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

Encapsulation of Volatile Hydrocarbons by Cucurbiturils CHAPTER 2
Figure 2.2.2. Fluorescence-based approach for time-resolved monitoring of
hydrocarbon encapsulation and sensing using CB6 in aqueous solution. The trace
refers to actual experiments with sequential uptake and release of n-butane and
isobutane.
Note in Figure 2.2.3 the markedly different fluorescence responses
corresponding to the investigated hydrocarbons upon addition to the NAS-P•CB6
complex. To our surprise, the affinities of neutral guests towards CB6 are
exceedingly high (in fact, the largest ones ever reported with macrocycles), [103-
113] and the high selectivity exhibited by CB6 stands out also when compared to
previously investigated containers (Table 2.2.1).
Table 2.2.1. Binding constants of hydrocarbons with CB6.
Hydrocarbon
[Volume / Å 3 ] [b]
PC [c]
[%]
K [10 3 M –1 ] [a]
water, NaOAc,
pH 3.0 [d] pH 5.5
C1 methane [29] 20 < 2 < 0.05
C2 ethane [45] 32 24 [e] 2.6 ± 0.7
ethene [41] 29 3.9 0.25 [e]
30