Photophysical Properties and Applications of Lanthanoid Helicates - Metallofoldamers: Supramolecular Architectures from Helicates to Biomimetics - page 217

Table 6.9 Limits of detection (LOD) for quantifying various types of DNA by the
AO/[Eu 2 (L5) 3 ] method [76].

Sample Actin sense-2 DNA Plasmid DNA l DNA/ Hin dIII Sheared salmon

sperm DNA

LOD (ng m l 1 )

0.32 0.18 0.57 0.66

Figure 6.12 Quenching of [Eu 2 (L5) 3 ]5mM in water (pH 7.4, Tris-HCl) by acridine orange
(left; AO) and ethidium bromide (right; EB). Reproduced with permission from [76]. Copyright
2008 The Royal Society of Chemistry.

albumin, sodium dodecylsulfate, Mn II and ascorbate alters the results by 5-10% while

Cu II and Co II have a much larger influence. But the concentrations of exogenous sub-
stances used (0.1mM) are far larger than those found in biological systems. As a matter
of fact, quantification of DNA in cell lysate results in an excellent linearity of the emis-
sion intensity versus the number of cells in the range 500-10 000 cells. Finally, the
method is also applicable to PCR products with small numbers of base pairs: comparisons
with conventional methods based on UV-vis absorption or fluorescence of PicoGreen #
dye give the same results [76].

6.2.6 Other Investigated Helicates

6.2.6.1 Dinuclear Triple-Stranded Helicates
The pyridine-2-6-dicarboxamide based ligand L21 (Scheme 6.5) reacts with Ln(CF 3 SO 3 ) 3
(Ln Sm, Eu, Tb, Lu) in acetonitrile to give rise to triple-stranded helicates [Ln 2 (L21) 3 ]

with a speciation of about 84% at stoichiometric ratio and total ligand concentration of
10 5 M, the other major species being a 2 : 2 species. Spectrophotometric absorption and
luminescence data allowed the determination of stability constants for both species, which
are large, in the range 19-22 for log

¼

5 D 0 Þ

decay is
monoexponential when the concentration of the 2 : 2 species is low and the corresponding
lifetime amounts to 1.57ms. Monitoring Eu luminescence also led to the conclusion that
the formation of the helicate is fast, since the emission intensity does not change after
only a few seconds [85].

b 22 and 26-29 for log b 23 .TheEu ð