Kromi-pohdintoja

Chromium(III) superoxo-kompleksi. esiintyyköhän tällaista  kehossa ?     Cr(III)O(•-) character.
http://www.ncbi.nlm.nih.gov/pubmed/26486819
http://www.ncbi.nlm.nih.gov/pubmed/24299279

Inorg Chem. 2015 Nov 2;54(21):10513-20. doi: 10.1021/acs.inorgchem.5b02068. Epub 2015 Oct 21.

Tuning the Reactivity of Chromium(III)-Superoxo Species by Coordinating Axial Ligands.

Goo YR¹, Maity AC¹ et al.

Metal-superoxo species have attracted much attention recently as key intermediates in enzymatic and biomimetic oxidation reactions. The effect(s) of axial ligands on the chemical properties of metal-superoxo complexes has never been explored previously. In this study, we synthesized and characterized chromium(III)-superoxo complexes bearing TMC derivatives with pendant pyridine and imidazole donors, such as [Cr(III)(O2)(TMC-Py)](2+) (1, TMC-Py = 4,8,11-trimethyl-1-(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane) and [Cr(III)(O2)(TMC-Im)](2+) (2, TMC-Im = 4,8,11-trimethyl-1-(2-methylimidazolmethyl)-1,4,8,11-tetraazacyclotetradecane). The reactivity of chromium(III)-superoxo complexes binding different axial ligands, such as 1, 2, and [Cr(III)(O2)(TMC)(Cl)](+) (3, TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), was then investigated in C-H bond activation and oxygen atom transfer reactions. Kinetic studies revealed that the reactivity of the Cr(III)-superoxo complexes depends on the axial ligands, showing the reactivity order of 1 > 2 > 3 in those electrophilic oxidation reactions. It was also shown that there is a good correlation between the reactivity of the chromium(III)-superoxo complexes and their redox potentials, in which the redox potentials of the chromium(III)-superoxo complexes are in the order 1 > 2 >3. DFT calculations reproduced the reactivity order between 1 and 3 in both C-H bond activation and oxygen atom transfer reactions, and the latter reaction is described using orbital interactions. The calculations are also in agreement with the experimentally obtained redox potentials. The present results provide the first example showing that the reactivity of metal-superoxo species can be tuned by the electron-donating ability of axial ligands bound trans to the metal-superoxo moiety. 

Saattaisi hyvinkin olla paikkaa kromi(III):lle ihmisen ROS, fysiologisten nukleofiilisten  tapahtumien ja redox -tapahtumein kartalla 
24.11. 2015