Chemistry Reference
In-Depth Information
7.4.2 Aryl Nitrenium Ion Reactions with Guanine Derivatives
Figures 7.22-7.24 present selected ns-TR
3
spectra obtained at different time-delays
subsequent to photoexcitation of 0.3mM 2-fluorenyl azide in water-acetonitrile
(50:50) with a 0.002M Na
2
HPO
4
:0.002M NaH
2
PO
4
buffer that contain 0.9 mM
guanosine (Fig. 7.22), 0.9mM C8-methylguanosine (Fig. 7.23), and 0.9 mM
C8-bromoguanosine (Fig. 7.24, see also Figures 1S to 3S in Ref. 46). The TR
3
spectra shown in Figures 7.22-7.24 are essentially the same at very short time-delays
(see the 10 ns spectra in the figures) indicating that the same species is seen at very
short times. This first species can be attributed to the 2-fluorenyl nitrenium ion that
we have seen previously after photolysis of 2-fluorenyl azide in aqueous environ-
ments.
39,40
The 10 ns spectra presented in Figures 4.9-4.11 are compared to the
TR
3
spectrum of the 2-fluorenyl nitrenium ion (see Figure 4S in Ref. 39 and Figure
4S in Ref. 46) and this comparison clearly demonstrates that the first species seen
in the ns-TR
3
spectra of Figures 7.22-7.24 is the 2-fluorenyl nitrenium ion.
Examination of the ns-TR
3
spectra of Figures 7.22-7.24 shows that the intensity
of the Raman bands of the 2-fluorenyl nitrenium ion decrease over the hundreds of
15 µs
1.8 µs
1.6 µs
1.5 µs
1.4 µs
1.3 µs
1.1 µs
1 µs
900 ns
10 ns
1200
1300
1400
1500
1600
1700
1800
Raman shift (cm
-1
)
FIGURE 7.22.
Selected TR
3
spectra acquired by 368.9 nm probe after 309.1 nm photo-
excitation of 0.3mM 2-fluorenyl azide in the presence of 0.9mM guanosine in a water-
acetonitrile (50:50) mixed solvent with a 0.002M Na
2
HPO
4
:0.002M NaH
2
PO
4
buffer are
shown. The time-delays between the pump (309.1 nm) and probe (368.9 nm) laser beams are
given to the right of each spectrumand the Raman shifts of selected bands are shown at the top of
the 15
m
s spectrum. See text for more details.
Source
: Reprinted with permission fromRef. 46.
Copyright (2007) American Chemical Society.
