The First Selenoanhydride in the Series of Chlorophyll a Derivatives, Its Stability and Photoinduced Cytotoxicity

In this work, we obtained the first selenium-containing chlorin with a chalcogen atom in exlocycle E. It was shown that the spectral properties were preserved in the target compound and the stability increased at two different pH values, in comparison with the starting purpurin-18. The derivatives have sufficiently high fluorescence and singlet oxygen quantum yields. The photoinduced cytotoxicity of sulfur- and selenium-anhydrides of chlorin p6 studied for the first time in vitro on the S37 cell line was found to be two times higher that of purpurin-18 and purpurinimide studied previously. Moreover, the dark cytotoxicity increased four-fold in comparison with the latter compounds. Apparently, the increase in the dark cytotoxicity is due to the interaction of the pigments studied with sulfur- and selenium-containing endogenous intracellular compounds. Intracellular distributions of thioanhydride and selenoanhydride chlorin p6 in S37 cells were shown in cytoplasm by diffusion distribution. The intracellular concentration of the sulfur derivative turned out to be higher and, as a consequence, its photoinduced cytotoxicity was higher as well.

The influence of chalcogen atom on conformation and phase transition in chalcogenazinoquinolinium monoiodides

Crystalline chalcogenazinoquinolinium monoiodides, where the chalcogen atom is oxygen and sulfur, have been studied using a combination of X-ray diffraction, Raman and UV-vis spectroscopies and photoluminescence experimental techniques. Periodic quantum-chemical calculations have been performed to characterize the features of electronic structure and vibrational assignment. X-ray diffraction and Raman spectroscopy experiments consistently reveal phase transition of thiazinoquinolinium monoiodide at low temperatures with the decrease of symmetry to P 1. The luminescence study for oxazinoquinolinium monoiodide reveals the excitation maximum at 532 nm and emission at 650 nm with significantly higher intensity than for the thiazinoquinolinium derivative. The studied chalcogenazinoquinolinium monoiodides demonstrate high values of Stokes shift up to 150 nm.

Selective cysteine-to-selenocysteine changes in a [NiFe]-hydrogenase confirm a special position for catalysis and oxygen tolerance

In [NiFe]-hydrogenases, the active-site Ni is coordinated by four cysteine-S ligands (Cys; C), two of which are bridging to the Fe(CO)(CN)2 fragment. Substitution of a single Cys residue by selenocysteine (Sec; U) occurs occasionally in nature. Using a recent method for site-specific Sec incorporation into proteins, each of the four Ni-coordinating cysteine residues in the oxygen-tolerant Escherichia coli [NiFe]-hydrogenase-1 (Hyd-1) has been replaced by U to identify its importance for enzyme function. Steady-state solution activity of each Sec-substituted enzyme (on a per-milligram basis) is lowered, although this may reflect the unquantified presence of recalcitrant inactive/immature/misfolded forms. Protein film electrochemistry, however, reveals detailed kinetic data that are independent of absolute activities. Like native Hyd-1, the variants have low apparent KMH2 values, do not produce H2 at pH 6, and display the same onset overpotential for H2 oxidation. Mechanistically important differences were identified for the C576U variant bearing the equivalent replacement found in native [NiFeSe]-hydrogenases, its extreme O2 tolerance (apparent KMH2 and Vmax [solution] values relative to native Hyd-1 of 0.13 and 0.04, respectively) implying the importance of a selenium atom in the position cis to the site where exogenous ligands (H−, H2, O2) bind. Observation of the same unusual electrocatalytic signature seen earlier for the proton transfer-defective E28Q variant highlights the direct role of the chalcogen atom (S/Se) at position 576 close to E28, with the caveat that Se is less effective than S in facilitating proton transfer away from the Ni during H2 oxidation by this enzyme.

Chalcogen-Atom Abstraction Reactions of a Di-Iron Imidophosphorane Complex

Reaction of the complexes [Fe2(2-NP(pip)3)2(NP(pip)3)2] (1-Fe) and [Co2(2-NP(pip)3)2(NP(pip)3)2] (1-Co), where [NP(pip)3]1– is tris(piperidinyl)imidophosphorane, with nitrous oxide, S8, or Se0 result in divergent reactivity. With nitrous oxide, 1-Fe forms [Fe2(2-O)(2-NP(pip)3)2(NP(pip)3)2] (2-Fe),...

Revealing Internal Heavy Chalcogen Atom Effect on the Photophysics of Dibenzo[a,j]phenazine-Cored Donor–Acceptor–Donor Triad

A new twisted donor–acceptor–donor (D–A–D) multi-photofunctional organic molecule comprising of phenoselenazine as the electron-donors (Ds) and dibenzo[a,j]phenazine (DBPHZ) as the electron-acceptor (A) has been developed. The developed selenium-incorporated D–A–D compound...

Computational investigation of the effect of OH on the hydrogen evolution reaction by Nickel-bis(dithiolene) and Nickel-bis(diselenolene) complexes

In the present study, the reactivity of OH with Ni(X2C2H2)2 and Ni(X2C2H2)2- (where X = S or Se) was investigated From the thermodynamics, it found that the OH radical attacks a backbone C-atom of the Ni(S2C2H2)2 complex. For the Ni(Se2C2H2)2 complex, the OH is predicted to target the ligating chalcogen atom. The significance of this is that with the attack of OH to a backbone C-atom, the thermodynamic cost to lose a proton or hydrogen atom ranges from exergonic to marginally endergonic depending on the oxidation state of the complex. Notably, such a process results in a rearrangement of the complex, likely leading to deactivation of the catalyst. Where OH has attacked a ligating chalcogenide atom, the thermodynamic cost to lose a proton or hydrogen is endergonic regardless of oxidation state of the complex. Where OH attacks a coordinating chalcogenide atom, the thermodynamics for the addition of a proton was considered. At the present level of theory, it was found that for the dithiolene and diselenolene monoanionic complexes, the addition of a proton is marginally endergonic. However, following protonation, the loss of water is significantly exergonic and results in the regeneration of the neutral non-oxidized Ni-complex. Given the greater tendency for OH to attack Se versus S it may be speculated that the use of diselenolene ligands may offer a means to protect the Ni-complex from damaging OH radicals due to the thermodynamic tendency for OH to attack Se atom of the diselenolene complexes not seen in the dithiolene complexes.

Post-synthesis Tellurium Doping Induced Mirror Twin Boundaries in Monolayer Molybdenum Disulfide

Mirror twin boundaries (MTBs) have brought intriguing one-dimensional physics into the host 2D crystal. In this letter, we reported a chalcogen atom exchange route to induce MTBs into as-formed MoS2 monolayers via post-synthesis tellurium doping. Results from annular dark-field scanning transition electron microscope (ADF-STEM) characterizations revealed that tellurium substituted the sulfur sublattices of MoS2 preferentially around the edge areas. A large number of MTBs in a configuration of 4|4P-Te was induced therein. Analysis of the lattice structures around MTBs revealed that such a tellurium-substitution-induced MTB formation is an energy-favored process to reduce the strain upon a high ratio of tellurium doping.

Rashba Effect on Buckled Square Lattice Ge and Sn chalcogenides (MX, M=Ge,Sn, X=O,S,Se,Te) using DFT method

The Rashba splitting are found in the buckled square lattice. Here, by applying fully relativistic density-functional theory (DFT) calculation, we confirm the existence of the Rashba splitting in the conduction band minimum of various two-dimensional MX monochalcogenides (M = Ge, Sn and X = S, Se, Te) exhibiting a pair inplane Rashba rotation of the spin textures. A strong correlation has also been found between the size of the Rashba parameter and the atomic number of chalcogen atom for Γ and M point in the first Brillouin zone. Our investigation clarifies that the buckled square lattice are promising for inducing the substantial Rashba splitting suggesting that the present system is promising for spintronics device.