to the performance of low achievers. High achievers performed in the same way independently of their cognitive styles.