Stability of mono- and bisbenzyloxime ethers of the acetylcholinesterase reactivator TMB-4.

Mono- and bisbenzyloxime ethers of the bispyridinium derivative TMB-4 (UNO, DUO) are potent allosteric modulators of the muscarinic receptor attracting clinical interest in case of organophosphate poisoning. In order to work out the stability of these compounds oximes, different oxime ethers and potential degradation products were synthesized and UV- and NMR-spectroscopically characterized. The process of degradation of all compounds was observed under stress conditions at varying pH-values and different temperatures by means of time-dependent NMR- und UV-measurements. The pyridinium aldoxime turned out to be rather stable, whereas the oxime ether and cyano derivatives convert to the pyridone at high pH-values and high temperature. The mechanism of degradation is discussed.

Calcium carbonate hexahydrate from organic-rich sediments of the antarctic shelf: precursors of glendonites.

Large euhedral crystals of calcium carbonate hexahydrate were recovered from a shelf basin of the Bransfield Strait, Antarctic Peninsula, at a water depth of 1950 meters and sub-zero bottom water temperatures. The chemistry, mineralogy, and stable isotope composition of this hydrated calcium carbonate phase, its environment of formation, and its mode of precipitation confirm the properties variously attributed to hypothetical precursors of the glendonites and thereby greatly expand their use in paleoceanographic interpretation.