Syntheses and crystal structures of neutral oxorhenium(V) complexes of N2O2-donor tripodal ligands

The neutral distorted octahedral complexes [ReOCl(L)] {H₂L = N,N-bis(2-hydroxybenzyl)-2-(2-aminoethyl)dimethylamine (H₂had); N,N-bis(2-hydroxybenzyl)-aminomethylpyridine (H₂hap); N,N-bis(2-hydroxybenzyl)-2-(2-aminoethyl)pyridine (H₂hae)} were prepared by the reaction of trans-[ReOCl₃(PPh₃)₂] with a twofold molar excess of H₂L in ethanol. X-ray structure determinations of [ReOCl(had)] (1) and [ReOCl(hap)] (2) were performed, and the structures compared. In both complexes the choride is coordinated trans to the tripodal tertiary amino nitrogen, with a phenolate oxygen trans to the oxo oxygen.     

稀土螯合物BCPDA-Eu3+标记蛋白质研究

通过自制的双功能螯合剂 4 ,7 二氯磺基苯 1,10啡啉 2 ,9二羧酸 (BCPDA)标记牛血清白蛋白(BSA)实验 ,对于BCPDA标记蛋白质的条件进行研究。结果表明 :BCPDA在温和的条件下能与蛋白质反应 ,并在一定条件下与铕离子形成稳定的BSA BCPDA Eu3 标记物。利用自建的分析方法 ,测定了标记过程的有关参数。并对标记物的某些光学特性进行了研究。     

Di- and tetranulcear Ru complexes of phenylene-1,4-diaminotetra(phosphonite), p-C6H4[N{P(OC6H4OMe-o)2}2]2 and their catalytic investigation towards transfer hydrogenation reactions

The stoichiometric reaction of phenylene-1,4-diaminotetra(phosphonite), p-C₆H₄[N{P(OC₆H₄OMe-o)₂}₂]₂ (P₂NФNP₂) (1) with [RuCl₂(p-cymene)]₂ in acetonitrile produces cis,cis-[{RuCl₂(CH₃CN)₂}₂(P₂NФNP₂)] (2), whereas the similar reaction of 1 with [RuCl₂(p-cymene)]₂ in THF medium affords a tri-chloro-bridged tetrametallic complex, [{(η⁶-p-cymene)Ru₂(μ₂-Cl)₃Cl}₂(P₂NФNP₂)] (3) irrespective of the stoichiometry and reaction conditions. The formation and structure of complexes 2 and 3 are assigned through various spectroscopic and micro analysis data. The molecular structure of 2 is confirmed by single crystal X-ray diffraction study. The catalytic activities of complexes 2 and 3 have been investigated in transfer hydrogenation reactions.     

Chemoenzymatic Synthesis of Select Intermediates and Natural Products of the Desferrioxamine E Siderophore Pathway

The NIS synthetase family of enzymes responsible for the biosynthesis of siderophores is increasingly associated with bacterial virulence. Proteins in this class represent outstanding potential drug targets, assuming that basic biochemical and structural characterizations can be completed. Towards this goal, we have mated an improved synthesis of the non-commercial amino acid N-hydroxy-N-succinylcadaverine (HSC, 6) with an isothermal titration calorimetry (ITC) assay that profiles the iterative stages of HSC trimerization and macrocyclization by NIS synthetase DesD from Streptomyces coelicolor. HSC synthesis begins with multigram-scale Gabrielle and tert-butyl N-(benzyloxy)carbamate alkylations of 1-bromo-5-chloropentane following prior literature, but the end-game reported herein has two advantages for greater material throughput: (1) hydrogenolysis of benzyl ether and Cbz blocking groups is best accomplished with Pearlman’s catalyst at 40 psi of H₂ and (2) purification of neutral (zwitterionic) HSC is effected by simple flash chromatography over silica gel in MeOH. HSC is subsequently shown to be a substrate for NIS synthetase DesD, which catalyzes three successive amide bond syntheses via adenyl monophosphate ester intermediates. We quantify and present the iterative and overall enzyme kinetic constants associated with formation of the cyclotrimeric siderophore desferrioxamine E (dfoE, 1).     

Synthesis and characterization of a bis-μ,η-carboxylate-bridged dinuclear manganese(II) complex containing a tetradentate tripodal ligand, N-(benzimidazol-2-ylmethyl)iminodiacetic acid

The dinuclear Mn(II) complex, [Mn₂(Hbida)₂(H₂O)₂], was prepared using a tetradentate tripodal ligand, N-(benzimidazol-2-ylmethyl)iminodiacetic acid (H₃bida) which has two carboxylate and one benzimidazole groups. The manganese ions are doubly bridged using μ,η¹-bridging monodentate carboxylate oxygen atoms. The Mn–Mn bond distance of 3.446 Å in the complex is comparable to that observed in the active site of the native manganese arginase enzyme (3.30 Å). The geometry of the complex with four carboxylates in two different types of binding modes, non-bridging monodentate and μ,η¹-type bridging monodentate, mimics the active site structure of manganese arginase. The magnetic properties of the complex show a coupling constant of J = −0.471(1) cm⁻¹, which is consistent with weakly coupled antiferromagnetic Mn^II (S = 5/2) centers. The cyclic voltammograms of the Mn(II) complex in DMF show irreversible oxidation occurring around 570 mV (versus Ag/AgCl).     

MALDI mass spectrometric determination of dendritic iron chelation stoichiometries and conditional affinity constants

The iron chelation stoichiometries of a dendritic iron(III) chelator with N(1), N(3), N(5)-trimethylbenzene-1,3,5-tricarboxamide at its core, and containing 3 identical hexadentate tris-hydroxypyridinone branches D was studied by MALDI mass spectrometry. At pH 7.2, the speciation of the system included FeD, Fe(2)D and Fe(3)D species with the respective conditional stability constants of 26.74, 26.03 and 25.36. The differences in the stepwise affinity constants arise from the statistical distribution of iron(III), and there was no evidence for cooperativity between the iron-binding sites.     

Synthesis and characterization of copper-specific tetradendate ligands as potential treatment for Alzheimer's disease

To regulate copper homeostasis for the therapy of Alzheimer's disease, a series of “tetradendate monoquinoline” (TDMQ) ligands consisting of an 8-aminoquinoline nucleus with a bidentate amine side chain attached at the C2 position of the quinoline moiety, both parts being able to take part in copper chelation, were designed. These TDMQ ligands are potentially able to provide the square planar tetradentate coordination sphere, which is preferred for the extraction of copper(II) from amyloids, with a lower as possible molecular weight, to optimize the passage through different physiological barriers.     

Water soluble chromone Schiff base derivatives as fluorescence receptor for aluminium(III)

A novel water-soluble chromone Schiff base derivatives bearing polyhydroxylated moiety were prepared and applied for specific recognition of metal ions in aqueous medium. Their selective fluorescence response to Al(III) over a variety of other biologically important metal ions were demonstrated. Electronic parameters of the sensors were also studied by quantum chemical computations.     

Diphenylmethane Oxidation Catalyzed by Mononuclear Mn(III) Complexes

Catalytic property of a series of manganese(III) complexes with tetradentate phenol‐ and pyridinebased ligands on the oxidation of the C‐H bond of diphenylmethane in the presence of hydrogen peroxide as an oxidant at ambient conditions were investigated. In this process, diphenylmethane was oxidized to the corresponding keton and alcohol. The catalytic selectivity of the complexes was evaluated.     

Organobismuth(III) Derivatives of Sterically Hindered Bifunctional Tetradentate Schiff Bases: Synthesis and Spectroscopic Characterization

The equimolar reactions of Ph 3 Bi with the bifunctional tetradentate Schiff bases proceed with cleavage of two Bi--C bond of Ph 3 Bi and result in the formation of phenylbismuth(III) derivatives PhBi[RC(NC 6 H 4 S)CH 2 (NC 6 H 4 S)CCOOCH 3 ] where R = C 6 H 5 , 4-ClC 6 H 4 ,4-BrC 6 H 4 , and 4-CH 3 C 6 H 4 . Physico-chemical, IR, and NMR ( 1 H and 13 C) spectral studies have been carried out to investigate the structural aspect of these derivatives which reveal a penta coordination around the central Bi atom.