Chemistry Reference
In-Depth Information
50 µs
2 µs
1.7 µs
1.5 µs
1.3 µs
1.1 µs
700 ns
10 ns
1300
1400
1500
1600
1700
1800
Raman shift (cm
-1
)
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 C8-methylguansoine 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 spectrum and the Raman shifts of selected bands are shown at the
top of the 50
m
s spectrum. See text for more details.
Source
: Reprinted with permission from
Ref. 46. Copyright (2007) American Chemical Society.
FIGURE 7.23.
nanoseconds to microseconds timescale and concurrently Raman bands from a
different species are formed with the same rate as the decay of the 2-fluorenyl
nitrenium ion.
The larger Raman features in the 1600 cm
1
part of the ns-TR
3
spectra in
1630 cm
1
Raman feature for the 2-fluorenyl nitrenium
ion, the 1618 cm
1
feature for the intermediate seen in Figure 7.22 the 1613 cm
1
feature for the intermediate seen in Figure 7.23 and the 1614 cm
1
feature for the
intermediate seen in Fig. 7.24) can be utilized to follow the decay of the 2-fluorenyl
nitrenium ion and the growth of the second species. Figure 7.25 presents plots of
the integrated intensities of the appropriate Raman bands for the reaction of the
2-fluorenyl nitrenium ion with guanosine (Fig. 7.25a), C8-methylguanosine
(Fig. 7.25b) and C8-bromoguanosine (Fig. 7.25c). The simultaneous decay of the
2-fluorenyl nitrenium ion and the growth of the new species (see line fits to the data of
Fig. 7.25) can be fitted well by common time constant. Because the new species are
only detected in the presence of the guanosine derivatives and their growths correlate
to the decay of the 2-fluorenyl nitrenium ion, the new species are directly produced
Figures 7.21-7.23 (the
