Factors affecting the interaction of lanthanide shift reagents with substituted pyridines

The complexation of five meaningful series of pyridines bearing substituents in 2,6 and other positions was investigated by ¹H-NMR with Eu(dpm)₃ and Eu(fod)₃. The former LSR leads to higher MIS values than the latter when small α-substituents are present, but the opposite effect is obtained with bulky α-substituents such as t-butyl groups.     

Synthesis of 2,4-dimethyl-6-oxo-2,4-heptadienoic acid derivatives from 2,4,6-trimethylpyrylium salts

Reaction 2,4,6-trimethylpyrylium salts with sodium cyanide in boiling water yielded the bicyclic lactone 1,3,5-trimethyl-6,8-dioxabicyclo[3.2.1]oct-2-en-7-one (6) along with a series of stereoisomers of 2,4-dimethyl-6-oxo-2,4-heptadienonitrile (5), which were the sole products when the reaction was carried out at room temperature. Compound 6, along with 3,5-dimethylphenol (7), was also obtained by refluxing 5 briefly in aqueous sodium hydroxide. However, when 5 was refluxed for a prolonged period in aqueous sodium acetate, 3,5-dimethyl-5-(2-oxopropyl)-furan-2-one (8), along with some 7, was generated instead. Compound 8 could also be produced from 6 on prolonged refluxing with aqueous sodium acetate, indicating that 6 was the kinetically-controlled and 8 the thermodynamically-controlled product.     

The measurement of enzyme catalysed rates of reaction by 2D NMR spectroscopy

Two-dimensional NMR spectroscopy is useful for studying exchange rates of complex enzyme catalysed reactions in the steady state. The technique provides various technical and interpretive advantages over conventional methods and will be useful for studying in vivo processes.     

Highly discriminating distance-based topological index

A new topological indexJ (based on distance sumss_i as graph invariants) is proposed. For unsaturated or aromatic compounds, fractional bond orders are used in calculatings_i. The degeneracy ofJ is lowest among all single topological indices described so far. The asymptotic behaviour ofJ is discussed, e.g. whenn → ∞ in C_nH_{2n = 2},Jar π for linear alkanes, andJ → ∞ for highly branched ones.     

Systematic classification and nomenclature of diamond hydrocarbons—I : Graph-theoretical enumeration of polymantanes

Diamond hydrocarbons are defined as hydrocarbons containing at least one adamantane unit wholly or largely superimposable on the diamond lattice. When two or more adamantane units are present, diamond hydrocarbons can be further classified according to the number of C atoms common to each pair of such units. Face-fused systems (polymantanes, e.g. diamantane (18), triamantane (19), etc) have six common carbons between each pair of adamantane units. The character of the dualist graphs connecting the centers of each adamantane unit divides polymantanes into catamantanes (tree-like dualist graphs) or perimantanes (cyclic graphs). These graphs are identical to the carbon skeletons of alkanes or cycloalkanes in ideal staggered conformations (“C-rotamers”). Polymantanes with n adamantane units are termed “regular” if their empirical formula is C_4n+6H_4n+12, and “irregular” otherwise. All perimantanes and some catamantanes are irregular. A notation system based on the four possible relative orientations of the edges of the dualist graphs provides a code not only designating each polymantane uniquely, but also allowing their enumeration. Three tetramantanes, seven pentamantanes, 24 hexamantanes (one of these a perimantane) and 88 heptamantanes (two perimantanes) are possible (not taking enantiomers into account). The codes provide a convenient nomenclature and reveal by patterns of repeating digits whether irregular catamantanes or perimantanes are involved. The smallest chiral polymantane is [123]tetra-mantane (2), the smallest irregular catamantane is [1231]pentamantane (45), and the smallest perimantane is [12312]hexamantane (35).     

Synthesis of 4-aryloxy-7-nitrobenzofurazan derivatives from 4-chloro-7-nitrobenzofurazan and various phenoxide anions (including pharmaceuticals) in the presence of crown ethers

4-Chloro-7-nitrobenzofurazan reacts by nucleophilic substitution with phenoxide anions derived from estriol (2c), ethynylestradiol (2d), phenol (3e), guaiacol (3f), 2,6-dimethoxyphenol (3g), eugenol (3h), isoeugenol (3i), the cytostatic Etoposide (4), and Reichardt’s betaine (5) in the presence of crown ethers affording the corresponding 4-aryloxy-7-nitrobenzofurazan derivatives 6c, 6d, 7e-7i, 8, and 9. The structure of these compounds was confirmed by NMR spectra. Hydrophobicity/hydrophilicity parameters were investigated by reverse phase thin-layer chromatography.     

Computer program for finding all possible cycles in graphs

A new approach is presented for identifying all possible cycles in graphs. Input data are the total numbers of vertices and edges, as well as the vertex adjacencies using arbitrary vertex numbering. A homeomorphically reduced graph (HRG) is constructed by ignoring vertices of degree less than three. The algorithm is based on successive generation of possible edge-combinations in the HRG. If a combination yields a cycle, it is either printed or stored and then finally printed in a list of all possible cycles arranged in the order of increasing ring size. A unique numbering of the cycle is used. The computer program is listed and exemplified. Computing times are given.     

Cr(III), Fe(III) and Co(III) complexes of tetradentate (ONNO) Schiff base ligands: synthesis, characterization, properties and biological activity

A series of metal complexes were synthesized from equimolar amounts of Schiff bases: 1,4-bis[3-(2-hydroxy-1-naphthaldimine)propyl]piperazine (bappnaf) and 1,8-bis[3-(2-hydroxy-1-naphthaldimine)-p-menthane (damnaf) with metal chlorides. All of synthesized compounds were characterized by elemental analyses, spectral (UV-vis, IR, (1)H-(13)C NMR, LC-MS) and thermal (TGA-DTA) methods, magnetic and conductance measurements. Schiff base complexes supposed in tetragonal geometry have the general formula [M(bappnaf or damnaf)]Cl.nH(2)O, where M=Cr(III), Co(III) and n=2, 3. But also Fe(III) complexes have octahedral geometry by the coordination of two water molecules and the formula is [Fe(bappnaf or damnaf)(H(2)O)(2)]Cl. The changes in the selected vibration bands in FT-IR indicate that Schiff bases behave as (ONNO) tetradentate ligands and coordinate to metal ions from two phenolic oxygen atoms and two azomethine nitrogen atoms. Conductance measurements suggest 1:1 electrolytic nature of the metal complexes. The synthesized compounds except bappnaf ligand have the antimicrobial activity against the bacteria: Escherichia coli (ATCC 11230), Yersinia enterocolitica (ATCC 1501), Bacillus magaterium (RSKK 5117), Bacillus subtilis (RSKK 244), Bacillus cereus (RSKK 863) and the fungi: Candida albicans (ATCC 10239). These results have been considerably interest in piperazine derivatives due to their significant applications in antimicrobial studies.     

Note on ordering and complexity of Platonic and Archimedean polyhedra based on solid angles

The missing values for the solid angles of the two snub semiregular polyhedra have been calculated, and integrated into the whole series of Platonic and Archimedean polyhedra. This is the only criterion which so far gives an unambiguous answer (without any degeneracy leading to posets) on how to order these polyhedra according to their increasing complexity.