Combination of the dithiol N,N'-bis(2-mercaptoethyl)isophthalamide, abbreviated as BDTH2 and as 1, with excess H2SeO3 in aqueous acidic (pH ≈ 1) conditions resulted in precipitation of BDT(S-Se-S) (6), with a (77)Se NMR chemical shift of δ = 675 ppm, and oxidized BDT. When the reaction is conducted under basic conditions Se(IV) is reduced to red Se(0) and oxidized 1. No reaction takes place between 1 and selenate (Se(VI)) under acidic or basic conditions. Compound 6 is stable in air but decomposes to red Se(0) and the disulfide BDT(S-S) (9) with heating and in basic solutions. Mechanisms and energetics of the reactions leading to 6 in aqueous solution were unraveled by extensive calculations at the ωB97X-D/aug-cc-pVTZ-PP level of theory. NMR chemical shift calculations with the gauge-independent atomic orbital (GIAO) method for dimethyl sulfoxide as solvent confirm the generation of 6 (calculated δ value = 677 ppm). These results define the conditions and limitations of using 1 for the removal of selenite from wastewaters. Compound 6 is a rare example of a bidentate selenium dithiolate and provides insight into biological selenium toxicity.
While many elements have been encapsulated in fullerene cages, the rare earth endohedral fullerenes are by far the most studied. The rare earth endohedral fullerenes can exist in various forms, but this article focuses on the more extensively studied types such as monometallofullerenes, dimetallofullerenes, and cluster fullerenes. The covalent bonding of the rare earth elements or clusters to the carbon cage is an important feature. Just as important is the charge transfer from encapsulated species to the carbon cage, which gives the endohedral fullerenes interesting electronic properties. The electronic properties can lead to novel materials for electronic device fabrication. Medical applications for imaging are also being studied because the fullerene cage protects the organism from the potential toxicity of the free rare earth element.
The arsenite removal from the water was attributed using thiol (S-H) coupled magnetic nanoparticles (MNPs). The composite Fe3O4-SiO2-linker-AB9 (AB-MNP) was made using MNPs coated with the amine-functionalized silica surface, which is then coupled to AB9= 2,2’-(isophthaloybis(azanaediyl))bis-3-mercaptopropanoic acid; (a sulfhydryl compound with pendant carboxylate groups). Complete arsenic removal was achieved with As(III) solutions of 200, 500, and 1000 ppb resulting in detectable arsenic dropped to below 10 ppb. This single solid-composite immobilize As(III) by forming strong covalent As-S bonds producing “proposed” structure As(III)-AB9@MNP (Figure 1). The components of this new composite material are made from non-toxic, earth-abundant elements, and rapid magnetic separation allows them to be used as an effective, affordable means of providing arsenic-free drinking water to at-risk populations around the world.
Figure 1
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