Wormlike micelles mediated by polyelectrolyte

Aqueous solutions of the anionic surfactant potassium oleate (K-oleate) were studied using small-angle neutron scattering (SANS), steady-state rheology, and cryogenic transmission electron microscopy (cryo-TEM). The micellar structural changes induced by the addition of potassium chloride (KCl) and sodium polystyrenesulfonate (PSS) of different molecular weights were investigated. Upon addition of KCl, a transition from spherical to wormlike micelles was detected from the SANS data and confirmed by the cryo-TEM pictures. The rheological measurements revealed a strong dependence of the low-shear viscosity on the concentration of salt: a broad maximum in the viscosity curve was observed upon addition of KCl, characteristic of the growth of micelles into long worms, followed by branching. The addition of PSS to salt-free solutions of K-oleate had a significant effect on the scattering patterns, revealing partial growth of the spherical micelles into rodlike micelles. In contrast, in the presence of high salt concentrations, addition of PSS to solutions of wormlike micelles did not bring any noticeable modifications in the scattering. However, in the same salt conditions, a clear effect was observed on the low shear viscosity upon addition of PSS, which was found to depend significantly on molecular weight. This suggests a novel way of impacting the viscosity of solutions of wormlike micelles.     

Cis‐ and trans‐bis(2‐cyano­ethyl­sulfan­yl)(decane‐1,10‐diyldithio)tetra­thia­fulvalene

The isomeric title compounds, 2,7‐bis(2‐cyanoethylsulfanyl)‐3,6‐(decane‐1,10‐diyldithio)tetrathiafulvalene and 2,6‐bis­(2‐cyanoethylsulfanyl)‐3,7‐(decane‐1,10‐diyldithio)­tetra­thiafulvalene, both C₂₂H₂₈N₂S₈, comprise bis­(2‐cyano­ethyl­sulfan­yl)tetra­thia­fulvalene units tethered by a saturated deca­methyl­enedithio linker attached in either a cis or a trans manner. The tetra­thia­fulvalene (TTF) group is planar in the cis isomer, but distorted significantly from planarity and twisted about its long axis in the trans isomer. In both structures, inter­molecular inter­actions are segregated into regions in which TTF units are brought into close contact and regions where the polymethyl­ene chains are brought into close contact. In the cis isomer, TTF units exhibit π–π stacking inter­actions, while in the trans isomer they do not.     

Friedel-crafts polymerisations with α,α′-dimethoxy-p-xylene—I The initiation step with stannic chloride as catalyst

A white insoluble 1:1 complex is formed between stannic chloride and α,α′-dimethoxy-p-xylene (DMPX) when the Friedel-Crafts copolymerisation of DMPX and benzene is carried out in a series of solvents using stannic chloride as catalyst. As the reaction proceeds, the precipitate dissolves, being converted to a 1:1 and later a 1:2 complex of stannic chloride and methanol, the latter being a product of the reaction. The 1:1 stannic chloride:methanol complex is an active catalyst for the polymerisation while the 1:2 complex is relatively inactive. The rate of the reaction is also strongly dependent upon the dielectric constant of the medium.For these reasons, a precise quantitative investigation of the kinetics of the polymerisation will be almost impossible but experimental conditions are specified whereby a partial investigation may be made for comparison with the SnCl₄/benzene/di(chloromethyl) benzene system previously studied.     

Multifunctional Tricarbazolo Triazolophane Macrocycles: One‐Pot Preparation,Anion Binding,and Hierarchical Self‐Organization of Multilayers

Programming the synthesis and self‐assembly of molecules is a compelling strategy for the bottom‐up fabrication of ordered materials. To this end, shape‐persistent macrocycles were designed with alternating carbazoles and triazoles to program a one‐pot synthesis and to bind large anions. The macrocycles bind anions that were once considered too weak to be coordinated, such as PF₆^?, with surprisingly high affinities (β₂=10¹¹ M ^?2 in 80:20 chloroform/methanol) and positive cooperativity, α=(4 K₂/K₁)=1200. We also discovered that the macrocycles assemble into ultrathin films of hierarchically ordered tubes on graphite surfaces. The remarkable surface‐templated self‐assembly properties, as was observed by using scanning tunneling microscopy, are attributed to the complementary pairing of alternating triazoles and carbazoles inscribed into both the co‐facial and edge‐sharing seams that exist between shape‐persistent macrocycles. The multilayer assembly is also consistent with the high degree of molecular self‐association observed in solution, with self‐association constants of K=300 000 M ^?1 (chloroform/methanol 80:20). Scanning tunneling microscopy data also showed that surface assemblies readily sequester iodide anions from solution, modulating their assembly. This multifunctional macrocycle provides a foundation for materials composed of hierarchically organized and nanotubular self‐assemblies.     

A Framework for Comparative Evaluation of Dosimetric Methods to Triage a Large Population Following a Radiological Event

BACKGROUND: To prepare for a possible major radiation disaster involving large numbers of potentially exposed people, it is important to be able to rapidly and accurately triage people for treatment or not, factoring in the likely conditions and available resources. To date, planners have had to create guidelines for triage based on methods for estimating dose that are clinically available and which use evidence extrapolated from unrelated conditions. Current guidelines consequently focus on measuring clinical symptoms (e.g., time-to-vomiting), which may not be subject to the same verification of standard methods and validation processes required for governmental approval processes of new and modified procedures. Biodosimeters under development have not yet been formally approved for this use. Neither set of methods has been tested in settings involving large-scale populations at risk for exposure. OBJECTIVE: To propose a framework for comparative evaluation of methods for such triage and to evaluate biodosimetric methods that are currently recommended and new methods as they are developed. METHODS: We adapt the NIH model of scientific evaluations and sciences needed for effective translational research to apply to biodosimetry for triaging very large populations following a radiation event. We detail criteria for translating basic science about dosimetry into effective multi-stage triage of large populations and illustrate it by analyzing 3 current guidelines and 3 advanced methods for biodosimetry. CONCLUSIONS: This framework for evaluating dosimetry in large populations is a useful technique to compare the strengths and weaknesses of different dosimetry methods. It can help policy-makers and planners not only to compare the methods' strengths and weaknesses for their intended use but also to develop an integrated approach to maximize their effectiveness. It also reveals weaknesses in methods that would benefit from further research and evaluation.     

Investigation of cosmic rays and their secondaries at aircraft altitudes

A very extensive study of the radiation field at aircraft altitudes has been carried out over the last few years. These investigations formed part of a European wide collaboration involving several laboratories with extensive experience in cosmic ray research and/or dosimetry. Among the main topics investigated were the charge spectra, LET spectra, anisotropy and dose values. The measurements were performed on subsonic and supersonic flights covering a wide range of altitudes and latitudes. Several active and passive instruments were employed in these studies and some results obtained with nuclear track detectors are described here. Comparisons are made with the results of other experiments and theoretical estimates using computer codes.     

Toward Electrochemically Controllable Tristable Three‐Station [2]Catenanes

Encouraged by the prospect of producing an electrochemical, color‐switchable red–green–blue (RGB) dye compound, we have designed, synthesized, and characterized two three‐station [2]catenanes. Both are composed of macrocyclic polyethers containing three π‐electron‐rich stations, which act as recognition sites for a π‐electron‐deficient tetracationic cyclophane. The molecular structures of the two three‐station [2]catenanes were characterized fully by mass spectrometry and ¹H NMR spectroscopy. To anticipate the relative occupancies of the three stations in each [2]catenane by the cyclophane, model compounds with the same constitutions in the vicinity of the stations were synthesized. The relative ground‐state populations of the three stations occupied in both [2]catenanes were estimated from the thermodynamic parameters for 1:1 complexes between all these model compounds and the cyclophane, obtained from isothermal titration calorimetry (ITC). The electrochemical and electromechanical properties of the three‐station [2]catenanes were analyzed by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and spectroelectrochemistry (SEC). The first three‐station [2]catenane was found to behave like a bistable system, whereas the second can be described as a quasi‐tristable system.     

Chromatographische Analyse

Ohne Zusammenfassung     

Effects of electrolytes on adsorbed polymer layers: poly(ethylene oxide)-silica system

The effects of various electrolytes on the adsorption of poly(ethylene oxide) onto silica have been studied. The salts were the chlorides of Na+, Mg2+, Ca2+, and La3+. The methods used were adsorption isotherms, found using a depletion method with phosphomolibdic acid, photon correlation spectroscopy, and solvent relaxation NMR. All the salts increased the particle-polymer affinity and adsorbed amount according to the adsorption isotherms, and a linear relationship was found between the initial slope of the isotherms and the ionic strength of the solution. Final adsorbed amounts were approximately 0.4-0.5 mg m(-2). The polymer layer thicknesses as found by PCS were of the same order as the radius of gyration of the polymer and increased with both the concentration and the valency of the salt due to increased adsorption. Solvent relaxation NMR showed that NaCl is too weak to have a noticeable effect on the polymer train layer, but the divalent salts clearly did increase both the strength of solvent binding close to the silica surface and the amount of PEO required to reach the maximum train density.     

A force field study of the chemical reaction between ethylene and cis-N2H2

The fully optimized geometry of the activated complex which occurs as an intermediate in the concerted H-transfer reaction between C₂H₄ and cis-N₂H₂ has been determined using the ab initio FORCE method of Pulay. The activation energy for the synchronous transfer of two hydrogen atoms from cis-N₂H₂ to ethylene is found to be 18.8kcal/mol, i.e. substantially lower than the previously estimated energy barrier of around 60 kcal/mol. The same method applied to trans-N₂H₂ and semilinear N₂H₂ gave an isomerization energy of 49.7 kcal/mol indicating that the isomerization of trans-N₂H₂ to the cis form might be the overall rate-controlling step.