Molecular Recognition and Complexation Thermodynamics of Dye Guest Molecules by Modified Cyclodextrins and Calixarenesulfonates

Application of sodium sulfobutylether-β-cyclodextrin based on encapsulation

Sodium Sulfobutylether-β-cyclodextrin (SBE-β-CD) is a derivative of β-cyclodextrin, characterized by its stereo structure, which closely resembles a truncated cone with a hydrophobic internal cavity. The solubility of insoluble substances within the hydrophobic cavity is significantly enhanced, reducing contact between the guest and the environment. Consequently, SBE-β-CD is frequently employed as a co-solvent and stabilizer. As the research progresses, it has been observed that the inclusion of SBE-β-CD is reversible and competitive. Besides, some inclusion complexes undergo distinct physicochemical property alterations compared to the guests. Additionally, certain guests exhibit varying inclusions with SBE-β-CD at different concentrations. These features have contributed to the expanding applications. SBE-β-CD finds widespread application in pharmaceutics as a protective agent and pKa regulator, in pharmaceutical analysis as a chiral substance separator, and in biomedical engineering for encapsulating dyes and modifying sensors. The article will elaborate in detail on the physicochemical properties of SBE-β-CD, encapsulation principles, and factors influencing the formation of inclusion complexes. Furthermore, the review focuses on the application of SBE-β-CD through encapsulation in pharmaceutics, pharmaceutical analysis, and biomedical engineering. Finally, the prospects and potential applications of SBE-β-CD are discussed.

Unique Metal-Ligand Interplay in Directing Discrete and Polymeric Derivatives of Isomeric Azole-Carboxylate. Varying Electronic Form, C-C Coupling, and Receptor Feature

This article dealt with the ruthenium and osmium derivatives of isomeric 1H-indazole-3-carboxylic acid/2H-indazole-3-carboxylic acid (H₂L1) and 1H-benzimidazole-2-carboxylic acid (H₂L2) along with the π-acidic bpy (bpy = 2,2'-bipyridine) and pap (pap = 2-phenylazopyridine) co-ligands. It thus extended structurally authenticated monomeric ([(bpy)₂Ru^II(HL1^-)]ClO₄ [1]ClO₄, (pap)₂Ru^II(L1^2-) 2, (bpy)₂Os^II(L1^2-) 3, (pap)₂Os^II(L1^2-) 4, (bpy)₂Ru^II(L2^2-) 5, (bpy)₂Os^II(L2^2-) 8, and (pap)₂Os^II(L2^2-) 9) and dimeric ([(bpy)₂Ru^II(μ-L2^2-)Ru^II(bpy)₂](ClO₄)₂ [6](ClO₄)₂) complexes. It also described modified L2'^2- (L2'^2- = 2,2'-bisbenzimidazolate)-bridged [(pap)₂Ru^II(μ-L2'^2-)Ru^II(pap)₂](ClO₄)₂ [7](ClO₄)₂, where L2'^2- was developed selectively with the {Ru(pap)₂} metal fragment via in situ intermolecular C-C coupling of the two units of decarboxylated benzimidazolate. Moreover, chemical oxidation (Os^II to Os^III) of (bpy)₂Os^II(L1^2-) 3 (E⁰ = 0.11 V versus SCE) and (bpy)₂Os^II(L2^2-) 8 (E⁰ = 0.12 V versus SCE) by AgClO₄ yielded unprecedented Os^III-Ag^I derived polymeric {[(bpy)₂Os^III-L1^2--Ag^I(CH₃CN)](ClO₄)₂}_n {[10](ClO₄)₂}_n and dimeric [(bpy)₂Os^III-L2^2--Ag^I(CH₃CN)](ClO₄)₂ [11](ClO₄)₂ complexes as a function of trans and cis orientations of the active N2 donor with special reference to the carboxylate O2 of L^2-, respectively. Microscopic (FE-SEM, TEM-EDX, and AFM) and DLS experiments suggested a homogeneously dispersed hollow spherical shaped morphology of {[10](ClO₄)₂}_n with an average particle size of 200-400 nm as well as its non-dissociative feature in the aprotic medium. Experimental (structure, spectroscopy, and electrochemistry) and theoretical (DFT/TD-DFT) explorations revealed a redox non-innocent feature of L^2- in the present coordination situations and the selective anion sensing (X = F^-, CN^-, and OAc^-) event of [1]ClO₄ involving a free NH group at the backface of HL1^-, which proceeded via the NH···X hydrogen bonding interaction.

Indazole-Derived Mono-/Diruthenium and Heterotrinuclear Complexes: Switchable Binding Mode, Electronic Form, and Anion Sensing Events

The article deals with the newer classes of mononuclear: [(acac)₂Ru^III(H-Iz)(Iz^-)] 1, [(acac)₂Ru^III(H-Iz)₂]ClO₄ [1]ClO₄/[1']ClO₄, and [(bpy)₂Ru^II(H-Iz)(Iz^-)]ClO₄ [2]ClO₄, mixed-valent unsymmetric dinuclear: [(acac)₂Ru^III(μ-Iz^-)₂Ru^II(bpy)₂]ClO₄ [3]ClO₄, and heterotrinuclear: [(acac)₂Ru^III(μ-Iz^-)₂M^II(μ-Iz^-)₂Ru^III(acac)₂] (M = Co:4a, Ni:4b, Cu:4c, and Zn:4d) complexes (H-Iz = indazole, Iz^- = indazolate, acac = acetylacetonate, and bpy = 2,2'-bipyridine). Structural characterization of all the aforestated complexes established their molecular identities including varying binding modes (N_a and N_b donors and 1H-indazole versus 2H-indazole) of the heterocyclic H-Iz/Iz^- in the complexes. Unlike [1']ClO₄ containing two NH protons at the backface of H-Iz units, the corresponding [1]ClO₄ was found to be unstable due to the deprotonation of its positively charged quaternary nitrogen center, and this resulted in the eventual formation of the parent complex 1. A combination of experimental and density functional theory calculations indicated the redox noninnocent feature of Iz^- in the complexes along the redox chain. The absence of intervalence charge transfer transition in the near-infrared region of the (Iz^-)₂-bridged unsymmetric mixed-valent Ru^IIIRu^II state in [3]ClO₄ suggested negligible intramolecular electronic coupling corresponding to a class I setup (Robin and Day classification). Heterotrinuclear complexes (4a-4d) exhibited varying spin configurations due to spin-spin interactions between the terminal Ru(III) ions and the central M(II) ion. Though both [3]ClO₄ and 4a-4d displayed ligand (Iz^-/Iz^•)-based oxidation, reductions were preferentially taken place at the bpy and metal (Ru^III/Ru^II) centers, respectively. Unlike 1 or [2]ClO₄ containing one free NH proton at the backface of H-Iz, [1']ClO₄ with two H-Iz units could selectively and effectively recognize F^-, OAc^-, and CN^- among the tested anions: F^-, OAc^-, CN^-, Cl^-, Br^-, I^-, SCN^-, HSO₄^-, and Η₂PΟ₄^- in CH₃CN via intermolecular NH···anion hydrogen bonding interaction. The difference in the sensing feature between [1']ClO₄ and 1/[2]ClO₄ could be rationalized by their pK_a values of 8.4 and 11.3/10.8, respectively.

Fluorescent Bis-Calix[4]arene-Carbazole Conjugates: Synthesis and Inclusion Complexation Studies with Fullerenes C60 and C70

Supramolecular chemistry has become a central theme in chemical and biological sciences over the last decades. Supramolecular structures are being increasingly used in biomedical applications, particularly in devices requiring specific stimuli-responsiveness. Fullerenes, and supramolecular assemblies thereof, have gained great visibility in biomedical sciences and engineering. Sensitive and selective methods are required for the study of their inclusion in complexes in various application fields. With this in mind, two new fluorescent bis-calix[4]arene-carbazole conjugates (4 and 5) have been designed. Herein, their synthesis and ability to behave as specific hosts for fullerenes C₆₀ and C₇₀ is described. The optical properties of the novel compounds and their complexes with C₆₀ and C₇₀ were thoroughly studied by UV-Vis and steady-state and time-resolved fluorescence spectroscopies. The association constants (K_a) for the complexation of C₆₀ and C₇₀ by 4 and 5 were determined by fluorescence techniques. A higher stability was found for the C₇₀@4 supramolecule (K_a = 5.6 × 10⁴ M⁻¹; ΔG = −6.48 kcal/mol). Evidence for the formation of true inclusion complexes between the host 4 and C₆₀/C₇₀ was obtained from NMR spectroscopy performed at low temperatures. The experimental findings were fully corroborated by density functional theory (DFT) models performed on the host–guest assemblies (C₆₀@4 and C₇₀@4).

Possible effects of fluxionality of a cavitand on its catalytic activity through confinement

The discovery of fullerenes was a huge milestone in the scientific community, and with it came the urge to discover and analyze various small and large atomic and molecular clusters having a cavity. These cavitands of varied shapes and sizes have wide applications in the encapsulation of rare gas atoms to induce bond formation between them, storage of hydrogen and hydrocarbons to be used as alternative sources of fuel, catalyzation of otherwise slow reactions without using a catalyst, activation of small gas molecules, etc. Various cavitands like fullerenes, [ExBox]4+, cucurbit[n]urils, borospherenes, octa acid, etc. have been used for this purpose. Some clusters including cavitands exhibit fluxional behaviour. Systems in a confined environment often manifest interesting variations in their properties and behaviour, compared to their unconfined counterparts, facilitating the aforementioned applications. In this perspective article, we explore the possibility of making use of this extra degree of freedom, viz., the fluxionality, in changing the catalytic activity of the cavitand.

Studying the Complex Formation of Sulfonatocalix[4]naphthalene and Meloxicam towards Enhancing Its Solubility and Dissolution Performance

The interaction between meloxicam and sulfonatocalix [4] naphthalene was investigated to improve the meloxicam solubility and its dissolution performance. Solubility behavior was investigated in distilled water (DW) and at different pH conditions. Besides, solid systems were prepared in a 1:1 molar ratio using coevaporate, kneading, and simple physical mixture techniques. Further, they were characterized by PXRD, FT-IR, DCS, and TGA. In vitro dissolution rate for coevaporate, kneaded, and physical mixture powders were also investigated. Solubility study revealed that meloxicam solubility significantly increased about 23.99 folds at phosphate buffer of pH 7.4 in the presence of sulfonatocalix [4] naphthalene. The solubility phase diagram was classified as A_L type, indicating the formation of 1:1 stoichiometric inclusion complex. PXRD, FT-IR, DCS, and TGA pointed out the formation of an inclusion complex between meloxicam and sulfonatocalix [4] naphthalene solid powders prepared using coevaporate technique. In addition, in vitro meloxicam dissolution studies revealed an improvement of the drug dissolution rate. Furthermore, a significantly higher drug release (p ≤ 0.05) and a complete dissolution was achieved during the first 10 min compared with the other solid powders and commercial meloxicam product. The coevaporate product has the highest increasing dissolution fold and RDR₁₀ in the investigated media, with average values ranging from 5.4-65.28 folds and 7.3-90.7, respectively. In conclusion, sulfonatocalix [4] naphthalene is a promising host carrier for enhancing the solubility and dissolution performance of meloxicam with an anticipated enhanced bioavailability and fast action for acute and chronic pain disorders.

Supramolecular and suprabiomolecular photochemistry: a perspective overview

In this perspective review article, we have attempted to bring out the important current trends of research in the areas of supramolecular and suprabiomolecular photochemistry. Since the spans of the subject areas are very vast, it is impossible to cover all the aspects within the limited space of this review article. Nevertheless, efforts have been made to assimilate the basic understanding of how supramolecular interactions can significantly change the photophysical and other related physiochemical properties of chromophoric dyes and drugs, which have enormous academic and practical implications. We have discussed with reference to relevant chemical systems where supramolecularly assisted modulations in the properties of chromophoric dyes and drugs can be used or have already been used in different areas like sensing, dye/drug stabilization, drug delivery, functional materials, and aqueous dye laser systems. In supramolecular assemblies, along with their conventional photophysical properties, the acid-base properties of prototropic dyes, as well as the excited state prototautomerization and related proton transfer behavior of proton donor/acceptor dye molecules, are also largely modulated due to supramolecular interactions, which are often reflected very explicitly through changes in their absorption and fluorescence characteristics, providing us many useful insights into these chemical systems and bringing out intriguing applications of such changes in different applied areas. Another interesting research area in supramolecular photochemistry is the excitation energy transfer from the donor to acceptor moieties in self-assembled systems which have immense importance in light harvesting applications, mimicking natural photosynthetic systems. In this review article, we have discussed varieties of these aspects, highlighting their academic and applied implications. We have tried to emphasize the progress made so far and thus to bring out future research perspectives in the subject areas concerned, which are anticipated to find many useful applications in areas like sensors, catalysis, electronic devices, pharmaceuticals, drug formulations, nanomedicine, light harvesting, and smart materials.

Cyclodextrin pendant polymer as an efficient drug carrier for scutellarin

A novel β-cyclodextrin pendant polymer (ε-PL-CD), composed of poly(ε-lysine) (ε-PL) main chain and glycine-β-cyclodextrin (Gly-CD) side chains, was prepared by a simple two-step procedure. The ε-PL-CD was investigated as a drug carrier of hydrophobic drug scutellarin (SCU). The characterization and complexation mode of the SCU:ε-PL-CD were researched in both solution and solid state by means of photoluminescence spectroscopy, ¹H and 2D NMR, X-Ray powder diffraction (XRPD), thermal gravimetric analysis, Particle size and Zeta potential. The solubility test indicated that the solubilizing ability of SCU:ε-PL-CD was significantly improved compared with SCU:β-CD and free SCU. Besides, in vitro cell experiment, it was found that SCU:ε-PL-CD has a strong inhibitory effect on the growth and invasion of tumor cells. The present study provides useful information for ε-PL-CD as a drug carrier material.

Mechanism and optimization of supramolecular complexation-enhanced fluorescence spectroscopy for the determination of SN-38 in plasma and cells

Quantitative detection of two different forms of SN-38 in biological samples is, currently, cumbersome and difficult. A revisit to the mechanism of supramolecular complexation-enhanced fluorescence spectroscopy helps to optimize the determination of SN-38 in plasma and the cellular pharmacokinetics in A549 cells based on the supramolecular complexation. Firstly, the inclusion mechanism dominated by thermodynamic constants was determined by measuring kinetic/thermodynamic parameters (k_on , k_off , ΔG, ΔH, ΔS). On this basis, the best effect of fluorescence sensitization was optimized through screening the interaction conditions (cyclodextrin species and concentrations, drug levels, temperature, pH of the buffer, and reaction time). Furthermore, the proportional relationship between the concentration of the inclusion complex and the fluorescence intensity was confirmed. Finally, a highly sensitive, selective spectrofluorimetric method was established and validated for quantitative analysis of the lactone and carboxylate molecular states of SN-38 plasma levels in rats and cell membrane transfer kinetics in A549 cell lines. The limits of detection for the lactone and carboxylate forms in plasma were found to be 0.44 ng·ml^-1 and 0.28 ng·ml^-1 , respectively. Precision and accuracy met the requirements of biological samples analysis. The proposed detection method provided a reference for elucidating the biodistribution of SN-38.

Highly Sensitive and Selective Fluorescent Probes for Cu(II) Detection Based on Calix[4]arene-Oxacyclophane Architectures

A new topological design of fluorescent probes for sensing copper ion is disclosed. The calix[4]arene-oxacyclophane (Calix-OCP) receptor, either wired-in-series in arylene-alt-ethynylene conjugated polymers or standing alone as a sole molecular probe, display a remarkable affinity and selectivity for Cu(II). The unique recognition properties of Calix-OCP system toward copper cation stem from its pre-organised cyclic array of O-ligands at the calixarene narrow rim, which is kept in a conformational rigid arrangement by a tethered oxacyclophane sub-unit. The magnitude of the binding constants (Ka = 5.30 - 8.52 × 104 M-1) and the free energy changes for the inclusion complexation (-ΔG = 27.0 - 28.1 kJmol-1), retrieved from fluorimetric titration experiments, revealed a high sensitivity of Calix-OCP architectures for Cu(II) species. Formation of supramolecular inclusion complexes was evidenced from UV-Vis spectroscopy. The new Calix-OCP-conjugated polymers (polymers 4 and 5), synthesized in good yields by Sonogashira-Hagihara methodologies, exhibit high fluorescence quantum yields (ΦF = 0.59 - 0.65). Density functional theory (DFT) calculations were used to support the experimental findings. The fluorescence on-off behaviour of the sensing systems is tentatively explained by a photoinduced electron transfer mechanism.

Does the degree of substitution on the cyclodextrin hosts impact their affinity towards guest binding?

The degree of substitution on βCD rims by sulfobutylether groups significantly modulates the binding affinity of the SBE_nβCD hosts for the studied cationic guest molecule.

Associations of Water-Soluble Macrocyclic Hosts with 4-Aminoazobenzene: Impact of pH

An investigation of the pH effect on the inclusion complexes of β-cyclodextrins and calixarenesulfonates with 4-aminoazobenzene was conducted both by experiments and molecular simulations. The whole thermodynamic characterizations of the association between hosts and 4-aminoazobenzene ( K, Δ_r G⁰, Δ_r H⁰, and TΔ_r S⁰) were determined by UV-visible spectroscopy. β-Cyclodextrin inclusion complexes are not affected by pH change unlike those obtained with calixarenes. All the studied systems were enthalpically favored. Nevertheless, the entropic behavior is different depending on the host. In order to interpret these experimental results, molecular simulations were used to calculate the number of atoms inserted into the cage-like host compounds and the number of water molecules expelled from the cavity.

Enhanced reductive de-chlorination of a solvent contaminated aquifer through addition and apparent fermentation of cyclodextrin

In a field study, aqueous cyclodextrin (CD) was investigated for its ability to extract chlorinated volatile organic compounds (cVOC), such as trichloroethylene (TCE), 1,1,1-trichloroethane (TCA), and dichloroethene (DCE) through in-situ flushing of a sandy aquifer. After cessation of aquifer flushing, a plume of CD was left. Changes in CD, cVOC, and inorganic terminal electron acceptors (TEAs) (DO, nitrate, sulfate, iron) were monitored in four rounds of wellwater sampling (20, 210, 342, and 425days after cessation of active pumping). Post-CD flushing VOC levels rebounded (850% for TCE, 190% for TCA, and 53% for DCE) between the first two sampling rounds, apparently due to rate-limited desorption from aquifer media and dissolution from remaining NAPL. However, substantial reduction in the mass of TCE (6.3 to 0.11mol: 98%) and TCA (2.8 to 0.73mol: 74%) in groundwater was observed between 210 and 425days. DCE should primarily be produced from the degradation of TCE and is expected to subsequently degrade to chloroethene. Since DCE levels decreased only slightly (0.23 to 0.17mol: 26%), its degradation rate should be similar to that produced from the decaying TCE. Cyclodextrin was monitored starting from day 210. The mass of residual CD (as measured by Total Organic Carbon) decreased from 150mol (day 210) to 66 (day 425) (56% decrease). The naturally anaerobic zone within the aquifer where residual CD mass decreased coincided with a loss of other major potential TEAs: nitrate (97% loss), sulfate (31%) and iron (31%). In other studies, TCE and 1,1,1-TCA have been found to be more energetically favorable TEAs than sulfate and iron and their degradation via reductive dechlorination has been found to be enhanced by the fermentation of carbohydrates. Such processes can explain these observations, but more investigation is needed to evaluate whether residual levels of CD can facilitate the anaerobic degradation of chlorinated VOCs.

Inhibition of the prototropic tautomerism in chrysazine by p-sulfonatocalixarene hosts

This study reveals the unusual inhibition of excited-state prototropic tautomerism of Chrysazine by p-sulfonatocalix[4,6]arene hosts.

Supramolecular Interaction-Assisted Fluorescence and Tunable Stimuli-Responsiveness of l-Phenylalanine-Based Polymers

Supramolecular host-guest interactions between randomly methylated β-cyclodextrin (RM β-CD) and side-chain phenylalanine (Phe) and Phe-Phe dipeptide-based homopolymers have been employed for the amplification of fluorescence emission of otherwise weakly fluorescent amino acid Phe. The host-guest complex has been characterized by ¹H and ¹³C NMR spectroscopy, two-dimensional rotating-frame overhauser spectroscopy, Fourier-transform infrared spectroscopy, UV-visible spectroscopy, and fluorescence spectroscopy. To gain insights into the origin of fluorescence in homopolymers, density functional theory calculations were performed where phenyl moieties inside the less polar core of β-CD were observed to form a π-π coupled complex resulting in an enhanced emission. Furthermore, the complex-forming ability of Phe, the guest molecule, has been employed in tuning the cloud point temperature (T_CP) of statistical copolymers derived from side-chain Phe/Phe-Phe-based methacrylate monomers and N-isopropylacrylamide. By varying the co-monomer feed ratios in the statistical copolymer and hence the concentration of RM β-CD throughout the polymer chain, host-guest interaction-assisted broad tunability in T_CP of the supramolecular polymeric complex has been achieved.

Synthesis, crystal structure and remote allosteric binding properties of cone thiacalix[4]pseudocrown receptors bearing anthraquinone function and different arms

Herein, three novel cone thiacalix[4]pseudocrown receptors 1–3, bearing anthraquinone and triazole functions as well as different side arms, were successfully synthesized via a double click reaction as the key step.

Role of donor-acceptor macrocycles in sequence specific peptide recognition and their optoelectronic properties: a detailed computational insight

In this study, we have considered an experimentally synthesized organic donor-acceptor (D-A) macrocycle (CPP-TCAQ) and have modified it by incorporating different acceptor groups. We have performed density functional theory and classical molecular dynamics studies on these D-A macrocycles. We have clearly shown that cyclo[10]paraphenylene-2,6-tetracyanoanthraquinodimethanylene (CPP-TCAQ) isomers interact specifically with one particular peptide sequence tyr-leu-ala, over its structural isomer, tyr-ala-leu. However, other functionalized macrocycles bind to the tyr-ala-leu peptide sequence over tyr-leu-ala. Our calculations show that the presence of hydrogen bonds as well as π-π interactions responsible for this specific selection. Interestingly, it is the additional charge transfer induced dipolar interactions that favour binding of the tripeptide with the bulky C-terminal leucine amino acid, tyr-ala-leu. We confirmed that these host-guest complexes are stable in water medium as well as at room temperature. Thus, these hosts can bind effectively to any protein fragment bearing a particular tripeptide. Interestingly, the macrocycle, which recognizes the peptide sequence with a bulky C-terminal amino acid, also shows photophysical properties. The reasons for this happen to be the same (dipolar interactions introduce dipole allowed states for optical absorption as well as attracting the oppositely oriented dipolar groups). Recognition of the peptide sequence with a bulky C-terminal group is carried out for the first time with this functionalised macrocycle, which in addition shows photophysical properties.

Substituent directed selectivity in anion recognition by a new class of simple osmium-pyrazole derived receptors

The present article deals with the structurally, spectroscopically and electrochemically characterised osmium-bipyridyl derived complexes [(bpy)2Os(II)(HL1)Cl]ClO4 [1]ClO4 and [(bpy)2Os(II)(HL2)Cl]ClO4 [2]ClO4 incorporating neutral and monodentate pyrazole derivatives (HL) with one free NH function (bpy = 2,2'-bipyridine, HL1 = pyrazole, HL2 = 3,5-dimethylpyrazole). The crystal structures of [1]ClO4 and [2]ClO4 reveal intramolecular hydrogen bonding interactions between the free NH proton of HL and the equatorially placed Cl(-) ligand (N-HCl) with donor-acceptor distances of 3.114(7) Å and 3.153(6) Å as well as intermolecular hydrogen bonding interactions between the NH proton and one of the oxygen atoms of ClO4(-) (N-HO) with donor-acceptor distances of 2.870(10) Å and 3.024(8) Å, respectively. The effect of hydrogen bonding interactions has translated into the less acidic nature of the NH proton of the coordinated HL with estimated pKa > 12. 1(+) and 2(+) exhibit reversible Os(II)/(III) and irreversible Os(III)/(IV) processes in CH3CN within ± 2.0 V versus SCE. The effect of 3,5-dimethyl substituted HL2 on 2(+) has been reflected in the appreciable lowering (40 mV) of the Os(II/III) potential, along with the further decrease in the acidity of the NH proton (pKa > 13.0) with regard to HL1 coordinated 1(+) (pKa: ∼ 12.3). The electronic spectral features of Os(ii) (1(+)/2(+)) and electrochemically generated Os(III) (1(2+)/2(2+)) derived complexes have been analysed by TD-DFT calculations. The efficacy of the 1(+) and 2(+) encompassing free NH proton towards the anion recognition process has been evaluated by different experimental investigations using a wide variety of anions. It however establishes that receptor 1(+) can recognise both F(-) and OAc(-) in acetonitrile solution, while 2(+) is exclusively selective for the F(-) ion.

Fostering protein–calixarene interactions: from molecular recognition to sensing

An highly selective direct sensing of cytochrome c by a bis-calix[4]arene-carbazole conjugate (CCC-1) in aqueous-based medium at nanomolar levels is disclosed. An electron transfer (ET) between complexed partners mediates the sensory event.

[Ru(phen)2dppz]2+ luminescence reveals nanoscale variation of polarity in the cyclodextrin cavity

Insertion of dppz with phosphorylated β-cyclodextrin results in multi-exponential [Ru(phen)₂dppz]²⁺ emission; binding is weaker than [Ru(phen)₃]²⁺, but shows stereoselectivity.

Inclusion complex formation of ternary system: Fluoroscein-p-sulfonato calix[4]arene-Cu(2+) by cooperative binding

The aqueous solution of fluorescein-para sulfonato calix[4]arene-metal ion complex has been studied based on absorption, fluorescence, (1)H NMR and FTIR spectroscopic results. It was found that the fluorescence intensity quenched regularly upon addition of pSCX4 and metal ion. The quenching constants and binding constants were determined for pSCX4-FL and pSCX4-FL-Cu(2+) systems. 1:1 stoichiometry is obtained for pSCX4-Cu(2+) system by continuous variation method. The NMR and IR results indicates the interaction among FL, pSCX4 and Cu(2+). The combined results demonstrate the cooperative binding to design the complex for ternary system. The life time for binary and ternary system has been studied.

Recognition of fractional non-innocent feature of osmium coordinated 2,2′-biimidazole or 2,2′-bis(4,5-dimethylimidazole) and their interactions with anions

The non-innocent feature of osmium coordinated doubly deprotonated 2,2′-biimidazole derivatives in symmetric dimeric complexes leads to a mixed electronic structural configuration.

High affinity of p-sulfonatothiacalix[4]arene with phenanthroline-diium in aqueous solution

The molecular binding behavior of sulfonated calixarenes with phenanthroline-diium guests were systemically investigated. p-Sulfonatothiacalix[4]arene shows a high affinity with phenanthroline-diium guests in the order of magnitude of 105 M⁻¹.

Sugar-functionalized water-soluble pillar[5]arene and its host–guest interaction with fullerene

The host–guest interaction between a neutral water-soluble pillar[5]arene containing ten sugar moieties and C₆₀ was investigated.

Investigation on the inclusion interaction of 4-sulfonatocalix[n]arenes with 1-(4-nitrophenyl)piperazine

The inclusion behaviors of 4-Sulfonatocalix[n]arenes (SCXn) (n=4, 6, 8) with 1-(4-nitrophenyl)piperazine (NPP) were investigated by UV spectroscopy and fluorescence spectroscopy at different pH values (pH=3.05, 6.50, 8.40). The UV absorption and fluorescence intensity of NPP remarkably increased in presence of SCXn revealing formation of the inclusion complexes between NPP and SCXn. Moreover, the formation constants (K) of inclusion complexes were also determined by the non-linear fitting method, and the obtained data showed that the formation constants decreasedgradually with the increasing of the pH value. When the pH value was 3.05, the formation constant of NPP with SCX8 reached a maximum of 1.7×10(7) L mol(-1). The stoichiometric ratio was verified to be 1:1 by the continuous variation method. Meanwhile FT-IR and DSC analysis also indicated that NPP could form the inclusion complex with SCXn. In order to explore the inclusion mechanism of NPP with SCXn, 1H NMR and molecular modeling studies were carried out and experimental results showed that the part of benzene ring of NPP penetrated into the hydrophobic cavity of SCXn.

Survey on the complexation character of p-sulfonatocalix[n]arenes and Caffeic acid

In this work the inclusion complex formation of Caffeic acid (CA) with p-sulfonatocalix[n]arenes (SCXn, n=4, 6, 8) is reported aiming to improve the antioxidant activity, thermal stability and photostability properties of CA. Evidence for the formation was obtained using fluorescence spectroscopy, nuclear magnetic resonance spectroscopy (NMR), pulsed field gradient NMR (PFG-NMR), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and scanning electron microphotographs (SEM). Experimental conditions including concentrations of SCXn and pH were investigated for the inclusion formation in detail. The results showed that CA was able to form inclusion complexes with SCXn in a molar ratio of 1:1, and the formation constants were varied with the pH conditions. NMR spectroscopy indicated that both the aromatic ring and the vinyl group of CA were partially covered by SCXn.

Investigation on the inclusion and toxicity of acriflavine with cyclodextrins: a spectroscopic approach

Acriflavine hydrochloride (AFN) is a prospective drug worn in the eradication of HIV1 infection. The toxicity and adverse side effects renders the potent drug to limits its usage. However, to overcome the dilemma we have aimed to select carriers with great complexation efficiencies in different cyclodextrins (CDs) of varying cavity size. The interaction of AFN with α, β and γ-CDs were investigated using absorption and steady state as well as lifetime measurements. From the obtained data it was found that AFN fits in the cavity of α and β-CDs but unable to form inclusion complex with γ-CD. The effect of quencher molecules during the inclusion phenomena of AFN with CDs was explored via steady state measurements. The nature of binding forces responsible for the inclusion of AFN with CDs was discussed by using thermodynamic parameters. Using Benesi-Hildebrand equation the stoichiometry of AFN with CDs was predominantly found to be 1:1. To get deeper in situ, the in vitro toxicity of AFN and its complexation product were probed by Artemia salina sp. The toxicity of AFN was reduced when complexed with α and β-CDs.

Host-guest interaction between herbicide oxadiargyl and hydroxypropyl-β-cyclodextrin

In the face of a growing human population and increased urbanization, the demand for pesticides will simply rise. Farmers must escalate yields on increasingly fewer farm acres. However, the risks of pesticides, whether real or perceived, may force changes in the way these chemicals are used. Scientists are working toward pest control plans that are environmentally sound, effective, and profitable. In this context the development of new pesticide formulations which may improve application effectiveness, safety, handling, and storage can be pointed out as a solution. As a contribution to the area, the microencapsulation of the herbicide oxadiargyl (OXA) in (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD) was performed. The study was conducted in different aqueous media (ultrapure water and in different pH buffer solutions). In all cases an increment of the oxadiargyl solubility as a function of the HP-β-CD concentration that has been related to the formation of an inclusion complex was verified. UV-Vis and NMR experiments allowed concluding that the stoichiometry of the OXA/HP-β-CD complex formed is 1 : 1. The gathered results can be regarded as an important step for its removal from industrial effluents and/or to increase the stabilizing action, encapsulation, and adsorption in water treatment plants.

Electronic structures and selective fluoride sensing features of Os(bpy)2(HL2−) and [{Os(bpy)2}2(μ-HL2−)]2+ (H3L: 5-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-4-carboxylic acid)

The non-innocence of coordinated HL²⁻ in [(bpy)₂Os(HL²⁻)]ⁿ (1ⁿ) and (2ⁿ) and their selectivity towards F⁻ recognition were evaluated.

Investigation of the inclusion interaction of p-sulfonatocalix[6]arene with triamterene

The inclusion complexation behavior of p-sulfonatocalix[6]arene (SCX6) with triamterene (TA) was investigated by fluorescence spectroscopy, UV-Vis spectroscopy, (1)H and 2D NMR, FT-IR, SEM and DSC. The results indicate that TA is able to form an inclusion complex with SCX6. The inclusion complex has a stoichiometry of 1:1 at pH 6.50. In addition, the water solubility of TA was obviously increased in the inclusion complex with SCX6.

Synergistically enhanced electrochemical response of host-guest recognition based on ternary nanocomposites: reduced graphene oxide-amphiphilic pillar[5]arene-gold nanoparticles

An amphiphilic pillar[5]arene (AP5) was modified onto the surface of reduced graphene oxide (RGO) to form the water-dispersive RGO-AP5 nanocomposite. And then, as-prepared gold nanoparticles (AuNPs) self-assembled onto the surface of RGO-AP5 through amido groups of AP5 to achieve RGO-AP5-AuNPs nanocomposites. It was verified that a large amount of AP5 molecules had been effectively loaded onto the surface of RGO and lots of AuNPs could be uniformly dispersed on RGO-AP5. Electrochemical results showed that the RGO-AP5 could exhibit selective supramolecular recognition and enrichment capability toward guest molecules. More significantly, in electrochemical sensing the guest molecules, ternary nanocomposites RGO-AP5-AuNPs performed the synergetic action of multifunctional properties, which were excellent performances of RGO, selective supramolecular recognition, and enrichment capability of AP5 and catalytic property of AuNPs for guest molecules. Therefore, RGO-AP5-AuNPs showed an outstanding analyzing performance for DA with broad linear range (1.5 × 10(-8) to 1.9×10(-5) M) and low detection limit (1.2 × 10(-8) M) at a signal-to-noise ratio of 3.

Inclusion complexes of quercetin with three β-cyclodextrins derivatives at physiological pH: spectroscopic study and antioxidant activity

Properties of the inclusion complexes of quercetin (QUE) with sulfobutyl ether-β-cyclodextrin (SBE-β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), and methylated-β-cyclodextrin (M-β-CD) in tris-HCl buffer solutions of pH 7.40 were investigated. The stoichiometry and thermodynamic parameters for the complexation process (stability constants K, Gibbs free energy change ΔG, enthalpy change ΔH and entropy change ΔS) were determined using phase-solubility and fluorescence spectra analysis. The thermodynamic studies indicated that the inclusion reactions between QUE and the three β-CDs are enthalpy-driven processes. Proton nuclear magnetic resonance spectroscopy indicated that B-ring, C-ring, and part of A-ring of QUE interact with the cavity of β-CDs. The antioxidant activity of QUE and its inclusion complexes were determined by the scavenging of stable radical DPPH(*). The results showed that the complexed QUE/CDs were more effective than free QUE, with the QUE/SBE-β-CD complex as the best form.