New Organic-Inorganic Hybrid Compounds Based on Sodium Peroxidomolybdates (VI) and Derivatives of Pyridine Acids: Structure Determination and Catalytic Properties.

Two organic-inorganic hybrids based on sodium peroxidomolybdates(VI) and 3,5-dicarboxylic pyridine acid (Na-35dcpa) or N-oxide isonicotinic acid (Na-isoO) have been synthesized and characterized. All compounds contain inorganic parts: a pentagonal bipyramid with molybdenum center, and an organic part containing 3,5-dicarboxylic pyridine acid or N-oxide isonicotinic acid moieties. The type of organic part used in the synthesis influences the crystal structure of obtained compounds. This aspect can be interesting for crystal engineering. Crystal structures were determined using powder X-ray diffraction or single crystal diffraction for compounds Na-35dcpa and Na-isoO, respectively. Elemental analysis was used to check the purity of the obtained compounds, while X-ray Powder Diffraction (XRPD) vs. temp. was applied to verify their stability. Moreover, all the compounds were examined by Infrared (IR) spectroscopy. Their catalytic activity was tested in the Baeyer-Villiger (BV) oxidation of cyclohexanone to ε-caprolactone in the oxygen-aldehyde system. The highest catalytic activity in the BV oxidation was observed for Na-35dcpa. The compounds were also tested for biological activity on human normal cells (fibroblasts) and colon cancer cell lines (HT-29, LoVo, SW 620, HCT 116). All compounds were cytotoxic against tumor cells with metastatic characteristics, which makes them interesting and promising candidates for further investigations of specific anticancer mechanisms.

Newly-Obtained Two Organic-Inorganic Hybrid Compounds Based on Potassium Peroxidomolybdate and Dicarboxypyridinic Acid: Structure Determination, Catalytic Properties, and Cytotoxic Effects of Eight Peroxidomolybdates in Colon and Hepatic Cancer Cells.

Two new organic-inorganic hybrid compounds containing dicarboxylic pyridine acids have been obtained and characterized. Both compounds are potassium oxidodiperoxidomolybdates with 2,6-dicarboxylicpyridine acid or 3,5-dicarboxylicpyridine acid moieties, respectively. The chemical formula for the first one is C14H7K3Mo2N2O18 denoted as K26dcpa, the second C7H4K1Mo1N1O11.5-K35dcpa. Their crystal structures were determined using single crystal (K26dcpa) or XRPD-X-ray powder diffraction techniques (K35dcpa). The purity of the compounds was confirmed by elemental analysis. Their thermal stability was determined with the use of non-ambient XRPD. In addition, they were examined by IR spectroscopy methods and catalytic activity studies were performed for them. Catalytic tests in the Baeyer-Villiger reaction and biological activity have been performed for eight compounds: K26dcpa, K35dcpa, and six peroxidomolybdates previously obtained by our group. The anti-proliferative activity of peroxidomolybdenum compounds after 24 h of incubation was studied in vitro against three selected human tumor cell lines (SW620, LoVo, HEP G2) and normal human cells (fibroblasts). The data were expressed as IC50 values. The structure of the investigated oxodiperoxomolybdenum compounds was shown to have influence on the biological activity and catalytic properties. It has been shown that the newly-obtained compound, K35dcpa, is a very efficient catalyst in the Baeyer-Villiger reaction. The best biological activity results were obtained for Na-picO (previously obtained by us), which is a very effective anti-cancer agent towards SW 620 colorectal adenocarcinoma cells.

Three Generations of Cobalt Porphyrins as Catalysts in the Oxidation of Cycloalkanes.

Three generations of cobalt porphyrins were synthesized, physicochemically characterized by FTIR and UV/Vis spectroscopy as well as cyclic voltammetry and applied as catalysts in the oxidation of cycloalkanes with atmospheric molecular oxygen under mild conditions. All examined catalysts were active in the tested reaction, and their catalytic activity varied with the nature and number of substituents on the porphyrin ring. Introduction of electron-withdrawing or electron-donating substituents at the porphyrin rings increases the activity of metalloporphyrin complexes. It was found, for the first time, that generation II cobalt porphyrins show higher activity in cycloalkane oxidation than cobalt porphyrins of generation III. The lower catalytic activity of generation III cobalt porphyrins can be attributed to the saddle-shaped deformation of the porphyrin macrocycle. DFT modeling of Co porphyrins and their interactions with molecular oxygen provided explanations for the observed effects. On the basis of prior reports and the obtained results, a reaction mechanism is proposed and discussed.

Keggin-Type Heteropoly Salts as Bifunctional Catalysts in Aerobic Baeyer-Villiger Oxidation.

The cobalt, manganese, and iron salts of tungstophosphoric or molybdophosphoric acid with growing content of metals were applied for the first time as catalysts in the Baeyer-Villiger (BV) oxidation of cyclohexanone to ε-caprolactone with molecular oxygen. The catalysts were characterized with Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), and ethanol decomposition reaction. Introduction of transition metals into the heteropoly structure increases the activity of resulting heteropoly salts in comparison with parent heteropolyacids. It was shown that the most active catalysts are salts of the heteropoly salts with one metal atom introduced and one proton left (HMPX) type, (where M = Co, Fe, Mn, and X = W, Mo) with the metal to proton ratio equal one. Among all of the studied catalysts, the highest catalytic activity was observed for HCoPW. The effect indicates that both the acidic and redox properties are required to achieve the best performance. The Baeyer-Villiger (BV) oxidation mechanism proposed identifies the participation of heteropoly compounds in three steps of the investigated reaction: oxidation of aldehyde to peracid (redox function), activation of carbonyl group (Lewis acidity), and decomposition of the Criegee adduct to ε-caprolactone (Brønsted acidity).