A. A. Moiseeva

Prospects of electroanalytical investigations of supramolecular complexes of a bis-crown stilbene with viologen-like compounds bearing two ammonioalkyl groups

Abstract Complexation of the bis-(18-crown-6) stilbene with viologen-like compounds, 1,2-bis{4-[ N -(3-ammoniopropyl)pyridylium]}ethylene, 1,2-bis{4-[ N -(2-ammonioethyl)pyridylium]}ethylene, 1,2-bis{4-[ N -(3-ammoniopropyl)pyridylium]}ethane, and 1,2-bis{3-[ N -(3-ammoniopropyl)pyridylium]}ethylene, bearing two ammonioalkyl groups has been studied in MeCN solutions using cyclic voltammetry and UV–vis spectroscopy. The bis-crown stilbene was found to form strong 1:1 charge-transfer complexes, with the viologen-like diammonium compounds via two-site H-bonding. The complexation results in a considerable positive shift of the first oxidation potential of the electron donor bis-(18-crown-6) stilbene molecule ranging from 160 to 240 mV depending on the nature of the diammonium viologen-like compounds. The magnitude of this shift was used as a measure of the thermodynamic stability of bimolecular complexes between bis-crown stilbene and these viologen-like compounds. The relative contributions of H-bonding and charge-transfer interactions on the complex stability are discussed.

Comparative study of redox characteristics and antioxidant activity of porphyrins with 2,6-dialkylphenol groups

152 The oxidative stress of an organism is a result of the acceleration of lipid peroxidation (LPO) in cells and the formation of reactive oxygen species and free rad icals. This process leads to destruction of membranes, the emergence of numerous pathologies, and prema ture aging of the organism. The search for new antiox idants, as well as for methods to assess the antioxidant activity, is an important and interesting task [1]. Of particular interest are synthesis and study of properties of polyfunctional compounds with several pharma cophoric centers in the molecule, because such a com bination is able not only to enhance the known physi ological activity but also to cause the appearance of new types of physiological activity [2–4]. Ionol I (2,6 di tert butyl 4 methylphenol) is a known anti oxidant used in the manufacture of foodstuffs (food additive E321). 2,6 Diisobornyl 4 methylphenol (dibornol) IV is currently undergoing preclinical tri als as a promising drug [5]. CHEMISTRY

Supramolecular Dimerization and [2 + 2] Photocycloaddition Reactions of Crown Ether Styryl Dyes Containing a Tethered Ammonium Group: Structure–Property Relationships

Molecular self-assembly is an effective strategy for controlling the [2 + 2] photocycloaddition reaction of olefins. The geometrical properties of supramolecular assemblies are proven to have a critical effect on the efficiency and selectivity of this photoreaction both in the solid state and in solution, but the role of other factors remains poorly understood. Convenient supramolecular systems to study the structure-property relationships are pseudocyclic dimers spontaneously formed by styryl dyes containing a crown ether moiety and a remote ammonium group. New dyes of this type were synthesized to investigate the effects of structural and electronic factors on the quantitative characteristics of supramolecular dimerization and [2 + 2] photocycloaddition in solution. Variable structural parameters for the styryl dyes were the size and structure of macrocyclic moiety, the nature of heteroaromatic residue, and the length of the ammonioalkyl group attached to this residue. Quantum chemical calculations of the pseudocyclic dimers were performed in order to interpret the relationships between the structure of the ammonium dyes and the efficiency of the supramolecular photoreaction. One of the dimeric complexes was obtained in the crystalline state and studied by X-ray diffraction. The results obtained demonstrate that the photocycloaddition in the pseudocyclic dimers can be dramatically affected by the electronic structure of the styryl moieties, as dependent on the electron-donating ability of the substituents on the benzene ring, and by the conformational flexibility of the pseudocycle, which determines the mobility of the olefinic bonds. The significance of electronic factors is highlighted by the fact that the photocycloaddition quantum yield in geometrically similar dimeric structures varies from ≤10(-4) to 0.38. The latter value is unusually high for olefins in solution.

Coordination Compounds of S- and Se-Containing Organic Ligands as Catalysts of Oxidation Reaction Under N2O Action

Abstract Nitrous oxide (N2O) would be preferable to many other oxidants because in the reactions of N2O with organic compounds the only byproduct is N2, which is perfect from the point of view of “green” chemistry. We recently reported a series of new sulfur- and selenoorganic ligands, their coordination compound with Co(II) or Cu(I,II), and the possibility for these complexes to activate nitrous oxide in the oxidation reactions with phosphines and alkenes. The electrochemical data confirm the stability of reduced form of investigated complexes and the capacity of these complexes to associate with nitrous oxide. GRAPHICAL ABSTRACT

Electrochemistry of complexes of dichlorogermylene and dihalostannylenes with chromium, molybdenum, and tungsten pentacarbonyls

Abstract Electrochemical behaviour of the transition metal complexes of dichlorogermylene and dihalostannylenes, (CO)5MEX2 · B (M=Cr, Mo, W; E=Ge, X=Cl; E=Sn, X=Cl, Br, I; B=THF, dioxane, DMF) has been studied in MeCN at 20°C. Both the reduction and the oxidation processes were found to be irreversible suggesting that the corresponding radical ions were unstable under these conditions; mechanisms of reduction and oxidation of (CO)5MEX2 · B were proposed. Electrochemical data obtained show that the electronic structures of (CO)5MEX2 · B complexes are similar to those of Fischer transition metal carbene complexes. Cyclic voltammetry data of (CO)5MGeCl2 · B (M=Cr, W; B=THF, dioxane, DMF) in DMF solutions clearly testify to the fact that the solvolytic cleavage of MGe bond in these complexes takes place leading to (CO)5M · DMF and GeCl2 · DMF species formation. The reduction of GeCl2 · dioxane complex in DMF is discussed.

Synthesis, isomerization and biological activity of novel 2-selenohydantoin derivatives

A set of novel selenohydantoins were synthesized via a convenient and versatile approach involving the reaction of isoselenocyanates with various amines. We also revealed an unexpected Z→E isomerization of pyridin-2-yl-substituted selenohydantoins in the presence of Cu(2+) cations. The detailed mechanism of this transformation was suggested on the basis of quantum-chemical calculations, and the key role of Cu(2+) was elucidated. The obtained compounds were subsequently evaluated against a panel of different cancer cell lines. As a result, several molecules were identified as promising micromolar hits with good selectivity index. Instead of analogous thiohydantoins, which have been synthesized previously, selenohydantoins demonstrated a relatively high antioxidant activity comparable (or greater) to the reference molecule, Ebselen, a clinically approved drug candidate. The most active compounds have been selected for further biological trials.

Synthesis, structure and complexation of biscrown-containing 1,4-distyrylbenzenes

An improved method for the synthesis of two symmetric biscrown-containing and one model tetramethoxy-substituted 1,4-distyrylbenzenes was suggested. The structures of compounds were established by 1H and 13C NMR spectroscopy and X-ray diffraction analysis. Spectrophotometric and fluorescent titration were used to determine spectral properties, stoichiometry, and stability of complexes of biscrown-containing 1,4-distyrylbenzenes with alkali and alkaline-earth metal cations. The stability of the complexes was found to depend on the metal cation size and charge, as well as on the size of the crown ether fragment. The electrochemical oxidation and reduction potentials of the biscrown-containing 1,4-distyrylbenzenes and the model compound in solution were determined and their basic differences from the corresponding characteristics of biscrown-containing stilbenes were identified.

Synthesis, structure, electrochemistry, and photophysics of 2,5-dibenzylidenecyclopentanones containing in benzene rings substituents different in polarity

A series of cross-conjugated dienones was synthesized to study the dependence of physicochemical characteristics on the nature of substituents in the aromatic groups of symmetric cyclopentanone dibenzylidene derivatives. The structure of compounds was established by electronic, IR, and NMR spectroscopy and X-ray diffraction study. All the compounds obtained possess the E,E-geometry. In the crystalline state, the arrangement of the dienone molecules is unfavorable for the intermolecular [2+2] photocycloaddition to take place. The low-temperature phases transition for unsubstituted diphenyl derivative of cyclopentanone was detected using variable-temperature X-ray diffraction and differential scanning calorimetry. Oxidation and reduction potentials of the dienones were measured by cyclic voltammetry. Their dependence on the nature and placement of substituents in the benzene rings was demonstrated. A linear correlation (R = 0.9343) between the difference of electrochemical oxidation and reduction potentials and the energy of the long-wavelength absorption maximum was found, that allows us to recommend the use of the data obtained in the correlation analysis of other compounds of this class.

1,7-Dimethyl-1,7-dichloromethyl-5,8-ethenodecalin-3-ene-2,6-dione. Structure, bromination, electrochemistry

The structures of 1,7-dimethyl-1,7-bis(dichloromethyl)-5,8-ethenodecalin-3-ene-2,6-dione, the dimer of 6-methyl-6-dichloromethyl-cyclohexa-2,4-dien-1-one, and of products of its bromination were established by XRD analysis. The dependence of composition of the products of bromination on the ratio of reactants was established. Electrochemical reduction of the dione and its bromine-containing derivatives was studied.

Regioselective bromination of palladium tetraphenyltetrabenzoporphyrin to benzo-rings: Synthesis of mono- and octabromotetrabenzoporphyrins and their properties

Bromination of palladium meso-tetraphenyl tetrabenzoporphyrin (Pd Ph4TBP, 1) by Me4NBr3 or Me4NBr/Br2 was shown to proceed regioselectively to the benzo-rings annelated to main porphyrin macrocycle. Conditions for preferential mono- and octa-bromination have been established. The respective mono- and octa-bromide (Pd Ph4TBP(Br), 2 and Pd Ph4TBP(Br)8, 3) have been isolated and characterized by UV-vis, NMR and LDI-TOF spectroscopy. Changes of electrochemical properties of tetrabenzoporphyrins induced by Br atoms were found to follow the same trends as the changes in analogous non-extended porphyrins. Room temperature phosphorescence is not substantially influenced by the substitution.