Applications of Fluorescent Displacement-Based ... - Jacobs University

Encapsulation of Volatile Hydrocarbons by Cucurbiturils CHAPTER 2
new findings with respect to the encapsulation of hydrocarbons by CBn. For
instance, as we will see in the next section, the highly electron-rich benzene (89
Å 3 ) was found to have a very low affinity towards CB6 (< 10 3 M –1 ), in contrast to
less polarizable cyclopentane (86 Å 3 ), which reveals an extraordinarily high
binding constant (~ 10 6 M –1 ).
In view of these particular properties of the CB inner cavity, we have
decided to explore in detail the complexation of neutral guests with this class of
macrocycles, whose chemistry is presently unfolding (an example is the special
issue on “Cucurbiturils” in the Israel Journal of Chemistry, May 2011).
Particularly, the binding of small neutral molecules is useful, not only because the
charge-dipole interactions are being eliminated, which otherwise become
dominant, but also since a complete immersion inside the inner cavity is feasible.
This allows for an exploration of size, properties, as well as the fundamental
intermolecular interactions between the guests and the inner CB cavity leading to
the formation of discrete supramolecular assemblies, which I will describe next.
2.2 A SUPRAMOLECULAR GAS-SENSING ENSEMBLE WITH CB6
SO 3
–
NH
NH 2
NAS-P
O
N
N O
N
N N
N
N O
N
O
O
O
N N N
O N
O
N
N N
N N N N
N
O
O
N N
N N
O
O
CB6
In order to monitor the binding of several volatile hydrocarbons to
cucurbit[6]uril, CB6, in a time-resolved fashion we chose the indicator
displacement methodology using our recently developed anchor dye approach. [77]
Specifically, the fluorescent dye, NAS-P has been synthesized by attaching a
putrescine anchor (ensuring strong binding with CB6) to the
microenvironmentally sensitive 1-naphtylamine-5-sulfonic acid chromophore
(ensuring a significant fluorescence change upon binding). The strong affinity
between NAS-P and CB6 in combination with the large fluorescence response
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