EPR study of the dynamic behavior of cis,cis-1,3,5-triaminocyclohexane Cu(II) complex on B-form DNA-fibers

摘要

The orientation and the dynamic behavior of [Cu(TACH)](2+) (TACH = cis,cis-1,3,5-triaminocyclohexane) on 13-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 degreesC. The thermodynamic parameters DeltaH and DeltaS of the equilibrium X reversible arrow Y are respectively -51.3 kJ mol(-1) and -1.9 x 10(2) J K-1 mol(-1) for the DNA-fibers prepared at pH 7 and -47.1 kJ mol(-1) and -1.7 x 10(2) J K-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 13-form DNA-fibers. The orientation of the species Y was completely randomized below -20 degreesC, 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