Probing the surface chemistry of different oxidized MWCNT for the improved electrical wiring of cytochrome c nitrite reductase

This work reports the evaluation of a set of multi-walled carbon nanotubes (MWCNT) presenting different surface chemistries, as interfaces for the direct electrochemistry of the multihemic nitrite reductase (ccNiR) from Desulfovibrio desulfuricans ATCC27774 (Dd). The carbon nanotubes (CNT) dispersions were prepared in aqueous media and deposited on pyrolytic graphite macroelectrodes, following a layer-by-layer methodology. The resulting MWCNT bed was coated with ccNiR and studied by cyclic voltammetry. Interestingly, although small non-catalytic cathodic waves were detected in all CNT bioconjugates, the complexity of these electrochemical signals was partially deconvoluted in some materials, the less acidic ones emphasizing the contribution of the catalytic centre. Consistently, these MWCNT were the most favourable for enzyme catalysis, highlighting the importance of the surface oxide functionalities to enzyme reactivity. Keywords: Multi-walled carbon nanotubes, Surface oxides, Nitrite reductase, Direct electrochemistr

Electron transfer and docking between cytochrome cd1 nitrite reductase and different redox partners - A comparative study

The authors acknowledge funding from UCIBIO@REQUIMTE Pest-C/EQB/LA0006/2013. CM Silveira and RM Almeida thank the financial support from Fundacao para a Ciencia e Tecnologia (Postdoctoral fellowships SFRH/BPD/79566/2011 and SFRH/BPD/80293/2011).Cytochrome cd1 nitrite reductases (cd1NiRs) catalyze the reduction of nitrite to nitric oxide in denitrifying bacteria, such as Marinobacter hydrocarbonoclasticus. Previous work demonstrated that the enzymatic activity depends on a structural pre-activation triggered by the entry of electrons through the electron transfer (ET) domain, which houses a heme c center. The catalytic activity of M. hydrocarbonoclasticus cd1NiR (Mhcd1NiR) was tested by mediated electrochemistry, using small ET proteins and chemical redox mediators. The rate of enzymatic reaction depends on the nature of the redox partner, with cytochrome (cyt) c552 providing the highest value. In situations where cyt c552 is replaced by either a biological (cyt c from horse heart) or a chemical mediator the catalytic response was only observed at very low scan rates, suggesting that the intermolecular ET rate is much slower. Molecular docking simulations with the 3D model structure of Mhcd1NiR and cyt c552 or cyt c showed that hydrophobic interactions favor the formation of complexes where the heme c domain of the enzyme is the principal docking site. However, only in the case of cyt c552 the preferential areas of contact and Fe-Fe distances between heme c groups of the redox partners allow establishing competent ET pathways. The coupling of the enzyme with chemical redox mediators was also found not to be energetically favorable. These results indicate that although low activity functional complexes can be formed between Mhcd1NiR and different types of redox mediators, efficient ET is only observed with the putative physiological electron donor cyt c552.publishersversionpublishe

Design of 1D and 2D molecule-based magnets with the ligand 4,5-dimethyl-1,2-phenylenebis(oxamato)

Three new bimetallic oxamato-based magnets with the proligand 4,5-dimethyl-1,2-phenylenebis-(oxamato) (dmopba) were synthesized using water or dimethylsulfoxide (DMSO) as solvents. Single crystal X-ray diffraction provided structures for two of them: [MnCu(dmopba)(H(2)O)(3)]n center dot 4nH(2)O (1) and [MnCu(dmopba)(DMSO)(3)](n center dot)nDMSO (2). The crystalline structures for both 1 and 2 consist of linearly ordered oxamato-bridged Mn(II)Cu(II) bimetallic chains. The magnetic characterization revealed a typical behaviour of ferrimagnetic chains for 1 and 2. Least-squares fits of the experimental magnetic data performed in the 300-20 K temperature range led to J(MnCu) = -27.9 cm(-1), g(Cu) = 2.09 and g(Mn) = 1.98 for 1 and J(MnCu) = -30.5 cm(-1), g(Cu) = 2.09 and g(Mn) = 2.02 for 2 (H = -J(MnCu)Sigma S(Mn, i)(S(Cu, i) + S(Cu, i-1))). The two-dimensional ferrimagnetic system [Me(4)N](2n){Co(2)[Cu(dmopba)](3)}center dot 4nDMSO center dot nH(2)O (3) was prepared by reaction of Co(II) ions and an excess of [Cu(dmopba)](2-) in DMSO. The study of the temperature dependence of the magnetic susceptibility as well as the temperature and field dependences of the magnetization revealed a cluster glass-like behaviour for 3.Conselho Nacional Cientifico e Tecnologico (CNPq)Fundacao de Amparo a Pesquisa do Estado de Minas Gerais (FAPEMIG)Financiadora de Estudos e Projetos (FINEP)Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Fundacao de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ