Kyonosuke Yamamoto

Correlation between metal NMR physical quantities and structures of metal complexes. I. 109Ag NMR spectroscopy of aqueous silver ions coordinated with nitroxide radical

Abstract Experimental 109 Ag NMR and theoretical MO methods have been used to investigate the electronic structure of silver complexes in aqueous solution. 109 Ag spectra of ionic silver solutions (⩽1.0 M ) can be obtained with a short repetition time (2–3 s) when 0.020 M 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl is added as a doping agent. By consideration of multiple equilibria, 109 Ag chemical shifts of silver complexes in aqueous solution were found to cover a range of 0 to 1300 ppm, relative to 1.0 M AgNO 3 . Tetrahedral silver complexes were at lowest field with linear silver complexes more shielded and hydrated silver ion at highest field. Our study suggests a correlation between 109 Ag chemical shielding and the structure of silver complexes in aqueous solution. An ab initio SCF MO method using a STO-3G basis set is used to clarify the nature of the ligand-silver interaction and to interprete the observed 109 Ag chemical shifts. The results indicate that electron density transfers from the lone pair of the ligand to vacant 5s and 5p orbitals on silver. Also back donation to ligand produces a hole in the 4d orbitals coincident with the bonding axes of silver complexes. The 109 Ag chemical shieldings are found to be explained by the paramagnetic term, which depends upon p electrons and d holes on the Ag atom according to qualitative perturbation theory.

Persistent Spectral Holes and Inhomogeneous Broadening Observed in Biological Systems with Mesoscopic Structures

Abstract Persistent spectral holes and absorption spectra are observed in two biological systems; daunomycin/adriamycin intercalated in DNA and DNA-oligomer and protonated cytochrome-c both are doped in buffer glass. They possess similar mesoscopic structures. Their relations to the hole widths and inhomogeneous band widths are discussed.

Photochemical Hole Burning Materials: Molecular Designing by Controlling Mesoscopic Structures

Our recent studies of organic dye doped glassy solvents and polymers by photochemical hole burning are reviewed. The series of experimental findings suggest a possible formation of gue-sthost complex dominating the various properties of holes. Based on these recognition we propose one working hypothesis of designing the functional materials for future memory systems through controlling their mesoscopic structures. The results on shikonin and daunomycin/adriamycin are described as prototypes of the hypothesis.