2- Hydroxybenzoic acid, cyclodextrin inclusion complexes with

Phenolic compounds form inclusion complexes with a-cyclodextrin (85), enhancing the fluorescent properties of the aromatic analytes. For example, p-hydroxybenzoic acid (86a),... 

High resolution carbon-13 NMR spectroscopy is one of the most useful methods in the analysis of the structure and molecular dynamics of cyclodextrin inelusion-complexes both in aqueous solution[1,2] and in the solid state[3]. Earlier cariDon-13 NMR studies of a-CD inclusion complexes with benzoic acid, p-nitrophenol, and p-nitrophenolate in aqueous solution have shown that the included lead(head see Fig.lA) carbons show high-field shifts compared to low-field shifts of corresponding para(tail Fig.lA) carbons[4,5]. Similar distinctive patterns of carbon-13 displacement s have been also observed for p-hydroxybenzoic acid and it has been concluded that the carboxyl group of p-hydroxybenzoic acid is directed into the a-CD cavity [4]. A variety of substituted benzenes are known to show quite similar carbon-13 high (head) and low (tail) field shifts, irrespective of the kinds of substituents if their size are matched to the a-CD cavity [4,5]. These characteristic carbon-13 displacements induced by complexation with a-CD... 

Fig. 3. GROESY spectra of the 1 1 inclusion complex of 4-hydroxybenzoic acid and /3-cyclodextrin (/3-CD), saturated solution in D2O. (a) Normal spectrum (b) and (c) GROESY spectra obtained after pulsing selectively the guest aromatic protons H-2 Ha and H-3 (Hb), respectively. The inner H-3 and H-5 protons of /3-CD are assigned on the traces. All spectra were acquired in about 40 min., using 1024 scans, with the settings described in...

Uekama, K., Ikeda, Y., Hirayama, F., Otagiri, M., and Shibata, M. 1980. Inclusion complexation of p-hydroxybenzoic acid esters with andfS-cyclodextrins dissolution behaviors and antimicrobial activities.Yakugaku Zasshi, 100 994-1003. 

---