Chemistry

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2, 4, 6-Tris (N-Salicylidenehydrazino) S-Triazine and its Copper (II) Complex-Synthesis, Characterization and Antimicrobial Screening
(Addis Ababa Universty, 2008-07) Haile Kiros; Raju V.J.T. (Professor)
A new tripodal ligand 2, 4, 6-Tris (N-Salicylidenehydrazino)-s-Triazine (L) was synthesized by the condensation of salicylaldehyde with 2, 4, 6-tris-(hydrazine)- s-triazine(THSTZ) in acetonitrile. Copper complex of the ligand was synthesized in chloroform-methanol 50% v/v medium. The ligand and the metal complex were characterized by employing spectral (IR,Uv-Vis,AAS, NMR), conductance and magnetic susceptibility studies. The purities of the compounds were established by TLC. The studies support formation of stable metal complex corresponding to the formulae: [Cu(II)LH2O] .4H2O. Conductivity measurement indicates that the complex is a non-electrolyte. Spectral and Magnetic data suggest dibasic ONN donor behavior of the ligand towards Cu(II). Square planar geometry for Cu2+ complex has been proposed. The ligand, metal complex and related compounds were screened for antimicrobial activities against Escherichia coli, Pseudomonas eruginosa, Staphylococcus aureus and Bacillus cereus bacteria by employing tetracycline as test control agent. The result showed that both the ligand and the metal complexes were inactive, while the ligand precursor (THSTZ) and the metal salt (CuCl2.2H2O) were active. As such derivatization and the complexation can help in detoxication purposes. Key words: 2, 4, 6-Tris (N-Salicylidenehydrazino)-s-Triazine (L), tripodal ONN donor, Cu2+ complex, Square planar geometry, antimicrobial.
9,9-Disubstituted Fluorene-Based Polymers: Preparation and Characterization
(Addis Ababa Universty, 2009-07) Hussen, Ayalew; Mammo, Wendimagegn (Professor)
A family of conjugated polymers based on 9,9-disubstituted fluorenes and cyanovinylenes were reported. The polymers were synthesized by employing a slightly modified Suzuki coupling polymerization reaction and condensation polymerization utilizing the Knoevenagel reaction. The resulting polymers showed good solubility in chloroform. The energetic positions of the band edges were determined by cyclic voltammetry. The synthesized polymers were characterized by using spectroscopic techniques such as UV-Vis and 1H- NMR. The presented polymers exhibited emission of blue to red colors.
A Computational Investigation of Hydrated Magnesium Sulfate Clusters and their FAU Composites for Improved Thermochemical Energy Storage
(Addis Ababa University, 2024-06) Belaynew Teshome; Getachew Gizaw; Ahmed Mustefa
The effective use of renewable energy sources and the decrease of greenhouse gas emissions are greatly dependent on thermal energy storage, or TES. We report a computational method for examining the hydrate clusters of hydrated magnesium sulfate (MgSO4) and their compounds with faujasite zeolite (FAU) for enhanced performance in thermoelectric sensing (TES). The optimal hydration states and structural characteristics of the hydrated MgSO4 clusters were revealed through modeling with density functional theory (DFT) calculations. Molecular dynamics techniques were used for optimization of composite structure implemented by Vienna Ab initio Simulation Package (VASP) software. After this, the TES capacity, reversibility, and thermal conductivity of the MgSO4 hydrate-FAU composites were assessed. As a result of their superior heat storage properties over their constituent parts, composite materials are a strong contender for advanced thermal energy storage applications, according to the research. This method of computational research gives a logical way to create high-performance thermoelectric solar materials while also shedding light on the interactions at the molecular level.
Advanced Electrochemical Sensors for the Determination of Selected Antibiotic Drug Residues in Food and Water Samples
(Addis Ababa University, 2024-06) Wondimeneh Dubale; Merid Tessema; B. S. Chandravanshi
The presence of antibiotic drug residues in food and water sources poses a critical challenge to the public health and environmental sustainability. Addressing this challenge requires the development of highly sensitive and selective detection methods capable of accurately quantifying trace levels of the residues in complex sample matrices. The aim of this study was to contribute to this vital area of research by focusing on the designing, fabrication, characterization, and application of advanced electrochemical sensors for the detection of antibiotic residues in various matrices. In this study, eight cutting-edge electrochemical sensors were developed, characterized, and successfully applied for the individual and simultaneous determination of selected antibiotic drug residues in food and water samples. Through thorough experimentation and optimization, novel electrochemical sensor architectures have been developed using innovative materials, including gold-silver alloy nanocoral clusters (Au-Ag-ANCCs), thermally annealed gold–silver alloy nanoporous matrices (TA-Au-Ag-ANpM), iron-doped polyaniline (Fe-dop-PANI), nickel oxide nanoparticles (NiO-NPs), zinc oxide nanoparticles (ZnO-NPs), functionalized multi-walled carbon nanotubes (f-MWCNTs), reduced graphene oxide (r-GO), poly(L-histidine), poly(L-serine), poly(glycine), polyethylene oxide (PEO), and choline chloride (ChCl), to improve sensitivity, selectivity, and stability. The surface morphology, elemental composition, and electrochemical properties of the developed sensors were characterized using an array of analytical techniques, including UV–Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction spectroscopy (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Among the developed sensors, ChCl/CPE was designed for the determination of ciprofloxacin (CPRO) in eye drops, river water, and egg samples. It exhibited outstanding performance with a wide linear range (0.005–200 μM), and impressive detection and quantification limits of 0.36 nM and 1.2 nM, respectively. ChCl/GCE was prepared for the simultaneous determination of tinidazole (TIN) and chloramphenicol (CAP) in egg, honey, and milk samples. It showed exceptional detection capability with a wide linear range of 0.010–170 μM and 0.005–300 μM for TIN and CAP, respectively. The limit of detection (LOD) and limit of quantification (LOQ) were 0.90 nM and 3.0 nM for TIN, and 0.27 nM and 0.89 nM for CAP, respectively. TA-Au-Ag-ANpM/r-GO/poly(glycine)/GCE was developed for the detection of life-threatening residues of metronidazole (MTZ) in milk powder, pork, and chicken meat samples. It performed exceptionally in the detection of MTZ with a wide linear range from 2.0 pM to 410 μM. The LOD and LOQ were determined to be 0.0312 pM and 0.104 pM, respectively. Au-Ag-ANCCs/r-GO/poly(L-histidine)/GCE was used for the simultaneous determination of vancomycin (VAN) and ceftriaxone (CFT) residues in chicken meat, fish, and milk samples. The sensor demonstrated outstanding performance in the determination of the analytes over a wide dynamic range, from 1.0 pM to 120 μM for VAN and from 1.0 pM to 290 μM for CFT. The LOD and LOQ values were determined to be 0.11 pM and 0.36 pM for VAN and 0.017 pM and 0.057 pM for CFT, respectively. TA-Au-Ag-ANpM/f-MWCNTs-CPE/poly(L-serine) was prepared for the simultaneous detection of sulfathiazole (SFT) and sulfamethoxazole (SFM) residues in honey, beef, and egg samples. It showed exceptional performance in a wide linear range (4.0 pM to 490 μM for SFT and 4.0 pM to 520 μM for SFM), with picomolar detection and quantification limits (0.53 pM and 1.75 pM for SFT, 0.41 pM and 1.35 pM for SFM). Au-Ag-ANCCs/f-MWCNTs-CPE/ChCl was developed for the simultaneous determination of rifampicin (RAMP) and norfloxacin (NFX) residues in water samples. It exhibited outstanding performance in a broad linear range, from 14 pM to 115 μM for RAMP and from 0.9 nM to 200 μM for NFX, with LOD and LOQ values of 2.7 pM and 8.85 pM for RAMP and 0.14 nM and 0.47 nM for NFX, respectively. Au-Ag-ANCCs/ZnO-NPs-CPE/PEO was prepared for the simultaneous detection of nitrofurantoin (NFT) and furazolidone (FZD) in poultry, fish, honey, dairy products, and municipal wastewater samples. The sensor demonstrated exceptional performance over a wide linear range, from 1.0 pM to 250 μM for NFT and 0.9 nM to 360 μM for FZD. The LOD and LOQ were found to be 0.26 pM and 0.88 pM for NFT and 0.023 pM and 0.076 pM for FZD, respectively. Finally, TA-Au-Ag-ANpM/Fe-dop-PANI/NiONPs/GCE was developed for simultaneously determining azithromycin (AZM) and enrofloxacin (ENF) residues in food and water samples. The sensor exhibited exceptional performance in a broad dynamic range from 0.8 pM to 250 μM for AZM and 0.1 pM to 550 μM for ENF, with LOD and LOQ values of 0.053 pM and 0.18 pM for AZM and 0.013 pM and 0.042 pM for ENF, respectively. In order to maximize the efficiency of the proposed sensors, an extensive optimization of various experimental parameters was performed. The optimization process included the selection of the appropriate supporting electrolytes, choice of the pH of the electrolyte solutions, determination of the number of electropolymerization cycles, optimization of the mixing ratio of the nanocomposites, adjustment of the volume of the drop-casting species, and selection of the square wave voltammetry (SWV) parameters, such as amplitude, frequency, and step potential, as well as other instrumental parameters. Under these optimized experimental conditions, the developed sensors exhibited remarkable selectivity and effectively discriminated between the target analytes and interferents present in complex sample matrices. In addition, the developed sensors exhibited exceptional reproducibility, repeatability, and long-term stability. Subsequently, the developed sensors were validated using real food and water samples that were suspected to contain antimicrobial drug residues. The results revealed impressive recoveries ranging from 95.6 to 103%, with relative standard deviations below 5%. In general, the results presented in this paper represent a significant advance in the field of electrochemical sensor technology, particularly in the vital area of identifying antibiotic residues in food and water samples. The introduction of these state-of-the-art sensors heralds a new era characterized by increased sensitivity, selectivity, and reliability. This advancement will change the landscape of monitoring, regulating, and controlling antibiotic residues in food chains and water sources. Beyond enriching scientific knowledge, this breakthrough offers tangible benefits for public health and environmental sustainability, and embodies the laudable pursuit of advancing knowledge for the benefit of society.
Alkaloids and Flavonoids of Erithrina Melanacantha
(Addis Ababa Universty, 1994-06) Abebe Abrham; Dagne Ermias
The tropical genus Erythril1a, which belongs to the family Leguminosae (sub-family Papilionoideae), locally known as "Korch" (Amharic) and "Wolensu" (Oromo) has folk medicinal uses such as in the treatment of stomach pain and female infertility. The seeds of this plant have been investigated before, whereas no previous phytochemical work has been reported from the stem bark of E. melanacantha. The isolation and characterization of alkaloids and flavonoids from the seeds and stem bark, respectively, of this species constitute the subject of this study. As a result, the seeds and stem bark of E. melanacantha afforded eleven compounds, of which two are new natural prodUCts. From the seeds three known alkaloids, namely, erythraline (11), erymelanthine (50) and erysovine (3) have been identified. Chemical investigation of the stem bark resulted in the isolation of two new compounds characterized on the basis of spectroscopic data as 5-hydroxy-7 ,8-(hydroxyisopropyl dihydrofurano)flavanone (152) and a biflavanone (159). In addition, from the stem bark of this plant, five known flavonoids, namely, glabranin (153), obovatin (155), 7-hydroxy-8-prenylflavanone (156) 3'-0- methylorobol (157), 3'-methoxydaidzein (158) and a known cinnamate ester, erythrinasinate (160) have been isolated. Search in the chemical literature indicated that compounds 153, 155, 156 and 158 have not been reported before from the genus Erythril1a. Glabranin (153) is proposed as the biosynthetic precursor of the three compounds 152, 155 and 156, while compounds 152 and 153 serve as building blocks of the dimer 159.
Amperometric Determination of Potassium and of Urease Activity in Plant Materials
(Addis Ababa Universty, 1997-06) Esubalew, Siraye; Hundhammer, Bemd (PhD)
Determination of potassium and urease activity of locally found plant seeds have been made. The membrane-stabilized water-nitrobenzene interface was used as an al11pcrometric sensor. The electroanalytical teclmiques employed were cyclic voItammetry, ac-voltanullelly and clu·onoamperomelly. The sensor was calibrated by the standard addition method. The detection of 0.025 mmol 1" of potassium ion as well as ammonium ion was possible. Since the sodium ion content of the seed powders investigated was extremely low, no interference of sodium ion was observed. Several plant seeds have been screened for urease activity. The transfer of anullonium ion produced by enzymatic hydrolysis of urea was followed by the sensor. Three new sources of enzyme urease have been found, namely, Kil (lagena/'ia siceraria), Berbera (iv!illitiafemiginea), and Gibto (lupinus a/bus).
Amperometric Sensor Based on MnO2 Film Modified Carbon Paste Electrode Coupled with Glucose Oxidase Immobilized Reactor for the Determination
(Addis Ababa,University, 1998-06) G/ Medhin, Kahsay; Alemu, Hailemichael (PhD)
An arnperometric system based on a carbon paste electrode modiri ed with Mn02 was in vestigated as a sensor for glucose in flow-injec tion analysis ( FIA). Enzymatic ox idation of glucose and catal yt ic ox idation of the intermcdiate (1-1 20 2) by MnQ is exploited for the u1l1perollletric monitoring of glucose. at an operating potential of + 0.59 V vs. Ag/Agci.
Anaiysis of Testicular Growth Factors by Quantitative Polymerase Chain Reaction
(Addis Ababa Universty, 1996-02) Ayele, Dereje; Worku, Yisehak (PhD)
Expression of testicular Interleukin-l a was anaIysed both at the lavel of biological active peptide and its encoding mRNA, using a sensitive bioassay, Thymocyte proliferation assay, and Polymerase Chain Reaction. In order to analyse the relative change in the level of IL -1 a mRNA expression a Quantitative PCR technique was developed involving an intemal standard IL -1 a RNA construct derived from rat macrophage IL -1 a cDNA preparation. The IL -1 a mRNA expression during postnatal rat development could be detected by PCR as early as 20 days, postnatal, and The intensity of amplified cDNA band was found to increase with increasing days of postnatal age. By using Quantitative PCR, a relative increase in the level of amplified IL-lacDNA could be demonstrated starting from day 20, and this increase in the level of amplified cDNA is found to reach a sustained high level from 30 to 60 postnatal days of rat testicular development. This study shows that the level of IL -1 a mRNA rises in parallel to the level of IL -1 a peptide during maturity, previously demonstrated, and suggests that it is controlled at the level of mRNA expression, probably attranscriptionalleve/. The role of testosterone in the regulation of tiL -1 a was analysed using rats treated with, EDS with and without testosterone replacement, and androgen receptor blocker, cyproterone acetate. The result showed that EDS pretreatment resulted in an increase in the level of both IL -1 a bioactivity and the level of its mRNA. Exogenous testosterone replacement along with EDS treatment significantly reduced the effect of EDS treatment on the expression of tiL-I a peptide and mRNA. Cyproterone acetate treatment in contrast resulted in a decrease in the IL -1 a mRNA levels. This study shows that tiL -1 a expression is developmentally regulated at the level of its mRNA expression. It also suggests that testosterone regulates testicular IL -1 a expression at the level of transcription. This finding further strengthens the importance of testicular IL -1 a as a paracrine growth factor in the regulation of testicular development and function.
Analyical Application of Ion Transfer Across the Memembrane Stabilized Interface Between Two Immiscible Electrolyte Solutions in a Flow Injection System
(Addis Ababa Universty, 1990-06) Abegaz, Mulat; Solomon, Theodros (PhD)
Using the voltammetric senor which is constracted in our laboratory and the membrane stabilized interface between two immiscible electrolyte solution in a flow injection system the transfer of anions (CIO ,NO & 01 land catiol's 4 '3 + + (i( Na lfrom the aqueous to the organic phase have been investiJ'(ated.ln order to determine the Horking potential region of the system the behaviour of the potential-current dependence of the support inA electrolytes Here studied. The iR drop resulting fron the dilution effect of tl,e distilled Ivate'!, at the interface has been investigated and it Has compensated by increasing 1;he concentration of the supporting electrolyte in t,he aqueous phase . Dependence of the peak current on the applied concentration of various ions (ClO , 4 been investigat,ed. The det,ermination potentials _. + + NO , K & Na 3 of K+ and Na+ in the presence of dibenzo-18-croHn-6 in the and on have Has made organic + phase. The method "as applyed to t),e determination of Na and + K in blood serum samples Hnd the values obtained \Vere in good agreement Iii th the values obtained by flame photometric method. The selectivity of the method Has also studied and lias found to be potential dependent and governed bv the partial sensitivity of the individual ion. A method has also been proposed for the deternd ngtion of a particu} ar ion in the presence of another ion. The detection limit of the detector has heen determined to be about 0.25 µM for perchlorate ion. Thus the method is rapid, precise, sensitive for the determination of some anions and cations.
Analyses of the Essential Oils of Artemisl Rehan and Cymbopogon Citratus
(Addis Ababa Universty, 1980-06) G.Yohannes Paulos; Abegaz Berhanu (PhD)
Artemisia rehan Chiov and Cyifopogon citratus (DC) Stapf are widely grown in thelighlands of Ethiopia. These plants occupy a significant|sition in Ethiopian I plantlore. | The oil of Artemisia rehan, anendemic plant to Ethiopia , has been analysed for the first time.' Eighteen components of the oil have Wen identified using GLC and/or MS. Two compounds, chamaiulene and dsvanone were isolated from the oil and characterized using ir , nmr and ms• Davanone (44/) and Camphor (27/) were found to be the major constituents of the oil. Cymbopogon citratus which is also widely grown in the tropics , is used as a. crop plant in many countries of the Western Hemisphere.' The oil of the Ethiopian variety was analysed for the first time. Fifteen - components of the oil have been identified using GLC and/or MS. The major component identified was geraniol (39D * The second major component (12/), not identified , is presumed to be an aromatic compound
Analysis and Determination of Acrylamide in Roasted Potato Chips (Potato Crisps) from Different Potato Chips Selling Centers In Addis Ababa
(Addis Ababa University, 2018-06-05) Yihune, Getasew; Ele, Estifanos (PhD)
Acrylamide or 2-propene amide is an organic compound formed in French fries, potato crisps, bread and coffee when they are fried, roasted or baked at a higher temperature. It is formed from the reaction of reducing sugars such as glucose and fructose with amino acids (asparagine). Many animal studies have shown that acrylamide is a carcinogenic, neurotoxic and genotoxic compound. In this study, GCMS instrument was used to analyze the presence and amount of acrylamide in roasted potato chips. The GCMS method to analyze acrylamide requires bromination type of derivatization to minimize interferences. Roasted potato chips samples were collected from Kebena, Arat kilo, Amist kilo, and Sidist kilo in Addis Ababa in 2018. From each sites light yellow color roasted potato chips (SFOPC) prepared from fresh palm oil and dark brown color roasted potato chips (SBOPC) prepared from the mixture of fresh and reused palm oil were collected. In all samples of roasted potato chips significant amount of acrylamide was investigated by using GCMS. The amount of acrylamide extracted from dark brown color potato chips (SBOPC) prepared from the mixture of fresh and reused palm oil is much higher than light yellow color potato chips (SFOPC) prepared from fresh palm oil. The highest amount was detected in samples collected from Kebena S5FOPC (light yellow potato chips) 10005μg/kg and S5BOPC (dark brown potato chips) 13933μg/kg while the lowest amount was detected in samples collected from Arat kilo S4FOPC (light yellow potato chips) 2511μg/kg and S4BOPC (dark brown potato chips) 7453μg/kg, respectively. Generally, to investigate the presence of acrylamide in roasted potato chips in this study samples were collected, grounded, extracted, purified by Solid phase extraction (SPE), brominated and 1 μL sample solution of 2-bromopropene amide (2-BPA) were injected and analyzed by GCMS.
Analysis of the Essential oils of Tagetes minuta and Artemisia rehan
(Addis Ababa Universty, 1995-06) Mulugeta Afework; Dagne Ermias (PhD)
The chemical compositions of the essential oils of the leaves and flowers of Tagetes minuta L. were determined by chromatographic and spectroscopic methods. The characteristic components of the essential oils produced from the leaves of T. minuta 'were found to contain (Z)-Ocimenone (41%) and (E)Ocimenone (18%) as the major components, while the oils from the flowers of T. minuta contained cis-p-ocimene (46%), (Z)-and (E)-Ocimenones (22% and 10%, respectively). The volatile oil constituents of the aerial parts of Artemisia rehan plants purchased at different times were investigated using gas chromatographic and spectroscopic techniques. Differences in the camphor (5%, 30%, 31%), chamazulene (7.6%, 1.9%, 1%) composition and yield (0.3%, 0.4%, 0.8%) of these oils was observed. Such differences in the essential oil composition and yield may be ascribed to the existence of different A. rehan chemotypes, seasonal variation or difference in stages of development of the plant material
Analytical Application of the Membrane-Stabilized, Enzyme-Modified Interface Between two Immiscible Electrolyte Solutions
(Addis Ababa Universty, 1995-06) Bekele, Tesfaye; Hundhammer, B.(PhD)
An amperometric urea biosensor based on facilitated transfer of urease-generated ammonium ion by a neutral carrier (ionophore) dibenzo-18-crown-6 across the polarizable membrane-stabilized interface between water and nitrobenzene is described and discussed. The enzyme urease employed for the investigation was immobilized on the sensor surface by physical entrapment as a gel between dialysis membranes. The current response of the anlperometric sensor was found to be directly proportional to the concentration of urea in the sample solution. In addition, correction for residual current due to interfering (residual) substances is relatively easy. The sensor gave a linear response to urea in the concentration range 5 x 10" to 5 x 10.3 M. The response time of the sensor was I min. The sensitivity appeared to be dependent on the conditions of immobilization of the enzyme. The effect of the thickness of the enzyme layer on the sensor response has been discussed. The life time of the sensor was more than 3 weeks when stored in the buffer solution at room temperature
Analytical Method Development for the Compositional Investigation of Khat (Catha Edulis Forsk) Leaves With Respect to its Active Constituents, Selected Secondary Metabolites and Inorganic Nutrients
(Addis Ababa University, 2013-01-01) Atlabachew Minaleshewa; Chandravanshi B.S. (Professor); Redi Mesfin (PhD)
The rapid growth of khat use and misuse in the countries of its origin and other parts of the world has led to the development of methods for extraction, clean-up, detection and quantification of its psychoactive alkaloids and other nutrients. However, the extraction and clean-up methods reported so far have a number of drawbacks and there is paucity of quality data with regard to the concentrations of its psychoactive alkaloids, phenolic compounds and mineral nutrients of Ethiopian khat accessions. Thus, this study addressed some of the challenges facing researchers in the area, such as the need to use easily accessible, simple, fast and plausible sample preparation techniques for khat alkaloids and tannins analysis. Furthermore, total polyphenols, selected essential and non-essential elements and fluoride accumulation in various khat cultivars were also investigated. Matrix solid phase dispersion (MSPD), molecularly imprinted polymer for solid phase extraction (MIP-SPE) and the modified quick, easy, cheap, effective, rugged and safe (QuEChERS) based methods were investigated for extraction and clean-up of khat alkaloids prior to HPLC-DAD detection. Under optimum conditions, good recoveries, selectivity and reproducibility were obtained. There was an assertion that drying khat leaves could significantly (if not completely) decompose cathinone to cathine. However, this study demonstrated that cathinone was persistently existed in dried plant material and it is wrong to assume that sun or oven drying the leaves could completely convert cathinone to cathine. This study also presents the quantitative determination of total phenolic compounds, flavonoids, tannins and their related in-vitro antioxidant activities of the young leaves, matured leaves and tips of tender stem near the young shoots. Simplified, rapid and robust method was also developed for the analysis of total tannins using egg albumin as a precipitating agent and Folin Denis reagent and FeCl3 solution for color developing moieties for spectrophotometric assay. In addition, the concentrations of selected major, minor and toxic metals as well as fluoride distribution in various khat cultivars and the corresponding soil samples were investigated by flame atomic absorption spectrometry and fluoride ion-selective electrode potentiometry, respectively. It was noticed that khat leaves could be a good sources of most of essential mineral nutrients and free from toxic metals like Pb and Cd. Analysis of fluoride in the edible portion of the khat leaves resolved the equivocal information about khat chewing and dental staining due to fluoride. It was found that the plant accumulated significantly lower concentrations of fluoride compared with similar stimulant plants.
Analytical Sample Preparation Methods Based on Miniaturized Extraction for Trace Level Enrichment of Selected Pesticide Residues from Environmental Water and Food Samples Utilizing High Performance Liquid Chromatographic Analysis
(Addis Ababa University, 2023-11) Habtamu Bekele; Negussie Megersa
The development and implementation of more environmentally friendly and sustainable microextraction techniques in recent years has provided alternative to traditional sample preparation approaches. In this thesis, we developed, optimized and validated different micro extraction methods for trace level multi residue and multiclass trace level pesticides from environmental water and food samples prior to their determination using chromatographic techniques. Salt assisted graphene oxide (GO) was utilized as a sorbent in dispersive solid phase extraction (DSPE), to enhance and extract certain s-triazine herbicides from environmental water samples. GO can generate scattered colloids in the aqueous phase and offers an extensive variety of functional groups for hydrogen bonding or electrostatic interaction with benzene ring organic compounds with functional groups comprising oxygen and nitrogen. GO was synthesized by modified Hummers method and characterized with Fourier transform infrared (FT-IR) spectroscopy. As complete collection of GO after adsorption process is difficult task, in this established salt-assisted (SA)-GO-DSPE method, it was found to be aggregated and centrifuged in the presence of NaCl. The optimum value for main parameters that influenced extraction efficiency were investigated. Under the optimized conditions, low limits of detection (LODs) (0.12–0.80 ng mL−1), limits of quantification (LOQ) (0.4–2.68 ng mL-1), and good extraction recoveries (69.06–95.53%) were obtained for simultaneous extraction of simazine, atrazine, propazine and prometryn. The relative standard deviations (RSD) of intra-day (n = 6) and inter-day (n = 9) precisions were 2.54 to 5.84% and 4.38 to 8.56%, respectively. When the method's applicability was ultimately assessed, the target analytes in the real water samples weren't detected. The proposed method is environment friendly and promising for trace analysis of other pesticides including the target herbicides in environmental water samples. Dispersive liquid–liquid microextraction based on surface floating organic droplet was designed to enable development of simple, fast, and environmentally friendly analytical technique utilizing for selective and quantitative enrichment of trace level pesticide contaminants from different fruit juice samples for subsequent detection by high pressure liquid chromatography–diode array detection (HPLC–DAD). The optimized method was investigated using spiked blank sample, and results of linearity at concentration levels from 3 to 1500 ng mL-1, with correlation coefficients (r2) ≥ 0.998 were obtained. LOD and LOQ were ranged from 1.3×10−2 to 5.3×10−2 μg L−1 and 4.2×10−2 to 1.8×10−1 μg L−1, respectively. Satisfactory accuracy, i.e, recoveries ranging from 87.23 to 99.45%, with %RSD between 1.37 and 8.39, and precision in terms of %RSD ≤ 10.78 were investigated. At the end, the method was successfully applied to analyze real fruit juice samples and target analytes were not detected in real samples. A simple, selective and fast salting out assisted liquid–liquid extraction (SALLE) technique coupled with HPLC–DAD was developed and optimized for extraction, and analysis of seven multiclass pesticide residues in pasteurized and raw cow milk samples. Under optimum conditions, for broad linear range concentration of 2–1500 μg L-1, r2 was within a range of 0.9982–0.9997. Reliable sensitivity was achieved with LODs and LOQs ranging from 0.58–2.56 ng mL-1 and 1.95–8.51 ng mL-1, respectively. While precision with intra-day and inter-day in terms of RSDs were observed in the range of 1.97–7.88% and 4.52–8.13%, respectively. The results of the precision studies reveal that good repeatability and reproducibility (RSDs < 9%) were achieved. Finally, the validated approach was effectively used to extract and determine pesticide residues in real milk matrices, however the target analytes were not detected in all samples. High density dispersive liquid–liquid microextraction method coupled HPLC-DAD was developed for extraction, enrichment and determination of six sulfonylurea herbicides; namely, metsulfuron-methyl, chlorosulfuron, niclosulfuron, prosulfuron, flazasulfuron and chlorimuron-ethyl in matrices of environmental waters. The optimum experimental parameters that influenced extraction efficiency were investigated. Under the optimized conditions, wide linear calibration curves with r2 > 0.997, LODs in the range of 0.8–1.5 ng mL−1, and LOQ in the range of 1.9–5.1 ng mL−1 were obtained. The precisions in terms of % RSDs of intra-day (n = 6) and inter-day (n = 9) were found to be 3.01 to 8.36 and 2.92 to 9.78, respectively. Applicability of the developed method was investigated by analyzing spiked tap, lake, river and underground water samples and satisfactory recoveries were obtained in the range of 84.3–101.7% with RSDs < 9.8% (n=6) and the target analytes were not detected in real samples.
Anthranoids of Some Kniphofia Species from Ethiopia
(Addis Ababa Universty, 1984-06) Berhanu, Esaiyas; Dngne, Ermias (PhD)
There are of least six reported s in Ethiopiil of a total of 65 species of Kniphofia in the world all of Vlhich are restricted to tropical Jifrica andYemen. Rniphofia foliosa (family Liliaceee) known in J\mharic as ilshenda or Shemetmete is used in Ethiopian traditional medicine for the treatment of abdominal cramps. Hecent eXilmination· of tl1e :vhizomes of this species l\)T our research group resulted in the isolation und chnructerization of chrysophanol and the llew anthranoid·k nipholone. Chloroform soluble fractions of the leaves of K. foliosa afforded a new anthracene derivative, aloeerJodin monoaceta-t;e, in midi tion to k.lipholone and chrysophanol. The structure of this net'7 compound was determined by spectral analysis of the natural product and its derivatives. The leaves, flowers and rhizomes of!li' folios a all contain knipholone as the major anthranoid with trelCe amounts of chrysophanol. Aloe-eModin -acetate is localized only in the leaves while the pigments desic;nated as Kf und K f are found 7 8 only in the rhizomes. l!'rom the acetone extract of the rhizomes of K. isoetifoli8 Of two pic;pwntH Kf and Kf were iso- 7 8 lated. The sodium dithionite reductive cleavage of Kf as well as a mixture of Kf and Kf c;ave chryso- 8 7 8 phanol and islBndicin as fruc;ments, a contribution tOl'lnrds tile final structural elucidation of these as yet unknown pigments. On further investigntion islnndicin Vias isolated for the first time from the rhizomes of ~. foliosa, K. isoetifolia Of and from the lenves of K. folios a and this finding probably constitutes the first detection of islandicin in higher plants as it was earlier reported only in func;i particularly in Penici- Ilium islandicum.
Anthraquinones and Fla Vonolds from the Pods of S. Didymobotrya
(Addis Ababa Universty, 1995-06) Hailu Ayele; Abegaz Berhanu (PhD)
Two hitherto unknown dimeric anthraquinones, lO-(Physcion-Tyl)-lO-hydroxy chrysophanol anthrone (122) and 9-(Physcion-T -yI)5, lO-dihdroxy-2-methyl-l,4- anthraquinone (124) along with chrysophanol (120), physcion (121), emodin (125) and knipholone (126) were isolated from the chloroform extract of the pods of Senna didymobotrya. Knipholone (126) is isolated from the genus Senna for the first time. The methanol extract of the pods yielded three flavonoids, kaempferoI4'-methyl ether (127), acacetin (129) and 3,5,6,7,8,3' ,4'-heptahydroxy flavone (130). Their presence in the genus Senna is reported for the first time. Structural elucidations were carried by chemical and spectroscopic methods.
Antifungal Natural Products Against two Plant Diseases: Root Rot/Wilt of Faba Bean and Late Blight of Potato
(Addis Ababa University, 2018-08-04) Gashu Minbale; Dagne Ermias (Professor); Alemu Melaku (PhD)
In Ethiopiafaba bean and potato are two important crops for food security and nutrition. Root rot/wilt is a notorious fungal disease of faba bean caused by Fusarium spp., while late blight is a potato disease due to attack by the fungus Phytophtra infestans. These two diseases cause from time to time severe crop losses. Hence it is important to control growth and spread of these fungal diseases.It is well known that although the use of synthetic fungicides contributes to enhance crop yield, toxic residues in treated crops cause environmental and health problems. Therefore, the search for eco-friendly plant-based antifungal agents is a worthwhile strategy. In this work, thetwo pathogenic fungi were isolated from diseased parts of crops, identified and maintained with periodic sub-culturing in Potato Dextrose Agar.In this studyfifty seven ethanol extracts of different plants were screened for their antifungal activity using optimized food poisoning technique. Dimethylsulfoxide (5% aq) and 0.5% Mancolaxyl were used as vehicle and standard, respectively. The standard fungicide showed respective growth inhibition percentage (%GI) of 68 and 88 against F. spp.and P. infestans at a concentration of 5 mg/mL. Bioactivity of screened plant extractswas classified into high, moderate and inactive by taking the minimum %GI of the standard (68%) as reference. Of these extracts, Inula confertiflora (69/78%), Echinops kebericho(73/80%) and Artemisia annua(71/73%) showed higher %GI in the control of F. spp./ P. infestans, respectively. The nonpolar portions were found comparable with that of the reference in inhibiting mycelial growth of tested fungi relative to their polar counterparts. The active compounds were isolated and characterized. In the bioassay study dehydrocostus lactone, carabrone, graveolide, carpesiolin and artemisinin demonstrated significant inhibition on the growth of tested fungi.
Antifungal Substances from Essential Oils
(Addis Ababa Universty, 2011-07) Lakew Shewaye; Dagne Ermias (PhD)
In vitro study of the antifungal activity of essential oils, plant extracts with MeOH : CHCl3, pure compounds and, condensed smoke extracts were conducted using agar disc diffusion method. Out of these 14 showed strong, 13 medium and 23 showed no activities to the fungal pathogen of Aspergillus niger. The essential oil of Origanum vulgare (oregano), Thymus schimperi (Tosign), Cymbopogon nardus (Citronella), Cymbopogon citratus (Lemongrass), Trachyspermum ammi (Nech azmud) and Eucalyptus citriodora showed strong inhibition zones compared to the essential oils and extracts. The GC and GC/MS analysis of essential oils revealed that O. vulgare contained thymol (56%) and carvacrol (43.5%), T. schimperi contained thymol (56.5%), linalool (18.5%), and carvacrol (8.9%) and T. ammi contained γ-terpinene (42%), thymol (26.2%), p-cymene (26.8%), and β-pinene (2.8%)
Application of an Official Spectrophotometric Method for Nitrite Determination in Tap and River Water Samples
(Addis Ababa Universty, 2008-12) Teklu, Eskinder; Tessema, Merid (PhD)
An internationally known test method for nitrite was applied to determine the anion in tap and river water samples. The method is based on the reaction of nitrite with sulphanilamide in acidic medium to form diazonium ion, which is then coupled with N-(1-napthyl)- ethylendiamine dihydrochloride to form an azo dye, showing absorption maximum at 540 nm. The method obeys Beer’s law in the concentration range 0.25 -1.5 μgmL-1of nitrite. The optimum reaction conditions and other analytical parameters were evaluated. The method was successfully applied to the determination of nitrite in tap water and river water samples.

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