A- and B-type hydrogen bond modifications of potassium hydrogen tartronate
ACCORDING to Speakman1 two types of intermolecular hydrogen bonds between carboxyl groups can be discerned in the crystal structures of acid salts of carboxylic acids. The first, type B, occurs when two carboxyl groups are not symmetry related, and have structural differences sufficient to characterise them, separately, as unionised (−CO2H) and ionised (−CO2−). Thus, any hydrogen bond between these groups must be asymmetric. The second, type A, occurs when two carboxyl groups are related by a symmetry element of the crystal, so that they are effectively equivalent. Thus any hydrogen bond between the groups must be, at least formally, symmetrical.
Preparation of Biologically Active Plague Murine Toxins labelled with 75Se-Methionine
ALTHOUGH the physiology and mechanism of action of the plague toxins have been investigated quite extensively, the target organ(s) is still unknown1. Pasteurella pestis toxin does not remain in a free soluble form either after injection or after infection with a virulent strain. It cannot be detected in the plasma of moribund animals, although whole blood is toxic to mice 48 h after infection. Thus, the toxin may be bound to erythrocytes or other particulate matter (cell debris), which is phagocytosed by macrophages and removed from circulation. This could provide an efficient way of concentrating the toxin in specific organs such as the spleen or the liver, after breakdown of erythrocytes2. If the spleen and liver are not the primary targets, the toxin could reach other organs through the circulation and exert its effect.
Thermodynamics on the Carbochlorination of Titanium-bearing Ores
The equilibrium compositions of the multi-component, multi-phase and multi-reaction system of carbochlorination of titanium-bearing ores are calculated with HSC, a computational chemistry software. The thermodynamic equilibrium calculation of the reaction system shows that a complete conversion of titanium-bearing ores is feasible at a temperature near 200oC. At temperatures ranging from 800 to 1600oC, the products of the reaction system are all in gaseous phase. Thermodynamic analysis accords with the industrial practice. The simulated results provide reasonable scientific basis for improving suitable technological conditions of the carbochlorination reduction.