Metal coordination and in situ S-C bond cleavage of the bis(2-pyridylthio)methane ligand

The compound [2bpytmH](2)[I(3)](2)[I(2)], which contains protonated 2bpytm, and four neutral monomeric complexes [CoCl(2)(2bpytm)]·H(2)O (1), [CoBr(2)(2bpytm)] (2), [CoI(2)(2bpytm)]·1/2H(2)O (3) and [NiBr(2)(2bpytm)]·H(2)O (4) have been obtained during a study into the reactivity of the bis(2-pyridylthio)methane (2bpytm) ligand towards cobalt(II) and nickel(II) halides. Furthermore, a cyclic dimer [CuBr(2)(2bpytm)](2) (5) and a 1D polymer [CuBr(2)(2bpytm)](n)·CH(3)CN (6) have been obtained from copper(II)/(I) bromide salts. An unprecedented S-CH(2)-S activation and cleavage in 2bpytm has been observed on using copper(II) salts with organic and voluminous inorganic anions. The cleavage of 2bpytm enabled the isolation of copper(II) complexes containing the in situ generated ligands 2-pyridinethiolate, 2-pyridinesulfenate or 2-pyridinesulfonate.     

Role of inorganic and organic anions in the formation of metallosupramolecular assemblies of silver(I) coordination polymers with the twisted ligand bis(4-pyridylthio)methane

Reaction of the twisted pyridyl dithioether ligand bis(4-pyridylthio)methane (4bpytm) with silver(I) salts afforded four complexes with 1:1 stoichiometries, namely [Ag(4bpytm)](NO₃) (1), [Ag(4bpytm)](ClO₄) (2) and [Ag(4bpytm)](ClO₄) ½CH₂Cl₂ ½dmf (2·Solv), [Ag(CH₃COO)(4bpytm)]·H₂O (3) and [Ag(CF₃COO)(4bpytm)] (4). X-ray structural analysis of these complexes showed that one-dimensional structures are obtained for 1, 2·Solv and 4 whereas a two-dimensional network is formed in 3. The ligand 4bpytm acts as an N,N′-bis(monodentate) bridging system in all cases except in 3, where an unprecedented coordination mode is obtained with the ligand acting in a tridentate manner using its two pyridine nitrogen atoms and a sulfur atom. The coordination polymers are assembled through secondary contacts: Ag···Ag in 4, Ag···S in 1, 2·Solv and 4, Ag···O in 2·Solv, and hydrogen bonding interactions between crystallization water that join the polymeric layers in 3. All of these weak interactions link the low-dimensional complexes to give high-dimensional supramolecular structures and further stabilize the crystal structures in the solid state.     

A direct assessment of refractive indices of nematic liquid crystals at broad VIS - MWIR range

We developed an interference method for determination refractive indices of nematic liquid crystals in a broad electromagnetic spectrum. Values of ordinary and extraordinary refractive indices were measured in VIS (from 0.4 to 0.8 μm), NIR (from 0.8 to 1.4 μm), SWIR (from 1.4 to 3.0 μm) and at an edge of MWIR (from 3.0 to 4.2 μm) regions. The main task of this work was to develop the efficient and accurate interference method. The absolute error of these measurements is not higher than 0.02. The method was tested on two newly designed mixtures. The first one was a high birefringence liquid crystal mixture for the laser rangefinder, while the second one is intentionally prepared for breathalyser application. The mixture does not possess high absorption bands at 3.4 μm. To measure a dispersion of the refractive indices cells with various thicknesses and dielectric mirrors were prepared. The paper presents a theoretical discussion and experimental results.     

Oxidation in vitro of chromium(III) dietary supplements <Emphasis Type="Italic">mer</Emphasis>-[Cr(pic)<Subscript>3</Subscript>] and <Emphasis Type="Italic">trans</Emphasis>(S,S)-[Cr(Cys)<Subscript>2</Subscript>]<Superscript>−</Superscript> by hydrogen peroxide

Biological tests performed using 3T3 fibroblasts indicated low cytotoxicities for the complexes mer-[Cr(pic)₃] and trans(S,S)-[Cr(Cys)₂]^?, where pic = picolinate anion and Cys = cysteine. Oxidation of these complexes by hydrogen peroxide was studied in NaOH and NaHCO₃ media. Electronic (UV–Vis) and EPR spectroscopies were used to monitor the reaction course. Hydrogen peroxide oxidizes chromium(III) to both [Cr^V(O₂)₄]^3? and Cr^VIO₄ ^2? anions in alkaline media and practically completely to CrO₄ ^2? anion in bicarbonate solution. The reactions follow consecutive biphasic or simple first-order kinetics. The first-order decay of [Cr^V(O₂)₄]^3? anion at pH ≈ 8 was followed by EPR spectroscopy. Based on the obtained kinetic and spectroscopic data, mechanisms for the redox transformations of these chromium(III) complexes are proposed.     

Synthesis,characterization and antimicrobial activity of nalidixic acid derivatives with spirohydantoins

This article presents the synthesis of a series of amides, based on the interaction of several 3-aminospirohydantoins with nalidixic acid. The target compounds were characterized by physicochemical parameters, IR, ¹H and ¹³C NMR spectral data. The antimicrobial activity of the products obtained was determined against Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis, Gram-negative bacteria Escherichia coli, Pseudomonas aeruginosa and Salmonella abony, the yeasts Candida albicans and Saccharomyces cerevisiae and the molds Penicillium chrysogenum and Aspergillus niger. The relationship between structure and biological activity of the products obtained was discussed. It was found that the most effective compounds are tetralin (5f) and indane (5g) derivatives, which exhibit a pronounced antimicrobial activity against both tested Gram-positive and Gram-negative bacteria.

     

Activation of methane by the iron dimer cation. A theoretical study

A detailed investigation of the reaction mechanisms underlying the observed reactivity of the iron dimer cation with respect to methane has been performed by density functional hybrid (B3LYP) and nonhybrid (BPW91) calculations. Minima and transition states have been fully optimized and characterized along the potential energy surfaces leading to three different exit channels for both the ground and the first excited states of the dimer. A comparison with our previous work covering the reactivity of the Fe(+) monomer was made to underline similarities and differences of the reaction mechanisms. Results show that geometric arrangements corresponding to bridged positions of the ligands with respect to iron atoms are always favored and stabilize intermediates, transition states and products, facilitating their formation. Binding energies of reaction products have been computed and compared with experimental measurements, and ELF analysis of the bond has been performed to rationalize trends as a function of the structure.     

The emergence of kinship behavior in structured populations of unrelated individuals

The paper provides an explanation for altruistic behavior based on the matching and learning technology in the population. In a infinite structured population, in which individuals meet and interact with their neighbors, individuals learn by imitating their more successful neighbors. We ask which strategies are robust against invasion of mutants: A strategy is unbeatable if when all play it and a finite group of identical mutants enters then the learning process eliminates the mutants with probability 1. We find that such an unbeatable strategy is necessarily one in which each individual behaves as if he is related to his neighbors and takes into account their welfare as well as his. The degree to which he cares depends on the radii of his neighborhoods. Received June 1996/Revised version October 1998     

Heat capacities,volumes and solubilities of pentanol in aqueous surfactant solutions

Apparent molar heat capacities and volumes of pentanol (PentOH) 0.05m in dodecyltrimethylammonium chloride (DTAC), dodecyldimethylammonium chloride (DDAC) and dodecylamine hydrochloride (DAC) micellar solutions were measured at 25°C. They were assumed to approach the standard infinite dilution values and rationalized by means of previously reported equations. The distribution constant between the aqueous and the micellar phase and heat capacity and volume of pentanol in both phases were thus derived. The results show that the presence of methyl groups on the surfactant head group does not appreciably influence the apparent molar volume and heat capacity of pentanol in micellar phase and the free energy of transfer of pentanol from the aqueous to the micellar phase. Also, the apparent molar heat capacities of pentanol in micellar solutions as a function of surfactant concentration show evidence of two maxima for DAC and of one maximum for DTAC whereas no maxima were detected for DDAC. According to the literature data for alkyltrimethylammonium bromides these maxima can be ascribed to the presence of structural post-micellar transitions. It is shown that the C_,PentOH vs. surfactant molality curve for DAC lies between that for hexadecyltrimethylammonium bromide and that for tetradecyltrimethylammonium bromide. This evidence, which is similar to that found for solubilities, agrees with the previously reported idea that the removal of a CH₃ group from the head group of surfactant is equivalent to the introduction of a CH₂ group in its hydrophobic moiety. By comparing data for DTAC with those for the corresponding bromide, the role of the nature of the counterion in the thermodynamics of solubilization of pentanol in micellar solutions is derived.     

Progress in the Study of Bioluminescent Earthworms

Even though bioluminescent oligochaetes rarely catch people's eyes due to their secretive lifestyle, glowing earthworms sighting reports have come from different areas on all continents except Antarctica. A major breakthrough in the research of earthworm bioluminescence occurred in the 1960s with the studies of the North American Diplocardia longa. Comparative studies conducted on 13 earthworm species belonging to six genera showed that N‐isovaleryl‐3‐aminopropanal (Diplocardia luciferin) is the common substrate for bioluminescence in all examined species, while luciferases appeared to be responsible for the color of bioluminescence. The second momentous change in the situation has occurred with the discovery in Siberia (Russia) of two unknown luminous enchytraeids. The two bioluminescent systems belong to different types, have different spectral characteristics and localization, and different temperature and pH optima. They are unique, and this fact is confirmed by the negative results of all possible cross‐reactions. The bioluminescent system of Henlea sp. comprises four essential components: luciferase, luciferin, oxygen and calcium ion. For Friderica heliota, the luminescent reaction requires five components: luciferase, luciferin, ATP, magnesium ion and oxygen. Along with luciferin, more than a dozen analogues were isolated from worm biomass. These novel peptide‐like natural compounds represent an unprecedented chemistry found in terrestrial organisms.