A spectroelectrochemical investigation of the heme-based sensor DevS from Mycobacterium tuberculosis: a redox versus oxygen sensor.

Tuberculosis is one of the oldest known infectious diseases, responsible for millions of deaths annually around the world. The ability of Mycobacterium tuberculosis (Mtb) to enter into a dormant state has been considered integral to the success of this bacterium as a human pathogen. One of the key systems involved in regulating the entrance into dormancy is the differentially expressed in virulent strain sensor protein (DevS) [(dormancy survival sensor protein (DosS)]. However, the physiological signal for DevS has remained unclear since it was first shown to be a heme-based sensor with conflicting reports on whether it is a redox or an oxygen sensor. To address this question and provide a better understanding of the electronic properties of this protein, we present here, for the first time, a series of spectroelectrochemistry measurements of the full-length holo DevS in anaerobic conditions as well as bound to CO, NO, imidazole (Imz), cyanide, and O2 . An interesting feature of this protein is its ability to bind Imz even in the ferrous state, implying small-molecule analogues could be designed as potential regulators. Nonetheless, a midpoint potential (Em ) value of +10 mV [vs normal hydrogen electrode (NHE)] for DevS as measured under anaerobic conditions is much higher than the expected cytosolic potential for Mtb or even within stimulated macrophages (~ -270 mV vs NHE), indicating this sensor works in a reduced ferrous state. These data, along with the high oxygen affinity and very slow auto-oxidation rate of DevS, provides evidence that it is not a redox sensor. Overall, this study validates the biological function of DevS as an oxygen sensor directly involved in the dormancy/latency of Mtb.

Effect of Crotalus basiliscus snake venom on the redox reaction of myoglobin.

In this work, we have studied the effect of Crotalus basiliscus snake venom on the redox reaction of myoglobin (Mb), and by means of electrochemical techniques, we have shown that this reaction is undoubtedly affected following the interaction with the venom. Surface plasmon resonance, electrophoresis, UV-Vis, and circular dichroism showed that the interaction involves the attachment of some constituent of the venom to the protein, although not affecting its first and secondary structures. Mass spectra support this suggestion by showing the appearance of signals assigned to the Mb dimer and to a new species resulting from the interaction between Mb and the venom proteins. In addition, the mass spectra suggest the aromatic amino acids of myoglobin, mainly tryptophan and phenylalanine, are more exposed to the solvent medium upon the exposure to the venom solution. The results altogether indicate that the harmful effects of the venom of Crotalus basiliscus snake are likely connected to the blocking of the redox site of Mb.

Magnetic nanoparticles as a support for a copper (II) complex with nuclease activity.

Magnetic nanoparticles have been extensively explored for the development of platforms for drug delivery and imaging probes. In this work, we have used a modular capping strategy to produce magnetic gold-coated Fe3O4 (Fe3O4@Au) nanoparticles, which have been decorated with a copper (II) complex containing a thioether derivative of clip-phen (Fe3O4@Au@Cu), where the complex [Cu(2CP-Bz-SMe)]2+ has affinity to bind DNA and proven nuclease activity (2CP-Bz-SMe=1,3-bis((1,10-phenanthrolin-2-yl)oxy)-N-(4-(methylthio)benzylidene)propan-2-imine). The functionalization of Fe3O4@Au with the copper complex occurs through the sulfur atom of the thioether moiety, as indicated by Raman scattering on surface. The magnetic measurements showed the nanomaterial Fe3O4@Au@Cu is still magnetic although the gold shell and the functionalization with the copper complex have diminished the magnetization due to the dilution of the magnetic core. The nuclease assays performed with Fe3O4@Au@Cu indicate that the nuclease activity of the nanomaterial toward the plasmid DNA involves an oxidative pathway in which H2O2 species is involved as intermediate in a Fenton-like reaction. Based on the electron paramagnetic resonance spectra (aN = 15.07 G, aH = 14.99 G), such nuclease activity is assigned, essentially, to the HO species indicating that the radical production property of [Cu(2CP-Bz-SMe)]2+ is successfully transferred to the core-shell gold-coated Fe3O4 magnetic nanoparticles. To the best of our knowledge, this is the first study reporting nuclease activity due to the reactive oxygen species generated by a copper complex immobilized on a gold-coated magnetic nanoparticle.

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

Nitric 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 class of these compounds. Here, two new ruthenium nitrosyl complexes containing a thiocarbonyl ligand, with the formula cis-[Ru(phen)2(L)(NO)](PF6)3 (phen = phenantroline, L = thiourea or thiobenzamide), were synthesized and characterized by electronic spectroscopy, FTIR, NMR, mass spectrometry and voltammetric techniques. Theoretical calculations using Density Functional Theory (DFT) and Time-dependent Density Functional Theory (TD-DFT) were also used and further supported the characterizations of these complexes. An efficient release of nitric oxide by blue light was validated using a NO/HNO probe: 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, known as cPTIO. Interestingly, the complex containing thiourea cleaved DNA even in the dark, while both complexes showed great DNA photocleavage activity in blue light. This process might work mainly through NO and hydroxyl radical production. Additionally, these complexes showed promising vasodilator activity, whose mechanism of action was investigated using N-Nitro-l-arginine methyl ester hydrochloride (L-NAME) and 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and compared to sodium nitroprusside. Both compounds were indeed NO-mediated heme-dependent activators of soluble guanylate cyclase. Additionally, they did not show any significant cytotoxicity against cancer cell lines U87 and GBM02. Altogether, these results supported both complexes having potential pharmacological applications that deserve further studies.

Chitosan Film Containing an Iron Complex: Synthesis and Prospects for Heterocyclic Aromatic Amines (HAAs) Recognition.

Hybrid organic-inorganic materials have been seen as a promising approach to produce sensors for the detection and/or recognition of heterocyclic aromatic amines (HAAs). This work shows the synthesis of a hybrid film as a result of the incorporation of [Fe(CN)5(NH3)]3- into chitosan (CS); CS-[(CN)5Fe(NH3)]3-. The sensitivity of CS-[(CN)5Fe(NH3)]3- toward HAA-like species was evaluated by using pyrazine (pz) as probe molecule in vapor phase by means of electrochemistry and spectroscopic techniques. The crystallinity (SEM-EDS and XRD) decrease of CS-[(CN)5Fe(NH3)]3- in comparison to CS was assigned to the disturbance of the hydrogen bond network within the polymer. Such conclusion was reinforced by the water contact angle measurements. The results presented in this work indicate physical and intermolecular interactions, mostly hydrogen bond, between [Fe(CN)5(NH3)]3- and CS, where the complex is likely trapped in the polymer with its sixth coordination site available for substitution reactions.