Inclusion complexation of hydrocortisone butyrate with cyclodextrins and dimethyl-β-cyclodextrin in aqueous solution and in solid state

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.

Study of the physicochemical properties of trimethoprim with β-cyclodextrin in solution

The behavior of trimethoprim (TMP) in aqueous solutions containing different concentration of beta-cyclodextrin (beta-CD) was characterized by the solubility method, UV spectrophotometry and differential scanning calorimetry (DSC). The UV spectra enhancement of TMP as result of complex with beta-CD was investigated. Complexation with beta-CD increase the TMP aqueous solubility and the phase solubility diagram was A(L) type. Thermodynamic parameters of the complex process, K, DeltaG, DeltaH and DeltaS, were determined from the phase solubility diagram at 298 and 318 K, respectively. The experimental results indicated that the complex process was an enthalpy-driven process. Mechanism of the complex of beta-CD with TMP was further discussed using the molecular model program. Results showed that the 3,4,5-trimethoxybenzyl group of the TMP was partly embedded in the cavity of beta-CD.

Solid-state nuclear magnetic resonance spectroscopy--pharmaceutical applications

Solid-state nuclear magnetic resonance (NMR) spectroscopy has become an integral technique in the field of pharmaceutical sciences. This review focuses on the use of solid-state NMR techniques for the characterization of pharmaceutical solids (drug substance and dosage form). These techniques include methods for (1) studying structure and conformation, (2) analyzing molecular motions (relaxation and exchange spectroscopy), (3) assigning resonances (spectral editing and two-dimensional correlation spectroscopy), and (4) measuring internuclear distances.

Determination of apparent association constants of steroid-cyclodextrin inclusion complexes using a modification of the Hummel-Dreyer method

A modified Hummel-Dreyer method was used to calculate the apparent association constants of steroid-cyclodextrin inclusion complexes. An external calibration technique was employed, using the y-intercept from a plot of peak area versus concentration to correct for sample solvent effects. Mobile phase temperature and sample diluent organic content were found to be critical factors affecting the accuracy and reproducibility of the results. For four of six sets of data, the modified Hummel-Dreyer method yielded statistically equivalent results to another HPLC method for determining apparent association constants. Limitations of the modified Hummel-Dreyer method are discussed. In particular, the accuracy of the method is poor when measuring small apparent association constants.

Characterization of inclusion complexes of betamethasone-related steroids with cyclodextrins using high-performance liquid chromatography

HPLC was used to study the inclusion complexes formed between various beta- and gamma-cyclodextrins and a series of corticosteroids related to betamethasone. Apparent association constants were measured in acetonitrile-water for a set of 13 steroids. An increase in the stability of the steroid-cyclodextrin complex is observed at lower concentrations of acetonitrile. The effects of the nature of the halide at the 9-position, the location of a double bond within the C-ring, substitution at the 9- and 11-positions, and modification of the D-ring of the steroid backbone were studied. The 11- and 17-positions were found to be critically involved in the inclusion process. Larger apparent association constants were obtained with gamma-cyclodextrin (gamma-CD) than with beta-cyclodextrin (beta-CD) due to the increased diameter of the gamma-CD cavity. Van't Hoff plots were constructed to examine the thermodynamic properties of the inclusion process. Plots constructed using retention factors were found to be nonlinear when gamma-CD was present in the mobile phase. This is due to an increase in the strength of the inclusion complex as temperature decreases. Plots constructed using apparent association constants were linear, indicating that the mechanism of inclusion does not change over the range of temperatures studied (10 to 80 degrees C). Enthalpy-entropy compensation was observed for 11 of the 13 steroids studied. The usefulness of cyclodextrins to achieve the separation of steroids in HPLC is discussed and a practical application for the analysis of a steroid and three potential impurities is described.

Simultaneous interaction of steroidal drugs with gamma- and hydroxypropyl-beta-cyclodextrin studied by charge-transfer chromatography

The simultaneous interaction of 15 steroidal drugs with tau-cyclodextrin (tauCD) and hydroxypropyl-beta-CD (HPbetaCD) was determined by charge transfer chromatography and the relative strength of interaction was calculated for each drug-tauCD-HPbetaCD ternary complex. The mixture of CDs interacted with each steroidal drugs decreasing the lipophilicity of the guest molecules. The chemical structure of steroidal drugs markedly influenced their capacity to interact with the mixture of CDs, the more lipophilic compounds formed stronger complexes with CDs. In the overwhelming majority of cases the stability of drug-tauCD-HPbetaCD system was higher than those of binary (drug-tauCD and drug-HPbetaCD) system indicating the probability of ternary complex formation. The data indicated that the ternary complex formation has to be taken into consideration in pharmaceutical formulations containing more than one type of CD or CD derivatives.

Inclusion complex formation of steroidal drugs with hydroxypropyl-beta-cyclodextrin studied by charge-transfer chromatography

The interaction between 17 steroidal drugs and hyroxypropyl-beta-cyclodextrin (HPbetaBCD) was determined by charge-transfer chromatography and the relative strength of interaction was calculated. HPbetaCD interacted with each steroidal drugs decreasing the hydrophobicity of the guest molecules. The relative strength of interaction considerably depended on the structure of the drug molecule. Hydrophobicity parameters of drugs significantly influenced the strength of interaction indicating the involvement of hydrophobic forces in the binding of drugs to HPbetaCD. The marked influence of HPbetaCD on the hydrophobicity of drugs suggests that this interaction may modify the biological properties (adsorption, uptake, half-life etc.) of drug-HPbetaCD complexes drug resulting in modified efficacy.

Interaction of taxol and other anticancer drugs with alpha-cyclodextrin

The interaction between 23 anticancer drugs and alpha-cyclodextrin (alpha-CD) was studied by reversed-phase charge-transfer thin-layer chromatography and the relative strength of interaction was calculated. As alpha-CD has smaller cavity than beta- and tau-CD it interacted only with 10 anticancer drugs proving the relatively poor complex forming capacity of alpha-CD. The hydrophobicity of host-guest inclusion complex was always different from that of the uncomplexed drug suggesting that the complex formation may influence the uptake, absorption, half-life etc. of the original drug. The inclusion forming capacity of drugs differed considerably according to their chemical structure. The intensity of interaction significantly depended on the hydrophobicity of the guest molecule proving the preponderant role of hydrophobic interactions in inclusion complex formation.

Interaction of carboxymethyl-gamma-cyclodextrin with anticancer drugs studied by charge-transfer thin-layer chromatography

The interaction between 22 anticancer drugs and carboxymethyl-gamma-cyclodextrin (CM-gamma-CD) was studied by reversed-phase charge-transfer thin-layer chromatography and the relative strength of interaction was calculated. CM-gamma-CD formed inclusion complexes with 11 compounds, the complex always being more hydrophilic than the uncomplexed drug. The inclusion forming capacity of drugs differed considerably according to their chemical structure. Both principal component analysis and cluster analysis found a relationship between the inclusion complex forming capacity and hydrophobicity parameters of anticancer drugs. This result suggests that the preponderant role of hydrophobic interactions is in inclusion complex formation.