Metallaboranes of the Early Transition Metals: Direct Synthesis and Characterization of [{(eta5-C5Me5)Ta}2BnHm] (n=4, m=10; n=5, m=11), [{(eta5-C5Me5)Ta}2B5H10(C6H4CH3)], and [{(eta5-C5Me5)TaCl}2B5H11

Reaction of [Cp*TaCl4] (Cp*=eta5-C5Me5) with a sixfold excess of LiBH(4)thf followed by BH3thf in toluene at 100 degrees C led to the isolation of hydrogen-rich metallaboranes [(Cp*Ta)2B4H10] (1), [(Cp*Ta)2B5H11] (2), [(Cp*Ta)2B5H10(C6H4CH3)] (3), and [(Cp*TaCl)2B5H11] (4) in modest yield. Compounds 1-3 are air- and moisture-sensitive but 4 is reasonably stable in air. Their structures are predicted by the electron-counting rules to be a bicapped tetrahedron (1), bicapped trigonal bipyramids (2, 3), and a nido structure based on a closo dodecahedron 4. Yellow tantalaborane 1 has a nido geometry with C2v symmetry and is isostructural with [(Cp*M)2B4H8] (M=Cr and Re); whereas 2 and 3 are C3v-symmetric and isostructural with [(Cp*M)2B5H9] (M=Cr, Mo, W) and [(Cp*ReH)2B5Cl5]. The most remarkable feature of 4 is the presence of a hydride ligand bridging the ditantalum center to form a symmetrical tantalaborane cluster with a long Ta--Ta bond (3.22 A). Cluster 4 is a rare example of electronically unsaturated metallaborane containing four TaHB bonds. All these new metallaboranes have been characterized by mass spectrometry, 1H, 11B, and 13C NMR spectroscopy, and elemental analysis, and the structural types were unequivocally established by crystallographic analysis of 1-4.     

Entire cyclic homology of stable continuous trace algebras

A central result in this paper is the computation of the entirecyclic homology of canonical smooth subalgebras of stable continuoustrace C*-algebras having smooth manifolds M as their spectrum.More precisely, the entire cyclic homology is shown to be canonicallyisomorphic to the continuous periodic cyclic homology for thesealgebras. By an earlier result of the authors, one concludesthat the entire cyclic homology of the algebra is canonicallyisomorphic to the twisted de Rham cohomology of M.     

Conformational isomers from rotation of diacetylenic bond in an ethynylpyrene-substituted molecular hinge

The first example of isolation and X-ray crystallographic structural characterization of two conformers arising from rotation along a diacetylenic bond is reported. In both the conformers extensive pi-pi interactions are observed in the solid state. VT-NMR and fluorescence spectroscopic studies in solution suggest that the closed and open conformers are in equilibrium and that the closed conformer is the predominant species at room temperature.     

Vibrational spectroscopic studies and ab initio calculations of Goniothalamin, a natural product

5,6-Dihydro-6-styryl-2-pyrone (Goniothalamin), is isolated from the leaves of Goniothalamus wightii and identified by spectral analysis and X-ray diffraction studies. FT-IR spectroscopy has also been used to characterize the vibrational bands. The vibrational wavenumbers and corresponding vibrational assignments are examined theoretically using the Gaussian03 set of quantum chemistry codes. Predicted IR and Raman intensities are reported.     

Vibrational spectroscopic studies and ab initio calculations of a substituted amide of pyrazine-2-carboxylic acid--C12H10ClN3O

A substituted amide of pyrazine-2-carboxylic acid was prepared and the IR spectrum is recorded and analysed. The vibrational frequencies and corresponding vibrational assignments are examined theoretically using the Gaussian03 set of quantum chemistry codes. Predicted infrared and Raman intensities are reported.     

IR, Raman and SERS spectra of disodium terephthalate

The IR and Raman spectra of disodium terephthalate were recorded and analysed. Surface enhanced Raman scattering (SERS) spectrum was recorded in silver colloid. The vibrational wavenumber of the compound have been computed using the Hartree-Fock/6-31G* basis and compared with the experimental values. SERS studies suggest a flat orientation of the molecule at the metal surface.     

Raman, IR and SERS spectra of methyl(2-methyl-4,6-dinitrophenylsulfanyl)ethanoate

Methyl(2-methyl-4,6-dinitrophenylsulfanyl)ethanoate was prepared by nucleophilic substitution. FT-IR and FT-Raman spectra of methyl(2-methyl-4,6-dinitrophenylsulfanyl)ethanoate were recorded and analyzed. Surface-enhanced Raman scattering (SERS) spectrum was recorded on a silver colloid. The vibrationl wavenumbers were computed by density functional theoretical (DFT) computations at the B3LYP/6-31G* level and they were found to be in good agreement with the experimental values. The molecule is adsorbed on the silver surface with the benzene ring in a 'tilted orientation'.     

Modular approach to functional hyaluronic acid hydrogels using orthogonal chemical reactions

A modular approach for the synthesis of hyaluronic acid hydrogels using orthogonal chemoselective reactions for subsequent enzymatic decomposition to nanoparticles is described.     

Two new fluorescent heterocyclic perimidines: first syntheses, crystal structure, and spectral characterization

An efficient one-pot synthesis of two new heterocyclic perimidines 4-(2,3-dihydro-1H-perimidin-2-yl)-2-methoxyphenol and 2-(quinoxalin-2-yl)-2,3-dihydro-1H-perimidine in good yields is presented. This methodology provides a simple, straightforward synthetic route to these interesting classes of heterocycles. Crystal structure, solvatochromism, and antibacterial activity of these organic compounds are discussed.