Binding and selectivity aspects of an expanded azamacrocycle for anions

An expanded azamacrocycle L, containing four secondary and two tertiary amines was synthesized, and its binding ability towards chloride, bromide, iodide, sulfate, nitrate and perchlorate were determined by (1)H NMR titrations in D(2)O at pH 1.7. The results suggest that the ligand is capable of forming a complex with each of the anions examined, showing the selectivity for sulfate in water. X-ray diffraction analysis of the perchlorate complex of L suggests that the ligand is tetraprotonated and is involved in interacting anions from both sides forming a ditopic complex with strong NH···O bonds. In the packing diagram, the macrocycles and external perchlorates are alternatively linked though hydrogen bonding to form a 1D chain.     

Synthesis,structure and luminescent property of a new europium-based coordination polymer constructed from biphenyl-3,4′,5-tricarboxylic acid

A new 3D lanthanide metal–organic framework Eu(BPT)(DMF)(H₂O)•(H₂O)_0.5] (1) has been synthesized by self-assembly of Eu(III) ions and ligand biphenyl-3, 4′, 5-tricarboxylate under solvothermal reaction conditions. X-ray crystallography reveals that 1 exhibits a (3, 6)-connected topology, with dinuclear europium clusters as 6-connected nodes and C₂-symmetric ligands BPT as 3-connected nodes. In addition, the luminescence sensitization of 1 via excitation of the ligand is highly efficient.     

Cu(Ⅱ)-phen超分子配合物的合成及结构表征

以Cu(phen)2Cl2为前体,采用水热合成方法,辅以均苯四甲酸酐合成了2个超分子配合物[Cu(phen)2Cl]+.[C10H5O8]-和[Cu(phen)2Cl]+.0.5[C10H4O8]2-。采用单晶X-射线衍射、X-粉末衍射、FT-IR对这2个配合物的晶体结构和组成进行了表征。单晶衍射结果表明,2个配合物均为三斜晶系,P-1空间群。在2个配合物中,金属Cu的配位数都由前体中的6转变为5,由原来前体中的畸变的八面体结构转变成畸变的三角双锥结构。配合物(2)通过游离的均苯四甲酸配体之间的氢键作用和phen配体之间的π-π堆积作用形成了3D超分子结构,而配合物(3)则只是通过phen配体之间的π-π堆积作用形成3D超分子结构。     

The Second Class of Tetrahydrofolate (THF-II) Riboswitches Recognizes the Tetrahydrofolic Acid Ligand via Local Conformation Changes

Riboswitches are regulatory noncoding RNAs found in bacteria, fungi and plants, that modulate gene expressions through structural changes in response to ligand binding. Understanding how ligands interact with riboswitches in solution can shed light on the molecular mechanisms of this ancient regulators. Previous studies showed that riboswitches undergo global conformation changes in response to ligand binding to relay information. Here, we report conformation switching models of the recently discovered tetrahydrofolic acid-responsive second class of tetrahydrofolate (THF-II) riboswitches in response to ligand binding. Using a combination of selective 2′-hydroxyl acylation, analyzed by primer extension (SHAPE) assay, 3D modeling and small-angle X-ray scattering (SAXS), we found that the ligand specifically recognizes and reshapes the THF-II riboswitch loop regions, but does not affect the stability of the P3 helix. Our results show that the THF-II riboswitch undergoes only local conformation changes in response to ligand binding, rearranging the Loop1-P3-Loop2 region and rotating Loop1 from a ~120° angle to a ~75° angle. This distinct conformation changes suggest a unique regulatory mechanism of the THF-II riboswitch, previously unseen in other riboswitches. Our findings may contribute to the fields of RNA sensors and drug design.     

两个苯并咪唑羧酸稀土配合物的合成、晶体结构及荧光性质

合成了1,3-二羧甲基苯并咪唑有机配体,并与氯化铕、氯化钐反应得到了两个新的稀土配合物,通过元素分析、X-射线单晶衍射及X-射线粉末衍射对其进行表征。晶体结构表明,两个配合物结构均为两个金属中心被4个配体桥联形成Ln_2O_8型双核次级结构基元,通过(κ~1-κ~1-μ_2)-(κ~1)-μ_3配位模式与配体形成(4,4)拓扑的二维网络结构。同时测定了这两个配合物的热稳定性及Eu配合物的荧光性质。     

High Resolution Crystal Structures of the Cerebratulus lacteus Mini-Hb in the Unligated and Carbomonoxy States

The nerve tissue mini-hemoglobin from Cerebratulus lacteus (CerHb) displays an essential globin fold hosting a protein matrix tunnel held to allow traffic of small ligands to and from the heme. CerHb heme pocket hosts the distal TyrB10/GlnE7 pair, normally linked to low rates of O(2) dissociation and ultra-high O(2) affinity. However, CerHb affinity for O(2) is similar to that of mammalian myoglobins, due to a dynamic equilibrium between high and low affinity states driven by the ability of ThrE11 to orient the TyrB10 OH group relative to the heme ligand. We present here the high resolution crystal structures of CerHb in the unligated and carbomonoxy states. Although CO binds to the heme with an orientation different from the O(2) ligand, the overall binding schemes for CO and O(2) are essentially the same, both ligands being stabilized through a network of hydrogen bonds based on TyrB10, GlnE7, and ThrE11. No dramatic protein structural changes are needed to support binding of the ligands, which can freely reach the heme distal site through the apolar tunnel. A lack of main conformational changes between the heme-unligated and -ligated states grants stability to the folded mini-Hb and is a prerequisite for fast ligand diffusion to/from the heme.     

Structural correlations in nickel(II)–thiodiacetato complexes: molecular and crystal structures and properties of [Ni(tda)(H2O)3]

Triaqua(thiodiacetato)nickel(II) has been synthesized and studied by X-ray crystallography, thermal, spectral and magnetic methods. The compound crystallizes in the triclinic system, space group , in contrast to the related compound [Ni(tda)(H₂O)₃] · H₂O (orthorhombic) reported long time ago. As in other four Ni–tda derivatives, the metal atom exhibits an octahedral coordination and tda ligand adopts a fac-tridentate chelating role. The studied compound is closely related to [Zn(tda)(H₂O)₃]. In addition, a structural comparison of the binary and ternary Ni–tda derivatives reveals that auxiliary N-donor ligands bind the metal atom using the trans-positions towards the Ni–O(carboxylato) bonds, but not in trans to the Ni–S(thioether) bond.     

A novel Zn6Co3 cluster-based heterometallic coordination polymer with PMG3 − linker formed via in situ decarboxylation from H4PMIDA

A novel Zn₆Co₃ cluster-based heterometallic coordination polymer, [Zn₆Co₃(PMG)₆(H₂O)₄]·12H₂O (1), has been hydrothermally synthesized, in which the PMG^3 − (N-(phosphonomethyl)glycinate) as a multifunctional ligand was firstly formed via in situ decarboxylation from original ligand N-(phosphonomethyl)imino-diacetic acid during the hydrothermal reaction. The complex was characterized by elemental analysis, FT-IR, powder X-ray diffraction, thermal analysis and single-crystal X-ray diffraction techniques. Its structure features a 2D framework constructed by [Zn₆Co₃(PMG)₆(H₂O)₄] pinwheel-like heteronuclear clusters, which contains rings with two tropisms. Through extensive O–H⋯O hydrogen bondings, the adjacent 2D layered structure further extends into a 3D supramolecular network. Moreover, the solid-state fluorescence property of this complex has also been investigated at room temperature, which exhibits a good fluorescent emission.     

Synthesis and Crystal Structure of Diaqua(1,10-Phenanthroline-N,N')(Thiosulfato-O,S)Manganese(II). Biological Properties

The synthesis of diaqua(1,10-phenanthroline-N,N')(thiosulfato-O,S)manganese(ll) [Mn(phen)(S(2)O(3))(H(2)O)(2)] was investigated. Its structure was determined by single crystal X-ray diffraction from 2418 reflections (I > 3 sigma(I)) to a final value of R = 0.047 and Rw = 0.054. Crystal data are as follows : space group P(2) (1); a = 10.356(3), b = 7.097(3), c = 20.316(2) A, beta = 94.29(2) degrees , V = 1489.1(8) , A(3), Z = 2. There are two independent title compounds in the asymetric unit. Each manganese atom has a distorted octahedral Mn(SO)N(2)O(2) geometry with the S and O atoms (from two neighbouring thiosulfate ligands) mutually trans, two N atoms from the 1,10-phenanthroline ligand and two water oxygen. The thiosulfate group behaves as a bridging ligand, connecting, through sulfur and oxygen, Mn atoms related by the binary b translation, thus forming infinite chains running parallel to this axis. Infrared and electronic spectra are reported.     

玻璃组成对Li_2O–Al_2O_3–SiO_2微晶玻璃热膨胀系数的影响(英文)

通过传统熔融法制备了具有低膨胀系数的Li2O-Al2O3-SiO2(LAS)微晶玻璃.利用扫描电镜、X射线衍射、差热分折及热膨胀系数测定等分 析手段,研究了玻璃组成中Li2O,Al2O3,SiO2的含量对微晶玻璃热膨胀系数的影响.结果表明:在标准样品的基础上,Li2O的含量对热膨胀系数影 响很大:Li2O的含量提高,由于形成β-锂辉石,微晶玻璃的结晶程度增加与晶粒尺寸增大,导致热膨胀系数增大.与此相比较,Al2O3和SiO2成分 的变化对膨胀系数的影响较小.当玻璃组成(质量分数,下同)为4%～6%Li2O,16%~18%Al203,66%~68%Si02时,Li2O-Al2Oy-SiO2玻璃的膨胀 系数为-1.5～1.5×10-7/℃(0~700℃)     

Structure-activity relationships and mechanism of action of Eph-ephrin antagonists: interaction of cholanic acid with the EphA2 receptor

The Eph-ephrin system, including the EphA2 receptor and the ephrinA1 ligand, plays a critical role in tumor and vascular functions during carcinogenesis. We previously identified (3α,5β)-3-hydroxycholan-24-oic acid (lithocholic acid) as an Eph-ephrin antagonist that is able to inhibit EphA2 receptor activation; it is therefore potentially useful as a novel EphA2 receptor-targeting agent. Herein we explore the structure-activity relationships of a focused set of lithocholic acid derivatives based on molecular modeling investigations and displacement binding assays. Our exploration shows that while the 3-α-hydroxy group of lithocholic acid has a negligible role in recognition of the EphA2 receptor, its carboxylate group is critical for disrupting the binding of ephrinA1 to EphA2. As a result of our investigation, we identified (5β)-cholan-24-oic acid (cholanic acid) as a novel compound that competitively inhibits the EphA2-ephrinA1 interaction with higher potency than lithocholic acid. Surface plasmon resonance analysis indicates that cholanic acid binds specifically and reversibly to the ligand binding domain of EphA2, with a steady-state dissociation constant (K(D) ) in the low micromolar range. Furthermore, cholanic acid blocks the phosphorylation of EphA2 as well as cell retraction and rounding in PC3 prostate cancer cells, two effects that depend on EphA2 activation by the ephrinA1 ligand. These findings suggest that cholanic acid can be used as a template structure for the design of effective EphA2 antagonists, and may have potential impact in the elucidation of the role played by this receptor in pathological conditions.     

NMR chemical shift perturbation study of the N-terminal domain of Hsp90 upon binding of ADP,AMP-PNP,geldanamycin, and radicicol

Hsp90 is one of the most abundant chaperone proteins in the cytosol. In an ATP-dependent manner it plays an essential role in the folding and activation of a range of client proteins involved in signal transduction and cell cycle regulation. We used NMR shift perturbation experiments to obtain information on the structural implications of the binding of AMP-PNP (adenylyl-imidodiphosphate-a non-hydrolysable ATP analogue), ADP and the inhibitors radicicol and geldanamycin. Analysis of (1)H,(15)N correlation spectra showed a specific pattern of chemical shift perturbations at N210 (ATP binding domain of Hsp90, residues 1-210) upon ligand binding. This can be interpreted qualitatively either as a consequence of direct ligand interactions or of ligand-induced conformational changes within the protein. All ligands show specific interactions in the binding site, which is known from the crystal structure of the N-terminal domain of Hsp90. For AMP-PNP and ADP, additional shift perturbations of residues outside the binding pocket were observed and can be regarded as a result of conformational rearrangement upon binding. According to the crystal structures, these regions are the first alpha-helix and the "ATP-lid" ranging from amino acids 85 to 110. The N-terminal domain is therefore not a passive nucleotide-binding site, as suggested by X-ray crystallography, but responds to the binding of ATP in a dynamic way with specific structural changes required for the progression of the ATPase cycle.     

Cu(Ⅱ)配合物的制备、结构多样性及超氧化物歧化酶活性

To construct superoxide dismutase (SOD) mimetics, three Cu(Ⅱ) coordination polymers (CPs), [Cu3(L1)4(OH)2(H2O)2]n (CP 1), [Cu(L2)(OH)]n (CP 2) and [Cu(L2)(CH3O)]n (CP 3), in which n is a positive integer, are synthesized by solvothermal method using nicotinate N-oxide (HL1) or isonicotinate N-oxide (HL2) as organic ligands and Cu(OAc)2·H2O as metal salt. Their structures and properties are characterized by single crystal X-ray diffraction, X-ray powder diffraction, infrared spectroscopy, elemental analysis, thermogravimetric analysis and ultraviolet spectroscopy. CPs 1~3 are synthesized under similar solvothermal conditions, but show a multi-dimensional configurations from one-dimensional, two-dimensional to three-dimensional, respectively, exploring the possible mechanisms of the relative position of functional groups in ligand, the coordination mode of ligand and the solvent system on the structural diversity of CPs. Thermogravimetric analysis shows that CPs 1~3 can be stabilized up to 202, 228, and 250 ℃, respectively, which display good thermal stability, and the higher the dimension of CPs 1~3, the better the thermal stability. Nitrotetrazolium blue chloride (NBT) photoreduction test shows that the semi-inhibitory concentration values (IC50) of CPs 1~3 are 0.21, 0.26 and 0.62 μmol/L, respectively, which display certain SOD activity, and the lower the dimension of CPs 1~3, the better the SOD activity. The lower IC50 of CP 1 and CP 2 indicating that they can be used as potential SOD mimetics.     

以解热镇痛药酮洛芬为配体合成钴配合物的晶体结构及表征

以解热镇痛药酮洛芬为配体构筑了钴的配合物,并通过元素分析、红外、单晶X射线衍射仪对该配合物的结构进行了表征。配合物[Co（C16H13O3）2（H2O）4]·H2O属于三斜晶系,空间群为p-1,a=8．5966（17）A,b=8．8939（18）A,c=21．872（4）A,α=92．08（3）°,β=99．69（3）°,γ=108．92（3）°。两个分子中每个钻原子位于反演中心,分别与两个酮洛芬配体中的两个羧基氧原子以及四个水分子中的四个氧原子配位,具有正八面体配位构型,且由分子内氢键和分子间氢键形成了三维氢键超分子网络结构。     

超分子化合物[Co(HL)(2,2′-bipy)_2]·9·5H_2O的合成、晶体结构和热性质

合成了超分子化合物[Co(HL)(2,2′-bipy)2]·9·5H2O(H3L=对羧基苯磺酰甘氨酸,2,2′-bipy=2,2′-联吡啶),并通过单晶X射线衍射确定了晶体结构,晶体结构分析表明化合物C29H42CoN5O15.5S属单斜晶系,C2/c空间群。Co(Ⅱ)离子为6配位的八面体结构,对羧基苯磺酰甘氨酸作为双齿配体与Co(Ⅱ)离子配位,2,2′-联吡啶和Co(Ⅱ)离子双齿螯合配位。配合物通过氢键和π-π堆积作用形成三维结构,配合物中含有一个由18个水分子组成的独立水簇。在氮气气氛中对该化合物进行了热重分析,结果表明:该化合物在30.1℃时开始失重,440℃时分解完全。     

New manganese-based catalyst systems for alkyd paint drying

The autoxidation and oligomerisation of ethyl linoleate (EL) catalyzed by manganese salts in combination with several Schiff-base ligands has been studied making use of time-resolved FT-IR spectroscopy. The results indicate that several of the combinations exhibit relatively high catalytic activity for the autoxidation of EL. One of the catalyst systems was studied in more detail. The reaction between MnCl₂·2H₂O and the Schiff-base ligand (L4) formed by the condensation of 2-pyridinealdehyde and 2-aminopyridine has been studied to clarify the catalytic reaction process. It was found that the Schiff-base ligand L4 reacts with water and the tridentate ligand (2-pyridyl)(2-pyridylamino)methanol (HOL4) is formed. A single crystal structure of [Mn^III(OL4)₂]Cl·3H₂O has been determined by X-ray diffraction methods.     

Reaction between the diaqua form of cisplatin and 2-methylsulfanylphenylphosphonic acid yields a dinuclear phosphonato-bridged complex via NH3 elimination

Reaction between cis-[Pt(NH₃)₂(H₂O)₂]²⁺ and (2-methylsulfanyl)phenyl phosphonic acid (H₂mspp) did not yield the expected cis-diammine [(2-methylsulfanylphenyl)phosphonato]platinum(II) but the dimeric compound [{Pt(mspp)(NH₃)}₂]·6H₂O in which the dianionic mspp²⁻ ligand acts both as chelator and bridging ligand. Thus, the high trans-effect of the sulfanyl group apparently leads to elimination of one NH₃ ligand. An X-ray crystal structure analysis of the dimeric complex is reported.     

Helical metallomacrocyclic nickel(II) complexes of a tetradentate N2S2 ligand derived from N-methyldithiocarbazic acid

The structure of the tetradentate sulphur–nitrogen chelating agent, 1,2-phenylenebis(methylene) bis(1-methylhydrazinecarbodithioate) (NSSN) has been determined by X-ray diffraction. In the solid state, the two arms of the ligand remain in E configurations about the hydrazinic C–N bonds. The ligand reacts with hydrated nickel(II) salts in a 3:2 ligand-to-metal ratio yielding dimeric triple helical complexes of general formula, [Ni₂(NSSN)₃]X₄·nH₂O (X = Cl, Br, I, NCS; n = 5, 6, 9) which contain two nickel(II) ions in distorted octahedral environments. An X-ray crystallographic structure determination of the [Ni₂(NSSN)₃]Cl₄·9H₂O complex shows that it is a metallomacrocycle in which each ligand acts as a bis-bidentate chelating agent providing NS donors of one arm to one nickel(II) ion and NS donors of the second arm to a second nickel(II) ion. Each nickel(II) ion adopts a distorted octahedral geometry with a NiN₃S₃ coordination core as shown by their common electronic spectra.     

2-巯基吡啶与Cu(I)配合物的合成、晶体结构及光物理性质

利用Cu(I)前体[Cu(CH3CN)4]BF4与配体2-巯基吡啶、邻菲罗啉进行反应,合成了一种新型铜(I)配合物:{[Cu3(py2tH)6](BF4)3.H2O}n。运用X-射线单晶衍射方法确定了其晶体结构。同时,利用现代波谱方法对配合物的光物理性质进行研究。发射光谱显示在632nm处的发射峰属于金属到配体的电荷跃迁,即MLCT。     

Structure and Energetics of Ligand–Fluorine Interactions with Galectin-3 Backbone and Side-Chain Amides: Insight into Solvation Effects and Multipolar Interactions

Multipolar fluorine–amide interactions with backbone and side-chain amides have been described as important for protein–ligand interactions and have been used to improve the potency of synthetic inhibitors. In this study, fluorine interactions within a well-defined binding pocket on galectin-3 were investigated systematically using phenyltriazolyl-thiogalactosides fluorinated singly or multiply at various positions on the phenyl ring. X-ray structures of the C-terminal domain of galectin-3 in complex with eight of these ligands revealed potential orthogonal fluorine–amide interactions with backbone amides and one with a side-chain amide. The two interactions involving main-chain amides seem to have a strong influence on affinity as determined by fluorescence anisotropy. In contrast, the interaction with the side-chain amide did not influence affinity. Quantum mechanics calculations were used to analyze the relative contributions of these interactions to the binding energies. No clear correlation could be found between the relative energies of the fluorine–main-chain amide interactions and the overall binding energy. Instead, dispersion and desolvation effects play a larger role. The results confirm that the contribution of fluorine–amide interactions to protein–ligand interactions cannot simply be predicted, on geometrical considerations alone, but require careful consideration of the energetic components.