a. Dimers of amides, boronic acids and carboxylic acids
(G. Theodorakopoulos, I. D. Petsalakis, D. Ajami and J. Rebek, Jr J. Am. Chem. Soc. 133, 16977(2011);
Study of homodimers and heterodimers of amides, boronic acids and carboxylic acids have been calculated in the gas phase and in solvents and using MP2, CCSD(T) and the DFT methods. Furthermore, their pairwise co-encapsulation was studied to examine its effect on the calculated properties of the hydrogen bonds via the ONIOM and DFT methodology. Some of the studies provide theoretical rationalization of recent experimental studies and they interpret the experimental results on hydrogen bonding in encapsulation complexes.
Figure 1. Structures of the cavitand 1 and glycoluril 2 components and structures of the cages 1.1 and 1.24.1. (H atoms = white spheres, C = grey spheres, O = red spheres and N = blue spheres)
Figure 2. Structures of the encapsulated dimers in the a capsule 1.24.1. (H atoms = white spheres, C = grey spheres, O = red spheres and N = blue spheres). The atoms of the capsule are designed with stick bonds for clarity.
b. Conformations and fluorescence of encapsulated stilbene
(D. Tzeli, G. Theodorakopoulos, I. D. Petsalakis, D. Ajami and J. Rebek, Jr J. Am. Chem. Soc. 134, in press (2012))
Absorption and emission spectra of free and encapsulated stilbene in two different capsules were calculated using the DFT and the TDDFT methodology. The present work is directed towards the theoretical interpretation of recent experimental results on control of stilbene conformation and fluorescence in capsules. The results of the calculations are in agreement with experiment and explain why the fluorescence of trans-stilbene persists in the large cage while it is quenched in the small one. It is found that the geometry of trans-stilbene in the ground as well as in the first excited singlet state is unaffected by encapsulation in the large cage and consequently the absorption and emission spectra are similarly unaffected. In the small cage, the ground state of encapsulated trans-stilbene is distorted with the two phenyl groups twisted while the geometry of the excited state, after relaxation, lies at the conical intersection with the ground state. Consequently, there is no emission similar to that of free trans-stilbene and the state decays non-radiatively to the ground state.
Figure 3. Optimized structures of encapsulated trans-stilbene (t) and cis-stilbene (c) in the capsules 1.1 and 1.24.1 viewed from two or three different angles, i.e, along the central axis of the capsule and end-on view. (H atoms = white spheres, C = grey spheres, O = red spheres and N = blue spheres). The atoms of the capsule are designed with stick bonds for clarity
Figure 4. Minimum energy structure of stilbene in the 1.1 cage, in the first excited state of stilbene viewed from two different angles. This structure corresponds to the S1 global minimum at the conical intersection.
Collaborators
The Skaggs Institute for Chemical Biology & Department of Chemistry, La Jolla, USA: D. Ajami, J. Rebek, Jr.
References
''Theoretical study of hydrogen bonding in homodimers and heterodimers of amide, boronic acid and carboxylic acid, free and in encapsulation complexes'', D. Tzeli, G. Theodorakopoulos, I. D. Petsalakis, D. Ajami and J. Rebek, Jr J. Am. Chem. Soc. 133, 16977 (2011).
''Conformations and fluorescence of encapsulated stilbene'', D. Tzeli, G. Theodorakopoulos, I. D. Petsalakis, D. Ajami and J. Rebek, Jr J. Am. Chem. Soc. 134, xxx (2012).
''Theoretical study of free and encapsulated carboxylic acid and amide dimers'', D. Tzeli, G. Theodorakopoulos, I. D. Petsalakis, D. Ajami and J. Rebek, Jr Int. J. Quantum Chem., 112, xxx (2012).
