Jian-Jun Zhang

Series of Structural and Functional Models for the ES (Enzyme–Substrate) Complex of the Co(II)-Containing Quercetin 2,3-Dioxygenase

A series of mononuclear Co(II)-flavonolate complexes [Co(II)L(R)(fla)] (L(R)H = 2-{[bis(pyridin-2-ylmethyl)amino]methyl}-p/m-R-benzoic acid; R = p-OMe (1), p-Me (2), m-Br (4), and m-NO2 (5); fla = flavonolate) were designed and synthesized as structural and functional models for the ES (enzyme-substrate) complexes to mimic the active site of the Co(II)-containing quercetin 2,3-dioxygenase (Co-2,3-QD). The metal center Co(II) ion in each complex shows a similar distorted octahedral geometry. The model complexes display high enzyme-type dioxygenation reactivity (oxidative O-heterocyclic ring opening of the coordinated substrate flavonolate) at low temperature, presumably due to the attached carboxylate group in the ligands. The reactivity exhibits a substituent group dependent order of -OMe (1) > -Me (2) > -H (3)14b > -Br (4) > -NO2 (5), and the Hammett plot is linear (ρ = -0.78). This can be explained as the electronic nature of the substituent group in the ligands may influence the conformation and redox potential of the bound flavonolate and finally bring different reactivity. The structures, properties, and reactivity of the model complexes show some dependence on the substituent group in the supporting model ligands, and there is some relationship among them. This study is the first example of a series of structural and functional ES models of Co-2,3-QD, with focus on the effects of the electronic nature of substituted groups and the carboxylate group of the ligands to the dioxygenation reactivity, that will provide important insights into the structure-property-reactivity relationship and the catalytic role of Co-2,3-QD.

A series of NiII-flavonolate complexes as structural and functional ES (enzyme-substrate) models of the NiII-containing quercetin 2,3-dioxygenase

Ni(II)-flavonolate complexes [Ni(II)L(R)(fla)] (L(R)H: 2-{[bis(pyridin-2-ylmethyl)amino]methyl}-p/m-R-benzoic acid, R: p-OMe (1), p-Me (2), m-Br (4) and m-NO2 (5), fla: flavonolate) were synthesized and characterized with relevance to structural and functional models for the ES (enzyme-substrate) adduct of the Ni(II)-containing quercetin 2,3-dioxygenase (2,3-QD). Their structures, spectroscopic features, redox properties and the reactivity toward molecular oxygen have been investigated. The complexes show a similar distorted octahedral structure and higher enzyme-type dioxygenation reactivity than other reported metal-flavonolate complexes in the oxidative O-heterocyclic ring-opening of the bound substrate flavonolate at lower temperature owing to the introduced carboxylate group in the supporting model ligands. The reaction rate shows first-order dependence on both of the complex and O2 and the second-order rate constant k fits a Hammett linear free energy relationship (ρ = -0.71) for the substituent group in the supporting model ligand L(R). The complexes exhibit substituent group dependent structures, properties and reactivity and there are some relationship among them, which could be ascribed to the electronic nature of the substituent group via the benzoate, Ni(II) ion and O(4)=C(27)-C(21)=C(22) electron conduit. In a word, the stronger electron donating group could induce a smaller torsion angle, larger λ(max) and lower redox potential of the bound flavonolate, making a higher reactivity finally. This study is the first example of a series of structural and functional ES models of the Ni(II)-containing 2,3-QD, providing important insights into the structure-property-reactivity relationship, the electronic substituent effects and carboxylate effects on the enzymatic reactivity and the catalytic role of the Ni(II)-containing 2,3-QD.

Linking heterometallic Cu–Ln chain units with a 2-methylenesuccinate bridge to form a 2D network exhibiting a large magnetocaloric effect

Four two-dimensional heterometallic Cu–Ln coordination polymers based on the 2-methylenesuccinic acid (H2MSA) ligand, {[Ln2Cu(MSA)4(H2O)6]·2H2O}n(Ln = La (1); Gd (2); Tb (3); Dy (4)), have been obtained under hydrothermal conditions. Complexes 1–4 bear a feature of one-dimensional [Ln2Cu] chains linked by 2-methylenesuccinate (MSA2−) bridges to form a 2D layer structure. Magnetic studies suggest the presence of weak antiferromagnetic Gd⋯Gd coupling and weak ferromagnetic Cu⋯Gd coupling in the 1D [Gd2Cu] chain unit of 2. The magnetic entropy change (−ΔSm) reached 36.05(1) J K−1 kg−1 for 2, making it an attractive refrigerant for low-temperature applications.

A colorimetric/luminescent benzene compound sensor based on a bis(σ-acetylide) platinum(II) complex: enhancing selectivity and reversibility through dual-recognition sites strategy

A square-planar bis(σ-acetylide) Pt(II) complex containing dual-recognition sites was designed, synthesized and used as a colorimetric/luminescent sensor for detecting the vapor of benzene compounds.

Two (5,5)-connected isomeric frameworks as highly selective and sensitive photoluminescent probes of nitroaromatics

Herein we report the first two (5,5)-connected isomeric frameworks, namely, (Me2NH2)[Zn2L(H2O)]·3.5DMF (1) and (Me2NH2) [Zn2L(H2O)]·6DMF·4H2O (2) (DMF = dimethylformamide, H5L = 5,5′-(6-(4-carboxyphenylamino)-1,3,5-triazine-2,4-diyldiimino) diisophthalic acid), obtained via assembly reactions between Zn2+ and a semi-rigid pentacarboxylate ligand (L5−). Single-crystal X-ray diffraction analyses reveal that both compounds are three dimensional metal–organic frameworks (MOFs) built of the same {Zn2(CO2)5} molecular building blocks (MBBs) and L5− ligands but have different topologies (point symbols of (44·66) and (46·64)(46·64) for 1 and 2, respectively). The mechanisms of the selective and efficient quenching of their photoluminescence (PL) by a series of nitroaromatic (NACs) solutions could be explained by electron transfer, long range energy transfer and/or electrostatic interactions. Remarkably, 1 and 2 can impressively detect the concentrations of dinoseb in solutions down to 0.09 and 0.11 ppm, respectively. Their PL could also be quenched by nitrobenzene (NB) and 4-nitrotoluene (4-NT) vapors, and the emission from 2 can be more quickly quenched than that from 1 possibly due to 2s larger pores and faster uptake of NAC vapors. 1 and 2 demonstrate significantly better performances than the two previously reported 4-connected MOFs using Zn2+ and a ligand isomeric to L5− in detecting NACs in both suspension and vapour mainly due to the ligands different LUMOs and arrangements of carboxylate groups (L. Di, J. J. Zhang, S. Q. Liu, J. Ni, H. Zhou and Y. J. Sun, Cryst. Growth Des., 2016, 16, 4539). This work sheds light on not only understanding of the formation of framework isomers but also the development of MOF-based NAC probes with better performances via judicious selection of suitable ligands.

Four (5,5)-connected three-dimensional metal organic materials based on pentacarboxylate ligand: Synthesis, structures and characterization

A new pentacarboxylate ligand, 5,5′-(6-(4-carboxyphenylamino)-1,3,5-triazine-2,4-diyldiimino) diisophthalic acid (H5L), was designed and used for the assembly of metal organic materials using Mn2+, Co2+, Cd2+ and Cu2+ as nodes. Four compounds, (Me2NH2)[Mn2L(H2O)]·3DMF·3H2O (1), (Me2NH2)[Co2L(H2O)]·3DMF·3H2O (2), (Me2NH2)[Cd2L(H2O)]·3DMF·3H2O (3) and [Cu4L(μ3-OH)2(NO3)(μ2-NMP)]·4.5NMP·2H2O (4) (DMF = dimethylformamide, NMP = N-methyl-2-pyrrolidone) have been synthesized and structurally characterized. Single crystal X-ray diffraction analyses show that 1 and 3 are isostructural, both based on {M2(CO2)5} molecular building blocks (MBBs) and L ligands. The topology of the 5-connected anionic framework may be described as (44)(66) (Schlafli symbol). Preliminary structural analysis indicates 2 may have the same structure as that of 1 and 3. 4 features a 5-connected 3D neutral framework based on “butterfly” {Cu4(μ3-OH)2(COO)5} MBBs and L ligands. The corresponding Schlafli symbol is (46)(64). N2 sorption isotherms of 2 shows typical type I behavior with BET surface area of 1251 m2 g−1 and a micropore volume of 0.491 cm3 g−1. Luminescent analysis indicates 3 exhibits linker-localized emission. Magnetic investigation of 4 reveals overall antiferromagnetic interactions. The compounds were further characterized by infrared (IR) and thermogravimetric analyses (TGA).

A One Dimensional 3d–4f Heterometallic Chain Based on Gd3+ Nodes and Tetranuclear {Cr4(hdpta)2} Complex Ligands: Synthesis, Structure and Magnetic Properties

Assembly reaction of 1,3-diamino-2-hydroxy-propane-N,N,N′,N′-tetraacetic acid (H5hdpta), sodium acetate and Cr3+ ion at pH 6.7 in aqueous solution leads to the formation of Na[Cr2(hdpta)(Ac)2] (1). Single crystal X-ray analysis show that 1 bears a 3D (4,4)-connected lon framework based on mononuclear Na+ nodes and dinuclear [Cr2(hdpta)(Ac)2]− complex ligands in which two Cr3+ ions are chelated by one hdpta5− and also bridged by two acetate auxiliary ligands. Further assemble of 1 with Gd3+ ions give rise to [Gd(NO3)3(H2O)4][Cr4Gd(hdpta)2(OH)4(H2O)5]·(NO3)·32H2O (2). The [Cr4Gd(hdpta)2(OH)4(H2O)5]+ cation of 2 exhibit a 1D chain structure based on [Cr4(hdpta)2(OH)4]2− complex ligands and mononuclear Gd3+ nodes. [Cr4(hdpta)2(OH)4]2− has a tetranuclear {Cr4} rectangular metal skeleton. Detailed synthesis experiments indicate heating is a simple and effective way to activate the inert Cr3+ ions to prepare oxygen-bridged Cr–Ln heterometallic compounds. Magnetic studies reveal that compound 2 shows overall antiferromagnetic interaction.Graphical AbstractStepwise synthesis of a Cr–Na compound based on dinuclear {Cr2} unit and a Cr–Gd compound bearing tetranuclear {Cr4} unit are presented.

Self-Assembly of Cluster-Based Nanoscopic Supramolecules into One-Dimensional Coordination Polymers

Octahedral metal clusters , (or ) (Salen = -ethylene-bis-(salicylidene)iminate) and ditopic organic linkers (-bpe (trans-1, 2-bis(4-pyridyl)-ethylene) or -dpyo (-dipyridyl -dioxide)) self-assemble to form three cluster-based 1D coordination polymers: [(Mn(Salen))2(Nb6Cl12(CN)6)]n (1), n(2), and (3). Single crystal X-ray diffraction analyses show that the frameworks of the three coordination polymers are built of heterotrimeric and/or heteropentameric supramolecular species linked by ditopic organic ligands. The framework of 1 consists of anionic chains built of heterotrimeric dianions (T) linked by -dpyo. The chains run along two directions ([0 2 −2] and [0 3 3]) leading to the formation of channels along the crystallographic (a) direction where the cations [Mn(Salen)]

Set of Fe(II)-3-Hydroxyflavonolate Enzyme–Substrate Model Complexes of Atypically Coordinated Mononuclear Non-Heme Fe(II)-Dependent Quercetin 2,4-Dioxygenase

With the aim of revealing the catalytic role of atypically coordinated (3His-1Glu) active site mononuclear non-heme Fe(II)-dependent quercetin 2,4-dioxygenase (Fe-2,4-QD) and the electronic effects of the model ligands on the reactivity toward dioxygen, a set of p/m-R-substituted carboxylate-containing ligand-supported Fe(II)-3-hydroxyflavonolate complexes, [FeIILR(fla)] (LRH: 2-{[bis(pyridin-2-ylmethyl)amino]methyl}-p/m-R-benzoic acid; R: p-OMe (1), p-Me (2), m-Br (4), and m-NO2 (5); fla: 3-hydroxyflavonolate), were synthesized and characterized as structural and functional models for the ES (enzyme–substrate) complexes of Fe-2,4-QD. [FeIILR(fla)] show relatively high enzyme-type reactivity (dioxygenative ring opening of the coordinated substrate fla, single-turnover reaction) at low temperatures (30–65 °C). The reaction shows a linear Hammett plot (ρ = −1.21), and electron donating groups enhance the reaction rates. The notable difference on the reactivity can be rationalized from the electronic nature of the substituent in the ligands, which could tune the reactivity via tuning Lewis acidity of the Fe(II) ion, electron density, and the redox potential of fla. The properties and the reactivity show approximately linear correlations between λmax or E1/2 of fla and the reaction rate constant k. This work sheds light not only on understanding of electronic effects of the ligands and the property–reactivity relationship but also on the role of the catalytic reaction by Fe-2,4-QD.

A Trichromatic and White-Light-Emitting MOF Composite for Multi-Dimensional and Multi-Response Ratiometric Luminescent Sensing

Present here is a new dual ratiometric luminescent probe D which is a trichromatic and white-light-emitting metal-organic framework (MOF) composite facilely obtained by incorporating red/green-emitting complex modules into a blue-emitting MOF. Probe D exhibits remarkable capabilities of sensing different volatile organic solvents (VOSs) via 2D code recognition of the two VOS-dependent MOF ligand-to-module ratios of the emission-peak intensities. For specific VOSs, the resultant luminescent color changes from the starting white color are sharp enough to be visible to the naked eye. Remarkably, D can differentiate solution-phase nitroaromatics and metal ions by recording the evolution of the two ratios during titration processes, enabling an unusual 3D code recognition using the titrant amount as the third dimension for the first time. D also can be used to detect dinoseb, Fe3+ and Al3+ ions quantitatively by analysis of the ratios with detection limits as low as 0.050, 0.41, and 0.12u2005ppm, respectively. Clearly, such a self-referencing trichromatic probe can maximize the output information and significantly enhance the detection selectivity and sensitivity via multi-dimensional sensing, and has great potentials for practical applications.