On the choice of optimal conformation in linear free-energy relationships. Reactivity of 2-[(carboxymethyl)sulfanyl]-4-oxo-4-arylbutanoic acids with diphenyldiazomethane

Rate constants for the esterification of eleven 2-[(carboxymethyl)sulfanyl]-4-oxo-4-arylbutanoic acids with diphenyldiazomethane in ethanol at 30 °C were determined, and correlated with substituent constants using classical Hammett and related methods. Statistically valid results for the para-substituted compounds were obtained by the Swain–Lupton approach. The compounds studied had significant conformational mobility due to seven rotatable bonds in their backbone. Going beyond the classical Hammett approach, we established a relatively fast procedure to find the optimal conformations that can be used in linear free-energy relationships, combining molecular dynamics with semiempirical calculations, and calculations using a higher level of theory (DFT and MP2). Fair correlations were observed with frontier orbitals, allowing inclusion of ortho-substituted derivatives and clarifying artifact-like data, as perceived by the Hammett-type approach.     

Conformational Analysis of Guaianolide-Type Sesquiterpene Lactones by Low-Temperature NMR Spectroscopy and Semiempirical Calculations

Conformational analysis of 9-acetoxycumambrine A 1 and 8-O-isobutiryl-9-acetoxycumambrine B 2 was carried out by low-temperature NMR studies. Results suggested that lactones 1 and 2 are mixtures of two distinctive conformers, I and II. Based on low-temperature ¹H NMR spectra, in four solvents, the thermodynamic parameters of I II exchange process were assessed. Energy of activation of I II reaction was obtained by dynamic NMR simulations for both compounds. Results revealed that conformational exchange of lactones 1 and 2 occurs due to chair twisted chair interconversion of a heptane ring. The same PM3 semiempirical method was applied for geometry optimization of lactones 1 and 2, as well as of 9-hydroxycumambrine A 3, 9-acetoxycumambrine B 4, and cumambrine B 5.     

Time-discretization scheme for quasi-static Maxwell's equations with a non-linear boundary condition

We study a time dependent eddy current equation for the magnetic field H$\mathit{H}$ accompanied with a non-linear degenerate boundary condition (BC), which is a generalization of the classical Silver–Müller condition for a non-perfect conductor. More exactly, the relation between the normal components of electrical E$\mathit{E}$ and magnetic H$\mathit{H}$ fields obeys the following power law ν×E=ν×(|H×ν|^α-1H×ν)$\mathit{\nu }\times \mathit{E}=\mathit{\nu }\times (|\mathit{H}\times \mathit{\nu }{|}^{\alpha -1}\mathit{H}\times \mathit{\nu })$ for some α∈(0,1]$\alpha \in (0,1]$. We establish the existence and uniqueness of a weak solution in a suitable function space under the minimal regularity assumptions on the boundary Γ$\Gamma$ and the initial data _H0${\mathit{H}}_0$. We design a non-linear time discrete approximation scheme based on Rothe's method and prove convergence of the approximations to a weak solution. We also derive the error estimates for the time-discretization.     

Crystal structure, spectroscopic and magnetic properties, and antimicrobial activities of cobalt(II) 2-methylthionicotinate complexes with N-heterocyclic ligands

Synthesis and characterization of 10 new 2-methylthionicotinate (2-MeSnic) Co(II) complexes, namely, [Co(2-MeSnic)₂L₂(H₂O)₂] · nH₂O (L is N,N-diethylnicotinamide—Et₂nia, ethylnicotinate—Etnic, nicotinamide—nia, isonicotinamide—isonia, N-methylnicotinamide—N-Menia, furo[3,2-c]pyridine—fpy, 2,3-dimethylfuro[3,2-c]pyridine—Me₂fpy or benzo[4,5]furo[3,2-c]pyridine—Bfp; n is 0, 1 or 2) as well as [Co(2-MeSnic)₂L₂] (L is ronicol—ron or 2-methylfuro[3,2-c]pyridine—Mefpy), are reported. The characterizations were based on physico-chemical and spectroscopic methods. The crystal structure of one of the complexes has been determined. In the molecular complex [Co(2-MeSnic)₂(Me₂fpy)₂(H₂O)₂], the Co(II) central atom, located at a symmetry centre, is octahedrally coordinated by an oxygen atom of the unidentate 2-MeSnic carboxyl group, the nitrogen atom of the pyridine ring of Me₂fpy, a water molecule and the corresponding centrosymmetrically located atoms. Also, biological activity of the complexes against various strains of bacteria and filamentous fungi has been investigated. It is concluded that by complexation of these nicotinate derivatives their biological activities are elevated. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Vibrational spectra of the Cu(II) complexes of L-asparagine and L-glutamine

The infrared and Raman spectra of the copper(II) complexes [Cu(L-asn)2] and [Cu(L-gln)2] (L-asn=L-asparagine; L-gln=L-glutamine), were recorded and analyzed in relation to its structural peculiarities. Some comparisons between the spectra of these complexes and with those of related systems are made. The characteristics of the carboxylate and amide groups of the bonded ligands are discussed in detail.     

Synthesis and characterization of novel Cd(II), Zn(II) and Ni(II) complexes with 2-quinolinecarboxaldehyde selenosemicarbazone. Crystal structure of bis(2-quinolinecarboxaldehyde selenosemicarbazonato)nickel(II)

New complexes of Cd(II), Zn(II) and Ni(II) with 2-quinolinecarboxaldehyde selenosemicarbazone (Hqasesc) were synthesized and structurally characterized. The structure of the ligand, Cd(II) and Zn(II) complexes was determined by NMR and IR spectroscopy, elemental microanalysis and molar conductivity measurements. Both complexes occur in solution in two forms, the major tetrahedral and minor octahedral. In the major Cd(II) complex one qasesc⁻ ligand is coordinated as a tridentate, the fourth coordination site being occupied by acetate, while in the major Zn(II) complex two qasesc⁻ ligands are coordinated as bidentates. In both minor complexes two qasesc⁻ ligands are coordinated as tridentates forming the octahedral geometry around the central metal ion. The only paramagnetic complex in the series is Ni(II) complex for which X-ray structure analysis was performed. The complex has the angularly distorted octahedral geometry with two qasesc⁻ ligands coordinated as tridentates, in a similar way as in the minor complexes of Cd(II) and Zn(II).     

Benzylammonium,imidazolium and pyridinium polyvanadates — Synthesis and characterization

Summary From the reaction systems,B-V₂O₅-HClO₄-H₂O andB-V₂O₅-H₂O, whereB is benzylamine (Bz), imidazole (Im) or pyridine (Py), eight new compounds were synthesized: at 20°C, the metavanadate and decavanadates of composition (BzH)VO₃, (BzH)₆V₁₀O₂₈·3H₂O, (ImH)₆V₁₀O₂₈·2H₂O, (PyH)₆V₁₀O₂₈·2H₂O, (ImH)₄H₂V₁₀O₂₈·2H₂O and (PyH)₄H₂V₁₀O₂₈·3H₂O, and at 60°C, the hexavanadates of composition (ImH)₂V₆O₁₆·H₂O and (PyH)₂V₆O₁₆·H₂O. ThepH ranges of solutions the polyvanadates can be isolated from, were estimated. The compounds prepared were characterized by chemical analysis and IR spectroscopy. The synthesis of deuterated analogues allowed to assign the IR bands corresponding to vibrations of water in the spectra of deca- and dihydrogendecavanadates and to V-OH vibrations in the spectra of dihydrogendecavanadates.

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Benzylammonium-, Imidazolium- und Pyridinium-Polyvanadate. Synthese und Charakterisierung

Zusammenfassung Aus dem ReaktionssystemB-V₂O₅-HClO₄-H₂O undB-V₂O₅-H₂O [B=Benzylamin (Bz), Imidazol (Im) oder Pyridin (Py)] wurden acht neue Verbindungen synthetisiert: bei 20°C entstanden die Metavanadate und Decavanadate der Zusammensetzung (BzH)VO₃, (BzH)₆V₁₀O₂₈·3H₂O, (ImH)₆V₁₀O₂₈·2H₂O, (PyH)₆V₁₀O₂₈·2H₂O, (ImH)₄H₂V₁₀O₂₈·2H₂O und (PyH)₄H₂V₁₀O₂₈·3H₂O, bei 60°C entstanden die Hexavanadate (ImH)₂V₆O₁₆·H₂O und (PyH)₂V₆O₁₆·H₂O. DiepH-Bereiche, innerhalb derer Polyvanadate isoliert werden können, wurden abgeschätzt. Die Verbindungen wurden mittels chemischer Analyse und IR-Spektroskopie charakterisiert, wobei die Synthese deuterierter Analoga die Zuordnung von Banden unterstützte.

     

Dispersion copolymerization of polyoxyethylene macronomer and styrene 4. Solution properties of polystyrene-graft-polyoxyethylene copolymers

The graft copolymers (polystyrene-graft-polyoxyethylene) (PSt-graft-PEO) were prepared by the radical dispersion copolymerization of methacryloyl (MA)-terminated PEO macromonomer and styrene. By means of size-exclusion chromatography, liquid chromatography at the critical adsorption point, and light scattering, the molecular weight parameters and the solution properties of PSt-graft-PEO were investigated. The apparent average molecular weight and the molecular weight distribution (MWD) of graft copolymers were found to decrease with increasing molecular weight of PEO-MA macromonomer. This decreased molecular weight was attributed to the chain transfer to PEO unit and increased contribution of the solution polymerization. The broad MWD varied with the ratio of the polymerization in the continuous phase and the polymer particles. The number of PEO grafts per PSt backbone decreased with increasing molecular weight of the PSt-graft-PEO copolymer, which was attributed to the intramolecular association of PEO segments. The intrinsic viscosity or the coil size of graft copolymer molecules varied with temperature as a result of the dehydration of PEO segments. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3087–3097, 1999     

Synthesis,spectroscopic properties,crystal structure and biological activities of copper(II) 2-methylthionicotinate complexes with furopyridines

The synthesis and characterization of six new 2-methylthionicotinate (2-MeSnic) copper(II) monomeric complexes [Cu(2-MeSnic)₂L₂] (L is furo[3,2-c]pyridine—fpy, 2-methylfuro[3,2-c]pyridine—Mefpy, 2,3-dimethylfuro[3,2-c]pyridine—Me₂fpy or benzo[4,5]furo[3,2-c]pyridine—Bfp), [Cu(2-MeSnic)₂(fpy)₂(H₂O)], as well as [Cu(2-MeSnic)₂(CF₃Phfpy)₂(H₂O)₂] (CF₃Phfpy is 2-(3-trifluoromethylphenyl)furo[3,2-c]pyridine) are reported. The characterizations were based on elemental analysis, infrared, electronic and EPR spectra. The crystal structure of one of the complexes has been determined. The Cu^II atoms of [Cu(2-MeSnic)₂(fpy)₂(H₂O)] are six-coordinated in a highly distorted tetragonal–bipyramidal arrangement by two nitrogen atoms, one from each fpy, in trans-positions, by three oxygen atoms of the carboxyl groups of 2-MeSnic ligands (one monodentate, one asymmetrically bidentate), one axial position being occupied by the oxygen of a water molecule. The antimicrobial effects have been tested on various strains of bacteria, yeasts and filamentous fungi. A comparison of the IC₅₀ and MIC values has shown a decrease of inhibition activities of tested compounds in the order: [Cu(2-MeSnic)₂(Bfp)₂] > Bfp > [Cu(2-MeSnic)₂(CF₃Phfpy)₂(H₂O)₂] > [Cu(2-MeSnic)₂(Me₂fpy)₂] > CF₃Phfpy > [Cu(2-MeSnic)₂(Mefpy)₂] > Me₂fpy > [Cu(2-MeSnic)₂(fpy)₂(H₂O)] > [Cu(2-MeSnic)₂(H₂O)]₂ > Mefpy > fpy = 2-MeSnicH = CuSO₄. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis of enantiomerically enriched α,α-disubstituted β,γ-epoxy esters using hydrolytic kinetic resolution catalyzed by salenCo(III)

Novel α,α-disubstituted epoxy esters were prepared in enantiopure form by hydrolytic kinetic resolution (HKR) of the corresponding racemic mixtures using chiral salenCo(III) as catalyst. The methodology provides a convenient route to enantioenriched β,γ-epoxy esters 2a, 2c and 2d.