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revealed the expected 1:2 inclusion compound of hydroquinone
within metallocycle
stacking
disposition of four aromatic systems (Fig. 11.7). The interplanar
separation between internal hydroquinones (HQ
M5a
·8NO
showing a parallel π
-
π
3
) is 3.63 Å and the
distance between the hydroquinone plane and the centroid of the
closest parallel bipyridine (BIPY
in
) system is 3.59 Å, so that the π
-
π
par
interactions are maximized. The cavity is almost square shaped; the
distances between the centroids of the central C-C bonds of BIPY
par
and the orthogonal bipyridine (BIPY
) were 10.80 and 11.07 Å,
ort
respectively.
⊂
M5a
Figure 11.7
Crystal structure of (
. Solvent molecules,
counter anions, and hydrogen atoms have been omitted for
clarity. Color labeling scheme as in Fig. 11.5.
S1a
)
·8NO
2
3
can be chemically
controlled by oxidation/reduction of the substrate. After addition
of cerium ammonium nitrate to a solution of (
The inclusion process of
S1a
or
S2a
⊂
M5a
S1a
)
·8NO
2
3
⊂
M5a
or (
S2a
)
·8NO
, the substrate signals (
δ
= 6.81 ppm for
S1a
2
3
and
) disappeared, while new
resonances for the corresponding quinone and the metallocycle
M5a
δ
= 5.01, 6.00, and 6.19 ppm for
S2a
were detected as a result of the oxidation. This process
can be reversed by addition of sodium borohydride; benzoquinone
was then reduced and the inclusion complex was reassembled.
Because of the very low solubility of 1,5-naphthoquinone in D
·8NO
3
O, the
2
⊂
M5a
complex (
S2a
)
·8NO
could not be reassembled upon addition
2
3
of NaBH
.
4
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