Chemistry Reference
In-Depth Information
Interestingly, the patterns of localisation were a function of the chain-length, with nuclear, nucleolar, and cytoplasmic staining
all being available by changing the alkyl chain lengths from ethyl to hexyl [34].
Lo has reported cell imaging ruthenium complexes conjugated with estradiol, which is known to target the estrogen
receptor-α (ER-α) [35]. These species show good uptake; however, studies indicate that regardless of the lipophilic structure
of estradiol, the uptake is mainly by an energy-dependent mechanism.
While osmium is generally regarded as too toxic to use in biological applications, an example of an emissive Os
II
complex
with a chelating diphosphine ligand capping the osmium bis-phenanthroline core has been embedded in nanoparticles and
applied in cell imaging. Os
II
polypyridyls are particularly attractive from a photophysical standpoint because they can exhibit
NIR emission, although lifetimes are consequently shorter, which gives good tissue penetration [36].
Ruthenium complexes have shown great promise in cell imaging applications, with attractive photophysics and sensing
ability, particularly as dNA and O
2
probes. It is likely that their progress will depend upon the development of general and
predictable methods to overcome problems associated with uptake and cellular distribution.
12.2.5
d
8
Metal Complexes in Cell imaging
The luminescence of platinum(II) and iridium(I) complexes is well established, but there are relatively few examples of their
applications in cell imaging. A time-gated study of a platinum(II) complex
16
with a lifetime of 580 ns allowed complete sep-
aration of the Pt-derived signal, localised in the nucleus, from a fluorescein (τ = 4 ns) co-stain [37]. Studies of the related
complexes
17
[38] and
18
(Figure 12.13) [39] showed preferential uptake in nuclei and cytoplasm respectively, indicating that
platinum may well be a promising candidate for the development of organelle-specific agents. Platinum complexes have also
been studied in cell imaging using 2-photon excitation, which avoids issues of tissue penetration of high energy excitation [37].
12.2.6
d
10
Complexes in Cell imaging
12.2.6.1 Au
I
Complexes in Cell Imaging
gold(I) complexes show emission from a variety of photophysical pathways,
typically LMCT, or those relying upon dimeric species showing aurophilic interactions. There have been relatively few
examples of gold lumophores applied in cell imaging, but the medicinal properties of certain gold complexes have led to
some effort in this area. gold phosphine complexes of thionaphthalimide have been shown to target the nucleus [40], while
a dinuclear gold NHC complex,
19
which emits due to aurophilic interactions, targets lysosomes (Figure 12.14) [41].
HN
N
N
N
O
Cl
Pt
N
Cl
Pt
N
Cl
Pt
N
O
-
N
N
N
16
17
18
FigUre 12.13
Pt complexes
16-18
.
N
N
Au
N
N
N
N
Au
N
N
19
FigUre 12.14
Au-NHC dimer
19
.
