Manganese oxides, photochemical production

Nowadays, not only Fe but other trace metals as well, for example, Mn, Co, or Cu, are thought to limit primary production. It is thus a real challenge for oceanographers not just to assess correctly the very low levels of Fe and Mn in the oceans but also to carry out the speciation of these elements (total dissolved concentrations are at the nM level, labile forms oxidation states in natural aquatic systems Fe(II), which is readily soluble, and Fe(III), which is almost insoluble. Flowever, both Fe ions can form diverse complexes with organic ligands with different labilities and solubilities, and colloidal particles, which are also considered part of the dissolved phase. Manganese also exists in two oxidation states in aquatic systems soluble Mn(II) and insoluble Mn(IV) both are present in a dynamic cycle in seawater. The nonlabile Mn pool consists of oxidized Mn(IV) species, but these can be photochemically reduced and thus solubilized.23... 

Several new natural products based on the ionone skeleton have been isolated. Damescenone (56), jS-damascone (57) and 3-keto-a-ionol (58) were isolated from tobacco, while 4-keto-/S-ionone (59) was isolated from black tea. Treatment of dehydro-/l-ionol [alcohol from (53)] with diborane gave 3-hydroxy- -ionol (60). Photochemical oxidation gave loliolide (67) and its C-3 epimer, and the allene (61). Manganese dioxide oxidation gave an isomer of grasshopper... 

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