Showing papers by "Ralph Puchta published in 2015"

Saalfrank-type {Fe2L3} host–guest complexes – prediction of ion selectivity by quantum chemical calculations VII

Abstract: Based on density functional calculations (B3LYP/LANL2DZp (LANL2DZp=LANL2DZ augmented with polarization functions on non-hydrogen atoms)), the selectivity of the {2}-metallocryptand [Fe2L3] (L2− = 2,6-dibutane-1,3-dionylpyridine dianion) was investigated and the experimentally known K+, Sr2+ and Ba2+ cation selectivity rationalized. The rigidity of L2−, visible in the small torsion angles compared to previously investigated classical organic cryptands, can be identified as the origin of this discrimination. Derived from the hosted alkali and alkaline earth cations, the size of the {2}-metallocryptand’s [Fe2L3] cavity is analogous to the cryptand [2.2.phen]. Additionally, the quantum chemical calculations identified the {2}-metallocryptand [Fe2L3] as the first experimentally verified metalloproton sponge (calculated (B3LYP/LANL2DZp) proton affinity −259.8 kcal mol−1). This high gas-phase proton affinity clearly explains why empty [Fe2L3] was never observed, and only [(HN)3Fe2L3]3+ or [MFe2L3]m+ are known.

Studies on the Reaction of Iron(II) with NO in a Noncoordinating Ionic Liquid.

Abstract: In an earlier study we investigated the reaction of iron(II) chloride with NO in a strongly coordinating ionic liquid 1-ethyl-3-methylimidazolium dicyanamide [emim][dca] and showed that the actual reactive species in solution was [FeII(dca)5Cl]4–. For the present report we investigated in detail how this reaction could proceed in a noncoordinating ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate [emim][OTf]. The donor ability of OTf– is much lower than that of dca–, such that the solubility of FeCl2 in [emim][OTf] strongly depended on other donors like water or chloride ions present or added to the ionic liquid. On increasing the chloride concentration in [emim][OTf], the tetrachloridoferrate complex [emim]2[FeCl4] was formed, as verified by X-ray crystallography. This complex undergoes reversible binding of NO, for which the UV–vis spectral characteristics of the green–brown nitrosyl product resembled that found for the corresponding nitrosyl complexes formed in water and [emim][dca] as ...

Kinetic and mechanistic insight into Lewis base and acid-mediated phenylselenoetherification of 2,6-dimethyl-hept-5-en-2-ol

Abstract: Mechanistic and kinetic aspects, as well as quantum chemical calculations, for the formation of a tetrahydrofurane ring by cyclization of the highly substituted alcohol–2,6-dimethyl-hept-5-en-2-ol with phenylselenohalides (PhSeCl and PhSeBr), in the presence of various Lewis bases (piperidine, triethylamine, pyridine and quinoline) and Lewis acids (CoCl2, SnCl2) as additives were studied. The substituted tetrahydrofuran ring is common motif in many natural products, especially in bioactive marine macrolides. Due to the presence of additives in reactions, the high regioselectivity was achieved, and the tetrahydrofuran type of ether in all studied reactions was obtained in excess in regard to the six-membered cyclic ether. In addition, kinetic aspects of reactions mediated by Lewis bases were studied by UV–Vis spectroscopy (in THF, at 288 K), as reactions of pseudo-first-order. Obtained values for rate constants proved catalytic role of additives and indicated that the reaction rate depends on pKa values of used base as well as on their ability for formation of hydrogen bond with OH–alcohols group.

Norfloxacin La(III)-based complex: synthesis, characterization, and DNA-binding studies

Abstract: A La(III) complex, [LaIIICl2(NOR)2]Cl (2), containing norfloxacin (NOR) (1), a synthetic fluoroquinolone antibacterial agent, has been synthesized and characterized by elemental analysis, IR, UV–vis spectra and 1H NMR spectroscopy, and molar conductance measurements. The interaction between 2 and CT-DNA was investigated by steady-state absorption and fluorescence techniques in different pH media, and showed that 2 could bind to CT-DNA presumably via non-intercalative mode and the La(III) complex showed moderate ability to bind CT-DNA compared to other La(III) complexes. The binding site number n, and apparent binding constant KA, corresponding thermodynamic parameters ΔG#, ΔH#, ΔS# at different temperatures were calculated. The binding constant (KA) values are 0.23 ± 0.05, 0.56 ± 0.05, and 0.18 ± 0.08 × 105 L mol−1 for pH 4, 7, and 11, respectively. It was also found that the fluorescence quenching mechanism of CT-DNA by La(III) complex was a static quenching process.

Preparation of candidate reference materials for the determination of phosphorus containing flame retardants in styrene-based polymers.

Abstract: Candidate reference materials (RM) for the analysis of phosphorus-based flame retardants in styrene-based polymers were prepared using a self-made mini-extruder. Due to legal requirements of the current restriction for the use of certain hazardous substances in electrical and electronic equipment, focus now is placed on phosphorus-based flame retardants instead of the brominated kind. Newly developed analytical methods for the first-mentioned substances also require RMs similar to industrial samples for validation and verification purposes. Hence, the prepared candidate RMs contained resorcinol-bis-(diphenyl phosphate), bisphenol A bis(diphenyl phosphate), triphenyl phosphate and triphenyl phosphine oxide as phosphorus-based flame retardants. Blends of polycarbonate and acrylonitrile-co-butadiene-co-styrene as well as blends of high-impact polystyrene and polyphenylene oxide were chosen as carrier polymers. Homogeneity and thermal stability of the candidate RMs were investigated. Results showed that the candidate RMs were comparable to the available industrial materials. Measurements by ICP/OES, FTIR and NMR confirmed the expected concentrations of the flame retardants and proved that analyte loss and degradation, respectively, was below the uncertainty of measurement during the extrusion process. Thus, the candidate RMs were found to be suitable for laboratory use.