Browsing by Author "Gelfand, Benjamin S."
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Item Open Access One-Pot Synthesis of Aryl Selenonic Acids and some Unexpected Byproducts(ASC Publications, 2021-07-16) Sands, Kai N.; Gelfand, Benjamin S.; Back, Thomas G.The synthesis of aryl selenonic acids was achieved from diverse aryl bromides via a one-pot method involving metalation, selenation and oxidation with hydrogen peroxide, followed by ion exchange to afford the pure products in 77-90% yield. An o-hydroxymethyl derivative was found to dehydrate readily, affording the first example of a cyclic selenonic ester, while two minor byproducts were isolated and shown by x-ray crystallography to be mixed salts of aryl selenonic acids with either the corresponding aryl seleninic or selenious acid.Item Open Access Reaction of dirhodium(II) tetraacetate with S-methyl-L-cysteine(Taylor & Francis, 2019-08-12) Brunskill, Valerie; Enriquez Garcia, Alejandra; Jalilehvand, Farideh; Gelfand, Benjamin S.; Wu, MengyaThe reaction of antitumor active dirhodium(II) tetraacetate, [Rh2(AcO)4], with S-methyl-L-cysteine (HSMC) was studied at the pH of mixing (=4.8) in aqueous media at various temperatures under aerobic conditions. The results from UV–vis spectroscopy and electrospray ionization mass spectrometry (ESI–MS) showed that HSMC initially coordinates via its sulfur atom to the axial positions of the paddlewheel framework of the dirhodium(II) complex, and was confirmed by the crystal structure of [Rh2(AcO)4(HSMC)2]. After some time (48?h at 25?°C), or at elevated temperature (40?°C), Rh-SMC chelate formation causes breakdown of the paddlewheel structure, generating the mononuclear Rh(III) complexes [Rh(SMC)2]+, [Rh(AcO)(SMC)2] and [Rh(SMC)3], as indicated by ESI–MS. These aerobic reaction products of [Rh2(AcO)4] with HSMC have been compared with those of the two proteinogenic sulfur-containing amino acids methionine and cysteine. Comparison shows that the (S,N)-chelate ring size influences the stability of the [Rh2(AcO)4] paddlewheel cage structure and its RhII–RhII bond, when an amino acid with a thioether group coordinates to dirhodium(II) tetraacetate.Item Open Access The effect of sodium thiosulfate on cytotoxicity of a diimine Re(I) tricarbonyl complex(The Royal Society of Chemistry, 2021-04-16) Capper, Miles S.; Enriquez Garcia, Alejandra; Lai, Barry; Wang, Baiwen O.; Gelfand, Benjamin S.; Shemanko, Carrie S.; Jalilehvand, FaridehRecently, diimine Re(I) tricarbonyl complexes have attracted great interest due to their promising cytotoxic effects. Here, we compare the cytotoxicity and cellular uptake of two Re(I) compounds fac-[(Re(CO)3(bpy)(H2O)](CF3SO3) (1) and Na(fac-[(Re(CO)3(bpy)(S2O3)])·H2O (bpy = 2,2?-bipyridine) (2). The Re-thiosulfate complex in 2 was characterized in two solvated crystal structures {Na(fac-[Re(CO)3(bpy)(S2O3)])·1.75H2O·C2H5OH}4 (2 + 0.75H2O + C2H5OH)4 and (fac-[Re(CO)3(bpy)(H2O)]) (fac-[Re(CO)3(bpy)(S2O3)])·4H2O (3). The cytotoxicity of 1 and 2 was tested in the MDA-MB-231 breast cancer cell line and compared with that of cisplatin. The cellular localization of the Re(I) complexes was investigated using synchrotron-based X-ray fluorescence microscopy (XFM). The results show that replacement of the aqua ligand with thiosulfate renders the complex less toxic most likely by distrupting its cellular entry. Therefore, thiosulfate could potentially have a similar chemoprotective effect against diimine fac-Re(CO)3 complexes as it has against cisplatin.Item Open Access Unexpected Formation and Potent Antioxidant Activity of Macrocyclic Dimers Containing Disulfide and Selenide Groups(Wiley, 2022-11-17) McMillan, Jacob D.R.; Sands, Kai N.; Cooney, Gary S.; Gelfand, Benjamin S.; Back, Thomas G.During attempts to prepare spirodithiaselenuranes as GPx mimetics, a series of unexpected dimeric macrocycles was obtained, each containing two selenide and two disulfide moieties in rings ranging from 18- to 26-membered. The products showed potent GPx-like activity in an NMR assay based on their ability to catalyze the reduction of hydrogen peroxide with benzyl thiol. The high catalytic activity was attributed to transannular effects during selenide to selenoxide oxidation. This redox process was also characterized by an induction period that indicated autocatalysis in the formation of an intermediate selenoxide from the oxidation of the corresponding selenide.