Combined use of ionic liquid and sulfobutylether-β-cyclodextrin as electrolyte additives for separation and determination of camptothecin alkaloids by CZE

Theoretical study on the solvation mechanism of camptothecin in ionic liquids

To reduce the environmental pollution caused by organic solvents and improve the extraction efficiency, a range of imidazolium-based ionic liquid (IL) combinations of [Omim]⁺ paired with [Br]^-, [BF₄]^-, [Cl]^-, [ClO₄]^-, [HsO₄]^-, [NO₃]^-, [NTf₂]^-, [OAc]^-, [PF₆]^-, and [TsO]^- are explored for the extraction of camptothecin (CPT) using molecular dynamics (MD) simulation and density functional theory (DFT) calculations. It is found that the ILs containing [Br]^-, [OAc]^-, and [TsO]^- anions are the most promising solvents for CPT solvation because they exhibit stronger interaction energy and the lowest self-diffusion coefficient of CPT among all ILs. The microscopic mechanism at the molecular level is revealed based on DFT calculations and MD simulations, and the results demonstrate that the IL (i.e., [Omim][TsO]) containing anions with strong hydrogen bond (HB) acceptability and aromatic ring structure corresponds to both the strongest van der Waals interaction and strongest HB interaction of CPT-anions. Therefore, it is recommended that anions with aromatic ring structures or strong HB acceptability are promising anion candidates, while anions containing electron withdrawing groups and bulky substituents should be avoided. This work provides intermolecular insight into designing and selecting effective ILs for natural insoluble active pharmaceutical ingredient dissolution and extraction in further research.

Entropy-Driven Inclusion of Natural Protoberberine Alkaloids in Sulfobutylether-β-Cyclodextrin

The understanding of the relationship between molecular structure and the thermodynamics of host-guest binding is essential for the rational design of the applications of inclusion complexes. To obtain insight into the factors governing the driving force of complex formation in aqueous solutions, the encapsulation of five pharmaceutically important protoberberine alkaloids was studied in sulfobutylether-β-cyclodextrin having on average 6.4 degrees of substitution (SBE6.4βCD). Spectrophotometric, fluorescence spectroscopic, and isothermal calorimetric measurements showed 1:1 complexation in dilute solutions. From 1.92 × 104 M−1, about an eight-fold decrease of the association constant was observed in the series of berberine ≈ coptisine >> palmatine > epiberberine > dehydrocorydaline. The embedment of these alkaloids in the SBE6.4βCD cavity was entropy-controlled with mildly negative enthalpy contributions. These findings suggest that the stabilization of the examined complexes arises primarily from the hydrophobic interaction between the constituents. The more than three orders of magnitude smaller association constants of protoberberine alkaloids with SBE6.4βCD than with cucurbit[7]uril, a host having similar cavity size, originates from the much smaller exothermicity of the confinement in the former macrocycle.

Ionic liquids in electrokinetic chromatography

There is an interest in the application of ionic liquids as additives into the separation media to improve achiral and chiral separations in electrokinetic chromatography (EKC). This review will critically discuss the developments on the use of ionic liquids in the different modes of EKC during the last five years (2015-mid 2020). A healthy number of 48 research articles searched through Scopus were categorised into two: ionic liquids as sole pseudophase (micelles, microemulsions, ligand exchange pseudophase or molecular pseudophase) and ionic liquids with pseudophase (achiral or chiral). More than half of the papers dealt with chiral separations that were mostly facilitated by another additive or pseudophase. The role of ionic liquids for improvement of separations were analysed, and we provided some recommendations for further investigations. Finally, the use of ionic liquids in different on-line sample concentration or stacking methods (i.e., field enhancement and sweeping) was briefly discussed.

Separation and determination of corynoxine and corynoxine B using chiral ionic liquid and hydroxypropyl-β-cyclodextrin as additives by field-amplified sample stacking in capillary electrophoresis

A sensitive, fast, and effective method, field-amplified sample stacking (FASS) in capillary electrophoresis, has been established for the separation and determination of corynoxine and corynoxine B. Hydroxypropyl-β-CD (HP-β-CD) and tetrabutylammonium-L-glutamic acid (TBA-L-Glu) were used as additives in the separation system. Electrokinetic injection was chosen to introduce sample from inlet at 10 kV for 50 s after a water plug (0.5 psi, 4 s) was injected to permit FASS. The running buffer (pH 6.1) was composed of 40 mM sodium dihydrogen phosphate solution, 130 mM HP-β-CD, and 10 mM TBA-L-Glu and the separation voltage was 20 kV. Under the optimum conditions, corynoxine and corynoxine B were successfully enriched and separated within 12 min and the sensitivity was improved approximately by 700-900 folds. Calibration curves were in a good linear relationship within the range of 62.5-5.00 × 10³  ng/mL for both corynoxine and corynoxine B. The limits of detection (S/N = 3) and quantitation (S/N = 10) were 14.9, 45.2 ng/mL for corynoxine and 11.2, 34.5 ng/mL for corynoxine B, respectively. Finally, this method was successfully applied for the determination of corynoxine and corynoxine B in the stems with hooks of Uncaria rhynchophylla and its formulations.

Quality evaluation of Guan-Xin-Ning injection based on fingerprint analysis and simultaneous separation and determination of seven bioactive constituents by capillary electrophoresis

The purpose of this study was to develop a comprehensive, rapid and practical capillary electrophoresis (CE) method for quality control (QC) of Guan-Xin-Ning (GXN) injection based on fingerprint analysis and simultaneous separation and determination of seven constituents. In fingerprint analysis, a capillary zone electrophoresis (CZE) method with a running buffer of 30 mM borate solution (pH 9.3) was established. Meanwhile, ten batches of samples were used to establish the fingerprint electropherogram and 34 common peaks were obtained within 20 min. The RSD of relative migration times (RMT) and relative peak areas (RPA) were less than 5%. In order to further evaluate the quality of GXN injection, a micellar electrokinetic chromatography (MEKC) method was developed for simultaneous separation and determination of bioactive constituents. Seven components reached baseline separation with a running buffer containing 35 mM SDS and 45 mM borate solution (pH 9.3). A good linearity was obtained with correlation coefficients from 0.9906 to 0.9997. The LOD and LOQ ranged from 0.12 to 1.50 μg/mL and from 0.40 to 4.90 μg/mL, respectively. The recoveries ranged between 99.0 and 104.4%. Therefore, it was concluded that the proposed method can be used for full-scale quality analysis of GXN injection.