SBA-15 obtained from rice husk ashes wet-impregnated with metals (Al, Co, Ni) as efficient catalysts for 1,4-dihydropyridine three-component reaction

A fully characterized mesoporous silica prepared from industrial waste was impregnated with metals and applied as a green heterogeneous catalyst.

Supramolecular kinetic effects by pillararenes: the synergism between spatiotemporal and preorganization concepts in decarboxylation reactions

Spatiotemporal and preorganization factors were both responsible for the catalytic and inhibitory supramolecular effects in decarboxylation reactions.

Coordination among Bond Formation/Cleavage in a Bifunctional-Catalyzed Fast Amide Hydrolysis: Evidence for an Optimized Intramolecular N-Protonation Event

A density functional theory (DFT) computational analysis, using the ωB97X-D functional, of a rapid amide cleavage in 2-carboxyphthalanilic acid (2CPA), where the amide group is flanked by two catalytic carboxyls, reveals key mechanistic information: (a) General base catalysis by a carboxylate coupled to general acid catalysis by a carboxyl is not operative. (b) Nucleophilic attack by a carboxylate on the amide carbonyl coupled to general acid catalysis at the amide oxygen can also be ruled out. (c) A mechanistic pathway that remains viable involves general acid proton delivery to the amide nitrogen by a carboxyl, while the other carboxylate engages in nucleophilic attack upon the amide carbonyl; a substantially unchanged amide carbonyl in the transition state; two concurrent bond-forming events; and a spatiotemporal-base rate acceleration. This mechanism is supported by molecular dynamic simulations which confirm a persistent key intramolecular hydrogen bonding. These theoretical conclusions, although not easily verified by experiment, are consistent with a bell-shaped pH/rate profile but are at odds with hydrolysis mechanisms in the classic literature.

Molecular recognition of methamphetamine by carboxylatopillar[5]arene: drug-dependent complexation stoichiometry and insights into medical applications

The molecular recognition of the carboxylatopillar[5]arene on methamphetamine showed interconversion between H₂:G ⇋ H:G stoichiometries with dependence on drug concentration.

Inhibitory and Cooperative Effects Regulated by pH in Host-Guest Complexation between Cationic Pillar[5]arene and Reactive 2-Carboxyphthalanilic Acid

The study of host-guest complexation between reactive 2-carboxyphthalanilic acid (CPA) and two cationic pillararenes has been carried out. Host-guest complexation with significant kinetic effects was observed only with the smaller cavity size pillararene (P5A). Kinetics in the pH range 1.50-6.40, ESI-MS, ¹H NMR titration, and ROESY experiments were performed to characterize the complexes. High binding stoichiometry (H:G₂) was observed for all CPA protonation states. The system is pH-dependent, and inversion of cooperativity (negative to positive) occurs by increasing the dianionic CPA^2- concentration (allosteric behavior). Toward physiological pH, association constant K_1:1 does not change (10⁴ M^-1), and K_1:2 increased from 10² to 10⁴ M^-1, as well as the inhibitory effect increased up to 222-fold. NMR results elucidated the structure of the complex and allowed us to create a map of H-H interactions that describes well the diversity and number of interactions in the complex.

Synthesis of Glycosyl Amides Using Selenocarboxylates as Traceless Reagents for Amide Bond Formation

Carbohydrate-derived amides were successfully prepared in good yields from a broad range of substrates, including furanosyl and pyranosyl derivatives. The methodology successfully relied on the in situ generation of lithium selenocarboxylates from Se/LiEt3BH and acyl chlorides or carboxylic acids and their reaction with sugar azides. A key aspect of the present protocol is that we start from elemental selenium; isolation and handling of all reactive and sensitive selenium-containing intermediates is avoided, therefore providing the selenocarboxylate the status of a traceless reagent.

Stereoselective glycoconjugation of steroids with selenocarbohydrates

A methodology that brings together sugar and steroid scaffolds linked by a selenium atom is discussed in this work.

Seleno- and telluro-xylofuranosides attenuate Mn-induced toxicity in C. elegans via the DAF-16/FOXO pathway

Organochalcogens are promising pharmacological agents that possess significant biological activities. Nevertheless, because of the complexity of mammalian models, it has been difficult to determine the molecular pathways and specific proteins that are modulated in response to treatments with these compounds. The nematode worm Caenorhabditis elegans is an alternative experimental model that affords easy genetic manipulations, green fluorescent protein tagging and in vivo live analysis of toxicity. Abundant evidence points to oxidative stress in mediating manganese (Mn)-induced toxicity. In this study we challenged worms with Mn, and investigated the efficacy of inedited selenium- and tellurium-xylofuranosides in reversing and/or protecting the worms from Mn-induced toxicity. In addition, we investigated their putative mechanism of action. First, we determined the lethal dose 50% (LD50) and the effects of the xylofuranosides on various toxic parameters. This was followed by studies on the ability of xylofuranosides to afford protection against Mn-induced toxicity. Both Se- and Te-xylofuranosides increased the expression of superoxide dismutase (SOD-3). Furthermore, we observed that the xylofuranosides induced nuclear translocation of the transcription factor DAF-16/FOXO, which in the worm is known to regulate stress responsiveness, aging and metabolism. These findings suggest that xylofuranosides attenuate toxicity Mn-induced, by regulating the DAF-16/FOXO signaling pathway.