Cascade of coil-globule conformational transitions of single flexible polyelectrolyte molecules in poor solvent

We show that hydrophobic flexible polyelectrolyte molecules of poly(2-vinylpyridine) and poly(methacryloyloxyethyl dimethylbenzylammonium chloride) are trapped and frozen due to adsorption on the mica surface, and the observed AFM single molecule structures reflect the molecular conformation in solution. An increase of the ionic strength of the solution induces the cascade of abrupt conformational transitions due to the intrachain segregation from elongated coil to compact globule conformations through intermediate pearl necklace-globule conformations with different amounts of beads per chain. The length of the necklaces and the number of beads decrease, while the diameter of beads increases with the increase of ionic strength. Coexistence at the same time of extended coils, necklaces with different amounts of beads, and compact globules indicates the cascade of the first-order-type phase transitions.     

Selective quantification of doxycycline in human plasma and urine with optimised chromatography

Summary A method for the selective quantification of doxycycline in human plasma and urine has been developed using HPLC with UV-detection at 350 nm. Analyte and internal standard were extracted from plasma by extraction columns filled with octadecylsilica. Urines were only mixed with diluted acid prio to injection. The influence of pH on peak shapes is discussed as well as comparative investigations on selectivity and peak symmetry on commerical octadecylsilica. The method was successfully applied to the samples of a clinical study with an oral single dose of 100 mg. Precision and accuracydata of the assay and calculated pharmacokinetic parameters are presented.     

Über Blei(II)-oxid- und -hydroxidchloride

Inhaltsübersicht. Bei der Reaktion von tetragonalem Blei(II)-oxid in wäßriger Suspension mit Calciumchlorid oder mit Ammoniumchlorid lassen sich für molare Verhältnisse Cl^–/PbO bis zu 4/1 nur drei kristalline basische Blei(II)-chloride in der festen Phase mit den Pb/Cl-Verhältnissen von 3,5, 2,0 bzw. 1,0 nachweisen. Lead(II) Oxide and Hydroxide Chloride Abstract. In the reaction between tetragonal lead(II) oxide in aqueous suspension and calcium chloride, or ammonium chloride, and for molar ratios of Cl^–/PbO up to 4/1 only three kinds of crystalline basic lead chlorides are detectable in the solid phase with Pb/Cl ratios of 3.5, 2.0 and 1.0, respectively.     

New Chiral Polyurethane Polymers Based on Functionalized Cyclotriphosphazenes

Abstract

Novel hybrid polymers using chiral phosphaznes were prepared in the following way: Starting from hexachlorocyclofriphosphazene, N₃,P₃,Cl₆, chelating phenolates were introduced by reaction with the corresponding sodium salt. Thus, reaction with two equivalents of atropisomeric binaphtolate yields chiral lb in high yield. Subsequently, p-methoxyphenolates were reacted with the remaining PCl₂, functionality and the p-MeO groups were converted to hydroxy groups [I] to give bifunctional 2a,b. Finally, polyadditions to diisocyanates lead to new cyclolinear polyurethanes 3a,b which were characterized by thermal analysis [2,3]. The T₁₀, is 320 and 240°C for 3a and 3b respectively. In particular, the chifal polymer 3b [α=lll°] may have interesting properties as catalyst support.     

Complexation Studies of Phosphorus Containing Bis and Tris (Benzocrown Ether) Moieties

The complexation behaviour between salts of Li⁺-Rb⁺ in CD₃CN and tris(benzocrown ether)s 2a,bX=P(NMeN=CH-B15C5)₃ (X = O, S) and tri[bis(benzocrown ether)][N=P(NMeN=CH-B15C5)₂]₃ 3 was investigated by ¹³ C NMR spectroscopy. Using the program RMNSTAB, the complexation constants for the different possible complexes (M₂L, ML andML₂ were L represents one benzo-15-crown-5) were obtained and were compared with those of the corresponding monomer material. A remarkable ``biscrown effect' for compounds 2a,b and 3 was found, especially for potassium and rubidium by the predominant formation of stable ML₂ complexes. The strong chelate effect make these ligands highly efficient extracting agents for alkali metal picrate salts of K⁺, Rb⁺ and Cs⁺,as shown by UV-Vis spectroscopy.     

Seabird satellite tracking validates the use of latitudinal isoscapes to depict predators' foraging areas in the Southern Ocean

Stable isotopes are increasingly being used to trace wildlife movements. A fundamental prerequisite of animal isotopic tracking is a good knowledge of spatial isotopic variations in the environment. Few accessible reference maps of the isotopic landscape ("isoscapes") are available for marine predators. Here, we validate for the first time an isotopic gradient for higher trophic levels by using a unique combination of a large number of satellite-tracks and subsequent blood plasma isotopic signatures from a wide-ranging oceanic predator. The plasma δ(13)C and δ(15)N values of wandering albatrosses (n = 45) were highly and positively correlated to the Southern Ocean latitudes at which the satellite-tracked individuals foraged. The well-defined latitudinal baseline carbon isoscapes in the Southern Ocean is thus reflected in the tissue of consumers, but with a positive shift due to the cumulative effect of a slight (13)C-enrichment at each trophic level. The data allowed us to estimate the carbon isotopic position of the main oceanic fronts in the area, and thus to delineate robust isoscapes of the main foraging zones for top predators. The plasma δ(13)C and δ(15)N values were positively and linearly correlated, thus suggesting that latitudinal isoscapes also occur for δ(15)N at the base of the food web in oceanic waters of the Southern Ocean. The combination of device deployments with sampling of relevant tissues for isotopic analysis appears to be a powerful tool for investigating consumers' isoscapes at various spatio-temporal scales.