Spectroscopic studies for the inclusion complexation of ketoprofen enantiomers with β-cyclodextrin

The Binding Mechanism Between Cyclodextrins and Anticancer Drug Noscapine: A Spectroscopic and Molecular Docking Study

In this paper the binding of noscapine (NOS) as an anticancer drug with poor bioavailability and low solubility with beta and methyl-beta cyclodextrins (β-CD and M-β-CD) as the biocompatible drug carriers were discussed using ultraviolet-visible, fluorescence and nuclear magnetic resonance spectroscopy, as well as molecular docking. The absorption of NOS changed when it was bound to both cyclodextrins, resulting in a hyperchromic shift. It formed a 1:1 stoichiometry inclusion complex with both cyclodextrins according to the Benesi-Hildebrand equation. The binding affinity was larger in NOS-M-β-CD (5.9 (± 0.66) × 103 M- 1) than NOS-β-CD (3.7 (± 0.22) × 103 M- 1) complex. The fluorescence emission band of NOS at 408 nm was quenched when NOS was complexed with β-CD, and enhanced in the presence of M-β-CD, while the shoulder at 350 nm was enhanced selectively when NOS was complexed with M-β-CD. The fluorescence quenching of NOS with β-CD showed a negative deviation from the Stern-Volmer. The thermodynamic parameters have been estimated with the help of the Van't Hoff equation in different temperatures, and a dynamic mechanism was proposed for quenching. Also, both ΔH and ΔS have positive values thus the main interactions result in hydrophobic forces. Moreover, the negative value of ΔG indicates that the bonding process is spontaneous. 1H NMR chemical shift changes were observable for NOS and both CDs protons due to the chemical environment changes of some nuclei upon complexation. The molecular docking results revealed that the 1:1 inclusion complex possesses a good molecular shape complementarity score for their most probable structures, and indicated that the M-β-CD inclusion system gave the higher complexation efficiency. The binding energy values for β-CD and M-β-CD were determined to be -6.7 and - 9.5 kcal/mol, respectively. These findings suggest the same as the result of experimental tests that the NOS-M-β-CD complex is more stable than the NOS-β-CD complex.

Histidine-modified pillar[5]arene-functionalized mesoporous silica materials for highly selective enantioseparation

Chiral enantiomers, especially the enantiomers of chiral drugs often exhibit different pharmacological activity, metabolism and toxicity, thus it is of great research significance to scientifically and reasonably develop single chiral drugs with low toxicity and high efficiency. Among them, high performance liquid chromatographic techniques based on chiral stationary phases (CSPs) has become one of the most attractive methods used to evaluate the enantiomeric purity of single-enantiomers compound of pharmacological relevance. In this work, pillar[5]arene functionalized with L- and D-histidine, respectively, were modified on the surface of mesoporous silica as novel chiral stationary phases called L/DHis-BP5-Sil. Notably, L/D-histidine had the characteristics of low steric hindrance and easy derivatization. Although the π-π interaction of imidazole group was weaker than that of benzene ring, the benzene ring bonding imidazole-conjugated ring in the structure produced better enantioseparation effect. The results showed that L/DHis-BP5-Sil can separate a variety of complex structural enantiomers with excellent reproducibility, thermal stability and separation performance. Hence, the unique advantage of the highly selective separation of L/DHis-BP5-Sil provides new insights into the enantioseparation field.

Cyclodextrin Inclusion Complexes for Improved Drug Bioavailability and Activity: Synthetic and Analytical Aspects

Many active pharmaceutical ingredients show low oral bioavailability due to factors such as poor solubility and physical and chemical instability. The formation of inclusion complexes with cyclodextrins, as well as cyclodextrin-based polymers, nanosponges, and nanofibers, is a valuable tool to improve the oral bioavailability of many drugs. The microencapsulation process modifies key properties of the included drugs including volatility, dissolution rate, bioavailability, and bioactivity. In this context, we present relevant examples of the stabilization of labile drugs through the encapsulation in cyclodextrins. The formation of inclusion complexes with drugs belonging to class IV in the biopharmaceutical classification system as an effective solution to increase their bioavailability is also discussed. The stabilization and improvement in nutraceuticals used as food supplements, which often have low intestinal absorption due to their poor solubility, is also considered. Cyclodextrin-based nanofibers, which are polymer-free and can be generated using environmentally friendly technologies, lead to dramatic bioavailability enhancements. The synthesis of chemically modified cyclodextrins, polymers, and nanosponges based on cyclodextrins is discussed. Analytical techniques that allow the characterization and verification of the formation of true inclusion complexes are also considered, taking into account the differences in the procedures for the formation of inclusion complexes in solution and in the solid state.

Chiral Discrimination Mechanisms by Silylated-Acetylated Cyclodextrins: Superficial Interactions vs. Inclusion

Cyclodextrin derivatives constitute a powerful class of auxiliary agents for the discrimination of apolar chiral substrates. Both host–guest inclusion phenomena and interactions with the derivatizing groups located on the surface of the macrocycle could drive the enantiodiscrimination; thus, it is important to understand the role that these processes play in the rational design of new chiral selectors. The purpose of this study is to compare via nuclear magnetic resonance (NMR) spectroscopy the efficiency of silylated-acetylated α-, β-, and γ-cyclodextrins in the chiral discrimination of 1,1,1,3,3-pentafluoro-2-(fluoromethoxy)-3-methoxypropane (compound B) and methyl 2-chloropropionate (MCP). NMR DOSY (Diffusion Ordered SpectroscopY) experiments were conducted for the determination of the bound molar fractions and the association constants, whereas ROESY (Rotating-frame Overhauser Enhancement SpectroscopY) measurements provided information on the hosts’ conformation and on the interaction phenomena with the guests. Compound B, endowed with fluorinated moieties, is not deeply included due to attractive Si-F interactions occurring at the external surface of the cyclodextrins. Therefore, a low selectivity toward the size of cyclodextrin cavity is found. By contrast, enantiodiscrimination of MCP relies on the optimal fitting between the size of the guest and that of the cyclodextrin cavity.

Controlled release and antibacterial properties of PEO/casein nanofibers loaded with Thymol/β-cyclodextrin inclusion complexes in beef preservation

There are still many limitations in the application of natural active compounds in meat preservation. Herein, thymol was first inserted into the cavity of β-cyclodextrin (β-CD) to form a stable inclusion complex (THY/β-CD-IC). The computational investigation showed that the optimized complexation energy for THY/β-CD-IC was -12.95 kcal mol^-1. It contributed to the improvement of the thermal stability of thymol in the inclusion compound. Furthermore, the functionalized nanofibers (THY/β-CD-IC-NFs) loaded with THY/β-CD-IC were successfully fabricated by electrospinning of the mixture of casein and polyethylene oxide. When dealing with protease-producing bacteria, controllable release of thymol from THY/β-CD-IC-NFs was achieved through the response of casein to the hydrolysis of bacterial protease. The application results indicated that the prepared THY/β-CD-IC-NFs had a long-term antimicrobial activity for chilled beef preservation during 7-days storage. The information from this study presents a feasible strategy for the development of natural extracts for use in meat preservation.

L-cysteine capped silver nanoparticles as chiral recognition sensor for ketoprofen enantiomers

A simple, inexpensive but effective approach for visual chiral recognition of ketoprofen enantiomers was developed using L-cysteine capped silver nanoparticles (L-Cys-AgNPs) as a colorimetric sensor. Upon the addition of R-ketoprofen to L-Cys-AgNPs, rapid aggregation occurred, and the solution changed color from yellow to green. However, the presence of S-ketoprofen did not induce any color change. The results were characterized using UV-Vis, FESEM, FT-IR, SERS, and zeta potential measurements. The chiral assay described in this work is easily distinguished with the naked eyes or using a UV-Vis spectrometer. The sensor revealed a good linear response to ketoprofen enantiomers in the concentration range of 8.33-33.3 μM with a detection limit of 4.52 μM and relative standard deviation of 3.73%. The proposed method was utilized for the determination of ketoprofen racemic mixtures in water samples and commercial tablets. The method excels by its simplicity, low cost, and good availability of materials.

Comprehensive Characterisation of the Ketoprofen-β-Cyclodextrin Inclusion Complex Using X-ray Techniques and NMR Spectroscopy

Racemic ketoprofen (KP) and β-cyclodextrin (β-CD) powder samples from co-precipitation (1), evaporation (2), and heating-under-reflux (3) were analysed using X-ray techniques and nuclear magnetic resonance (NMR) spectroscopy. On the basis of NMR studies carried out in an aqueous solution, it was found that in the samples obtained by methods 1 and 2, there were large excesses of β-CD in relation to KP, 10 and 75 times, respectively, while the sample obtained by method 3 contained equimolar amounts of β-CD and KP. NMR results indicated that KP/β-CD inclusion complexes were formed and the estimated binding constants were approximately 2400 M^-1, showing that KP is quite strongly associated with β-CD. On the other hand, the X-ray single-crystal technique in the solid state revealed that the (S)-KP/β-CD inclusion complex with a stoichiometry of 2:2 was obtained as a result of heating-under-reflux, for which the crystal and molecular structure were examined. Among the methods used for the preparation of the KP/β-CD complex, only method 3 is suitable.

Computational investigation on the chiral differentiation of D- and L-penicillamine by β-cyclodextrin

The identification of chiral penicillamine (Pen) is of great significance for clinical medication safety. The host-guest systems formed by enantiomers and macromolecule can be applied to differentiate the chiral drugs and enable the drug delayed release. We hereby performed the dispersion corrected density functional theory (DFT-D) calculation on the complex formed by β-cyclodextrin(β-CD) and D/L-penicillamine (D/L-Pen). The diverse encapsulation configurations with different interaction energy show that both D-Pen and L-Pen tend to longitudinally embedded into the narrow aperture of β-CD with the front part of the sulfur group and the methyl group, and the interaction energy between L-Pen and β-CD is 5.47 kJ/mol(M062XD3) lower than that between D-Pen and β-CD. Based on the computed vibration frequency of host, guest, and the most stable complex, it is found that the featured peaks attributed to the vibration of the carboxyl group of guest and the skeleton vibration of complex are the most significant spectral standard to distinguish the β-CD-D/L-Pen and β-CD. Moreover, the peaks resulted from the skeleton vibration in terahertz spectra can be also used to distinguish the complex of β-CD with chiral Pen. Through the topological analysis and the Independent Gradient Model (IGM) analysis, the O-H^…O hydrogen bond in β-CD-D-Pen is stronger than that in β-CD-L-Pen, and the van der Waals interactions such as C-H…O,C-H…N,C-H…S, O…S and C-H…C-H have the most contributions to the intermolecular interaction in β-CD-D/L-Pen. It is also noted that the H(-OH) in D-Pen and S in L-Pen contribute the most to the intermolecular interaction with β-CD in comparison with other atoms in Pen.