Formation Of Host-guest Inclusion Complexes Research Articles

Pillar[5]arene-based dually crosslinked supramolecular gel as a sensor for the detection of adiponitrile

An SPR-based dually crosslinked gel sensor for adiponitrile bearing pillar[5]arene responsive sites with a low limit of detection was developed.

Electrochemically Controlled Release from a Thin Hydrogel Layer.

In this study, we present a thermoresponsive thin hydrogel layer based on poly(N-isopropylacrylamide), functionalized with β-cyclodextrin groups (p(NIPA-βCD)), as a novel electrochemically controlled release system. This thin hydrogel layer was synthesized and simultaneously attached to the surface of a Au quartz crystal microbalance (QCM) electrode using electrochemically induced free radical polymerization. The process was induced and monitored using cyclic voltammetry and a quartz crystal microbalance with dissipation monitoring (QCM-D), respectively. The properties of the thin layer were investigated by using QCM-D and scanning electron microscopy (SEM). The incorporation of β-cyclodextrin moieties within the polymer network allowed rhodamine B dye modified with ferrocene (RdFc), serving as a model metallodrug, to accumulate in the p(NIPA-βCD) layer through host-guest inclusion complex formation. The redox properties of the electroactive p(NIPA-βCD/RdFc) layer and the dissociation of the host-guest complex triggered by changes in the oxidation state of the ferrocene groups were investigated. It was found that oxidation of the ferrocene moieties led to the release of RdFc. It was crucial to achieve precise control over the release of RdFc by applying the appropriate electrochemical signal, specifically, by applying the appropriate potential to the electrode. Importantly, the electrochemically controlled RdFc release process was performed at a temperature similar to that of the human body and monitored using a spectrofluorimetric technique. The presented system appears to be particularly suitable for transdermal delivery and delivery from intrabody implants.

Inclusion Complex Formation with Tetra-PEGylated Tetraphenylporphyrin and Face-to-Face Cyclodextrin Dimer through Unprecedented Molecular Threading.

Herein, a host-guest inclusion complex formation between tetra-PEGylated tetraphenylporphyrin with a per-O-methylated cyclodextrin (CD) dimer through the molecular threading process that is physically unexpected to occur is described. Although the molecular size of the PEGylated porphyrin is much greater than that of the CD dimer, the sandwich-type porphyrin/CD dimer 1 : 1 inclusion complex was spontaneously formed in water. The ferrous porphyrin complex binds O2 reversibly in aqueous solution, which functions as an artificial O2 carrier in vivo. Pharmacokinetic study using rats revealed that the inclusion complex showed a long circulation in blood in contrast to the complex without PEG. We further demonstrate the unique host-guest exchange reaction from the PEGylated porphyrin/CD monomer 1/2 inclusion complex to the 1/1 complex with the CD dimer through the complete dissociation process of the CD monomers.

A Fluorescein-Substituted Perbrominated Dodecaborate Cluster as an Anchor Dye for Large Macrocyclic Hosts and Its Application in Indicator Displacement Assays.

Perhalogenated boron clusters derived from B12Br122-, a superchaotropic dianion with a globular icosahedral shape, serve as inorganic cavity binders for cyclodextrins (CDs), in particular for large CDs (γ-CD and δ-CD), with high binding affinity (Ka > 106 M-1) in aqueous solution. This opens the door for applications of this anchoring moiety by linking it to organic residues, prominently fluorescent dyes. We report here the synthesis of a novel fluorescein-substituted perbrominated dodecaborate cluster by a copper(I)-catalyzed azide-alkyne click reaction. The formation of host-guest inclusion complexes between the dodecaborate-modified fluorescein dye and CDs can be readily followed by optical titrations, which afforded a binding constant of ∼1 × 104 M-1 with γ-CD; that is, the cluster functionalization allows binding of an otherwise nonbinding dye to the macrocycle ("anchor dye"). The formation of the 1:1 host-guest inclusion complex between the dye and γ-CD occurs over a broad range of pH values, which allows its application as a sensitive reporter pair according to the indicator displacement method, e.g., for drug detection. In addition, the substituted dye shows outer-wall binding to cucurbiturils through the dodecaborate moiety, leading to the formation of aggregates and significant fluorescence quenching of the dye.

Assessing the use of host-guest chemistry in conjunction with cyclic ion mobility separations for the linkage-specific characterization of human milk oligosaccharides

Human milk oligosaccharides (HMOs) are a class of glycans that are highly abundant in human milk and contribute to the healthy growth of an infant's immune system. While new advancements in analytical methodologies have been made in glycomics, the high degree of isomeric heterogeneity and lack of authentic standards have made the high-resolution separation and accurate characterization of linkage positioning of all HMO species very challenging. Herein, we present an evaluation of the use of host-guest chemistry in conjunction with cyclic ion mobility spectrometry-mass spectrometry (cIMS-MS)-based separations for the identification of linkage positioning in three pairs of di-, tetra-, and hexasaccharide HMO isomers that only differ in the positioning of one glycosidic linkage (β1,3 versus β1,4). Suitable hosts, such as α/β cyclodextrins, cucurbit[n]urils (n = 5, 7), crown ethers, cyclic peptides, and an ionophore, were used to assess host-guest inclusion complex formation as well as linkage-specific cIMS-MS trends. Our results indicated a linkage-specific trend for the [M + 2α + 2H]2+ cyclodextrin-based host-guest inclusion complexes where the β1,3 linkage-containing isomers were always higher mobility than the β1,4 linkage-containing ones as well one for the [M + α + β + 2H]2+ complexes where the β1,4 linkage-containing isomers were always higher mobility than the β1,3 linkage-containing ones. We also observed diagnostic mobility fingerprints for the cucurbituril-based complexes. We anticipate that linkage-specific and mobility fingerprint trends can potentially aid in identifying linkage positioning for other HMO isomers as well as in complex human milk samples.

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.

β-Cyclodextrin anchored neem carbon dots for enhanced electrochemical sensing performance of an anticancer drug, lapatinib via host-guest inclusion

By utilizing the merits of β-Cyclodextrin and neem carbon dots (C-dots), a simple, eco-friendly, and sensitive electrode material, β-CD functionalized neem carbon dots modified glassy carbon electrode (β-CD@C-dots/GCE) was developed for electrochemical determination of an anticancer drug, lapatinib (LAP). A green and cost-effective approach was adopted for the synthesis of neem carbon dots (C-dots) via the one-pot hydrothermal treatment of leaf extracts of neem (Azadirachta indica). The β-CD was integrated onto C-dots through hydrogen bonding. XRD, FTIR, TEM, fluorescence, UV–Vis, TGA, electrochemical impedance, and cyclic voltammetric studies confirmed the formation of nanocomposite, β-CD@C-dots and used as an electrode material for sensing application. Factors affecting the activity of the sensing interface were investigated by cyclic voltammetry and optimized for sensitive performance. The proposed sensor has displayed the analyte capturing ability (via host-guest inclusion complex formation) as evident from the accumulation of more LAP on the electrode surface. The peak current of LAP was observed to be enhanced by about 30-fold at the modified electrode compared to that at the bare electrode. LAP exhibited three anodic peaks at 0.55 V (Ep, a3), 0.90 V (Ep, a1), and 1.12 V (Ep, a2), and one cathodic peak at 0.47 V (Ep, c1) in phosphate buffer of pH 2.5. Electrode processes were realized under adsorption controlled for peak a1 and diffusion–adsorption mixed controlled process for peak a2, respectively. The synergistic effect of β-CD and C-dots electrode material exhibited a wide linear relationship between the oxidation peak current (peak a1) and concentration of LAP in the range of 1.99 × 10−8 − 8.59 × 10−6 mol L−1, 0.99 × 10−8 − 6.17 × 10−6 mol L−1 and 4.99 × 10−8 − 6.17 × 10−6 mol L−1 for differential pulse voltammetric, square wave voltammetric and linear sweep voltammetric methods, respectively. The lowest LOD value of 1.81 × 10−10 mol L−1 was achieved with the SWV method. The proposed sensor demonstrated satisfactory applicability for the determination of LAP in pharmaceutical formulations and urine samples. Thus, β-CD@C-dots/GCE is a promising and high-performing electrochemical sensor for the determination of LAP.

Photophysics of a cyanine dye within cyclodextrin cavity

The modulated photophysical and dynamical behavior of a potent anti-tumor photosensitizer 3,3/-diethyloxadicarbocyanine iodide (DODCI) following host-guest inclusion complex formation with α-, β- and γ-Cyclodextrins (CDs) has been studied using steady-state and time-resolved spectroscopic methods. The cavity size of the CDs (α-CD <β-CD <γ-CD) is argued to play an instrumental role underlying the formation of the host-guest inclusion complex. While negligible interaction with α-CD is found to be succeeded by prominent quenching of monomeric fluorescence of the dye within β-CD and γ-CD with the degree of quenching being greater within γ-CD. The most appealing fact attained from the experimental results is the anticipation of dimer formation of DODCI within the large cavity of γ-CD which can entrap more than one molecule of DODCI. The steady-state results are found to be adequately corroborated by time-resolved fluorescence decay studies. Such encapsulation of the cyanine dye within the carrier cargo can be designed for targeted delivery inside biological systems.

Host-guest interactions accompanying the cationic nitrogen heterocyclic guests encapsulation within pillar[5]arene: A theoretical research

The formation of host-guest inclusion complexes by Pillar [5]arene (P [5]) and cationic nitrogen heterocyclic molecules were studied by DFT calculations at B3LYP-D3/6-311 + G** level, together with their equilibrium geometries, binding energies and electronic structures. MESP, NCI-RDG and AIM topography analysis were performed to explore underlying interactions. Geometric structures of inclusion complexes were changed compared with the individual molecules; MESP analysis revealed the driving force for the binding process; QTAIM and NCI-RDG methods were utilized to reveal the underlying non-covalent interactions. The inclusion complexes in 1:1 ratio were stabilized through weak C–H⋯O hydrogen bonds, C–H···π, π+···π and van der Waals interactions. The calculated electrophilic charge transfer indicated that charge flowed from P [5] to guests. Gibbs free energy accompanying the recognition process certified that formation of complexes were spontaneous and thermodynamically favorable.

Anion-binding properties of π-electron deficient cavity in tetraoxacalix[2]arene[2]triazine by a computational study

Host-guest inclusion complex formation of tetraoxacalix[2]arene[2]triazine (1) with anions X(CH3COO−, ClO4−, BrO4−, IO4−, SO42−, SO32−, CO32−, SiO32−) was studied by DFT calculations at M062X/6-311+G** level, together with their equilibrium geometries, binding energies and electronic structures. MESP, NCI-RDG and AIM topography analysis were performed to explore underlying interactions. The inclusion complexes in 1:1 ratio were stabilized through a cooperative effect of non-covalent interactions, including anion-π, σ-interactions, hydrogen bonds and van der Waals interactions. The recognition process of anions within 1 was spontaneous both thermodynamically and dynamically. The structure of molecule 1 changed slightly after encapsulation, reflected in IR and NMR spectra. After complexation, the red shifts of CH stretching and triazine rings bending in IR were attributed by hydrogen bonds and anion-π interactions. Anions encased in the host cavity exhibited magnetic shielding; those bifurcate hydrogen bonds could cause chemical shifts signals in 1H NMR spectra.

Organophosphorus hydrolase-poly-β-cyclodextrin as a stable self-decontaminating bio-catalytic material for sorption and degradation of organophosphate pesticide.

A region suffering from an attack of a nerve agent requires not only a highly sorptive material but also a fast-acting catalyst to decontaminate the lethal chemical present. The product should be capable of high sorptive capacity, selectivity and quick response time to neutralize the long lasting harmful effects of nerve agents. Herein, we have utilized organophosphorus hydrolase (OPH) as a non-toxic bio-catalytic material held in with the supporting matrix of poly-β-cyclodextrin (PCD) as a novel sorptive reinforced self-decontaminating material against organophosphate intoxication. OPH coated PCD (OPH-PCD) will not only be providing support for holding enzyme but also would be adsorbing methyl paraoxon (MPO) used as a simulant, in a host-guest inclusion complex formation. Sorption trend for PCD revealed preference towards the more hydrophobic MPO against para-nitrophenol (pNP). The results show sorption capacity of 1.26 mg/g of 100 μM MPO with PCD which was 1.7 times higher compared to pNP. The reaction rate with immobilized OPH-PCD was found to be 23% less compared to free enzyme. With the help of OPH-PCD, continuous hydrolysis (100%) of MPO into pNP was observed for a period of 24 h through packed bed reactor with good reproducibility and stability of enzyme. The long-term stability also confirmed its stable nature for the investigation period of 4 days where it maintained activity. Combined with its fast and reactive nature, the resulting self-decontaminating regenerating material provides a promising strategy for the neutralization of nerve agents and preserving the environment.

Synthesis,characterization of 1-butyl-4-methylpyridinium lauryl sulfate and its inclusion phenomenon with β-cyclodextrin for enhanced applications

1-Butyl-4-methylpyridinium lauryl sulfate was synthesized and a number of spectroscopic techniques were used for the characterization. The surface active property was explored in different ways. The Host Guest inclusion complex formation with the synthesized compound inside the β-Cyclodextrin has been studied qualitatively as well as quantitatively with physicochemical, spectroscopic and advanced microscopic techniques. The Job plot from the UV–vis spectroscopy indicates the formation of both 1:1 and 2:1 inclusion. The inclusion complex has given the determining morphology with further evidence of 2:1 inclusion in HRTEM supported by DLS. Lastly, the 2D-NOESY has provided a conclusive mechanism for the inclusion phenomenon.

Encapsulation of quercetin in β-cyclodextrin and (2-hydroxypropyl)-β-cyclodextrin cavity: In-vitro cytotoxic evaluation

ABSTRACTThe formation of host-guest inclusion complex of Quercetin (QRC) with β-Cyclodextrin (β-CD) and (2-Hydroxypropyl)-β-Cyclodextrin (HP-β-CD) is prepared by various methods such as physical method (PM), kneading method (KM) and co-precipitation method (CP). The solid inclusion complex is characterized by UV, Fluorescence, FT-IR, SEM, powder XRD and TG/DTA analysis. The cytotoxic activity of the solid complex is performed against breast cancer cell line and it is noticed that there is better activity than the QRC alone. Hence, the solid complex showed an improvement in the anticancer activity against MDA MB 231 cell line.

Mechanism study of selected phenolic compounds determination using β-cyclodextrin-coated CdSe/ZnS quantum dots

β-Cyclodextrin (βCD)-coated CdSe/ZnS quantum dots (QDs), provide a sensitive method for the determination of phenolic compounds. The current study aimed to explain the mechanisms involved in photoluminescence quenching of CdSe/ZnS QDs, during the determination of quercetin and gallic acid, and select derivatives thereof. Quercetin, quercetin glycosides, gallic acid and gallate esters, were investigated to understand how the glycoside moiety in glycosides and the hydrocarbon chain in esters, affect the interactions of the investigated polyphenols with βCD-coated QDs. The phenomenon of βCD-coated CdSe/ZnS photoluminescence quenching, is caused by the effective formation of host-guest inclusion complexes between polyphenols and βCD. The presence of the glycoside moiety in the quercetin molecule reduced the effectiveness of the complex formation, while, in contrast, the efficiency of complexation increased with increasing hydrocarbon chain length of the gallate ester molecule. QD photoluminescence quenching may be a consequence of the proximity between the interacting phenolic compounds with the QD surface, rather than βCDs peeling off from the QD surface, resulting in structural destabilization. From the thermodynamic parameters, it was concluded that the formation of the complexes is based both on the van der Waals interactions forces and hydrophobic interactions between guest and host molecules. Ionic interactions may also play an important role in the effectiveness of polyphenol-βCD inclusion complex formation. In order to obtain QDs with long-term stability, there is a need to increase the zeta potential value of the QD surface. Recognition of the above-described mechanisms, should enable the optimization of existing methods and the development of new applications of βCD-coated CdSe/ZnS QDs, such as determination of octyl gallate in foodstuffs.

Attached β-cyclodextrin/γ-(2,3-epoxypropoxy) propyl trimethoxysilane to graphene oxide and its application in copper removal.

The environmental applications of graphene oxide and β-cyclodextrin (β-CD) have attracted great attention since their first discovery. Novel nanocomposites were successfully prepared by using an esterification reaction between β-cyclodextrin/γ-(2,3-epoxypropoxy) propyl trimethoxysilane grafted graphene oxide (β-CD/GPTMS/GO). The β-CD/GPTMS/GO nanocomposites were used to remove the Cu2+ from aqueous solutions. The characteristics of β-CD/GPTMS/GO were detected by scanning electron microscopy (SEM), Fourier transform infrared, X-ray diffraction (XRD), thermogravimetric analysis (TG) and energy dispersive X-ray (EDX). The dispersibility of graphene oxide was excellent due to the addition of β-CD. The adsorption isotherms data obtained at the optimum pH 7 were fitted by Langmuir isotherm model. The excellent adsorption properties of β-CD/GPTMS/GO for Cu2+ ions could be attributed to the apolar cavity structure of β-CD, the high surface area and abundant functional groups on the surface of GO. The adsorption patterns of β-CD/GPTMS/GO were electrostatic attraction, formation of host-guest inclusion complexes and the ion exchange adsorption. The efficient adsorption of β-CD/GPTMS/GO for Cu2+ ions suggested that these novel nanocomposites may be ideal candidates for removing other cation pollutants from waste water.

SERS-Based Flavonoid Detection Using Ethylenediamine-β-Cyclodextrin as a Capturing Ligand.

Ethylenediamine-modified β-cyclodextrin (Et-β-CD) was immobilized on aggregated silver nanoparticle (NP)-embedded silica NPs (SiO2@Ag@Et-β-CD NPs) for the effective detection of flavonoids. Silica NPs were used as the template for embedding silver NPs to create hot spots and enhance surface-enhanced Raman scattering (SERS) signals. Et-β-CD was immobilized on Ag NPs to capture flavonoids via host-guest inclusion complex formation, as indicated by enhanced ultraviolet absorption spectra. The resulting SiO2@Ag@Et-β-CD NPs were used as the SERS substrate for detecting flavonoids, such as hesperetin, naringenin, quercetin, and luteolin. In particular, luteolin was detected more strongly in the linear range 10−7 to 10−3 M than various organic molecules, namely ethylene glycol, β-estradiol, isopropyl alcohol, naphthalene, and toluene. In addition, the SERS signal for luteolin captured by the SiO2@Ag@Et-β-CD NPs remained even after repeated washing. These results indicated that the SiO2@Ag@Et-β-CD NPs can be used as a rapid, sensitive, and selective sensor for flavonoids.

Single-isomer carboxymethyl-γ-cyclodextrin as chiral resolving agent for capillary electrophoresis

Herein we report on the synthesis, characterization and the novel capillary electrophoretic use of octakis-(2,3-di-O-methyl-6-O-carboxymethyl)-γ-cyclodextrin sodium salt (ODMCM). ODMCM is the first single-isomer carboxymethyl-γ-cyclodextrin that is fully methylated on its secondary side and carries ionizable carboxymethyl functions on its primary side. ODMCM was prepared with high isomeric purity through a four-step synthetic procedure. The purity of each intermediate was characterized by appropriate chromatographic methods, while the isomeric purity of the carboxymethylated product was determined by an HPLC method using a CD-Screen-IEC column and by a capillary electrophoretic method using indirect UV detection, as well. The structural identification of the ODMCM was carried out by 1D, 2D NMR spectroscopy and ESI-MS. The acid-base characterization of the chiral selector was carried out by 1H NMR-pH titration. The chiral separation ability of the synthesized selector was studied by chiral capillary electrophoresis. ODMCM was used as a background electrolyte additive to separate enantiomers of representative pharmacologically significant model molecules such as propranolol, citalopram, ketamine, tapentadol and dapoxetine. The effects of the selector concentration and the pH of the background electrolyte on the enantiorecognition properties were investigated. 1H NMR spectroscopy was further applied to get deeper insight of the host-guest inclusion complex formation. The pH-dependent enantioselectivity of this new single-isomer chiral selector was demonstrated by chiral capillary electrophoresis and 1H NMR spectroscopy.

Ultrasensitive QRS made by supramolecular assembly of functionalized cyclodextrins and graphene for the detection of lung cancer VOC biomarkers.

A novel electronic nose system comprising functionalized β-cyclodextrin wrapped reduced graphene oxide (RGO) sensors with distinct ability of discrimination of a set of volatile organic compounds has been developed. Non-covalent modification of chemically functionalized cyclodextrin with RGO is carried out by using pyrene adamantane as a linker wherever necessary, in order to construct a supramolecular assembly. The chemical functionality on cyclodextrin is varied utilising the principle of selective chemical modification of cyclodextrin. In the present study, the combined benefits of the host-guest inclusion complex formation ability and tunable chemical functionality of cyclodextrin, as well as the high surface area and electrical conductivity of graphene, are utilized for the development of a set of highly selective quantum resistive chemical vapour sensors (QRS), which can be assembled in an electronic nose.

Study on the Determination of Carbendazim in Water and Vegetable Samples

The host-guest inclusion complex formation between 3, 3’-benzidine/β-cyclodextrin derivative (BDCD) and pesticide carbendazim was studied and characterized by TEM and XRD. The result showed that inclusion complex had hydrophobic small-molecule fluorophores. The fluorescence titration was performed to calculate binding constant, sensitivity factor and limit of detection of the resulting complex. Based on the enhancement of the fluorescence intensity of carbendazim produced throught complex formation, a new sensitive method for the determination of carbendazim was established. A linear relationship was obtained between the fluorescence intensity and carbendazim concentration in the range of 3.57 and 17.83 μmol/L. The correlation coefficient, the lowest limit of detection and RSD were 0.9916, 15.51 nmol/L and 2.13%, respectively. This method has better anti-interference ability and stability. The proposed method have been successfully applied to the determination of carbendazim pesticide residues in water, vegetable and fruit samples with satisfactory results, recoveries in the range of 87.56 % to 104.04 % were obtained.

Visible Intramolecular Charge Transfer Absorption of Bipyridinium-Crown Ether Conjugates in Response to the Alkali and Alkaline Earth Metal Ions

Two bipyridinium-benzocrown ether conjugates, 1 and 2, each appending styrene and naphthalene units at the nitrogen atom of pyridine in pyridyl-pyridinium-benzocrown ether conjugates via methylene spacer, respectively, have been prepared to investigate their guest responsive color changes and sensing abilities. Non-crown ether compounds, 3 and 4, have been also prepared as the analogue of 1 and 2, respectively. All compounds showed yellow color associated with intramolecular charge transfer (CT) absorptions, where the benzocrown ether or non-crown ether unit and bipyridinium unit act as π-electron donor and π-electron acceptor, respectively. Upon addition of metal ions as the guest, 1 and 2 showed color change to colorless with the blue shift in their CT absorptions, although 3 and 4 did not changed their color by the presence of the guest. This is due to the formation of host-guest inclusion complexes of 1 and 2 with metal ions. Such guest-induced color changes of 1 and 2 were used for alkali and alkaline earth metal ion sensing. The high sensitivities of 1 and 2 were observed for Li+ and Mg2+ among alkali and alkaline earth metal ions, respectively. The sensitivity value of 1 was roughly proportional to its binding constants. Similar trend of 2 was observed for alkali metal ions but not for alkaline earth metal ions. The substituent introduced at N-position in the bipyridinium-benzocrown ether conjugate may affect the ion sensing property.