Table 2. Spectroscopic properties of ethidium derivatives.

Compound	λmax exc/emi (nm)	Φrel	λmax exc/emi (nm)	Φrel
	freea	freeb	bounda	boundb
Ethidium	480/613	0.14	518/599	ndd
1	558/c	<<0.01	586/c	<0.01
2	477/597	0.06	508/595	0.25
3	551/c	0.02	577/c	0.03
4	464/603	0.04	494/592	0.20

The compounds used in this study are shown in Figure 1C.

^aThe positions of the maxima of absorption in the visible region (left) and fluorescence emission (right) are given in nm.

^bRelative fluorescence quantum yield, as compared to ethidium bound to dsDNA (Φrel = 1). For 1, 2, 3 and 4 these values correspond to the dye bound to saturating amounts (2× molar excess) of quadruplex DNA (22A) in a 10 mM sodium cacodylate, 0.1 M KCl, pH 7.3 buffer.

^cVery weak emission.

^dDue to its low affinity for quadruplex DNA, the fluorescence quantum yield of ethidium bound to 22A could not be determined under identical conditions.