Action spectra (660-700 nm) for virus inactivation and red cell damage photosensitized by the silicon phthalocyanine Pc 4

The silicon phthalocyanine HOSiPcOSi(CH3)(2)(CH2)(3)N(CH3)(2) (Pc 4) is being studied as a photosensitizer for decontamination of blood for transfusion. In order to optimize the treatment conditions, ie reduce damage to red blood cells (RBC) while maintaining virucidal activity, action spectra were obtained for Pc 4, Using monochromatic light from a dye laser pumped by an argon-ion laser, in the range of 660-700 nm, a red shift of the action spectra was observed with respect to the absorption spectrum of Pc 4 in methanol solution. This shift was a uniform 4 nm for induction of red cell damage, A similar shift was observed for the absorption spectrum of Pc 4 bound to RBC membranes. For virus inactivation, there was a 4 nm red shift on the blue side and approximately a 12 nm shift on the red side of the spectrum. It is concluded that using light of 690-700 nm would increase the specificity of the virucidal treatment several fold.