Strong inclusion of inorganic anions into β-cyclodextrin immobilized to gold electrode

Influence of Surface Chemistry on Host/Guest Interactions: A Model Study on Redox-Sensitive β-Cyclodextrin/Ferrocene Complexes

While host/guest interactions are widely used to control molecular assembly on surfaces, quantitative information on the effect of surface chemistry on their efficiency is lacking. To address this question, we combined electrochemical characterization with quartz crystal microbalance with dissipation monitoring to study host/guest interactions between surface-attached ferrocene (Fc) guests and soluble β-cyclodextrin (β-CD) hosts. We identified several parameters that influence the redox response, β-CD complexation ability, and repellent properties of Fc monolayers, including the method of Fc grafting, the linker connecting Fc with the surface, and the diluting molecule used to tune Fc surface density. The study on monovalent β-CD/Fc complexation was completed by the characterization of multivalent interactions between Fc monolayers and β-CD-functionalized polymers, with new insights being obtained on the interplay between the surface chemistry, binding efficiency, and reversibility under electrochemical stimulus. These results should facilitate the design of well-defined functional interfaces and their implementation in stimuli-responsive materials and sensing devices.

Large anion binding in water

Large water-soluble anions with chaotropic character display surprisingly strong supramolecular interactions in water, for example, with macrocyclic receptors, polymers, biomembranes, and other hydrophobic cavities and interfaces. The high affinity is traced back to a hitherto underestimated driving force, the chaotropic effect, which is orthogonal to the common hydrophobic effect. This review focuses on the binding of large anions with water-soluble macrocyclic hosts, including cyclodextrins, cucurbiturils, bambusurils, biotinurils, and other organic receptors. The high affinity of large anions to molecular receptors has been implemented in several lines of new applications, which are highlighted herein.

Structural Distortion of β-Cyclodextrin Plays a Key Role in the pH-dependent Host-Guest Chemistry with Doxorubicin, Evident by the Electrochemical and Molecular Dynamics Approach

β-Cyclodextrin (β-CD) is the potential drug carrier to deliver antitumor drugs like doxorubicin (DOX). However, the mechanism for the inclusion complex formation is still unclear and needs to be explored. This study investigated the effect of pH on the inclusion of DOX into thiolated β-CD (β-CD-SH) by electrochemical and molecular dynamics (MD) simulation. The electrochemical study shows a clear difference at different pH values. The redox peak due to the DOX is strongly influenced by pH. At neutral pH, the peak intensity decreases with time, while slight variation is observed at acidic and basic pH, depicting the association of DOX to the β-CD-SH cavity at neutral pH. Also, due to the association, the charge transfer resistance variation increased with time at neutral pH and decreased at basic and acidic pH. The electrochemical study was further supported by MD simulation, suggesting that the cyclodextrin (CD) ring gets slightly elongated due to the flipping of glucose units, specifically at neutral pH leading to a strong association. Also, another significant result observed that the DOX forms an inclusion complex with β-CD-SH in quinol conformation, not in quinone. Briefly, the study provides the necessary molecular binding information for designing an effective β-CD-based targeted drug delivery system.

Tuned synthesis and characterizational insight into β-cyclodextrin amended hydrous iron-zirconium hybrid oxide: a promising scavenger of fluoride in aqueous solution

Fluoride adsorption on CHIZO takes place with H-bonding inside the core, thus forming an encapsulated moiety.

Water Structure Recovery in Chaotropic Anion Recognition: High-Affinity Binding of Dodecaborate Clusters to γ-Cyclodextrin

Dodecaborate anions of the type B12X12(2-) and B12X11Y(2-) (X=H, Cl, Br, I and Y=OH, SH, NH3(+), NR3(+)) form strong (K(a) up to 10(6) L mol(-1), for B12Br12(2-)) inclusion complexes with γ-cyclodextrin (γ-CD). The micromolar affinities reached are the highest known for this native CD. The complexation exhibits highly negative enthalpies (up to -25 kcal mol(-1)) and entropies (TΔS up to -18.4 kcal mol(-1), both for B12I12(2-)), which position these guests at the bottom end of the well-known enthalpy-entropy correlation for CDs. The high driving force can be traced back to a chaotropic effect, according to which chaotropic anions have an intrinsic affinity to hydrophobic cavities in aqueous solution. In line with this argument, salting-in effects revealed dodecaborates as superchaotropic dianions.

How does the dehydration change the host-guest association under homogeneous and heterogeneous conditions?

In this study, the thermodynamic properties of association of some inorganic ions (ClO4(-) and SO4(2-)) with β-cyclodextrins (β-CD) in aqueous solution are determined under both free β-CD and surface confined β-CD conditions using atomistic simulations. The potential of mean force (PMF) is calculated as a function of the environment and the thermodynamic properties of association are deduced by integrating the free energy profiles. No inclusion complex between SO4(2-) and β-CD is detected. Nevertheless, the PMF curve obtained for gold-confined CD seems to evidence a small minimum at a larger separation distance that shows specific interactions such as hydrogen bonding outside the cavity. As concerns ClO4(-), our simulations reveal the formation of an inclusion complex with free β-CD in perfect agreement with the available experimental results. Nevertheless, we do not detect any formation of the host-guest inclusion complex under heterogeneous conditions. Finally, the differences observed as a function of the anions are interpreted through an atomistic description. The general trend of weaker complex stabilities with the increasing free energy of hydration of the anions is found in homogeneous systems.

Sensitivity and selectivity determination of bisphenol A using SWCNT-CD conjugate modified glassy carbon electrode

In this study, we demonstrated a highly sensitive electrochemical sensor for the determination of bisphenol A (BPA) in aqueous solution by using single-walled carbon nanotubes (SWCNTs)/β-cyclodextrin (β-CD) conjugate (SWCNT-CD) modified glassy carbon electrode (GCE). The cyclic voltammetry results show that the modified GCE exhibits strong catalytic activity toward the oxidation of BPA with a well-defined cyclic voltammetric peak at 0.543 V. The response current exhibits a linear range between 10.8 nM and 18.5 μM with a high sensitivity (1256 μA mM(-1)). The detection limit of BPA is 1.0 nM (S/N=3). The enhanced performance of the fabricated sensor can be attributed to the combination of the excellent electrocatalytic properties of SWCNTs and the molecular recognition ability of β-CD. The sensor was successfully applied to determine BPA leached from real plastic samples with good recovery, ranging from 95% to 103%.