Nature of Supramolecular Complexes Controlled by the Structure of the Guest Molecules: Formation of Octa Acid Based Capsuleplex and Cavitandplex

Abstract

Factors that govern inclusion of organic molecules within octa acid (OA), a synthetic deep cavity cavitand, have been delineated by examining the complexation behavior of a number of organic molecules with varying dimensions and functionalities with OA. The formation of two types of complexes has been noted: the one which we call cavitandplex is a partially open complex in which a part of the guest molecule remains exposed to water, and the other termed capsuleplex is formed through assembly of two OA molecules. In capsuleplex, the guest is protected from water. Generally, guest molecules that possess ionic head groups form cavitandplex, and all others form capsuleplex. Capsuleplex may contain one or two guest molecules within the capsule. Small organic molecules (<10 A in length) may form both 2:1 and 2:2 capsuleplex, while longer ones (>12 A) preferentially form 2:1 capsuleplex. Extensive 1H NMR experiments have been carried out to characterize host-guest complexes. In the absence of the guest, OA tends to aggregate in water. The extent of aggregation depends on the concentration of OA and the presence of salts in solution. We expect the information obtained from this study to be of great value in predicting the nature of complexes with a given guest and facilitating appropriate guest chosen by researchers.

Closed Nanocontainer Enables Thioketones to Phosphoresce at Room Temperature in Aqueous Solution

“…For a hydrodynamic radius of 1:1 complex being closer to that of free OA, one would expect the diffusion constant for free OA and the 1:1 complex to have a similar value. 39,40 On the basis of this logic, the measured diffusion constants being smaller than for free OA, we believe that thioketones form a 2:2 rather than 1:1 complex with OA.…”

“…39,40 1 H NMR titration experiments performed by the gradual stepwise addition of 0.25 equiv of camphorthione to a 10 -3 M OA solution helped us infer the stoichiometry of the thioketone-OA complex (Figure 2). At early stages of addition (when excess OA is present in the solution), the signals due to H d and H e of OA and Me B and H 2 of the guest were slightly broad (Figure 2 ii, iii, and iv), suggesting the host-guest complex to be weak under these conditions.…”

Role of Free Space and Conformational Control on Photoproduct Selectivity of Optically Pure α-Alkyldeoxybenzoins within a Water-Soluble Organic Capsule

“…This is an indication of inclusion of guests within the OA host. 28 (Table S1, Supporting Information) suggested the 1a−d location within the capsule formed by two molecules of OA. During the titration experiments as followed by 1 H NMR there was only one set of upfield-shifted signal for the guest molecules, suggesting that there are no free molecules in solution.…”

Photoisomerization and Photooxygenation of 1,4-Diaryl-1,3-dienes in a Confined Space

“…It is known that two molecules of OA self-assemble in borate buffer (pH ∼9) in the presence of hydrophobic guest molecule(s). 41 Capsular host−guest complexes (2:1) of OA and 1−6 were prepared by stirring an aliquot of DMSO stock solution of the guests with OA in 2:1 (host-to-guest) ratio in borate buffer solution (0.6 mL; pH ∼9). Figure 2, all methyl, olefinic, and aromatic hydrogen signals of the guests were upfield shifted relative to those in CDCl 3 .…”

“…Figure 2, all methyl, olefinic, and aromatic hydrogen signals of the guests were upfield shifted relative to those in CDCl 3 . 43,44 The spectral data for the guests DPB and DTB in CDCl 3 available in the literature were used for comparison. 14,35 In the spectra, the signals due to the cavitand OA hydrogens are marked as a, b, and g. The two cavitand OA molecules of the capsule in the presence of a symmetrical guest, as in the case of trans,trans and cis,cis, experience the same magnetic environment to result in the observed single set of signals for both OA hydrogens.…”