Asymmetric Mannich Reaction of Isatin-Derived Ketimines with α-Fluoroindanones Catalyzed by a Chiral Phase-Transfer Catalyst.

A highly enantioselective Mannich reaction of α-fluoroindanones with isatin-derived N-Boc-ketimines catalyzed by a quinine-derived phase-transfer catalyst was developed. A variety of 3-substituted 3-amino-2-oxindoles bearing fluorine-containing, vicinal, tetrasubstituted stereocenters were constructed using this protocol in high yields (83-95%), with moderate to excellent enantioselectivities (66-91%) and high diastereoselectivities (up to >99:1).

Sustainable aggregation-induced emission material based on pectin-l-lysine: Potential antibacterial and monitoring in food spoilage.

The demand of smart food detection system which in detecting food spoilage is increasing. In this work, a new type of aggregation-induced emission (AIE) compound was synthesized based on pectin (P) and l-lysine (Lys). P-Lys is an AIE active compound which has the advantages of simple synthesis, easy modification and processability, it also has good water solubility and biocompatibility. Moreover, P-Lys has potential application in detecting Fe3+ (oxidation from Fe2+) and bacterial in monitoring pork spoilage. In addition, P-Lys also has spectral antibacterial properties which can prevent pork spoilage. The research results shown that P-Lys, as a new type of food testing agent has a useful future in monitoring and protecting the freshness of food.

Corrigendum to "Photoluminescence of Tilapia skin collagen: Aggregation-induced emission with clustering triggered emission mechanism and its multiple applications" [Int. J. Biol. Macromol. 182 (2021) 1437-1444].

There is an urgent need for natural sources of aggregation-induced emission (AIE) materials which have good water solubility, biocompatibility, and can be produced in large quantities. Here, Tilapia skin collagen (Tsc) is a very abundant protein in nature, with solid-phase and solution-state fluorescence emission effect and its multiple applications was explored.Due to Tsc was in high concentration or aggregation state which shown AIE property. This obvious emission can be account for clustering-triggered emission (CTE) mechanism. The photoluminescence property of Tsc not only provide a deeper understanding of the emission characteristics of proteins, but also has important guiding significance for further elucidating the basis of fluorescence properties.

Aymmetric Aza-Friedel-Crafts Reaction of Isatin-Derived Ketimines with Indoles Catalyzed by a Chiral Phase-Transfer Catalyst.

A highly enantioselective aza-Friedel-Crafts reaction of 1H-indoles with isatin-derived N-Cbz-ketimines catalyzed by quinine-derived phase-transfer catalysts was developed. A series of chiral 3-aminobisindole compounds containing a tetrasubstituted stereocenter were constructed by this protocol in high yields (82-91%) and moderate to excellent enantioselectivities (46-94% ee).

Seeking Aggregation-Induced Emission Materials in Food: Oat ß-Glucan and Its Diverse Applications.

With the basic understanding and broad application prospects of luminescent materials, the emission mechanism of unconventional luminescent agents has been revealed gradually. Here, we report a non-conjugated biomass material, oat ß-glucan (oat-ß-Glu), which actually does not emit light in a dilute solution but emits significantly when forming aggregates. Inherently visible emission of oat-ß-Glu from the concentrated solutions and solid state could be observed. In addition, we have observed room temperature phosphorescence in oat-ß-Glu powders, which is also unusual in pure organic materials. It can be proposed that the luminescence property of oat-ß-Glu originates from the spatial conjugation of the oxygen atoms of oat-ß-Glu. This clustering-triggered emission mechanism may well be expanded to other unconventional biomacromolecules, inspiring the rational design of luminescent agents. Due to its good biocompatibility and intrinsic emission characteristics, oat-ß-Glu has shown great potential application prospects in bioimaging and biosensors.

Photoluminescence of Tilapia skin collagen: Aggregation-induced emission with clustering triggered emission mechanism and its multiple applications.

There is an urgent need for natural sources of aggregation-induced emission (AIE) materials which have good water solubility, biocompatibility, and can be produced in large quantities. Here, Tilapia skin collagen (Tsc) is a very abundant protein in nature, with solid-phase and solution-state fluorescence emission effect and its multiple applications was explored. Due to Tsc was in high concentration or aggregation state which shown AIE property. This obvious emission can be account for clustering-triggered emission (CTE) mechanism. The photoluminescence property of Tsc not only provide a deeper understanding of the emission characteristics of proteins, but also has important guiding significance for further elucidating the basis of fluorescence properties.

Novel Chiral Thiourea Derived from Hydroquinine and l-Phenylglycinol: An Effective Catalyst for Enantio- and Diastereoselective Aza-Henry Reaction.

A series of chiral thiourea bearing multiple H-bond donors derived from hydroquinine has been reported. The aza-Henry reaction of isatin-derived ketimines and long-chain nitroalkanes catalyzed by these chiral thioureas can achieve high enantioselectivity (78-99% ee) and excellent diastereoselectivity (up to 99:1). This work is the first report on long-chain nitroalkanes as substrates with excellent diastereoselectivity in metal-free catalytic systems.

Enantioselective addition of thiols to trifluoromethyl ketimines: synthesis of N,S-ketals.

An efficient enantioselective addition of thiols to acyclic trifluoromethyl ketimines has been established by using a bifunctional squaramide catalyst, which was derived from quinine, and the reaction was completed in 5 to 10 min. The construction of chiral tetrasubstituted carbon centers bearing trifluoromethylated N,S-ketals has been achieved in high yields (up to 96% yield) with excellent enantioselectivities (up to 99% ee).

Synthesis of 4-Azaindolines Using Phase-Transfer Catalysis via an Intramolecular Mannich Reaction.

A series of bifunctional asymmetric phase-transfer catalysts containing novel fluorine-containing urea groups derived from cinchona alkaloids have been synthesized and successfully applied in the asymmetric intramolecular Mannich reaction. The 4-azaindoline products bearing multiple substrates were obtained in excellent yield (90-99%), with high enantioselectivity (up to 95%) and diastereoselectivity (up to >99:1).

Highly Enantioselective Synthesis of Acyclic N,N'-Acetals by Chiral Urea Derived from Quinine Catalyzed the Addition of Aryl Amines to Isatin-Derived Ketimines.

N,N'-Acetals are sensitive compounds, and the challenging asymmetric synthesis of acyclic N,N'-acetals by the general addition of amines to ketimines has never been reported so far. In this study, highly enantioselective addition of aryl amines to isatin-derived ketimines catalyzed by chiral urea derived from quinine was developed. A series of new acyclic N,N'-acetals were constructed by this protocol in high to excellent yields (78-99%) and high to excellent enantioselectivities (76-96% ee).

Unusual temperature-sensitive excimer fluorescence from discrete π-π dimer stacking of anthracene in a crystal.

Herein, an unusual blue shift in excimer fluorescence with increasing temperature was observed from a crystal with a discrete π-π anthracene dimer, originating from the more temperature-sensitive intermolecular geometry of the π-π dimer (e.g., π-π distance) compared to the intramolecular geometry of the monomer, which is confirmed by temperature-dependent single-crystal X-ray diffraction (XRD) measurements.

Direct enantio- and diastereoselective Mannich reactions of isatin-derived ketimines with oxo-indanecarboxylates catalyzed by chiral thiourea derived from hydroquinidine.

A highly diastereo- and enantioselective Mannich reaction of isatin-derived ketimines with oxo-indanecarboxylates catalyzed by chiral thiourea derived from hydroquinidine has been developed. A series of 3-substituted 3-amino-oxindoles containing assembled bicyclic rings linked by a C-C bond were constructed by this protocol in excellent yields (92-99%) with high enantioselectivities (85-99% ee) and diastereoselectivities (up to >99 : 1 dr).

Cobalt Nanoparticles/Black Phosphorus Nanosheets: An Efficient Catalyst for Electrochemical Oxygen Evolution.

Black phosphorus (BP) nanosheet (NS) is an emerging oxygen evolution reaction (OER) electrocatalyst with both high conductivity and abundant active sites. However, its ultrathin structure suffers instability because of the lone pair electrons exposed at the surface, which badly restricts durability for achieving long-term OER catalysis. Herein, a facile solvothermal reduction route is designed to fabricate Co/BP NSs hybrid electrocatalyst by in situ growth of cobalt nanoparticles on BP NSs. Notably, electronic structure engineering of Co/BP NSs catalyst is observed by electron migration from BP to Co due to the higher Fermi level of BP than that of Co. Because of the preferential migration of the active lone pairs from the defect of BP NSs, the stability and high hole mobility can be effectively retained. Consequently, Co/BP NSs electrocatalyst exhibits outstanding OER performance, with an overpotential of 310 mV at 10 mA cm-2, and excellent stability in alkaline media, indicating the potential for the alternatives of commercial IrO2. This study provides insightful understanding into engineering electronic structure of BP NSs by fully utilizing defect and provides a new idea to design hybrid electrocatalysts.

Bifunctional Thiourea-Ammonium Salt Catalysts Derived from Cinchona Alkaloids: Cooperative Phase-Transfer Catalysts in the Enantioselective Aza-Henry Reaction of Ketimines.

An efficient enantioselective aza-Henry reaction of aryl α-ketoester-derived ketimines has been realized by using bifunctional thiourea-ammonium salt phase-transfer catalysts, which were derived from quinine. A variety of aryl α-ketoester-derived N-Ts ketimines were investigated, and the corresponding products were obtained in high to excellent yields (up to 99%) with good to high enantioselectivities (up to >99% ee).

Novel α-amino acid-derived phase-transfer catalyst application to a highly enantio- and diastereoselective nitro-Mannich reaction.

New quaternary ammonium types of bifunctional asymmetric phase-transfer catalysts bearing multiple hydrogen-bonding donors derived from α-amino acids were readily prepared and found to be highly efficient in the asymmetric nitro-Mannich reactions of amidosulfones. Very broad substrate generality was observed, and the products were achieved in high enantio-/diastereoselectivities (90->99.9% ee, 90 : 10 to 92 : 8 dr). Compared with previous reports, the enantioselectivity of aliphatic amidosulfones has been improved to a high level (91-93% ee).

Spatial separation of the hydrogen evolution center from semiconductors using a freestanding silica-sphere-supported Pt composite.

Spatial separation of the reduction center (photosystem I) and oxidation center (photosystem II) is an obvious characteristic of natural photosynthesis. Enlightened by this natural process, a simple material based on silica-sphere-supported Pt nanoparticles (SSP) was designed as a freestanding hydrogen evolution center for semiconductor photocatalysts. In situ photoluminescence characterization showed that the radiation recombination of electron-hole pairs in semiconductors (i.e. TiO2 and CdS) was well suppressed due to the presence of SSP. And the quenching efficiency increases with the hydrogen evolution rate of photocatalysts. These results indicated that SSP could effectively trap electrons from the photoexcited semiconductors during collision between SSP and semiconductor, and then complete the hydrogen evolution reaction over the Pt nanoparticles. Detailed investigation also showed that the performance of SSP was influenced by several factors, including the particle size of the silica sphere and the physical and chemical states of Pt nanoparticles. Besides, it was demonstrated that the loaded metal was not limited to Pt. Pd, Ni and Au can also be used as active sites in this freestanding cocatalyst strategy.

Enantio- and Diastereoselective Nitro-Mannich Reaction of α-Aryl Nitromethanes with Amidosulfones Catalyzed by Phase-Transfer Catalysts.

A high-yield, highly diastereo- and enantioselective nitro-Mannich reaction of α-aryl nitromethanes with amidosulfones catalyzed by a novel chiral phase-transfer catalyst, bearing multiple H-bonding donors, derived from quinine was developed. A variety of α-aryl nitromethanes and amidosulfones were investigated; and the corresponding products were obtained in excellent yields with excellent diastereo- and enantioselectivities (up to 99% yield, > 99:1 dr and >99% ee). As a demonstration of synthetic utility, the resulting ß-nitroamines could be converted to corresponding meso-symmetric and optically pure unsymmetric anti-1,2-diarylethylenediamines.

Base-Promoted Intermolecular Cyclization of Substituted 3-Aryl(Heteroaryl)-3-chloroacrylaldehydes and Tetrahydroisoquinolines: An Approach to Access Pyrrolo[2,1-a]isoquinolines.

We have developed a new base-promoted intermolecular cascade cyclization reaction of substituted 3-aryl(heteroaryl)-3-chloroacrylaldehydes and tetrahydroisoquinolines in one pot. The reaction provides a facile and practical synthesis of pyrrolo[2,1-a]isoquinolines. A number of pyrrolo[2,1-a]isoquinolines were synthesized in moderate to high yields (up to 97%).

Investigation of c ions formed by N-terminally charged peptides upon collision-induced dissociation.

Peptide fragments such as b and y sequence ions generated upon low-energy collision-induced dissociation have been routinely used for tandem mass spectrometry (MS/MS)-based peptide/protein identification. The underlying formation mechanisms have been studied extensively and described within the literature. As a result, the 'mobile proton model' and 'pathways in competition model' have been built to interpret a majority of peptide fragmentation behavior. However, unusual peptide fragments which involve unfamiliar fragmentation pathways or various rearrangement reactions occasionally appear in MS/MS spectra, resulting in confused MS/MS interpretations. In this work, a series of unfamiliar c ions are detected in MS/MS spectra of the model peptides having an N-terminal Arg or deuterohemin group upon low-energy collision-induced dissociation process. Both the protonated Arg and deuterohemin group play an important role in retention of a positive charge at the N-terminus that is remote from the cleavage sites. According to previous reports and our studies involving amino acid substitutions and hydrogen-deuterium exchange, we propose a McLafferty-type rearrangement via charge-remote fragmentation as the potential mechanism to explain the formation of c ions from precursor peptide ions or unconventional b ions. Density functional theory calculations are also employed in order to elucidate the proposed fragmentation mechanisms. Copyright © 2016 John Wiley & Sons, Ltd.