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Heidari, Sima,Najafpour, Mohammad Mahdi,Hołyń,ska, Małgorzata,Singh, Jitendra Pal,Chae, Keun Hwa,Khatamian, Masoumeh The Royal Society of Chemistry 2018 Dalton transactions Vol.47 No.5
<P>For the first time, using scanning electron microscopy, transmission electron microscopy, X-ray absorption near edge structure and extended X-ray absorption fine structure X-ray diffraction, it is showed that MnCO3, MnWO4, Mn3(PO4)2·3H2O, MnS and Mn(VO3)2·<I>x</I>H2O under the water-oxidation conditions and in the presence of cerium(iv) ammonium nitrate, are converted to Mn oxide without a high-range order. A mechanism is proposed for such conversion and as Mn oxide is an efficient water-oxidizing catalyst, it is thus a candidate as a contributor to the observed catalytic activity.</P>
A new strategy to make an artificial enzyme: photosystem II around nanosized manganese oxide
Najafpour, Mohammad Mahdi,Madadkhani, Sepideh,Akbarian, Somayyeh,Hołyń,ska, Małgorzata,Kompany-Zareh, Mohsen,Tomo, Tatsuya,Singh, Jitendra Pal,Chae, Keun Hwa,Allakhverdiev, Suleyman I. The Royal Society of Chemistry 2017 Catalysis Science & Technology Vol.7 No.19
<▼1><P>A new strategy to make an artificial enzyme was reported.</P></▼1><▼2><P>Herein we report a new strategy to disperse Mn oxide into the apoenzyme of photosystem II. The compound was characterized by scanning electron microscopy, transmission electron microscopy, UV-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray absorption near edge structure, extended X-ray absorption fine structure, X-ray diffraction and some electrochemical methods. Under electrochemical conditions, the peaks attributed to Mn(ii)/(iii), Mn(iii)/(iv) and Mn(ii)/(iv) were assigned and compared with other manganese oxides. Linear sweep voltammetry shows that water electro-oxidation occurs at 80 mV less than that for the apoenzyme of photosystem II. Thus, Mn oxide maintains its water-oxidizing activity under these conditions. The compound is a new type of structural and functional model for the water-oxidizing complex in photosystem II.</P></▼2>
Links between peptides and Mn oxide: nano-sized manganese oxide embedded in a peptide matrix
Najafpour, Mohammad Mahdi,Madadkhani, Sepideh,Akbarian, Somayyeh,Zand, Zahra,Hołyń,ska, Małgorzata,Kompany-Zareh, Mohsen,Tatsuya, Tomo,Singh, Jitendra Pal,Chae, Keun Hwa,Allakhverdiev, Suleyman I The Royal Society of Chemistry 2018 NEW JOURNAL OF CHEMISTRY Vol.42 No.12
<P>Herein we report on a poly-peptide/Mn oxide nanocomposite as a model for the water-oxidizing catalyst in Photosystem II. The material is obtained by the reaction of poly-l-tyrosine, Mn(OAc)2·4H2O and KMnO4. HRTEM images of the nanocomposite indicate the presence of nanoparticles dispersed in a poly-l-tyrosine matrix with no crystalline phases. A broad peak at ∼400-550 nm in the UV-visible spectrum is related to Mn oxide formation. X-ray absorption studies suggest that the Mn atoms are in the oxidation state of +IV and a coordination number of around three was obtained for Mn in the structure. The water-oxidizing activity of the material under electrochemical conditions was also investigated. Electrochemical experiments proved the presence of Mn(iv) oxide. Determination of oxygen coupled to electrochemistry revealed the role of poly-l-tyrosine in decreasing the overpotential for water oxidation. In the next step, the interaction of the nanocomposite and imidazole as a model for the tyrosine 161 and histidine 190 residues in Photosystem II was studied with fluorescence spectroscopy using the multivariate curve resolution-alternating least squares method.</P>