Lakes have historically been classified based on mixing regimes (Hutchinson & Loffler, 1956;Lewis Jr., 1983) as mixing frequency drives key ecosystem processes, including benthic oxygen availability, sediment resuspension, nutrient and carbon recycling, and greenhouse gas production and emissions (

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Oxygen availability, an important property of cerium oxide catalysts, has been investigated over a wide range of concentrations for the substitutional solid solution Zn x Ce1–x O2 in nanocrystalline (∼2.5 nm) form. X-ray diffraction data of the as-synthesized materials indicates Zn x Ce1–x O2 to be a single-phase system up to approximately x = 0.16, with the lattice parameter decreasing linearly with zinc concentration, signifying a homogeneous distribution of the Zn2+ cation within the bulk of the nanoparticle. X-ray photoelectron spectroscopy (XPS) of the Zn x Ce1–x O2 samples shows stoichiometric to slightly enriched zinc surface concentrations accompanied by oxygen surface reduction and an increased ratio of Ce3+/Ce4+ upon zinc incorporation, which correlate with increased oxygen surface reactivity. The ability of Zn x Ce1–x O2 to oxidize chemical reactants, taken here as a measure of oxygen availability, is measured by two different reactions, H2 temperature-programmed reduction (H2-TPR) to measure total oxygen storage capacity and the oxidation of methanol by temperature-programmed desorption (MeOH-TPD), both of which show enhancement in total oxidation and lower peak reaction temperatures with increased zinc concentration. H2-TPR gives evidence of involvement of both the outermost surface and sub-surface lattice oxygens, whereas XPS of methanol adsorption indicates the presence of both molecular and dissociative methoxy adsorbates as well as formate and carbonate intermediates. Methoxy decomposes into the intermediate species, leading to both CO partial oxidation and total oxidation to CO2 at higher zinc concentrations. Both H2-TPR and MeOH-TPD are sensitive to zinc concentration, indicating increasing oxygen availability as zinc is added up to the 16% miscibility limit.

A series of metalloporphyrin dimers as Tröger’s bases 1 or spiro-Tröger’s bases 2 was prepared starting from five different C 4-symmetry porphyrin derivatives substituted in meso-positions by Ph, 3-MeO-Ph, 4-MeO-Ph, 3,4-(MeO)2-Ph, or 3,5-(MeO)2-Ph. Free-base porphyrins were converted to metalloporphyrins, which were subsequently nitrated with nickel(II), copper(II), or zinc(II) nitrate to give β-nitrometalloporphyrins. These were further reduced to β-aminometalloporphyrins and treated with a methanal equivalent under acidic conditions to selectively obtain Tröger’s base 1, spiro-Tröger’s base 2, or a mixture of both, in yields up to 41% of 1 and 45% of 2 depending on the reaction conditions used. The ratio of 1 to 2 was influenced by the methanal equivalent used, the strength of the acid, and, above all, the solvent. The presence of a metal ion within the porphyrin core and the use of a chlorinated solvent were found to be essential for the formation of spiro-Tröger’s base 2. The molecular structure of spiroTB 2a-Ni 2 was proven by electron diffraction.