Thermodynamic parameters for the complexation of water‐insoluble betulin derivatives with (2‐hydroxypropyl)‐γ‐cyclodextrin determined by phase‐solubility technique combined with capillary zone electrophoresis

Evaluation of the effect of background electrolyte composition and independence of parameters in determining binding constants of betulin derivatives to β- and dimethyl-β-cyclodextrins by affinity capillary electrophoresis

The values of the apparent binding constants for β-cyclodextrin complexes of betulin derivatives determined by mobility shift affinity capillary electrophoresis were found to be independent of the composition of the two background electrolytes used (tetraborate buffer, pH 9.18, and phosphate buffer, pH 8.00, both of them with 20 mM ionic strength). It has been found that, if there is not a constant plateau on the binding curve, then four independent parameters can be determined: binding constants (also referred to as stability, association or formation constants) and ionic mobilities of 1:1 and 1:2 complexes. However, at least 10-12 data points in the binding curve should be used to reliably estimate the parameters. For the first time, the apparent binding constants for complexes of ester betulin derivatives with dimethyl-β-cyclodextrin have been determined by mobility shift affinity capillary electrophoresis. The logarithms of the constants for 1:1 and 1:2 complexes at 25°C for betulin 3,28-diphthalate with a 95 % confidence interval are 4.98 (4.95-5.01) and 7.52 (7.26-7.68); for betulin 3,28-disulfate, the values are 4.97 (4.89-5.03) and 8.24 (6.82 - 8.52). It has been found that betulin 3,28-disuccinate forms only a 1:1 complex and the binding constant logarithm is 5.25 ± 0.02. This article is protected by copyright. All rights reserved.

The Role of Cyclodextrins in the Design and Development of Triterpene-Based Therapeutic Agents

Triterpenic compounds stand as a widely investigated class of natural compounds due to their remarkable therapeutic potential. However, their use is currently being hampered by their low solubility and, subsequently, bioavailability. In order to overcome this drawback and increase the therapeutic use of triterpenes, cyclodextrins have been introduced as water solubility enhancers; cyclodextrins are starch derivatives that possess hydrophobic internal cavities that can incorporate lipophilic molecules and exterior surfaces that can be subjected to various derivatizations in order to improve their biological behavior. This review aims to summarize the most recent achievements in terms of triterpene:cyclodextrin inclusion complexes and bioconjugates, emphasizing their practical applications including the development of new isolation and bioproduction protocols, the elucidation of their underlying mechanism of action, the optimization of triterpenes’ therapeutic effects and the development of new topical formulations.

Electrophoretic mobility of ester betulin derivatives and their complexation with γ-cyclodextrin studied by capillary electrophoresis in aqueous solutions at different pH values

In this article, capillary electrophoresis was used to measure the effective electrophoretic mobility of ester betulin derivatives as a pH function and to study their complexation with γ-cyclodextrin (γ-CD). The electrophoretic mobility of betulin 3,28-diphthalate (DPhB) and 3,28-disuccinate (DScB) changed unusually with decreasing pH: instead of decreasing, it first increased and then decreased. This fact as well as the turbidity of sample solutions at pH from 2.5 to 6, broadening of electrophoretic peaks and a decrease in the surface tension of the solutions indicates that these betulin derivatives, being amphiphilic compounds and weak acids, exist as micelles in aqueous solutions at pH 6 and below. The inclusion complexation of betulin derivatives with γ-CD at pH 9.18 and 4.5 was studied by mobility shift affinity capillary electrophoresis. At pH 9.18, the apparent binding (stability) constant logarithms for 1:1 γ-CD complexes of DPhB, betulin 3,28-disulfate (DSB) and DScB with 95% confidence interval limits were equal to 7.44 ± 0.02, 7.09 (7.01-7.19), and 6.97 (6.87-7.08) at 25°C, respectively. At pH 4.5, the binding constant for the DSB complex was slightly lower, while the micelle formation did not allow determining the exact values of the constants for the DPhB and DScB complexes.

Molecular encapsulation of andrographolide in 2-hydroxypropyl-β-cyclodextrin cavity: synthesis, characterization, pharmacokinetic and in vitro antiviral activity analysis against SARS-CoV-2

In present investigation, AND-2-HyP-β-CYD (Andrographolide-2-Hydroxypropyl-β-cyclodextrin) complex was synthesized and characterized for antiviral and pharmacokinetic profile. The linear host-guest relation suggested synthesis of a 1:1 complex of AND with 2-HyP-β-CYD by inclusion mode. The Kc, stability constant of the two phase system of AND with 2-HyP-β-CYD computed to be 38.60 x 10⁻³M. ¹H NMR spectrum of AND indicated the presence of triplet at 6.63-ppm which was up-fielded in AND-2-HyP-β-CYD complex at 6.60-ppm (doublet) confirmed the insertion of AND in cavity of 2-HyP-β-CYD through lactone ring. AND-2-HyP-β-CYD complex exhibited the IC₅₀ of 0.1-μg.mL⁻¹ (E gene) and 0.29-μg.mL⁻¹ (N gene) against SARS-CoV-2 infected Vero6 cells. Moreover, a 1.5-fold increment in extent of absorption of AND was noticed post complexation. The bioavailability was estimated to be 15.87 ± 3.84% and 23.84 ± 5.46%, respectively for AND and AND-2-HyP-β-CYD complex. AND-2-HyP-β-CYD complex may be a prospective candidate for further studies to evolve as a clinically viable formulation against SARS-CoV-2.

Determining binding constants for 1:1 and 1:2 inclusion complexes of ester betulin derivatives with (2-hydroxypropyl)-β-cyclodextrin by affinity capillary electrophoresis

The complexation of ester betulin derivatives with (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD) was studied by mobility shift affinity CE. Electrophoretic mobility for triangular peaks was calculated using the parameter a₁ of the Haarhoff-Van der Linde function instead of the peak top time. Dependences of the viscosity corrected electrophoretic mobility on HP-β-CD concentration were not described on the basis of only complexes with 1:1 stoichiometry due to the fact that these binding curves did not reach a plateau. However, the dependences were well described taking into account both 1:1 and 1:2 complexes. The presence of higher order equilibria was also revealed by x-reciprocal plots. The values of apparent binding constant logarithm, obtained for the first time, for 1:1 and 1:2 HP-β-CD complexes of betulin 3,28-diphthalate and betulin 3,28-disuccinate with 95% confidence interval limits in brackets are the same within error and are equal to 4.85 (4.73-4.95), 8.56 (7.75-8.82), 4.92 (4.86-4.97), and 8.54 (8.23-8.72) at 25°C, respectively. These values for 1:1 and 1:2 HP-β-CD complexes of betulin 3,28-disulfate at 25°C are 4.61 (4.57-4.64) and 7.11 (6.57-7.34), respectively. The binding constants for betulin 3,28-disulfate agree with the previously obtained results from the separation in the thermostatted capillary segment.

A LSER-based model to predict the solubilizing effect of drugs by inclusion with cucurbit[7]uril

A LSER model was built for predicting the solubility of inclusion complexes.