Determination of the stability of complexes between DNA and the thiazole orange derivatives TO6 and TOTO by surface-enhanced resonance Raman spectroscopy

Complexes of the two thiazole orange derivatives TO6 [1‐(N,N′‐tetramethyl‐1,3‐propanediaminopropyl)‐4‐[3‐methyl‐2,3‐dihydro(benzo‐1,3‐thiazole)‐2‐methylidene] quinolinium triiodide] and TOTO [1,1'‐(4,4,8,8‐tetramethyl‐4,8‐diazaundecamethylene)bis‐4‐[3‐methyl‐2,3‐dihydro(benzo‐1,3‐thiazole)‐2‐methylidene] quinolinium tetraiodide] with DNA oligonucleotide strands are investigated by the use of surface‐enhanced resonance Raman spectroscopy. TO6 and TOTO contain protons that are exchangeable with deuterium when dissolved in D2O. The exchange sites can be identified by use of nuclear magnetic resonance spectroscopy. The degree of exchange observed in the surface‐enhanced resonance Raman spectra is used to measure the stability of the complexes formed. TOTO forms a highly stable complex with the d(5′‐CCGCTAGCG‐3′): d(5′‐CGCTAGCGG‐3′) oligonucleotide, whereas a less stable complex is formed with d(5′‐CGCGTTAACGCG‐3′)2, indicating some degree of site specificity in the binding of TOTO to DNA. TO6 does not bind strongly to any single site in the d(5′‐CGCGTTAACGCG‐3′)2 oligonucleotide. © 1997 John Wiley & Sons, Inc. Biospect 3: 207–213, 1997