Fikru Tafesse

Fabrication of new solid state phosphate selective electrodes for environmental monitoring

A highly selective and sensitive phosphate sensor has been fabricated by constructing a crystal disk consisting of variable mixtures of aluminium powder (Al), aluminium phosphate (AlPO(4)) and powdered copper (Cu). The membrane sensor exhibits linear potential response in the concentration range of 1.0×10(-1) to 1.0×10(-6) mol L(-1). The proposed sensor also exhibits a fast response time of <60s. Its detection limit is lower than 1.0×10(-6) mol L(-1). The electrode has a long lifetime and can be stored in air when not in use. The selectivity of the sensor with respect to other common ions is excellent.

Efficient hydrolysis of 4-nitrophenylphosphate catalyzed by copper bipyridyl in microemulsions.

The hydrolysis of 4-nitrophenylphosphate (NPP) in the presence of copper bipyridyl [Cu(bpy)(H(2)O)(2)](2+) in oil in water microemulsion media was investigated. The reaction was monitored by measuring the absorbance of the nitrophenolate ion produced in the reaction aliquots with time. The order of effectiveness of the microemulsion system towards the hydrolysis of NPP in the presence of the copper dipyridyl complex was found to be cationic>anionic>aqueous at neutral pH. The result of the present investigation exhibits catalytic turnovers for metal to NPP ratio of 1:20. Catalysis in the microemulsion mediated reaction solutions was evident even in low concentrations of the metal ions in 1:2000 metal to NPP ratio. An explanation for the enhanced catalytic activity of the [Cu(bpy)(H(2)O)(2)](2+) complex for the hydrolysis of NPP is afforded. The application of the above systems for possible environmental decontamination of aryl organophosphates is anticipated.

Nitric oxide assisted hydrolysis of nitrophenylphosphate.

In this study the use of sodium nitroprusside as nitric oxide donor in solutions was utilized. It has been established that maximum release of nitric oxide is achieved under irradiation by UV light at 254nm. The synergistic effects of cobalt trimethylene diamine and nitroprusside towards the hydrolysis of nitrophenylphosphate under the above conditions for different cobalt to nitrophenylphosphate ratio were investigated. This study demonstrates that besides the effect of hydroxyl radicals, the direct interaction of nitric oxide with the phosphorous center also play a role in decontamination reactions of poorly biodegradable phosphate esters in natural waters, due to phototransformation.

Phosphate Sensitive Electrodes in Model Studies for Phosphorylation and Dephosphorylation Reactions

Highly selective and sensitive phosphate sensors have been fabricated by constructing a solid membrane disk consisting of variable mixtures of aluminium powder (Al), aluminium phosphate (AlPO4), and powdered copper (Cu). Both binary and ternary electrode systems were produced. The ternary membranes exhibited greater selectivity over a wide range of concentrations. The ternary electrode with the composition 25% AlPO4, 25% Cu, and 50% Al was selected as our preferred electrode for the study. Complexation and dephosphorylation reactions of model compounds which mimic enzyme and substrates were monitored. The results showed that the complexation reactions are fast and diffusion controlled.

Hydrolysis of 4-nitrophenyl phosphate in microemulsions assisted by polymetallic complexes: A bio-mimetic model for decontamination of organophosphate pollutants

The hydrolysis of 4‐nitrophenyl phosphate (NPP) in the presence of several metal ions and polymetallic complexes in oil‐in‐water microemulsion was investigated at 10−3 M concentration. The reaction was monitored by measuring the absorbance of the Nitrophenolate ion produced in the reaction aliquots with time. The order of effectiveness of the metal ions and polymetallic complexes at neutral pH towards hydrolysis of NPP was found to be turnbulls blue>magnetite>Fe(III)>Fe(II)>Co(II)>Ca(II)>Cu(II). The possible application of the above systems for environmental decontamination of organophosphates is discussed.

Model Chemical Decontamination Studies of Phosphate Esters in Aqueous and Microemulsion Media

The hydrolysis of 4-nitrophenylphosphate (NPP) in the presence of several cobalt(III) amine model systems in oil-in-water microemulsion media was investigated. The reaction was monitored by measuring the absorbance of the nitrophenolate ion produced in the reaction aliquots with time under the experimental condition. The order of effectiveness of the microemulsion system toward the hydrolysis of NPP was found to be cationic > anionic > aqueous. [Cotn 2 (OH)(H 2 O)] 2 + complexes were found to be better promoters of hydrolysis compared to [Coen 2 (OH)(H 2 O)] 2 + in both aqueous and microemulsion systems. Explanation for the above is afforded and the application of the systems for possible environmental decontamination of organophosphates is envisioned.

Detection mechanisms of phosphate sensitive electrodes

Phosphate sensors are composed of inorganic solid/ solid solutions and have a three dimensional network structure with interstitial ions. They have been fabricated by constructing a crystal disk consisting of mixtures of aluminum powder (Al), aluminum phosphate (AlPO4), and powdered copper (Cu). The membrane sensor exhibits linear potential response in the concentration range of 10−1 to 10−6 mol L−1. The electrode/solution interfaces presumably aid phosphate selective crystallizations or phosphate ion chemisorptions thereby leading to a membrane potential charge. The charge separation process caused by phosphate ion adsorption and the potentiometric response of the electrode contribute to the response mechanism.

Application of Layered Double Hydroxide Membranes as Phosphate-Sensitive Electrodes

GRAPHICAL ABSTRACT Abstract Highly selective and sensitive phosphate sensors have been fabricated by constructing a solid membrane disk comprising variable mixtures of aluminum powder (Al), aluminum phosphate (AlPO4), and powdered copper (Cu). Both binary and ternary electrode systems were produced. The ternary membranes exhibit greater selectivity over a wide range of concentrations. The ternary electrode with the composition 25% AlPO4, 25% Cu, and 50% Al was selected as our preferred electrode. The ternary membrane electrodes exhibited linear potential response in the concentration range of 1.0 × 10−1 to 1.0 × 10−6 molL−1. The mechanism for the selectivity of phosphates by the electrodes includes adsorption, absorption, and ion-exchange processes. An understanding of these processes reveals that the composition of the membrane material and its molecular structural framework are all important. The layered double hydroxides which form within the interstitial layers of the phosphate selective membranes contribute to the selectivity of the ions.

An Insight into Phosphorylase Mechanism from Model Study

Mechanistic aspects of phosphorylation reaction that mimic phosphorylase enzymes have been studied in the biologically important middle pH region by utilizing nitrophenol as substrate and bistrimethylenediaminecobalt(III) phosphate complexes as the enzyme model. Significant phosphorylation was noted from reactions of 1:1 molar ratio of nitrophenol and bistrimethylenediamincobalt(III) phosphate, [Co(III)tn2Pi]. Enhanced phosphorylation was depicted for reaction solutions that contained 1:1 molar ratio of nitrophenol and di-bistrimethylenediamincobalt(III) phosphate, [(Co(III)tn2)2Pi]. Specific mechanistic features and the possible roles metal ions play in phosphorylase enzyme are highlighted.

Development of Graduates' Attributes in Chemistry within an Open Distance Learning (ODL) Environment: UNISA's Experience.

ABSTRACT Discipline-specific knowledge and associated technical skills as well as generic skills have represented distinct and separate aspects of chemical sciences in university studies (linear training). In addition to technical skills gained through laboratory training, employers now require a soft skill set such as strengths in analytical thinking, problem-solving, written and oral communication, and collaboration. These skills require further integration with the human qualities needed to remain resilient to changing conditions and they do not come naturally, but through training. Since community engagement forms an integral part of tuition or learning and research, the the Department of Chemistry at the University of South Africa (UNISA) needed to blend these components to enhance and strengthen the requisite graduate attributes. The authors discuss the strategies employed by the department on how to inculcate these graduate attributes into modern-day chemistry students within an open distance learning (ODL) context.