Preparation of Unconventional Dendrimers that Contain Rigid NH?Triazine Linkages and Peripheral tert‐Butyl Moieties for CO2‐Selective Adsorption

Three unconventional dendrimers that contained rigid NH? triazine linkages and peripheral tert‐butyl moieties were prepared by using a convergent approach and characterized by ¹H and ¹³C NMR spectroscopy, mass spectrometry, and elemental analysis. Based on a thermogravimetric analysis study, these dendrimers were observed to display thermal stability at about 300 °C. The NH? triazine moiety, which possessed protonated and proton‐free nitrogen sites (like the imidazole unit), displayed the capture of polarizable CO₂ molecules through hydrogen‐bond and/or dipole–quadrupole interactions. In addition, the adsorption of various amounts of CO₂ and N₂ at different pressures suggests that the dendritic pores, which arise from the stacking of the middle co‐planar and rim protuberant dendrimers, G _n ‐N～N‐G _n (n=1–3), either swell or shrink at high pressure, thus indicating that these dendrimers may have a breathing ability.     

Exploring the Reactivity of Multicomponent Photocatalysts: Insight into the Complex Valence Band of BiOBr

The band structure of multicomponent semiconductor photocatalysts, as well as their reactivity distinction under different wavelengths of light, is still unclear. BiOBr, which is a typical multicomponent semiconductor, may have two possible valence‐band structures, that is, two discrete valence bands constructed respectively from O 2p and Br 4p orbitals, or one valence band derived from the hybridization of these orbitals. In this work, aqueous photocatalytic hydroxylation is applied as the probe reaction to investigate the nature and reactions of photogenerated holes in BiOBr. Three organic compounds (microcystin‐LR, aniline, and benzoic acid) with different oxidation potentials were selected as substrates. Isotope labeling (H₂¹⁸O as the solvent) was used to determine the source of the O atom in the hydroxyl group of the products, which distinguishes the contribution of different hydroxylation pathways. Furthermore, a spin‐trapping ESR method was used to quantify the reactive oxygen species (^.OH and ^.OOH) formed in the reaction system. The different isotope abundances of the hydroxyl O atom of the products formed, as well as the reverse trend of the ^.OH/^.OOH ratio with the oxidative resistance of the substrate under UV and visible irradiation, reveal that BiOBr has two separate valence bands, which have different oxidation ability and respond to UV and visible light, respectively. This study shows that the band structure of semiconductor photocatalysts can be reliably analyzed with an isotope labeling method.     

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.     

Three‐Dimensional Architectures Incorporating Stereoregular Donor–Acceptor Stacks

We report the synthesis of two [2]catenane‐containing struts that are composed of a tetracationic cyclophane (TC⁴⁺) encircling a 1,5‐dioxynaphthalene (DNP)‐based crown ether, which bears two terphenylene arms. The TC⁴⁺ rings comprise either 1) two bipyridinium (BIPY²⁺) units or 2) a BIPY²⁺ and a diazapyrenium (DAP²⁺) unit. These degenerate and nondegenerate catenanes were reacted in the presence of Cu(NO₃)₂?2.5 H₂O to yield Cu‐paddlewheel‐based MOF‐1050 and MOF‐1051. The solid‐state structures of these MOFs reveal that the metal clusters serve to join the heptaphenylene struts into grid‐like 2D networks. These 2D sheets are then held together by infinite donor–acceptor stacks involving the [2]catenanes to produce interpenetrated 3D architectures. As a consequence of the planar chirality associated with both the DNP and hydroquinone (HQ) units present in the crown ether, each catenane can exist as four stereoisomers. In the case of the nondegenerate (bistable) catenane, the situation is further complicated by the presence of translational isomers. Upon crystallization, however, only two of the four possible stereoisomers—namely, the enantiomeric RR and SS forms—are observed in the crystals. An additional element of co‐conformational selectivity is present in MOF‐1051 as a consequence of the substitution of one of the BIPY²⁺ units by a DAP²⁺ unit: only the translational isomer in which the DAP²⁺ unit is encircled by the crown ether is observed. The overall topologies of MOF‐1050 and MOF‐1051, and the selective formation of stereoisomers and translational isomers during the kinetically driven crystallization, provide evidence that weak noncovalent bonding interactions play a significant role in the assembly of these extended (super)structures.     

Dynamic Electrosorption Analysis as an Effective Means to Characterise the Structure of Bulk Graphene Assemblies

Restacking of graphene sheets to a graphite‐like structure is a prevailing problem that is known to compromise the performance of individual graphene sheets in an assembled bulk form. To address this common problem efficiently and monitor the structure and quality of graphene products comprehensively, it is highly desirable to develop reliable metrology techniques for characterising graphene‐based materials on a bulk assembly level and in a quantitative manner. Here, by revisiting the physicochemical principle of electrosorption, we propose a simple electrochemical approach, namely dynamic electrosorption analysis (DEA), as an easily accessible and effective technique for evaluation of the self‐stacking behaviour of graphene. Taking multilayered chemically converted graphene films as a model, we demonstrate that the DEA technique can effectively reveal very subtle variation in accessible surface area and pore size of graphene assemblies in the liquid phase and thus can provide useful insights to the experimental design relating to restacking control. This work also reveals the huge effect some routine processing conditions, such as heat treatment and drying, can have on the structure and performance of graphene‐based bulk materials, providing useful guidance for future manufacturing of this class of materials.     

Distinct Stepwise Reduction of a Nickel?Nickel‐Bonded Compound Containing an α‐Diimine Ligand: From Perpendicular to Coaxial Structures

A nickel? nickel‐bonded complex, [{Ni(μ‐L^.?)}₂] ( 1 ; L=[(2,6‐iPr₂C₆H₃)NC(Me)]₂), was synthesized from reduction of the LNiBr₂ precursor by sodium metal. Further controllable reduction of 1 with 1.0, 2.0 and 3.0 equiv of Na, respectively, afforded the singly, doubly, and triply reduced compounds [Na(DME)₃] ? [{Ni(μ‐L^.?)}₂] ( 2 ; DME=1,2‐dimethoxyethane), [Na(Et₂O)]Na[(L^.?)Ni? NiL^2?] ( 3 ), and [Na(Et₂O)]₂Na[L^2?Ni? NiL^2?] ( 4 ). Here L represents the neutral ligand, L^.? denotes its radical monoanion, and L^2? is the dianion. All of the four compounds feature a short Ni? Ni bond from 2.2957(6) to 2.4649(8) Å. Interestingly, they display two different structures: the perpendicular ( 1 and 2 ) and the coaxial ( 3 and 4 ) structure, in which the metal? metal bond axis is perpendicular to or collinear with the axes of the α‐diimine ligands, respectively. The electronic structures, Ni? Ni bonding nature, and energetic comparisons of the two structure types were investigated by DFT computations.     

Effect of hydrolysis degree of hydrolyzed polyacrylamide grafted carboxymethyl cellulose on dye removal efficiency

In this present work, a series of hydrolyzed polyacrylamide grafted carboxymethyl cellulose (CMC-g-HPAM) was prepared. The structure and solution properties of CMC-g-HPAM were characterized by FTIR, ¹H-NMR, elemental analysis and zeta potential measurements. The graft copolymers were applied as flocculants to remove methylene blue (MB), a cationic dye, from aqueous solutions. In comparison with its precursors, carboxymethyl cellulose (CMC) and polyacrylamide CMC-g-PAM, CMC-g-HPAM exhibited higher removal efficiencies. Furthermore, the flocculation performance of the copolymers was significantly improved with the increase of the hydrolysis degree, and the MB removal efficiency was more than 90 % when the hydrolysis degree of CMC-g-HPAM was higher than 80 %. More importantly, image analysis in combination with fractal theory demonstrated that the graft copolymers could produce notably denser and larger flocs, which was of great significance in practical water treatment. The improved flocculation performance was ascribed to both charge neutralization and bridging effects.     

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.     

Li+掺杂对Y2SiO5:Pr3+上转换发光性能影响

采用溶胶-凝胶法制备Li+掺杂改性的Y2SiO5:Pr3+上转换发光材料,考察了Li+掺杂对样品晶型及发光性能的影响。采用XRD,DSC-TGA,FS对所制备的材料进行表征,结果表明Li+掺入浓度在7%～8%(摩尔分数)之间会引起Y2SiO5晶体类型由X1型转变为X2型,且Li+掺入后样品转晶型温度由950℃降至800℃;样品经800℃煅烧处理后以X1型Y2SiO5为主相,850℃煅烧处理后以X2型Y2SiO5为主相;Li+掺入同时会提高Y2SiO5:Pr3+材料的上转换发光强度,Li+最佳掺杂浓度为10%,对于双掺杂Pr3+,Li+:Y2SiO5体系中Pr3+最佳掺杂浓度为1.2%。     

Eu（TTA）3AA-NBR/PVP同轴超细纤维的制备及荧光性能研究

用同轴静电纺丝制备了含有稀土铕配合物(Eu(TTA)3AA)的芯-壳结构的丁腈橡胶/聚乙烯吡咯烷酮(NBR/PVP)超细荧光纤维。考察了在外层PVP纺丝参数不变的情况下,改变芯层丁腈橡胶纺丝液的纺丝速度、Eu(TTA)3AA含量等对纤维形貌的影响。通过研究Eu(TTA)3AA-NBR/PVP同轴超细纤维中Eu(TTA)3AA微观结构、含量与纤维的荧光性能之间的关系,发现在同轴纤维形成过程中由于溶剂的快速挥发可使Eu(TTA)3AA形成无定形结构,进而在纤维中形成分子簇级别的分散,在Eu(TTA)3AA含量为30%时,同轴纤维比Eu(TTA)3AA粉末的荧光强度提高了2倍。