title: EPR study of the dynamic behavior of cis,cis-1,3,5-triaminocyclohexane Cu(II) complex on B-form DNA-fibers.
abstract: The orientation and the dynamic behavior of [Cu(TACH)](2+)(TACH = cis,cis-1,3,5-triaminocyclohexane) on B-form DNA-fiber have been investigated by electron paramagnetic resonance (EPR) spectroscopy. The complex showed novel EPR spectra indicating that a rapidly moving species (X) is in equilibrium with a stereospecifically oriented species (Y) on the DNA-fiber in the range 20 and -20 degrees C. The thermodynamic parameters Delta H and Delta S of the equilibrium X right arrow over left arrow Y are respectively -51.3 kJmol(-1) and -1.9 x 10(2) JK(-1)mol(-1) for the DNA-fibers prepared at pH 7 and -47.1 kJmol(-1) and -1.7 x 10(2) JK(-1)mol(-1) for the DNA-fibers prepared at pH 9. These results suggest that the equilibrium involved a concerted structural change of the coordination sphere and the hydrogen bonding network around the complex on the B-form DNA-fibers. The orientation of the species Y was completely randomized below -20 degrees C, indicating that the freezing of the water molecules in the DNA-fibers breaks down the hydrogen bonding network which regulated the orientation of the complex in the DNA-fibers. The correlation between the observed dynamic behavior and the hydrolytic ability of the complex was also discussed.
authors.affiliation: Department of Applied Chemistry, Chuo University, 1-13-27, Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan.
authors.forename: Tomoya
authors.initials: T
authors.lastname: Hirohama
authors.forename: Akiko
authors.initials: A
authors.lastname: Chiba
authors.forename: Makoto
authors.initials: M
authors.lastname: Chikira
authors.forename: Yuki
authors.initials: Y
authors.lastname: Fujii
mesh_terms: D003300:Copper / Q000378:metabolism; D003514:Cyclohexylamines / Q000737:chemistry* / Q000378:metabolism; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D006860:Hydrogen Bonding; D009690:Nucleic Acid Conformation; D009942:Organometallic Compounds / Q000737:chemistry* / Q000378:metabolism; D013816:Thermodynamics
chemical_list: C472375:(1,3,5-triaminocyclohexane)copper(II); D003514:Cyclohexylamines; D009942:Organometallic Compounds; D003300:Copper; D004247:DNA