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ii
are very similar
to those of Ptii
analogues
M2b
and
M3b
, reflecting
the similarity of their cavity sizes.
-
bipydinium-based metallomacrocyclic receptors, we considered
the design of a larger host capable of forming inclusion complexes
with polycyclic aromatic hydrocarbons (PAHs) such as pyrene in
aqueous media. PAHs are an important group of environmental
pollutants characterized by owning two or more fused aromatic
rings, their hydrophobicity and tendency to accumulate in the
organic matter [23]. Their omnipresent distribution, environmental
persistence, and potentially deleterious effect on human health have
resulted in an increasing interest by the research community [24].
Appropriate extraction techniques able to enhance the solubility
of the compounds, in order to remove their entire labile fraction
to an aqueous media, are highly required [25]. In order to achieve
this goal, the use of water-soluble Pd
Continuing our systematic investigation on
N
-monoalkyl-4,4
II
II
-based metallocycles of
adequate dimensions, capable of complexing a given PAH by means
of size complementarity and noncovalent interactions, was explored
by our research group for the complexation of pyrene [26].
Simple quantum chemical calculations in order to determine
the dimensions of the host and guest prompted us to synthesize a
dinuclear molecular rectangle with the appropriate cavity length
(ca. 11.31 Å) to bind pyrene. Thus, we proposed the receptors
M4a
/Pt
as potential receptors for pyrene, where the distance
between the centroids of the short sides of the rectangle grows
owing to the elongation of the long side from a bipyridine (in our
previous metallocycles) to a phenylene
,
b
bipyridine system. Indeed,
these metallocycles form a very stable 1:1 inclusion complex with
pyrene in aqueous solution (
6
) through π-stacking
and hydrophobic forces. The host-guest association constants in
acetonitrile and methanol are several orders of magnitude smaller
than in water indicating that hydrophobic forces play an important
role in the complexation process.
The formation of the 1:1 inclusion complex with pyrene was
also confirmed in the solid state by X-ray crystallography analysis
of a single crystal obtained from a solution of pyrene and
K
= 2.3
×
10
a
M4a
·6NO
3
. The resulting data were sufficient to enable an
unambiguous assignment of the molecular structure (Fig. 11.6). The
pyrene molecule is clearly located inside the cavity, the distance
in aqueous NaNO
3
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