Chemorheology of linear polymers. II

The chemical stress relaxation of crosslinked polymers had long been studied. The chemorheology of linear polymers is difficult to study because molecular flow by diffusion is generally much more rapid than relaxation or flow caused by chemical reaction. Our previous paper dealt with the chemorheology of linear polymers on taking such physical flow into consideration. By using another modified expression suggested by Tobolsky, good consistency between the theoretical chemical stress relaxation curve and an experimental one was obtained for polydisperse polystyrene and the commercial polystyrene used.     

Spectroscopy of quasiparticle excitations of superconducting bismuth cuprate at high pressures

We study the energy spectrum of Bi2223 (Bi_1.6Pb_0.4Sr_1.8Ca_2.2Cu₃O_x) at high hydrostatic pressures by Andreev-and tunneling-spectroscopy methods. We determine the gap anisotropy in the basal ab plane and find the following values for the parameters Δ(ϕ): Δ_max=42 mV, and Δ_min=19.5 mV (T _c =110 K and dT _c /dP=0.16 K/kbar). We detect an increase in the ratio R=2Δ_max/kT _c with pressure P; for Bi2223 cuprate, dR/dP≈0.017 kbar⁻¹. In the phonon-frequency region we detect a “softening,” due to pressure, of the high-frequency part of the phonon spectrum corresponding to “breathing” modes of oxygen, as well as other optical modes of Cu-O. The characteristic frequencies of the spectrum for ℏΩ>60 mV are found to decrease, with increasing pressure, at a rate d ln(ℏΩ)/dP≈−6.5±0.5×10⁻³ kbar⁻¹. This result explains the observed increase in the ratio 2Δ/kT _c (P) in the model of strong electron-phonon interaction. Zh. éksp. Teor. Fiz. 113, 1397–1410 (April 1998)     

Studies on iron(III) complex with 5,6-diamino-1,3-dimethyluracil

Reaction of 5,6-diamino-1,3-dimethyluracil (DDU) with iron(III) ion gave a fine blue colouration due to the formation of Fe[(DDU—H)₃]·2HClO₄. An oxidation product (7), C₁₂H₁₂N₆O₄, was also isolated from the reaction mixture.     

Spectral Changes of Light and Scattering Phenomena

In the last few years renewed attention has been paid to the study of light scattering from random media. This is due to the recent discovery of a phenomenon that dynamic light scattering from a fluctuating random medium may produce shifts of spectral lines, even when the source and the scattering medium are at rest relative to the observer. It has also been demonstrated that a similar phenomenon may occur in static light scattering from spatially random media without dynamic fluctuations. By the well-known analogy between the processes of scattering and radiation, these phenomena in scattering are found to be closely related to the correlation-induced spectral changes in the coherence theory which are often referred to as the Wolf effect. In this paper some recent developments are reviewed on research regarding the phenomena of changes in the spectrum of light induced by scattering from random media. Emphasis is placed on a number of up-to-date attempts for elucidating the effects of multiple scattering on these phenomena.This review was presented as an invited paper at the Symposium on Spectral Effects in Collective Phenomena organized as a satellite meeting of the Seventh Rochester Conference on Coherence and Quantum Optics, June 7–10 1995 (Rochester, NY).     

New Low‐Molecular‐Mass Gelators Based on L‐Lysine: Amphiphilic Gelators and Water‐Soluble Organogelators

The new L ‐lysine alkali‐metal salts 1 – 5 (M⁺=Na⁺ and K⁺) with different alkyl groups at the N^α‐position were easily synthesized, and their hydro‐ and organogelation properties were investigated. All compounds were H₂O‐soluble, and some salts, especially the potassium salts, functioned as a hydrogenator that could gel water below 2 wt‐%. These salts also had organogelation abilities for many organic solvents.     

Interaction between dyes and polyelectrolytes. VI. Metachromatic behavior of methylene blue induced by potassium poly(vinyl sulfate) and its homologs

Effect of structure of potassium poly(vinyl sulfate) and its homologs on the metachromatic behavior of methylene blue was investigated spectrophotometrically. The metachromatic behavior with addition of polyanions was followed by the changes in the molar extinction coefficient of the 664 nm band of methylene blue and in the wavelength of metachromatic band. Important factors for metachromasy were the number of anionic sites per polymer molecule, the degree of polymerization, and the flexibility of polymer chain. It was found that the amount of KCl or urea required to destroy the metachromasy was a useful measure for estimating the binding strength of methylene blue to polyanions.     

Diastereoselective synthesis of D- and L-myo-inositol 3,4,5,6-tetrakisphosphates from D-glucose via dihydroxylation of (+)-conduritol B derivatives

Syntheses of D- and L-myo-inositol 3,4,5,6-tetrakisphosphates were achieved via diastereoselective 1,2-addition of vinylcopper reagent with the chiral aldehyde prepared from 1,2,5,6-diisopropylidene-D-glucose, ring-closing metathesis of 1,7-diene with Grubbs catalyst followed by catalytic OsO(4) dihydroxylation of (+)-conduritol B derivatives.     

Fibre-optic potassium ion sensors based on a neutral ionophore and a novel lipophilic anionic dye

A novel lipophilic anionic dye, N-2,4-dinitro-6-octyloxyphenyl-2′,4′-dinitro-6′-trifluoromethylphenylamine (LAD), was synthesized. On deprotonation at neutral Ph it forms anions and brings about a change in the absorption spectrum in the visible region. This anionic dye was incorporated into a poly(vinyl chloride) matrix membrane with dibenzo-18-crown-6 (DB18C6) or valinomycin, which are K⁺-selective neutral ionophores. An optical K⁺ sensor was prepared using the polymeric membrane set 1 mm apart from the tip of a bifurcated optical fibre with a cylindrical plastic support. This sensor could detect a wide range of K⁺ concentrations (10^?6?1 M K⁺ for the DB18C6-based sensor, 10^?8?10^?2 M K⁺ for the valinomycin-based sensor) at Ph 7.0 by measuring the absorbance change at 513 nm. The factors that influence the response sensitivity of the sensor are discussed theoretically.