Biomedical Engineering Reference
In-Depth Information
Zn2+
Cu2+
Ni2+
Pb2+
Cd2+
1, 6
1, 4
1, 2
1, 0
0,8
0,6
0,4
0,2
0,0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15
M e 2+ /3
Fig. 13 Relative intensity emission of fluorescence (l exc ¼ 340 nm) in tritiation of 12 in the
presence of different transition metal cations in acetonitrile ( T ¼ 20 C). Concentration of 12
4.4 10 6 M, TMAOH 1.3 10 5 M and TBAPF 6 1 10 4 M
Reducing the amide groups to the corresponding amino derivatives gives rise to
compounds 13-15.
N
R
N
N
n
13 R=Me, n=1
14 R=H, n=1
15 R=Me, n=2
N
N
n
R
N
The sensing properties of these compounds were studied with Zn 2+ ,Cd 2+ ,Pb 2+ ,
Ni 2+ , and Cu 2+ as triflate salts. The results obtained with Cd 2+ ,Pb 2+ , and Ni 2+ are
similar for all three ligands, and fluorescence quenching occurs (Fig. 14 ). This
behavior may be due not only to the presence of the transition metal cation in the
solution but also to the modification in the dihedral angle between aromatic rings or
the conformational restriction induced by the complexation event.
In contrast, Cu 2+ and Zn 2+ display a completely different behavior when com-
plexation experiments are carried out with ligands 13-15. The behavior observed
with these two cations depends on salt concentration. Thus in the case of Zn 2+ ,
when the cation is in solution, a quenching of the main emission band is observed,
which also occurs with other studied cations. Nonetheless, when the presence of
Zn 2+ is above 1 equiv., the broadband centered at ca. 550 nm increases in intensity.
Similar behavior is noted for Cu 2+ but, in this case, the band starts growing even
with smaller amounts of the cation (0.7 equiv.). A very large amount of Zn 2+ (about
16 equiv.) is required to achieve a band of a similar intensity to that obtained with
 
Search WWH ::




Custom Search