The heme-based oxygen sensor Rhizobium etli FixL: influence of auxiliary ligands on heme redox potential and implications on the enzyme activity

Conformational changes associated to sensing mechanisms of heme-based protein sensors are a key molecular event that seems to modulate not only the protein activity but also the potential of the Fe redox couple of the heme domain. In this work, midpoint potentials (E) assigned to the Fe redox couple of the heme domain of FixL from Rhizobium etli (ReFixL) in the unliganded and liganded states were determined by spectroelectrochemistry in the presence of inorganic mediators. In comparison to the unliganded ReFixL protein (+ 19 mV), the binding to ligands that switch off the kinase activity induces a negative shift, i. e. E = − 51, − 57 and − 156 mV for O, imidazole and CN, respectively. Upon binding to CO, which does not affect the kinase active, E was observed at + 21 mV. The potential values observed for Fe of the heme domain of ReFixL upon binding to CO and O do not follow the expected trend based on thermodynamics, assuming that positive potential shift would be expected for ligands that bind to and therefore stabilize the Fe state. Our results suggest that the conformational changes that switch off kinase activity upon O binding have knock-on effects to the local environment of the heme, such as solvent rearrangement, destabilize the Fe state and counterbalances the Fe-stabilizing influence of the O ligand

Asymmetric heterobimetallic mixed-valence complex trans-[(S'O IND.3')Co(cyclam)(NCS)Ru'(N'H IND.3') IND.4'(NCS)](B'F IND.4'): synthesis and characterization

[(SO3)Co(cyclam)(NCS)] and [(SO3)Co(cyclam)-NCS-Ru(NH3)4(NCS)](BF4) complexes were synthesized and characterized by means of X-ray diffraction, electrochemistry, elemental analysis, and spectroscopic techniques. Crystallographic and FTIR data indicated NCS- ligand is coordinated to Co through the nitrogen atom in the monomer species. Electrochemistry and FTIR data of the material isolated after reductive electrolysis of [(SO3)Co(cyclam)(NCS)] hint that NCS- and SO32- are released thus forming [Co(cyclam)(L)2]2+, where L is solvent molecules. The formation of the heterobimetallic mixed-valence complex induced a thermodynamic stabilization of Co and Ru metal atoms in the oxidized and reduced states, respectively. According to the Robin and Day classification, a Class II system with a comproportionation constant of 5.78 × 106 is suggested for the mixed-valence complex based on the electrochemical and UV-Vis-NIR results.CNPq (303530/2008-1)CAPESFAPESPFUNCA

On the correlation between electronic intramolecular delocalization and Au-S bonding strength of ruthenium tetraammine SAMs

Trans-[Ru(L)(NH3)4(L’)](PF6)n type complexes, where L = 4-cyanopyridine (CNpy), NCS-, CN-, and L’ = CNpy, 1,4-dithiane (1,4-dt), 4-mercaptopyridine (pyS) and thionicotinamide (tna), were synthesized and characterized. SAMs on gold of the complexes containing sulfur were studied by reductive desorption and SERS spectroscopy. Depending on the nature of L’, the withdrawing capability of the CNpy ligand is strong enough to partially oxidize the ruthenium atom and, as a consequence, delocalize the s electronic density from the trans located ligand. The reductive desorption results showed that the stability of the SAMs is directly related to this effect

Thiocarbonyl-bound metallonitrosyl complexes with visible-light induced DNA cleavage and promising vasodilation activity

CAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICONitric oxide has been involved in many key biological processes such as vasodilation, platelet aggregation, apoptosis, memory function, and this has drawn attention to the development of exogenous NO donors. Metallonitrosyl complexes are an important clas1828391CAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOsem informação303732/2014-8312030/2015-0The authors thank CENAUREM-UFC and CENAPAD-UFC for NMR and DFT facilities, respectively. Additionally we are thankful to CAPES, CNPq (L. G. F. Lopes 303732/2014-8, E. H. S. Sousa 312030/2015-0, Edital Universal 01/2016 403866/2016-2), FUNCAP (PPSUS 12535