Biology Reference
In-Depth Information
In principle, many other cyclic structures such as
1
x
1
,
3
,
1
x
2
,
1
x
3
,
4
, etc., could have formed from reactant
1I
or its assemblies
1I:1I
, and so on (Scheme 5.7), but in practice,
dynamic self-assembly chooses to amplify only two products,
2A
,
1I:1I:1I
,
1I:1I:1I:1I
at the expense of the others. Thermodynamically, all
these cyclic compounds have approximately the same formation
enthalpy per monocyclic unit (C
and
2
x
2
,
) because they have
exactly the same number and the same types of primary bonds. The
difference among them comes from secondary
H
N
O
S
40
40
2
10
2
π−π
stabilization.
π
Both cyclic dimer
-stacked
conformations and should be among the thermodynamically
stabilized cyclic compounds with restricted lateral and longitudinal
offsets from
2A
and its catenane
2
x
2
have favorable
the energy-minimized perylene stacks [50,51]. However,
π
the
-stacking contribution to the stabilization energy is small and
cyclic dimer
−
−
2A
and its catenane
2
x
2
have approximately
3
5 kcal/
mol of extra stabilization enthalpy [17,18] due to
-stacking and are
by no means located in deep potential energy wells. In fact, they
were formed through thermodynamically stable organization (an
enthalpy effect) directed by dynamic self-assembly, which brought
the two thiol groups into proximity for disulfide bond formation (an
entropy effect). The monocyclic dimer ring
π
was produced by two
disulfide linkages between the nearest stacked building blocks of
2A
1I
,
and catenane
was formed by reactions between the next nearest
neighboring thiol groups in the assembly of
2
x
2
1I
.
Dynamic Molecular Self-assembly
SAc
SAc
SAc
SAc
SAc
SAc
SAc
SAc
SAc
SAc
etc
1
I
1I:1I:1I:1I
1I:1I
1I:1I:1I
SAc
SAc
SAc
SAc
SAc
SAc
SAc
SAc
SAc
SAc
NaOMe/MeOH/CH
2
Cl
2
, Air
Possible Products
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
2A
1
2
x
2
1
x
1
1
x
2
1x3
3
4
Scheme 5.7
Possible cyclic products if the reaction occurs via random
collision mechanisms.
, the reaction proceeded
quantitatively through face-to-face ordered assemblies of perylene
In dilute solution (0.1 mM) of
1I
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