Ola R. Shehab

New selenite ion-selective electrodes based on 5,10,15,20-tetrakis-(4-methoxyphenyl)-21H,23H-porphyrin-Co(II).

New polymeric membrane (PME), modified carbon paste (MCPE), and coated wire (CWE) selenite ion-selective electrodes based on 5,10,15,20-tetrakis-(4-methoxyphenyl)-21H,23H-porphyrin-Co(II) (CoTMeOPP) are reported. The best composition was the electrode containing 2% CoTMeOPP as the active material and 49% TCP as plasticizer. The electrodes reveal a Nernstian behavior over a concentration range of 5.5x10(-5) to 1.1x10(-2) M for PME, 5.2x10(-5) to 1.2x10(-2) M for MCPE and 1.2x10(-4) to 4.4x10(-3) M for CWE. The potentiometric response is pH dependent, since selenous acid is a diprotic acid. The slope of the selenite PVC electrode was -57.0 mV for the monovalent anion at pH 6.47, and -26.0 mV for the divalent anion at pH 11.00. The detection limits were 3.4x10(-5) and 4.7x10(-5) M at pH values 6.47 and 11.00, respectively. The electrodes manifest advantages of low resistance, very short response time (15 s), and most importantly good selectivities relative to a wide variety of other anions. In fact, the proposed selenite ion-selective electrodes show a great improvement compared to previously reported electrodes for selenite ion. The electrode was used for the determination of selenite in selenite/selenate mixture, in sodium selenite raw material powder, and in VitaFit Selenium ACE antioxidant tablets with recovery ranges of 90.0-103.3%.

Effect of steric factors on mesomorphic stability I. 4‐(4‐Substituted phenylazo)‐1‐naphthyl 4‐alkoxybenzoates

Four homologous series belonging to the family of 4‐(4‐substituted phenylazo)‐1‐naphthyl 4‐alkoxybenzoates (I a–d) (C n H2 n +1O–C6H4–COO–C10H6–N = N–C6H4–X) were prepared in which the 4‐ substituent (X) was varied between CH3O, CH3, Cl and NO2; while, within each homologous series, the number of carbon atoms, n, was varied between 8 and 14. The compounds were characterized by infrared spectroscopy, 1H NMR spectroscopy and elemental analysis. Their mesophase behaviour was investigated by differential scanning calorimetry and polarizing‐optical microscopy. The results are discussed in terms of mesomeric, polarizability, and steric effects. In each group of compounds bearing the same alkoxy group, attempts were made to correlate the mesophase–isotropic transition temperatures (T c) with the polarizability anisotropy, Δα x , of bonds to the small compact substituent X.

New thiocyanate potentiometric sensors based on sulfadimidine metal complexes: experimental and theoretical studies.

Three sulfadimidine metal complexes (M=Fe(III), Cu(II), and Ag(I)) were prepared, characterized, and examined as neutral carriers for the determination of SCN(-) using modified carbon paste electrode. These sensors were successfully applied in the pure samples, and biological fluids. The electrode mechanism was investigated by UV-vis and FT IR. The experimental studies were complemented by quantum chemical calculations at DFT/B3LYP level of theory. The best performance was observed for Cu(II) electrode (C) containing 7.0% complex, 53.0% o-nitrophenyloctyl ether, 37.0% graphite and 3.0% cetylpyridinium chloride, and also for Fe(III)-electrode (A) having 6.0% complex, 52.0% o-nitro phenyloctyl ether, 40.5% graphite and 2.5% cetylpyridinium chloride.

Effect of Steric Factor on Mesomorphic Stability, II: Binary Mixtures of Homologues of 4-(4′-Substituted Phenylazo)-1-naphthyl-4″-alkoxybenzoates

Sixteen mesomorphic derivatives of the title compounds have been investigated for their phase behavior. These compounds constitute four homologous series that differ from each other by the substituent X. The latter varies between CH3O, CH3, Cl, and NO2, and the number (n) of carbons in the alkoxy chain varies, within a homologous series, between 8, 10, 12, and 14. All possible binary mixtures made from any two homologues were prepared and characterized for their mesophase behavior by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). Phase diagrams for the 24 binary combinations were constructed to investigate the effect of inclusion of the 1,4-naphthalene moiety, as well as the variation in the alkoxy chain length, on the mesomorphic properties in mixed systems.

Potentiometric multi-walled carbon nanotube Zn-sensor based on a naphthalocyanine neutral carrier: experimental and theoretical studies

A new multi-walled carbon nanotube graphite paste sensor based on 2,11,20,29-tetra-tert-butyl-2,3-naphthalocyanine as a neutral carrier (2.0%), 2-flouorophenyl-2-nitrophenyl ether (50.0%) as a plasticizer, and sodium tetrakis-imidazolyl borate (1.0%) as an anionic additive has been explored as a selective sensor for determination of Zn2+ in real samples. The electrode showed a fast response time of 5 s, gave a Nernstian response (29.9 mV per decade) over the concentration range 1.0 × 10−8 to 1.5 × 10−4 mol L−1, and could be used in the pH range of 4.3–7.5 with a detection limit of 5.0 × 10−9 mol L−1. The response mechanism of the electrode was investigated using UV-vis and FT IR spectroscopy. Scanning electron microscopy combined with energy dispersive X-ray spectra were used to confirm the reaction between Zn2+ ions and naphthalocyanine on the surface of the electrode. In order to predict the selectivity of the naphthalocyanine sensor for different metal ions, the corresponding binding energies of the metal complexes were calculated at the Hartree–Fock level of theory.

Trapping of muscle relaxant methocarbamol degradation product by complexation with copper(II) ion: spectroscopic and quantum chemical studies.

Structural properties of methocarbamol (Mcm) were extensively studied both experimentally and theoretically using FT IR, (1)H NMR, UV-Vis., geometry optimization, Mulliken charge, and molecular electrostatic potential. Stability arises from hyper-conjugative interactions, charge delocalization and H-bonding was analyzed using natural bond orbital (NBO) analysis. Mcm was decomposed in ethanol/water mixture at 80°C to guaifenesin [(RS)-3-(2-methoxyphenoxy)propane-1,2-diol] and carbamate ion [NH2COO(-)], where the degradation mechanism was explained by trapping the carbamate ion via the complexation with copper(II) ion. The structure of the isolated complex ([Cu(NH2COO)2(H2O)]⋅4H2O) was elucidated by spectral, thermal, and magnetic tools. Electronic spectra were discussed by TD-DFT and the descriptions of frontier molecular orbitals and the relocations of the electron density were determined. Calculated g-tensor values showed best agreement with experimental values from EPR when carried out using both the B3LYP and B3PW91 functional.

Photodegradation of sulfadiazine catalyzed by p-benzoquinones and picric acid: application to charge transfer complexes

As the treatment of effluents containing the antibiotic drug sulfadiazine (SZ) is one of the challenging problems in the field of environmental chemistry, it is essential to determine the concentration of SZ by a rapid and accurate method and then find a suitable method to degrade the assayed products into harmless chemicals. The color of the charge transfer (CT) complexes developed from the reaction of SZ with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), chloranilic acid (CHL) and picric acid (PA) was used to determine the concentration of SZ at 528, 510 and 410 nm, respectively. The Lambert–Beers law is obeyed in the ranges of 6.80–68.06, 13.61–136.12 and 6.80–27.22 μg mL−1 for DDQ, CHL and PA complexes. The photolysis of SZ → DDQ in presence of sodium nitrite at 256 nm leads to faster degradation of SZ compared with the control experiments. This was simply spectrophotometrically followed by a decrease in the intensity of the CT band. The effect of some additives such as oxalic acid, and hematite nano particles was studied. For comparison, other π-acceptor reagents such as CHL and PA were used. About 80% of SZ is degraded in 45 min upon the illumination of SZ → DDQ at 256 nm, whereas 90 min is required in the case of CHL and PA to attain the same degradation limit.