β-Cyclodextrin Inclusion Complexes of 2-Hydroxyfluorene and 2-Hydroxy-9-fluorenone: Differences in Stoichiometry and Excited State Prototropic Equilibrium

Probing the interaction between encapsulated ethoxyquin and its β-cyclodextrin inclusion complex with bovine serum albumin

Ethoxyquin (EQ) is a synthetic antioxidant that is derived from quinolines and found in many meat products. EQ is strictly regulated in feed due to its potential health implications. An investigation of the interaction mechanism between EQ and transporter protein before and after β-cyclodextrin (β-CD) encapsulation was conducted with the use of multi-spectroscopy, cyclic voltammetry, and molecular docking. EQ formed complexes with bovine serum albumin (BSA), and affected secondary structure and microenvironment polarity of BSA. However, at 298 K, EQ's fluorescence quenching constants decreased from (9.81 ± 0.05) × 103 L mol-1 to (4.94 ± 0.09) × 103 L mol-1, binding constants decreased from (10.28 ± 0.02) × 103 L mol-1 to (2.08 ± 0.07) × 103 L mol-1, after encapsulation in β-CD as well as the binding distance increased. β-CD contains part of EQ in its hydrophobic cavity, inhibiting its binding to BSA. β-CD inclusion complex prevented adverse effects of EQ on BSA conformation. However, β-CD encapsulation had no effect on EQ's antioxidant activity.

Interactions of Sodium Salicylate with β-Cyclodextrin and an Anionic Resorcin[4]arene: Mutual Diffusion Coefficients and Computational Study

The interaction between sodium salicylate (NaSal) and the two macrocycles 5,11,17,23-tetrakissulfonatomethylene-2,8,14,20-tetra(ethyl)resorcinarene (Na₄EtRA) and β-cyclodextrin (β-CD) has been studied by the determination of ternary mutual diffusion coefficients, and spectroscopic and computational techniques. The results obtained by the Job method suggest that the complex formation is given in a 1:1 ratio for all systems. The mutual diffusion coefficients and the computational experiments have shown that the β-CD-NaSal system presents an inclusion process, whereas the Na₄EtRA-NaSal system forms an outer-side complex. This fact is also in line with the results obtained from the computational experiments, where the calculated solvation free energy has been found to be more negative for the Na₄EtRA-NaSal complex because of the partial entry of the drug inside the Na₄EtRA cavity.

Affinity variation in the interactions of tryptophan- β-cyclodextrin-platinum complex with G-quadruplex and duplex DNAs

DNA forms non-canonical Guanine-rich-quadruplex structures that play crucial roles such as maintenance of the telomere, transcription, and replication. Selective binding of small molecular ligands to G-quadruplexes and stabilization of them gain importance in the control of cell proliferation and development of therapeutics. In this paper, we report the synthesis of a tryptophan-β-cyclodextrin complex and its platinum complex. The binding interaction of the synthesized Trp-β-CD-Pt compound with various DNAs, including a duplex DNA and three quadruplexes, are investigated. The binding of the compound to quadruplexes shows a general increase in the binding strength compared to the strength of binding with the duplex, CT-DNA. The compound reveals the strongest binding with kit22. An enhancement of fluorescence is generally observed when the ligand binds to all the DNAs, except myc22. The structure of the host: guest complex with Berberine, a model G-quadruplex binding ligand, is investigated using 2 D ROESY spectroscopy. The host: guest binding is strong and the DNA interaction does not extract much of the Berberine molecule from the complex. The differential bindings of the ligand in free- and Berberine-loaded forms with different G-quadruplexes are discussed in detail based on binding strengths and the modulation of fluorescence.Communicated by Ramaswamy H. Sarma.

Synthetic approach toward spiro quinoxaline-β-lactam based heterocyclic compounds: Spectral characterization, SAR, pharmacokinetic and biomolecular interaction studies

Series of spiro quinoxaline-β-lactam based heterocyclic compounds (QL 1 - QL 21) were synthesized and characterized by spectroscopic techniques like ¹H-NMR, LC-MS, FT-IR spectroscopy and elemental analysis. The binding mode and binding strength between compounds and calf thymus-DNA were estimated by UV-visible spectroscopy, viscosity measurement and molecular docking studies. The compounds bind with the DNA through partial intercalation mode. In the absorption titration experiment, the K_b values for all the synthesized compounds were found in the range of 0.24-0.64 × 10⁵ M^-1. The protein binding studies of all the synthesized compounds were evaluated by absorption titration experiment, and the K_b value for all the compounds was obtained in the range of 0.030-1.571 × 10⁴ M^-1. The compounds were screened against two Gram (+ve) and three Gram (-ve) bacteria for antimicrobial activity. The MIC values for all the synthesized compounds were found in 95-255 µM. The LC₅₀ values (cytotoxicity) of the synthesized compounds (QL 1-QL 21) were found in the range of 4.00-12.89 µg/mL. The ADME study was carried out using the online platform SwissADME and admetSAR to evaluate the pharmacokinetic profile of all the synthesized compounds. All the compounds were screened for anticancer activity against the human osteosarcoma (MG-63) cell line. The result shows that all the compounds exhibit effective anticancer activity.Communicated by Ramaswamy H. Sarma.

Loading of atorvastatin and linezolid in β-cyclodextrin-conjugated cadmium selenide/silica nanoparticles: A spectroscopic study

The preparation of β-cyclodextrin-conjugated cadmium selenide-silica nanoparticles, the loading of two drugs viz., Atorvastatin and linezolid in the cyclodextrin cavity, and the fluorescence energy transfer between CdSe/SiO2 nanoparticles and the drugs encapsulated in the cyclodextrin cavity are reported in this paper. IR spectroscopy, X-ray diffractometry, transmission electron microscopy, and particle size analysis by light-scattering experiment were used as the tools of characterizing the size and the crystal system of the nanoparticles. The nanoparticles fall under hexagonal system. The silica-shell containing CdSe nanoparticles were functionalized by reaction with aminoethylamino-β-cyclodextrin. Fluorescence spectra of the nanoparticles in their free and drug-encapsulated forms were studied. The FÖrster distances between the encapsulated drugs and the CdSe nanoparticles are below 3nm. The change in the FÖrster resonance energy parameters under physiological conditions may aid in tracking the release of drugs from the cavity of the cyclodextrin.

A DFT study of infrared spectra and Monte Carlo predictions of the solvation shell of Praziquantel and β-cyclodextrin inclusion complex in liquid water

In this paper, we report a theoretical study of the inclusion complexes of Praziquantel (PZQ) and β-cyclodextrin (β-CD) in liquid water. The starting geometry has been carried out by molecular mechanics simulations, and afterwards optimized in B3LYP level with a 6-311G(d) basis set. Monte Carlo simulations have been used to calculate the solvation shell of the PZQ/β-CD inclusion complexes. Moreover, the vibrational frequencies and the infrared intensities for the PZQ/β-CD complex were computed using the B3LYP method. It is demonstrated that this combined model can yield well-converged thermodynamic data even for a modest number of sample configurations, which makes the methodology particularly adequate for understanding the solute-solvent interaction used for generating the liquid structures of one solute surrounded by solvent molecules. The complex solvation shell showed an increase of the water molecule level in relation to the isolated PZQ molecule because of the hydrophilic effect of the CD molecule. The infrared spectra showed that the contribution that originated in the PZQ molecule was not predominant in the upper-wave number region in the drug/β-CD. The movement that purely originated in the PZQ molecule was localized in the absorption band, ranging from 1328 to 1688cm(-1).

Enhanced Zn2+ion-sensing behavior of a benzothiazole derivative on encapsulation by β-cyclodextrin

We report, in this paper, a benzothiazole derivative which shows selective binding of zinc ions among a pool of metal ions and the enhanced selectivity of the same metal ion by the derivative in its β-cyclodextrin bound form.

Molecularly imprinted electrochemical sensor based on an electrode modified with an imprinted pyrrole film immobilized on a β-cyclodextrin/gold nanoparticles/graphene layer

A novel molecularly imprinted electrochemical sensor was constructed for the sensitive detection of quercetin (Qu) based on a glassy carbon electrode (GCE) modified with β-cyclodextrin (β-CD), gold nanoparticles(AuNPs) and graphene (GR).

The role of encapsulation by β-cyclodextrin in the interaction of raloxifene with macromolecular targets: a study by spectroscopy and molecular modeling

We report the binding of the drug raloxifene with Calf thymus DNA (ctDNA) and bovine serum albumin (BSA) in the presence and absence of β-cyclodextrin (β-CD) and explain the influence of β-cyclodextrin on the binding of the drug to macromolecules. UV-Vis absorption, fluorescence, proton nuclear magnetic resonance and two-dimensional rotating-frame nuclear overhauser effect spectroscopic techniques are used to study the stoichiometry and the binding strength of the complexes. Molecular modeling is used in combination with other techniques to propose the structure of the inclusion complex and the interaction with ctDNA. The Stern-Volmer quenching constants of the interaction of raloxifene with ctDNA in aqueous and in β-CD solution are compared. The competition for binding of ctDNA with raloxifene and Methylene Blue is studied. The apparent binding constant and the number of binding sites for the binding of raloxifene with BSA in aqueous solution are significantly different from those in the presence of β-CD. The influence of β-CD on the binding of the small molecules with biological macromolecules is discussed. We infer that the binding strengths between raloxifene and macromolecules, viz., ctDNA and BSA are influenced by the β-CD encapsulation. These results may suggest new ways to tune the drug binding to biomacromolecules by encapsulating specific moieties of drugs.

The Unusual Fluorescence Quenching of Coumarin 314 by β-Cyclodextrin and the Effect of β-Cyclodextrin on its Binding with Calf Thymus DNA

This paper discusses the binding of a laser dye, Coumarin 314 with β-cyclodextrin, studied mainly by UV-visible spectroscopy, 2D rotating-frame nuclear Overhauser effect spectroscopy (ROESY), steady-state spectroscopy and time-resolved fluorescence spectroscopy. The role of β-cyclodextrin on the binding of Coumarin 314 with calf thymus DNA was investigated. Coumarin 314 shows a hyperchromic shift of absorption and a quenching of fluorescence due to binding with β-cyclodextrin. The fluorescence quenching is non-linear and the reason for the non-linearity is discussed. The unusual fluorescence quenching on Coumarin 314–β-cyclodextrin binding is rationalised from the effect of acidity on absorption, fluorescence, and molecular modelling studies. Additional proof for the mode of binding is given by 2D ROESY. The capped and exposed portions of the Coumarin 314 molecule in the Coumarin 314–β-cyclodextrin complex when binding with calf thymus DNA were visualised based on spectral and molecular modelling studies.