A STRUCTURAL STUDY OF THE NARINGIN-BETA-CYCLODEXTRIN COMPLEX

The structure of the inclusion complex formed between naringin (naring enin-7-0-beta-neohesperidoside) and beta-cyclodextrin (BCD) was studie d in detail by UV and NMR spectroscopic techniques and potentiometry. A binding constant value of 1016 +/- 150M-1 was arrived at from UV stu dies. Potentiometric studies showed that pK values of 4'-OH and 5-OH w ere affected by ce and beta-cyclodextrins. One-dimensional difference NOE and spin-lattice relaxation time (T1) measurements indicated that the aglycone portion was affected more than the neohesperidoside porti on. The T1 values analysed for local motions indicated that tau(c) val ues of complexed naringin was higher than that of free naringin. The i nternal rotation calculated for different groups showed tau(i) values for the phenolic and dihydrobenzopyran portion decrease by a factor of 2. Also a xi value of 0.12-0.17 observed for the aglycone portion ind icated that the coupling between guest and host is weak. All the studi es have shown that the disposition in which the phenol group at 2 is i nside the BCD cavity with 4-keto and 5-OH hydrogen bonded to the secon dary hydroxyl groups at the rim of the wider end of the BCD cavity is the most probable one.