Untersuchungen mit optischer Rotationsdispersion, CXIV. Molybdat-Polyalkohol-Komplexe

Comparative study of various polyols as complexing agents for the acidimetric titration of tungstate

Most polyols (L = alditol or carbohydrate) form dinuclear tungstate complexes according to the over-all equilibrium 2WO4(2-) + 2H+ + L equal equilibrium [W2O7L]2- + H2O. When the reaction is fast and complete, it allows the acidimetric titration of tungstate. The formation constants of the complexes of a series of polyols were determined by potentiometry. Their values were higher at low ionic strengths. Opposite structural factors govern the stabilities and the formation rates of complexes: alditols of threo configuration react with tungstate faster than those of erythro configuration, but the stability order is erythro greater than threo. Of the polyols investigated, only xylitol and D-glucitol (sorbitol) allowed a fast and accurate potentiometric titration. Using 0.02 M HCl as titrand, 0.04 mmol of tungstate was determined in a volume of 100 cm3. The interference of molybdate is discussed in detail.

Blue molybdenum oxides: a stain for light and electron microscopy

Blue molybdenum oxides (molybdenum blues) have been prepared from aqueous phosphomolybdic acid solutions and applied to thin and semi-thin sections of glutaraldehyde-fixed, epoxy-embedded tissues. A light blue colour and high electron opacity were found in mast cell granules, the secretion content of goblet cells, and cytoplasmic granules in Drosophila salivary glands. The possibility that binding of blue molybdenum oxides to polyhydroxylic components accounts for the staining and contrasting reactions in some cell structures is briefly discussed.