Density functional calculation of the 2D potential surface and deuterium isotope effect on 13C chemical shifts in picolinic acid N-oxide. Comparison with experiment

2D free energy surfaces V = V(rOH, rO...O) for the intramolecular H-bond in the title compound were calculated by the DFT method and used in the calculation of primary and secondary chemical shifts of the compound dissolved in chloroform and acetonitrile. Solvent effects were accounted for by the SCRF/PCM method. The corresponding two-dimensional chemical shift surfaces with included solvent reaction field were obtained using the Continuous Set of Gauge Transformations approach at the B3LYP/6-311+G(2d,2p) level of theory. The chemical shifts were estimated as quantum averages along the two internal coordinates in the hydrogen bond and along several vibrational levels according to the Boltzmann distribution at room temperature. Fairly good agreement between the experimental and calculated isotope effects was obtained. 1D and 2D NMR spectra of solutions of picolinic acid N-oxide and its deuterated analogue were recorded and assigned.     

Synthesis and characterisation of Pd(II) complexes with a derivative of aminoazobenzene: Dynamic H-NMR study of cyclopalladation reactions in DMF

Three new Pd(II) complexes, i.e. [PdCl₂L]₂ (A), PdCl₂L₂ (B) and [Pd(μ-Cl)(L-H)]₂ (C), each with two diethyl [α-(4-benzenazoanilino)-2-hydroxybenzyl]phosphonates (L) bound to either one or two palladium atoms, are synthesized and characterized by elemental analysis, by IR, UV-vis and solid-state ¹³C-NMR spectra. Complexes B and C are additionally characterized by ¹H-, ¹³C- and ³¹P-NMR and electrospray mass spectrometry (ESMS) studies using dimethylformamide (DMF) as a solvent. In DMF solution adducts A and B undergo spontaneous rearrangement into the cyclopalladated complex C. Dynamic ¹H-NMR study of this rearrangement as well as of the reactions of L with PdCl₂ and Na₂PdCl₄ revealed a complex equilibrium in DMF solutions and enabled the formation mechanism of all involved species to be resolved. The complex A is immediately solvolyzed producing two molecules of intermediate M [PdCl₂(L)(DMF)]. Complex M was also the first intermediate in the reaction of L with PdCl₂. Once present in concentration above 10⁻⁵ mol dm⁻³M dimerizes very fast into chloro-bridged dimer [PdCl(μ-Cl)(L)]₂ (D) which undergoes cyclopalladation and converts into the complex C. The formation of C from the intermediate D is clearly demonstrated by the concentration dependence of the cyclopalladation reaction which has order greater than one. Chloride ions, released by cyclopalladation, react with D by splitting chloro-bridge and binding to metal atoms to produce byproduct [PdCl₃(L)]⁻ (T). The same species T are formed in the reaction of L with Na₂PdCl₄ whereby a chloride ion is replaced by the ligand L. The complex B undergoes similar, but slower, solvolytic reaction producing M and L while further reaction steps are identical as in the solvolysis of A.     

Spin label EPR-based characterization of biosystem complexity

Following the widely spread EPR spin-label applications for biosystem characterization, a novel approach is proposed for EPR-based characterization of biosystem complexity. Hereto a computational method based on a hybrid evolutionary optimization (HEO) is introduced. The enormous volume of information obtained from multiple HEO runs is reduced with a novel so-called GHOST condensation method for automatic detection of the degree of system complexity through the construction of two-dimensional solution distributions. The GHOST method shows the ability of automatic quantitative characterization of groups of solutions, e.g. the determination of average spectral parameters and group contributions. The application of the GHOST condensation algorithm is demonstrated on four synthetic examples of different complexity and applied to two physiologically relevant examples--the determination of domains in biomembranes (lateral heterogeneity) and the study of the low-resolution structure of membrane proteins.     

Über die Trennung von gasgemischen in laminarer Strömung

Summary The separation effect in a gas mixture laminary and hydrodynamically flowing through a cylindrical pipe with constant wall temperature is calculated.     

Potentiometric discrimination of neutral forms of nitrophenol isomers by liquid membrane electrodes incorporated with corroles

The results of studies on the use of corrole derivatives as a host ligand in the PVC liquid membrane electrodes and their ability for the potentiometric high-throughput discrimination of nitrophenol guests have been presented. The significance of parameters which govern the mechanism of generation of potentiometric signals such as the attachment of substituents in the corrole structure, acidity and lipophilicity of the guests, and pH of the aqueous solutions has been discussed in details. Supramolecular recognition processes between corroles and para-nitrophenol molecules have been confirmed by independent NMR measurements.     

Note on prehomogeneous vector spaces

Let \(V\) be a complex prehomogeneous vector space under the action of a linear algebraic group \(G\) . Assume the poset of orbit closures in the Zariski topology \(\{\overline{Gx}:x\in V\}\) coincides with a (partial) flag \(V_0=0<V_1<\dots <V_k=V\) in \(V\) . Then for any Borel subgroup \(B\) of \(G\) , the poset \(\{\overline{B x}:x\in V\}\) coincides with a full flag in \(V\) .     

Coumarin-based dual fluorescent spin-probes

New, dual profluorescent spin-probes and their fluorescent amine analogues, as potential spin traps, have been synthesized and characterized. Comparison between the fluorescence spectra of amines and their corresponding nitroxides established spacer distance dependent quenching of fluorescence.     

1-(2-Picolyl)-substituted 1,2,3-triazole as novel chelating ligand for the preparation of ruthenium complexes with potential anticancer activity

The 1,4-disubstituted 1,2,3-triazole ligand prepared by click chemistry 1-(2-picolyl)-4-phenyl-1H-1,2,3-triazole (ppt) was investigated as novel chelating ligand for Ru(II) complexes with potential antitumor activity. The preparation and structural characterization, mainly by NMR spectroscopy in solution and by X-ray crystallography in the solid state, of four new Ru(II) complexes is reported: two isomeric Ru-dmso compounds, trans,cis-[RuCl(2)(dmso-S)(2)(ppt)] (1) and cis,cis-[RuCl(2)(dmso-S)(2)(ppt)] (2), and two half-sandwich Ru-[9]aneS(3) coordination compounds, [Ru([9]aneS(3))(dmso-S)(ppt)][CF(3)SO(3)](2) (3) and [Ru([9]aneS(3))Cl(ppt)][CF(3)SO(3)] (4). In all compounds ppt firmly binds to ruthenium in a bidentate fashion through the pyridyl nitrogen atom and the triazole N2, thus forming a puckered six-membered ring. The chemical behavior in aqueous solution of the water-soluble complexes 3 and 4 was studied by UV-Vis and NMR spectroscopy and compared to that of the previously described organometallic analogue [Ru(η(6)-p-cymene)Cl(ppt)][Cl] (5) in view of their potential antitumor activity. Compounds 3-5 were tested also in vitro for cytotoxic activity against two human cancer cell lines, one sensitive and one resistant to cisplatin, in comparison with cisplatin. Compound 4, the one that aquates faster, was found to be more cytotoxic than cisplatin against human lung squamose carcinoma cell line (A-549).