Chemistry Reference
In-Depth Information
proposed two reasons for the cytotoxicity: (1) the size of the 1.4 nm Au
55
clusters
fits perfectly to the height of the major grooves of DNA (1.3-1.5 nm) and thus may
block transcription of DNA and (2) it induces the formation of reactive oxygen
species (ROS) as a consequence of its electronic properties, leading to oxidative
damage of adjacent biomolecules and subcellular units. Studies with smaller and
larger gold phosphine-stabilised nanoparticles show a much less toxicity,
supporting their contention that [Au
55
(Ph
2
PC
6
H
4
SO
3
Na)
12
Cl
6
] has a very special
bio-response. Therefore, a contradiction remains - the specificity of the
bio-response suggests a well-defined molecular species, but the more detailed
analytical studies suggest that the material has the characteristics of a colloid
with a narrow range of dispersities.
Au
13
Centred
Cuboctahedron
Au
42
2nd Layer
Cuboctahedron
Au-PPh
3
Au-Cl
II
I
The study of gold colloids has similarly provided some new inroads and insights
into molecular gold cluster chemistry and thereby blurred the distinction between
the two disciplines. For example, the synthesis of gold colloids using the method
developed by Brust et al. which is discussed more fully in the next section has also
proved to be very versatile and useful for making thiolato-protected colloids which
can be handled using the experimental techniques of modern inorganic and organic
chemistry. These techniques have been used to refine the spread of species formed
by focusing the syntheses. The dispersities of the colloids are reduced to such an
extent that single molecular species may be isolated and crystallised. This has
resulted in the single-crystal characterisation of [Au
25
(SR)
18
], [Au
38
(SR)
24
] and
[Au
102
(SR)
44
] for example and the development of the important “divide and
protect concept” whereby the central gold cluster is stabilised by gold thiolato
ligands in the manner illustrated in Fig.
2
[
44
,
61
-
66
]. The successful crystallisation
and structural elucidation of [Au
102
(
p
-MBA)
44
] by Kornberg and co-workers [
63
]
was pivotal in redefining the nature of the gold-sulphur bonding in colloids and
nanoclusters. It established that the SR group is not as previously thought a simple
2e Lewis base or a 4e bridging ligand bonded to the surface of the gold particle but
plays a unique role in forming the novel oligomeric gold thiolato-motifs ([Au(SR)
2
]
and [Au
2
(SR)
3
] shown in Fig.
2
) which are capable of protecting the central gold
