Inosine — Adenosine base pairing in d-GGTACIAGTACC: Duplex and hairpin with a two-base loop

An oligonucleotide dodecamer d-GGTACIAGTACC containing two inosine-adenosine mismatched base-pairs has been studied by¹H and³¹P NMR spectroscopy. Unique assignments of¹H and³¹P spins have been achieved by using a recently proposed two-dimensionalheteronuclearlong rangecorrelation (2D-HELCO) technique. The 2D nuclear Overhauser enhancement spectroscopy (NOESY) spectrum recorded in a mixed solvent of 90% H₂O+10%²H₂O has been used to assign all the exchangeable imino and amino proton resonances. NMR results indicate that at concentrations above 5 mM, the molecule adopts a duplex structure where the inosine imino protons are hydrogen bonded. Cross-strand NOEs between the imino proton of I6 and H2 proton of A7 and that between H2 of I6 and H2 of A7 provide evidence for inosine-adenosine base-pairing, with both bases I6 and A7 inanti conformation. The observed NOE connectivitiesd1,d2 andd3 from almost the middle of the molecule to the two ends are consistent with a right handed B-DNA conformation. However, the molecule adopts a more extended conformation in the mismatch region to accomodate the bulky purine-purine (IA) base pairs. NMR experiments at lower concentrations indicate the coexistence of a monomeric hairpin with a two base loop, consisting of I6 and A7 units, in equilibrium with the duplex. 2D-ROESY experiment at such a concentration shows that the conformation of the stem of the hairpin does not deviate much from the corresponding region of the duplex and four nucleotides C5, I6, A7 and G8 undergo significant structural changes during the formation of hairpin loop.     

Manganese(II) complexes with 3,5-diphynylisoxazole, 3-amino-5-methylisoxazole and 5-amino-3,4-dimethylisoxazole

Summary The complexes of manganese(II) halide and thiocyanate with 3.5-diphenylisoxazole (3,5-diPhisox), 3-amino-5-methyl-isoxazole(3-AMI) and 5-amino-3,4-dimethylisoxazole (5-ADI) have been prepeared and characterized by spectrocopic and magnetic methods and by conductivity measurements. The 3,5-diPhisox ligand is N-bonded, while the isoxazolamine ligands are bridging N(ring)- and O-bonded. All the compounds are nonelectrolytes, high-spin, with an octahedral stereochemistry.     

Electrospray ionization studies of transition-metal complexes of 2-acetylbenzimidazolethiosemicarbazone using collision-induced dissociation and ion-molecule reactions

The complexes of transition-metal ions (M2+, where M = Fe, Co, Ni, Cu, Zn, Cd, and Hg) with 2-acetylbenzimidazolethiosemicarbazone (L) are studied under electrospray ionization (ESI) conditions. The ESI mass spectra of Fe and Co complexes showed the complex ions corresponding to [M+2L-2H]+, and those of Ni and Zn complexes showed [M+2L-H]+ ions, wherein the metal/ligand ratio is 1:2 and the oxidation state of the central metal ion is +3 in the case of Fe and Co and +2 in the case of Ni and Zn. The Cd and Cu complexes showed preferentially 1:1 complex ions, i.e., [M+L-H]+ or [M+L+Cl]+, whereas Hg formed both 1:1 and 1:2 complex ions. During formation of the above complex ions one or two ligands are deprotonated after keto-enol tautomerism, depending on the nature and oxidation state of central metal ion. The structures and coordination numbers of the metal ions in the complex ions were studied by their collision-induced dissociation spectra and ion-molecule reactions with acetonitrile or propylamine in the collision cell. Based on these results it is concluded that Fe, Co, Ni and Zn form stable octahedral complexes, whereas tetrahedral or square planar complexes are formed preferentially for other metals. In addition, the Cu complex showed a [2L+2Cu-3H]+ ion with a Cu-Cu bond.     

Characterization and catalytic functionalities of copper oxide catalysts supported on zirconia

A series of zirconia supported copper oxide catalysts with varying copper loadings (1.2-19.1 wt %) were prepared by impregnation method. The catalysts were characterized by X-ray diffraction, UV-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and temperature-programmed desorption of CO2. Copper dispersion and metal area were determined by N2O decomposition method. X-ray diffraction patterns indicate the presence of crystalline CuO phase beyond 2.7 wt % of Cu on zirconia. UV-visible diffuse reflectance spectra suggest the presence of two types of copper species on the ZrO2 support. XPS peaks intensity ratio of Cu 2p3/2 and Zr 3d5/2 was compared with Cu dispersion calculated from N2O decomposition. TPR patterns reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The basicity of the catalysts was found to increase with Cu loading, and the activity of the catalysts was also found to increase with the increase in Cu loading up to 2.7 wt % Cu loading. The catalytic properties were evaluated for the dehydrogenation of cyclohexanol to cyclohexanone and were related to surface properties of the copper species supported on zirconia.     

Skeletons and Central Sets

Let be an open proper subset of Rⁿ. Its skeleton is the setof points with more than one nearest neighbour in the complementof its central set is the set of centres in maximal open ballsincluded in . Intuitively, if we think of as a land mass inwhich height is proportional to distance from the sea, its skeletonand central set can be thought of as corresponding to ridgesin the mountains of . In this note I discuss the metric andtopological properties of such sets. I show that any skeletonin Rⁿ is F, and has dimension at most n – 1, by any ofthe usual measures of dimension; that if is bounded and connected,its skeleton and central set are connected; and that separatesRⁿ iff its skeleton does iff its central set does. Any centralset in Rⁿ is a G set of topological dimension at most n –1. In the plane, I show that both skeletons and central setsare locally path-connected, and indeed include many paths offinite length. For any , its central set includes its skeleton;I give examples to show that the central set can be significantlylarger than the skeleton. 1991 Mathematics Subject Classification:54F99.     

EPR studies on copper(II) complexes of 2,2',2″-triamino-triethylamine and its hexamethyl derivative

This paper presents EPR, and optical absorption studies on [Cu(tren)NCS]SCN and [Cu(Me₆tren)NCS]SCN in solutions. Expressions derived by Barbucci and Bencini are evaluated. It is shown that the molecular motion of the complexes is anisotropic and nondiffusional.     

EPR studies on some polyamine copper(II) complexes in various solvents

EPR studies have been carried out on a series of copper(IIcomplexes with the general formula CuL(NCS)_xY_2-x[L = N,N,N',N″,N″-pentamethyldiethylenetriamine (Me₅den); x = 1 or 2; and Y = ClO₄, NO₃ or B?₄], dissolved in different solvents. These studies have revealed that the symmetry around copper(II) in [Cu(Me₅den)(NCS)₂] and [Cu(Me₅,den)-NCS]NO₃ is not trigonal-bipyramidal as predicted by IR, conductivity and optical data. The 4s contribution to the ground state is found to influence the isotropic contact term and bond parameters. The hyperfine line-widths observed for the copper(II) ion in solutions of these complexes dissolved in pyridine at room temperature are explained using the theory of Wilson and Kivelson. The isotropic spin—rotational relaxation contribution to the residual line-width is found to be smaller for all the complexes when they are dissolved in pyridine.     

Infra-red spectroscopic studies of solvent-solute interactions in parachlorophenol and thiophenol with tertiary amides

Hydrogen bonding of O-H ... O=C and S-H ... O=C type has been studied in parachlorophenol and thiophenol with dimethyl and diphenyl amides and from the equilibrium constants, variation in the integrated absorption intensities and frequency shifts, the strength of the interaction in these complexes is discussed. In these systems diphenyl amides form weaker H-bond compared to that with the corresponding dimethyl amides. In dimethyl amides, the interaction is in the order dimethyl acetamide > dimethyl propionamide > dimethyl formamide. Similar results are obtained with diphenyl amides.