Examination of the physicochemical properties of caffeic acid complexed with γ-cyclodextrin

Abstract

Caffeic acid (CA) is a hydrophobic polyphenol with a high antioxidant capacity and γ-cyclodextrin (γ-CD) is a cyclic polysaccharide. The current study prepared a coprecipitate (CP), a freeze-dried (FD) preparation, a ground mixture (GM), and a physical mixture (PM) of CA and γ-CD, and this study then assessed the physicochemical properties and antioxidant capacity of these preparations. PXRD patterns revealed that a PM and a GM prepared at a certain molar ratio (CA/γ-CD =1/1) produced a diffraction peak due to CA crystals. Diffractions peaks characteristic of CA and γ-CD disappeared with the CP, but new peaks were noted. In addition, an FD with CA and γ-CD at a molar ratio of 1/1 produced a halo pattern. DSC measurements revealed that the PM produced an endothermic peak at 220 º C due to the melting of CA, but the endothermic peak due to CA disappeared with the CP, FD, and GM. IR spectra revealed that the absorption peak due to the carbonyl group (C=O) of CA shifted for both the CP and the FD. The absorption peak due to C=C in the aromatic ring of CA also shifted. These findings presumably indicate molecular interaction between CA and γ-CD when the 2 substances are present at a molar ratio of 1/1 (CA/γ-CD). In the GM, molecular interaction presumably occurred as a result of heat. The preparations were compared to CA alone in dissolution testing, which revealed that the CP and FD both had a high rate of dissolution. 1 H-1 H NMR (NOESY) spectra revealed cross peaks involving protons of the γ-CD cavity and protons of the aromatic ring of CA. Thus, the formation of CA and γ-CD inclusion complexes helped to improve the dissolution of CA and γ-CD at a molar ratio of 1/1. The CP and FD had a higher antioxidant capacity than did CA alone. This presumably indicates that the formation of CA and γ-CD inclusion complexes helped to increase the electron density of CA in the CD cavity.

Evaluation of the Molecular State of Piperine in Cyclodextrin Complexes by Near-Infrared Spectroscopy and Solid-State Fluorescence Measurements

“…In the γ CD system, the diffraction profile of GM (PP/ γ CD = 1/1) shows a halo pattern (Figure 5(j)). No peaks corresponding to PP alone are observed in the heated GM (PP/ γ CD = 1/1) pattern, but diffraction peaks corresponding to mixed hexagonal-type (2 θ = 5.9°) and monoclinic-type (2 θ = 16.7°) structures (Figure 5(k)) are discerned [15]. The characteristic diffraction pattern of the inclusion complex was thus confirmed.…”

“…Furthermore, the pattern of humidified-heat GM (PP/ γ CD = 1/1) shows the characteristic diffraction peaks of hexagonal-type (2 θ = 6.0°), tetragonal-type (2 θ = 7.5°), and monoclinic-type (2 θ = 16.7°) structures (Figure 5(m)). Tetragonal-type of γ CD complexes has been reported to change into hexagonal or monoclinic-type structures by decreasing crystalline water [15]. However, the diffraction peaks for the heated, humidified, and humidified-heated GM (PP/ γ CD = 1/1) samples were those corresponding to mixed tetragonal-type, hexagonal-type, and monoclinic-type structures.…”

“…The van der Waals forces and hydrogen bonds in the crystal structure of CD complexes have been reported to vary with the moisture and inclusion conditions [13]. In addition, a variety of methods, such as ground-mixing, freeze drying, and coprecipitation, are available for the preparation of inclusion complexes [15, 16]. The preparation of inclusion complexes using ground mixtures (GMs) is easy by exploiting mechanochemical effects.…”

Ferulic acid-β-cyclodextrin inclusion complexes: Application on the preservation of hairtail (Trichiurus lepturus)

“…FCIC was prepared using the coprecipitation method, slightly modified from Inoue et al (2015). [24] β-Cyclodextrin (0.1 M) was dissolved in 100 mL of ethanol (0.1 M) with stirring at 60°C until completely dissolved. Then, the FA solution was mixed with cyclodextrin solution to obtain cyclodextrin to FA ratios of 1:0.5, 1:1 and 1:2, which were named IC 1:0.5, IC 1:1, and IC 1:2, respectively.…”

Preparing γ-Cyclodextrin-Immobilized Starch and the Study of its Removal Properties to Dyestuff from Wastewater

“…Among three common cyclodextrins (α, β, and γ), the γ-CD has the largest cavity dimension (up to about 427 Å 3 , compared with 174 Å 3 of α-CD and 262 Å 3 of β-CD), thus it is regarded as the greater and wider inclusion capabilities to various organic molecules, and is supposed to be a more effective adsorbing material in dyestuff wastewater treatment. While the water solubility and shaping difficulty of γ-CD have restricted its application in wastewater treatment [16,17].…”