Calix[4]arene-triazine conjugate intermediate: optical properties and gas sensing responses against aromatic hydrocarbons in Langmuir–Blodgett films

Research on Chemical Intermediates - The detection of organic vapors by chemically based sensors was achieved with macromolecules having convenient molecular cavities. Addressed herein, a...     

A novel triazine‒bearing calix[4]arene: Design,synthesis and gas sensing affinity for volatile organic compounds

A novel triazine-calix[4]arene conjugate was designed and synthesized with the aim to study gas sensing against volatile organic compounds (VOCs) such as dichloromethane, chloroform and carbon tetrachloride. This novel compound was fully characterized by spectroscopic techniques such as FTIR, ¹H and ¹³C NMR along with HRMS and BET analysis. The triazine based calix[4]arene organic materials were fabricated onto quartz glasses and quartz crystal substrates to form a thin film chemical sensor element by using Langmuir-Blodgett (LB) technique. Quartz Crystal Microbalance, UV–Visible Spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy techniques were employed to characterize all these LB thin film layers. Fick's Equations were used for analyzing the swelling process of LB thin film sensor and diffusion coefficient values of organic vapours for swelling were obtained. The initial experiments have revealed that new triazine appended calix[4]arene derivative exhibited an effective chemical gas sensor characteristic with a large response to dichloromethane vapour.     

Implementation of the Nitsche approach for various contact kinematics

Numerical approaches are in case of contact problems mainly dealing with additional terms enforcing constraints. Within the Nitsche approach the inclusion of constraints for the non-penetration and equilibrium of stresses of the contacting bodies is carried out in a fully variational sense. Taking into account a specific choice and the physical meaning of the encountered Lagrange multipliers two different schemes for the Nitsche formulation are obtained. Both types of the Nitsche approach are implemented in a nonlinear element and verification with numerical examples is done. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoelectrochemical sensor for determination of naringin at low oxidation potential using a modified FTO electrode with cadmium sulfide and titanium dioxide sensitized with chloroprotoporphyrin IX iron(III)

Journal of Solid State Electrochemistry - Naringin is a flavanone that has been studied due to its important properties, such as anti-inflammatory, anti-oxidant, anti-microbial, anti-viral,...     

Detecting Counterion Dynamics in DNA–Protein Association

Due to a high density of negative charges on its surface, DNA condenses cations as counterions, forming the so‐called “ion atmosphere”. Although the release of counterions upon DNA–protein association has been postulated to have a major contribution to the binding thermodynamics, this release remains to be confirmed through a direct observation of the ions. Herein, we report the characterization of the ion atmosphere around DNA using NMR spectroscopy and directly detect the release of counterions upon DNA–protein association. NMR‐based diffusion data reveal the highly dynamic nature of counterions within the ion atmosphere around DNA. Counterion release is observed as an increase in the apparent ionic diffusion coefficient, which directly provides the number of counterions released upon DNA–protein association.     

Comparison of adsorption performances of metal–chelated polyamide hollow fibre membranes in lysozyme separation

Commercially available microporous polyamide hollow fibres are modified by acid hydrolysis to activate the reactive groups and subsequently binding of the ligand, i.e. Cibacron Blue F3GA. Then the Cibacron Blue F3GA-derived hollow fibres were loaded with different metal ions (i.e. Zn(II), Cu(II), Ni(II)) to form the metal chelate. The internal polymer matrix was characterised by scanning electron microscopy. The effects of pH, initial concentration of lysozyme, metal type and temperature on the adsorption of lysozyme to the metal–chelated hollow fibres were examined in a batch reactor. The non-specific adsorption of lysozyme onto the polyamide hollow fibres was 1.8 mg/g. Cibacron Blue F3GA immobilisation increased the lysozyme adsorption up to 62.3 mg/g. Metal–chelated hollow fibres showed a significant increase of the adsorption efficiency. Lysozyme adsorption capacities of Zn(II), Cu(II) and Ni(II)-chelated hollow fibres were different. The maximum capacities of Zn(II), Cu(II) or Ni(II)-chelated hollow fibres were 144.2, 75.2 and 68.6 mg/g, respectively. Significant amount of the adsorbed lysozyme (up to 97%) was eluted in 1 h in the elution medium containing 1.0 M NaSCN at pH 8.0 and 25 mM EDTA at pH 4.9. Repeated adsorption–desorption process showed that this novel metal–chelated polyamide hollow fibres are suitable for lysozyme adsorption.     

Flow system exploiting multicommutation to increase sample residence time for improved sensitivity. Simultaneous determination of ammonium and ortho-phosphate in natural water

A flow system for the simultaneous determination of ammonium and phosphate in river water at the mug ml(-1) level employing a low expensive LED-based photometer is described. The manifold of the flow system comprised four analytical pathways containg a set of three-way solenoid valves and an automatic injector commutator. The signal measurements of both analytes were carried out using two LED-based photometers attached to the flow cells. A microcomputer running a programme written in quickbasic 4.5 provided facilities to control the system and to carry out simultaneously two analytical procedures also performing data acquisition. For the determination of ortho-phosphate the method based on reaction with molybdate and ascorbic acid was employed, while for ammonium the method based on reaction with hypochlorite and salicylic acid was selected. The four-pathway structure of the manifold allowed the sample incubation time to be increased to 130 s to permit the reaction to occur without a decrease in sample throughput. The usefulness of the system was ascertained by analyzing a set of water samples. Applying the paired t-test to results obtained employing reference methods, no significant difference at the 95% confidence level was observed for both analytes. Other profitable features such as an analytical throughput of 112 analyte determination per hour; relative standard deviations of 1.1 and 0.7% (n=6) ammonium and phosphate, respectively, reagent consumption of 0.3 mg ammonium molybdate, 0.75 mg salicylic acid, 3.3 mg ascorbic acid and sodium hypochlorite per determination; detection limits of 7.0 mug l(-1) NH(4)(+) and 17.0 mug l(-1) PO(4)(3-) were also achieved.     

Protein recognition via ion-coordinated molecularly imprinted supermacroporous cryogels

Molecular imprinting is a method for making selective binding sites in synthetic polymers using a molecular template. The aim of this study is to prepare lysozyme-imprinted supermacroporous cryogels which can be used for the purification of lysozyme (Lyz) from egg white. N-Methacryloyl-(L)-histidinemethylester (MAH) was chosen as the metal-coordinating monomer. In the first step, Cu2+ was complexed with MAH and the lysozyme-imprinted poly(HEMA-MAH) [Lyz-MIP] cryogel were produced by free radical polymerization initiated by N,N,N',N'-tetramethylene diamine (TEMED) in an ice bath. After that, the template (i.e., lysozyme) was removed using 0.05 M phosphate buffer containing 1M NaCl (pH 8.0). The maximum lysozyme adsorption capacity was 22.9 mg/g polymer. The relative selectivity coefficients of Lyz-MIP cryogel for lysozyme/bovine serum albumin and lysozyme/cytochrome c were 4.6 and 3.2 times greater than non-imprinted poly(HEMA-MAH) (NIP) cryogel, respectively. Purification of lysozyme from egg white was also monitored by determining the lysozyme activity using Micrococcus lysodeikticus as substrate. The purity of the desorbed lysozyme was about 94% with recovery about 86%. The Lyz-MIP cryogel could be used many times without decreasing the adsorption capacity significantly.     

Removal of heavy metal ions from water by using poly(ethyleneglycol dimethacrylate-co-acrylamide) beads

Poly(ethyleneglycol dimethacrylate-co-acrylamide) (poly(EDGMA-co-AAm)) copolymer beads have been prepared for use in the separation Pb(II), Hg(II), and Cd(II), metal ions in aqueous solution by a batch equilibration technique. Adsorption capacity were increased with pH for Pb(II), Cd(II) and Hg(II) and then reached almost plateau value around 6.0. The high initial rate of metal ions uptake (<10 min) suggests that the adsorption occurs mainly at the bead surface. The metal uptake results show that poly(EGDMA-co-AAm) can be used for the adsorption of the following metals in the indicated order: Pb(II) > Cd(II) > Hg(II) expressed on a molar basis. However, when the uptake was expressed in terms of the amount of metal removed from solution was as follows: Pb(II) > Hg(II) > Cd(II). The beads still showed preference toward Pb(II) when this metal was in a mixture with Hg(II) and Cd(II). A linearized form of the Freundlich and the Langmuir isotherm model fits the experimental equilibrium concentration data of Hg(II) and Cd(II) better than isotherm type model of Pb(II). The recovery of the metal ions after adsorption and the regeneration of the adsorbent can be carried out by treatment of the loaded beads with either 0.5 M NaCl, or 1 M HNO₃.