Photobiological properties of positively charged methylene violet analogs

O-Methyl methylene violet (OMeMV), O-methyl bromomethylene violet (OMeBrMV) and O-methyl iodomethylene violet (OMeIMV) have been prepared in order to test their potential utility as anti-viral and anti-tumor phototoxic dyes. Rates of photosensitized toxicity of KB cells with 633 mn irradiation are ( x10(-19) photon(-1)): 2.4, 2.2, 1.9 and 0.17 for OMeIMV, OMeBrMV, methylene violet (MV) and OMeMV, respectively. Rates of photosensitized inactivation of Sindbis virus in phosphate-buffered saline with 633 nn irradiation are (x10(-18) photon(-1)): 3.3, 1.8, 0.99, 0.15 for MV, OMeIMV, OMeBrMV and OMe MV, respectively, Quantum efficiencies for singlet oxygen formation were de termined as OMeIMV, 0.64; OMeBrMV, 0.40; OMeMV, 0.054, Titration of the dye s with double-stranded (ds)DNA resulted in bathochromic shifts and hypochro mic effects in the visible absorption spectra, Association constants for in teraction of the methylated dyes with dsDNA of similar to 1 x 10(5) M-1 wer e determined by Scatchard analysis of equilibrium dialysis and UV absorptio n titration data. Photolysis of the halogenated dyes with DNA under argon l ed to covalent bond formation with the nucleic acid; there was no evidence of covalent binding in the dark.