Interaction of cyanine dyes with nucleic acids. XVII. Towards an aggregation of cyanine dyes in solutions as a factor facilitating nucleic acid detection

Spectral properties of newly synthesized cyanine dyes, namely 1-[6-(4-{6-[2,6-dimethyl-4-(3-methyl-2,3-dihydro-1,3-benzothiazol-2-ylidenmethyl)-1-pyridiniumyl]hexanoyl}piperazino)-6-oxohexyl]-2,6-dimethyl-4-(ethyl-2,3-dihydro-1,3-benzothiazol-2-ylidenmethyl)pyridinium (K-6) (bichromophoric dye) and 1-[5-di(3-{5-[2,6-dimethyl-4-(3-methyl-2,3-dihydro-1,3-benzothiazol-2-ylidenmethyl)-1-pyridiniumyl]pentylcarboxamido}propyl) carbamoylpentyl]-2.6-dimethyl-4-(3-methyl-2,3-dihydro- 1,3-benzothiazol-2-ylidenmethyl) pyridinium (K-T) (trichromophoric dye) in solutions in the presence of and without deoxyribonucleic acid (DNA) were studied within a wide concentration range. It has been established that absorption, as well as fluorescence of investigated dye solutions, without DNA are mainly determined by H-aggregates of dye molecules. On the contrary, the fluorescence of dye solutions in the presence of DNA gives an intrinsic dye molecular fluorescence. H-aggregates are broken because of binding dye molecules with DNA. It has been suggested that both K-T and K-6 molecules bind mainly with DNA via the interaction of two chromophores. As the ratio of the number of dye molecules to that of DNA base pairs increases with an increase in dye concentration, a formation of dye molecule H-aggregates on DNA molecules are observed. Such aggregates have a different structure than those formed in the solutions without DNA. On the grounds of the data obtained, it is concluded that it is possible to use a dye aggregation capable of obtaining higher values for fluorescence enhancement of the DNA stains. (C) 2000 Elsevier Science B.V. All rights reserved.