Design of Unconventional Polymers with Thermal Contraction Units for High-Performance Dental Adhesives.

The coefficient of thermal expansion (CTE) of adhesives is considered to be a vital parameter for dental restoration due to the oral temperature fluctuation induced by hot and cold drinks in daily life. Even more challenging, the adhesives need to bond various materials with different CTE values, and mismatched thermal expansion at the interface of two materials will produce thermal stress and cause cracking, leading to bond failure. In this study, we designed and synthesized a divinyl monomer containing a dibenzocyclooctadiene (DBCOD) unit, which was incorporated into a commercial adhesive, Single Bond Universal (SBU) to prepare low CTE adhesives.

Molecular dynamics study on thermal conductance between a nanotip and a substrate under vertical forces and horizontal sliding.

The heat transfer between a nanotip and its substrate is extremely complex but is a key factor in determining the measurement accuracy in tip-assisted nanomanufacturing and thermometry. In this work, the heat transfer from the nanotip to the substrate during sliding is investigated using molecular dynamics simulations. Interfacial interaction and bond formation are analyzed during the sliding process.

Ballistic Thermal Transport at Sub-10 nm Laser-Induced Hot Spots in GaN Crystal.

Ballistic thermal transport at nanoscale hotspots will greatly reduce the performance of a Gallium nitride (GaN) device when its characteristic length reaches the nanometer scale. In this work, the authors develop a tip-enhanced Raman thermometry approach to study ballistic thermal transport within the range of 10 nm in GaN, simultaneously achieving laser heating and measuring the local temperature. The Raman results show that the temperature increase from an Au-coated tip-focused hotspot up to two times higher (40 K) than that in a bare tip-focused region (20 K).

A DFT study on the C-H oxidation reactivity of Fe(iv)-oxo species with N4/N5 ligands derived from l-proline.

The hydroxylation of hexane by two FeO complexes bearing a pentadentate ligand (N5, Pro3Py) and a tetradentate ligand (N4, Pro2PyBn) derived from l-proline was studied by DFT calculations. Theoretical results predict that both FeO complexes hold triplet ground states. The hydrogen atom abstraction (HAA) processes by both FeO species proceed through a two-state reactivity, thus indicating that HAA occurs a low-barrier quintet surface.

Catalytic Enantioselective Methylene C(sp)-H Hydroxylation Using a Chiral Manganese Complex/Carboxylic Acid System.

Achieving direct C-H hydroxylation in a highly diastereo- and enantioselective manner is still a challenging goal. This reaction is mainly hindered by the potential for overoxidation of the generated alcohols as well as low stereoselectivity. Herein, we present an enantioselective benzylic C-H hydroxylation catalyzed by a manganese complex, HO, and a carboxylic acid in 2,2,2-trifluoroethanol.

Ligand regulation for manganese-catalyzed enantioselective epoxidation of olefins without acid.

A novel manganese catalyst bearing an l-proline-derived N4 ligand has been developed for enabling acid-free asymmetric epoxidation of olefins with tert-butyl hydroperoxide as the oxidant. A variety of olefins that are well-matched in size with the ligand pocket can be transformed to epoxides with excellent enantioselectivities. The smaller ligand pocket is also beneficial to the enantioselective epoxidation of simple olefins.

Bioinspired Manganese and Iron Complexes for Enantioselective Oxidation Reactions: Ligand Design, Catalytic Activity, and Beyond.

The development of efficient methods for the enantioselective oxidation of organic molecules continues to be an important goal in organic synthesis; in particular, the use of earth-abundant metal catalysts and environmentally friendly oxidants in catalytic asymmetric oxidation reactions has attracted significant interest over the last several decades. In nature, metalloenzymes catalyze a wide range of oxidation reactions by activating dioxygen under mild conditions. Inspired by selective and efficient oxidation reactions catalyzed by metalloenzymes, researchers have developed a number of synthetic model compounds that mimic the functionality of metalloenzymes.

Manganese-Catalyzed Asymmetric Oxidation of Methylene C-H of Spirocyclic Oxindoles and Dihydroquinolinones with Hydrogen Peroxide.

A highly efficient strategy for the enantioselective oxidation of methylene C-H of spirocyclic oxindoles and dihydroquinolinones has been established, in which an earth-abundant manganese catalyst and hydrogen peroxide are used. Noteworthy, the manganese catalyst can be applied to the asymmetric hydroxylation of spirocyclic 2,3-dihydroquinolin-4-ones with 94-99% ee.

Efficient Aliphatic C-H Bond Oxidation Catalyzed by Manganese Complexes with Hydrogen Peroxide.

A tetradentate nitrogen ligand containing a benzimidazole ring and an electron-rich pyridine ring was developed, the resulting manganese complex exhibited good activity in the C-H oxidation of simple alkanes. In particular, cyclic aliphatic alkanes were transformed into ketones in very good yields (up to 89 %) by using environmentally benign H O as the terminal oxidant. This protocol was also applied successfully in benzylic C-H oxidation, giving the corresponding ketones with very good selectivities.

CO as a C1 Source: B(CF)-Catalyzed Cyclization of o-Phenylene-diamines To Construct Benzimidazoles in the Presence of Hydrosilane.

The catalytic construction of benzimidazoles using CO as a carbon source represents a facile and sustainable approach to obtaining these valuable compounds. Herein, we describe the B(CF)-catalyzed synthesis of benzimidazoles via cyclization of o-phenylenediamines with CO and PhSiH. This metal-free catalytic route achieves the desired products in high yield under convenient reaction conditions and is applicable to a broad substrate scope.

Enantioselective synthesis of spirooxindole benzoquinolizines via organo-catalyzed cascade reactions.

A Michael-Mannich-hemiaminalization-dehydration cascade reaction was developed for the construction of spirooxindole benzoquinolizine derivatives. Additionally, spirooxindole benzoindolizidine was prepared conveniently through a ring-contracted rearrangement reaction from spirooxindole benzoquinolizine.

Squaramide-Catalyzed Synthesis of Enantioenriched Spirocyclic Oxindoles via Ketimine Intermediates with Multiple Active Sites.

A new method for the construction of five-membered spirocyclic oxindoles is based on a Michael-Mannich cascade reaction of a ketimine intermediated catalyzed by a bifunctional quinine-derived squaramide. The desired products were obtained in excellent yields (up to 94%) and stereoselectivities (up to >20:1 d.r.