CONICET | Buscador de Institutos y Recursos Humanos

Interaction studies of New Fuchsin derivates with proteins. Ivana Aiassa, Natasha Schvezov, Maria Noel Montes de Oca, Cristina Ortiz y Gerardo Arg¨¹ello. iaiassa@fcq.unc.edu.ar Photodynamic Therapy (PDT) is based on the concept that certain photosensitizers can be localized in neoplasic tissue and subsequently, these photosensitizers can be activated with the appropriate wavelength of light to generate active molecular species that are toxic to cells. The requisites that should have an effective photosensitizer are long absorbing wavelength, and high molar absorption coefficients in zones of effective penetration in the human tissue (wavelength shifts to the red). The cationic dyes derivates of triarylmethanes present attractive properties to be used in PDT. So that it is very interesting to study the behavior of this kind of photosensitizers in different media and the environment effect to the spectroscopic, photophysics and photochemistry properties. In this work we present the study on the interaction between New Fuchsin (NF) and Bovine Serum Albumin (BSA) using fluorescence and ultraviolet spectroscopy. It was observed that the fluorescence intensity of the tryphtophanes of BSA decreased regularly with the concentration increase of NF, but there was no significant lem. shift with the addition of NF. These data indicated that NF could interact with BSA and quench its intrinsic fluorescence. The quenching mechanism can be described by the Stern-Volmer equation. In order to confirm the quenching mechanism, the procedure of the fluorescence quenching was first assumed to be a dynamic quenching process. Considering that the KSV decreased with increased temperature, we should consider that the quenching is not initiated by dynamic quenching, but probably by static quenching resulting from the formation of NF-BSA complex. We obtained negative curved Stern-Volmer plots that are indicative that there is more than one specie with different quenchability. According to the modified Stern-Volmer plots we had estimated the association constants (Ka), for our experimental data we obtained a biphasic behavior with two defined slopes at high and low quencher concentrations. This biphasic behavior suggests that BSA has two different kinds of binding sites with two different constants, Ka1 = 4.23 105, Ka2 = 8.16 104 (site 1 and 2 at 298K) and Ka1 = 3.99 105, Ka2 = 6.89 104 (site 1 and 2 at 308K). For static quenching, the relationship between log [(F0-F)/F] and log [Q] gives a straight line from which slope we could obtain the number of each kind of site (n). According to the site-binding model, we obtained n1= 0.72; n2= 1.09 (298K) and n1= 0.66, n2= 1.44 (308K). We also studied the effect of temperature, and we obtained the thermodynamics parameters ¦¤H, ¦¤G and ¦¤S, indicating that the binding process is spontaneous, and it is favored by enthalpy.