[Bis(2,4-dimethyl-6-tert.butyl-phenyl)ketone]chromium tricarbonyl—Stable torsional isomers

Complexation of bis(2,4-dimethyl-6-tert.butyl)ketone with chromium hexacarbonyl yields a mixture of two diastereomeric mono complexes in a ratio of 5 : 1. They can be separated by chromatography on silica gel at room temperature thus representing stable torsional isomers (isolable residual diastereomers).Dedicated to Prof. Dr.A. Neckel with cordial wishes on the occasion of the 60th anniversary of his birthday.     

Study of complexation between perrhenate ion and N-methyl-N-vinylacetamide and N-methyl-N-vinylamine copolymers in aqueous solutions by fast monolith high-performance liquid chromatography (HPLC)

Complexation between perrhenate ion and N-methyl-N-vinylacetamide and N-methyl-N-vinylamine copolymers in aqueous solutions was studied by high-performance liquid chromatography on monolith ultrashort columns. It was demonstrated that complexation has slow kinetics and strongly depends on the length of alkyl substituent.     

Capillary electrophoresis method to determine siRNA complexation with cationic liposomes

Small interfering RNA (siRNA) inducing gene silencing has great potential to treat many human diseases. To ensure effective siRNA delivery, it must be complexed with an appropriate vector, generally nanoparticles. The nanoparticulate complex requires an optimal physiochemical characterization and the complexation efficiency has to be precisely determined. The methods usually used to measure complexation in gel electrophoresis and RiboGreen^® fluorescence‐based assay. However, those approaches are not automated and present some drawbacks such as the low throughput and the use of carcinogenic reagents. The aim of this study is to develop a new simple and fast method to accurately quantify the complexation efficiency. In this study, capillary electrophoresis (CE) was used to determine the siRNA complexation with cationic liposomes. The short‐end injection mode applied enabled siRNA detection in less than 5 min. Moreover, the CE technique offers many advantages compared with the other classical methods. It is automated, does not require sample preparation and expensive reagents. Moreover, no mutagenic risk is associated with the CE approach since no carcinogenic product is used. Finally, this methodology can also be extended for the characterization of other types of nanoparticles encapsulating siRNA, such as cationic polymeric nanoparticles.     

Yttrium(III) bonding to organic ligands: A comparison with the lanthanoid(III) cations

Summary The yttrium(III) bonding to organic substrates (oximes, -diketonates and (poly)amino-(poly)carboxylates) has been compared with that of the lanthanoid(III) cations. The complexation constants of Y³⁺ with the examined organic ligands are similar to those of some cations of the first half of the lanthanoid series, in contrast with the fact that the Y³⁺ ionic dimensions are similar to those of Ho³⁺. This has been explained by correlating the formation constants of the Y³⁺ and the lanthanoids(III) complexes by the equation logK ₁=C _AC_B+E _AE_B, where the parametersC andE indicate the tendency of each Lewis acidA and Lewis baseB to undergo covalent or ionic bonding, and where the ratioH=E/C indicates the charge control on the bond formation tendency of each speciesA orB. The results are commented in terms of the utility of Y³⁺ in assisting organic reactions.

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Bindung von Yttrium(III) an organische Liganden: Vergleich mit Lanthanoid(III)-Kationen

Zusammenfassung Es wurde die Bindung von Yttrium(III) an organische Substanzen [Oxime, -Diketonate und (Poly)Amino(poly)carboxylate] im Vergleich mit Lanthanoid(III)-Kationen behandelt. Die Komplexierungskonstanten von Y³⁺ sind ähnlich denen einiger Kationen der ersten Hälfte der Lanthanoidenserie; dies steht im Gegensatz zur Tatsache, daß die Dimensionen des Y³⁺-Ions denen des Ho³⁺ entsprechen. Die Erklärung wurde mittels der für die Bildungskonstanten der Y³⁺- und Lanthanoid(III)-Komplexe gültigen Gleichung logK ₁=C _AC_B+E _AE_B gefunden, wobeiC undE Parameter sind, die die Tendenz der Lewis-SäurenA und der Lewis-BasenB zum Eingehen von kovalenten oder ionischen Bindungen charakterisieren und wo das VerhältnisH=E/C den Steuerungseffekt der Ladung auf die Bindungstendenz der SpeziesA oderB beschreibt. Die Ergebnisse werden im Hinblick auf den Nutzen von Y³⁺ zur Unterstützung organischer Reaktionen diskutiert.

     

Crayfish Shell Waste as Safe Biosorbent for Removal of Cu2+ and Pb2+ from Synthetic Wastewater

Crayfish shell is an abundant natural waste and is also a potential biosorbent for pollutants, especially, heavy metals. In this study, the safety of the use of crayfish shell as a biosorbent was first assessed by release experiments involving primary heavy metal ions, such as Cu²⁺, Zn²⁺, and Cr³⁺, in aqueous solution under different environmental conditions. The release concentrations of heavy metals were dependent on pH, ionic strength, and humic acid; and the maximum release concentrations of heavy metals were still lower than the national standard. Specifically, Cu²⁺ and Pb²⁺ removal by crayfish shell in synthetic wastewater was investigated. The removal process involved biosorption, precipitation, and complexation, and the results indicate that crayfish shell is an excellent biosorbent for Cu²⁺ and Pb²⁺ removal. The precipitation step is particularly dependent on Ca species, pH, and temperature. The maximum removal capacities of Pb²⁺ and Cu²⁺ were 676.20 and 119.98 mg/g, respectively. The related precipitates and the generated complex products include Cu₂CO₃(OH)₂, Ca₂CuO₃, CuCO₃, Pb₂CO₃(OH)₂, CaPb₃O₄, and PbCO₃.     

Interactions of ligands with lithium picrate in dioxane

The interaction of several cyclic ethers, poly(ethylene glycol dimethyl ether)s, nitriles, esters and ketones with lithium picrate in dioxane at 25°C was investigated by means of a competition method using cross-linked poly(ethylene oxide) (PEO) as the insoluble ligand. The Langmuir-Klotz isotherm of LiPi binding to the PEO gel gave an apparent binding constant, K, as a function of the concentration of added ligand. Plots of 1/K vs. the ligand concentration then yielded the formation constant, K _L , of the ligand complex with LiPi. The results demonstrate that in dioxane one ligand molecule binds to LiPi. While there is some dependence on the Gutmann donicity number of the respective ligands, steric factors often play a dominant role in determining the value of K _L . The results were compared with complexation data obtained on similar systems but by different methods.     

The influence of isomerism on the self-assembly behavior and complexation property of 1,3-alternate tetraaminopyridyl-thiacalix[4]arene derivatives

A series of 1,3-alternate conformation thiacalix[4]arenes containing different isomeric aminopyridyl pendent arms have been synthesized. It was found that their self-assembly behaviors and complexation properties strongly depended on the structures of aminopyridyl pendent arms. The crystal structures demonstrate that tetra(meta-aminopyridyl)-thiacalix[4]arene motif is capable of forming intramolecular hydrogen bondings between the sp² nitrogen donors in the meta position of the aminopyridyl groups and the facing amide N-H of the adjacent aminopyridyl groups, and self-assembles via C-H?O weak hydrogen bondings and C-H?π interaction to generate a double stranded rectilineal networks. By contrast, in the case of tetra(para-aminopyridyl)-thiacalix[4]arene, the presence of para-aminopyridyl units enables the formation of N-H?N strong hydrogen bondings between the individual molecules leading to the solid-state structure with water-bridged double strands. Their complexation properties had been also studied by measurement of the stability constants for their complexation in a range of metal cations and investigation of their binding models via ¹H NMR titration and ESI-MS experiments. It was found that the three ligands exhibited high and selective extractability toward Ag⁺, and their stoichiometry of ligand to Ag⁺ was 1:1, while the meta-aminopyridyl derivative showed the best extraction capacity and possessed the most efficient binding sites.     

The (salophen)-bridged Fe/Cr (III) capped complexes with triphenylene core: Synthesis and characterization

This article describes synthesis of the difference carboxylic acid derivatives of triphenylene and its complexation properties with Fe/Cr (III)-salophen. For this purpose, the carboxylic acid derivatives of 2,3,6,7,10,11-hexahydroxytriphenylene were synthesized and then reacted with four new Fe(III) and Cr(III) complexes involving tetradenta Schiff bases bis(salicylidene)-o-phenylenediamine-(salophenH₂). The prepared compounds were characterized by means of elemental analysis carrying out infrared spectroscopy (IR), thermogravimetric analysis (TG), nuclear magnetic resonance (¹H NMR), elemental analysis and magnetic susceptibility measurement. The complexes can also be characterized as low-spin distorted octahedral Fe(III) and Cr (III) bridged by carboxylic acids.     

Thermally activated and light-induced metal ion complexation of 5′-(hydroxy)spiroindolinonaphthooxazines in polar solvents

Chelation with Al(III), Fe(II) or Cu(II) of the open photomerocyanine form obtained under steady irradiation of spiroindolinonaphthooxazines, with a hydroxyl group at the 5′ position in the naphthooxazine moiety, induces a slight hypsochromic shift of its visible absorption band and increases the lifetime of this form, slowing down its thermal bleaching in the dark (rate constant  10⁻³ s⁻¹). Complexation with Al(III), Fe(II) or Cu(II) allows the spiroindolinonaphthooxazines to isomerize to their open coloured form even under dark conditions giving a complex spectroscopically identical to the photoinduced product. The activation energy of thermal complexation is independent of the metal ion which implies the ring opening as the rate determining step.     

Investigation of the complexation reaction between 2-diethylaminomethyl-4-methylphenol and ZnCl2. Reaction mechanism and solvent effects

The reaction mechanism of the chemical reaction of 2-diethylaminomethyl-4-methylphenolate with ZnCl₂ is investigated by means of the PM3 semi-empirical method. We propose two different but competitive stepwise pathways going from the isolated reactants to the tetra-coordinated bidentate final complex, where the zinc atom is bonded both to the oxygen and to the nitrogen atom of the ligand. Each pathway proceeds via different monodentate intermediate complexes. This study shows that either the first chemical bond formed between ZnCl₂ and 2-diethylaminomethyl-4-methylphenolate is the Zn–O bond or the Zn–N bond. The direct pathway going from the reactants to the final product through a concerted asynchronous mechanism is found to be unrealistic, since it involves a second order saddle point.

Solvent effects are taken into account with the SCRF dielectric continuum model at the PM3 and (RHF/3-21G) levels of theory. This preliminary study shows that the complex formation is favored by the use of polar solvent.