Carboxyl groups in pre-treated regenerated cellulose fibres

The influence of peroxide bleaching and slack-mercerization on the amount of acidic groups in regenerated fibres (viscose, modal and lyocell) were studied. Conductometric titration was used to determine the total content of acidic carboxylic groups. Polyelectrolyte titration was used for surface and total charge determination, and to obtain information about the charge distribution and accessibilities of charged groups. Changes in fibre crystallinity to pre-treatment processes were characterized using iodine sorption (Schwertassek method) and correlated to treatments and the amount of carboxylic groups. For all three types of fibres the amount of accessible carboxyl groups was lowered by an increase in the degree of crystallinity. Bleaching with hydrogen peroxide causes some oxidative cellulose damage and, therefore, a larger amount of carboxyl groups (presumably formed at the end of cellulose chains). Slack-mercerization did not significantly change the total amount of acidic groups in the fibres, but their accessibility to cationic polyelectrolytes, in particular to polymers with high molecular weight was substantially lowered. Lidija Fras Zemljič, Zdenka Peršin, and Karin Stana Kleinschek are the members of the European Polysaccharide Network of Excellence (EPNOE).     

Packing Chromatic Number of Base-3 Sierpiński Graphs

The packing chromatic number \(\chi _{\rho }(G)\) of a graph G is the smallest integer k such that there exists a k-vertex coloring of G in which any two vertices receiving color i are at distance at least \(i+1\). Let \(S^n\) be the base-3 Sierpiński graph of dimension n. It is proved that \(\chi _{\rho }(S^1) = 3\), \(\chi _{\rho }(S^2) = 5\), \(\chi _{\rho }(S^3) = \chi _{\rho }(S^4) = 7\), and that \(8\le \chi _\rho (S^n) \le 9\) holds for any \(n\ge 5\).     

The cell model of the electrolyte transport mechanisms for cultured human colonocytes. Electromotive forces of the cellular pathways

The purpose of this work was to explain the chloride secretory model of the human colonocytes in terms of the equivalent electromotive forces and the relative apical ionic permeabilities using a conventional micro-electrode technique and different ion-substitution experiments. Both equivalent electromotive forces (for apical and basolateral membranes: E_a=−47.7±5.1 mV and E_b=−65.2±2.9 mV, respectively) depend strongly on the external K⁺ concentration. The most important conclusion is that both cell membrane potentials are largely dominated by a K⁺ permeability. The apical membrane has low Na⁺ and Cl⁻ permeabilities in non-stimulated conditions (P_Na/P_K=0.06±0.01 and P_Cl/P_K=0.23±0.09). An interesting response was found for the basolateral Na⁺ substitutions. Lowering the basolateral Na⁺ concentration at 1 mM we have seen a slow, but large depolarisation of the cell membrane potential of about 30 mV. We think that this is mostly caused by the presence of the basolateral Na⁺/H⁺ exchanger mechanism for the intracellular pH regulation. The Na⁺/K⁺ pump has a significant contribution to the basolateral electromotive force. The basolateral membrane has also a Cl⁻ permeability in non-stimulated conditions, but the basolateral Na⁺ permeability is undetectable.     

Preparation of an ion-selective electrode by chemical treatment of copper wire for the measurement of copper(II) and iodide by batch and flow-injection potentiometry

The preparation of an ion-selective electrode by chemical treatment of copper wire and its application for the measurements of copper (II) and iodide ions is described. The proposed reaction mechanism at the sensing surface, which explains the response of the electrode to Cu²⁺ and iodide ions, is discussed. The prepared electrode was suitable for direct potentiometric measurements of iodide and copper (II) in batch experiments down to concentrations of 1 × 10^–5 mol L^–1. A tubular electrode, prepared in the same way, may be used as a potentiometric sensor in a flow-injection analysis for Cu (II) and/or iodide determinations. Received: 4 December 1998 / Revised: 31 March 1999 / Accepted: 6 April 1999     

Mappings preserving spectrum and commutativity on Hermitian matrices

The general form of a continuous mapping φ acting on the real vector space of all n × n complex Hermitian or real symmetric matrices, and preserving spectrum and commutativity, is derived. It turns out that φ is either linear or its image forms a commutative set.