Evidence for the 2:1 molecular recognition and inclusion behaviour between β- and γ-cyclodextrins and cinchonine

Ion Mobility-Mass Spectrometry Strategies to Elucidate the Anhydrous Structure of Noncovalent Guest/Host Complexes

Structural mass spectrometry (MS) techniques are fast and sensitive analytical methods to identify noncovalent guest/host complexation phenomena for desirable solution-phase properties. Current MS-based studies on guest/host complexes of drug and drug-like molecules are sparse, and there is limited guidance on how to interpret MS information in the context of host nanoencapsulation and inclusion. Here, we use structural MS strategies, combining energy-resolved MS (ERMS), ion mobility-MS (IM-MS), and computational modeling, to characterize 14 chemically distinct drug and drug-like compounds for their propensity to form guest/host complexes with the widely used excipient, beta-cyclodextrin (βCD). The majority (11/14) yielded a 1:1 guest/host complex, and ion mobility collision cross section (CCS) analysis provided subtle evidence of gas-phase compaction of complexes in both polarities. The three distinct dissociation channels observed in ERMS (i.e., charged βCD, charged guest, and partial guest loss) were used to direct charge-site assignments for computational modeling, and structural candidates were prioritized using helium-derived CCS measurements combined with root-mean-square distance analysis. The combined analytical information from ERMS, IM-MS, and computational modeling suggested that the majority of anhydrous complexes are inclusion complexes with βCD. Taken together, this work demonstrates a roadmap for how multiple MS-based analytical measurements can be combined to interpret the structures that guest/host complexes adopt in the absence of water.

Mass Spectrometry as a Complementary Approach for Noncovalently Bound Complexes Based on Cyclodextrins

An important and well-designed solution to overcome some of the problems associated with new drugs is provided by the molecular encapsulation of the drugs in the cyclodextrins (CDs) cavity, yielding corresponding inclusion complexes (ICs). These types of non-covalent complexes are of current interest to the pharmaceutical industry, as they improve the solubility, stability and bioavailability of the guest molecules. This review highlights several methods for cyclodextrin ICs preparation and characterization, focusing mostly on the mass spectrometry (MS) studies that have been used for the detection of noncovalent interactions of CDs inclusion complexes and binding selectivity of guest molecules with CDs. Furthermore, the MS investigations of several ICs of the CD with antifungal, antioxidants or fluorescent dyes are presented in greater details, pointing out the difficulties overcome in the analysis of this type of compounds.

Factors Affecting the Formation of 2:1 Host:Guest Inclusion Complexes of 2-[(R-Phenyl)amine]-1,4-naphthalenediones (PAN) in β- and γ-Cyclodextrins

The molecular hosts cyclodextrins form inclusion complexes with a wide variety of guests, resulting in complexes with various host:guest stoichiometries. In the case of a series of 19 1,4-naphthoquinolines as guests with either β- or γ-cyclodextrin studied using electrospray mass spectroscopy, in most cases only 1:1 complexes were observed, with 2:1 host:guest complexes observed in just 6 out of 38 host:guest combinations. It is shown that these higher-order complexes were observed only in the case of small (or no) electronically withdrawing substituents, and were much less likely in the case of the larger γ-cyclodextrin host. The size and electronic properties of the substituents involved shows that both steric and electronic factors must be taken into account in predicting which cyclodextrin host:guest stoichiometries will be stable enough to form (or once formed, be robust enough to be observed in the ESI-MS experiments). It is clear that the prediction of host-guest stoichiometry for a specific host-guest pair is complicated, and involves a subtle interplay of both electronic and steric factors. However, there are definite trends, which can be used to help predict host:guest stoichiometry for a given host-guest pair.

Utilizing ion mobility and tandem mass spectrometry to evaluate the structure and behaviour of multimeric cyclodextrin complexes

Characterizing noncovalent complexes of molecular dimers and higher complexes using tandem mass spectrometry (MS/MS) can be hindered due to spectral overlap in both the MS and the MS/MS. We investigated the structures and dissociation energetics of multimeric β-cyclodextrin (β-CD) complexes alone or with substrates using combinations of ion mobility spectrometry (IMS), MS/MS, and Rice–Ramsperger–Kassel–Marcus (RRKM) unimolecular rate modelling. The doubly charged β-CD dimers ([(β-CD)2 – 2H+]2−) dissociate to two [β-CD – H+]− ions with the same m/z. IMS was used to separate source generated [(β-CD)2 – 2H+]2− from [β-CD – H+]− and the extent of [(β-CD)2 – 2H+]2− dissociation versus collision energy was determined by modelling changes in the ion’s isotopic profile. The RRKM derived critical energy (E0) for dissociation of [(β-CD)2 – H+]− and [(β-CD)2 – 2H+]2− were 1.85 ± 0.11 eV and 1.79 ± 0.09 eV, respectively, corresponding to a slight decrease in complex stability due to increased charge–charge repulsion in the dianion. This approach was extended to include dimeric complexes complexed to 4,4′-(propane-1,3-diyl) dibenzoic acid (PDDA) and ibuprofen (Ibu).

Novel water-soluble fisetin/cyclodextrins inclusion complexes: Preparation, characterization, molecular docking and bioavailability

Novel water-soluble inclusion complexes for fisetin (FIT) were developed by introducing β-cyclodextrin (β-CD) and γ-CD. Properties of the obtained complexes, as well as the interactions between each component, were systematically investigated in both solution and solid states by means of ESI-MS, NMR, FT-IR, XRD, DSC, SEM etc. All characterization information demonstrated that FIT/CDs inclusion complexes were formed, and exhibited different spectroscopic features and properties from FIT. A complex with 1:1 stoichiometry of FIT and CDs was confirmed with Job's method. Meanwhile, as supported by molecular modeling calculations, we suggested that phenyl group (C ring) of FIT molecule was included in the CDs cavity from the wide side. Moreover, the water solubility of FIT/CDs was successfully improved from 2.8 mg/mL (in ethanol aqueous solution) to 4.5 mg/mL (FIT/β-CD complex) and 7.8 mg/mL (FIT/γ-CD complex), and higher thermal stability results were shown by thermal analysis for those complexes. Notably, the inclusion complexes displayed almost two times higher cytotoxicity compared to free FIT against Hela and MCF-7 cells. These results suggested that FIT/CDs complexes could be potentially useful in food industry and healthcare area.

Preparation of inclusion complex of perfluorocarbon compound with β-cyclodextrin for ultrasound contrast agent

A novel FC-77/β-CD inclusion complex was prepared and used as a ultrasound imaging contract to enhance the ultrasonic echo signal.

Supramolecular polymerization of supramonomers: a way for fabricating supramolecular polymers

This communication describes a new method of fabricating supramolecular polymers through supramolecular polymerization of supramonomers.

Review on supermolecules as chemical drugs

Supramolecular medicinal chemistry field has been a quite rapidly developing, increasingly active and newly rising interdiscipline which is the new expansion of supramolecular chemistry in pharmaceutical sciences, and is gradually becoming a relatively independent scientific area. Supramolecular drugs could be defined as medicinal supermolecules formed by two or more molecules through non-covalent bonds. So far a lot of supermolecules as chemical drugs have been widely used in clinics. Supermolecules as chemical drugs, i.e. supramolecular chemical drugs or supramolecular drugs, which might have the excellences of lower cost, shorter period, higher potential as clinical drugs for their successful research and development, may possess higher bioavailability, better biocompatibility and drug-targeting, fewer multidrug-resistances, lower toxicity, less adverse effect, and better curative effects as well as safety, and therefore exhibit wide potential application. These overwhelming advantages have drawn enormous special attention. This paper gives the definition of supramolecular drugs, proposes the concept of supramolecular chemical drugs, and systematically reviews the recent advances in the research and development of supermolecules, including organic and inorganic complex ones as chemical drugs in the area of antitumor, anti-inflammatory, analgesic, antimalarial, antibacterial, antifungal, antivirus, anti-epileptic, cardiovascular agents and magnetic resonance imaging agents and so on. The perspectives of the foreseeable future and potential application of supramolecules as chemical drugs are also presented.

Solubility-excipient classification gradient maps

This study assessed the effect of excipients (sodium taurocholate, 2-hydroxypropyl-f-cyclodextrin, potassium chloride, propylene glycol, 1-methyl-2-pyrrolidone, and polyethylene glycol 400) on the apparent intrinsic solubility properties of eight sparingly soluble drugs (four bases, two neutrals, and two acids): astemizole, butacaine, clotrimazole, dipyridamole, griseofulvin, progesterone, glibenclamide, and mefenemic acid. Over 1,200 UV-based solubility measurements (pH 3-10) were made with a high-throughput instrument. New equations, based on the "shift-in-pKa" method, were derived to interpret the complicated solubility-pH dependence observed, and poorly predicted by the Henderson-Hasselbalch equation. An intrinsic solubility-excipient classification gradient map visualization tool was developed to rank order the compounds and the excipients. In excipient-free solutions, all of the ionizable compounds formed either uncharged or mixed-charge aggregates. Mefenamic acid formed anionic dimers and trimers. Glibenclamide displayed a tendency to form monoanionic dimers. Dipyridamole and butacaine tended to form uncharged aggregates. With strong excipients, the tendency to form aggregates diminished, except in the case of glibenclamide. We conclude that a low-cost, compound-sparing, and reasonably accurate high-throughput assay which can be used in early screening to prioritize candidate molecules by their eventual developability via the excipient route is possible with the aid of the "self-organized" intrinsic solubility-excipient classification gradient maps.

Solubility of sparingly-soluble ionizable drugs

The experimental and computational basis of the pH-dependent measurement of solubility of sparingly-soluble ionizable drugs is reviewed. Recently described compound-sparing (but still accurate) approaches, suitable for application in preclinical development, and appropriate for the analysis of solubility of "problematic" molecules, are critically examined. A number of useful experimental methods are reviewed, including the miniaturized shake-flask microtitre plate, the micro solubility self-calibrating direct UV, potentiometric, and the micro dissolution methods. Several molecules were selected as case studies to illustrate important concepts, with re-analysis of literature data using recently established computational tools.

Bioactive Permethrin/β-Cyclodextrin Inclusion Complex

Permethrin is popularly used in a variety of therapeutic areas. However, the poor water solubility of permethrin seriously limits its wider clinical applications. The present study demonstrates that solubility of permethrin in aqueous solution can considerably increase in the presence of beta-cyclodextrin (beta-CD). Extensive experimental data along with computational modeling reveal the formation of stable permethrin/beta-CD inclusion complexes, including permethrin(beta-CD) and permethrin(beta-CD)2, through hydrophobic binding. Both permethrin(beta-CD) and permethrin(beta-CD)2 complexes coexisted in aqueous solution, and the ratio of the concentration of permethrin(beta-CD) complex to that of permethrin(beta-CD)2 complex was dependent on the concentration of beta-CD. The complexation of permethrin with beta-CD significantly improved the bioavailability of permethrin and, therefore, increased the bioactivity. The significant increase of the bioactivity of permethrin in the presence of beta-CD provides an effective approach to improve the practical use of permethrin in public health and agriculture.