Hydrogels of β-cyclodextrin crosslinked by acylated poly(ethylene glycol): Synthesis and properties

Networks of β-cyclodextrin have been prepared by reaction with acylated poly(ethylene glycol) with a molar mass of 600 g/mol. Samples with different β-cyclodextrin/poly(ethylene glycol) ratios: 1/4, 1/6, 1/8 and 1/10 have been prepared. Both components are bonded by ester groups, resulting in a network that can be degraded by hydrolysis in basic and acidic media. The maximum stability of the hydrogels is reached at pH 4. The hydrogel percentage water content depends on β-cyclodextrin content ranging from 82 to 98, and the swelling data obtained for these hydrogels fit well with a second order kinetics. The sorption behavior of these hydrogels has been tested by employing 1-naphthol as model molecule. The sorption capacity is close to other cyclodextrin networks previously reported and depends on the hydrogel composition and the concentration of 1-naphthol.     

In-situ thermal crosslinked PA66/β-cyclodextrin/PA66 nanofibrous membranes with high mechanical strength for removal of heavy metal ions by flow through adsorption

β-cyclodextrin (β-CD) based materials have been studied widely as adsorbents and filter membranes for removing pollutants in air or water applications. The present study aimed to develop a sandwich structure of eletrospun nanofibrous membrane based on β-cyclodextrin and PA66 to achieve the high mechanical strength and flow-through adsorption of heavy metal ions in water. The surface and cross section morphology of PA66/β-cyclodextrin/PA66 nanofibrous membranes (PA66/β-CD/PA66 NMs) were examined using scanning electron microscopy (SEM). The physicochemical and mechanical properties of PA66/β-CD/PA66 NMs were analyzed by differential scanning calorimetry (DSC), thermogravimetric (TG) analysis and universal testing machine. The diameter of β-CD and PA66 electrospun fibers are 300–400 nm and 20–40 nm respectively. PA66/β-CD/PA66 NMs show a loosely arranged fibers and layer by layer structure. The tensile strength increases remarkably for PA66/β-CD/PA66 NMs, from 1.33 MPa of β-CD NMs to 23.17 MPa and the Young's modulus increases from 34.8 MPa to 253.3 MPa. The mechanical behavior of PA66/β-CD/PA66 NMs is a typical brittle fracture, and its microcosmic fracture diagrams are also involved. TGA/DSC results confirm the thermal crosslinking reaction is effective and complete. On the basis of SEM, DSC, TG and mechanical behavior analysis results, the molecular mechanism of in situ thermal crosslinking reaction is discussed. Fe³⁺、Ni²⁺ were used to confirm the ability to absorb heavy metal ions of PA66/β-CD/PA66 NMs. In conclusion, PA66/β-CD/PA66 NMs could be a promising solution for removal of metal ions by flow-through adsorption.     

Disposition of copper(II) inβ-cyclodextrin

Distances of glucose protons in-cyclodextrin (BCD) from copper(II) in copper(II)--cyclodextrin have been determined from¹H NMR spin-lattice relaxation time (T ₁) measurements for the first time. Very lowT _1p /T _2p values indicated the dipolar mechanism to be the most dominant one in determining the paramagnetic contribution to relaxation. The distances of copper(II) from BCD glucose protons indicated copper(II) to be present almost in the centre, inside the cavity in the same plane as H-1 and H-4. An average distance of about 5.0–5.9 Å was obtained for copper(II) from the H-2, H-3, H-1, H-4 and H-6 a and b protons in BCD.     

Strontium(II) sorption by complexing o-hydroxy-azo-o’-hydroxy functionalized polystyrene polymer sorbents

Optimal parameters for strontium(II) complexing and sorption from aqueous solutions by sorbents based on styrene/divinylbenzene copolymers functionalized with a complexing o-hydroxy-azo-o-hydroxy functionality have been studied, namely, pH_opt, 50% sorption pH (pH₅₀), and the time and temperature of quantitative strontium(II) sorption. Strontium(II) sorption capacities have been determined for the sorbents under study; sorption isotherms have been constructed. For a complex formed with polystyrene-o-hydroxy-azo-o’-hydroxy-sulfobenzene, which is an efficient sorbent, the structure has been determined.     

Effect of coexisting cations on the adsorption of cesium onto poly (β-cyclodextrin)/bentonite composite

A novel poly(β-cyclodextrin)/bentonite composite (β-CD/BNC) was successfully prepared through graft polymerisation by using ammonium persulphate–sodium bisulphate as initiators, and characterized by FT-IR and EDS. The equilibrium data fit Freundlich isotherm satisfactorily. Adsorption kinetic was fitted with pseudo-second-order. The maximum adsorption capacities for Cs⁺ by β-CD/BNC in absence and presence of Na⁺ and Mg²⁺ were 48.83 ± 0.35, 47.30 ± 0.28, and 42.52 ± 0.85 mg g^?1, respectively. Adsorption of Cs⁺ was suppressed by presence of Mg²⁺ more than Na⁺. β-CD/BNC had a higher affinity to Cs⁺ than Na⁺ and Mg²⁺. β-CD/BNC was an effective sorbent for the treatment cesium waste water.     

pH-controlled quaternary ammonium herbicides capture/release by carboxymethyl-β-cyclodextrin functionalized magnetic adsorbents: Mechanisms and application

In our work, the pH-controlled magnetic solid phase extraction for the determination of paraquat and diquat was introduced firstly. Furthermore, to clarify the mechanism of carboxymethyl-β-cyclodextrin functionalized magnetic adsorbents, we studied the pH-responsive supramolecular interaction between carboxymethyl-β-cyclodextrin (CM-β-CD) and paraquat/diquat by ultraviolet–visible (UV–vis) spectroscopy and nuclear magnetic resonance (NMR) experiment, and the energy-minimized structures were also obtained. Then, the functional group CM-β-CD was modified on the surface of magnetic materials to synthesize the adsorbent. The Fourier transform infrared spectrum (FT-IR) results proved the successful modification of CM-β-CD. Thus, this absorbent was applied for the determination of paraquat and diquat in water. Under the optimal condition, limits of detection (LODs) of paraquat and diquat were 0.8 μg L⁻¹ and 0.9 μg L⁻¹, relative standard deviations (RSD) and recoveries varied 0.7–4.6% and 86.5–106.6%, respectively. Good recoveries (70.2–100.0%) and low RSD (1.7–9.6%) were achieved in analyzing spiked water samples. Furthermore, with the capillary electrophoresis (CE) as the analyser, the whole analytical process did not need the attendance of organic solvents.     

Synergistic catalytic oxidation of cinnamaldehydes by poly(vinyl alcohol) functionalized β-cyclodextrin polymer in CaO2/HCO3− system

Poly (vinyl alcohol) (PVA)–functionalized β-cyclodextrin (β-CD) polymer crosslinked by citric acid (PVA-g-CD) was synthesized, characterized and evaluated for the catalytic oxidation of cinnamaldehydes. The polymer showed good activity and selectivity to aldehydes for some structurally diverse cinnamaldehydes. The enhanced catalytic activity may be attributed to the synergistic effect of the intermolecular weak interactions between β-CD and the functional group of PVA. In addition, calcium peroxide as a solid oxidant was found to significantly affect the reaction. This catalyst can be recovered and reused for five times without a significant loss in its activity and selectivity.     

The adsorption of mercury(II) on the surface of silica modified with β-cyclodextrin

Multistage chemical modification of the surface of silica with β-cyclodextrin was performed. IR spectroscopy and quantitative analysis of surface compounds were used to prove the structure of modified silica. The adsorption of Hg(II) from dilute solutions was studied. The adsorption affinity of silica for mercury ions increased because of the formation of supramolecular structures with chemically immobilized β-cyclodextrin.     

Binding of vitamin A byβ-cyclodextrin and heptakis(2,6-O-dimethyl)-β-cyclodextrin

Inclusion complexation of all-trans-retinol, retinal and retinoic acid with -cyclodextrin (-CD) and heptakis(2,6-O-dimethyl)--cyclodextrin (DM--CD) were investigated by means of UV-vis spectroscopy. The association constants (K _a) obtained for vitamin A with DM--CD is greater than with -CD. On the other hand, for the same host compoundK _a values of retinol, retinal and retinoic acid are very close to each other.     

The Aldol Condensation Catalyzed by Metal(II)-β-cyclodextrin Complexes

Aldol-condensation reaction were catalyzed by use of metal(II)-β-cyclodextrin systems. The β-hydroxy ketones were obtained in a good yield. The resulting products were optically active.     

Preparation,structure and magnetic study of a new linear 1-D Cu(II)–Gd(III) coordination polymer

A carboxylate-bridged Cu(II)–Gd(III) complex, [GdCu(CH₂CH(CH₃COO)₄(H₂O)₄] _n (NO₃) _n , was prepared and characterized. Single crystal X-ray analysis reveals the complex as a carboxylate-bridged 1-D Cu(II)–Gd(III) coordination polymer. The magnetic measurement showed this complex exhibiting weak ferromagnetic behavior.     

Alkylation of indoles by aziridinium ions: new rapid access to tetrahydro-β-carbolines (THBCs)

The alkylation of indoles by aziridinium ions generated in situ from β-amino chlorides was explored. The outcome of this reaction strongly relied on the substitution pattern of the starting β-amino chloride and requires silver tetrafluoroborate activation to proceed in reasonable yield. Ephedrine- and pseudoephedrine-derived N-cyanomethyl-β-amino chlorides afforded the corresponding tryptamines in a regio- and stereoselective manner and subsequent silver(I)-promoted Pictet–Spengler reactions produced 4-phenyl substituted THBCs in good yields. Unexpected epimerization at C-3 was found in these reactions, producing trans-3,4-disubstituted THBCs stereoselectively.     

Preparation of a Cu(II)‐Immobilized Co‐polymer(CIC) for Effective Removal of Urea

The study describes the preparation of Cu(II)‐immobilized copolymer(CIC) under optimum conditions for the effective removal of urea. The copolymeric hydrogels, synthesized by free‐radical aqueous copolymerization of monomers acrylamide and sodium acrylate, have been analyzed for their Cu(II) uptake behavior. The sorption of Cu(II) into polymer follows a Langmuir–type pattern and amount sorbed depends upon the composition of copolymeric gels, presence of other co‐ions in the solution, pH of the solution, initial concentration of sorbate, degree of crosslinking of the copolymeric hydrogel, temperature of the solution etc. In the preliminary study, the Cu(II) immobilized co‐polymer(CIC) sorbent demonstrated a fair tendency to remove urea from aqueous solutions.     

β-Cyclodextrin-based polyurethane (β-CDPU) polymers as solid media for adsorption and determination of Pb(II) ions in dust and water samples

In this work, β-CD-based polyurethane copolymers (β-CDPU) have been prepared by reacting β-CD with hexamethylene diisocyanate as cross-linked agent in dry DMF. This polymer showed high selectivity for preconcentration of Pb(II) at trace level prior to its flame atomic absorption spectrometric determination. The effect of several parameters such as pH, flow rate of sample, eluent kind and volume was investigated. The adsorption behaviors and mechanisms of Pb(II) on the samples were also studied. The maximum adsorption amount of Pb(II) was 8 mg g^?1 with the preconcentration factor of 250 for Pb(II). The Langmuir isotherm was proved to describe the adsorption data better than the Freundlich isotherm and a pseudo-first-order kinetic model fits the adsorption kinetic processes well. The calibration curve was linear in the range of (3–200 ng mL^?1) with a correlation coefficient of 0.9996. The limit of detection based on three times the standard deviation of the blank was 1.15 ng mL^?1. The relative standard deviations for the determination of 10 and 100 ng mL^?1 of Pb(II) were 3.60 and 0.43 % (n = 10), respectively. The method was successfully applied to the determination of lead in some environmental samples such as Tehran and Bushehr drinking water, river water and dust samples.     

Kinetic and equilibrium studies of lead(II) adsorption from aqueous media by KIT-6 mesoporous silica functionalized with –COOH

An organic–inorganic hybrid mesoporous silica was synthesized via post-grafting of KIT-6 with 4-(triethoxysilyl)butyronitrile. All samples were characterized using their N₂ adsorption–desorption isotherms, XRD, FT–IR, TEM, SEM, and PT. The adsorption potential of this material for removing Pb(II) from aqueous solutions was investigated via the batch technique, and the effects of pH and contact time were studied. Experimental data showed that the maximum Pb(II) adsorption, 76%, occurred in the pH range around 6. The adsorption equilibrium was reached within 40 min for 10 wt.%COOH/KIT-6. The adsorption data were fitted using the Langmuir and Freundlich isotherms, and the obtained modeling equilibrium adsorption data suggested that the 10 wt.%COOH/KIT-6 sample contained homogeneous adsorption sites that fit the Langmuir adsorption model well. The pseudo-second-order model described well the 10 wt.%COOH/KIT-6 adsorption process. The desorption and regeneration experiments indicated that ≈95% of the metal desorbed and the adsorbent could be regenerated via an acid treatment without altering its properties.     

Separation and extraction of Co(II) using magnetic chitosan nanoparticles grafted with β-cyclodextrin and determination by FAAS

A novel and selective method for the fast determination of trace amounts of Co(II) ions in water samples has been developed. The procedure is based on the selective sorption of Co(II) ions using magnetic chitosan nanoparticles grafted with β-cyclodextrin at different pH followed by elution with organic eluents and determination by atomic absorption spectrometry The preconcentration factor was 100 (1 mL elution volume) for a 100 mL sample volume. The limit of detection of the proposed method is 1.0 ng mL^?1. The maximum sorption capacity of sorbent under optimum conditions has been found to be 5 mg of Co per gram of sorbent. The relative standard deviation under optimum conditions was 3.0% (n = 10). Accuracy and applicability of the method was estimated using test samples of natural and model water with different amounts of Co(II).     

Interactions of metal ions with the intermediate of thiamine catalysis: Crystal structures of Cd(II), Hg(II) and Pt(II) complexes of 2-(α-hydroxybenzyl)thiamine

Five complexes of formulae Cd(HBT)X₃·H₂O, Hg₂X₅(HBT) (X=Cl, Br), and Pt(HBT)(NO₂)₃ were prepared by reacting CdX₂, HgX₂ and K₂Pt(NO₂)₄ with 2-(α-hydroxybenzyl)thiamine (HBT), an active intermediate of thiamine catalysis, and their crystal structures were determined by X-ray diffraction. The metal ion binds to the N(1′) site of the pyrimidine ring in each case, despite the different shapes and sizes of metal coordination units; a tetrahedral unit in the cadmium complexes, a double-metal unit consisting of two tetrahedral Hg(II) ions in the mercury complexes and a square-planar unit in the platinum complex. The HBT ligands in these complexes adopt the S conformation, as usually observed in C(2)-substituted derivatives of thiamine, with average torsion angles ϕ_T being ±99° and ϕ_P being ±175°. A ‘two-point’ anion-bridge between the amino group of the pyrimidine ring and the cationic thiazolium ring of the same molecule is found in all the structures, being of the form N(4′α)–H…X₁–M–X₂…thiazolium-ring (M=metal ion), which is one of the factors that affect the S conformation. Stacking interactions between the pyrimidine and phenyl rings play an important role in the molecular conformation and crystal packing. The intramolecular close contact between the oxygen of the C(2)-substituent and the sulfur of the thiazolium ring is also a common feature to these complexes, which gives the mechanistic implications.     

Characterization and spectroscopic study of new complexes of Cd(II), Hg(II) and Pb(II) with the sodium salt of morin-5′-sulfonic acid

Solid compounds of Cd(II), Hg(II) and Pb(II) with the sodium salt of morin-5′-sulfonic acid (NaMSA) were obtained. The molecular formula of the complexes are: Cd(C₁₅H₈O₁₀SNa)₂?·?6H₂O, CdOH(C₁₅H₈O₁₀SNa)?·?4H₂O, Hg(C₁₅H₈O₁₀S)?·?4H₂O and Pb(C₁₅H₈O₁₀S)?·?3H₂O. Some of their physicochemical properties such as UV-Vis, infrared, ¹³C NMR and mass spectra, thermogravimetric analysis, and solubility were studied. On the basis of spectroscopic data NaMSA was bound to Cd²⁺ via 4C=O and 3C?–?oxygen and the Hg²⁺ and Pb²⁺ ions by 5C–OH, 4C=O and 3C–OH.