Nitrogen-Doped Carbon Enables Heterogeneous Asymmetric Insertion of Carbenoids into Amines Catalyzed by Rhodium Nanoparticles

Development of stable heterogeneous catalyst systems is a crucial subject to achieve sustainable society. Though metal nanoparticles are robust species, the study of asymmetric catalysis by them has been restricted because methods to activate metal nanoparticles without causing metal leaching were limited. We developed Rh nanoparticle catalysts (NCI-Rh) supported on nitrogen-doped carbon as a solid ligand to interact with metals for asymmetric insertion of carbenoids into N-H bonds cocatalyzed by chiral phosphoric acid. Nitrogen dopants played a crucial role in both catalytic activity and enantioselectivity while almost no catalysis was observed with Rh nanoparticles immobilized on supports without nitrogen dopants. Various types of chiral α-amino acid derivatives were synthesized in high yields with high enantioselectivities and NCI-Rh could be reused in seven runs. Furthermore, we demonstrated the corresponding continuous-flow reaction using a column packed with NCI-Rh. The desired product was obtained efficiently for over 90 h through the reactivation of NCI-Rh and the chiral source could be recovered.

Cyclic Thiosulfinates as a Novel Class of Disulfide Cleavable Cross-Linkers for Rapid Hydrogel Synthesis

We recently reported that cyclic thiosulfinates are cysteine selective cross-linkers that avoid the "dead-end" modifications that contribute to other cross-linkers' toxicity. In this study, we generalize the chemistry of cyclic thiosulfinates to that of thiol selective cross-linking and apply them to the synthesis of hydrogels. Thiol-functionalized four-arm poly(ethylene glycol) and hyaluronic acid monomers were cross-linked with 1,2-dithiane-1-oxide to form disulfide cross-linked hydrogels within seconds. The synthesized hydrogel could be reduced with physiological concentrations of glutathione, which modulated hydrogel mechanical properties and degradation kinetics. Bovine serum albumin protein was successfully encapsulated in hydrogel, and diffusion-mediated release was demonstrated in vitro. Hep G2 cells grew in the presence of preformed hydrogel and during hydrogel synthesis, demonstrating acceptable cytotoxicity. We encapsulated cells within a hydrogel and demonstrated cell growth and recovery up to 10 days, with and without cell adhesion peptides. In summary, we report cyclic thiosulfinates as a novel class of cross-linkers for the facile synthesis of biodegradable hydrogels.

Metal Catalysis in Thiolation and Selenation Reactions of Alkynes Leading to Chalcogen-Substituted Alkenes and Dienes

This review covers recent achievements in metal-catalyzed Z-H and Z-Z (Z=S, Se) bond addition to the triple bonds of alkynes-a convenient and atom-efficient way to carbon-element bond formation. Various catalytic systems (both homogeneous and heterogeneous) developed to date to obtain mono- and bis-chalcogen-substituted alkenes or dienes, as well as carbonyl compounds or heterocycles, starting from simple and available alkynes and chalcogenols or dichalcogenides are described. The right choice of metal and ligands allows us to perform these transformations with high selectivities under mild reaction conditions, thus tolerating unprotected functional groups in substrates and broadening ways of further modification of the products. The main aim of the review is to show the potential of the catalytic methods developed in synthetic organic chemistry. Thus, emphasis is made on the scope of reactions, types of products that can be selectively formed, convenience, and scalability of the catalytic procedures. A brief mechanistic description is also given to introduce new readers to the topic.

One-pot conversion of cellobiose to mannose using a hybrid phosphotungstic acid–cerium oxide catalyst

Two-step conversion of cellobiose to mannose using hybrid catalyst.

Steric effect of the dithiolato linker on the reduction mechanism of [Fe2(CO)6{μ-(XCH2)2CRR′}] hydrogenase models (X = S, Se)

Investigations of the electrochemical properties of [Fe₂(CO)₆{μ-(XCH₂)₂CRR′}] (X = S, Se; R or R′ = H or Me) showed that the complex with the bulkiest CMe₂moiety undergoes reduction with potential inversion.

Self-assembled selenium monolayers: from nanotechnology to materials science and adaptive catalysis

Self-assembled monolayers (SAMs) of selenium have emerged into a rapidly developing field of nanotechnology with several promising opportunities in materials chemistry and catalysis. Comparison between sulfur-based self-assembled monolayers and newly developed selenium-based monolayers reveal outstanding complimentary features on surface chemistry and highlighted the key role of the headgroup element. Diverse structural properties and reactivity of organosulfur and organoselenium groups on the surface provide flexible frameworks to create new generations of materials and adaptive catalysts with unprecedented selectivity. Important practical utility of adaptive catalytic systems deals with development of sustainable technologies and industrial processes based on natural resources. Independent development of nanotechnology, materials science and catalysis has led to the discovery of common fundamental principles of the surface chemistry of chalcogen compounds.