A STRUCTURAL STUDY OF THE NARINGIN-BETA-CYCLODEXTRIN COMPLEX

The structure of the inclusion complex formed between naringin (naringenin-7-0-beta-neohesperidoside) and beta-cyclodextrin (BCD) was studied in detail by UV and NMR spectroscopic techniques and potentiometry. A binding constant value of 1016 +/- 150M-1 was arrived at from UV studies. Potentiometric studies showed that pK values of 4'-OH and 5-OH were 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 portion. The T1 values analysed for local motions indicated that tau(c) values of complexed naringin was higher than that of free naringin. The internal 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 indicated that the coupling between guest and host is weak. All the studies have shown that the disposition in which the phenol group at 2 is inside the BCD cavity with 4-keto and 5-OH hydrogen bonded to the secondary hydroxyl groups at the rim of the wider end of the BCD cavity is the most probable one.