D-Glucose as green ligand for selective copper-catalyzed phenol synthesis from aryl halides with an easy catalyst removal

With the growing demand of environmentally friendly reagents for organic reactions, for the first time the utility of D-glucose as a ligand in its direct form has been described using a typical example of copper-catalyzed coupling reaction for phenol synthesis with a high degree of selectivity and easy catalyst removal.     

Bioinorganic and medicinal chemistry: aspects of gold(I)-protein complexes

Gold(I)-based drugs have been used successfully for the treatment of rheumatoid arthritis (RA) for several years. Although the exact mechanism of action of these gold(I) drugs for RA has not been clearly established, the interaction of these compounds with mammalian enzymes has been extensively studied. In this paper, we describe the interaction of therapeutic gold(I) compounds with mammalian proteins that contain cysteine (Cys) and selenocysteine (Sec) residues. Owing to the higher affinity of gold(I) towards sulfur and selenium, gold(I) drugs rapidly react with the activated cysteine or selenocysteine residues of the enzymes to form protein-gold(I)-thiolate or protein-gold(I)-selenolate complexes. The formation of stable gold(I)-thiolate/selenolate complexes generally lead to inhibition of the enzyme activity. The gold-thiolate/selenolate complexes undergo extensive ligand exchange reactions with other nucleophiles and such ligand exchange reactions alter the inhibitory effects of gold(i) complexes. Therefore, the effect of gold(I) compounds on the enzymatic activity of cysteine- or selenocysteine-containing proteins may play important roles in RA. The interaction of gold(I) compounds with different enzymes and the biochemical mechanism underlying the inhibition of enzymatic activities may have broad medicinal implications for the treatment of RA.     

Deiodination of thyroid hormones by iodothyronine deiodinase mimics: does an increase in the reactivity alter the regioselectivity?

Organoselenium compounds as functional mimics of iodothyronine deiodinase are described. The naphthyl-based compounds having two selenol groups are remarkably efficient in the inner-ring deiodination of thyroxine. The introduction of a basic amino group in close proximity to one of the selenol moieties enhances the deiodination. This study suggests that an increase in the nucleophilic reactivity of the conserved Cys residue at the active site of deiodinases is very important for effective deiodination.     

Shape and size transformation of gold nanorods (GNRs) via oxidation process: A reverse growth mechanism

The anisotropic shape transformation of gold nanorods (GNRs) with H₂O₂ was observed in the presence of “cethyl trimethylammonium bromide” (CTAB). The adequate oxidative dissolution of GNR is provided by the following autocatalytic scheme with H₂O₂: Au⁰ → Au⁺, Au⁰ + Auⁿ⁺ → 2Au³⁺, n = 1 and 3. The shape transformation of the GNRs was investigated by UV-vis spectroscopy and transmission electron microscopy (TEM). As-synthesised GNRs exhibit transverse plasmon band (TPB) at 523 nm and longitudinal plasmon band (LPB) at 731 nm. Upon H₂O₂ oxidation, the LPB showed a systematic hypsochromic (blue) shift, while TPB stays at ca. 523 nm. In addition, a new emerging peak observed at ca. 390 nm due to Au(III)-CTAB complex formation during the oxidation. TEM analysis of as-synthesised GNRs with H₂O₂ confirmed the shape transformation to spherical particles with 10 nm size in 2 h, whereas centrifuged nanorod solution showed no changes in the aspect ratio under the same condition. Au³⁺ ions produced from oxidation, complex with excess free CTAB and approach the nanorods preferentially at the end, leading to spatially directed oxidation. This work provides some information to the crystal stability and the growth mechanism of GNRs, as both growth and shortening reactions occur preferentially at the edge of single-crystalline GNRs, all directed by Br⁻ ions.     

Highly Efficient Glutathione Peroxidase and Peroxiredoxin Mimetics Protect Mammalian Cells against Oxidative Damage

Novel isoselenazoles with high glutathione peroxidase (GPx) and peroxiredoxin (Prx) activities provide remarkable cytoprotection to human cells, mainly by exhibiting antioxidant activities in the presence of cellular thiols. The cytotoxicity of the isoselenazoles is found to be significantly lower than that of ebselen, which is being clinically evaluated by several groups for the treatment of reperfusion injuries and stroke, hearing loss, and bipolar disorder. The compounds reported in this paper have the potential to be used as therapeutic agents for disorders mediated by reactive oxygen species.     

Catalytic Reduction of Graphene Oxide Nanosheets by Glutathione Peroxidase Mimetics Reveals a New Structural Motif in Graphene Oxide

A catalytic reduction of graphene oxide (GO) by glutathione peroxidase (GPx) mimics is reported. This study reveals that GO contains peroxide functionalities, in addition to the epoxy, hydroxyl and carboxylic acid groups that have been identified earlier. It also is shown that GO acts as a peroxide substrate in the GPx‐like catalytic activity of organoselenium/tellurium compounds. The reaction of tellurol, generated from the corresponding ditelluride, reduces GO through the glutathione (GSH)‐mediated cleavage of the peroxide linkage. The mechanism of GO reduction by the tellurol in the presence of GSH involves the formation of a tellurenic acid and tellurenyl sulfide intermediates. Interestingly, the GPx mimics also catalyze the decarboxylation of the carboxylic acid functionality in GO at ambient conditions. Whereas the selenium/tellurium‐mediated catalytic reduction/decarboxylation of GO may find applications in bioremediation processes, this study suggests that the modification of GO by biologically relevant compounds such as redox proteins must be taken into account when using GO for biomedical applications because such modifications can alter the fundamental properties of GO.     

Halogen-Mediated Membrane Transport: An Efficient Strategy for the Enhancement of Cellular Uptake of Synthetic Molecules

The poor uptake of fluorescent probes and therapeutics by mammalian cells is a major concern in biological applications ranging from fluorescence imaging to drug delivery in living cells. Although gaseous molecules such as oxygen and carbon dioxide, hydrophobic substances such as benzene, and small polar but uncharged molecules such as water and ethanol can cross the cell plasma membrane by simple passive diffusion, many synthetic as well as biological molecules require specific membrane transporters and channel proteins that control the traffic of these molecules into and out of the cell. This work reports that the introduction of halogen atoms into a series of fluorescent molecules remarkably enhances their cellular uptake, and that their transport can be increased to more than 95 % by introducing two iodine atoms at appropriate positions. The nature of the fluorophore does not play a major role in the cellular uptake when iodine atoms are present in the molecules, as compounds bearing naphthalimide, coumarin, BODIPY, and pyrene moieties show similar uptakes. Interestingly, the introduction of a maleimide-based fluorophore bearing two hydroxyethylthio moieties allows the molecules to cross the plasma and nuclear membranes, and the presence of iodine atoms further enhances the transport across both membranes. Overall, this study provides a general strategy for enhancing the uptake of organic molecules by mammalian cells.