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Sometimes unusual redox chemistry and modulation of enzyme activity Cu‐proteins can be encountered by the presence of a trace amount of Cu−Tris interaction (Tris‐(hydroxymethyl) aminomethane) during vitro studies. Herein, we addressed a redox chemistry of CuII−Tris with variable stoichiometric ratios in the presence of ascorbic acid (H2A) and O2. The redox chemistry of Bs3 (Cu : Tris; 1 : 3) with H2A/O2 was passed through several intermediates with progress on time yielding initially yellow precipitate, (Yp3), then green solution, (Gs3) and finally cyan solution (Cs3). The UV‐Vis spectra of Bs3, Gs3 and Cs3 displayed peaks at 640, 690 and 710 nm respectively suggesting CuII. The redox potential of CuII/CuI in Bs3, Gs3 and Cs3 were −0.18 V, −0.15 V and −0.19 V (vs. Ag/AgCl) respectively. The EPR spectrum of Bs3 showed an axial signal with g∥,⊥=2.483/2.105&A∥=160×10−4 cm−1 whereas Gs3 and Cs3 showed rhombic signal with g1,2,3=2.302/2.063/2.018&A∥=177×10−4 cm−1 and g1,2,3=2.274/2.064/2.016&A∥=164×10−4 cm−1 respectively suggesting a distorted tetragonal geometry. ESI−MS data indicated the probable composition of Bs2‐Bs5, Gs3 and Cs3 in solution. Integration of all spectroscopies data demonstrated the probable composition and redox mechanism. [ABSTRACT FROM AUTHOR]

Living organisms use selenium mainly in the form of selenocysteine in the active site of oxidoreductases. Here, selenium's unique chemistry is believed to modulate the reaction mechanism and enhance the catalytic efficiency of specific enzymes in ways not achievable with a sulfur-containing cysteine. However, despite the fact that selenium/sulfur have different physicochemical properties, several selenoproteins have fully functional cysteine-containing homologues and some organisms do not use selenocysteine at all. In this review, selected selenocysteine-containing proteins will be discussed to showcase both situations: (i) selenium as an obligatory element for the protein's physiological function, and (ii) selenium presenting no clear advantage over sulfur (functional proteins with either selenium or sulfur). Selenium's physiological roles in antioxidant defence (to maintain cellular redox status/hinder oxidative stress), hormone metabolism, DNA synthesis, and repair (maintain genetic stability) will be also highlighted, as well as selenium's role in human health. Formate dehydrogenases, hydrogenases, glutathione peroxidases, thioredoxin reductases, and iodothyronine deiodinases will be herein featured. [ABSTRACT FROM AUTHOR]

Herein, we report two newly synthesized salen‐type ligands, 2,3‐bis((3,5‐di‐tert‐butyl‐2‐hydroxybenzyl)thio)maleonitrile (H2L1) and 2,3‐bis((3,5‐di‐tert‐butyl‐2‐hydroxybenzyl)amino)malenonitrile (H4L2), bearing different coordination sites (sulfur vs amine) at maleonitrile tethered moiety to investigate metal mediated non‐innocence chemistry of these ligands. Upon metallation, ligand H2L1 did not yield simple metal‐ligand complex, rather ligand was split into two organic fragments, dithiolene moiety (mnt)2− and phenol moiety via C−S bond cleavage wherein (mnt)2− formed a stable metal complex [M(mnt)2]2−. The C−S bond cleavage was interpreted in terms of strong p(π) ... d(π) interaction between metal and dithiolene moiety in H2L1 ligand that invoked the intramolecular rearrangement facilitating C−S bond cleavage. Interestingly, the phenol moiety further transformed to either unprecedented 2,4‐di‐tert‐butyl‐6‐methylenecyclohexa‐2,4‐dienone (i. e. spiro compound; 5) or 2,4‐di‐tert‐butyl‐6‐(hydroxymethyl)phenol (6) depending on the temperature of reaction and type of metal ion used which was further predicted using DFT calculation. On the other hand, combined experimental and DFT studies explained that upon metallation, ligand H4L2 yielded non‐cleavage [M(H2L2)] (3 for M=Cu(II) and 4 for M=Ni(II)) complex, which slowly oxidized at −NH−CH2‐(amine) region to −N=CH− (imine) in H2L2 ligand under aerobic environment via C−H bond activation, yielding [CuII(L3)] (1) (or [NiII(L3)] (2) complex (H2L3=oxidatively dehydrogenated product of H4L2 ligand. [ABSTRACT FROM AUTHOR]

The nitration of tyrosine residues in proteins represents a specific footprint of the formation of reactive nitrogen species (RNS) in vivo. Here, the fusion product of orange protein (ATCUN‐ORP) was used as an in vitro model system containing an amino terminal Cu(II)‐ and Ni(II)‐binding motif (ATCUN) tag at the N‐terminus and a native tyrosine residue in the metal‐cofactor‐binding region for the formation of 3‐NO2‐Tyr (3‐NT). It is shown that NiII‐ATCUN unusually performs nitration of tyrosine at physiological pH in the presence of the NO2−/SO32−/O2 system, which is revealed by a characteristic absorbance band at 430 nm in basic medium and 350 nm in acidic medium (fingerprint of 3‐NT). Kinetics studies showed that the formation of 3‐NT depends on sulfite concentration over nitrite concentration suggesting key intermediate products, identified as oxysulfur radicals, which are detected by spin‐trap EPR study by using 5,5‐dimethyl‐1‐pyrroline‐N‐oxide (DMPO). This study describes a new route in the formation of 3‐NT, which is proposed to be linked with the sulfur metabolism pathway associated with the progression of disease occurrence in vivo. NiII‐ATCUN in action! The NiII ions bound to the amino terminal Cu(II)‐ and Ni(II)‐binding (ATCUN) motifs in orange protein unusually perform nitration of tyrosine at physiological pH in the presence of the NO2−/SO32−/O2 system over the H2O2/NO2− system. This result may provide the sulfur metabolism pathway to yield 3‐nitrotyrosine, which may be associated with sulfur‐related human diseases in vivo. [ABSTRACT FROM AUTHOR]

The complex [Ph4P]2[Cu(bdt)2] (1red) was synthesized by the reaction of [Ph4P]2[S2MoS2CuCl] with H2bdt (bdt = benzene-1,2-dithiolate) in basic medium. 1red is highly susceptible toward dioxygen, affording the one electron oxidized diamagnetic compound [Ph4P][Cu(bdt)2] (1ox). The interconversion between these two oxidation states can be switched by addition of O2 or base (Et4NOH = tetraethylammonium hydroxide), as demonstrated by cyclic voltammetry and UV-visible and EPR spectroscopies. Thiomolybdates, in free or complex forms with copper ions, play an important role in the stability of 1red during its synthesis, since in its absence, 1ox is isolated. Both 1red and 1ox were structurally characterized by X-ray crystallography. EPR experiments showed that 1red is a Cu(II)-sulfur complex and revealed strong covalency on the copper-sulfur bonds. DFT calculations confirmed the spin density delocalization over the four sulfur atoms (76%) and copper (24%) atom, suggesting that 1red has a "thiyl radical character". Time dependent DFT calculations identified such ligand to ligand charge transfer transitions. Accordingly, 1red is better described by the two isoelectronic structures [CuI(bdt2, 4S3-,*)]2- [CuII(bdt2, 4S4-)]2-. On thermodynamic grounds, oxidation of 1red (doublet state) leads to 1ox singlet state, [CuIII(bdt2, 4S4-)]1-. [ABSTRACT FROM AUTHOR]

Abstract: Three fluorinated Mo–Cu–thiolate isomers, [Ph4P]2[S2MoS2Cu(n-SPhF)], [n-SPhF =2-fluorothiophenol (1a)], 3-fluorothiophenol (1b), and 4-fluorothiophenol (1c)] were synthesized and spectroscopically characterized. The 19F-NMR signal of the fluorine atom in the benzene has different chemical shift for each isomer, which is highly influenced by the local environment that can be manipulated by different solvents and solutes. The fluorine-19 chemical shift is an advantageous NMR structural probe in alternative to 1H-NMR [B.K. Maiti, T. Avilés, M. Matzapetakis, I. Moura, S.R. Pauleta, J.J.G. Moura, Eur. J. Inorg. Chem. (2012) 4159.], that can be used to provide local information on the pocket of the metal cluster in the Orange Protein (ORP). [Copyright &y& Elsevier]

Two synthetic strategies of tetrathiomolybdate-metal clusters with the potential to be used as NMR structural probes for the location of the metal cofactor in the orange protein (ORP) are described. The first strategy is based on the substitution reaction in which small organic ligands bind directly to the metal centre in a molybdenum-copper hetero-dinuclear cluster. Interaction between [PPh4]2[MoS4CuCl] and either aliphatic [β-mercaptoethanol (b-me)] or aromatic [ o-aminobenzenethiol (abt)] thiols in the presence of a strong base resulted in the formation of [Ph4P]2[S2MoS2Cu(b-me)] ( 1a) and [Et4N]2[S2MoS2Cu(abt)] ·H2O ·0.25DMF ( 1b), which can be used to obtain intermolecular NOEs. The compound 1a readily hydrolyzed to [Ph4P]2[OSMoS2Cu(b-me)] ( 1ahydro) in contact with a protic solvent. The second strategy consisted of the incorporation of cadmium into tetrathiomolybdate ([MoS4]2-), which gives rise to the trinuclear cluster compound [PPh4]2[(MoS4)2Cd] ( 2). All clusters were characterized spectroscopically and their structure determined by X-ray diffraction. The NMR spectroscopic data are consistent with the formation of a complex with a 1:1 ratio of {MoS4Cu} and thiol. The 113Cd NMR chemical shift of compound 2 is consistent with the cadmium having a tetrahedral geometry and coordinated by four sulfur ligands. The tetraphenylphosphonium cation in compound 1a was replaced by a tetramethylammonium countercation originating in the water-soluble compound [Me4N- 1a]. Solubility in aqueous buffers is a requirement for incorporating this cluster into apo-ORP. These compounds will be used to identify the exact location of the ORP heterometallic cluster using NMR methodologies. [ABSTRACT FROM AUTHOR]