Synthesis and characterization of a novel tantalum chalcogen-rich molecular cluster with square planar metal core

Black single crystals of Ta(4)Se(9)I(8) are obtained in a high yield by heating Ta, Se, and I(2) at 300 degrees C in 1:2.2:1.0 molar ratio. In the structure, the tantalum atoms form a square, with four Se(2) ligands bridging the Ta-Ta edges and one capping the square. Each Ta atom has two terminal iodine atoms. The compound is diamagnetic and has only two electrons for metal-metal bonding.     

A very large diversity space of synthetically accessible compounds for use with drug design programs

We have constructed a very large virtual diversity space containing more than 10¹³ chemical compounds. The diversity space is built from about 400 combinatorial libraries, which have been expanded by choosing sizeable collections of suitable R-groups that can be attached to each link point of their scaffolds. These R-group collections have been created by selecting reagents that have drug-like properties from catalogs of available chemicals. As members of known combinatorial libraries, the compounds in the diversity space are in general synthetically accessible and useful as potential drug leads. Hence, the diversity space can be used as a vast source of compounds by a de novo drug design program. For example, we have used such a program to generate inhibitors of HIV integrase enzyme that exhibited activity in the micromolar range.     

A geometrically constraining bis(benzimidazole) ligand and its nearly tetrahedral complexes with Fe(II) and Mn(II)

2,2'-Bis[2-(1-propylbenzimidazol-2-yl)]biphenyl), 4, and its bis complexes with Fe(II) and Mn(II) have been prepared and characterized structurally and spectroscopically. Ligand 4 adopts an open, "trans" conformation in the solid state with the benzimidazole (BzIm) groups on opposite sides of the biphenyl unit. In its complexes with metal ions, a "cis" conformation is observed, and 4 behaves as a geometrically constraining bidentate ligand with four planar groups connected by three "hinges". Reaction of 4 with Fe(II) or Mn(II) yielded isomorphous crystals (space group Pnn2) of Fe(II)(4)2.(ClO4)2 and Mn(II)(4)2.(ClO4)2, in which the M(II)(4)2 cations exhibit distorted-tetrahedral coordination geometries (N-M-N angles, 109 +/- 11 degrees ) enforced by rigid, chiral nine-membered M(4) rings in the twist-boat-boat conformation. Individually, the cations show R,R or S,S stereochemistry, and the crystals are racemates. Mn(II)(4)2.(ClO4)2 exhibits a quasi-reversible Mn(II) --> Mn(III) oxidation at E(1/2) = 0.64 V; the corresponding Fe(II) --> Fe(III) oxidation occurs at E(1/2) = 1.76 V. The electrochemical stability of the Fe(III) oxidation state in this system suggests the possibility of isolating an unusual pseudotetrahedral Fe(III)N(BzIm)(4) species. Ultraviolet spectra of the iron and manganese complexes are dominated by absorptions of the ligand 4 blue-shifted by approximately 2000-3000 cm(-1). Ligand-field absorptions were observed for the Fe(II) complex; those for the Mn(II) complex were obscured by tailing ultraviolet absorptions. Electron paramagnetic resonance and magnetic susceptibility measurements are consistent with a high-spin Mn(II) complex, while for the Fe(II) complex, the falloff of the magnetic moment with decreasing temperature is indicative of zero-field splitting with D approximately 4 cm(-1).     

Sequential superparamagnetic clustering for unbiased classification of high-dimensional chemical data

For the clustering of chemical structures that are described by the Similog, ISIS count, and ISIS binary fingerprints, we propose a sequential superparamagnetic clustering approach. To appropriately handle nonbinary feature keys, we introduce an extension of the binary Tanimoto similarity measure. In our applications, data sets composed of structures from seven chemically distinct compound classes are evaluated and correctly clustered. The comparison, with results from leading methods, indicates the superiority of our sequential superparamagnetic clustering approach.     

Research on benz[c,d]indolin-2-one derivatives. Bromination of benz[c,d]indolin-2-onecarboxylic acids

It was experimentally observed that electrophilic substitution in, respectively, the 6 and 8 positions or the 8 position occurs when a carboxy group is present in the peri positions (in the 5 or 6 position) of benz[c,d]indolin-2-one. When two carboxy groups are simultaneously present in the 5 and 6 positions or when there is one carboxy group in the 6 position and a bromo substituent in the 5 position, the carboxy group is readily replaced by bromine. The electronic structures and reactivities of benz[c,d]indolin-2-one derivatives were investigated by spectroscopy and quantum chemistry.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1363–1367, October, 1985.     

Quantum-chemical investigation of the π-electronic structure of 3-hydroxy-4-phenylazoquinoline and 4-hydroxy-3-phenylazoisoquinoline

The total bond energies, the atomization energies, the molecular diagrams in the ground and first excited states, the interatomic distances in the ground state, and the electronic spectra of the azo and quinonehydrazone forms of 3-hydroxy-4-phenylazoquinoline and 4-hydroxy-3-phenylazoisoquinoline were calculated by the MO LCAO method within the Pariser-Parr-Pople approximation with the utilization of optimization of the internuclear distances with respect to the minimum of the atomization energy. It follows from an analysis of the ΔH values that the azo form in the first case is energetically more advantageous than the quinonehydrazone form, while the opposite is true in the second case. The calculated interatomic distances and bond orders of the tautomers correspond to those in the azo and quinonehydrazone structures. The absorption bands in the electronic spectra were assigned. The long-wave band in the absorption spectra of the quinonehydrazone tautomers is due primarily to charge transfer from the bridge-amino-nitrogen atom to the quinoid system.     

Direct decompositions of Artinian modules over hypercyclic groups

Let G be a hypercyclic group and A be an Artianian G-module. A class of simple G-modules is defined and it is proved that there exists a direct decomposition A=C B, where C is a G-submodule, each G-composition factor of which belongs to the class , and B is a G-submodule that does not have G-composition factors belonging to .Deceased.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 43, Nos. 7 and 8, pp. 930–934, July–August, 1991.     

Observation of the decaya 2 − (1320)→π − η′

The reaction ^– C ^– C has been studied at 36 GeV/c. A clear signal for the decaya ₂ ^– (1320) ^– · is observed in the ^– mass spectrum. The measured ratio of branchings is BR (a ₂ ^{– –} )/BR(a ₂ ^{– –} );(3.4±0.8±0.5)·10^–2.