Synthesis and characterization of a new reusable calix[4]arene-bonded silica gel sorbent for antidiabetic drugs.

A novel calix[4]arene-bonded silica gel (C4BS) is prepared by covalent attachment of a calix[4]arene derivative to silica gel through a thiol-ene process. The structure and properties of C4BS were studied by Fourier Transform Infra-Red (FTIR) spectroscopy, thermal gravimetric analysis (TGA), elemental analysis (CHN), scanning electron microscopy (SEM), and surface area analysis (BET). In addition, the binding affinity of some antidiabetic drugs towards C4BS was investigated, by quantitative measurement of the drugs in aqueous solution using UV-visible spectroscopy. Results showed that C4BS has higher affinities than plain silica gel for binding to empagliflozin, dapagliflozin and linagliptin at neutral pH, while metformin hydrochloride was not adsorbed efficiently using either C4BS or plain silica gel. Thus, C4BS can be introduced as a promising binder for selective adsorption of the quoted antidiabetic drugs in pharmaceutical effluents, while being reusable by aqueous/acetonitrile (1 : 1) extraction.

Synthesis of a new chitosan-p-tert-butylcalix[4]arene polymer as adsorbent for toxic mercury ion.

In this paper, we have synthesized a novel chitosan-p-tert-butylcalix[4]arene polymer (CCP) as a highly efficient adsorbent for mercury ion (Hg2+) removal from water. In fact, a lower rim diamine derivative of p-tert-butylcalix[4]arene has been cross-linked with chitosan chain by carbonyl diimidazole (CDI) as the linker. CDI forms a urea linkage between calix[4]arene diamine derivative and amine groups of the chitosan polymeric chain. The structure and properties of the new polymer were characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscope. Also, the adsorption capacity of CCP was studied towards Hg2+ in aqueous medium by inductively coupled plasma-optical emission spectrometry. Interestingly, the results showed a considerable adsorption capacity for CCP in comparison with chitosan. Therefore, CCP can be introduced as a promising adsorbent for the elimination of Hg2+ from wastewaters. Moreover, because of the conformity of adsorption kinetic with pseudo-second-order kinetic models, it can be concluded that chemical adsorption has an important role between functional groups on CCP polymer and Hg2+ ions. In addition, according to Freundlich isotherm, the CCP surface was heterogeneous with different functional groups.

Synthesis and Application of Silica Supported Calix[4]arene Derivative as a New Processing Aid Agent for Reducing Hysteresis of Tread Rubber Compounds Used in Low Rolling Resistance Tires.

Rolling resistance is one of the most important properties of a tire which is highly dependent on the viscoelastic properties of its rubber compounds. There are a lot of ways to reduce this parameter both in construction improvement of the tire and changing in rubber compound formulation especially in tire tread formulation. Rubber scientists have been trying to introduce new processing aid agents beyond the traditional tire components for reducing the rolling resistance. In this study, a unique structure of silica-supported calix[4]arene (SS-CSC[4]A) has been synthesized and applied as a processing aid agent in tire tread formulation. Fourier-transform infrared spectroscopy (FTIR), Nuclear Magnetic Resonance (1HNMR and 13CNMR), 29Si CP/MAS spectroscopy, thermal gravimetric analysis (TGA), elemental analysis, and acid-base titration were used to characterize its structure. Scanning Electron Microscopy (SEM) use to investigate the effect of prepared material on qualification of filler dispersion in the rubber matrix. The viscoelastic properties of the prepared rubber compound were measured by Dynamic Mechanical Thermal Analysis (DMTA) which showed the great decrease in rolling resistance of rubber compound based on SS-CSC[4]A as a processing aid agent. The mechanical and rheological properties of obtained tread rubber compound measured by tensometer and MDR rheometer showed no sensible changes in these properties.

Efficiency of milk proteins in eliminating practical limitations of ß-carotene in hydrated polar solution.

The objective of this work was to study ß-carotene functionalities (color and antioxidant activity) and practical limitations (aggregate formation, poor solubility and low stability) when included in the aqueous systems containing milk proteins. According to the results, self-association constant of ß-carotene in the presence of casein is 1.7-fold of that calculated for WPI. Casein and WPI were capable of conserving ß-carotene against chemical oxidation up to 15 and 12%, respectively, at 1:5 M ratio of ß-carotene to protein. While, WPI reduced its photodegradation quantum yield from 0.03 to 0.012 compared to 0.017 obtained for casein. A 2.7- and 3.6-fold enhancement in ß-carotene solubility was observed in the presence of 1.5 mg/mL of casein and WPI, respectively. The study of ß-carotene interaction with proteins showed, on the one hand, a negative effect on electron transfer and, on the other hand, improved hydrogen transfer to the radical species in the solution.

Determination of iron(II) and iron(III) via static quenching of the fluorescence of tryptophan-protected copper nanoclusters.

"Tryptophan-coated blue fluorescent copper nanocluster (CuNC@Trp) was prepared by a strategy where Trp acts as both the reducing and capping agent. The fluorescence of the CuNC, with excitation/emission peaks at 340/405 nm, is selectively quenched by iron(II) and iron(III) ions. Studying the mechanism of this interaction revealed that Fe2+ and Fe3+ ions can make a ground state complex with the protecting ligand which can result in quenching of the cluster emission. Structural and optical properties of the modified CuNC were investigated by ESI-MS, DLS, TEM, UV-vis and photoluminescence. The effects of pH value and temperature, time of interaction, and cluster volume were optimized. Under optimized conditions, the probe response is linear in concentration range of 10-1000 µM for Fe(II) and Fe(III) with the relative standard deviations of 0.13 and 0.14% (n = 5) respectively. The respective limits of detection are 3.0 and 2.2 µM. The method was successfully used for determination of trace amount of both ions in spiked water, blood and iron supplement tablets. The results were in good agreement with those obtained by the ICP-AES method." Graphical abstractThe scheme represents the synthesis of CuNC@Trp at basic conditions and at elevated temperature. The emission of the cluster decreases due to static quenching of fluorescence by iron ions.

Recent progress to construct calixarene-based polymers using covalent bonds: synthesis and applications.

The combination of supramolecular chemistry and polymer sciences creates a great possibility to afford calixarene-based polymers offering unique features and applications. The enhancement of calixarene's versatility in this manner has made chemists better able to achieve different objectives in host-guest chemistry. The calixarene-based polymers can be divided into covalent polymers and supramolecular polymers regarding the interactions. Although there are several studies available on the calixarene-based supramolecular polymers, there is a paucity of studies on the calixarene-based covalent polymers. In this paper, the most recent developments and applications of the calixarene-based covalent polymers in the last two decades have been reviewed. We have particularly focused on the polymers, including those where the calixarene molecules have been used as macromonomers and polymerize through covalent bonds. Moreover, covalent polymers or solid supports functionalized with calixarenes are highlighted as well.

Binding of ß-carotene to whey proteins: Multi-spectroscopic techniques and docking studies.

The objective of this work was to study molecular binding between ß-carotene (ß-C) and whey protein isolate (WPI) as a function of pH (4-9), temperature (15, 25, and 35 °C), and NaCl concentration (0-0.25 M) using spectroscopic techniques and docking studies. The fluorescence quenching data showed that binding affinity increased with pH, temperature and ionic strength. The binding was entropy driven and involved mostly hydrophobic interactions. Three major whey proteins including ß-lactoglobulin (ß-Lg), α-lactalbumin (α-Lac), and bovine serum albumin (BSA) were bound to ß-C with overall binding constant values of 1.31 × 107, 1.80 × 104, and 4.51 × 104 M-1, respectively. A single class of binding sites for ß-C on whey fractions was recognized using Job's method. Docking results revealed ß-C was bound to the subdomain IIA of BSA, the residues of aromatic cluster II in α-lactalbumin and into the calyx of ß-lactoglobulin resulting in conformational changes in the secondary and tertiary structures of proteins.

Highly functionalized calix[4]arenes via multicomponent reactions: synthesis and recognition properties.

Multicomponent reactions (MCRs) include several aspects of green chemistry principles, so it is obvious that chemists in different areas are increasingly interested in providing their product by multicomponent approaches. MCRs can be very useful in supramolecular chemistry, especially to produce novel supramolecular derivatives. Therefore, there are several reports of highly-functionalized calix[4]arene derivatives obtained by MCRs instead of conventional stepwise protocols during the last decade. In this paper, we have particularly focused on the exploitation of upper rim and lower rim substituted calix[4]arenes in multicomponent approaches as a facile and convenient synthetic strategy. The value of this method lies in its operational simplicity, mild reaction conditions and structural diversity of the products. Interestingly, in most cases the products afforded by this method offer unique features and applications which are highlighted in the following sections.

Covalent Immobilization of Protein A on Chitosan and Aldehyde Double-Branched Chitosan as Biocompatible Carriers for Immunoglobulin G (Igg) Purification.

High-affinity ligands, such as protein A, can be used to develop biocompatible matrices for antibody purification. In this paper, two methods were used for immobilization of protein A on the chitosan. In the first approach, amino groups of chitosan beads were functionalized with tris(2-aminoethyl)amine to produce amine double-branched moieties, which were subsequently activated with glutaraldehyde. In the second approach, chitosan beads were directly modified by glutaraldehyde to produce aldehyde groups. Structural characterization and successful modification of the functional groups on the supports were confirmed by scanning electron microscopy, FTIR spectroscopy and elemental analysis. Covalent immobilization of protein A was then performed on the surface of both supports. The immobilization yield was determined by using fluorescence spectroscopy, showing almost 15% increased capacity for the double-branched derivatized chitosan. The Immunoglobulin G (IgG) purification ability of the double-branched support was also almost 1.7-fold higher than the monoaldehyde derivative at the same condition.

Spectroscopic and docking studies on the interaction between caseins and ß-carotene.

Natural occurrence of ß-carotene in bovine milk and the leading role of milk proteins in low-fat or fat-free dairy products necessitate investigating the possibility of interaction between ß-carotene and casein constituting up to 80% of bovine milk proteins. In this study, molecular interaction of caseins and ß-carotene was analyzed using fluorescence, UV-Vis absorption, circular dichroism (CD), and computer-aided molecular modeling. Casein and its fractions were bound to ß-carotene with a binding constant of the order 104 M-1 and a 1:1 binding stoichiometry. The binding was favored at alkaline pHs, low ionic strength and temperatures. κ-Casein had the highest binding affinity to ß-carotene, among casein fractions. The negative values of entropy and enthalpy changes and docking studies proved Van der Waals interactions are predominant forces in the binding process. The casein conformation was also altered through inducing a more folded structure in ß-casein and a looser conformation in α- and κ-casein.

Preparation and evaluation of a deoxycholic-calix[4]arene hybrid-type receptor as a chiral stationary phase for HPLC.

We report the synthesis and enantioseparation characteristics of two novel covalently immobilized deoxycholic acid derivatives as chiral stationary phases for high-performance liquid chromatography. In the structure of the first stationary phase, the 3-position of deoxycholic acid is substituted with a 3,5-dinitrophenylcarbamoyl group and the second one has an additional calix[4]arene attached to the carboxylic group of the deoxycholic acid. The chromatographic performance of the stationary phases was evaluated with enantioseparation of N-(3,5-dinitrobenzoyl)-dl-leucine, N-(3,5-dinitrobenzoyl)-dl-valine, omeprazole, diclofop-methyl, dl-mandelic acid and (RS)-pregabalin. Comparison of the performance characteristics of the prepared chiral stationary phases provided evidence for the active involvement of the calix[4]arene unit in the chiral recognition process. Both stationary phases are chemically bonded to the silica and can be used in both normal-phase and reversed-phase modes.

Preparation and evaluation of a chiral HPLC stationary phase based on cone calix[4]arene functionalized at the upper rim with l-alanine units.

Here we report a new chiral stationary phase (CSP) immobilized on silica gel based on cone calix[4]arene functionalized at the upper rim with two l-alanine units as new chiral selector that has been used in high-performance liquid chromatography. The CSP was prepared by covalently bonding the allyl groups at the lower rim of calix[4]arene to silica gel by thiol-ene click chemistry reaction. Elemental analysis of the CSP showed that 120 µmol of chiral selector bonded per gram of silica gel. 1-Hexene was used for end-capping of unreacted mercapto groups on silica gel. Since the CSP is chemically bonded to the silica, it can be used in the normal-phase and reversed-phase mode and with halogenated solvents as mobile phases, if desired. The chromatographic performance of the CSP was evaluated in the enantioseparation of the 3,5-dinitrobenzoyl derivatives of some amino acids, diclofop-methyl and dl-mandelic acid.

Equilibrium Isotherm, Kinetic Modeling, Optimization, and Characterization Studies of Cadmium Adsorption by Surface-Engineered Escherichia coli

Background: Amongst the methods that remove heavy metals from environment, biosorption approaches have received increased attention because of their environmentally friendly and cost-effective feature, as well as their superior performances. Methods: In the present study, we investigated the ability of a surface-engineered Escherichia coli, carrying the cyanobacterial metallothionein on the cell surface, in the removal of Ca (II) from solution under different experimental conditions. The biosorption process was optimized using central composite design. In parallel, the kinetics of metal biosorption was studied, and the rate constants of different kinetic models were calculated. Results: Cadmium biosorption is followed by the second-order kinetics. Freundlich and Langmuir equations were used to analyze sorption data; characteristic parameters were determined for each adsorption isotherm. The biosorption process was optimized using the central composite design. The optimal cadmium sorption capacity (284.69 nmol/mg biomass) was obtained at 40°C (pH 8) and a biomass dosage of 10 mg. The influence of two elutants, EDTA and CaCl2, was also assessed on metal recovery. Approximately, 68.58% and 56.54% of the adsorbed cadmium were removed by EDTA and CaCl2 during desorption, respectively. The Fourier transform infrared spectrophotometer (FTIR) analysis indicated that carboxyl, amino, phosphoryl, thiol, and hydroxyl are the main chemical groups involved in the cadmium bioadsorption process. Conclusion: Results from this study implied that chemical adsorption on the heterogeneous surface of E. coli E and optimization of adsorption parameters provides a highly efficient bioadsorbent.

Multivalent calix[4]arene-based fluorescent sensor for detecting silver ions in aqueous media and physiological environment.

A new derivative of dipodal 1,3-calix[4]arene-based chemosensor (R), which was containing several binding sites have been synthesized and characterized by NMR, IR and LC-MS spectroscopic methods. The selectivity of Rhas been investigated in aqueous methanol, resulting in fluorescence shift and selective recognition of Ag+ among 20 various alkali, alkaline earth and transition metal ions. Microstructural features of R and its complex with Ag+have been investigated by Atomic Force Microscopy (AFM). AFM images can clearly differentiate R from its complex of Ag+. Moreover; the complicated binding mode of metal-ligand complex has been explored by UV-Vis, LC-MS, FIR, Fluorescence titration, Job's plot method and theoretical approaches. Density functional theory (DFT) method at B3LYP/LANL2DZ level of theory was employed for computational studies. Theoretical calculations revealed that selectivity and specificity of R toward Ag+ could be attributed to structural conformation of 1,3-alternate-calix[4]arene scaffold and molecular electrostatic potential of its surface. Furthermore; the competitive experiments were carried out to test sensor's ability for practical uses. Finally, the efficiency of R in matrix of physiological cations was examined and showed gradual emission enhancement which makes R an ideal candidate for monitoring of Ag+ in physiological environment.

DNA Binding and Recognition of a CC Mismatch in a DNA Duplex by Water-Soluble Peptidocalix[4]arenes: Synthesis and Applications.

Water-soluble peptidocalix[4]arenes were synthesized by the introduction of arginine-rich narrow groove-binding residues at lower rims through solid-phase synthesis. The study of binding of these water-soluble bidentate ligands to well-matched and mismatched DNA duplexes by fluorescent titrations, ethidium bromide (EB) displacement assays, DNA-melting experiments, and circular dichroism (CD) analysis revealed a sequence-dependent groove-binding mechanism.

Amidofluorene-appended lower rim 1,3-diconjugate of calix[4]arene: synthesis, characterization and highly selective sensor for Cu(2.).

Functionalization of calix[4]arene with amidofluorene moieties at the lower rim led to formation of the 1,3-diconjugate of calix[4]arene L as a novel fluorescent chemosensor for Cu(2+). The receptor molecule L exhibited a pronounced selectivity towards Cu(2+) over other mono and divalent ions. The formation of the complex between L and Cu(2+) was evaluated by absorption, fluorescence and (1)H NMR spectroscopy. The sensor L showed a remarkable color change from colorless to purple and a fluorescence quenching only upon interaction with Cu(2+). The 1:1 stoichiometry of the obtained complex has been determined by Job's plot. The association constant determined by fluorescence titration was found to be 1.8 × 10(6) M(-1). The sensor showed a linear response toward Cu(2+) in the concentration range from 1 to 10 µM with a detection limit of 9.6 × 10(-8) M.

A New Fluorescence Sensor for Cerium (III) Ion Using Glycine Dithiocarbamate Capped Manganese Doped ZnS Quantum Dots.

A new fluorescence sensor for Ce(3+)ions is reported in this paper. This sensor is based on the fluorescence quenching of glycine dithiocarbamate (GDTC)-functionalized manganese doped ZnS quantum dots (QDs) in the presence of Ce(3+)ions. The synthesis of ultra-small GDTC-Mn:ZnS quantum dots (QDs) is based on the co-precipitation of nanoparticles in aqueous Solution. The nanoparticles are characterized with fluorescence spectroscopy, UV-vis absorption spectra, high-resolution transmission electron microscopy, X-ray power diffraction (XRD), and infrared spectroscopy. In the test carried out, it was found that the interaction between Ce(3+)ions and GDTC capped Mn:ZnS QDs quenches the original fluorescence of QDs according to the Stern-Volmer equation and the results show the existence of collisional quenching process. A linear relationship was observed between the extent of quenching and the concentration of Ce(3+)in the range of 2.0 × 10(-6) to 3.2 × 10(-5) mol.L(-1), with a detection limit of 2.29 × 10(-7) mol.L(-1). The relative standard deviation of 1.61% was obtained for five replicate measurements. The possible quenching mechanism was also examined by fluorescence and UV-vis absorption spectra. The interference of other cations was negligible on the quantitative determination of Ce(3+). This method proved to be simple, sensitive, low cost, and also reliable for practical applications.

Immobilization of Bioactive Protein A from Staphylococcus aureus (SpA) on the Surface of Bacillus subtilis Spores.

Protein A from Staphylococcus aureus (SpA) is a 40-60 kDa cell-wall component, composed of five homologous immunoglobulin (Ig)-binding domains folded into a three-helix bundle. Each of these five domains is able to bind Igs from many different mammalian species. Recombinant SpA is widely used as a component of diagnostic kits for the detection and purification of IgGs from serum or other biological fluids. In this study, purified SpA was adsorbed and covalently linked to Bacillus subtilis spores. Spores are extremely stable cell forms and are considered as an attractive platform to display heterologous proteins. A sample containing about 36 µg of SpA was covalently immobilized on the surface of 4 × 10(10) spores. Spore-bound SpA retained its IgG-binding activity, even after seven consecutive binding and washing steps, suggesting that it can be recycled and utilized several times. FACS analysis revealed that spores with covalently attached SpA had significantly improved fluorescence intensities when compared to those of spores with adsorbed SpA, suggesting that the covalent approach is more efficient than sole adsorption regarding protein attachment to the spore surface.

Separation of amino acids by high performance liquid chromatography based on calixarene-bonded stationary phases.

In this work, we present a new method for synthesis of silica gel stationary phases based on calix[4]arene derivatives. In order to achieve it, 25,27-dipropoxy-26,28-bis-[3-propyloxydimethylsililoxy]calix[4]arene has been synthesized in six steps and immobilized on silica via chlorotrimethylsilane. Stationary phases were characterized by elemental analysis, infrared spectroscopy and thermal analysis and used for the separation of amino acid derivatives by high performance liquid chromatography. The effect of isocratic and gradient elution, pH and column temperature on retention and selectivity of the Fmoc-protected amino acids were studied. The retention mechanism was also discussed. The results indicated that the stationary phase behaves like a reverse phase packing. Size exclusion, electron-π, π-π and hydrophobic interactions seem to be involved in the separation process.

On the performance of multiway methods for simultaneous quantification of two fluoroquinolones in urine samples by fluorescence spectroscopy and second-order calibration strategies.

In the present work, the analytical performance of three multi-way algorithms has been evaluated. The proposed analytical problem was the simultaneous determination of moxifloxacin and ciprofloxacin in human urine samples using fluorescence spectroscopy. Parallel factor analysis (PARAFAC), self-weighted alternating trilinear decomposition (SWATLD) and unfolded partial least squares combined with the residual bilinearization procedure (U-PLS/RBL) have been compared, regarding their ability to solve the proposed problem. In this study, "second-order advantage" was also exploited for the mentioned algorithms through different calibration strategies. The three-way data was obtained via fluorescence spectroscopy, so that excitation-emission matrices (EEM) of the samples were recorded as the analytical signals. The accuracy and precision of each individual algorithm for analyzing the drugs in urine samples were compared using root mean square error of prediction (RMSEP), recovery and elliptical joint confidence region (EJCR) plots. The results revealed that each of the three algorithms could be applied for determination of moxifloxacin and ciprofloxacin, despite different EEM subsets and calibration strategies. However, better analytical performances were observed through PARAFAC and U-PLS/RBL modeling for MOX and CIP, respectively. So, by coupling the multi-way decomposition algorithms with fluorescence spectroscopy, a main part of preliminary sample preparation steps can be eliminated and experimental procedure might be significantly simplified, while achieving desirable analytical performance.