M. Enescu et L. Lindqvist, PHOTOPHYSICS OF METHYLENE BLUE-POLYNUCLEOTIDE COMPLEXES IN THE PICOSECOND TIME RANGE - INFLUENCE OF THE LOCAL-STRUCTURE OF THE POLYNUCLEOTIDE, Photochemistry and photobiology, 62(1), 1995, pp. 55-59
The photophysics of methylene blue (MB) complexed with 2'-deoxycytidyl
yl-2'-deoxyguanosine, polydeoxyguanylic-deoxycytidylic acid, polydeoxy
guanylic-polydeoxycytidylic acid and polyguanylic acid, respectively,
was investigated by transient absorption spectroscopy with a time reso
lution of similar to 1 ps. The decays of the transient difference spec
tra indicate that the radiationless process responsible for the strong
shortening of the S-1 state lifetime of MB associated with a guanine
in the polynucleotide chain is similar to that already observed in the
case of the MB-guanosine-5'-monophosphate complex, that is, the excit
ed state decays by return of molecules to the ground state without for
mation of a detectable intermediate state. The local structure of the
polynucleotide apparently does not change the nature of the deactivati
on process but influences significantly the deactivation rate. Thus, t
he intercalation of MB between guanosine and cytosine increases this r
ate constant (as compared to that of the MB-guanosine-5'-monophosphate
complex) while the interaction of MB intercalated with a supplementar
y guanine has an opposite effect. The results are discussed in connect
ion with the photosensitizing effect of MB in nucleic acid damage.