Amplified Intermolecular Forces

As mentioned in the introduction, a molecule inside a capsule—typically for one second or so—appears isolated in time and in space. Its interactions with the capsule and other coencapsulated molecules are extended and, compared to the random and rapid collisions (10 per second) and exchange of partners that occur in bulk solution outside the capsule, they are intensified or amplified. The capsule provides a synthesized solvent cage that lasts a long time. 

In the cylindrical capsule especially, it is possible to ahgn the two molecules inside so that only certain areas of their surfaces come into contact. To our knowledge this cannot be achieved by other methods. Coencapsulation provides a means by which weak, intermolecular forces can be evaluated at the level of a prolonged, one-on-one molecular encounter. We applied this to the subtie interactions known as halogen bonds. 

We studied the series of such alkanes in the cylindrical capsule and found normal decane (10 carbons long) and its homologs Cn, C12, C, and C14 all went in the capsule, but C15 did not at all. NMR allowed us to look at the conformations and showed us a real surprise. Cn featored the NOEs for a perfectly extended stmcture. In contrast, C14 shows NOEs that can only be interpreted in terms of a coiled or helical structure in Fig. 7.10. This structure has never before been seen for normal alkanes but represents a compromise of filling space, making attractive CH-ti contacts and the avoidance of vacuums. The price paid for the contortion is reflected in the reduced affinity of C14 for the capsule direct competition experiments that Ci3 is some 120 times a better guest than C14 [25]. 

Finally, to what extent do the encapsulated molecules respond to events outside Of course, for these systems that are at equilibrium with the outside, their very existence represents a response to the situation in bulk solution. But there is evidence that more subfle influences also exist. Specifically, a chiral environment outside an achiral capsule can affect the spectrum of a molecule inside. Accordingly, the steric effects and magnetic effects can be separated by encapsulation. It appears that the capsule is best regarded as a window rather than a wall [26]. 

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As described in X-ray Crystal Analyses section, DBF oligomers have been shown to have a jc-stacked, single-handed helical conformation in crystal. A jc-stacked structure was indicated also for poly(PDBF) by remarkable hypochromicity in absorption and exclusive dimer emission in fluorescence spectra (Fig. 34). Therefore, it will be reasonably assumed that the CD absorptions observed in this work are based on a helical conformation of poly(PDBF) with excess single handedness. Because the polymers showing clear CD bands in film did not show chiroptical properties in solution, molecular aggregation may amplify and stabilize the single-handed helical conformation induced by the asymmetric polymerization possibly due to intermolecular cooperative effects in the solid state. Atomic force microscopic (AFM) analyses supported this assumption (Fig. 39). The samples were prepared by... 

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