Dr. Mohammed Zaitoun
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Zaitoun@mutah.edu.jo |
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Office Phone |
3089 |
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Academic Rank |
Associate Professor |
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Faculty |
Science |
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Department |
Chemistry |
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Research of Interests |
Luminescence of rare earth complexes Chemical and biosensors Spectrophotometry |
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Abstract:
The Lanthanide complexes Eu-2.2.1 and Eu-2.2.2 were synthesized and then incorporated into silica based transparent organic–inorganic hybrid material by the sol–gel method as an example of how doped xerogel materials are emerging as an important means of producing new materials. The produced gels were diagnosed to monitor emission spectra of the luminescent trivalent europium (Eu3+) complexes; emissions were compared to those for gels containing uncomplexed Eu3+. Results of the experiments (emission and lifetimes) concerning the coordination sphere composition showed that a cryptand ligand with aromatic groups (short range effect) and the hydrophobic gel host (long range effect) settle efficient action in the antenna effect and isolate the central ion from efficient quenchers, as e.g. water molecules. Each ligand imposed a distinct splitting pattern on the europium emission bands that helps identify them.
Publication Date: 2008 On Pages: 227-231
Location : Journal of Luminescence ISSN: 0022-2313
Publisher: Elsevier
Abstract: In comparing emissions of the inorganic Eu3+ salts (chloride or nitrate) to organoeuropium complexes doped into optically transparent sol-gel glass, previous studies have indicated that changes in the local chemical environment by chelation or variation of the ligand or gel matrix compositions were found to leave the main spectral features of Eu3+ essentially unchanged; complexation just increases the emission intensity of europium and leads to broadening and splitting of the peaks. In all cases studied and irrespective of the excitation energy, the observable emission peaks result only from relaxations out of the 5D0 excited state of Eu3+ to the first five levels of the 7F ground manifold. The present research examines the luminescence behavior of EuCl3 and Eu-TETA (TETA is the macro cycle, 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraaceticacid) doped into a sol-gel host; in addition to emissions from the 5D0, emission from the 5D1 excited state of Eu3+ is observed for the first time. Publication Date: 2006 On Pages: 418-422
Location : Applied Spectroscopy
ISSN 0003-7028, Online ISSN: 0003-7028
Volume 60, Issue 4
Publisher:Society for Applied Spectroscopy
Abstract:
A kinetic-spectrophotometric method is proposed to determine glucose in solutions. Measurements were performed at 400 nm; the negative peak was obtained by subtracting the absorption spectra of myoglobin (Mb) before and after oxidation. In this method, glucose is added to a mixture of Mb and glucose oxidase. Glucose is oxidized by glucose oxidase and oxygen to gluconate and hydrogen peroxide is generated. The liberated hydrogen peroxide oxidizes the Mb heme (Fe2+) into Fe3+. The higher the glucose concentration added, the more the H2O2 generation, and the more the Mb oxidation (Fe2+ to Fe3+) and, as a result, the higher the absorbance at 400 nm (negative peak, lower absorbance value). The increments of added glucose are monitored by measuring the absorbance decay versus time (0-250 s) at 400 nm. Each glucose concentration has an accompanying unique absorbance value at 250 s. The higher the glucose concentrations, the lower the absorbance at 250 s (measured at 400 nm). The calibration curve for glucose was linear from 0.1 to 3.0 mM; the detection limit was found to be 0.025 mM. There was no interference from major substances present; the only interference was from species that react with H2O2 (ascorbic acid, uric acid, and urea) or that react with glucose (Cu2+ and Fe3+). Standard deviation in the determination was ±0.01 mM for a 1.3 mM glucose solution (n = 10). Publication Date: 2006 On Pages: 1010-1014
Location: Journal of Analytical Chemistry
ISSN: 1061-9348 (print version) ISSN: 1608-3199 (electronic version)
Volume 61, number10
Publisher: MAIK Nauka/Interperiodica
Abstract: Previous studies indicated that the organization of native porphyrins and their intentionally designated derivatives in solid substrates is of current interest because of the biological and practical importance of these compounds. In this paper, we report herein for the first time the incorporation of a functionalized diacid, protoporphyrin IX Zn(II) (Zn-pp-IX), successfully in a silica based transparent organic-inorganic hybrid material by choosing proper alkoxy silane containing amino-group via the sol–gel method. The entrapped guest was diagnosed using UV–vis sectrophotometry, emission spectroscopy, and infrared spectrometry; the properties of the encapsulated porphyrin were compared to those of the compound in solution. The results indicate that Zn-pp-IX is well distributed and homogeneously in the glass.
Publication Date: 2005 On Pages: 1715-1719
Location : Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
ISSN: 1386-1425
Publisher: ELSEVIER
5. Zaitoun, Mohammed " Spectrophotometric determination of Chromium(VI) using cyclam as a reagent"
Abstract: A simple, rapid, sensitive, and inexpensive method for spectrophotometric determination of chromium(VI), based on the absorbance of its complex with 1,4,8,11-tetraazacyclotetradecane (cyclam) is presented. The complex showed a molar absorbtivity of 1.5?×?10 4 ?L?mol -1 ?cm -1 at 379?nm. Under optimum experimental conditions, a pH of 4.5 and 1.960?×?10 3 ?mg?L -1 cyclam were selected, and all measurements were performed 10?min after mixing. Major cations and anions did not show any interference; Beer's law was applicable in the concentration range 0.2–20?mg?L -1 with a detection limit of 0.001?mg?L -1 . The standard deviation in the determination is ±0.5?mg?L -1 for a 15.0?mg?L -1 solution ( n ?=?7). The described method provides a simple and reliable means for determination of Cr(VI) in real samples.
Publication Date: 2005 On Pages: 399-407
Location : International Journal of Environmental and Analytical Chemistry Print ISSN: 0306-7319
Online ISSN: 1029-0397
Publisher: Taylor and Francis Ltd
Abstract: A spectrophotometric method is presented to determine glucose employing the sol-gel technique. Myoglobin (Mb) and glucose oxidase are encapsulated in a transparent and porous silica glass. The produced gel (xerogel) is then immersed in water where increments of glucose are added to the solution with stirring; glucose diffuses into the sol-gel glass pores and a series of reactions take place. Glucose is first oxidized by glucose oxidase and oxygen to gluconate and hydrogen peroxide is generated. The liberated hydrogen peroxide oxidizes the Mb heme (Fe2+ into Fe3+). The higher is the glucose concentration added, the more is the H2O2 generated, and the more is the Mb oxidation (Fe2+ to Fe3+) and as a result the higher is the absorbance at 400 nm (negative peak, lower absorbance value). All measurements are performed at this wavelength (400 nm), the negative peak obtained by subtracting the absorption spectra of Mb before and after oxidation. Measuring the slope of the absorbance decay versus time at 400 nm monitors increments of added glucose. Each glucose concentration has an accompanying unique decay curve with a unique slope. The higher is the glucose concentration; the steeper is the decay curve (higher slope value). The calibration curve was linear up to 40 mM.
Publication Date: 2005 On Pages: 119-126
Location: Spectroscopy
ISSN 0712-4813 (Print) 1875-922X (Online)
Publisher: IOS press
7. Zaitoun, Mohammed; Bailey, L.; Brinkley, J.; Dickerson, C; Lin, C. " Reduction of Cr(VI) Assisted by Sol-Gel Generated Electron-Hole Centers "
Abstract: We report an in-situ harvesting technique of electron-hole (e−-h+) carriers (e.g., the defect electrons in the O2 − matrix and the self-trapped holes, Si–O−–Si) generated during sol-gel processing. In the absence of redox species, the e−-h+ centers created during room temperature sol-gel polycondensation steps are quickly annihilated and deactivated. However, when Cr(VI) ions are pre-dispersed in sol-gel solutions, the ejected electrons can be effectively harvested for the reduction of Cr(VI) to Cr(III) ions which are encapsulated in the silica gel matrix. The Cr(VI) ions, the possible intermediate oxidation states of chromium ions such as Cr(V) and/or Cr(IV), and the stable Cr(III)-hole complexes in the sol-gel matrix are investigated using uv-visible spectroscopy, electron paramagnetic resonance spectroscopy, and cyclic voltammetry. The chemical stability of Cr(VI) and Cr(III) in sol-gel networks is compared to that in aqueous solutions. The results indicate that the utilization of e−-h+ carriers generated in the sol-gel can be an effective and selective means for investigating the redox process of Cr(VI) and encapsulating the stable Cr(III) ions in the confined sol-gel environments. Publication Date: 2005 On Pages: 173-182
Location: Journal of Sol-Gel Science and Technology ISSN : 0928-0707 (Print) 1573-4846 (Online)
Publisher: Springer
8. QASEM M. JARADAT∗, ADNAN M. MASSADEH, MOHAMMED A. ZAITOUN " FRACTIONATION AND SEQUENTIAL EXTRACTION OF HEAVY METALS IN THE SOIL OF SCRAPYARD OF DISCARDED VEHICLES"
Abstract:
Chemical and physical size fractionation of heavy metals were carried out on 20 soil samples from the scrap yard area. Tessier method was used in sequential extraction. Cadmium showed the highest levels among the other elements studied in the exchangeable fraction (about 33%), while other elements showed low levels in this fraction (≥1%). Lead and manganese were mostly found in the Fe–Mn oxide fraction, zinc and iron were mostly in residual fraction, while copper was mostly found in the organic fraction of the soil. Soil samples were size-fractionated into four sizes: 1000–500, 500–125, 125–53, and less than 53 μm. The highest levels of Fe, Cu, Pb, Mn, and Cd were found in the medium fraction (500–125 μm), while zinc showed its highest levels in the fine fraction (125–53μm). The order of heavy metal load in the size fractions was found to be medium > fine > coarse > silt for Fe, Mn, Cu, Pb, and Cd, where it was found as fine > medium > coarse > silt for zinc.
Publication Date: 2006 On Pages: 197–210
Location: Environmental Monitoring and Assessment
ISSN: 0167-6369 (print version) ISSN: 1573-2959 (electronic version)
Publisher: Springer
9. Jaradat, Qasem M, Masadeh, Adnan, Zaitoun, Mohammed A " Heavy Metal Contamination of Soil, Plant and Air of Scrapyard of Discarded Vehicles at Zarqa City, Jordan"
Publication Date: 2005 On Pages: 449-462.
Location: Soil & Sediment Contamination
Print ISSN: 1532-0383
Online ISSN: 1549-7887
Volume 14, number 5
Publisher: Taylor & Francis
10. Zaitoun, Mohammed "Enhancement of Eu3+ emission in solution by bulky chelating ligands and deuterium substitution"
Abstract:
Binding the europium ion with a bulky chelating ligand provides one strategy for minimizing the quenching effects of water on the luminescence of the ion. 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraaceticacid tetrahydrochloride (TTT) was used as a chelating agent to isolate Eu3+ from hydroxyl deactivation in water. A large enhancement in the Eu3+ emission was observed for the chelated Eu3+ compared to the unchelated. Absorption and emission spectra are reported together with lifetime measurements. The latter were used to study concentration quenching and quenching by water.
Publication Date: 2002 On Pages: 29-35
Location: Spectroscopy
ISSN 0712-4813 (Print) 1875-922X (Online)
Volume 16, number 1
Publisher: IOS Press
11. Zaitoun, Mohammed; W. Roy Mason, and C. T. Lin " Magnetic Circular Dichroism Spectra for Colloidal Gold Nanoparticles in Xerogels at 5.5 K"
Abstract: Colloidal gold nanoparticles (
Publication Date: 2001 On Pages: 6780–6784
Location: J. Phys. Chem. B
Volume 105 (29)
Publisher: American Chemical Society
12. Zaitoun, Mohammed; D. M. Goken, L. S. Bailey, T. Kim, and C. T. Lin " Thermoanalysis and Emission Properties of Eu3+/Eu2+ in Eu3+-Doped Xerogels"
Abstract:
A series of Eu3+-doped silica sol−gels are prepared under various conditions: (1) pH values of the sols are controlled at 3.0, 5.5, and 7.5; (2) the counterions of dopants are selected from acetate, chloride, and nitrate of europium (III) compounds; (3) two chelating agents, namely ethylenediaminetetraacetic acid (EDTA) and ethylenediaminetriacetic (HEDTA) are used for complexing the europium (III) dopants; (4) a sol−gel matrix containing low O−H functionality is synthesized by using deuterated solvents (D2O and C2D5OD) and under an extremely dry N2 environment; and (5) a mixture of 1% of aluminum or antimony alkoxide and 99% of silicon alkoxide is adopted as precursors. The conditions that these differences have on the network structures of a gel matrix are examined in order to determine the optimal conditions for the creation of structural defects in an SiO2 network, generation of electron−hole centers and utilization of them to reduce Eu3+ to Eu2+ during the sol−gel processing. Both differential scanning calorimetric (DSC) measurements and thermogravimetric and differential thermal analysis (TG/DTA) are employed to illustrate which gel samples are the most liquidlike and have the greatest cross-linking density. The results from thermoanalysis are then correlated to the emission intensity and lifetimes of each Eu3+-doped sample. The relative emission intensity of Eu2+/Eu3+ gives the degree of conversion of Eu3+ to Eu2+ which is produced from the defect electron−hole pair generation. The absolute emission intensity of Eu3+ and Eu2+ is strongly quenched by the presence of OH groups in xerogels and is shown to be enhanced by laser irradiation due to water evaporation. The results show that a basic gel prepared by the mixed metal alkoxides most efficiently converts Eu3+ to Eu2+ because of its liquidlike nature, reduced cross-linking density, and low OH quenching.
Publication Date: 2000 On Pages: 189–196
Location: J. Phys. Chem. B ISSN (printed): 1089-5647. ISSN (electronic): 1520-5207.
Volume 104 (2)
Publisher: American Chemical Society
13. Zaitoun, Mohammed" Preparation and spectroscopic study of zirconia xerogels. Luminescence characterization of Europium and Terbium Incorporated into zirconia matrix using sol-gel method" The sol-gel preparations of optically transparent zirconia gel monoliths by controlled hydrolysis of stabilized zirconium alkoxide were investigated. Gelation, drying and shrinkage were all performed at room temperature. The produced xerogels were characterized by FTIR, emission spectroscopy, and thermal analysis. The blank zirconia xerogel displays a broad emission band maximum at 390 nm. The results showed that most residual water and organic molecules in the dried gel (xerogel) had vaporized in the temperature range from room temperature to 500 deg C. Zirconia gel glass-containing Eu(III) and Tb(III) were prepared by hydrolysis of zirconium alkoxide. The Eu, Tb-doped xerogels were studied by time resolved emission spectroscopy. The emission lines for f-f transitions of Eu exp 3+ and Tb exp 3+ in zirconia xerogel were quite sharp. The homogeneous broadening of exp 5 D sub 0 - > exp 7 F sub i , i = 0,1,2,3,4 for Eu(III) and of exp 5 D sub 4 - > exp 7 F sub j , j = 3,4,5,6 for Tb(III) indicates that Tb(III), Eu(III) ions are surrounded in a random environment of zirconia xerogel. Electronic transition intensities and the exp 5 D sub 0 (Eu exp 3+ ) and exp 5 D sub 4 (Tb exp 3+ ) excited states lifetimes were measured.
Publication Date: 2001 On Pages: 19-28
Location: Journal of Materials Science and Technology (Bulgaria) ISSN : 08619786
Volume 9 (1)
Publisher: Bulgarian Academy of Science
14. Zaitoun, Mohammed; , Taesam Kim, and C. T. Lin "Observation of Electron−Hole Carrier Emission in the Eu3+-Doped Silica Xerogel"
Abstract: The luminescence properties of Eu3+ encapsulated in sol−gel-derived optically transparent silica gels were investigated by time-resolved laser spectroscopy. At the xerogel stage, the emission spectra originated mainly from Eu2+ at 410 nm, and only a small contribution from Eu3+ at 580 nm and electron−hole (e-−h+) carrier at 530 nm were observed. It is proposed that in the presence of Eu3+ the carriers, e-−h+, were generated during the polycondensation reaction of silica and trapped at the defect sites of sol−gel matrix. The formation of e-−h+ carrier was illustrated to be responsible for the surface-assisted reduction of europium ions, where the ejected electrons from the oxygen-associated hole centers react with Eu3+ encapsulated in silica gel to produce Eu2+ ions.
Publication Date: 1998 On Pages: 1122–1125 Location: J. Phys. Chem. B ISSN (printed): 1089-5647. ISSN (electronic): 1520-5207.
Volume 102 (7)
Publisher: American Chemical Society
15. Mohammed A. Zaitoun and C. T. Lin " Chelating Behavior between Metal Ions and EDTA in Sol−Gel Matrix"
Abstract:
Ethylenediamine tetraacetic acid (EDTA) was encapsulated in a sol−gel-derived optically transparent glass. The complexation of metal cations, Cu(II), Ni(II), Fe(III), Cr(III), Co(II), Mn(II), Pd(II), and Ir(IV), with EDTA in solutions and in gels was evidenced by the formation of individual colors. A comparison of the absorption spectra of Mn+/EDTA in solution, Mn+/EDTA in gel, and Mn+/EDTA complex in gel was performed. The results show that (i) all six chelating sites in EDTA remain active in a sol−gel matrix as they bind readily with Cu2+, Ni2+, Fe3+, Pd2+, and Ir4+, (ii) EDTA is rigidly oriented in a sol−gel matrix that inhibits its heat- or catalyst-assisted complexation with Cr3+, Co2+, and Mn2+, (iii) no absorption spectral shift for the d−d metal transitions was observed compared to those in solution, yet a 10−30 nm shift for the MLCT transitions of Cu2+, Ni2+, Fe3+, Pd2+, Ir4+ was detected, and (iv) the level of sensitivity in detecting metal cations using EDTA in gel is at least an order of magnitude higher than that in solution. The response time of Mn+/EDTA complexation in gel is quite short, ranging from 1/30 to 15 min. This response time and the mode of sensing device guarantee that no leaching of EDTA from the sol−gel matrix is possible.
Publication Date: 1997 On Pages: 1857–1860 Location: J. Phys. Chem. B ISSN (printed): 1089-5647. ISSN (electronic): 1520-5207.
Volume 101 (10)
Publisher: American Chemical Society
16. Zaitoun, Mohammed " Preparation and Luminescence Characteristics of Europium Complexes Incorporated intro Optically Transparent Silica Matrix By the Sol-Gel Method. Effect of Complexation on the reduction of Eu3+ to Eu2+ in The Silica Glass"
Abstract
Europium complexes such as tris [444-trifluoro-1-(2-thienyl)1-3-butanedione] Europium (Eu-TTT), Europium Diethylenetriaminepentaacetic acid (Eu-DTPA), and Europium Nitrilotriacetic acid (Eu-NTA) were prepared by the sol-gel method and the incorporated complexes into the optically transparent silica glass were diagnosed by luminescence properties. The aim of the study was to prove the reduction of some of the Eu3+ to Eu2+.
Publication Date: 2002 On Pages: 847-859 Location: Abhath Al-Yarmouk ISSN : 10230149
Volume 11, number 2B
Publisher: Yarmouk University
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25 nm) and Au9(PPh3)83+
complex ions (<2 nm) are separately encapsulated in optically transparent
xerogels. The high quality xerogel is found to be isotropic with no material
strain or birefringence that would interfere with the magnetic circular
dichroism (MCD) measurements. The MCD and absorption spectra for the surface
plasmon band at 523 nm for