Investigation of the interactions between the hydrophobic cavities of cyclodextrins and pullulanase

Stability, Antioxidant Activity and Intestinal Permeation of Oleuropein Inclusion Complexes with Beta-Cyclodextrin and Hydroxypropyl-Beta-Cyclodextrin

Compared to beta-cyclodextrins (beta-CD), hydroxypropyl-beta-cyclodextrins (HP-beta-CD) are a more popular material used to prepare inclusion complexes due to their superior solubility and intestinal absorption. In this study, oleuropein (OL) inclusion complexes with beta-CD (beta-CD:OL) and HP-beta-CD (HP-beta-CD:OL) were prepared and the formation of inclusion complexes was validated by IR, PXRD, and DSC. A phase solubility test showed that the lgK (25 °C) and binding energy of beta-CD:OL and HP-beta-CD:OL was 2.32 versus 1.98, and −6.1 versus −24.66 KJ/mol, respectively. Beta-CD:OL exhibited a more powerful effect than HP-beta-CD:OL in protecting OL from degradation upon exposure to light, high temperature and high humidity. Molecular docking, peak intensity of carbonyls in IR, and ferric reducing power revealed that beta-CD:OL formed more hydrogen bonds with the unstable groups of OL. Both inclusion complexes significantly enhanced the solubility, intestinal permeation and antioxidant activity of OL (p < 0.05). Though HP-beta-CD:OL had higher solubility and intestinal absorption over beta-CD:OL, the difference was not significant (p > 0.05). The study implies that lower binding energy is not always associated with the higher stability of a complex. Beta-CD can protect a multiple-hydroxyl compound more efficiently than HP-beta-CD with the intestinal permeation comparable to HP-beta-CD complex.

Microbial starch debranching enzymes: Developments and applications

Starch debranching enzymes (SDBEs) hydrolyze the α-1,6 glycosidic bonds in polysaccharides such as starch, amylopectin, pullulan and glycogen. SDBEs are also important enzymes for the preparation of sugar syrup, resistant starch and cyclodextrin. As the synergistic catalysis of SDBEs and other starch-acting hydrolases can effectively improve the raw material utilization and production efficiency during starch processing steps such as saccharification and modification, they have attracted substantial research interest in the past decades. The substrate specificities of the two major members of SDBEs, pullulanases and isoamylases, are quite different. Pullulanases generally require at least two α-1,4 linked glucose units existing on both sugar chains linked by the α-1,6 bond, while isoamylases require at least three units of α-1,4 linked glucose. SDBEs mainly belong to glycoside hydrolase (GH) family 13 and 57. Except for GH57 type II pullulanse, GH13 pullulanases and isoamylases share plenty of similarities in sequence and structure of the core catalytic domains. However, the N-terminal domains, which might be one of the determinants contributing to the substrate binding of SDBEs, are distinct in different enzymes. In order to overcome the current defects of SDBEs in catalytic efficiency, thermostability and expression level, great efforts have been made to develop effective enzyme engineering and fermentation strategies. Herein, the diverse biochemical properties and distinct features in the sequence and structure of pullulanase and isoamylase from different sources are summarized. Up-to-date developments in the enzyme engineering, heterologous production and industrial applications of SDBEs is also reviewed. Finally, research perspective which could help understanding and broadening the applications of SDBEs are provided.

Supramolecular Interactions between β-Cyclodextrin and the Nucleobase Derivatives of Ferrocene

Novel conjugates of ferrocene with uracil, 5-fluorouracil, tegafur, or acyclovir are reported. Their synthesis involved (i) the azide-alkyne 1,3-dipolar cycloaddition or (ii) the formation of the ester linkage. For the first time, we present an in-depth insight into the supramolecular interactions between β-cyclodextrin and ferrocene-nucleobase derivatives. Spectroscopic and voltammetric analyses performed within this work suggested that the ferrocene or adamantane unit of the conjugates interacted with the β-cyclodextrin's inner cavity. The methods applied for the supramolecular studies included ¹H-¹H ROESY NMR, ¹H NMR titration, Fourier-transform infrared spectroscopy, cyclic voltammetry, fluorescence spectra titration, and ¹H DOSY NMR. ¹H DOSY NMR was also employed to evaluate the apparent binding constants for all the complexes. The ferrocene-acyclovir conjugate Fc-5 featured the highest apparent binding constant value among all the complexes tested.

Inclusion Complex of O-phthalaldehyde-Buprofezin with Dimethyl-β-Cyclodextrin Using Thermochemically-Induced Fluorescence Derivatization (TIFD) Method and its Analytical Application in Waters

Improvement of the TIFD method to determine buprofezin (BUP) founded on the O-phthalaldehyde (OPA)-thermoproduct complex of buprofezin (OPA-BUP) with dimethyl-β-cyclodextrin (DMβCD) was investigated at 25 °C. The TIFD method developed in DMβCD medium, was optimized with respect to the reaction time, DMβCD concentration and pH. Based on the inclusion reaction, the OPA-BUP: DMβCD inclusion complex was developed in two aqueous media pH 7 and pH 13. A 1:1 stoichiometric ratio of OPA-BUP: DMβCD complex was obtained. The binding constants (K) and Gibbs energy (ΔG°) values increasing and decreasing with pH, respectively, show the spontaneous and thermodynamically favorable at 25 °C of the inclusion complexes formation. Normalized TIFD spectra were measured at 425 nm for emission and at 345 nm for excitation. Limits of detection (LOD) and quantification (LOQ) obtained, according to the pH, were in the ranges 0.05-0.1 ng mL ^{̶ 1} and 0.2-0.4 ng mL ^{̶ 1}, respectively. Relative standard deviation (RSD) values, less than 1.3% corroborated TIFD method repeatability in DMβCD medium. Solid phase extraction (SPE) procedure which was used for quantitative analysis of natural water samples collected from Niayes area, led to satisfactory recovery rates values 99.5-117.3%.

Preservation of Bacillus firmus strain 37 and optimization of cyclodextrin biosynthesis by cells immobilized on loofa sponge

The preservation of Bacillus firmus strain 37 cells by lyophilization was evaluated and response surface methodology (RSM) was used to optimize the β-cyclodextrin (β-CD) production by cells immobilized on loofa sponge. Interactions were studied with the variables temperature, pH and dextrin concentration using a central composite design (CCD). Immobilization time influence on β-CD production was also investigated. B. firmus strain 37 cells remained viable after one year of storage, showing that the lyophilization is a suitable method for preservation of the microorganism. From the three-dimensional diagrams and contour plots, the best conditions for β-CD production were determined: temperature 60 °C, pH 8, and 18% dextrin. Considering that the amount of dextrin was high, a new assay was carried out, in which dextrin concentrations of 10, 15, and 18% were tested and the temperature of 60 °C and pH 8 were maintained. The results achieved showed very small differences and therefore, for economic reasons, the use of 10% dextrin is suggested. Increasing the immobilization time of cells immobilized on synthetic sponge the β-CD production decreased and did not change for cells immobilized on loofa sponge. The results of this research are important for microorganism preservation and essential in the optimization of the biosynthesis of CD.