Formation Of Host-guest Complexes Research Articles

Affinity and putative entrance mechanisms of alkyl sulfates into the β-CD cavity

Cyclodextrins (CDs) are novel pharmaceutical excipients and are widely used in the pharmaceutical industry and drug delivery due to their ability to form host–guest complexes. There are countless structural features of guest molecules responsible for the efficiency of guest–CD interactions. Among these factors, the hydrophobic moieties of a guest and their size are commonly considered to govern its binding affinity to CD molecules. Experimentally, it is often challenging to extract structural and dynamic information at the atomic scale about CD inclusion complexes, especially in the aqueous phase. Therefore, this study consisted of experimental (isothermal titration calorimetry and conductometric titration) and in silico analysis to rigorously characterize the interactions of β -CD with three alkyl sulfates of different hydrophobic chain lengths: sodium dodecyl sulfate (S12S), sodium decyl sulfate (S10S) and sodium octyl sulfate (S8S) in aqueous solutions. We find that the hydrophobic interactions are not always a key factor leading to the formation of stable inclusion complexes. Our results demonstrate that van der Waals interactions contribute more to complexation efficiency for sulfates with a longer hydrophobic tail, whereas electrostatic interactions are more pronounced for sulfates with shorter ones. Furthermore, we propose and discuss for the first time the putative mechanisms of the guest entering the host cavity conditioned by the lengths of hydrocarbon chains of alkyl sulfates. Finally, we prove that different types of inclusion complexes can exist in a conformational equilibrium depending on the size of a guest tail.

α-Cyclodextrin affects the acid-base properties of octanoic acid/sodium octanoate

The interaction of octanoic acid and its conjugate base sodium octanoate with α-cyclodextrin was studied by 1H NMR and isothermal titration calorimetry, respectively, at 298.15 K. The results are in agreement with a 1:1 stoichiometry in the complex. The binding of octanoate with α-cyclodextrin is characterized by a positive entropy, stressing the relevance of hydrophobic interactions. Based on the host-guest complex formation, the effect of α-cyclodextrin on the acidity behavior of the acid was evaluated by potentiometric titration. The results are interpreted in terms of the Henderson-Hasselbalch equation and by using an analytical equation for the titration curve. The apparent ionization constants of the complexes are higher than those obtained in water, indicating that octanoic acid becomes a weaker acid after complexation.

Analysis of the host–guest complex formation involving bridged hexameric pyridinium–phenyl rings in the HexaCage6+ host in suit[3]ane: insights from dispersion-corrected DFT calculations for a nanometric mechanically interlocked device

Analysis of the host–guest complex formation involving bridged hexameric pyridinium–phenyl rings in the HexaCage6+ host in suit[3]ane: insights from dispersion-corrected DFT calculations for a nanometric mechanically interlocked device

Binding and Assembly of a Benzotriazole Cavitand in Water

AbstractA water‐soluble cavitand bearing a benzotriazole upper rim was prepared and characterized. It exists as a dimeric velcraplex in D2O, but forms host–guest complexes with hydrophobic and amphiphilic guests. Alkanes (C5 to C10), cyclic ketones (C6–C10), cyclic alcohols (C6–C8) and various amphiphilic guests form 1 : 1 cavitand complexes. A cyclic array of hydrogen bonds, bridged by solvent/water (D2O) molecules, stabilizes the vase conformation of the complexes. With longer alkanes (C12–C15), symmetrical dialkyl amine, urea and phosphate, 2 : 1 host:guest capsules are formed. Computations indicate that additional waters on the upper rim create a self‐complementary hydrogen‐bonding pattern for capsule formation.

Construction of stable beta-cyclodextrin grafted polypropylene nonwoven fabrics for the adsorption of bisphenol A

Herein, a convenient and environment-friendly grafting strategy was used to anchor beta-cyclodextrin (β-CD) on polypropylene (PP) fabric, which includes grafting of GMA onto PP nonwoven fabric via 60Co γ-ray and introduction of β-CD by the ring-opening reaction between the hydroxyl group of β-CD and the epoxy group of GMA. The as-prepared fabric composite (PP-g-GMA-βCD) showed a bisphenol A (BPA) adsorption amount of 27.72 mg/g in the single BPA solution (75 ppm). The BPA adsorption amount by PP-g-GMA-βCD was not sensitive to pH condition, and the anti-interference ability to ions was also strong. The Langmuir isotherm model was found to be suitable for the adsorption of BPA, and the entire adsorption process followed the pseudo-second-order kinetics. PP-g-GMA-βCD showed excellent stability and reusability that the BPA adsorption amount remained almost unchanged after 10 successive recycles. In the BPA and methyl orange (MO) mixed solution (BPA: 75 ppm; MO: 50 ppm), the adsorption amounts of BPA and MO by PP-g-GMA-βCD were 23.88 and 20.83 mg/g, respectively. The presence of MO resulted in a little decrease in the adsorption amount of BPA, as β-CD can also form host–guest complexes with MO, and there would also be π-π and H-bond interactions between BPA and MO.

Electron catalysis expands the supramolecular chemist’s toolbox

Molecular recognition is at the heart of the noncovalent synthesis of supramolecular assemblies and, at higher length scales, supramolecular materials. In a recent publication in <i>Nature</i>, Stoddart and co-workers demonstrate that the formation of host-guest complexes can be catalyzed by one of the simplest possible catalysts: the electron.

Discrete, Cationic Palladium(II)-Oxo Clusters via f-Metal Ion Incorporation and their Macrocyclic Host-Guest Interactions with Sulfonatocalixarenes.

We report on the discovery of the first two examples of cationic palladium(II)‐oxo clusters (POCs) containing f‐metal ions, [PdII 6O12M8{(CH3)2AsO2}16(H2O)8]4+ (M=CeIV, ThIV), and their physicochemical characterization in the solid state, in solution and in the gas phase. The molecular structure of the two novel POCs comprises an octahedral {Pd6O12}12− core that is capped by eight MIV ions, resulting in a cationic, cubic assembly {Pd6O12MIV 8}20+, which is coordinated by a total of 16 terminal dimethylarsinate and eight water ligands, resulting in the mixed PdII‐CeIV/ThIV oxo‐clusters [PdII 6O12M8{(CH3)2AsO2}16(H2O)8]4+ (M=Ce, Pd6Ce8 ; Th, Pd6Th8 ). We have also studied the formation of host‐guest inclusion complexes of Pd6Ce8 and Pd6Th8 with anionic 4‐sulfocalix[n]arenes (n=4, 6, 8), resulting in the first examples of discrete, enthalpically‐driven supramolecular assemblies between large metal‐oxo clusters and calixarene‐based macrocycles. The POCs were also found to be useful as pre‐catalysts for electrocatalytic CO2‐reduction and HCOOH‐oxidation.

"Lock and Key" and "Induced-Fit" Host-Guest Models in Two Digold(I)-Based Metallotweezers.

Two different metallotweezers, each with two pyrene-imidazolylidene-gold(I) arms, were used as hosts for a series of planar aromatic guests. The metallotweezer with a dibenzoacridinebis(alkynyl) spacer (1) orients the two pyrene-imidazolylidene-gold(I) arms in a parallel disposition, with an interpanel distance of about 7 Å. The second metallotweezer (2) contains a carbazolylbis(alkynyl) spacer that directs the two pyrene panels in a diverging orientation. Determination of the association constants via 1H NMR titrations demonstrates that the binding strength shown by 1 is significantly larger than that found by 2, with binding affinities as large as 104 M-1 (in CDCl3), for the encapsulation of N,N'-dimethylnaphthalenetetracarboxydiimide with 1. The differences in the binding affinities are due to binding models associated with formation of the related host-guest complexes. While 1 operates via a "lock and key" model, in which the host does not suffer distortions upon formation of the inclusion complex, 2 operates via a guest-induced fit model. The large association constants shown by 1 with two planar guests were used for promotion of the template-directed synthesis of 1, which in the absence of an external template is produced in an equimolecular mixture with its self-aggregated congener, clippane [12]. This observation strongly suggests that the mechanically interlocked clippane is formed through a self-template-directed mechanism, while bonds are broken/formed during the synthetic protocol.

Sulfobutylation of Beta-Cyclodextrin Enhances the Complex Formation with Mitragynine: An NMR and Chiroptical Study

Mitragynine (MTR), the main indole alkaloid of the well-known plant kratom (Mitragyna speciosa), is one of the most studied natural products nowadays, due to its remarkable biological effects. It is a partial agonist on the opioid receptors, and as such relieves pain without the well-known side-effects of the opioids applied in the clinical practice. MTR and its derivatives therefore became novel candidates for drug development. The poor aqueous solubility and low bioavailability of drugs are often improved by cyclodextrins (CyDs) as excipients through host-guest type complex formation. Among the wide variety of CyDs, sulfobutylether-beta-cyclodextrin (SBEβCyD) is frequently used and official in the European and U.S. Pharmacopoeia. Herein, the host-guest complexation of MTR with βCyD and SBEβCyD was studied using chiroptical and NMR spectroscopy. It was found by NMR measurements that MTR forms a rather weak (logβ11 = 0.8) 1:1 host-guest complex with βCyD, while the co-existence of the 2MTR∙SBEβCyD and MTR∙SBEβCyD species was deducted from 1H NMR titrations in the millimolar MTR concentration range. Sulfobutylation of βCyD significantly enhanced the affinity towards MTR. The structure of the formed inclusion complex was extensively studied by circular dichroism spectroscopy and 2D ROESY NMR. The insertion of the indole moiety was confirmed by both techniques.

Supramolecular self-associating amphiphiles as aqueous pollutant scavengers.

We present a series of supramolecular self-associated amphiphiles, which spontaneously self-assemble into aggregated species. These aggregates are shown to absorb a variety of (polar) micropollutants from aqueous mixtures and as a result we determine the suitability for this technology to be developed further as aqueous environmental clean-up agents.

Molecular Recognition by Pillar[5]arenes: Evidence for Simultaneous Electrostatic and Hydrophobic Interactions.

The formation of inclusion complexes between alkylsulfonate guests and a cationic pillar[5]arene receptor in water was investigated by NMR and ITC techniques. The results show the formation of host-guest complexes stabilized by electrostatic interactions and hydrophobic effects with binding constants of up to 107 M−1 for the guest with higher hydrophobic character. Structurally, the alkyl chain of the guest is included in the hydrophobic aromatic cavity of the macrocycle while the sulfonate groups are held in the multicationic portal by ionic interactions.

Nanoassemblies formed from amphiphilic pillar[5]arene–rod–coil macromolecules in water for the detection of aliphatic diamines

An amphiphilic pillar[5]arene–rod–coil macromolecule (H1) composed of pillar[5]arene, biphenyl, and oligo(ethylene oxide) groups, was synthesized, and its applicability as a soft material for detecting aliphatic diamines was verified. Amphiphile H1 self-assembled into unique nanorings and shows an obvious lower critical solution temperature effect in aqueous solution. Interestingly, nanoaggregates of H1 exhibit certain aggregate-induced emission properties owing to the presence of ten electron-rich biphenyl units on the upper and lower sides of the pillar[5]arene block. In addition, various nanoassemblies were precisely constructed from H1, through the addition of small molecules with electron-acceptor units. This implies that charge-transfer interactions and hydrophilic/hydrophobic effects cooperatively influence the morphology of H1 to form diverse nanoassemblies in water. Moreover, macromolecule H1 with the pillar[5]arene block has a good ability to form host–guest complexes with aliphatic diamines in water, with high selectivity; this significantly affects the process of supramolecular nanoassembly.

Detoxification of the Toxic Sulfur Mustard Simulant by a Supramolecular Antidote in Vitro and in Vivo.

Although great potential hazards and threats still occur from sulfur mustard, there are no specific medicine or therapy for the intoxication of sulfur mustard. Herein, we have demonstrated a supramolecular approach for the detoxification of the sulfur mustard simulant CEES (4) in vitro and in vivo by carboxylatopillar[5]arene potassium salts (CP[5]AK 1) efficiently based on host-guest interactions. The encapsulation of CEES (4) by the cavity of the pillar[5]arene 2 is driven by C-H···π interactions between CEES (4) and the electron-rich cavity of pillar[5]arene 2, which was investigated by 1H NMR titration, density functional theory studies, and the independent gradient model studies. CEES (4) is degradated to the reactive sulfonium salts quickly in aqueous media, resulting in the alkylation of DNA and proteins. The sulfonium salts can be encapsulated by CP[5]AK 1 efficiently, which accelerates the degradation of the sulfonium salts about 14 times. The cell and animal experiments indicated that the bioactivities of the sulfonium salts are inhibited with the formation of stable host-guest complexes, and CP[5]AK 1 has a good therapeutic effect on the damages caused by CEES (4) at either pre- or post-treatments. Due to the low cytotoxicity and good therapeutic effect, the anionic pillar[5]arenes are expected to be developed as specific antidotes against sulfur mustard (HD).

Environmentally Sound Approach for Fabrication of Antibacterial/Anti-UV/Anti-crease and Fragrant Denim Fabrics

A green approach for imparting multifunctional properties namely antibacterial, anti-UV, anti-crease and fragrance property to indigo dyed cotton denim fabrics using environmentally benign finishing, hosting and bioactive agents was investigated. In the current work, pre-loading of MCT-βCD, as a hosting agent, via ester-crosslinking using CA/SHP, as formaldehyde-free crosslinking system using pad-dry-cure method, followed by post-treatment with selected bio active agents namely Clove oil, Lavender oil, Tulsi oil and Vanillin R were carried out to add new, durable and desirable functional properties. The obtained results demonstrated that the variation in the efficacy and durability of the imparted functional properties is governed by extent of loading the modified βCD, number and availability of hydrophobic hosting-cavities, type and chemical constituents of the guest molecule and its extent of inclusion into the created cavities via formation of host-guest complex, as well as its retention or release during the washing process. The remarkable improvement in antibacterial activity against the pathogenic bacteria followed the decreasing order: Tulsi≥ Clove> Vanillin> Lavender>> None. The obtained results also demonstrated that, the imparted anti-UV capability of post-loaded denim samples follows the descending order: Vanillin>Tulsi>Clove>Lavender>>None. The imparted functional properties showed a high durability even after 15 washes.

Electrospinning and Catalytic Properties of Cyclodextrin Functionalized Polyoxymethylene (POM) Nanofibers Supported by Silver Nanoparticles

A series of novel composite microfibers composed of β-cyclodextrin (β-CDs) functionalized POM (polyoxymethylene) were prepared using electrospining technology with a mixture of hexafluoroisopropanol (HFIP) and N,N-dimethylformamide (DMF) as solvent. The concentration of β-CDs with respect to the POM was varied from 0 to 50 wt.%. The effect of β-CDs content on the morphology of POM/β-CD composite microfiber was investigated. The results showed that the introduction of β-CDs reduced the surface roughness and porosity of the microfibers, and the morphology of the fibers was changed. The increase of β-CDs content from 10% to 50% has led to increased average diameter of POM/β-CD composite fiber from 2.1 μm to 6.4 μm. The mechanical properties of the blend fiber mats were further investigated. In addition, silver nanoparticles were introduced to the POM/β-CD composite microfiber matrices during electrospinning. The POM/β-CD composite fiber allows CDs to form host–guest complexes with various small molecules and macromolecules. The TEM, SEM, XRD, and XPS were utilized to characterize the prepared samples. The data suggest that Ag nanoparticles were homogeneously distributed within the POM/β-CD fibers, and no aggregation was observed. The catalytic activity of Ag nanoparticles was tracked by ultraviolet-visible (UV-vis) spectroscopy which showed excellent catalytic degradation performance of organic dyes in the presence of NaBH4. The Ag/POM/β-CD mats are promising for use in waste treatment, molecular recognition, catalysis, and so on.

Perylene Diimide-Based Multicomponent Metallacages as Photosensitizers for Visible Light-Driven Photocatalytic Oxidation Reaction

Perylene Diimide-Based Multicomponent Metallacages as Photosensitizers for Visible Light-Driven Photocatalytic Oxidation Reaction

Supramolecular Viologen–Cyclodextrin Electrolytes for Aqueous Organic Redox Flow Batteries

Along with a primary modification of redox active materials, an additional introduction of secondary noncovalent interactions can synergistically enhance bulk properties of electrolytes for redox flow batteries. Herein, we highlight the host–guest complex formation between tailored viologens and highly water soluble (2-hydroxypropyl)-β-cyclodextrin as a key electrolyte interaction to modulate relevant electrochemical properties of aqueous redox flow batteries (AORFBs). The cyclodextrin-modified AORFB anolytes demonstrated a complex interrelation of molecular structure and inherent binding activity as well as bulk electrochemical stability of the anolyte. The screening of different combinations of viologen substituents in the presence of cyclodextrin enabled an electrochemically stable AORFB performance for more than 500 cycles with a temporary capacity fade rate of 0.26%/day at high energy (>70%) and Coulombic (>99.7%) efficiencies. A selective interplay of supporting electrolytes and engineered redox active materials is a promising strategy for enhanced energy characteristics of AORFB electrolytes.

Cocrystalline Polymer Films Exhibiting Second-Order Nonlinear Optical Properties.

Tailored polymer materials exhibiting high-glass transition temperatures, cross-linked matrices, and/or strong intermolecular interactions containing electric-field poled nonlinear optical (NLO) chromophores are promising materials for applications in optical telecommunication, high-performance computing, and data transmission. Although the current design parameters have led to significant advances in NLO materials, we introduce an alternative, yet highly effective, approach in which a NLO chromophore is cocrystallized with a polymer, forming a noncentrosymmetric hybrid host-guest complex. Specifically, poly(ethylene oxide) (PEO) and 2-chloro-4-nitroaniline (CNA) will cocrystallize and exhibit second harmonic generation (SHG) activity due to the formation of a noncentrosymmetric cocrystalline unit cell where the chromophore exhibits acentric alignment. Furthermore, the hybrid PEO/CNA films exhibit interesting SHG activity at elevated temperature in which SHG intensity decreases to zero when the cocrystal orientation randomizes due to sample melting. Aligning and maintaining a cocrystalline domain orientation via the formation of hybrid host-guest complexes, while imparting SHG properties, is an innovative approach for creating materials exhibiting SHG properties.

Mass Spectrometric Evaluation of β-Cyclodextrins as Potential Hosts for Titanocene Dichloride.

Bent metallocene dichlorides (Cp2MCl2, M = Ti, Mo, Nb, …) have found interest as anti-cancer drugs in order to overcome the drawbacks associated with platinum-based therapeutics. However, they suffer from poor hydrolytic stability at physiological pH. A promising approach to improve their hydrolytic stability is the formation of host-guest complexes with macrocyclic structures, such as cyclodextrins. In this work, we utilized nanoelectrospray ionization tandem mass spectrometry to probe the interaction of titanocene dichloride with β-cyclodextrin. Unlike the non-covalent binding of phenylalanine and oxaliplatin to β-cyclodextrin, the mixture of titanocene and β-cyclodextrin led to signals assigned as [βCD + Cp2Ti–H]+, indicating a covalent character of the interaction. This finding is supported by titanated cyclodextrin fragment ions occurring from collisional activation. Employing di- and trimethylated β-cyclodextrins as hosts enabled the elucidation of the influence of the cyclodextrin hydroxy groups on the interaction with guest structures. Masking of the hydroxy groups was found to impair the covalent interaction and enabling the encapsulation of the guest structure within the hydrophobic cavity of the cyclodextrin. Findings are further supported by breakdown curves obtained by gas-phase dissociation of the various complexes.

Aqueous compatibility of 15 pharmaceutical antimicrobial preservatives with the macrocycles cucurbit[7]uril and para-sulfonatocalix[4]arene

ABSTRACT The compatibility of 15 antimicrobial preservatives used in liquid/semi-solid pharmaceutical dosage formulations with the macrocycles cucurbit[7]uril (CB[7]) and para-sulfonatocalix[4]arene (sCX[4]) was examined by 1H NMR. A preservative was deemed to be compatible with one, or both, of the macrocycles if there was no evidence of host-guest complex formation. Eight preservatives (benzoic acid, ethanol, glycerine, methyl paraben, potassium sorbate, propylene glycol, sodium ethylenediaminetetraacetic acid, and sodium metabisulfite) were determined to be compatible with both CB[7] and sCX[4]. Three preservatives (benzalkonium chloride, cetrimide, and chlorhexidine) were determined to be not compatible with either macrocycle, whereas chlorobutanol and chlorocresol were found to be compatible with sCX[4] but not with CB[7]. Phenoxyethanol was incompatible with sCX[4] but possibly incompatible with CB[7] depending on the concentration of the preservative used with the cucurbituril. Finally, sodium propanoate was compatible with sCX[4] but only possibly compatible with CB[7].