A structural study of the naringin-?-cyclodextrin complex

Preparation, Physicochemical Characterization, and Antioxidant Activity of Naringin–Silk Fibroin–Alginate Microspheres and Application in Yogurt

Naringin is the major polyphenol in bitter orange peel with antioxidant property. However, its pH sensitivity, low solubility, and bitter taste limit its application in food. In this study, naringin–sodium alginate–silk fibroin microspheres were prepared by the ionic gel method. The loading capacity and encapsulation efficiency of naringin in microspheres were 13.2% and 77.6%, respectively. The morphology of microspheres was characterized by scanning electron microscopy. The X-ray diffractometry and differential scanning calorimetry results showed naringin was amorphous after encapsulation. Fourier-transform infrared spectroscopy and molecular docking analysis confirmed the intermolecular hydrogen bonds between naringin and sodium alginate. Naringin could release from the microspheres continuously under different pH conditions. Compared with free naringin, the 2,2-diphenyl-1-picrylhydrazyl scavenging activity and the stability of naringin microspheres were significantly improved. The application of naringin microspheres in yogurt indicated the precipitation of whey could be effectively reduced and the decline rate of pH was inhibited. The study suggested that naringin encapsulated microspheres were beneficial for improving the shelf life of this bioactive product as well as providing a new idea for functional yogurt.

Effect of β-cyclodextrin complexation on solubility and enzymatic conversion of naringin

In the present paper, the effect of beta-cyclodextrin (beta-CD) inclusion complexation on the solubility and enzymatic hydrolysis of naringin was investigated. The inclusion complex of naringin/beta-CD at the molar ratio of 1:1 was obtained by the dropping method and was characterized by differential scanning calorimetry. The solubility of naringin complexes in water at 37 ± 0.1 °C was 15 times greater than that of free naringin. Snailase-involved hydrolysis conditions were tested for the bioconversion of naringin into naringenin using the univariate experimental design. Naringin can be transformed into naringenin by snailase-involved hydrolysis. The optimum conditions for enzymatic hydrolysis were determined as follows: pH 5.0, temperature 37 °C, ratio of snailase/substrate 0.8, substrate concentration 20 mg·mL(-1), and reaction time 12 h. Under the optimum conditions, the transforming rate of naringenin from naringin for inclusion complexes and free naringin was 98.7% and 56.2% respectively, suggesting that beta-CD complexation can improve the aqueous solubility and consequently the enzymatic hydrolysis rate of naringin.

Encapsulation of complex extracts in beta-cyclodextrin: an application to propolis ethanolic extract

Propolis ethanolic extracts (PE) are rather complicated mixtures of bioactive compounds belonging to several chemical classes. The potential use of beta-cyclodextrin (beta-CD) cavity for the incorporation of specific PE components, aiming to increase their solubility in water, was studied in a Greek propolis, which was rich in polyphenols and terpenes. The PE/beta-CD inclusion complexes were prepared by sonication of PE suspensions in aqueous solutions of beta-CD, followed by filtration and freeze-drying. The aqueous solubility of PE in the presence of beta-CD was studied by the construction of solubility diagrams and by determining the fraction of PE constituents that was dissolved in water. Encapsulation efficiencies were found to be higher (9.4-23.3%) for relatively small aromatic molecules like cinnamic and benzoic acid derivatives and lower for terpenic acids (5.0-6.7%), anthraquinones (3.6-8.4%) and flavonoids (4.0-10.7%). The respective in vitro solubilities in simulated gastric fluid followed an opposite trend, being lower for the relatively small aromatic molecules. It is concluded that the encapsulation in beta-CD may increase the solubility of PE constituents in a manner related to their structure, while the amount of substances released will depend both on their chemical properties and on their relative abundance in the matrix.

Studies on the interactions between some flavonols and cyclodextrins

The interactions of some natural flavonols with alpha, beta- and gamma-Cds have been investigated. Guest molecules were galangin, kaempferol and quercetin. Inclusion complexes were prepared by kneading and freeze-drying. The complexes were characterized using different physico-chemical methods based on differential scanning calorimetry (DSC), infrared spectroscopy (IR) and NMR spectroscopy. In the proton and carbon spectra the effects of complexation on the chemical shifts of the internal and external protons of Cds in the presence of each flavonoid were observed. Moreover, the water-solubility of the flavonols in the presence of Cds was also evaluated. The increased solubility of quercetin and kaempferol in the presence of beta-Cd was evidenced. For all three guests, multidimensional NMR experiments in DMSO and water are consistent with dynamic binding processes, dominated by insertion of the B ring into the wider rim of the Cd cavity.

1H NMR study of inclusion compounds of phenylurea derivatives in beta-cyclodextrin

Proton nuclear magnetic resonance spectroscopy ((1)H NMR), which has become an important tool for the study "in situ" of beta-cyclodextrin (beta-CD) complexes, was used to study and structurally characterize the inclusion complexes formed between beta-CD and isoproturon, fenuron, monuron and diuron. The high variation of the chemical shifts from the proton located inside the cavity (H-3, H-5 and H-6) coupled with the non variation of the one located outer sphere of the beta-CD (H-1, H-2 and H-4) provided clear evidence of the inclusion phenomena. Two-dimensional rotating frame Overhauser effect spectroscopy (ROESY) experiments were carried out to further support the proposed inclusion mode.

Use of 1H-NMR spectroscopy to determine the enantioselective mechanism of neutral and anionic cyclodextrins in capillary electrophoresis

One-dimensional (ID) and two-dimensional (2D) 1H nuclear magnetic resonance (NMR) techniques have been used to investigate the chiral recognition process in capillary electrophoresis (CE) for seven different cyclodextrins (CDs) with the calcium channel blocker amlodipine as a model compound. These include five neutral CDs (alpha-CD, beta-CD, gamma-CD, hydroxypropyl-beta-CD and hydroxyethyl-beta-CD) and two anionic CDs (sulphobutyl-ether-beta-CD and carboxymethyl-beta-CD) where mixtures of amlodipine with each of the seven CDs were examined by 1D NMR in deuterated phosphate buffer at pD 3.4. The resonance shift of signals with added CD, relative to the CD-free position (shift displacement, delta delta) and shift non-equivalence (delta delta *) of enantiomeric signals shifted relative to each other after addition of CD were examined for non-overlapped protons of amlodipine. The possible correlations of NMR shift non-equivalence data with chiral separation in CE for amlodipine have been critically assessed. Qualitative differences in the 1D NMR shifts and enhanced enantioselectivity in CE were observed for amlodipine with sulphobutyl-ether-beta-CD. Further experiments on the through-space interactions using 2D rotating frame nuclear Overhauser effect spectroscopy (ROESY) indicated that there was no association between internal glucopyranose hydrogen atoms and the aromatic hydrogens of amlodipine. This gives evidence for the aromatic ring not being included in this CD. Moreover, data from spin-lattice relaxation times (T1) measured for amlodipine in the free state and after addition of the anionic sulphobutyl-ether-beta-CD indicate that the aromatic moiety of amlodipine is not included into the sulphobutyl-ether-beta-CD cavity. There is evidence that it interacts with the sulphobutyl side chains, and may adopt a preferred orientation outside the sulphobutyl-ether-beta-CD toroid itself.