Photophysical, photochemical and DNA interaction of a Rhenium complex with dipyrido[3,2-a:2,3-c]phenazine (dppz) and norharmane (nHo) as ligands, Re(CO)3(dppz)(nHo)+. A Laser Flash Photolysis study

MAISULS, IVÁN; FERRAUDI, GUILLERMO J.; CABRERIZO, FRANCO M.; RUIZ, GUSTAVO T.

Congreso; XIII ELAFOT; 2017

The formation of adducts between complexes of Re(I), andbiological macro-molecules such as DNA has been a subject of considerableinterest because of the potential biochemical and technical applications [1].Adducts are formed when cationic transition metal complexes are stronglyattracted by phosphate groups in the periphery of the DNA double helix. Becauseof the medium-dependent photophysical and photochemical properties of the Re(I)complexes, they fulfill the necessary conditions of a probe and aphotosensitizer of DNA redox reactions [2]. Recently, we have synthesized anovel complex of Re(I) with norharmane (9H-Pyrido[3,4-b]indole)and a well known DNA intercalator, dppz (dipyrido[3,2-a:2,3-c]phenazine)as ligands, Re(CO)3(dppz)(nHo)+. In neat MeOH, laserirradiations at 351 nm, of the complex produced a transient with ?Émax= 460 nm, attributed to the dppz triplet state, 3IL. The transientabsorbance decay was monoexponential with a ?Ñ = 3.54 ?Ês. In pure H2O,this state is totally deactivated, thus, in water it was not possible to observea transient formation. After adding Calf-Thymus DNA (DNAct) to the aqueoussolution and subsequent laser irradiations, the formation of an absorbancetransient was seen. The contrast between the photobehavior of the complex inthe absence and presence of DNA suggest that the [Re(CO)3(dppz)(nHo)]+is intercalated into the DNA strand. Therefore, the intercalation of thecomplex in the presence of DNAct must provide some sort ofhydrophobic environment to the complex.Also, toascertain if the 3MLCTRe?¨dppz or 3MLCTRe?¨nHoand 3IL excited states of the intercalated [Re(CO)3(dppz)(nHo)]+were present and able to participate in redox procceses, their electrontransfer reactions with the electron donor TEA and with the electron acceptorMV+2 were investigated both in prescence and absence of DNAct.  Figure 1: Flash photolysis spectrum of Re(CO)3(dppz)(nHo)+in Methanol. Inset: chemical structure of the complex. [1] L. Wei, J. Babich, J.Subieta, Inorg. Chim. Acta, 2005, 358, 3691.[2] G. T. Ruiz, M. P.Juliarena, R. O. Lezna,  E. Wolcan, M. R.Feliz, G. J. Ferraudi, Dalton Trans.,2007, 20, 2020.