Changsheng Lu

Ligand-to-metal ratio controlled assembly of nanoporous metal–organic frameworks

Two bilayered metal-organic frameworks with nanoporous channels were synthesized at different ligand-to-metal ratios, which demonstrated an interesting crystal-to-crystal transformation property and a special fluorescent response to the different guest molecules included.

Three-dimensional metal–organic frameworks constructed from bix and 1,2,4-benzenetricarboxylate

Two new metal–organic complexes [Cd1.5(btrc)(bix)]n (1) and [Zn2(btrc)(Hbtrc)0.5(bix)2]n(2) (H3btrc = 1,2,4-benzenetricarboxylate; bix = 1,4-bis(imidazol-1-ylmethyl)-benzene) have been hydrothermally synthesized and characterized by single crystal X-ray diffraction. Complex 1 represents a three-dimensional (3D) structure based on the 2D sheets and bix pillars. Complex 2 exhibits unique architecture. The two complexes exhibit strong fluorescent emissions in their solid states at room temperature.

Structural, morphological, and magnetic study of nanocrystalline cobalt-nickel-copper particles

Nanocrystalline Co(x)Ni(y)Cu(100-x-y) particles were synthesized by the reduction of metal acetates in a mixture of polyol and Tween 80. Inductively coupled plasma (ICP) analysis revealed that the actual wt% of Co, Ni, and Cu in these nanoparticles was nearly the same as in the starting solutions. The structures of the particles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) spectroscopy, and vibrating sample magnetometry (VSM). The results of XRD and VSM confirmed that there was no metastable alloying in the particles. The particles were composites, consisting of nanoscale crystallites of face-centered cubic (fcc) Cu, face-centered cubic (fcc) Ni, and face-centered cubic (fcc) Co. During preparation the nucleation of Cu occurred first; then small Cu nuclei acted as cores for the precipitation of Co and Ni. The particles showed an increase in saturation magnetization (M(s)) as the concentration of Co or Ni in the particles was increased. The changes of both M(s) and coercivity of the particles with increasing annealing temperatures were studied. The coercivity of the particles was very high; it could reach as high as 489 Oe for Co34.3Ni31.2Cu34.5) .

A novel 2D coordination polymer with unprecedented [Ag]7 chains and two 3D silver–organic frameworks constructed by methylenediisophthalic acid (H4MDIP) with strong Ag–Ag interactions

Using a hydrothermal synthesis method, three novel silver complexes {Ag2(H2MDIP)(o-bix)2·H2O}n(1) (H4MDIP = methylenediisophthalic acid, o-bix = 1,2-bis (imidazol-1-ylmethyl)- benzene, {Ag8(MDIP)2(m-bix)}n(2) (m-bix = 1,3-bis(imidazol-1-ylmethyl)-benzene), {Ag4(MDIP)(p-bix)3·H2O}n(3) (p-bix = 1,4-bis(imidazol-1-ylmethyl)-benzene) were synthesized based on tetracarboxylic acid and auxiliary ligands containing N donors. Their structures have been characterized by X-ray crystallography. Complexes 1 and 3 have special 3D supramolecular networks constructed by hydrogen bonding, π–π stacking and electronic interactions to link the metal cations, anions and water molecules together. Complex 2 exhibits a unique 2D architecture with unprecedented [Ag]7 chains connected by strong Ag–Ag interactions. Thermal stabilities and luminescent properties of complexes 1–3 were investigated.

Synthesis, crystal structure and magnetic properties of A[Ni(mnt)2] complexes [A = 1-(4-nitrobenzyl)quinolinium or 1-benzylpyridinium; mnt2− = maleonitriledithiolate]

Two new ion-pair complexes A[Ni(mnt)2], [A = 1-(4-nitrobenzyl)quinolinium (1), and 1-benzylpyridinium (2)] have been prepared and characterized. The crystal structure of (1) has been determined by X-ray diffraction analysis. In the solid state, anions and cations of (1) form completely segregated stacking columns, with the Ni···Ni distances alternating between 3.890(4) and 4.965(5) Å in the [Ni(mnt)2]− stacking column. The variable temperature magnetic susceptibilities of (1) and (2) have been measured over the 77–300 K range and the results reveal that (1) is diamagnetic and that (2) shows a weak antiferromagnetic spin exchange interaction between the metal ions. The e.p.r. spectra of (1) and (2) in MeCN at room temperature were similar, the g-values being almost identical.

Highly-Emissive Organic Single-Molecule White Emitters by Engineering o-Carborane-based Luminophores

The development of organic single-molecule solid-state white emitters holds a great promise for advanced lighting and display applications. Highly emissive single-molecule white emitters were achieved by the design and synthesis of a series of o-carborane-based luminophores. These luminophores are able to induce multiple emissions to directly emit high-purity white light in solid state. By tuning both molecular and aggregate structures, a significantly improved white-light efficiency has been realized (absolute quantum yield 67 %), which is the highest value among the known organic single-molecule white emitters in the solid state. The fine-tuning of the packing modes from H- to J- and cross-stacking aggregates as well as intermolecular hydrogen bonds are successful in one molecular skeleton. These are crucial for highly emissive white-light emission in the solid state.

Single mutation on the surface of Staphylococcus aureus Sortase A can disrupt its dimerization.

Staphylococcus aureus Sortase A (SrtA) is an important Gram-positive membrane enzyme which catalyzes the anchoring of many cell surface proteins conserved with the LPXTG sequence. Recently SrtA has been demonstrated to be a dimer with a Kd of 55 microM in vitro. Herein, we show that a single point mutation of amino acid residue on the surface of SrtA can completely disrupt the dimerization. Native polyacrylamide gel electrophoresis and analytical gel filtration chromatography were used to detect the dimer-monomer equilibrium of SrtA mutants. Circular dichroism spectrum experiments were performed to study the conformational change of each SrtA mutant. An enzyme activity assay confirmed that all the SrtA mutants were active in vitro. Our results not only are important for understanding the SrtA protein self-associating mechanism but also provided the necessary starting materials for the study of sortase A pathway in vivo, which may have significant implications for discovering microbial physiology and give a potential target for novel Gram-positive antibiotics.

Preparation and electrochemistry of azobenzene self-assembled monolayers on gold-long range tunneling and end-group hydrogen bonding effect

A series of thiol-functionalied azobenzene derivatives (RAzoCnSH: R=H for n=3-6, abbreviated as AzoCnSH; R=CH(3)CONH for n=4, abbreviated as aaAzoC4SH) on gold electrodes were prepared and their self-assembly and electrochemical properties were studied by cyclic voltammetry. They all formed uniform and reproducible self-assembled monolayers (SAMs) on gold and showed well-behaved voltammetric responses in aqueous solution. Both the length of the alkyl chain spacer and the H-bonding of the end acetamino group had effects on the stability and the electrochemical kinetics of the SAMs, and the effect of the H-bonding was dominant. The surface coverage of the SAMs (AzoCnSH) is gradually increased with an increase of the alkyl chain spacer length, whereas the presence of the terminal acetamino group leads to a greater increase of the surface coverage. At a low scan rate, voltammetric responses corresponding to an irreversible two-electron, two-proton reduction/oxidation of the trans-azobenzene redox center were obtained in the range of +300 mV and -800 mV, which exhibited very large peak-to-peak splitting. At a high scan rate of 500 mV/s, two steps of reversible one-electron, one-proton reduction/oxidation corresponding to the cis-isomer in azobenzene-thiol SAMs (n is odd) was clearly observed between +300 and -200 mV. The apparent electron-transfer rate is decreased with increasing distance between the azobenzene redox center and the gold electrode. The existence of the end acetamino group which restricted the conformational change during the redox process also led to a decrease of the standard rate constant, and this restriction effect is more predominant than the distance effect.

Synthesis, crystal structure, and properties of [Cu(LH)]2[M(mnt)2] [M = Ni or Cu; H2L = 3,3′-(1,3-propanediyldinitrilo)-bis(2-butanone oxime); mnt2− = maleonitriledithiolate] complexes containing bridging cyano groups

Interesting complexes containing a mnt2− bridge, based on the reaction of [M(mnt)2]2− [M = Ni or Cu] with [Cu(LH)]+, have been prepared and characterized by e.s.m.s., i.r and u.v–vis. spectroscopic techniques and by electrochemistry. The complexes show weak antiferromagnetic interactions between magnetic centers. The X-ray analysis of the molecular structure of [Cu(LH)]2[Ni(mnt)2] has been completed. It structurally features the CN group of mnt2− which can act as a bridging ligand between two transition metals.

Aggregation-Induced Emission Characteristics of o-Carborane-Functionalized Tetraphenylethylene Luminogens: the Influence of Carborane Cages on Photoluminescence

Tetraphenylethylene (TPE)-carborane hybrids are constructed, and the impact of carborane substituents on the aggregation-induced emission (AIE) characteristics of TPE-cores has been investigated. When altering the 2-R-group on the carborane unit with -H, -CH3 or phenyl group, the luminescent quantum yield of the corresponding TPE derivatives can be manipulated from 0.18 to 0.63 in the solid state. The emission color exhibits an obvious 100 nm shift (from blue to yellow).