Václav Eigner

Design and synthesis of a novel trinuclear palladium(II) complex containing an oxime chelate ligand: determining the interaction mechanism with the DNA groove and BSA site I by spectroscopic and molecular dynamics simulation approaches

The novel trinuclear Pd(II) complex with an aryl oxime ligand, [Pd3(C,N-(C6H4C(Cl)NO)-4)6], was synthesized and structurally characterized by elemental analysis (C, H, N), IR, resonance signals in the NMR, and single crystal X-ray crystallography. The interaction ability of the complex with native calf thymus DNA (CT-DNA) was monitored as a function of the metal complex–DNA molar ratio by UV-Vis absorption spectrophotometry, fluorescence spectroscopy, circular dichroism (CD) and thermal denaturation methods. All the experimental evidence indicated that this complex could strongly bind to CT-DNA via a groove mechanism. Further, the albumin interactions of the complex were investigated using fluorescence quenching and synchronous fluorescence spectra. The results of fluorescence titration suggested that the fluorescence quenching of BSA by the complex was a static quenching procedure. The site marker displacement experiment has suggested the location of the complex binding to BSA was Sudlows site I in subdomain IIA. Finally, the molecular docking experiment confirmed the above results and effectively proved the binding of the Pd(II) complex to BSA and DNA.

Dimercuration of Calix[4]arenes: Novel Substitution Pattern in Calixarene Chemistry

A mercuration reaction of tetrapropoxycalix[4]arene immobilized in the cone conformation gave a mixture of two dimercurated products (meta,meta and meta,para) in approximately a 1:1 ratio. Both regioisomers represent inherently chiral compounds, which makes them very attractive for design of novel receptors. As demonstrated by Pd-catalyzed arylation, the different reactivity of HgCl functions in the meta,para-disubstituted isomer opens the door for regioselective introductions of two different functional groups to achieve a substitution pattern so far unknown in calixarene chemistry.

Synthesis, spectral characterization, structural studies, molecular docking and antimicrobial evaluation of new dioxidouranium(VI) complexes incorporating tetradentate N2O2 Schiff base ligands

Two new uranyl(VI) Schiff base complexes [UO2(L1)(DMSO)] (1), where L1 = N,N′-di(5-bromosalicylidene)-1,2-cyclohexyldiaminate ligand and [UO2(L2)(MeOH)] (2), where L2 = N,N′-di(5-bromosalicylidene)-o-phenylenediaminate ligand, were synthesized and characterized by elemental analysis, 1H NMR, FTIR, UV-vis, fluorescence spectroscopy and molar conductivity measurements. The structure of the H2L1 free ligand and both complexes (1) and (2) were also determined by single crystal X-ray diffraction. According to the results obtained, the title complexes have a distorted pentagonal bipyramidal geometry where positions around the U(VI) centre are occupied by the ONNO donors of the deprotonated dibasic Schiff base ligands (L1 for 1 and L2 for (2)), two oxido groups and the oxygen of coordinated solvent. The antimicrobial activity of ligands and complexes was also screened against Gram positive bacteria Staphylococcus aureus PTCC 1112, Micrococcus luteus PTCC 1110, Bacillus cereus PTCC 1015, Enterococcus faecalis; Gram negative bacteria Pseudomonas aeruginosa PTCC 1214, Escherichia coli PTCC1330, Pseudomonas sp., Klebsiella pneumoniae; and fungus strain (Candida albicans). The molecular docking of GlcN-6-P synthase with the synthesized compounds was also performed. According to the results, complex 2 displayed minimum binding energy and can be considered as a good antimicrobial agent.

Database analysis of hydrogen bond patterns in phosphoric triamides completed with seven new compounds: a crystallographic and 15N NMR study

We present the synthesis and characterization of seven new phosphoric triamides followed by analysis of hydrogen bond patterns of the new compounds as well as the phosphoric triamides found in the Cambridge Structural Database (CSD). The analysis of hydrogen bond patterns updates the previous work (Toghraee, Pourayoubi and Divjakovic in Polyhedron, 2011, 30, 1680) on phosphoric triamides with a C(O)NHP(O)[N]2 skeleton, and extends the analysis to other phosphoric triamides i.e. ones without a CO attached to the N of N–PO. For the new phosphoric triamides we also investigated their spectroscopic features (31P, 1H, 13C, and 15N NMR, mass spectroscopy, IR spectroscopy), measured the 1J(15N,31P) coupling constants and discussed the effective parameters.

Palladium complexes with 3-phenylpropylamine ligands: synthesis, structures, theoretical studies and application in the aerobic oxidation of alcohols as heterogeneous catalysts

The reaction of 3-phenylpropylamine with Pd(OAc)2 by heating in toluene resulted in the nearly square-planar complex trans-[Pd(C6H5(CH2)3NH2)2(OAc)2] (1). Complex 1 reacted with NaCl in methanol to obtain the corresponding product trans-[Pd(C6H5(CH2)3NH2)2Cl2] (2). Treatment of 2 with triphenylphosphine in dichloromethane afforded trans-[Pd(C6H5(CH2)3NH2)2(PPh3)2]2Cl− (3). All the palladium(II) complexes (1–3) were fully characterized by IR and NMR spectroscopy. In addition, the crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction analysis. In these structures, the acetate and chloride ligands are in trans geometry. Density functional theory (DFT) calculations gave bond lengths and angles that were noted as experimental values. Palladium nanoparticles that were derived from complexes (1–3) were supported on cucurbit[6]uril (CB[6]) and identified by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma analysis (ICP) and high-resolution X-ray powder spectroscopy (HR-XPS). CB[6]-supported palladium nanoparticles (NPs) were used as heterogeneous catalysts for the aerobic oxidation of alcohols to the corresponding aldehydes or ketones without over-oxidation. CB[6]-Pd NPs (3) (prepared from complex 3) show better catalytic activity than CB[6]-Pd NPs (1), (2), as a higher yield was observed with them in a relatively short time. Factors such as the amount of catalyst, solvent, temperature and reaction time were all systematically investigated to determine their effects on the yield of catalytic alcohol oxidation reactions. This catalytic system displayed high activity and selectivity toward alcohols in mild conditions. The catalyst was reused five times without any significant loss of catalytic activity.

Discontinuous modulation functions and their application for analysis of modulated structures with the computing system JANA2006

Abstract Discontinuous modulation functions called crenel and saw-tooth have been developed for description and refinement of strongly modulated crystal structures with abrupt changes of modulation parameters. Although used for refinement of many modulated structures and mentioned in books on aperiodic crystals, technical details of such refinements have never been published and remained hidden in the source code of the refinement program Jana2006. In this article we explain how to recognize discontinuous modulations in a Fourier map and how to refine structures where crenel or saw-tooth functions are combined with additional secondary modulation. Three sets of functions suitable for such combination are presented: the traditional ortho-harmonics, and newly developed sets of Legendre polynomials and x-harmonics. Tiny differences between refinements based on particular function sets are demonstrated using simulated as well as existing modulated structures.

Intramolecularly Bridged Calix[4]arenes with Pronounced Complexation Ability toward Neutral Compounds

Regioselective derivatization via an organomercury intermediate allowed for the introduction of carboxylic acid functionality into the meta position of the calix[4]arene skeleton. Intramolecular Friedel-Crafts cyclization led to a novel type of calixarene containing a ketone bridging moiety. Subsequent attack of the ketone by organometallic compounds occurred selectively from outside providing tertiary alcohols with the OH group oriented inside the cavity. These compounds can complex neutral molecules both in the solid state (X-ray) and in solution (NMR) using the cooperative effect of hydrogen bonding (OH) and CH-π interactions from within the cavity.

Regioselective Halogenation of Thiacalix[4]arenes in the Cone and 1,3-Alternate Conformations

Monohalogenation of thiacalix[4]arene in the cone conformation gave either the meta- or para-substituted isomers depending on the halogen and reaction conditions used. Surprisingly, the same reaction with the 1,3-alternate conformer led only to the meta isomer. This is the first example of such a conformation-dependent regioselectivity in calixarene/thiacalixarene chemistry. As the halogen-substituted calixarenes are useful synthetic intermediates, this provided the unique opportunity to functionalize the basic skeleton at two different positions.

Synthesis, characterization, crystal structure, catalytic activity in oxidative bromination, and thermal study of a new oxidovanadium Schiff base complex containing O, N-bidentate Schiff base ligand

A new oxidovanadium(IV) Schiff base complex, VOL2 (1), HL = 2-{(E)-[2- (bromoethyl)imino]methyl}-6-methoxy phenol, containing ethyl bromide pendant group was synthesized by direct reaction of HL and VO(acac)2 in the ratio of 2 : 1 in methanol at reflux. The Schiff base ligand and its vanadyl complex were characterized by FT-IR spectra and CHN analysis. Additionally, the Schiff base ligand has been characterized by 1H NMR spectroscopy. The crystal structure of 1 was also determined by single-crystal X-ray analysis, showing the distorted square-pyramidal N2O3 coordination around vanadium(IV). The catalytic activity of 1 was studied in the oxidative bromination of 2-nitrophenol as a model substrate, and different reaction parameters were investigated. The oxidative bromination of some organic compounds in the presence of 1 in optimal conditions showed that it was an effective and selective catalyst in those optimal conditions. Thermogravimetric analysis of 1 showed that it decomposed in two stages. 1 was thermally decomposed in air at 660 °C, and the XRD pattern of the obtained solid showed the formation of the V2O5 nanoparticles with average size of 34 nm . Graphical Abstract

Synthesis, structural investigation and kinetic studies of uranyl(VI) unsymmetrical Schiff base complexes

AbstractUranyl(VI) complexes with unsymmetrical N2O2 Schiff base ligands were synthesized and characterized. Their characterization was performed using UV-Vis, 1H NMR, cyclic voltammetry, single-crystal X-ray crystallography, IR, TG and C.H.N. techniques. X-ray crystallography of the complexes show that beside coordination of the tetradentate Schiff base, one DMF molecule is also coordinated. In order to investigate the effect of the substitutional groups of the Schiff base on the oxidation and reduction potentials, we used the cyclic voltammetry method. Electrochemistry of these complexes showed that the presence of electron releasing groups accelerates oxidation of the complexes. The kinetics of thermal decomposition was studied using thermal gravimetric method (TG) and Coats-Redfern equation. According to Coats-Redfern plots, the kinetics of thermal decomposition of the studied complexes is first-order in all stages. Also the kinetics and mechanism of the exchange reaction of the coordinated solvent with tributylphosphine was carried out in solution, using spectrophotometric method. As a result, the second order rate constants at four temperatures and the activation parameters were calculated showing an associative mechanism for all corresponding complexes. It was concluded that the steric and the electronic properties of the complexes influence the reaction rate significantly. Graphical AbstractX-ray crystallography of the Uranyl (VI) complexes shows that besides coordination of the tetradentate Schiff base, one DMFmolecule is also coordinated.