Differential pulse voltammetric determination of theophylline at poly(4-amino-3-hydroxyl naphthalene sulfonic acid) modified glassy carbon electrode

A glassy carbon electrode (GCE) was modified with electropolymerized film of 4-amino-3-hydroxynaphthalene sulfonic acid (AHNSA) in 0.1 M HNO3. Cyclic voltammetry (CV) was used to study the electrochemical properties of the polymer film. The polymer film-modified electrode was used to electrochemically detect theophylline (TP) in drug samples. The polymer-modified electrode showed excellent electrocatalytic activity for the oxidation of TP. Under optimal experimental conditions, there was a good linear relationship between anodic peak current and TP concentration in the range from 1.0 x 10-6 to 1.0 x 10-4 M with the correlation coefficient of 0.9983 and a detection limit of 4.7 x 10-8 M (S/N = 3 for n = 6). The application of the polymer-modified GCE for the determination of TP in drug formulations showed good recovery and reproducible results. KEY WORDS: Cyclic voltammetry, Differential pulse voltammetry, Theophylline, 4-Amino-3-hydroxynaphthalene sulfonic acid Bull. Chem. Soc. Ethiop. 2012, 26(1), 73-84.DOI: http://dx.doi.org/10.4314/bcse.v26i1.

Polypyrrole–polyaniline-water hyacinth leaf protein concentrate composite for the removal of Cr(VI) from aqueous solution: kinetics, isotherm and thermodynamic studies

ABSTRACT. This work focused on the extraction of “water hyacinth leaf protein concentrate” (WHLPC) and preparation of polypyrrole (PPy), polyaniline (PANI) and polypyrrole-polyaniline copolymer (PPy/PANI) coated WHLPC by in situ polymerization and investigate their application for the removal of Cr(VI) from aqueous solution. After optimizing the experimental conditions like pH, adsorbent dosage, contact time and initial concentration it was found that the kinetics and isotherm data were well fitted to the pseudo-second-order and Langmuir models, respectively. PPy/PANI/WHLPC was found to be an efficient material compared to the other polymer-coated adsorbents with maximum adsorption capacity of 230 mg/g. The presence of counter ions ((NO3-, Cl-, HPO42-, SO42+ and HCO3- ions) slightly decreases the Cr(VI) removal efficiency PPy/PANI/WHLPC. The thermodynamic study reveals that the adsorption of Cr(VI) onto PPY/PANI/WHLPC is endothermic, thermodynamically feasible, and spontaneous. In addition, reusability of the material indicated high removal efficiency for two adsorption cycles.   KEY WORDS: Polypyrrole, Polyaniline, Protein concentrate, Water hyacinth, Chromium Bull. Chem. Soc. Ethiop. 2022, 36(3), 571-584.                                                               DOI: https://dx.doi.org/10.4314/bcse.v36i3.

Effect of side chain length on the stability and structural properties of 3-(2’,5’-dialkoxyphenyl)thiophenes: a theoretical study

We report on the effect of the alkoxy chain length on the thermodynamic properties of neutral and the corresponding radical cations of 3-(2’,5’-dibutyloxyphenyl)thiophene (DBOPT), 3-(2’,5’-diheptyloxyphenyl)thiophene (DHOPT), and 3-(2’,5’-dioctyloxyphenyl)thiophene (DOOPT) and their dimers studied by Hartree-Fock (HF) and Density Functional Theory (DFT) methods. The DFT calculations suggest that dimers of the dialkoxyphenylthiophenes with longer side chains are thermodynamically more stable by about 61.39 kJ/mol than the ones with shorter side chains at the radical cation state. The results correlate well with the experimental observations made during the electrochemical synthesis of these polymers from their monomers.KEY WORDS: Density functional theory, Hartree-Fock, DialkoxyphenylthiophenesBull. Chem. Soc. Ethiop. 2010, 24(1), 93-102

MWCNTs/Ag-ZnO nanocomposite for efficient photocatalytic degradation of congo red

Three nanomaterials namely, zinc oxide (ZC), silver-doped zinc oxide (AZ) and multi-walled carbon nanotubes coupled with silver doped zinc oxide nanocomposite (MWAZ) were synthesized, characterized and employed for photo degradation of an organic pollutant, congo red (CR). The photocatalytic activity study showed efficient degradation of CR upon irradiation with UV and visible light in the order of MWAZ > AZ > ZC > Commercial ZnO (ZCO). Percentage photodegradation of 99% and a pseudo 1st order rate constant of 2.3 x 10-2 min-1 were achieved by MWAZ as a catalyst under visible light irradiation, implying photo- sensitizing ability of MWCNTs and the capability of MWCNTs to hinder recombination of photogenerated holes and electrons. The control experiment in the dark condition gave only 7.9% of degradation efficiency and 5.56 x 10-4 min-1 rate constant, implying the significant role of light source for catalytic degradation of CR.   Bull. Chem. Soc. Ethiop. 2020, 34(1), 55-66. DOI: https://dx.doi.org/10.4314/bcse.v34i1.

CHROMIC TRANSITIONS IN PHENYL-SUBSTITUTED POLYTHIOPHENES

The solvatochromic and thermochromic behaviours of phenyl-substituted polythiophenes were studied. The pristine polymers, upon dissolution in chloroform, exhibited blue-shifted absorption. The solid films of the polymers showed significant blue-shifted as well as red-shifted absorptions when heated. While the addition of methanol to the chloroform solutions of the polymers caused dramatic chromic changes and development of red-shifted spectra for many of the polymers investigated, the symmetrically phenyl-substituted and sterically hindered polymer (polymer 1) does not show significant changes. These chromic behaviours have been examined in terms of substituent effects and attempt has been made to explain these effects by calculating the energy barrier for rotation to a planar structure using the HF SCF method and 3-21G* basis set. KEY WORDS: Chromic transitions, Phenyl-substituted polythiophenes Bull. Chem. Soc. Ethiop. 2005, 19(2), 267-276

Synthesis, optical and electrochemical characterization of anthrancene and benzothiadiazole-containing polyfluorene copolymers

New solution-processable, anthrancene- and benzothiadiazole-containing polyfluorene copolymers (P1-P3) have been synthesized and characterized. The preparation and characterization of the corresponding blue light-emitting devices are also reported. Polymers P2 and P3 show high photoluminescence efficiency while polymer P2 does not show any significant light emission up to 8.0 V. The results show the need for balance of electron and hole transport in polymer light emitting diodes. KEY WORDS: Anthracene, Benzothiadiazole, Polyfluorene copolymers, Photoluminescence, Light emitting diode  Bull. Chem. Soc. Ethiop. 2006, 20(2), 309-317

Variable denticity of a multidentate terthiophene derivative towards Ni(II) and Zn(II) - structural studies

A multidentate ligand, 3,4-bis(2-iminomethylphenol)-2,2’:5,2’’-terthiophene (L), has been synthesized by the condensation of 3,4-diamino-2,2’:5,2’’-terthiophene and salicylaldehyde. The ligand and Ni(II) and Zn(II) complexes were synthesized and characterized by IR, NMR, UV-Vis, AAS, MS, molar conductivity and magnetic susceptibility measurements. The ligand behaves as neutral ONS-ONS bis-chelant towards Ni(II) in [Ni<sub>2</sub>LCl<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]×4H<sub>2</sub>O and as dibasic ONNO donor towards Zn(II) in [ZnL(NH<sub>3</sub>)<sub>2</sub>]. The dinuclear Ni(II) complex exhibits subnormal magnetic moment at room temperature due to metal-metal interaction through extended conjugation. The participation of the ring sulfur in bonding towards Ni(II) and the non-participation of the same towards Zn(II) are notable features. Octahedral geometries are proposed for both complexes. Cyclic voltammetric studies revealed electrochemical polymerization of the free ligand (L) but not of the Ni(II) and Zn(II) complexes. KEY WORDS: Variable denticity, 3,4-bis(2-Iminomethylphenol)-2,2’:5,2’’-terthiophene, Octahedral, Ni(II) complex, Zn(II) complex, Voltammetric studies Bull. Chem. Soc. Ethiop. 2011, 25(2), 221-23

Electrochromic, magnetotransport and AC transport properties of vapor phase polymerized PEDOT(VPP PEDOT)

Poly(3,4-ethylenedioxy)thiophene (PEDOT) doped with tosylate ion (PEDOT-tosylate or VPP PEDOT) was synthesized by vapor phase polymerization (VPP) technique on glass as well as on glass/ITO and the electrochromic properties were investigated. Compared with that of PEDOT-PSS spin-coated on glass/ITO, the studies showed that VPP PEDOT has a lower work function and better electrochromic properties. The magneto and AC transport properties studies were done on VPP PEDOT coated on glass substrate. The system shows 2-dimensional variable range hopping and wave function shrinkage of charge carriers

Quantification of lead in cooking utensils and vegetables using square wave anodic stripping voltammetry

A simple and sensitive voltammetric method using in-situ bismuth film modified glassy carbon electrode (BiFGE) and Nafion-coated bismuth film modified glassy carbon electrode (NC-BiFGE) were used to determine the amount of lead(II) present in locally produced (at Kombolcha, 376 km North of Addis Ababa, Ethiopia) and imported cooking utensils and vegetable samples before and after cooking with the utensils. The voltammetric method was validated using standard spectroscopic method and recovery tests. The amount of lead(II) found in the locally produced utensil (6.48 mg L−1) was very high compared to the imported utensil (0.007 mg L−1). Moreover, a 3–5 fold increase in the amount of lead(II) was found when different vegetables were cooked with the local utensil as a result of the leaching out of the lead(II) from the cooking utensil

Voltammetric Determination of Paracetamol with Poly(3,4-Ethylenedioxythiophene) Modified Glassy Carbon Electrode Analytical & Bioanalytical Electrochemistry

Abstract-This study describes the preparation and application of a poly(3,4-ethylenedioxythiophene) (PEDOT) modified glassy carbon electrode for paracetamol determination in pharmaceutical samples. The PEDOT modified electrode was prepared by electropolymerizing 3,4-ethylenedioxythiophene (EDOT) on a glassy carbon electrode in a non-aqueous medium. The best performance of the PEDOT modified electrode in 0. , respectively. Finally, the proposed method was applied for paracetamol determination in commercial tablets with a mean recovery of (1016) %