Physical Characterization of Inclusion Complexes of Triphenyl Phosphate and Cyclodextrins in Solution

Computational Insights into Cyclodextrin Inclusion Complexes with the Organophosphorus Flame Retardant DOPO

Cyclodextrins (CDs) were used as green char promoters in the formulation of organophosphorus flame retardants (OPFRs) for polymeric materials, and they could reduce the amount of usage of OPFRs and their release into the environment by forming [host:guest] inclusion complexes with them. Here, we report a systematic study on the inclusion complexes of natural CDs (α-, β-, and γ-CD) with a representative OPFR of DOPO using computational methods of molecular docking, molecular dynamics (MD) simulations, and quantum mechanical (QM) calculations. The binding modes and energetics of [host:guest] inclusion complexes were analyzed in details. α-CD was not able to form a complete inclusion complex with DOPO, and the center of mass distance [host:guest] distance amounted to 4-5 Å. β-CD and γ-CD allowed for a deep insertion of DOPO into their hydrophobic cavities, and DOPO was able to frequently change its orientation within the γ-CD cavity. The energy decomposition analysis based on the dispersion-corrected density functional theory (sobEDAw) indicated that electrostatic, orbital, and dispersion contributions favored [host:guest] complexation, while the exchange-repulsion term showed the opposite. This work provides an in-depth understanding of using CD inclusion complexes in OPFRs formulations.

Insights into the Formations of Host-Guest Complexes Based on the Benzimidazolium Based Ionic Liquids-β-Cyclodextrin Systems

Inclusion complexation is one of the best strategies for developing a controlled release of a toxic drug without unexpected side effects from the very beginning of the administration to the target site. In this study, three benzimidazolium based ionic liquids (ILs) having bromide anion and cation bearing long alkyl chains, hexyl- ([C₆CFBim]Br), octyl- ([C₈CFBim]Br), and decyl- ([C₁₀CFBim]Br) were designed and synthesized as antibacterial drugs. Inclusion complexes (ICs) of studied ILs have been prepared by the combination of β-cyclodextrin (β-CD), considering these conjugations should enhance the benignity of ILs and make them potential candidates for the controlled drug release. Characterizations and structural analysis of studied ICs have been performed by ¹H NMR, 2D-ROESY NMR, FT-IR, HRMS, TGA, DSC, surface tension, ionic conductivity, dynamic light scattering (DLS), and isothermal titration calorimetry (ITC). Further, the morphology of the ICs has been analyzed by SEM and TEM. Furthermore, neat ILs and ICs have been treated against Escherichia coli and Bacillus subtilis to investigate their antibacterial activity, which confirms the prevention of bacterium growth and the shrinkage of the bacterial cell wall. The findings of this work provide the proof of concept that studied benzimidazolium based ILs-β-CD host-guest complexes should act as a potential candidate in controlled drug delivery and other biomedical applications.

Delivery of pharmaceuticals and other active ingredients with their crystalline cyclodextrin inclusion compounds

In honor of Prof. Thorsteinn Loftsson's 70th birthday, we offer this personal review of our work using cyclodextrins (CDs) complexed with a variety of active ingredients, including pharmaceuticals, for the purpose of improving their delivery to polymer materials, e.g., fibers, films, hydrogels, etc. Using the affinity of CDs to host and form non-covalent inclusion complexes (ICs) with guest molecules, including a variety of high molecular weight polymers, it is possible to readily deliver these guest molecules into polymer materials via either melt or solution processing of their crystalline or soluble guest molecule-CD-ICs or -rotaxanes. This provides the following advantages: i. CDs are non-toxic, implantable, and biodegradable and have earned the GRAS rating from the FDA. ii. Guest molecules, even those that are neat liquids, can form solid crystalline CD-ICs that are thermally stable to ~ 200 °C and above. This approach permits facile melt-processing into polymer materials for delivery without migration, loss, or degradation of the active guest ingredient. iii. For guests harmful and toxic to their users and the environment, delivery in the form of crystalline CD-ICs can limit any contact with and release of the included toxic guests before they function and are used. iv. It has been demonstrated that, by simple precipitation methods, neat as-received CDs that adopt cage crystal structures can be readily transformed to their columnar crystal structures containing only water in their channels, which can be easily displaced by small molecule, as well as polymer guests. v. Guest-CD-rotaxanes are water soluble, they protect the threaded guest from sources of degradation, and the CD hydroxyl groups may be modified to direct the guest-CD-rotaxane to specific substrates. For these reasons, here we summarize our contributions to the study of CD inclusion and delivery of a variety of guest molecules, including antibacterials, spermicides, insecticides, flame retardants, and dyes, that can more usefully functionalize polymer materials.