Water-soluble Calix Research Articles

Molecular Modelling Comparisons, Optical and Band Gap Characterisation of 4-Sulfocalix[4]arene Thin Film

The advantageous property of water-soluble calixarenes is their ability to form stable complexes with inorganic guest molecules. Due to these attributes, their application in areas including molecular recognition, sensing, and supramolecular chemistry is extraordinarily alluring. The 4-sulfocalix[4]arene (SC[4]) is a water-soluble molecule and a derivative of the calixarene family that has both aromatic rings and sulfonate groups. The thin films were prepared using a spin-coating technique and characterised by Ultraviolet-Visible Spectroscopy (UV-Vis). By employing the Corey-Pauling-Koltun (CPK) model in conjunction with density functional theory (DFT), the height and diameter of SC[4] were precisely determined by devotedly representing its molecular shape and size. Then, the calixarene thin film’s optical properties and light absorption by the thin film were determined using the absorbance graph and Beer-Lambert law equation. The band gap energy of the thin film was determined to be equal to 4.44 eV through the Tauc-plot method. These results substantiate the integration of CPK models validated using DFT for measuring the size of SC[4] molecules and characterising the thin film’s optical characteristics. In a nutshell, the implementation of the CPK models was validated with DFT to determine the height and diameter of the SC[4] and the optical characterisation of its thin film was thoroughly determined in this study. The results obtained from this study are not only essential for understanding the properties of SC [4] but also inspire further research for multiple applications such as molecular recognition, adsorption and supramolecular chemistry.

Enhanced binding of methyl alkylammonium cations through preorganization of a water-soluble calix[4]pyrrole.

We describe the synthesis of two tetra-α aryl-extended calix[4]pyrroles (C[4]Ps) 4a-b bearing four terminal carboxylic groups in their meso-propyl chains defining the lower rims. The synthesized C[4]Ps became soluble (1-3 mM) in water at pD = 10. We probed the interaction of 4a towards tetra-methylammonium (G1) chloride in water using 1H NMR spectroscopy. The C[4]P 4a includes G1 in the shallow aromatic cavity defined by the pyrrole rings in cone conformation forming a 1 : 1 complex G1⊂4a. Pyridine-N-oxide (PNO) binding in the larger polar aromatic cavity of 4a results in the quantitative self-assembly of the supramolecular receptor PNO@4a featuring the pyrrole rings preorganized in cone conformation. The PNO@4a receptor displays improved binding properties towards G1 than the parent C[4]P 4a. We thermodynamically characterized (1H NMR titrations and ITC experiments) the 1 : 1 complexes of PNO@4a with a series of tetra-alkylammonium salts, including biologically relevant examples. The PNO@4a supramolecular receptor displays significant affinity (log K = 3-4) but lacks selectivity in water binding of methyl trialkyl ammonium cations. Cation-π and coulombic interactions are the main intermolecular forces stabilizing the complexes. We also performed DFT calculations to gain some insights into the complexes' structures.

Protein-macrocycle polymorphism: crystal form IV of the Ralstonia solanacearum lectin-sulfonato-calix[8]arene complex.

Controlled protein assembly and crystallization is necessary as a means of generating diffraction-quality crystals as well as providing a basis for new types of biomaterials. Water-soluble calixarenes are useful mediators of protein crystallization. Recently, it was demonstrated that Ralstonia solanacearum lectin (RSL) co-crystallizes with anionic sulfonato-calix[8]arene (sclx8) in three space groups. Two of these co-crystals only grow at pH ≤ 4 where the protein is cationic, and the crystal packing is dominated by the calixarene. This paper describes a fourth RSL-sclx8 co-crystal, which was discovered while working with a cation-enriched mutant. Crystal form IV grows at high ionic strength in the pH range 5-6. While possessing some features in common with the previous forms, the new structure reveals alternative calixarene binding modes. The occurrence of C2-symmetric assemblies, with the calixarene at special positions, appears to be an important result for framework fabrication. Questions arise regarding crystal screening and exhaustive searching for polymorphs.

Improvement effect of p-sulfonatocalix[4]arene on the performance of the PEG/salt aqueous two-phase system.

The PEG/salt aqueous two-phase system (ATPS) is the most common ATPS, but its application is still limited due to the restricted polarity difference between the two phases and the poor enhancement effect of adjuvants on ATPS performance so far. Unlike the adjuvants used so far, calixarenes can bind ions and molecules via multiple noncovalent interactions. In the present study, a water-soluble calixarene, p-sulfonatocalix[4]arene (SC[4]), was used for the first time as the adjuvant to improve the performance of the PEG 600/(NH4)2SO4 ATPS through multiple interactions. It is found that when the SC[4] and the SC[4]/imidazole ionic liquid ([Cnmim]Br) complex were used as the adjuvants, the formation of PEG 600/(NH4)2SO4 ATPS was enhanced, and the transfer of the extracts (including S-mandelic acid, L-tryptophan, and L-phenylalanine) into the PEG phase was promoted. Moreover, although the single [Cnmim]Br, a commonly used adjuvant, does not promote the migration of the target molecules into the polymer phase, the SC[4]/[Cnmim]Br complex is superior to SC[4] in enhancing the performance of the ATPS because the SC[4]/[Cnmim]Br aggregates enable more binding sites to combine with the extract. Besides, the partition coefficient of SC[4] in the PEG/trisodium citrate ATPS is much smaller than that in the PEG/(NH4)2SO4 ATPS, which is helpful for the recovery of extracts into the citrate phase.

Calix[4]arene Polyamine Triazoles: Synthesis, Aggregation and DNA Binding

Artificial gene delivery systems are in great demand from both scientific and practical biomedical points of view. In this paper, we present the synthesis of a new click chemistry calix[4]arene precursor with free lower rim and new water-soluble calixarene triazoles with 12 amino-groups on the upper rim (one with free phenol hydroxyl groups and two another containing four butyl or tetradecyl fragments). Aggregation in the series of amino-triazole calixarenes of different lipophilicity (calixarene with free phenol hydroxyl groups or butyl and tetradecyl fragments on the lower rim) was studied using dynamic light scattering and fluorescent pyrene probe. It was found that calix[4]arene with a free lower rim, like alkyl-substituted butyl calix[4]arene, forms stable submicron aggregates 150-200 nm in size, while the more lipophilic tetradecyl -substituted calix[4]arene forms micellar aggregates19 nm in size. Using UV-Vis spectroscopy, fluorimetry and CD, it was shown that amino-triazole calix[4]arenes bind to calf thymus DNA by classical intercalation. According to DLS and TEM data, all studied macrocycles cause significant DNA compaction, forming stable nanoparticles 50-20 nm in size. Among all studied calix[4]arenes the most lipophilic tetradecyl one proved to be the best for both binding and compaction of DNA.

Inclusion complexes of water-soluble calix[n]arenes with quercetin: preparation, characterization, water solubility, and antioxidant features

Inclusion complexes of water-soluble calix[n]arenes with quercetin: preparation, characterization, water solubility, and antioxidant features

The hydrophobic core effect in model bacterial membranes upon interaction with tetra-p-guanidinoethylcalix[4]arene

The calixarene derivative used in this study (tetra-p-guanidinoethylcalix[4]arene) shows in vitro activity against different Gram-positive and Gram-negative bacteria. The interaction between bacterial cell membranes and the water-soluble calixarene was investigated using model lipids spread as monomolecular films at the air–water interface. Compression and adsorption experiments, as well as Brewster angle microscopy, polarization modulation-infrared reflection–absorption spectroscopy and computer modeling permitted understanding of the intra- and intermolecular interaction in several lipid-calixarene systems. Because the affinity of the calixarene derivative for the membranes may be linked to the interaction with negative charges, phosphatidylglycerols were used as model lipids; the phosphatidylglycerols contained saturated or unsaturated hydrocarbon chains with different lengths. It was showed that the affinity of the calixarene for the monolayer depends on the structure of the phosphatidylglycerols side chains. This observation may be of interest for a further development of new antibiotics.

Protein-macrocycle framework engineering: supramolecular copolymerisation with two disparate calixarenes

ABSTRACT Water soluble calixarenes are versatile mediators of protein assembly, including the fabrication of crystalline frameworks. Here, we report the X-ray crystal structure of cytochrome c (cytc) co-crystallised with two different calixarenes: phosphonato-calix[6]arene (pclx6 ) and sulfonato-calix[8]arene (sclx8 ). Each calixarene type acts as an independent molecular glue that mediates cytc dimers within the crystal. The calixarene-mediated dimers combine to yield chains of cytc-sclx8 -cytc-pclx6-pclx6 repeating units. These supramolecular copolymer units pack together, via a protein-protein interface, to yield a porous dendrite-like assembly. Interestingly, the tri-component framework has features in common with previously reported structures of cytc in complex with pclx6 or sclx8 . Known protein-calixarene ‘building blocks’ combine in novel ways to yield the tri-component assembly, highlighting the versatility of calixarene molecular glues in protein crystal engineering.

Host–guest complex properties of calix[4]arene derivatives: a DFT study of adsorption and sensing of an anticancer drug, 5-fluorouracil

In this study, it has been reported the host–guest complex properties of calix[4]arene compounds (the 3rd generation supramolecule) against the 5-fluorouracil (5-FU) anticancer drug by density functional theory calculations at room temperature. The B3LYP hybrid method was used to determine the optimized structures of the host and guest molecules and their complexes. The adsorption energy changes of the complexes formed between calix[4]arene compounds and 5-FU drug were calculated to be negative values. The strongest interaction was determined for the water-soluble calix[4]arene compound with sulfonyl (–SO3H) groups (ΔE = − 98 kJ/mol and ΔH = − 100.5 kJ/mol). Moreover, it was determined that HOMO–LUMO gaps of all calix[4]arene compounds decreased. The charge transfer has occurred between the four calix[4]arene compounds and the drug molecule. The work function values of calix[4]arene compounds have been changed. These results indicate that calix[4]arene derivatives can be used as well-suited 5-FU sensor at room temperature. Solvent effect calculations have stated that the interaction of 5-FU molecule with the calix[4]arene compound with sulfonyl (–SO3H) groups weakens and the ΔE becomes less negative value (− 71.6 kJ/mol).

Self-Assembly of Discrete Porphyrin/Calix[4]tube Complexes Promoted by Potassium Ion Encapsulation.

The pivotal role played by potassium ions in the noncovalent synthesis of discrete porphyrin-calixarene nanostructures has been examined. The flattened-cone conformation adopted by the two cavities of octa-cationic calix[4]tube C4T was found to prevent the formation of complexes with well-defined stoichiometry between this novel water-soluble calixarene and the tetra-anionic phenylsulfonate porphyrin CuTPPS. Conversely, preorganization of C4T into a C4v-symmetrical scaffold, triggered by potassium ion encapsulation (C4T@K+), allowed us to carry out an efficient hierarchical self-assembly process leading to 2D and 3D nanostructures. The stepwise formation of discrete CuTPPS/C4T@K+ noncovalent assemblies, containing up to 33 molecular elements, was conveniently monitored by UV/vis spectroscopy by following the absorbance of the porphyrin Soret band.

Substitution Activated Precise Phototheranostics through Supramolecular Assembly of AIEgen and Calixarene.

Photodynamic therapy (PDT) is a promising noninvasive therapeutic technique and has attracted increasing interests in preclinical trials. However, the translation from laboratory to clinic often encounters the problem of undesired dark cytotoxicity of photosensitizers (PSs). Now, this challenge can be addressed by cascaded substitution activated phototheranostics using the host-guest strategy. Through electrostatical complexation of pyridinium-functionalized tetraphenylethylene, namely, TPE-PHO, and water-soluble calixarene, the dark cytotoxicity of TPE-PHO is dramatically inhibited. The nanoassemblies of the complex show enhanced biocompatibility and selectively locate at the cytoplasm in vitro. When TPE-PHO is competitively displaced from the cavity of calixarene by 4,4'-benzidine dihydrochloride at the tumor site, its dark cytotoxicity and photoactivity in tumor tissue are restored to give efficient PDT efficacy under light irradiation. The result from cell imaging reveals that TPE-PHO undergoes translocation from cytoplasm to mitochondria to kill the cancer cells during the cascaded supramolecular substitution process. In vivo tumor imaging and therapy are successfully implemented to evaluate the curative effect. Such a supramolecular strategy avoids tedious molecular synthesis and opens a new venue to readily tune the PS behaviors.

Specific Binding and Cooperative Binding of Dodecylpyridinium Chloride to Water-Soluble Calix[n]arenes and Effect of Cerium and Uranyl Cations

Abstract Binding of dodecylpyridinium chloride (DPC) to water-soluble calix[n]arenes (n = 4, 6, 8) (CALXSn) has been studied by potentiometric titration. The binding isotherms were found to be composed of two phases; one is strong specific binding to one site and the other is cooperative binding to residual sites. Thermodynamic parameters for the specific binding suggests that the complex is stabilized by van der Waals force between the alkyl chain of DPC and hydrophobic cavity of CALXSn in addition to electrostatic force between opposite charges of DPC and CALXSn. The specific site was highly reduced in the presence of cerium cation for CALXS4 and of uranyl cation for CALXS6 and by the pH change from 7.0 to 12.5 for CALXS8. These effects were interpreted by competitive binding of the metal cations and the pyridinium cation of DPC to the specific sites of CALXS4 and CALXS6, and by deprotonation of hydroxyl group having pKa = 10.1 and/or accompanying conformational change of CALXS8. The cooperative binding takes place in one stage for CALXS4 and CALXS6 but in two stages for CALXS8. The multiple-stage cooperativity was consistent with ‘inverted double cone’ conformation of CALXS8. The results were discussed as a model of ligand binding to protein local structure.

New water soluble p-sulphonatocalix[4]arene chemosensor appended with rhodamine for selective detection of Hg2+ ion

In this study, we present the synthesis of water soluble calixarene appended with rhodamine (CR) at lower rim as fluorescent moiety. The synthesized water soluble fluorescent derivative was characterized with spectroscopic techniques and fluorescence response was evaluated towards Hg2+ ion in aqueous environment. Fluorescence studies shows that upon addition of Hg2+, CR induce OFF-ON behaviour which follow CHEF process. Stoichiometric data show 1:1 coordination of metal and ligand with sensitivity of 3.55 × 10−13 molL−1 concentration range. Selectivity of CR towards Hg2+ ion was compared in the presence of other metal ions such as Pb2+, Cu2+, Zn2+, Cr3+, Ni2+, Co2+, Al3+, Cd2+ and Fe2+. Results show that these metal ions have not pronounced effect on fluorescence intensity on CR-Hg2+ complex.

Calixarene capture of partially unfolded cytochrome c.

Supramolecular receptors such as water-soluble calixarenes are in development as 'molecular glues' for protein assembly. Here, we obtained cocrystals of sulfonato-calix[6]arene (sclx6 ) and yeast cytochrome c (cytc) in the presence of imidazole. A crystal structure at 2.65Å resolution reveals major structural rearrangement and disorder in imidazole-bound cytc. The largest protein-calixarene interface involves 440Å2 of the protein surface with key contacts at Arg13, Lys73, and Lys79. These lysines participate in alkaline transitions of cytc and are part of Ω-loop D, which is substantially restructured in the complex with sclx6 . The structural modification also includes Ω-loop C, which is disordered (residues 41-55 inclusive). These results suggest the possibility of using supramolecular scaffolds to trap partially disordered proteins.

The Spectrophotometric Investigation of Interaction of Water-Soluble Calixarene with Coloring Agent Bioactive Giemsa Dye

Bu çalışmada, Giemsa floresan boyasının suda çözünür sülfonat kaliksaren türevleri ile etkileşimleri spektrofotometrik yöntemlerle incelenmiştir. Bu araştırmanın amacı sülfonat kaliks[n]arenler ve Giemsa arasındaki olası moleküller arası etkileşimi değerlendirmektir. Spektrofotometrik veriler, bu etkileşimin absorbsiyon ve emisyon ölçümlerindeki değişimlere bağlı olarak kaliks[n]arenler ve Giemsa arasında muhtemel bir bağlanma meydana geldiğini göstermiştir. Sülfonat kaliks[n]arenler ve Giemsa arasındaki moleküler etkileşim, Giemsa'nın, lökosit, eritrosit, nükleus ve sitoplazma morfolojisi gibi biyolojik boyama uygulamaları sırasında kullanılmasına ilişkin bazı durumlara yön verebilir.

A novel chrome-free tanning approach based on sulfonated tetraphenyl Calix[4]resorcinarene: Preparation and application

Chrome tannage is the main tanning method because of its excellent hydrothermal stability and physical performances. However, the chromium absorption is limited, so the emissions of solid wastes can bring many environmental issues and human health risks. Therefore, a novel chrome-free tanning agent based on a water-soluble calixarene has been attempted. Water-soluble calixarene is a chemical with a unique molecular structure, thermal stability and high chemical stability, it contains a lot of more active coordination of phenolic hydroxyl. In this work, tetraphenyl calix [4]resorcinarene (TC4R) was synthesized with one-step process, and then was sulfonated by concentrated sulfuric acid, which obtained the sulfonated tetraphenyl calix [4]resorcinarene (STC4R). The chemical structure of the TC4R and STC4R were detected by IR and H-NMR. Then STC4R was added to the tanning process as an experimental process and 6% conventional chrome tannage was added to tanning as control. The result shows that the Ts of tanned leather is 77.2 °C using 10% STC4R at final pH 4.0. SEM analyses show that collagen fibers have been dispersed, STC4R makes the fiber loosen and the fullness is increased. FT-IR shows that the hydrogen bond is formed between phenol hydroxyl of sulfonated calixarenes and amino of collagen in the tanning process. At the same time, STC4R does not enter the micro fibrils within the collagen, so three helix structures are not damaged and consistent with AFM.

Electrochemical properties of outer-sphere associates of bipyridyl and sepulchrate metal complexes with (thia)calix[4]arenes

The electrochemical one-electron reduction (oxidation) of bipyridyl metal complexes ([Co(bipy)3]3+, [Cr(bipy)3]3+, [Fe(bipy)3]2+, [Ru(bipy)3]2+ (as well as Co(III) sepulcrate)) with water-soluble (thia)calix[4]arenes has been studied by means of cyclic voltammetry. It has been shown that [M(bipy)3]3+/2+ bind to (thia)calix[4]arenes via sulfonate groups of the upper rim. Oxidized forms bind stronger than reduced ones leading to reduction (oxidation) of half-wave cathodic shift. The effect of predominant stabilization of oxidized forms of metal complexes for carboxylated calix[4]arene is stronger than for thiacalix[4]arene (ΔΔG0 = − 7.8 ÷ − 12.5 and − 3.7 kJ/mol, respectively). The redox-switchable outer-sphere binding of Co(III) sepulchrate via lower rim of carboxylated calix[4]arene has been revealed using cyclic voltammetry. The binding constants of outer-sphere associates based on calix[4]arenes and unstable metal complexes ([Co(sep)]2+, [Ru(bipy)3]3+, [Co(bipy)3]2+) have been calculated for the first time using 1H NMR titration and cyclic voltammetry data.

Supramolecular Organocatalysis in Water Mediated by Macrocyclic Compounds.

In the last decades many efforts have been devoted to design supramolecular organocatalysts able to work in water as the reaction medium. The use of water as solvent provides promising benefits with respect to environmental impact. In this context, macrocyclic compounds played a role of primary importance thanks to their ease of synthesis and their molecular recognition abilities toward the reactants. The aim of this review is to give an overview of the recent advances in the field of supramolecular organocatalysis in water, focusing the attention on calixarene and cyclodextrins derivatives. Calixarenes and cyclodextrins, thanks to their hydrophobic cavities, are able to host selectively the substrates isolating they from the reaction environment. In addition, the synthetic versatilities of these macrocycles permits to introduce useful functional groups in close proximity of the hydrophobic binding sites. Regarding the cyclodextrins (CDs), we have here reviewed the their most recent uses as organocatalysts for the synthesis of heterocyclic compounds, in multi-component reactions and in carbon-carbon bond forming reactions. Examples have been reported in which CD catalysts are able to drive the regiochemistry of common organic reactions. In addition, cyclodextrins bearing catalytically active chiral groups, have shown excellent enantioselectivity in the catalysis of organic reactions. Recently reported results have shown that calixarene derivatives are able to accelerate organic reaction under “on-water” conditions with a significant selectivity toward the reactants. Under “on-water conditions” the hydrophobic effect, induced by insoluble calixarene derivatives, forces the reactants and the catalyst to aggregate and thus accelerating the reaction between them thanks to an amplification of weak secondary interactions. Regarding the use of water-soluble calixarene organocatalysts, we have here reviewed their role in the acceleration of common organic reactions.

Comparison of Binding Affinities of Water-Soluble Calixarenes with the Organophosphorus Nerve Agent Soman (GD) and Commonly-Used Nerve Agent Simulants.

The formation of inclusion complexes of the water-soluble p-sulfonatocalix[n]arenes, where n = 4 or 6, with the Chemical Warfare Agent (CWA) GD, or Soman, and commonly used dialkyl methylphosphonate simulants has been studied by experimental solution NMR methods and by Molecular Mechanics (MMFF) and semi-empirical (PM6) calculations. Complex formation in non-buffered and buffered solutions is driven by the hydrophobic effect, and complex stoichiometry determined as 1:1 for all host:guest pairs. Low affinity complexes (Kassoc < 100 M−1) are observed for all guests, attributed to poor host–guest complementarity and the role of buffer cation species accounts for the low affinity of the complexes. Comparison of CWA and simulant behavior adds to understanding of CWA–simulant correlations and the challenges of simulant selection.

Identification of number and type of cations in water-soluble Cs+ and Na+ calix[4]arene-bis-crown-6 complexes by using ESI-TOF-MS

The treatment of cesium-contaminated wastewater has become one of the biggest issues. The selective Cs+ removal from wastewater containing competitive alkali metal ions such as Na+ is desired to reduce the volume of sludge. Therefore, the present work focused on water-soluble calix[4]arene-bis-crown-6 (W-BisC6) to selectively capture Cs+. For characterization of the complex, UV–vis spectroscopy is commonly used, however, due to the limited availability of information it can be hard to quickly identify the specific structures of some complexes. In this work, the electrospray ionization time of flight spectrometry (ESI-TOF-MS) is successfully utilized to identify the number and type of cations in W-BisC6-cation complexes. ESI-TOF-MS accurately recognized 4 types of complex (W-BisC6–Na+, W-BisC6–Cs+, W-BisC6–2Na+, W-BisC6–Na+–Cs+), and the experimental and simulated results were almost perfectly matched. It also revealed the difficulty of W-BisC6–2Cs+ complex formation under the present conditions. Thus, this technique is significantly helpful for rapid identification of the specific structures of complexes during Cs+-contaminated wastewater treatment.