Molecular Assembly And Recognition Investigation Of β-Cyclodextrin To Characteristic Aromatic Compounds

(3-Cyclodextrin is a host molecule with hydrophobic cavity and hydrophilic surface, able to recognize molecules and can coordinate organic molecules selectively to form host-guest supramolecular compounds. Due to its hydrophile-lipophile characters, after forming supramolecular compounds, the aqueous solubility of guest molecules is increased in a ramarkable extent. Hence,β-cyclodextrin has an extensive application in organic synthetic chemistry, environmental science, food chemistry, pharmaceuticals, etc.In this paper, the molecular assembly and recognition between p-cyclodextrin and nine aromatic compounds anisole, ethyl benzoate, m-cresol,1,5-naphthalenediamine, 1,8-naphthalenediamine,1,5-dichloronaphthalene,9,10-anthraquinone, authrone, and five heterocyclic aromatic compounds N-benzylmorpholine, N-benzoylindol, N-benzoyltriazole, N,N’-dibenzoylo-phenylinediamine, N,N’-dibenzoyl 1,8-naphthalenediamine are discussed. The inclusion compounds were characterized by means of NMR and IR spectroscopy. Based on the chemical shift variations of host and guest molecules before and after the inclusion process, the molecular recognition ofβ-cyclodextrin is investigated in the case of molecular size mutual match or approximate match, the recognition rule ofβ-cyclodextrin to aromatic compounds is elucidated. Among which,β-cyclodextrin has different recognition to aromatic compounds and the alkyl groups connected inside. In comparison to aromatic groups, alkyl groups are only affected by the shielding of magnetic filed from the ring current of (3-cyclodextrin cavity, the chemical shift variation is more sensitive than that of aromatic groups. While, the aromatic guest molecules are affected by the shielding effect of ring current, as well as the deshileding of its own. Meanwhile, they are also affected by the steric compression due to the tight contact of hydrogen atoms between aromatic hydrogen atoms and H-3/H-5 from the cavity ofβ-cyclodextrin, which results in the complicated chemical shift variations. The NMR analysis of the supramolecular system elucidated the stoichiometric proportion of host-guest molecules, eg, N, N’-dibenzoylo-phenylinediamine and N, N’-dibenzoyl 1,8-naphthalenediamine form a 1:2 supramolecular system with P-cyclodextrin, respectively. The others form a 1:1 supramolecular system. Based on the chemical shift variation of host and guest molecules, the conformation of guest molecules inside p-cyclodextrin is elucidated, among which, symmetric conformation forms betweenβ-cyclodextrin and anisole, ethyl benzoate,1,5-naphthalenediamine,1,8-naphthalenediamine, 1,5-dichloronaphthalene, N-benzylmorpholine, N-benzoylindol,N-benzoyltriazole, N,N’-dibenzoyl o-phenylinediamine, N,N’-dibenzoyl 1,8-naphthalenediamine is formed. 9,10-anthraquinone, authrone and m-cresol form an unsymmetrical conformation inside the cavity ofβ-cyclodextrin. (3-Cyclodextrin was modified by diethylene triamine or triethylene tetraamine to synthesize mono[6-(diethylene triamino)-6-deoxy]-β-cyclodextrin(DTCD) and mono[6-(triethylene tetraamino)-6-deoxy]-β-cyclodextrin(TTCD), which reacted with 1,5-naphthalenediamine or 1,8-naphthalenediamine and four different rare earth metal ions(samarium, yttrium, ytterbium, neodymium) respectively, sixteen ternary supramolecular coordination compounds were prepared, which were characterized by means of NMR and IR spectra. After the chemical modification, the side chain self inclusion ofβ-cyclodextrin decreased the effective cavity which can match benzene ring. As a result, in the series of ternary supramolecular system, the stoichiometric proportion between host and guest molecules is 2:1, a kind of "sandwich" ternary supramolecular assembly system is formed. Their fluorescence spectroscopy was also studied. Guest molecules only exhibit weak fluorescence, after forming the ternary supramolecular system with DTCD/TTCD and rare earth metal ions, the fluorescence strength of guest molecules was increased in a remarkable extent, meanwhile, the fluorescent absorption peaks of 1,5-naphthalenediamine series exhibit a pronounced blue shift, and that of 1,8-naphthalenediamine only exhibits weak red shift.