五-和六配位的三核锌配合物{[ZnL(OAc)]2Zn}∙CH3COCH3的合成，晶体结构及荧光性质

合成并结构表征了一种新型的线性三核锌(II)配合物,{[ZnL(OAc)]2Zn}∙CH3COCH3（H2L：乙二氧双(5-溴-2-羟基苯亚甲基胺)）。X-射线结构表明配合物中三个锌(II)离子配位到了两个四齿的L2-单元和两个桥联的的乙酸根基团。围绕两端的Zn(1) 或 Zn(1)#1原子形成了扭曲的四方锥配位几何体,围绕中心Zn(2) 原子构成了一个稍微扭曲的八面体配位结构。同时,观察到锌(II)配合物能发出蓝绿色荧光,其最大发射波长为464 nm。     

Catenation and Aggregation of Multi‐Cavity Coordination Cages

A series of metal‐mediated cages, having multiple cavities, was synthesized from Pd^II cations and tris‐ or tetrakis‐monodentate bridging ligands and characterized by NMR spectroscopy, mass spectrometry, and X‐ray methods. The peanut‐shaped [Pd₃L¹₄] cage deriving from the tris‐monodentate ligand L¹ could be quantitatively converted into its interpenetrated [5Cl@Pd₆L¹₈] dimer featuring a linear {[Pd‐Cl‐]₅Pd} stack as an unprecedented structural motif upon addition of chloride anions. Small‐angle neutron scattering (SANS) experiments showed that the cigar‐shaped assembly with a length of 3.7 nm aggregates into mono‐layered discs of 14 nm diameter via solvophobic interactions between the hexyl sidechains. The hepta‐cationic [5Cl@Pd₆L¹₈] cage was found to interact with polyanionic oligonucleotide double‐strands under dissolution of the aggregates in water, rendering the compound class interesting for applications based on non‐covalent DNA binding.     

The recognition of a noncanonical RNA base pair by a zinc finger protein.

BACKGROUND: The zinc finger (ZF) is the most abundant nucleic-acid-interacting protein motif. Although the interaction of ZFs with DNA is reasonably well understood, little is known about the RNA-binding mechanism. We investigated RNA binding to ZFs using the Zif268-DNA complex as a model system. Zif268 contains three DNA-binding ZFs; each independently binds a 3 base pair (bp) subsite within a 9 bp recognition sequence. RESULTS: We constructed a library of phage-displayed ZFs by randomizing the alpha helix of the Zif268 central finger. Successful selection of an RNA binder required a noncanonical base pair in the middle of the RNA triplet. Binding of the Zif268 variant to an RNA duplex containing a G.A mismatch (rG.A) is specific for RNA and is dependent on the conformation of the mismatched middle base pair. Modeling and NMR analyses revealed that the rG.A pair adopts a head-to-head configuration that counterbalances the effect of S-puckered riboses in the backbone. We propose that the structure of the rG.A duplex is similar to the DNA in the original Zif268-DNA complex. CONCLUSIONS: It is possible to change the specificity of a ZF from DNA to RNA. The ZF motif can use similar mechanisms in binding both types of nucleic acids. Our strategy allowed us to rationalize the interactions that are possible between a ZF and its RNA substrate. This same strategy can be used to assess the binding specificity of ZFs or other protein motifs for noncanconical RNA base pairs, and should permit the design of proteins that bind specific RNA structures.     

Synthesis,Structures, Magnetic and Luminescent Properties of a Series of Iron(II) and Zinc(II) Coordination Frameworks with Versatile 4‐Substitued 1, 2,4‐Triazole Ligands

Three multi‐dentate 1, 2,4‐triazole derivative ligands containing different 4‐substituted groups, namely N‐1, 2,4‐triazol‐4‐yl(pyridin‐3‐yl)methylenimine (L₁), N‐1, 2,4‐triazol‐ 4‐yl(pyridin‐4‐yl)methylenimine (L₂), and 4‐(2‐pyridine)‐1, 2,4‐triazole (L₃) were used to isolate five iron(II) and zinc(II) coordination frameworks, [Zn(μ₂‐L₁)Cl₂] ( 1 ), [Zn(μ₂‐L₂)Br₂] ( 2 ), [Fe(L₁)₂(NCS)₂(H₂O)₂] ( 3 ), [Fe(L₃)₂(dca)₂(H₂O)₂] ( 4 ), and [Fe(L₃)₂(μ₂‐dca)] ( 5 ) (dca = dicyanamide anion). When different zinc(II) salts were used to react with L₁ and L₂ under solvothermal conditions, two one‐dimensional (1D) zinc(II) coordination frameworks 1 and 2 containing four‐coordinate central zinc(II) atoms were isolated. 1 is a 3D achiral supra‐molecular framework, whereas 2 is a 3D chiral supra‐molecular framework containing helical chains on a 2₁ axis. 3 is a mono‐nuclear iron(II) coordination framework containing six‐coordinate central Fe^II atoms. When L₃ was employed, mono‐nuclear iron(II) framework 4 and 1D iron(II) chain 5 could be isolated when different amounts of Nadca were introduced into the reaction system. Variable‐temperature magnetic susceptibility data of 3 – 5 were recorded in the 2–300 K temperature range indicating weak anti‐ferromagnetic interactions. The solid‐state luminescent properties of coordination polymers 1 and 2 were also investigated at room temperature.     

Anticancer Potencies of PtII‐ and PdII‐linked M2L4 Coordination Capsules with Improved Selectivity

Pt^II‐ and Pd^II‐linked M₂L₄ coordination capsules, providing a confined cavity encircled by polyaromatic frameworks, exhibit anticancer activities superior to cisplatin against two types of leukemic cells (HL‐60 and SKW‐3) and pronounced toxicity against cisplatin‐resistant cells (HL‐60/CDDP). Notably, the cytotoxic selectivities of the Pt^II and Pd^II capsules toward cancerous cells are up to 5.3‐fold higher than that of cisplatin, as estimated through the non‐malignant/malignant‐cells toxicity ratio employing normal kidney cells (HEK‐293). In addition, the anticancer activity of the coordination capsules can be easily altered upon encapsulation of organic guest molecules.     

Entropy directs the self-assembly of supramolecular palladium coordination macrocycles and cages

The self-assembly of palladium-based cages is frequently rationalized via the cumulative enthalpy (ΔH) of bonds between coordination nodes (M, i.e., Pd) and ligand (L) components. This focus on enthalpic rationale limits the complete understanding of the Gibbs free energy (ΔG) for self-assembly, as entropic (ΔS) contributions are overlooked. Here, we present a study of the M₂^linL₃ intermediate species (M = dinitrato(N,N,N′,N′-tetramethylethylenediamine)palladium(ii), ^linL = 4,4′-bipyridine), formed during the synthesis of triangle-shaped (M₃^linL₃) and square-shaped (M₄^linL₄) coordination macrocycles. Thermochemical analyses by variable temperature (VT) ¹H-NMR revealed that the M₂^linL₃ intermediate exhibited an unfavorable (relative) ΔS compared to M₃^linL₃ (triangle, ΔTΔS = +5.22 kcal mol⁻¹) or M₄^linL₄ (square, ΔTΔS = +2.37 kcal mol⁻¹) macrocycles. Further analysis of these constructs with molecular dynamics (MD) identified that the self-assembly process is driven by ΔG losses facilitated by increases in solvation entropy (ΔS_solv, i.e., depletion of solvent accessible surface area) that drives the self-assembly from “open” intermediates toward “closed” macrocyclic products. Expansion of our computational approach to the analysis of self-assembly in Pd_n^benL_2n cages (^benL = 4,4''-(5-ethoxy-1,3-phenylene)dipyridine), demonstrated that ΔS_solv contributions drive the self-assembly of both thermodynamic cage products (i.e., Pd₁₂^benL₂₄) and kinetically-trapped intermediates (i.e., Pd₈^cL₁₆).

These studies demonstrate that ΔS drives the self-assembly of supramolecular palladium-based coordination macrocycles and cages. As this ΔS contribution arises from solvation, these findings broadly reflect the thermodynamic drive of self-assembly to form compact structures.     

RuII,OsII, and IrIII Complexes with Chelating Pyridyl–Mesoionic Carbene Ligands: Structural Characterization and Applications in Transfer Hydrogenation Catalysis

Chelating ligands with one pyridine donor and one mesoionic carbene donor are fast establishing themselves as privileged ligands in homogeneous catalysis. The synthesis of several new Ir^III–Cp*‐ and Os^II–Cym complexes (Cp*=pentamethylcyclopentadienyl, Cym=p‐cymene=4‐isopropyl‐toluene) derived from chelating pyridyltriazolylidenes where the additional pyridine donor was incorporated via the azide part of the triazole is presented. Furthermore, different 4‐substituted phenylacetylene building blocks have been used to introduce electronic fine‐tuning in the ligands. The ligands thus can be generally described as 4‐(4‐R‐phenyl)‐3‐methyl‐1‐(pyridin‐2‐yl)‐1H‐1,2,3‐triazol‐5‐ylidene (with R being H (L¹), Me (L²), OMe (L³), CN (L⁴), CF₃ (L⁵), Br (L⁶) or NO₂ (L⁷)). The corresponding complexes (Ir‐ 1 to Ir‐ 7 and Os‐ 1 to Os‐ 7 ) were characterized by standard spectroscopic methods, and the expected three‐legged, piano‐stool type coordination was unambiguously confirmed by X‐ray diffraction analysis of selected compounds. Together with Ru^II analogues previously reported by us, a total of 21 complexes were tested as (pre)catalysts for the transfer hydrogenation of carbonyl groups, showing a remarkable reactivity even at very low catalyst loadings. The electronic effects of the ligands as well as different substrates were investigated. Some mechanistic elucidations are also presented.     

Efficient initiators for the ring‐opening polymerization of L‐lactide: Synthesis and characterization of NNO‐tridentate Schiff‐base zinc complexes

A series of efficient catalysts, based on zinc alkoxides coordinated with NNO‐tridentate Schiff‐base ligands (L¹H‐L⁶H), for ring opening polymerization of L ‐lactide have been prepared. The reactions of diethyl zinc (ZnEt₂) with L¹H‐L⁶H yielded [(μ‐L)ZnEt]₂ ( 1a–6a ), respectively. Further reaction of compounds 1a–6a with benzyl alcohol (BnOH) produced the corresponding compounds of [LZn(μ‐OBn)]₂ ( 1b–6b), respectively. X‐ray crystal structural studies reveal that all of these compounds 1a–6a are dimeric bridging through the phenolato oxygen atoms of the Schiff‐base ligand. However, the molecular structures of 1b–6b show a dimeric character bridging through the benzylalkoxy oxygen atoms. Ring‐opening polymerization of L ‐lactide, initiated by 1b–6b , proceeds rapidly with good molecular weight control and yields polymer with a very narrow molecular weight distribution. Experimental results show that the substituents on the imine carbon of the NNO‐ligand affect the reactivity of zinc complexes dramatically. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6466–6476, 2008     

Chiral M3L2 Self‐Assembled Capsules through Metal Coordination of Enantiopure Ligating Benzocyclotrimers: NMR Spectroscopic and ESI Mass Spectrometric Investigation

The synthesis of enantiopure (+)‐benzotricamphor syn‐ 5 , an important chiral C₃‐symmetric rigid building block for supramolecular applications, was studied in detail to reduce the number of steps and to increase the diastereoselectivity and overall yield. The new synthetic procedure allowed larger amounts of syn‐ 5 to be obtained and used for the preparation of new derivatives, such as the corresponding tris‐trifluoromethanesulfonate syn‐ 12 , which was efficiently transformed into (+)‐benzotribornenetrinitrile syn‐ 1 and (+)‐benzotribornenetris(ethynyl‐4‐pyridine) syn‐ 2 . The previously reported (+)‐benzotricamphortrioxime syn‐ 6 was transformed into tris‐nitrile syn‐ 3 by Beckman reaction. Compounds syn‐ 1 – 3 were employed as multidentate ligands for silver(I) and platinum(II) centres in apolar solvents. The linear coordination geometry of Ag^I and square‐planar geometry of cis‐chelated Pt^II in combination with the chiral tripodal ligands syn‐ 1 – 3 led to the formation of chiral enantiopure capsules with M₃L₂ stoichiometry, as confirmed by 2D NMR NOESY and DOSY experiments as well as ESI mass spectrometry.     

Excitation of He(31 D) by electron impact

We report new results of the Stokes parametersP ₁ toP ₄ and of the coherence parametersP _lin, γ _a , ρ₀₀ andL _∝ for He(3¹ D) excitation by electron impact in the energy range 40 eV to 81.6 eV obtained by the scattered electron-polarized photon coincidence technique. The present results are, where available, in fair agreement with previous measurements of other groups but disagree with the available calculations based on different models.     

Zinc(II) complexes of Triaza and Amidinate ligands: Efficient initiators for the ring‐opening polymerization of ε‐Caprolactone and rac‐Lactide

Zinc complexes supported by tertiary 1,3,5‐triazapenta‐1,3‐dienate ligand (L¹) and N ‐benzoyl‐N′ ‐arylbenzamidinate [aryl =2,6‐diisopropylphenyl (L²), phenyl (L³)] ligands have been synthesized and characterized. The reaction of L¹H with ZnEt₂ affords a mononuclear zinc complex [L¹ZnEt] ( 1 ) in good yield. Tetra nuclear zinc complex [(L¹)₂Zn₄O(OAc)₄] ( 2 ) is prepared by treating L¹H with one equivalent of Zn(OAc)₂ in toluene. Further, dinuclear zinc complexes [L²ZnEt]₂ ( 3 ) and [L³ZnEt]₂ ( 4 ) are obtained in good yields from L²H and L³H with ZnEt₂ in toluene respectively_. The complexes 1–4 have been characterized by ¹H/¹³C NMR spectroscopy and single crystal X‐ray diffraction studies. All of the complexes have been explored for their catalytic activity toward the ring‐opening polymerization (ROP) of ε ‐caprolactone. It has been found that complex 1 is an active catalyst for the polymerization of ε ‐caprolactone in presence of a cocatalyst benzyl alcohol (BnOH). While complex 2 is as active as 1 there is no need for a cocatalyst for the polymerization to proceed. Dinuclear zinc complexes 3 and 4 show very high activity for the ROP of ε ‐caprolactone (CL) and rac ‐lactide (LA) without requiring a cocatalyst. The resultant polymers are found to have very high molecular weight (M _n = 296 X 10³ g mol⁻¹) and relatively narrow polydispersity index compared to 1 and 2 .     

Effect of Heavy‐Atom (Br) at the Phenyl Rings of Schiff‐Base Ligands on the NIR Luminescence of their Bimetallic Zn‐Nd Complexes

Two heterobimetallic Zn‐Nd phenylene‐bridged Schiff‐base ligands complexes [ZnNd L¹ (Py)(NO₃)₃] ( 1 ) and [Zn L² Nd(Py)(NO₃)₃]·MeCN ( 2 ) (Py = pyridine, H₂L¹ = N,N′‐bis‐ (3‐methoxy‐salicylidene)phenylene‐1,2‐diamine, H₂L² = N,N′‐bis‐5‐bromo‐3‐methoxy‐salicylidene)phenylene‐1,2‐diamine) were obtained. Both 1 and 2 were structurally characterized by X‐ray crystallography, and their near‐infrared (NIR) luminescent properties were determined. For the two complexes, the occupation of pyridine at the axial position of 3d Zn²⁺ ions could effectively prevent luminescent quenching arising from OH‐, NH‐ or CH oscillators of the solvates around the 4f Nd³⁺ ions, and the heavy‐atom (Br) effect of the Schiff‐base ligands on their NIR luminescent properties is also discussed.     

A binuclear zinc polymer with paddlewheel building units and intersecting helical chains based on a flexible 4‐[(carboxymethyl)sulfanyl]benzoic acid ligand

The asymmetric unit of the title compound, poly[{μ₄‐4‐[(carboxylatomethyl)sulfanyl]benzoato}(N,N‐dimethylformamide)zinc], [Zn(C₉H₆O₄S)(C₃H₇NO)]_n, consists of one crystallographically independent Zn^II cation, one 4‐[(carboxylatomethyl)sulfanyl]benzoate (L²⁻) ligand and one coordinated dimethylformamide (DMF) molecule. The zinc ion is coordinated by five O atoms from four separate L²⁻ ligands and one DMF molecule, and the ZnO₅ unit displays a distorted square‐based‐pyramidal geometry. Two ZnO₅ units form a binuclear zinc–tetracarboxylate paddlewheel cluster, and these are bridged by L²⁻ ligands to generate an intersecting helical chain (Zn²⁺ ions as nodes), which is composed of right‐handed (P) and left‐handed (M) helices. Weak C—H...O hydrogen bonds extend the one‐dimensional coordinated chain into a weakly bound three‐dimensional supramolecular architecture.     

基于杯[4]芳烃和S-联萘酚的荧光传感器的合成及其对N-Boc保护谷氨酸阴离子的对应选择性识别性能研究

合成了一种基于杯[4]芳烃和S-联萘酚单元的新型手性大环受体4,并用荧光光谱和核磁氢谱研究了该受体与阴离子的键合性质。非线性曲线拟合结果表明受体4与N-Boc保护L-和D-谷氨酸阴离子都能通过多重氢键形成1:1的络合物,而且对N-Boc保护谷氨酸阴离子对映体显示了较好的对应选择性识别性能（Kass(L) / Kass(D) = 4.65）。不同的荧光响应表明受体4可以用作N-Boc保护谷氨酸阴离子的对应选择性的荧光化学传感器。     

Structure and properties of double‐C,N‐chelated tri‐ and diorganotin(IV) halides

Tri‐ and di‐organotin(IV) compounds containing one or two 2‐(dimethylaminomethyl)phenyl‐ (L^CN) groups as chelating ligands were prepared by reactions of lithium compound L^CNLi with an appropriate amount of (organo)tin halide. The geometry of tin in 1 ((L^CN)₂SnPhCl) is on the boundary between octahedral and trigonal bipyramidal. The diorganotin compounds 2–4 ((L^CN)₂SnX₂, where X = Cl, Br, I) have a distorted octahedral geometry in the solid state and show dynamic processes in solution with a lowering of activation energy of the dynamic process going from diiodide to dichloride derivative. Compound 5 (L^CNSnPhCl₂) has a trigonal bipyramidal structure with non‐equivalent chlorine atoms. Copyright © 2005 John Wiley & Sons, Ltd.     

Amplified Electrochemical Response of Phenol by Oxygenation of Tyrosinase Coupling with Electrochemical‐chemical‐chemical Redox Cycle

In this work, an novel electrochemical‐chemical‐chemical (ECC) redox cycle was designed in an enzyme‐based sensor for acquiring additional signal amplification. The tyrosinase (Tyr) was entrapped in a sulfonated polyaniline?chitosan (SPAN?CS) composite which was used as a redox capacitor on a glass carbon electrode. Firstly, the substrate, phenol was catalyzed to catechol and further catalyzed to o‐benzoquinone by Tyr. Next, in the presence of Ru(NH₃)₆Cl₂, the reduced state of SPAN(SPAN_red) was reacted with o‐benzoquinone to form it's oxidized state (SPAN_ox) and catechol, then SPAN_ox was reduced back to SPAN_red by Ru(II) in the solution. Finally, the amplified anodic current of catechol was obtained on electrode through above ECC redox cycle system. In addition, the ECC redox cycling led to a high signal‐to‐background ratio. The voltammetric response showed excellent analytical performance to phenol over two linear range of 3.5 to 200.0 nmol L^?1 and 200.0 to 2000.0 nmol L^?1 with a high sensitivity of 2204 μA mM^?1. The detection limit was obtained to be 0.8 nmol L^?1 (S/N=3). Furthermore, the proposed approach exhibited good repeatability, stability and specificity, and could offer practicality in the detection of phenol in tap water.     

[3+2] Cycloadditions of Metallo Nitrile Ylides and Metallo Nitrile Imines with Metal Carbonyl,Thiocarbonyl, and Isocyanide Complexes: Heterodimetallic Systems with Bridging Heterocycles [1]

The reactions of [Re(CO)₆]⁺, [FeCp(CO)₂CS]⁺ and [FeCp(CNPh)₃]⁺ with the metallo nitrile ylides [M^–{C⁺=N–C^–(H)CO₂Et}(CO)₅]^– (M = Cr, W) and the chromio nitrile imine [Cr^–{C⁺=N–N^–H}(CO)₅]^– (generated by mono‐α‐deprotonation of the parent isocyanide complexes) to give neutral 5‐metallated 1,3‐oxazolin‐ ( 1 ), 1,3‐thiazolin‐ ( 2 ), imidazolin‐ ( 3 , 4 ), 1,3,4‐oxdiazolin‐ ( 5 ), 1,3,4‐thiadiazolin‐ ( 6 ) and 1,3,4‐triazolin‐2‐ylidene ( 8 ) chromium and tungsten complexes represent the first all‐organometallic versions of Huisgen’s 1,3‐dipolar cycloadditions. The formation of 6 and 8 is accompanied by partial decomposition to (OC)₅Cr–C≡N–FeCpL₂ {L = CO ( 7 ), CNPh ( 9 )}. The structures of 4a and 5 have been characterized by X‐ray diffraction.     

Stepwise Encapsulation of Sulfate Ions by Ferrocenyl‐Functionalized Tripodal Hexaurea Receptors

Three ferrocenyl‐functionalized tripodal hexaurea anion receptors with ortho‐ ( L² ), meta‐ ( L³ ), and para‐phenylene ( L⁴ ) bridges, which showed strong binding affinities toward sulfate ions, have been designed and synthesized. In particular, meta‐phenylene‐bridged ligand L³ , owing to its trigonal bipyramidal structure, can encapsulate two SO₄^2? ions in its “inner” and “outer” tripodal clefts, respectively, as supported by their clearly distinct NMR resonances and by molecular modeling. The sulfate complex of ortho‐ligand L² , (TBA)₂[SO₄? L² ] ? 2 H₂O ( 1 ), displays a caged tetrahedral structure with an encapsulated sulfate ion that is hydrogen bonded by the six urea groups of ligand L² . CV studies showed two types of electrochemical response of the ferrocene/ferrocenium redox couple upon anion binding, that is, a shift of the wave and the appearance of a new peak. Quantitative binding data were obtained from the NMR and CV titrations.