Direct determination of sulfite in food samples by a biosensor based on plant tissue homogenate

In the work described here, a biosensor was developed for the determination of sulfite in food. Malva vulgaris tissue homogenate containing sulfite oxidase enzyme was used as the biological material. M. vulgaris tissue homogenate was crosslinked with gelatin using glutaraldehyde and fixed on a pretreated Teflon membrane. Sulfite was enzymatically converted to sulfate in the presence of the dissolved oxygen, which was monitored amperometrically. Sulfite determination was carried out by standard curves, which were obtained by the measurement of consumed oxygen level related to sulfite concentration. Several operational parameters had been investigated: the amounts of plant tissue homogenate and gelatin, percentage of glutaraldehyde, optimum pH and temperature. Also, some characterization studies were done. There was linearity in the range between 0.2 and 1.8 mM at 35 °C and pH 7.5. The results of real sample analysis obtained with the biosensor agreed well with the enzymatic reference method using spectrophotometric detection.     

First principles investigations of hydrazine adsorption conformations on Ni(111) surface

Theoretical investigation on hydrazine (N₂H₄) adsorption on Ni(111) was done by using density functional theory. Stability and mechanism of hydrazine adsorption in anti, gauche and cis conformation on nickel surface were studied. Charge transfer between lone-pair orbital and d-band was found to stabilize the anti-conformation as the most stable conformation, in contrast with hydrazine in the gas-phase where gauche conformation is more favored. However, the derived anti-bonding state between adsorbate and substrate is partially occupied due to the spin-polarization in the local states near the Fermi level and thus contributes in weakening the bonding. The stable adsorption structure was further verified by comparing the calculated vibrational frequencies with HREELS measurement results. The results were found to be in agreement with experimental results. It was also found that the adsorption in cis-conformation is a transition state as evident from the existence of imaginary frequency on its lowest vibrational mode which belongs to NH₂ torsional movement around N–N axis.     

Alginate/Polyoxyethylene and Alginate/Gelatin Hydrogels: Preparation,Characterization, and Application in Tissue Engineering

Hydrogels are attractive biomaterials for three-dimensional cell culture and tissue engineering applications. The preparation of hydrogels using alginate and gelatin provides cross-linked hydrophilic polymers that can swell but do not dissolve in water. In this work, we first reinforced pure alginate by using polyoxyethylene as a supporting material. In an alginate/PEO sample that contains 20 % polyoxyethylene, we obtained a stable hydrogel for cell culture experiments. We also prepared a stable alginate/gelatin hydrogel by cross-linking a periodate-oxidized alginate with another functional component such as gelatin. The hydrogels were found to have a high fluid uptake. In this work, preparation, characterization, swelling, and surface properties of these scaffold materials were described. Lyophilized scaffolds obtained from hydrogels were used for cell viability experiments, and the results were presented in detail.     

A High Sensitive,Reproducible and Disposable Immunosensor for Analysis of SOX2

In this study, an ITO (indium tin oxide) based biosensor was constructed to detect SOX2. SOX2 helps the regulation of cell pluripotency and is closely related to early embryonic development, neural and sexual differentiation. SOX2 is amplified and overexpressed in some malignant tumors such as squamous cell, lung, prostate, breast, esophageal cell, colon, ovarian, glioblastoma, pancreatic cancer, gastric cancer, head and neck squamous cell carcinoma. To generate a hydroxylated clean electrode surface, ITO electrodes were treated with NH₄OH/H₂O₂/H₂O. Later, ITO‐PET electrode surfaces were modified with 3‐glycidoxypropyl trimethoxysilane (3‐GOPS). Then, Anti‐SOX2 was covalently immobilized onto the electrode surfaces. 3‐GOPS concentration, Anti‐SOX2 concentration and incubation time, SOX2 incubation time were optimized. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were utilized in order to follow up the immobilization processes and the optimization steps of the biosensor. To characterize the analytical properties of constructed immunosensor; linear range, repeatability, reproducibility and regeneration studies were investigated. The linear range of the immunosensor was detected as 0.625 pg/mL–62.5 pg/mL. Square wave voltammetry technique was also applied to the biosensor. Storage life of the biosensor was determined for identifying the possible usability of the biosensor in clinical field. Finally, the designed biosensor was applied to the real human serum samples. The results obtained with the presented biosensor were also compared with ELISA results.     

Full-trapped three-level ion in the lamb–dicke limit: analyzing and comparing quantum entanglement measures of two qudits

Our aim is to investigate the entanglement dynamics and quantum correlations of a full-trapped ion interacting with two time-independent laser beams in view of the Lamb–Dicke parameter. For this purpose, the three probability amplitudes in the trapped ion is taken as ?{1

The stabilities, electronic structures and elastic properties of Rbben As systems

The structural, electronic and elastic properties of Rb-As systems (RbAs in NaP, LiAs and AuCu structures, RbAs₂ in the MgCu₂ structure, Rb₃As in Na₃As, Cu₃P and Li₃Bi structures, and Rb₅As₄ in the A₅B₄ structure) are investigated with the generalized gradient approximation in the frame of density functional theory. The lattice parameters, cohesive energies, formation energies, bulk moduli and the first derivatives of the bulk moduli (to fit Murnaghan's equation of state) of the considered structures are calculated and reasonable agreement is obtained. In addition, the phase transition pressures are also predicted. The electronic band structures, the partial densities of states corresponding to the band structures and the charge density distributions are presented and analysed. The second-order elastic constants based on the stress-strain method and other related quantities such as Young's modulus, the shear modulus, Poisson's ratio, sound velocities, the Debye temperature and shear anisotropy factors are also estimated.     

Improving image quality of diagnostic ultrasound by using the safe use time model with the dynamic safety factor and the effect of the exposure time on the image quality

Resolution and penetration are primary criteria for image quality of diagnostic ultrasound. In theory (and usually in practice), the maximum depth of imaging in a tissue increases as power (pressure) is increased. Alternatively, at a particular effective penetration, an increased power may be used to allow a higher ultrasound frequency for higher resolution and tissue contrast. Recently, Karagoz and Kartal [29] proposed a safety parameter for thermal bioeffects of diagnostic ultrasound; that is, SUT (safe use time). The SUT model is constructed to determine how long one piece of tissue can be insonated safely according to a threshold exposure. Also, Karagoz and Kartal [29] suggested that an increase in acoustic intensity beyond the current US Food and Drug Administration (FDA) limit of intensity can be theoretically possible by using SUT model while staying within the safe limit. The present study was motivated particularly by the goals of higher resolution and/or deeper penetration by using SUT model. The results presented here suggest that the safe use of higher exposure levels than currently allowed by the FDA may be possible for obtaining substantial improvements in penetration depth and/or resolution. Also, the study reveals that image quality can be functionally related to exposure time in addition to acoustic energy and frequency.     

Glycan–protein cross-linking mass spectrometry reveals sialic acid-mediated protein networks on cell surfaces

A cross-linking method is developed to elucidate glycan-mediated interactions between membrane proteins through sialic acids. The method provides information on previously unknown extensive glycomic interactions on cell membranes. The vast majority of membrane proteins are glycosylated with complicated glycan structures attached to the polypeptide backbone. Glycan–protein interactions are fundamental elements in many cellular events. Although significant advances have been made to identify protein–protein interactions in living cells, only modest advances have been made on glycan–protein interactions. Mechanistic elucidation of glycan–protein interactions has thus far remained elusive. Therefore, we developed a cross-linking mass spectrometry (XL-MS) workflow to directly identify glycan–protein interactions on the cell membrane using liquid chromatography-mass spectrometry (LC-MS). This method involved incorporating azido groups on cell surface glycans through biosynthetic pathways, followed by treatment of cell cultures with a synthesized reagent, N-hydroxysuccinimide (NHS)–cyclooctyne, which allowed the cross-linking of the sialic acid azides on glycans with primary amines on polypeptide backbones. The coupled peptide–glycan–peptide pairs after cross-linking were identified using the latest techniques in glycoproteomic and glycomic analyses and bioinformatics software. With this approach, information on the site of glycosylation, the glycoform, the source protein, and the target protein of the cross-linked pair were obtained. Glycoprotein–protein interactions involving unique glycoforms on the PNT2 cell surface were identified using the optimized and validated method. We built the GPX network of the PNT2 cell line and further investigated the biological roles of different glycan structures within protein complexes. Furthermore, we were able to build glycoprotein–protein complex models for previously unexplored interactions. The method will advance our future understanding of the roles of glycans in protein complexes on the cell surface.

The cell surface glycocalyx is highly interactive defined by extensive covalent and non-covalent interactions. A method for cross-linking and characterizing glycan–peptide interactions in situ is developed.     

Ni(II), Cu(II), and Zn(II) complexes of tetradentate schiff base containing two thiadiazoles units: Structural,spectroscopic, magnetic properties,and molecular modeling studies

Four new mononuclear metal complexes with a mononucleating Schiff base ligand containing two thiadiazoles units have been synthesized. The ligand and metal complexes were characterized by elemental analyses, IR, ¹H, and ¹³C NMR, UV–vis, ESR, electrospray ionization mass spectra, and magnetic susceptibility measurements. Electronic spectra, magnetic susceptibility measurement, and molecular modeling studies support octahedral geometry around the Ni(II), Cu(II), and Zn(II) ions. The magnetic properties were investigated, and ferromagnetic coupling is observed in Cu(II) and Ni(II) complexes. In addition, total energy and heat of formation calculated for conformers of the Schiff base ligand by the semiempirical AM1 calculations have shown that E,Z‐isomer of the ligand is more stable (about 5.3 kcal/mol) than E,E‐ and Z,Z‐isomers. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:700–712, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20496     

4,4′‐Butane‐1,4‐diylbis[3‐ethyl‐1H‐1,2,4‐triazol‐5(4H)‐one] and 4‐hydr­oxy‐3‐n‐prop­yl‐1H‐1,2,4‐triazol‐5(4H)‐one

The title compounds, C₁₂H₂₀N₆O₂, (I), and C₅H₉N₃O₂, (II), display the characteristic features of 1,2,4‐triazole derivatives. Compound (I) lies about an inversion centre which is at the mid‐point of the central C—C bond. Compound (II) also contains a planar 1,2,4‐triazole ring but differs from (I) in that it has a hydr­oxy group attached to the ring. Mol­ecules of (I) are held together in the crystal structure by inter­molecular N—H⋯O contacts and by weak π–π stacking inter­actions between the 1,2,4‐triazole moieties. Compound (II) contains inter­molecular O—H⋯O and N—H⋯O hydrogen bonds.