Resonance Raman and Transient Absorption Studies on Ni(TMpy-P4) in a Water Buffer and Bound to DNA Model Compounds: Excited-States Dynamics and State of Coordination

Abstract

Nanosecond resonance Raman (RR) spectra of water-soluble Ni(TMpy-P4) bound to DNA model compounds, poly(dA-dT) and poly(dG-dC), show prominent transient features under increasing power density of the excitation pulses. Careful comparison with RR spectra of four- and six-coordinate Ni(TMpy-P4) in water buffer, as well as of the related Ni(II)-porphyrin, Ni-TPP, in both non-coordinating (like benzene) and coordinating nitrogen-containing solvents, revealed that it is the low-lying excited (d,d) state of Ni(TMpy-P4) that manifests itself in RR spectra under increasing excitation power density (Figure 1). The results of picosecond transient absorption studies on the kinetics and relaxation pathways for Ni(TMpy-P4) in different molecular environment are also presented. Although transient RR spectra of Ni(TMpy-P4) in both poly(dA-dT) and poly(dG-dC) reveal similar peculiarities, application of picosecond absorption technique permits to find distinct difference in photophysics of above mentioned objects, depending on the type of Ni-porphyrin complexation with the polynucleotides, with more complex behaviour for Ni(TMpy-P4) in poly(dA-dT).