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Although kinetically inert cationic Co(III)TMPyP 5+ (H2TMPyP 4+ = 5,10,15,20-tetrakis(methylpyridinium-4-yl)porphyrin) was considered earlier to be very weakly emissive, both the spectrum and the lifetime of its fluorescence could be determined. Besides, this complex proved to be favorable for outer-sphere photoinduced reduction of the metal center in the presence of triethanolamine (TEOA) as electron donor quenching the triplet excited state of this metalloporphyrin. The corresponding cobalt(II) porphyrin formed in this way was also photoactive; it forwarded an electron to a suitable acceptor (e.g., methylviologen) upon irradiation, regenerating the starting complex. Hence, this system may be a candidate for hydrogen generation from water by utilization of visible light. Metalloporphyrins play important roles in nature, due to their special spectral, coordination and redox features. Their advantageous photoinduced properties can also be exploited in various photocatalytic procedures [1]. Water-soluble derivatives can be utilized in environmentally benign systems not containing organic solvents. Kinetically inert in-plain metalloporphyrins, in which the metal center coplanarly fits into the cavity of the ligand, may offer promising possibilities for realization of photocatalytic systems based on outer-sphere electron transfer [2]. The so-called hyper-porphyrins can be especially interesting in this respect, due to their distorted structure, which may increase the (photo)redox reactivity of these complexes. From water-soluble metalloporphyrins of this type, photoredox reactions of manganese(III) complexes were thoroughly studied [1,3,4], while scarce attention was paid to the corresponding cobalt(III) porphyrins in this respect. Keywords: cobalt(III) porphyrinPhotocatalytic oxidation of the sulfide content of a wastewater to sulfate was studied with Co(III)TMPyP 5+ , Mn(III)TMPyP 5+ , and Fe(III)TMPyP 5+ (H2TMPyP 4+ = 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin) [5]. Upon irradiation in the range of the Soretbands, the cobalt(III) complex proved to be the most efficient, but the results have not been interpreted. This metalloporphyrin can also connect to the chain of DNA and oxidatively split it in the presence of suitable electron acceptors [6]. Since cationic manganese(III) porphyrins proved to be efficient photocatalysts in the presence of appropriate electron donors (such as EDTA and TEOA) and methylviologen as electron acceptor [1,3,7], cationic cobalt(III) porphyrins, the other characteristic representatives of water-soluble hyper-porphyrins, are also worth investigating in this respect. Hence, in this work, some photophysical and photochemical properties of Co(III)TMPyP 5+ were studied, also confirming its photocatalytic behavior, which may be utilized in water-splitting by solar radiation.The compounds used for our experiments were of reagent grade. Water purified in a Millipore/Milli-Q system was applied as solvent. Stock solutions of Co(III)TMPyP 5+ were prepared by in situ generation ...

Although Mn(III) porphyrins were considered earlier to be very weakly emissive, the fluorescence displayed by Mn(III) complexes with the cationic TMPyP 2+ ligand (H2TMPyP 4+ = 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin) as well as with its other alkyl (such as hexyl and dodecyl) derivatives proved to be strong enough for a comparative study. Elongation of the alkyl substituent increased both the quantum yield and the lifetime of the emission for the Mn(III) porphyrins, while resulted in an opposite effect for the corresponding free bases in homogeneous solutions. The presence of cationic micelles, however, reversed this tendency regarding the emission lifetime of the complexes. These cationic metalloporphyrins were applied in a photocatalytic system involving triethanolamine (TEOA) as a sacrificial electron donor and methylviologen (MV 2+ ) as an acceptor. In the first step of the catalytic process outer-sphere photoinduced reduction of the metal center took place via quenching of the triplet excited state of these metalloporphyrins by TEOA. The corresponding manganese(II) porphyrins formed in this way were also photoactive; they forwarded an electron to MV 2+ upon irradiation, regenerating the starting complex. Elongation of the alkyl substituents increased the quantum yield of the formation of methylviologen radical (MV + ) in this system, but considerably decreased the durability of the photocatalyst. Anionic micelles totally hindered the photoinduced generation of Mn(II) porphyrins, while cationic micellar environment appreciably increased the efficiency of the accumulation of MV + .

In many environments calcium carbonate minerals precipitate in the presence of clay minerals, and observations suggest that clays, particularly smectites, facilitate carbonate formation. In order to understand the interactions between clay surfaces and carbonate-precipitating solutions, we built model aqueous solutions of various compositions (containing Ca 2+ , Mg 2+ and CO 3 2ions) between layers of clay minerals (montmorillonite and kaolinite), and performed extensive molecular dynamics simulations. The results were compared with simulations for bulk solutions. Contrary to intuition, ionic clusters formed preferentially in the interlayer solution (instead of on the clay surface). The clusters grew both by the association of individual ions and aggregation, and were adsorbed to the clay surfaces with distinctly different efficiencies in the various systems. Montmorillonite was found to be more efficient than kaolinite in capturing clusters from solution. However, the efficiency of anchoring ionic clusters to the clay surfaces strongly depended on the Na + concentration of the solution, since Na + appeared to strongly attach to the surface and thereby block it from clusters in the solution. Montmorillonite (and probably other smectite clays as well) may thus have an important role in certain, primarily freshwater, systems in the localization of ionic clusters on its surface, thereby promoting the nucleation and templated growth of crystalline calcium-magnesium carbonate minerals.