Serkan Sayin

Synthesis and evaluation of chromate and arsenate anions extraction ability of a N-methylglucamine derivative of calix[4]arene immobilized onto magnetic nanoparticles

In this study, 5,17-bis-[(N-methylglucamine)methyl]-25,26,27,28-tetrahydroxy-calix[4]arene (3) was synthesized by the treatment of calix[4]arene with a secondary amine N-methylglucamine and formaldehyde. The calixarene derivative (3) was characterized by a combination of FTIR, (1)H NMR and elemental analyses. Followingly, using the macrocyclic building block, the compound 3 was immobilized by [3-(2,3-epoxypropoxy)propyl]trimethoxysilane-modified Fe(3)O(4) magnetite nanoparticles (EPPTMS-MN). The prepared calix[4]arene immobilized material was characterized by a combination of Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and thermogravimetric analyses (TGA). Moreover, the studies regarding the removal of arsenate and dichromate ions from the aqueous solutions were also carried out by using the compound in solid-liquid extraction experiments. It was found that the calix[4]arene-based magnetic material has high extraction ability towards dichromate and arsenate anions in 66% (at pH 1.5) and in 86% (at pH 3.5), respectively.

Improvement of catalytic properties of Candida rugosa lipase by sol-gel encapsulation in the presence of magnetic calix[4]arene nanoparticles.

Candida rugosa lipase (CRL) was encapsulated within a chemically inert sol-gel support prepared by polycondensation with tetraethoxysilane (TEOS) and octyltriethoxysilane (OTES) in the presence of N-methylglucamine based calix[4]arene magnetic nanoparticles. The results indicate that the magnetic calix[4]arene based encapsulated lipase particularly has shown high conversion and enantioselectivity. It has also been noticed that the magnetic calix[4]arene based encapsulated lipase has excellent enantioselectivity (E = 460) as compared to the free enzyme (E = 166) with an ee value of >98% for S-Naproxen.

Improving catalytic hydrolysis reaction efficiency of sol-gel-encapsulated Candida rugosa lipase with magnetic β-cyclodextrin nanoparticles.

A silica-based β-cyclodextrin was immobilized on magnetic nanoparticles to obtain a macrocyclic compound with magnetic property. Then, the β-cyclodextrin-grafted magnetic nanoparticles were encapsulated with Candida rugosa lipase in sol-gel matrices using alkoxysilane precursors. The catalytic activity of the encapsulated lipases was evaluated with model reactions, i.e., the hydrolysis of p-nitro-phenylpalmitate (p-NPP) and the enantioselective hydrolysis of rasemic Naproxen methyl ester that was studied in an aqueous buffer solution/isooctane reaction system. The results indicate that the cyclodextrin-based, encapsulated lipase particularly exhibited high conversion and enantioselectivity behavior compared to the sol-gel free lipase. It was also observed that excellent enantioselectivity (E=399) was obtained for the encapsulated lipase with magnetic β-cyclodextrin that has an ee value of S-Naproxen acid of about 98%.

Two novel calixarene functionalized iron oxide magnetite nanoparticles as a platform for magnetic separation in the liquid-liquid/solid-liquid extraction of oxyanions.

This article focuses on the syntheses of 25,27-bis[3-(N-ethylsulfonic acid)aminopropxy]-26,28-dihydroxy-5,11,17,23-tetra-tert-butyl-calix[4]arene (3) and 25,27-bis[3-(N-ethyl-dihydrogen phosphate)aminopropxy]-26,28-dihydroxy-5,11,17,23-tetra-tert-butyl-calix[4]arene (4) as well as their immobilization onto [3-(2,3-epoxypropoxy)-propyl]-trimethoxysilane-modified Fe3O4 magnetite nanoparticles, and the extraction abilities of four new extractants which were characterized by a combination of FTIR, (1)H NMR, elemental analyses, transmission electron microscopy (TEM) and thermogravimetric analyses (TGA) involving electrostatic and hydrogen bonding interactions between the calixarene and oxide anions such as arsenate and dichromate anions. The extraction results indicate that these new calixarene derivatives having high extraction capabilities would be used as effective extractants for the removal of the dichromate/arsenate ions from water.

Enzyme immobilization in biosensor constructions: self-assembled monolayers of calixarenes containing thiols

Herein, an amperometric glucose oxidase (GOx) biosensor is presented using calixarenes as an immobilization matrix of the biomolecule. Firstly, thiol-containing calixarenes (Calix-SH) were synthesized, then self-assembled monolayers (SAMs) of Calix-SH on a gold surface were formed and hydroxyl groups of Calix-SH were activated using 1,1′-carbonyldiimidazole (CDI) chemistry. To test the usability of Calix-SH modified surfaces as a biosensor, glucose oxidase was used as a model biological component. After optimization of preparation and working conditions, our results indicate that the Calix-SH/GOx biosensor has a linear range in the range 0.1–1.0 mM (LOD: 0.015 mM) for glucose with a 25 s response time. Finally, the application of the biosensor was examined to detect glucose in real samples. The glucose amounts were calculated as 19.460 ± 0.521 and 31.647 ± 2.125 mM in coke and fizzy drink (with orange), respectively. To confirm the reliability of the Calix-SH/GOx biosensor, the calculated glucose concentrations which were analyzed by the Calix-SH/GOx biosensor were compared to conventional spectrophotometric glucose kits. The glucose amounts in coke and fizzy drink were calculated as 18.509 ± 0.732 mM and 31.579 ± 4.466 mM, respectively.

The synthesis of new calix[n]arene quaternary ammonium salts and investigation of their catalytic affinities for three component Mannich-type reactions in water

Two new calix[n]arenes and a non-cyclic analogue substituted with 1-(2-furoyl)piperazine have been synthesized. Moreover, their quaternary ammonium salts have been prepared by treatment with methyl iodide. All of the new quaternary ammonium salts have been employed as catalysts in one-pot Mannich reactions to afford β-aminocarbonyl compounds. The combination of good to excellent yields, the need for a small amount of catalyst and simple work-up, mean that this route can be considered to be green chemistry.

A novel architecture based on a conducting polymer and calixarene derivative: its synthesis and biosensor construction

In this study, a novel amperometric glucose biosensor based on a selenium comprising conducting polymer and calixarene was developed. Firstly, poly(2-(2-octyldodecyl)-4,7-di(selenoph-2-yl)-2H-benzo[d][1,2,3]triazole), poly((SBTz)) was electrodeposited onto a graphite electrode by an electropolymerization technique. Then, a newly synthesized calixarene and gold nanoparticle (AuNP) mixture was used for the improvement of biosensor characteristics. GOx, as a model enzyme was immobilized on the modified electrode surface. The constructed surface serves as a sufficient immobilization platform for the detection of glucose. Calixarenes and their derivatives may be a favouring agent for enzyme immobilization due to their specific configurations. Moreover, through the covalent binding between the carboxylic groups of the calixarenes and amino groups of the biomolecule, effective enzyme immobilization can be achieved while protecting the well-ordered structure of the enzyme molecule. Amperometric detection was carried out following oxygen consumption at −0.7 V vs. the Ag reference electrode in phosphate buffer (50 mM, pH 6.5). The proposed biosensor showed a linear amperometric response for glucose within a concentration range of 0.005 to 0.5 mM (LOD: 0.004 mM). Kappm and sensitivity were calculated as 0.025 mM and 102 μA mM−1 cm−2, respectively. Scanning Electron Microscopy (SEM) was used to investigate the surface morphologies of successive modifications. Finally, the constructed biosensor was tested successfully to detect glucose in beverage samples.

New Amperometric Cholesterol Biosensors Using Poly(ethyleneoxide) Conducting Polymers

Accumulation of cholesterol in human blood can cause several health problems such as heart disease, coronary artery disease, arteriosclerosis, hypertension, cerebral thrombosis, etc. Therefore, simple and fast cholesterol determination in blood is clinically important. In this study, two types of amperometric cholesterol biosensors were designed by physically entrapping cholesterol oxidase in conducting polymers; thiophene capped poly(ethyleneoxide)/polypyrrole (PEO-co-PPy) and 3-methylthienyl methacrylate-co-p-vinyl benzyloxy poly(ethyleneoxide)/polypyrrole (CP-co-PPy). PEO-co-PPy and CP-co-PPy were synthesized electrochemically and cholesterol oxidase was immobilized by entrapment during electropolymerization. The amperometric responses of the enzyme electrodes were measured by monitoring oxidation current of H2O2 at +0.7 V in the absence of a mediator. Kinetic parameters, such as Km and Imax, operational and storage stabilities, effects of pH and temperature were determined for both entrapment supports. Km values were found as 1.47 and 5.16 mM for PEO-co-PPy and CP-co-PPy enzyme electrodes, respectively. By using these Km values, it can be observed that ChOx immobilized in PEO-co-PPy shows higher affinity towards the substrate.

Development of a pH sensing membrane electrode based on a new calix[4]arene derivative.

A new pH sensing poly(vinyl chloride) (PVC) membrane electrode was developed by using recently synthesized 5,17-bis(4-benzylpiperidine-1-yl)methyl-25,26,27,28-tetrahydroxy calix[4]arene as an ionophore. The effects of membrane composition, inner filling solution and conditioning solution on the potential response of the proposed pH sensing membrane electrode were investigated. An optimum membrane composition of 3% ionophore, 67% o-nitrophenyl octyl ether (o-NPOE) as plasticizer, 30% PVC was found. The electrode exhibited a near-Nernstian slope of 58.7±1.1 mV pH(-1) in the pH range 1.9-12.7 at 20±1 °C. It showed good selectivity for H(+) ions in the presence of some cations and anions and a longer lifetime of at least 12 months when compared with the other PVC membrane pH electrodes reported in the literature. Having a wide working pH range, it was not only applied as a potentiometric indicator electrode in various acid-base titrations, but also successfully employed in different real samples. It has good reproducibility and repeatability with a response time of 6-7s. Compared to traditional glass pH electrode, it exhibited excellent potentiometric response after being used in fluoride-containing media.

Calixarene modified montmorillonite: a novel design for biosensing applications†

Here we report the synthesis, characterization and application of calixarene (Calix) modified montmorillonite (Mt) as a platform for bio-applications such as biomolecule immobilization and biosensing technologies. This modification enhanced the biomolecule immobilization capability of Mt. Initially, amino-functionalised calixarenes (Calix-NH2) were synthesized and used as a modifier. X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential and thermal gravimetric analysis were performed to verify the modification of the clay minerals. For the biosensor construction, Calix-NH2 modified Mt (Calix-NH2/Mt), bovine serum albumin (BSA), glutaraldehyde (GA) and pyranose oxidase were immobilized on the surface of a glassy carbon electrode which was then referred to as a Calix-NH2/Mt/PyOx biosensor. After optimization of the enzyme amount and pH, analytical characteristics were investigated in detail.