Underpotential Deposition‐Induced Synthesis of Composition‐Tunable Pt?Cu Nanocrystals and Their Catalytic Properties

Pt? Cu alloy octahedral nanocrystals (NCs) have been synthesized successfully by using N,N‐dimethylformamide as both the solvent and the reducing agent in the presence of cetyltrimethylammonium chloride. Cu underpotential deposition (UPD) is found to play a key role in the formation of the Pt? Cu alloy NCs. The composition in the Pt? Cu alloy can be tuned by adjusting the ratio of metal precursors in solution. However, the Cu content in the Pt? Cu alloy NCs cannot exceed 50 %. Due to the fact that Cu precursor cannot be reduced to metallic copper and the Cu content cannot exceed 50 %, we achieved the formation of the Pt? Cu alloy by using Cu UPD on the Pt surface. In addition, the catalytic activities of Pt? Cu alloy NCs with different composition were investigated in electrocatalytic oxidation of formic acid. The results reveal that the catalytic performance is strongly dependent on Pt? Cu alloy composition. The sample of Pt₅₀Cu₅₀ exhibits excellent activity in electrocatalytic oxidation of formic acid.     

Bioconjugation of Proteins with a Paramagnetic NMR and Fluorescent Tag

Site‐specific labeling of proteins with lanthanide ions offers great opportunities for investigating the structure, function, and dynamics of proteins by virtue of the unique properties of lanthanides. Lanthanide‐tagged proteins can be studied by NMR, X‐ray, fluorescence, and EPR spectroscopy. However, the rigidity of a lanthanide tag in labeling of proteins plays a key role in the determination of protein structures and interactions. Pseudocontact shift (PCS) and paramagnetic relaxation enhancement (PRE) are valuable long‐range structure restraints in structural‐biology NMR spectroscopy. Generation of these paramagnetic restraints generally relies on site‐specific tagging of the target proteins with paramagnetic species. To avoid nonspecific interaction between the target protein and paramagnetic tag and achieve reliable paramagnetic effects, the rigidity, stability, and size of lanthanide tag is highly important in paramagnetic labeling of proteins. Here 4′‐mercapto‐2,2′: 6′,2′′‐terpyridine‐6,6′′‐dicarboxylic acid (4MTDA) is introduced as a a rigid paramagnetic and fluorescent tag which can be site‐specifically attached to a protein by formation of a disulfide bond. 4MTDA can be readily immobilized by coordination of the protein side chain to the lanthanide ion. Large PCSs and RDCs were observed for 4MTDA‐tagged proteins in complexes with paramagnetic lanthanide ions. At an excitation wavelength of 340 nm, the complex formed by protein–4MTDA and Tb³⁺ produces high fluorescence with the main emission at 545 nm. These interesting features of 4MTDA make it a very promising tag that can be exploited in NMR, fluorescence, and EPR spectroscopic studies on protein structure, interaction, and dynamics.     

Breathing Effect in a Cobalt Phosphonate upon Dehydration/Rehydration: A Single‐Crystal‐to‐Single‐Crystal Study

Two cobalt phosphonates, [Co₂(2,2′‐bpy)₂(H₂O)(pbtcH)] ( 1 ) and [Co₂(H₂O)(pbtcH)(phen)₂] ( 2 ; pbtcH₅=5‐phosphonatophenyl‐1,2,4‐tricarboxylic acid, 2,2′‐bpy=2,2′‐bipyridine, phen=1,10‐phenanthroline), with layer structures are reported. Compound 1 contains O‐C‐O and O‐P‐O bridged tetramers of Co₄, which are further connected by pbtcH^4? units to form a layer. In compound 2 , the cobalt tetramers made up of water‐bridged Co₂ dimers and O‐P‐O linkages are connected into a layer by pbtcH^4? units. Upon dehydration, compounds 1 and 2 experience single‐crystal‐to‐single‐crystal (SC–SC) structural transformations to form [Co₂(2,2′‐bpy)₂(pbtcH)] ( 1 a ) and [Co₂(pbtcH)(phen)₂] ( 2 a ), respectively. The process is reversible in each case. Notably, a breathing effect is observed for 1 , accompanied by pore opening and closing due to the reorientation of the coordinated 2,2′‐bpy molecules. The transformation was also monitored by in situ IR measurements. Magnetic studies reveal that antiferromagnetic interactions are mediated between the magnetic centers in compounds 1 and 1 a , whereas ferromagnetic interactions are dominant in compound 2 .     

A New Series of C‐6 Unsubstituted Tetrahydropyrimidines: Convenient One‐Pot Chemoselective Synthesis,Aggregation‐Induced and Size‐Independent Emission Characteristics

A new series of C‐6 unsubstituted tetrahydropyrimidines 6 have been directly synthesized via a convenient urea‐catalyzed chemoselective five‐component reaction (5CR) under mild conditions. Compounds 6 show typical aggregation‐induced emission enhancement (AIEE) characteristics because they are practically no emissive in solution but emit blue or green fluorescence in aggregates with fluorescence yield up to 93 %. One of the 5CR products, 6 aa , exhibits blue‐ and green‐fluorescence aggregates (bf‐ and gf‐aggregates). The bf‐ and gf‐aggregates are prepared under different conditions and proved to result from different J‐aggregations by single‐crystal X‐ray analysis. In addition, the bf‐ and gf‐aggregates of 6 aa show unusual size‐independent emission (SIE) characteristics because their maximum emission wavelengths in different sizes (suspension particles, film, powder and crystals) are the same, 434 and 484 nm, respectively. Based on the obtained experimental results, the 5CR mechanism, the origins of AIEE and SIE characteristics are discussed.     

Graphene Oxide Protected Nucleic Acid Probes for Bioanalysis and Biomedicine

Recently, the binding ability of DNA on GO and resulting nuclease resistance have attracted increasing attention, leading to new applications both in vivo and in vitro. In vivo, nucleic acids absorbed on GO can be effectively protected from enzymatic degradation and biological interference in complicated samples, making it useful for targeted delivery, gene regulation, intracellular detection and imaging with high uptake efficiencies, high intracellular stability, and very low toxicity. In vitro, the adsorption of ssDNA on GO surface and desorption of dsDNA or well‐folded ssDNA from GO surface result in the protection and deprotection of DNA from nucleic digestion, respectively, which has led to target‐triggered cyclic enzymatic amplification methods (CEAM) for amplified detection of analytes with sensitivity 2–3 orders of magnitude higher than that of 1:1 binding strategies. This Concept article explores some of the latest developments in this field.     

Preparation and characterization of oxidized regenerated cellulose film for hemostasis and the effect of blood on its surface

Hemostatic effects of oxidized regenerated cellulose (ORC) are well-known but its mechanism has never been demonstrated clearly. Since thrombus formation is a kind of surface phenomenon, we changed the morphology of cellulose to form a kind of membrane with ionic liquid as solution, and also we prepared ORC films with nitrogen dioxide(NO₂)/carbon tetrachloride(CCl₄) oxidation system reacting for 16, 40, 64 and 88 h, respectively. FTIR and NMR spectra showed that NO₂/CCl₄ oxidation system had a high selectivity on hydroxyl group at C6 of regenerated cellulose. With the oxidation time prolonging, the carboxyl content was enhanced and the DP was reduced. The XPS results suggested that a new carboxyl bond was formed due to the increasing of oxygen content. From contact angle analysis, the wettability of blood on the ORC film surface was better than that of the regenerated cellulose film, which was beneficial for the blood to spread. SEM photographs showed that the ORC film oxidized for 40 h could adsorb and activate more platelets and erythrocytes. Hemostatic evaluation and enzyme-linked immunosorbent assay indicated that the ORC film had a dramatic hemostatic performance, and the products of platelets release reaction, activated platelets glycoprotein and activated clotting enzymes were increased simultaneously. Moreover, the possible mechanism of the hemostasis for ORC film was discussed.     

Impacts of some macromolecules on the characteristics of hydrogels prepared from pineapple peel cellulose using ionic liquid

Composite hydrogels were prepared from pineapple peel cellulose with the combinations of polyethylene glycol (PEG), polyvinyl alcohol (PVA), к-carrageenan (CN), or soluble starch (SH) in 1-allyl-3-methylimidazolium chloride solvent. Impacts of these macromolecules on the texture profile analysis (TPA) parameters, equilibrium swelling ratio (ESR), and sodium salicylate (NaSA) load of the prepared hydrogels were studied. The NaSA release kinetics of the composite hydrogels were also compared. The composite hydrogels exhibited differences in Fourier transform infrared spectroscopy (FTIR), TPA parameters, ESR, NaSA load ratio, and release kinetics. CN addition increased the hardness of the hydrogels, while PEG played an opposite role. SH and PVA could decrease hardness, gumminess, and resilience, and SH could increase the springiness and cohesiveness of the hydrogels. Most of the composite hydrogels exhibited the same basic FTIR features as the simple hydrogel. Freeze-dried composite hydrogels exhibited a markedly higher ESR than the oven-dried ones, and additions of PEG, PVA, CN, and SH showed the same effect. Addition of the PEG and PVA combination could lower the ESR of the hydrogels, whereas additions of the PEG and CN combination or PEG and SH combination could markedly increase the ESR of the hydrogels. Addition of PEG, PVA, CN, and SH respectively could increase the NaSA load ratio of the hydrogels. Oven-drying treatment, additions of the PEG and PVA combination or PEG and CN combination were propitious for extending the NaSA fast-release phase of the hydrogels.     

Rational Design of an “OFF–ON” Phosphorescent Chemodosimeter Based on an Iridium(III) Complex and Its Application for Time‐Resolved Luminescent Detection and Bioimaging of Cysteine and Homocysteine

Biothiols, such as cysteine (Cys) and homocysteine (Hcy), play very crucial roles in biological systems. Abnormal levels of these biothiols are often associated with many types of diseases. Therefore, the detection of Cys (or Hcy) is of great importance. In this work, we have synthesized an excellent “OFF‐ON” phosphorescent chemodosimeter 1 for sensing Cys and Hcy with high selectivity and naked‐eye detection based on an Ir^III complex containing a 2,4‐dinitrobenzenesulfonyl (DNBS) group within its ligand. The “OFF‐ON” phosphorescent response can be assigned to the electron‐transfer process from Ir^III center and C^N ligands to the DNBS group as the strong electron‐acceptor, which can quench the phosphorescence of probe 1 completely. The DNBS group can be cleaved by thiols of Cys or Hcy, and both the ³M LCT and ³LC states are responsible for the excited‐state properties of the reaction product of probe 1 and Cys (or Hcy). Thus, the phosphorescence is switched on. Based on these results, a general principle for designing “OFF‐ON” phosphorescent chemodosimeters based on heavy‐metal complexes has been provided. Importantly, utilizing the long emission‐lifetime of phosphorescence signal, the time‐resolved luminescent assay of 1 in sensing Cys was realized successfully, which can eliminate the interference from the short‐lived background fluorescence and improve the signal‐to‐noise ratio. As far as we know, this is the first report about the time‐resolved luminescent detection of biothiols. Finally, probe 1 has been used successfully for bioimaging the changes of Cys/Hcy concentration in living cells.     

Facile Self‐Assembly Synthesis of PdPt Bimetallic Nanotubes with Good Performance for Ethanol Oxidation in an Alkaline Medium

PdPt bimetallic nanotubes were prepared by the self‐assembly of Pt and Pd on Te nanowires at room temperature. The morphologies of the as‐prepared PdPt nanotubes were investigated by scanning electron microscopy and transmission electron microscopy, and the results display a large amount of PdPt bimetallic nanotubes with a diameter of 10–20 nm and a length of several micrometers. The composition and structure of the nanotubes were characterized by X‐ray diffraction, high‐resolution transmission electron microscopy, scanning transmission electron microscopy, and energy spectrum analysis, and the results display uniform compositional distributions of both elements (Pd and Pt). The mechanism of the formation of the nanotube structure was supposed. The electrocatalytic performance of PdPt nanotubes were studied by cyclic voltammetry and chronoamperometry. Electrochemical results show that the as‐prepared PdPt nanotube catalysts have not only high activity but also good stability for ethanol oxidation in alkaline medium.