Experimental investigations and ab initio studies of selenium(ii) dialkanethiolates, Se(SR)2

The Effects of Selenium on Bone Health: From Element to Therapeutics

Osteoporosis, characterized by low bone mass and a disruption of bone microarchitecture, is traditionally treated using drugs or lifestyle modifications. Recently, several preclinical and clinical studies have investigated the effects of selenium on bone health, although the results are controversial. Selenium, an important trace element, is required for selenoprotein synthesis and acts crucially for proper growth and skeletal development. However, the intake of an optimum amount of selenium is critical, as both selenium deficiency and toxicity are hazardous for health. In this review, we have systematically analyzed the existing literature in this field to determine whether dietary or serum selenium concentrations are associated with bone health. In addition, the mode of administration of selenium as a supplement for treating bone disease is important. We have also highlighted the importance of using green-synthesized selenium nanoparticles as therapeutics for bone disease. Novel nanobiotechnology will be a bridgehead for clinical applications of trace elements and natural products.

Quantum chemical calculations of 77 Se and 125 Te nuclear magnetic resonance spectral parameters and their structural applications

An accurate quantum chemical (QC) modeling of ⁷⁷ Se and ¹²⁵ Te nuclear magnetic resonance (NMR) spectra is deeply involved in the NMR structural assignment for selenium and tellurium compounds that are of utmost importance both in organic and inorganic chemistry nowadays due to their huge application potential in many fields, like biology, medicine, and metallurgy. The main interest of this review is focused on the progress in QC computations of ⁷⁷ Se and ¹²⁵ Te NMR chemical shifts and indirect spin-spin coupling constants involving these nuclei. Different computational methodologies that have been used to simulate the NMR spectra of selenium and tellurium compounds since the middle of the 1990s are discussed with a strong emphasis on their accuracy. A special accent is placed on the calculations resorting to the relativistic methodologies, because taking into account the relativistic effects appreciably influences the precision of NMR calculations of selenium and, especially, tellurium compounds. Stereochemical applications of quantum chemical calculations of ⁷⁷ Se and ¹²⁵ Te NMR parameters are discussed so as to exemplify the importance of integrated approach of experimental and computational NMR techniques.

Inhibition of lactoperoxidase-catalyzed oxidation by imidazole-based thiones and selones: a mechanistic study

Herein, we describe the synthesis and biomimetic activity of a series of N,N-disubstituted thiones and selones that contain an imidazole pharmacophore. The N,N-disubstituted thiones do not show any inhibitory activity towards LPO-catalyzed oxidation reactions, but their corresponding N,N-disubstituted selones exhibit inhibitory activity towards LPO-catalyzed oxidation reactions. Substituents on the N atom of the imidazole ring appear to have a significant effect on the inhibition of LPO-catalyzed oxidation and iodination reactions. Selones 16, 17, and 19, which contain methyl, ethyl, and benzyl substituents, exhibit similar inhibition activities towards LPO-catalyzed oxidation reactions with IC50 values of 24.4, 22.5, and 22.5 μM, respectively. However, their activities are almost three-fold lower than that of the commonly used anti-thyroid drug methimazole (MMI). In contrast, selone 21, which contains a N-CH2CH2OH substituent, exhibits high inhibitory activity, with an IC50 value of 7.2 μM, which is similar to that of MMI. The inhibitory activity of these selones towards LPO-catalyzed oxidation/iodination reactions is due to their ability to decrease the concentrations of the co-substrates (H2O2 and I2), either by catalytically reducing H2O2 (anti-oxidant activity) or by forming stable charge-transfer complexes with oxidized iodide species. The inhibition of LPO-catalyzed oxidation/iodination reactions by N,N-disubstituted selones can be reversed by increasing the concentration of H2O2. Interestingly, all of the N,N-disubstituted selones exhibit high anti-oxidant activities and their glutathione peroxidase (GPx)-like activity is 4-12-fold higher than that of the well-known GPx-mimic ebselen. These experimental and theoretical studies suggest that the selones exist as zwitterions, in which the imidazole ring contains a positive charge and the selenium atom carries a large negative charge. Therefore, the selenium moieties of these selones possess highly nucleophilic character. The (77)Se NMR chemical shifts for the selones show large upfield shift, thus confirming the zwitterionic structure in solution.

Molecular structures of Se(SCH3)2 and Te(SCH3)2 using gas-phase electron diffraction and ab initio and DFT geometry optimisations

The molecular structures of Se(SCH(3))(2) and Te(SCH(3))(2) were investigated using gas-phase electron diffraction (GED) and ab initio and DFT geometry optimisations. While parameters involving H atoms were refined using flexible restraints according to the SARACEN method, parameters that depended only on heavy atoms could be refined without restraints. The GED-determined geometric parameters (r(h1)) are: rSe-S 219.1(1), rS-C 183.2(1), rC-H 109.6(4) pm; angleS-Se-S 102.9(3), angleSe-S-C 100.6(2), angleS-C-H (mean) 107.4(5), phiS-Se-S-C 87.9(20), phiSe-S-C-H 178.8(19) degrees for Se(SCH(3))(2), and rTe-S 238.1(2), rS-C 184.1(3), rC-H 110.0(6) pm; angleS-Te-S 98.9(6), angleTe-S-C 99.7(4), angleS-C-H (mean) 109.2(9), phiS-Te-S-C 73.0(48), phiTe-S-C-H 180.1(19) degrees for Te(SCH(3))(2). Ab initio and DFT calculations were performed at the HF, MP2 and B3LYP levels, employing either full-electron basis sets [3-21G(d) or 6-31G(d)] or an effective core potential with a valence basis set [LanL2DZ(d)]. The best fit to the GED structures was achieved at the MP2 level. Differences between GED and MP2 results for rS-C and angleS-Te-S were explained by the thermal population of excited vibrational states under the experimental conditions. All theoretical models agreed that each compound exists as two stable conformers, one in which the methyl groups are on the same side (g(+)g(-) conformer) and one in which they are on different sides (g(+)g(+) conformer) of the S-Y-S plane (Y = Se, Te). The conformational composition under the experimental conditions could not be resolved from the GED data. Despite GED R-factors and ab initio and DFT energies favouring the g(+)g(+) conformer, it is likely that both conformers are present, for Se(SCH(3))(2) as well as for Te(SCH(3))(2).