Adhesion forces between hybrid colloidal particles and concanavalin A

Hybrid particles of poly(methyl methacrylate) and carboxymethylcellulose, PMMA/CMC, were attached to atomic force microscopy cantilevers and probed against concanavalin A (ConA) films formed either on Si wafers or on CMC substrate. Regardless of the substrate, the approach curves showed different inclinations, indicating that the probe first touches a soft surface and then a hard substrate. The distance corresponding to the soft layer was estimated as 20 +/- 10 nm and was attributed to the CMC layers attached to the hybrid particles surfaces. Probing PMMA/CMC particles against ConA adsorbed onto Si wafers yielded retract curves with a sawlike pattern. The average range of adhesion forces (maximum pull-off distance) and mean adhesion force were estimated as 100 +/- 40 nm and -11 +/- 7 nN, respectively, evidencing multiple adhesions between CMC sugar residues and ConA. However, upon probing against ConA adsorbed onto CMC substrates, the mean pull-off distance and mean adhesion force were reduced to 37 +/- 18 nm and -3 +/- 1 nN, respectively, indicating that the ConA molecules immobilized onto CMC films are less available to interact with the hybrid particle than the ConA molecules adsorbed onto Si wafers. Another set of experiments, where PMMA/CMC particle probed against ConA-covered Si wafers in the presence of mannose, showed that the addition of mannose led to a considerable decrease in the mean adhesion force from -11 +/- 7 to -3 +/- 1 nN. Two hypotheses have been considered to explain the effect caused by mannose addition. The first suggested the desorption of ConA from the substrate so that the hybrid particle would probe bare Si wafer (weak adhesion). The second proposed the adsorption of mannose onto the ConA layer so that mannose layer would probe against another mannose layer, leading to low adhesion forces. In situ ellipsometry and capillary electrophoresis have been applied to check the hypotheses.     

A molecular tool kit for the variable design of logic operations (NOR, INH, EnNOR)

A simple set of five components was used to design molecular logic gates based on phthalimide-sensitised Tb(III) luminescence, including the first report of an enabled NOR (EnNOR) gate.     

[(NHC)NiIIH]‐Catalyzed Cross‐Hydroalkenylation of Cyclopropenes with Alkynes: Cyclopentadiene Synthesis by [(NHC)NiII]‐Assisted C−C Rearrangement

A cross‐hydroalkenylation/rearrangement cascade (HARC), using a cyclopropene and alkyne as substrate pairs, was achieved for the first time by using new [(NHC)Ni(allyl)]BAr^F catalysts (NHC=N‐heterocyclic carbenes). By controlling the (NHC)Ni^IIH relative insertion reactivity with cyclopropene and alkyne, a broad scope of cyclopentadienes was obtained with highly selectively. The structural features of the new (NHC)Ni^II catalyst were important for the success of the reaction. The mild reaction conditions employed may serve as an entry for exploring (NHC)Ni^II‐assisted vinylcyclopropane rearrangement reactivity.     

Isotopic Labeling Reveals Active Reaction Interfaces for Electrochemical Oxidation of Lithium Peroxide

The unresolved debate on the active reaction interface of electrochemical oxidation of lithium peroxide (Li₂O₂) prevents rational electrode and catalyst design for lithium‐oxygen (Li‐O₂) batteries. The reaction interface is studied by using isotope‐labeling techniques combined with time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and on‐line electrochemical mass spectroscopy (OEMS) under practical cell operation conditions. Isotopically labelled microsized Li₂O₂ particles with an Li₂¹⁶O₂/electrode interface and an Li₂¹⁸O₂/electrolyte interface were fabricated. Upon oxidation, ¹⁸O₂ was evolved for the first quarter of the charge capacity followed by ¹⁶O₂. These observations unambiguously demonstrate that oxygen loss starts from the Li₂O₂/electrolyte interface instead of the Li₂O₂/electrode interface. The Li₂O₂ particles are in continuous contact with the catalyst/electrode, explaining why the solid catalyst is effective in oxidizing solid Li₂O₂ without losing contact.     

Unveiling the Intrinsic Catalytic Activities of Single‐Gold‐Nanoparticle‐Based Enzyme Mimetics

Gold nanoparticles (AuNPs) have been demonstrated to serve as effective nanomaterial‐based enzyme mimetics (nanozymes) for a number of enzymatic reactions under mild conditions. The intrinsic glucose oxidase and peroxidase activities of single AuNPs and Ag–Au nanohybrids, respectively, were investigated by single NP collision electrochemical measurements. A significantly high turnover number of nanozymes was obtained from individual catalytic events compared with the results from the classical, ensemble‐averaged measurements. The unusual enhancement of catalytic activity of single nanozymes is believed to originate from the high accessible surface area of monodispersed NPs and the high activities of carbon‐supported NPs during single‐particle collision at a carbon ultramicroelectrode. This work introduces a new method for the precise characterization of the intrinsic catalytic activities of nanozymes, giving further insights to the design of high‐efficiency nanomaterial catalysts.     

Catalytic Generation of C1 Ammonium Enolates from Halides and CO for Asymmetric Cascade Reactions

A general strategy for the design of asymmetric cascade reactions using readily available halides and carbon monoxide (CO) as substrates is developed. The key is the catalytic generation of C1‐ammonium enolates for the subsequent asymmetric cascade reactions through the combination of palladium‐catalyzed carbonylation and chiral Lewis base catalysis. Utilizing this strategy, we have established asymmetric formal [1+1+4] and [1+1+2] reactions to afford chiral dihydropyridones and β‐lactams with high yields and high enantio‐ and diastereoselectivities.     

Reversible Sodium Metal Electrodes: Is Fluorine an Essential Interphasial Component?

Alkaline metals are an ideal negative electrode for rechargeable batteries. Forming a fluorine‐rich interphase by a fluorinated electrolyte is recognized as key to utilizing lithium metal electrodes, and the same strategy is being applied to sodium metal electrodes. However, their reversible plating/stripping reactions have yet to be achieved. Herein, we report a contrary concept of fluorine‐free electrolytes for sodium metal batteries. A sodium tetraphenylborate/monoglyme electrolyte enables reversible sodium plating/stripping at an average Coulombic efficiency of 99.85 % over 300 cycles. Importantly, the interphase is composed mainly of carbon, oxygen, and sodium elements with a negligible presence of fluorine, but it has both high stability and extremely low resistance. This work suggests a new direction for stabilizing sodium metal electrodes via fluorine‐free interphases.     

Cleavage of C(aryl)−CH3 Bonds in the Absence of Directing Groups under Transition Metal Free Conditions

Organic chemists now can construct carbon–carbon σ‐bonds selectively and sequentially, whereas methods for the selective cleavage of carbon–carbon σ‐bonds, especially for unreactive hydrocarbons, remain limited. Activation by ring strain, directing groups, or in the presence of a carbonyl or a cyano group is usually required. In this work, by using a sequential strategy site‐selective cleavage and borylation of C(aryl)?CH₃ bonds has been developed under directing group free and transition metal free conditions. Methyl groups of various arenes are selectively cleaved and replaced by boryl groups. Mechanistic analysis suggests that it proceeds by a sequential intermolecular oxidation and coupling of a transient aryl radical, generated by radical decarboxylation, involving a pyridine‐stabilized persistent boryl radical.     

Designed Synthesis of a 2D Porphyrin‐Based sp2 Carbon‐Conjugated Covalent Organic Framework for Heterogeneous Photocatalysis

The construction of stable covalent organic frameworks (COFs) for various applications is highly desirable. Herein, we report the synthesis of a novel two‐dimensional (2D) porphyrin‐based sp² carbon‐conjugated COF (Por‐sp²c‐COF), which adopts an eclipsed AA stacking structure with a Brunauer—Emmett—Teller surface area of 689 m² g^?1. Owing to the C=C linkages, Por‐sp²c‐COF shows a high chemical stability under various conditions, even under harsh conditions such as 9 m HCl and 9 m NaOH solutions. Interestingly, Por‐sp²c‐COF can be used as a metal‐free heterogeneous photocatalyst for the visible‐light‐induced aerobic oxidation of amines to imines. More importantly, in comparison to imine‐linked Por‐COF, the inherent structure of Por‐sp²c‐COF equips it with several advantages as a photocatalyst, including reusability and high photocatalytic performance. This clearly demonstrates that sp² carbon‐linked 2D COFs can provide an interesting platform for heterogeneous photocatalysis.     

Protecting‐Group‐Controlled Enzymatic Glycosylation of Oligo‐N‐Acetyllactosamine Derivatives

We describe a chemoenzymatic strategy that can give a library of differentially fucosylated and sialylated oligosaccharides starting from a single chemically synthesized tri‐N‐acetyllactosamine derivative. The common precursor could easily be converted into 6 different hexasaccharides in which the glucosamine moieties are either acetylated (GlcNAc) or modified as a free amine (GlcNH₂) or Boc (GlcNHBoc). Fucosylation of the resulting compounds by a recombinant fucosyl transferase resulted in only modification of the natural GlcNAc moieties, providing access to 6 selectively mono‐ and bis‐fucosylated oligosaccharides. Conversion of the GlcNH₂ or GlcNHBoc moieties into the natural GlcNAc, followed by sialylation by sialyl transferases gave 12 differently fucosylated and sialylated compounds. The oligosaccharides were printed as a microarray that was probed by several glycan‐binding proteins, demonstrating that complex patterns of fucosylation can modulate glycan recognition.