Effect of counterion substitution on the viscosity anomaly in AOT microemulsions

AOT-based water-in-oil microemulsions display an anomalous maximum in the viscosity with X, the water to surfactant ratio. Several explanations for this phenomenon have been offered. In this work, we investigate viscosity and droplet interactions in Ca(AOT)(2)/water/n-decane and KAOT/water/n-decane microemulsions and compare our results with the commonly studied NaAOT/water/oil system. The Ca(AOT)(2) system demonstrates a maximum in relative viscosity and droplet attraction near X=15, similar to the NaAOT system, although the maximum occurs at a higher value of X in the Ca(AOT)(2) system. By contrast, the viscosity and interparticle interactions in the KAOT system do not strongly depend on the amount of water in the system. We attribute the differences in behavior between the two systems to different hydration characteristics of the counterion, and we believe that our results are consistent with a previously proposed model that attributes interdroplet attractions to charge fluctuations and surfactant exchange. Our findings support the connection between the viscosity anomaly and interparticle interactions.     

Nanoparticle-reinforced associative network hydrogels

ABA triblock copolymers in solvents selective for the midblock are known to form associative micellar gels. We have modified the structure and rheology of ABA triblock copolymer gels comprising poly(lactide)-poly(ethylene oxide)-poly(lactide) (PLA-PEO-PLA) through addition of a clay nanoparticle, laponite. Addition of laponite particles resulted in additional junction points in the gel via adsorption of the PEO corona chains onto the clay surfaces. Rheological measurements showed that this strategy led to a significant enhancement of the gel elastic modulus with small amounts of nanoparticles. Further characterization using small-angle X-ray scattering and dynamic light scattering confirmed that nanoparticles increase the intermicellar attraction and result in aggregation of PLA-PEO-PLA micelles.     

Design,Synthesis, and Biomedical Applications of Glycotripods for Targeting Trimeric Lectins

In the last decades, various efforts have been made to synthesize optimal glycotripods for targeting trimeric glycoproteins like asialoglycoprotein receptor, hemagglutinin, and langerin. All these trimeric glycoproteins have sugar binding pockets which are highly selective for a particular carbohydrate ligand. Optimized glycotripods are high affinity binders and have been used for delivering drugs or even applied as drug candidates. The selection of the tripodal base scaffold together with the length and flexibility of the linker between the scaffold and sugar residue, as important design parameters are discussed in this review.     

The Prenucleation Equilibrium of the Parathyroid Hormone Determines the Critical Aggregation Concentration and Amyloid Fibril Nucleation

Nucleation and growth of amyloid fibrils were found to only occur in supersaturated solutions above a critical concentration (c_crit). The biophysical meaning of c_crit remained mostly obscure, since typical low values of c_crit in the sub-μM range hamper investigations of potential oligomeric states and their structure. Here, we investigate the parathyroid hormone PTH₈₄ as an example of a functional amyloid fibril forming peptide with a comparably high c_crit of 67±21 μM. We describe a complex concentration dependent prenucleation ensemble of oligomers of different sizes and secondary structure compositions and highlight the occurrence of a trimer and tetramer at c_crit as possible precursors for primary fibril nucleation. Furthermore, the soluble state found in equilibrium with fibrils adopts to the prenucleation state present at c_crit. Our study sheds light onto early events of amyloid formation directly related to the critical concentration and underlines oligomer formation as a key feature of fibril nucleation. Our results contribute to a deeper understanding of the determinants of supersaturated peptide solutions. In the current study we present a biophysical approach to investigate c_crit of amyloid fibril formation of PTH₈₄ in terms of secondary structure, cluster size and residue resolved intermolecular interactions during oligomer formation. Throughout the investigated range of concentrations (1 μM to 500 μM) we found different states of oligomerization with varying ability to contribute to primary fibril nucleation and with a concentration dependent equilibrium. In this context, we identified the previously described c_crit of PTH₈₄ to mark a minimum concentration for the formation of homo-trimers/tetramers. These investigations allowed us to characterize molecular interactions of various oligomeric states that are further converted into elongation competent fibril nuclei during the lag phase of a functional amyloid forming peptide.     

Angular distributions of light projectile fragments in deep inelastic Pb + Em interactions at 160 A GeV

The nuclear emulsion was exposed at CERN by the lead projectile at 160 A GeV. The angles between any pair of fragments with Z = 2-4 have been measured in the emulsion plane for the events which did not contain heavy fragments. The constant characterizing the normal angle (J) distribution of the fragment momentum projection onto the emulsion plane with respect to initial projectile momentum p₀ is found to be C_J = (0.37 - 0.02) mrad. Corresponding value C₀ = (121 - 6) MeV/c of nucleon momentum distribution in the lead nucleus coincides with that expected from Fermi momentum distribution for this nucleus. The peak in the pair-angle distribution of double-charged fragments, ⁸Be M 2!, is presented for the region of small angles (<0.1 mrad). The fraction of !-particles coming from the decay of the ground state ⁸Be is found to be (13 - 2)% of their whole number.     

Effects of structural properties of silicon carbide-derived carbons on their electrochemical double-layer capacitance in aqueous and organic electrolytes

High surface area silicon carbide-derived carbons (Si-CDCs) synthesized by chlorination of beta silicon carbide (βSiC) with two different particle sizes (6 μm and 50 nm) show different porosities with graphitic structure. Transmission electron microscopy, Raman spectroscopy and argon (Ar) and carbon dioxide (CO₂) sorption analyses are used to examine the textural properties of the Si-CDCs. The results show that the particle size of the precursor affects the surface area and porosity of carbons. Furthermore, an additional heat treatment of the Si-CDC with 50-nm particle size for 24 h at 1,000 °C results in a collapse of the pore structure and reduces the surface area. The capacitive behaviours are investigated in H₂SO₄ and in tetraethyl ammonium tetrafluoroborate (TEABF₄)/acetonitrile (AN). The electrochemical performance of the Si-CDCs is influenced by the particle size, surface area, pore volume and pore size distribution. The Si-CDCs exhibit capacitances in 1 M H₂SO₄ of up to 179 F g^?1 and very stable charge–discharge performance over 5,000 cycles. This study shows the crucial importance of ultramicropores less than 1 nm combined with nanosized particles for achieving high capacitance in aqueous electrolyte. Moreover, the graphitic degree at the surface of the Si-CDCs enhances considerably the rate capability and stability in both electrolytes.     

Use of zirconium(IV) and antimony(III) for structural investigation of flavonoids

Summary The absorption spectra (in the visible and ultraviolet) of the complexes formed in absolute methanol between Zr⁴⁺, V⁴⁺, Y³⁺ and Sb³⁺ with 3-hydroxyflavone, apigenin, hesperidin, naringenin, morin, kaempferol, quercetin, rutin and myricetin have been studied. Zr⁴⁺ and Sb³⁺ form complexes that are stable in acid medium. The stoichiometry of the vairous Zr⁴⁺-flavonoid complexes formed in methanol and methanol/HClO₄ media has been determined by the molar ratio method. The preferred sites for complex formation of flavonoids with Zr⁴⁺ are postulated. Zr⁴⁺ forms chelates with the 3-hydroxy-4-keto and 5-hydroxy-4-keto systems simultaneously. Sb³⁺ forms complexes only with the 3,5-dihydroxy system in flavonoids. The results permit estimation of the relative order of chelating power of each type of binding site and are useful in elucidation of the structure of the flavonoids.

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Verwendung von Zirkonium(III) und Antimon(III) für die Erforschung der Flavonoide

Zusammenfassung Die Absorptions-Spektren (im sichtbaren und UV-Bereich) der in absolutem Methanol hergestellten Komplexe von Zr⁴⁺, V⁴⁺, Y³⁺ und Sb³⁺ mit 3-Hydroxyflavon, Apigenin, Hesperidin, Naringenin, Morin, Kaempferol, Quercetin, Rutin und Myricetin wurden untersucht. Zr⁴⁺ und Sb³⁺ bilden in saurem Milieu beständige Komplexe. Die Stöchiometrie der verschiedenen Zr⁴⁺-Flavonoid-Komplexe, die in Methanol bzw. Methanol/ HClO₄ hergestellt wurden, wurde durch Bestimmung der Molarverhältnisse ermittelt. Die für die Komplexbildung bevorzugten Stellen (im Molekül) wurden angegeben. Zr⁴⁺ bildet Chelate mit der 3-Hydroxy-4-keto- und mit der 5-Hydroxy~4-ketogruppe. Sb³⁺ bildet solche Komplexe nur mit der 3,5-Dihydroxy-4-keto-Gruppe in Flavonoiden. Die Untersuchungsergebnisse ermöglichen die Abschätzung der Komplexbildungsfähigkeit der verschiedenen Gruppierungen und sind für die Strukturaufklärung von Nutzen.

     

Correlation of mesogenic properties with intermolecular interaction energy for homologous series of HnCBP

Intermolecular interaction energy between a pair of molecules of homologous series 4, 4′-disubstituted biphenyl of the general formula HO?(CH₂)_n?O?C₆H₄?C₆H₄?CN(n = 3 ? 11) (H_nCBP) has been evaluated under various interacting conditions viz. stacking, in-plane and terminal interaction. Molecular geometry of the studied molecules was fully optimized without any constraint and checked for imaginary frequencies using hybrid density functional B3LYP combined with 6–31 g^** basis set. Electronic structure of the molecules obtained through these calculations has been utilized to calculate electrostatic and polarization energies under Rayleigh-Schrodinger perturbation theory modified with multi-centered multi-pole expansion method. Dispersion and repulsion energies have been evaluated using Kitaigorodskii formula. The identified minimum energy complexes have been further utilized to evaluate interaction energy under super molecular approach by employing M06 and DFT-D methods. A comparative analysis of the results has been reported with a view to examine suitability of different methods to study molecular aggregations in moderately large organic systems.     

More Operator Versions of the Schwarz Inequality

Some new operator versions of the Schwarz inequality are obtained. One of them is a counterpart of the variance-covariance inequality in the context of noncommutative probability. Received: 14 April 2000 / Accepted: 10 May 2000