Assembly of a highly stable luminescent Zn5 cluster and application to bio-imaging

OBJECTIVE To explore a novel pH-sensitive fluorescent probe for in vivo tumor imaging.METHODS Zn5 were obtained in 140℃ after mixed with Me OH,water,Zn(NO_3)2·6 H_2O,H4L and trimethylamine.The fluorescence spectra of Zn5 with the same concentration in different pH aqueous solutions were detected.And the stability of Zn5 was investigated by time dependent fluorescence emission spectra of Zn5 in BSA aqueous solution and 5.0% serum solution.Then,the cytotoxicity of Zn5 was detected by MTT assays.To clarify whether a similar fluorescence response occurs in biological organisms,He La cells were pretreated with probe Zn5(0.5 μmol·L^(-1)) and fluorescence imaging were collected for targeting lysosomes in living cells because of lysosomes′ acidic microenvironment.The A375 tumor-bearing mice were used to assess the imaging ability of Zn5 in vivo.Mouse tumor xenografts were established by injection of A375 cells with 2×10~6 cells per flank.Probe(1 μg·g^(-1)) was administered to mice by injection.Images were obtained using IVIS Spectrum CT Imaging System.RESULTS There is a 11-fold intensity increasing as the pH values changing from 8 to 2.The almost unchanged emission intensities suggest Zn5 is stable in both BSA and serum.Zn5 has negligible cytotoxicity for He La,293 T and CHO-K1 cells.Zn5 can selectively display lysosomes in living cells.Both the 2D and 3D images in vivo distinguish the tumor from other tissues with good fluorescence contrast.CONCLUSION The high chemical stability,emission in the Vis/NIR range,pH sensitivity,a pKa located in the tumor pH range,and low toxicity make Zn5 is suitable for application as a pH-sensitive fluorescent probe for bio-imaging.

Heptanuclear brucite disk with cyanide bridges in a cocrystal and tracking its pyrolysis to an efficient oxygen evolution electrode

The development of efficient oxygen evolution reaction(OER)catalysts is still lacking in exploration of the mechanism of controlled pyrolysis of precursors among new material platforms.Here,a novel Co-based coordination molecular cluster has been first introduced as precursor to obtain metallic cobalt core shelled by N-doped carbon(Co@NC)structure which operates as an oxygen evolution electrode.Specifically,a new cocrystal compound,[Co7II(l3-CN)6(mmimp)6][CoIICl3N(CN)2]á3CH3OH(Co7+1,mmimp=2-methoxy-6-((methylimino)-methyl)phenol),was isolated consisting of Brucite disks of cobalt where the usual bridging l3-OH is replaced by l3-CN produced by the in-situ decomposition of dicyanamide(NC-N-CNà).The cobalt atoms are bonded through the nitrogen atom of the cyanide.Remarkably,time dependent thermogravimetric-mass spectrometry(TG-MS)analysis was utilized to track its pyrolysis process.It allowed us to propose a possible formation process of the Co@NC structure from Co7+1.Interestingly,an extremely superior OER electrode is optimized for Co@NC-600 having the lowest overpotential of257 m V at 10 m A/cm2in 1 mol/L KOH solution.The present study pins down the importance of clusters of transition metals on realizing distinct nanostructures operating as highly efficient OER electrocatalyst.

Tracking the multiple-step formation of an iron(Ⅲ) complex and its application in photodynamic therapy for breast cancer

A tandem reaction of pyridin-2-ylmethanamine(L1′) with 8-hydroxyquinoline-2-carbaldehyde(HL1) assisted by FeCl_3 was observed to give the new nitrogen heterocycle HL3(HL3=2-(imidazo[1,5-a]pyridin-3-yl)quinolin-8-ol) as its Fe(Ⅲ) complex,[Fe(L3)Cl_2](Fe1). Electrospray ionization mass spectrometry(ESI-MS) reveals its formation involves three steps:(1) coordination of both HL1 and L1′ to Fe,(2) aldehyde-amine coupling, and(3) ring closure. The results of electronic absorption spectroscopy, cyclic voltammetry, and density functional theory(DFT) calculations show the proximity of the optical transition energy to that of the excitation of ~3O_2 to ~1O_2, which prompted us to explore its application as a photosensitizer for photodynamic therapy(PDT). Photo-toxicity studies show that Fe1 exhibits the highest anti-proliferation efficiency in human breast cancer MDA-MB-231 cells under light irradiation. Moreover, studies with orthotopic models of breast cancer further expounded the anti-tumor activity of Fe1 with no significant toxicity to other organs and low retention in the body.

How to create MOF glasses and take advantage of emerging opportunities

Glasses are a kind of amorphous solids with scientific significance and wide applications vital to human life."What is the nature of the glassy state" was one of the most difficult and challenging questions that has puzzled so many scientists for quite a long-time [1]. Currently, there are mainly three different categories, including inorganic, organic and metallic glasses.

In-situ evolution process understanding from a salan-ligated manganese cluster to supercapacitive application

The goal of material chemistry is to study the relationship among hierarchical structure,chemical reaction and precision preparation for materials,yet tracking pyrolysis process on multi-dimensional scale is still at primary stage.Here we propose packing mode analysis to understand evolution process in high temperature reaction.As a proof of concept,we first design a salan-ligated Mn3(Mn3(3-MeOsalophen)_(2)(Cl)_(2))cluster and pyrolyze it under an inert atmosphere directly to a mixed valence MnOx embedded in a porous N-doped carbon skeleton(MnOx/C).Meanwhile,combining thermogravimetry-mass spectrometry(TG-MS)with other characterization techniques,its pyrolysis process is precisely tracked real-time and Mn^(2+)/Mn^(3+)ratios in the resulting materials are deduced,ensuring excellent electrochemical advantages.As a result,the as-preferred MnOVC-900 sample reaches 943 F/g at 1 A/g,maintaining good durability under 5,000 cycles with 90%retention.The highlight of packing mode analysis strategy in this work would provide a favorable approach to explore the potential relationship between structure and performance in the future.

Exploring the Pyrolysis Mechanism towards OER Performance Optimization of Salophen-ligated Binuclear Cobalt Complex

Exploring pyrolysis process is an efficient way to study the relationship between molecular level of the precursor structure and electrocatalytic functional materials in practice.Here,the unique semi-enclosed sector structure of Salophen ligands with highly symmetric N,N,0,0 mode was introduced to construct binuclear Co complex[Co2(salophen)(CI)2(C2H3N)](compound 1),which provides pre-liminary theoretical basis for the efficient coreshell structure electrocatalysts obtained by pyrolysis regulation.Moreover,we adopted TG-MS to real-time track the pyrolysis process from precursors of binuclear Co complexes with Salophen ligand to efficient catalytic materials with core-shell nano structures.As expected,the 1-600 sample achieves ultra-low overpote ntial of 256 mV at 10 mA·cm^(-2) and high catalytic stability within 10 h in 1 mol/L KOH solution.This work highlights salophen-ligated complex as excellent precursor material system for the an alysis of pyrolysis evoluti on process,and provides an opport unity for targeted preparati on of efficie nt oxy-gen evoluti on reacti on(OER)nano catalysts.

Tracking the Process of Domino Ring-Opening and Coupling of Fused Imidazole and Direct Observation of Peroxide Intermediates

Comprehensive Summary,A domino ring-opening and coupling of imidazolyl annulated heterocycles 1(1a:4-methyl-1-(1-methyl-1H-benzo[d]imidazol-2-yl)-4H-benzo[d]imidazo[1,5-a]imidazole,1b:1-(1,5-dimethyl-1H-benzo[d]imidazol-2-yl)-4,7-dimethyl-4H-benzo[d]imidazo[1,5-a]imidazole)with dioxygen was developed at solvothermal condition,leading to conjugated 1,2-diamidoalkenes derivatives 2((E)-ArCONHArC=CArNHCOAr(Ar:1-methyl-1H-benzo[d]imidazolyl(2a),1,5-dimethyl-1H-benzo[d]imidazolyl(2b)))as single crystals directly.The reaction process was tracked by electrospray ionization mass spectrometry(ESI-HRMS)and a series of reaction intermediates are detected.^(18)O_(2) labeling experiment verified the source of oxygen in 2.Combining evidence from control experiments,nuclear magnetic resonance(NMR)tracking,and crystallography,a seven-step reaction pathway involving oxygen addition,ring opening,Friedel-Crafts alkylation,oxidation,and dehydration was proposed and further supported by DFT calculation.

CuBr-promoted domino Biginelli reaction for the diastereoselective synthesis of bridged polyheterocycles:Mechanism studies and in vitro anti-tumor activities

The low-cost CuBr-promoted domino Biginelli reaction among readily available ketones,salicylaldehyde derivatives and 3-amino-1,2,4-triazole was studied under solvothermal conditions,giving the novel bridged polyheterocycles bearing two or three stereocenters depending on the starting ketones.This multicomponent reaction proceeded with high diastereoselectivity(dr>20:1)based on a combined~1 H NMR,crystallographic and supercritical fluid chromatographic(SFC)analysis of the product.Time-dependent high-resolution mass spectrometry(HRMS)was performed to track the reaction process,and several key intermediates were identified,leading to the drawing of a plausible reaction mechanism.Density functional theory(DFT)calculation was supplemented,and two reaction pathways were differentiated.Moreover,in vitro antitumor activity was evaluated using HeLa and HepG2 cell lines,and two of these polyheterocycles demonstrated promising activities against HepG2 cells with EC50 down to 10μmol/L.Additionally,ESI-MS/MS studies on all the polyheterocycles suggest a common fragmentation pathway(loss of one molecule of amino-triazole)they shared,providing the first-hand fragmentation rules for future rapid structural identification of them.The multicomponent domino reaction presented here may offer prospects for future design of more efficient strategies to access medicinally important bridged polyheterocycles.

Bond Order Analysis, Packing Ratio, and Electronic Structures of Two Structural Polymorphs Based on Manganese Complexes

The bond order and packing ratios in the single-crystal of the two structural polymorphs as well as the detailed electronic structures of the molecular model were studied using density functional theory. The strength of different Mn coordination bonds was analyzed in detail through Mayer bond order. Besides bond length, many other factors such as the orientation of ligand and nature of metal also significantly influence the bond order. Packing ratios cal- culated using cluster model reveals that packing along b direction in Dimer is more favorable than other directions due to the associated interactions of π-π and CI…H when packing in this direction. Electronic structure helps ex- plain the formation of Dimer from monomer or direct forming of Chain from ligand/Cl and metal. This would shed light on further understanding the importance of supramolecular interaction on crystal engineering.

Directly imaging the in-situ chemical transformation of nickel cubane nanoclusters for promoting electrocatalytic urea-oxidation reaction

We report the stepwise in-situ manipulation of a nickel cubane nanocluster capped with a specially designed multidentate ligand [Ni^(Ⅱ)_(4)(HL)_(3)(CH_(3)O)(CH_(3)OH)_(3)](CH_(3)COO)(Ni_(4),H_(3)L=(E)-3-((2-hydroxy-3-mehoxybenzylidene)amino)propane-1,2-diol) to firstly [Ni^(Ⅱ)_(4)(HL)_(3)(CH_(3)O)(CH_(3)OH)_(2)(H_(2)O)](CH_(3)COO)(Ni4-1min) and finally to [Ni^(Ⅱ)_(4)(HL)_(3)(CH_(3)O)(H_(2)O)_(3)](CH_(3)COO)Ni4-20h)during the urea electrolysis.A combination of mass spectrometry,single crystallography and pair distribution function were employed to analyze the structural correlations of this catalyst in crystal/solution/gas phases for confirming the dynamic ligand replacement while preserving the cubic Ni4 core during catalysis.The key feature of their structures is that:(i)three ligands wrap the Ni_(4)O_(4)cubane center on one side forming the rounded outside of a calix;(ii)the opposite flat side containing labile methanol as the active site.This structure facilitates the binding of the substrate to the active central nickel atoms during catalysis.Furthermore,due to the different modes of packing,the structure of Ni4-20 h sustains two-dimensional(2D)net of open space while the structures of Ni4 and Ni4-1 min have only closed void inaccessible to solvent molecules or ions.Interestingly,the overpotential initially decreased(up to 45 min)until it is stabilized.The result showed a low potential of 1.32 V(urea oxidation reaction(UOR))at 10 mA·cm^(-2)as reflected in the Gibbs free energy decrease of~0.4 eV from Ni4 to Ni4-20 h.This work demonstrates a convincing approach for elucidating the exact nature of the active clusters in electrocatalytic process,and confirms that in-situ modification of electrode materials might alter the direct electronic interaction between substrate and active sites in improving the catalytic performance.