Design and characteristics of tin (II) optode based on immobilization of dithizone on a triacetylcellulose membrane and its application in canned foods

Abstract  

The characterization of an optical sensor membrane is described for the determination of tin (II) based on the immobilization of dithizone on a triacetylcellulose membrane. The membrane responds to tin (II) ions by changing color reversibly from green to red in buffer solution at pH 6 and wavelength 611 nm. This optode has a linear range of 0.3–6.33 μg cm⁻³ (2.52–53.32 μmol dm⁻³) of Sn²⁺ ions with a limit of detection of 0.15 μg cm⁻³ (1.26 μmol dm⁻³). The response time of the optode was about 8–10 min depending on the concentration of Sn²⁺ ions. The selectivity of the optode to tin (II) ions at pH 6 was good. The sensor can be readily regenerated by exposure with EDTA solution. The color is fully reversible, and the optical sensor could be fully regenerated. Experimental results showed that the optode could be used as an effective tool in analyzing the tin content in canned foods.     

Study of the oxidation of some catechols in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole by digital simulation of cyclic voltammograms

Electrochemical oxidation of catechol and its derivatives ( 1a–d ) has been studied in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole ( 3 ) at various pHs. Some electrochemical techniques such as cyclic voltammetry using the diagnostic criteria derived by Nicholson and Shain for various electrode mechanisms and controlled‐potential coulometry were used. Results indicate the participation of catechols ( 1a–d ) with 3 in an intramolecular cyclization reaction to form the corresponding 1,2,4‐triazino[5,4‐b]‐1,3,4‐thiadiazine derivatives. In various scan rates, based on an electron transfer–chemical reaction–electron transfer–chemical reaction mechanism, the observed homogeneous rate constants (k_obs) for Michael addition reaction were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results. The oxidation reaction mechanism of catechols ( 1a–d ) in the presence of 4‐amino‐3‐thio‐1,2,4‐triazole ( 3 ) was also studied. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 340–345, 2007     

Preparation and evaluation of polymer-coated adsorbents for the expanded bed recovery of protein products from particulate feedstocks

A novel prototype polymer-coated adsorbent (PCA) has been developed for the effective expanded bed recovery of protein products from particulate feedstocks. The adsorbents were manufactured using the three-phase emulsification process by which the selected core phases (anion- and cation-exchangers and a custom-assembled pseudo-affinity adsorbent) were coated by an agarose gel. This new non-stick exterior coating acts as a sieve reducing the non-specific binding of cell and cell debris without diminution of selective capture of target protein from complex feedstocks such as whole microbial broths and cell disruptates. The new coated adsorbents were subjected to physical and hydrodynamical comparison with the performance of their uncoated adsorbents. Hydrodynamic characteristics (e.g. axial dispersion coefficient (D(axl)) and Bodenstein number (B(o))) of PCA demonstrated a marked robustness in the face of biomass loading disrupted yeast cells. In addition, each adsorbent was compared with its uncoated native form during the expanded bed adsorption of one of two intracellular proteins (i.e. glyceraldehyde 3-phosphate dehydrogenase and cytochrome c) from a 20% (ww/v) yeast disruptate. The performance parameters of efficiency of washing, purification factor, turbidity of the eluted product and protein recovery in all analysed cases were favourable to the coated materials. In particular, exploiting PCA reduced significantly undesirable adsorption of cells without significant loss of binding capacity for the target product. The generic application of such adsorbents and their potential for the recovery of target products from complex feedstock is discussed, whilst other application such as the subtractive purification of nanoparticles were detailed in our previous publication.     

Neutral Higgs sector of the MSSM with explicit CP violation and non-holomorphic soft breaking

Using the effective potential method, we computed one-loop corrections to the mass matrix of neutral Higgs bosons of the Non-Holomorphic Supersymmetric Standard Model (NHSSM) with explicit CP violation, where the radiative corrections due to the quarks and squarks of the third generation were taken into account. We observed that the non-holomorphic trilinear couplings can compete with the holomorphic ones in CP violating issues for the mass and mixing of the neutral Higgs bosons.     

Composite cryogel with immobilized concanavalin A for affinity chromatography of glycoproteins

Composite cryogels containing porous adsorbent particles were prepared under cryogelation conditions. The composites with immobilized concanavalin A (Con A) were used for capturing glycoproteins. Adsorbent particles were introduced into the structure in order to improve the capacity and to facilitate the handling of the particles. The monolithic composite cryogels were produced from suspensions of polyvinyl alcohol particles and porous adsorbent particles and cross‐linked under acidic conditions at sub‐zero temperature. The cryogels were epoxy activated and Con A was immobilized as an affinity ligand. Binding and elution of horseradish peroxidase (HRP) was studied in batch experiment and in a chromatographic setup. Increasing adsorbent concentration in composite cryogels will increase ligand density, which therefore enhances the amount of bound HRP from 0.98 till 2.9 (milligram enzyme per milliliter of gel) in the chromatographic system. The material was evaluated in 10 cycles for binding and elution of HRP.     

Low-cost low-threshold diode end-pumped Tm:YAG laser at 2.016?μm

We report a low-threshold continuous-wave Tm:YAG laser that can be excited near 785?nm with low-cost, single-mode AlGaAs laser diodes. Low-threshold operation was achieved using a tightly focused, astigmatically compensated x-cavity containing a 2-mm-thick Tm:YAG crystal with 5?% Tm³⁺ concentration. Two linearly polarized single-mode diodes operating at 785.8?nm were polarization coupled to end pump the resonator. With a 6?% output coupler, as high as 32?mW of output power could be obtained at 2016?nm with 184?mW of incident pump power. The output could be further tuned in the 1935?C2035?nm range. Slope efficiency measurements indicated that cross-relaxation was very effective at this doping level. With a 2?% output coupler, lasing could be obtained with as low as 32.3?mW of pump power. In the limit of vanishing output coupling, the incident threshold pump power could be reduced to as low as 25?mW. To our knowledge, this is among the lowest lasing thresholds reported to date for continuous-wave, room-temperature thulium lasers.     

General Inertia and Circle Criterion

In this paper we extend the well known Kalman-Yacubovic-Popov (KYP) lemma to the case of matrices with general regular inertia. We show that the version of the lemma that was derived for the case of pairs of stable matrices whose rank difference is one, extends to the more general case of matrices with regular inertia and in companion form. We then use this result to derive an easily verifiable spectral condition for a pair of matrices with the same regular inertia to have a common Lyapunov solution (CLS), extending a recent result on CLS existence for pairs of Hurwitz matrices that can be considered as a time-domain interpretation of the famous circle criterion. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetic recyclable eggshell-based mesoporous catalyst for biodiesel production from crude neem oil: Process optimization by central composite design and artificial neural network

A magnetically recyclable eggshell-based catalyst (MKEC) was synthesized to circumvent saponification during the conversion of neem, Jatropha, and waste cooking oils (free fatty acid, 2.3–6.6%) to biodiesel. The characterization results indicated that MKEC had a mesoporous structure with the pore width of 3.24 nm, a specific surface area of 128 m²/g, and a pore volume of 0.045 cm³/g. The results confirmed that the MKEC is more tolerant to fatty acid poisoning than calcined eggshell. The effects of process parameters for maximum fatty acid methyl ester (FAME) content were evaluated by central composite design (CCD) and artificial neural network (ANN). The experimental FAME content of 94.5% was achieved for neem oil with a standard deviation (SD) of 0.68, which was in reasonable agreement with predicted values (CCD, 96.9%; ANN, 95.9%; SD, 0.73). The reusability studies showed that the mesoporous catalyst can be reused efficiently for five cycles without much deterioration in its activity.     

Mixed micelles of oppositely charged poly(N‐isopropylacrylamide) diblock copolymers

Mixed micelle formation between two oppositely charged diblock copolymers that have a common thermosensitive nonionic block of poly(N‐isopropylacrylamide) (PNIPAAM) has been studied. The block copolymer mixed solutions were investigated under equimolar charge conditions as a function of both temperature and total polymer concentrations by turbidimetry, differential scanning calorimetry, two‐dimensional proton nuclear magnetic nuclear Overhauser effect spectroscopy (2D ¹H NMR NOESY), dynamic light scattering, and small angle X‐ray scattering measurements. Well‐defined and electroneutral cylindrical micelles were formed with a radius and a length of about 3 nm and 35 nm, respectively. In the micelles, the charged blocks built up a core, which was surrounded by a corona of PNIPAAM chains. The 2D ¹H NMR NOESY experiments showed that a minor block mixing occurred between the core blocks and the PNIPAAM blocks. By approaching the lower critical solution temperature of PNIPAAM, the PNIPAAM chains collapsed, which induced aggregation of the micelles. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1457–1469