Conductivity studies of aqueous solutions of stereoisomers of tartaric acids and tartrates. Part II: D-, L-, andmeso-tartaric acids

Conductivity measurements on aqueous solutions of D-tartaric acid, L-tartaric acid, andmeso-tartaric acid were performed in the temperature range 278.15–308.15 K. The equivalent limiting conductivity of the bitartrate anion, λ°(HTar^-), is evaluated with regard to the primary and secondary steps of dissociation of the acids in aqueous solutions by use of the Quint and Viallard equation for unsymmetrical electrolytes.     

Jets of nuclear matter in He-A T inelastic collisions at 4.5 A GeV/c

The problem of the nuclear matter jets in nucleus-nucleus collisions at 4.5 A GeV/c is discussed. The global analysis of experimental data, namely the sphericity tensor, is used to evidence such jets. The experimental results are compared with those obtained in the same collisions for hydrodynamic flow and thrust. The experiments have been performed in the frame of the SKM 200 Collaboration from JINR Dubna. Received: 20 March 1997 / Revised version: 20 July 1997     

<Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">K</Emphasis></Subscript> from the lattice with Wilson quarks

We report our results for the bag parameter B _K obtained from the quenched simulations on the lattice with Wilson fermions for three values of the lattice spacing. We implemented the method by which no subtraction of the mixing with other four-fermion operators is needed. Our final result, in terms of the renormalization group invariant bag parameter, is .Received: 9 July 2004, Revised: 27 July 2004, Published online: 21 September 2004     

Cross sections and rate coefficients of transitions in He and He-like ions induced by collisions with heavy particles

An approach to calculating the exitation cross sections and rate coefficients for a wide class of transitions in atoms and ions induced by collisions with heavy charged particles in considered. Calculations were carried out in terms of the Born approximation in the impact parameter representation with the normalization and Coulomb repulsion (in the case of an ionic target). Transitions between levels in He and He-like ions without changes of the principal quantum number are considered for n=2–4. Fitting formulas are suggested for transition rate coefficients. Tables of cross sections and parameters of fitting formulas are given for He and C⁴⁺.     

Lifetimes of some excited states in 64Ni, 66Zn and 68Zn

Mean lives and excitation energies of the lowest levels in⁶⁴Ni,⁶⁶Zn and⁶⁸Zn were measured with the aid of the (α, α′γ) and (α, pγ) reactions. The γ-rays were detected in coincidence with the outgoing particles. The following mean lives were determined from DSA measurements: 400 ± 150 fs for the level at E_x = 1.35 MeV in ⁶⁴Ni; 270 ± 100, 210 ± 110, 330 ± 200, 80 ± 70 fs for the levels at E_x = 1.87, 2.45, 2.83, 2.94 MeV in ⁶⁶Zn, and 1300 ± 300, > 160, 600 ± 200 fs for the levels at E_x = 1.08, 1.89 and 2.76 MeV in ⁶⁸Zn, respectively.     

A stereoselective total synthesis of the HCl salts of mycestericins F,G and ent-F

The total synthesis of the HCl salts of two natural sphingolipid-related amino acid derivatives, mycestericins F 4 and G 5 together with unnatural ent-4·HCl, starting from the four crucial scaffolds 6, 8, 9, 11 and utilizing the Wittig reaction to build the C₂₀ backbone, has been achieved. The selection of selective functional group interconversions accompanied with suitable protection–deprotection protocols in the coupling products 20 and 34 gave the desired structures.     

(E)-2-Benzylidenebenzocyclanones, part VIII: spectrophotometric determination of pKa values of some natural and synthetic chalcones and their cyclic analogues

Abstract  

UV–Vis spectrophotometry was used to determine acid dissociation constant (pK _a) values of the natural flavonoids phloretin, phlorizin, naringenin, and naringin, as well as 4′-hydroxychalcone, 4′-(dimethylamino)chalcone, and their cyclic analogues. Comparison of the results with those previously reported for the natural flavonoids showed the applied method is a relatively straightforward and easy-to-perform technique for the determination of pK _a values of compounds with relatively low solubility. Comparative analysis of the pK _a values of the synthetic chalcones showed a strong correlation between the degree of conjugation and the acid strength of the respective compounds with different geometry. Our results provide further evidence that modification of the three-dimensional structure of open-chain bioactive compounds is the method of choice to modify not only their stereochemistry but also their physicochemical properties.     

Fluorescence of a Histidine-Modified Enhanced Green Fluorescent Protein (EGFP) Effectively Quenched by Copper(II) Ions

Two histidines were introduced by site-directed mutagenesis into the structure of Enhanced Green Fluorescent Protein, replacing the serine at position 202 and the glutamine at position 204 for increasing the sensitivity of the protein towards different metal ions by creating possible metal binding sites near the chromophore group. There is no appreciable difference between the absorbance and fluorescence spectra of the two proteins (wild type and the double-histidine mutant) indicating that the mutation does not change the environment of the fluorophore. Fluorescence quenching was measured at different pH (6.5–8) and temperatures (20–45 °C) varying the concentration of metal ions. Under optimal conditions (pH?=?7.5, 20 °C) the mutant’s K_d is 16 nM, it binds copper more than 200fold stronger than the wild type EGFP.     

Analysis of wet pressing of paper: the three-phase model. Part I: constant air density

In this study, we consider a one-dimensional three-phase model describing wet pressing of paper. Part I is devoted to the simplified case in which air is assumed incompressible. In Part II we drop this assumption. The model is formulated in terms of water saturation and void ratio and it uses a material coordinate to describe spatial dependence. It also involves cross or matching conditions between the wet paper and the felt. In mathematical terms, we end up with a coupled system of equations: a nonlinear diffusion equation and a first order hyperbolic equation. We present some analytical observations to explain the essential behaviour of the model and we carry out numerical experiments using an upwind and a front tracking method.