Chemistry Reference
In-Depth Information
H
2
O (Figure 16.3k), a CH
3
Hg
II
- 1 - methylthymine complex in H
2
O (Figure 16.3 l) and
a crystalline Hg
II
- 1 - methylthymine complex (Figure 16.3 m) were presented.
39
In
addition, they presented IR spectra from solid samples of organomercury-guanosine/
thymidine complexes (Figures 16.3 n - q).
40
In 1982, Beauchamp, Savoie and cowork-
ers also reported IR/Raman spectra of methylmercury-adenine complexes (Figures
16.3 r - t).
41
Interestingly, in 1977, Mansy, Tobias and coworkers recorded Raman
spectra of calf thymus DNA in the presence of CH
3
Hg
II
OH (Figure 16.3 u).
39
This
data provided Raman spectroscopic information on Hg
II
and natural DNA
molecules.
As mentioned in Section 16.2, there are three types of Hg
II
- T/U complexes,
namely N3-, O4- and C5-mercurated ones. In the above noted vibrational studies,
all types of complexes in water solutions were characterized by Raman spectra and
several marker bands for detecting each Hg
II
-U/T complex were found. Notably,
not only solution samples, but also crystal samples prepared by means of Kosturko's
method
14
(with N3 - Hg
II
bonds) and Carrabine ' s method
13
(with O4 - Hg
II
bonds) were
employed. This fact implied that the derived FT-IR/Raman spectra surely originate
from the crystal structure and are not from any other structure. Therefore, the data
obtained from the studies provides rigid and reliable basal data for the assignment
of Raman bands from other systems.
In 2001, Morzyk-Ociepa and Michalska reported very fi ne FT-IR and Raman
spectra of solid samples of Hg
II
complexes with 1-methylthymine.
42
Furthermore,
they performed quantum chemical calculations of vibrational spectra, and exten-
sively assigned IR/Raman bands.
42
In 2003, they reported FTIR and FT-Raman
spectra of Ag
I
- 1 - methyluracil complexes (U - Ag
I
- U complex) (Figure 16.3 v) that
could be used as reference data for the T-Hg
II
- T base pair.
43
In 2004, they recalcu-
lated the theoretical frequency of vibrational spectra, and refi ned the assignments
of Raman and IR bands.
44
Therefore, these data can be applied to the interpretation
of FT-IR/Raman spectra in relation to specifi c vibrational modes. For vibrational
spectroscopy, suffi cient amounts of accurate spectral data of Hg
II
- nucleoside com-
plexes have been collected, along with data on neutral thymine.
45
Especially, in terms
of the structural studies on T-Hg
II
- T base pairs, Hg
II
- ligand interactions within T -
Hg
II
-T base pairs can be precisely analysed.
16.4 NMR Spectral Studies
16.4.1 Nucleoside - Metal Ion Systems
NMR studies on nucleobase-metal ion(Zn
II
) interactions in dimethyl sulfoxide
(DMSO) began in the 1960s.
46,47
These studies extended to nucleoside-Hg
II
interac-
tions.
48,49
At that time, NMR chemical shifts and their perturbations upon metal salt
titrations were used to understand the nucleoside-metal cation/counteranion inter-
actions.
46 - 52
In 1975, Sohma and coworkers extensively studied chemical shift per-
turbations of
1
H and
13
C nuclei in cytidine upon the addition of various metal cations
and counteranions to study how they affect
1
H and
13
C chemical shifts.
52
