A PORPHYRIN DNA EXCIPLEX - RESONANCE RAMAN-SPECTRA OF ELECTRONICALLY EXCITED CU(TMPY-P4) BOUND TO POLY(DA-DT).POLY(DA-DT)

The resonance Raman spectra of water‐soluble porphyrins, Cu(TMpy‐P4) and Ni(TMpy‐P4), and their mixtures with DNA, Poly(dG‐dC)‐Poly(dG‐dC), and Poly(dA‐dT)‐Poly(dA‐dT) were measured using 426 nm pulsed laser excitation (and 556 nm for some applications). At high laser power, the solution of Cu(TMpy‐P4) mixed with DNA or Poly(dA‐dT)‐Poly(dA‐dT) exhibits new bands at 1550 and 1349 cm−1 that are not observed for Cu(TMpy‐P4) alone or for Cu(TMpy‐P4) mixed with Poly(dG‐dC)‐Poly(dG‐dC). These extra bands do not appear when the resonance Raman spectra are measured by a cw laser or by a pulsed laser with low power. Similar mixtures of M(TMpy‐P4) (where M = Ni, Zn, Co, Mn, and H2) with these nucleic acids exhibit no such bands even by high power pulsed laser excitation. We attribute the new resonance Raman bands to an electronically excited Cu(TMpy‐P4), stabilized by forming an exciplex with the A‐T site of the nucleic acid. The minimum lifetime value of such an exciplex was estimated to be on the order of 10 ps. Copyright © 1990, Wiley Blackwell. All rights reserved