Studies of chromophore-DNA interaction by vibrational spectroscopy

The binding of dye molecules onto DNA strands is an important process in biochemistry [28]. Depending on its nature, this interaction may result in mutagenic, carcinogenic, and cytotoxic properties of the chromophore so that specific dyes have been suggested for the use as antitumor pharmaceuticals. Furthermore DNA binding dyes have been extensively used as stains in biochemical fluorescence microscopy work. 

In the present project we have investigated whether surface enhanced resonance Raman spectroscopy (SERRS) could be used to study various types of DNA-chromophore interactions. In this technique, a silver colloid is added to the solution containing the molecule to be studied [34]. First, we had to test whether the complex, between dye and DNA, would remain unaltered upon adsorption to the silver colloid surface which is a necessary condition for a valid application of the method. A second system specific question concerns the useful information that can be extracted from frequency shifts and relative intensity alterations in the vibrational spectrum of the DNA-bound chromophore [35-37]. 

As a first example, the complex of acridine orange (AO) with calf thymus DNA has been studied [38]. The stability of the complex upon adsorption on the silver colloid was confirmed by absorption spectroscopy (Fig. 20.14, right). In solution the absorption maximum at 504 nm (trace b) of AO in the complex is red shifted as compared to 495 mn (trace a) of the spectrum of the free AO molecule. The analogous red shift is maintamed when the complex is added into a solution containing the silver colloid (trace d). 

Highly sensitive SERS spectra have been recorded at the remarkably low AO concentration of 2.5 X 10 M (Fig. 20.14, left). The spectra of the free (trace a) and of the DNA-bound dye (trace b) appear to be quite similar and only small changes in relative band intensities are detected in the difference spectra (trace c). A carefiil analysis has been based on a 

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Vibrational spectroscopy and conformational analysis of oligonucleotides 20.3.3 Studies of chromophore-DNA interaction by vibrational spectroscopy... 

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