Prof. Osama K. Abou-Zied Profile

Prof. Osama K. Abou-Zied

Professor at Sultan Qaboos Univ

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Publications (8)

Proceedings Article | 8 June 2023 Presentation

New liquid crystal systems for photochemical energy storage

Osama Abou-Zied

Proceedings Volume PC12584, PC125840C (2023) https://doi.org/10.1117/12.2670193

KEYWORDS: Liquid crystals, Ultraviolet radiation, Absorbance, Picosecond phenomena, Glasses, Thin films, Photonic crystals, Molecular aggregates, Liquids, Ground state

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Proceedings Article | 13 March 2015 Paper

Spectroscopic characterization of the binding mechanism of fluorescein and carboxyfluorescein in human serum albumin

Saba A. Sulaiman, H. Udani Kulathunga, Osama Abou-Zied

Proceedings Volume 9339, 933908 (2015) https://doi.org/10.1117/12.2077520

KEYWORDS: Luminescence, Absorbance, Proteins, Spectroscopy, Absorption, Molecules, Fluorescence spectroscopy, Quantum efficiency, Ionization, Plasma

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Proceedings Article | 12 March 2015 Paper

Fluorescence characterization of water-driven self-assembled lipids and their temperature-induced phase transitions

N. Idayu Zahid, Osama Abou-Zied, Rauzah Hashim

Proceedings Volume 9339, 93390L (2015) https://doi.org/10.1117/12.2083677

KEYWORDS: Luminescence, Molecules, Head, Molecular self-assembly, Molecular interactions, Crystals, Bioalcohols, Excimers, Liquid crystals, Thermodynamics

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Proceedings Article | 12 March 2015 Paper

Amphitropic liquid crystal phases from polyhydroxy sugar surfactants: Fundamental studies

Osama Abou Zied, Rauzah Hashim, B. Timimi

Proceedings Volume 9338, 933818 (2015) https://doi.org/10.1117/12.2083676

KEYWORDS: Liquid crystals, Hydrogen, Head, Molecules, Crystals, Chromium, Liquids, Molecular self-assembly, Glucose, Water

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Proceedings Article | 2 February 2012 Paper

Water participation in molecular recognition and protein-ligand association: Probing the drug binding site "Sudlow I" in human serum albumin

Najla Al-Lawatia, Thomas Steinbrecher, Osama Abou-Zied

Proceedings Volume 8233, 82331D (2012) https://doi.org/10.1117/12.905809

KEYWORDS: Luminescence, Molecules, Proteins, Molecular interactions, Absorption, Molecular spectroscopy, Hydrogen, Spectroscopy, Energy transfer, Blood

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Proceedings Article | 17 February 2010 Paper

Specific interaction of 7-hydroxyquinoline with Trp-214 in the drug-binding site IIA of human serum albumin

Osama K. Abou-Zied, Najla Al-Lawatia

Proceedings Volume 7576, 757618 (2010) https://doi.org/10.1117/12.840485

KEYWORDS: Luminescence, Molecules, Absorption, Proteins, Molecular interactions, Energy transfer, Binary data, Absorbance, Solids, Resonance energy transfer

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The drug-binding site subdomain IIA of human serum albumin (HSA) was characterized by absorption and fluorescence spectroscopy using 7-hydroxyquinoline (7-HQ) as a local reporter. The spectra of 7-HQ in solution indicate that a ztitterionic tautomer is stabilized by water in the ground state and produces a unique absorption peak at 400 nm and a fluorescence peak at 510 nm. By examining the spectral change in binary mixtures of water and 1,4-dioxane, three water molecules were estimated to stabilize this tautomer through direct interactions with the polar regions of the molecule. When 7-HQ is mixed with HSA, a reduction in the absorbance of the zwitterionic tautomer was observed which indicates a less polar environment around the molecule. The 7-HQ molecule is found to specifically bind in subdomain IIA of HSA and causes a reduction in the fluorescence intensity of the Trp-214 residue which is located in the same binding site. The reduction in the fluorescence of Trp-214 is due to energy transfer from the Trp-214 residue to the 7- HQ probe. The distance between Trp-214 and the probe was calculated using Förster theory for energy transfer to be 1.95 nm. This distance and the calculated quenching rate constant using a Stern-Valmer plot (k_q = 3.04 x 10¹² M^-1s^-1) both point to a static quenching mechanism. The binding constant and the number of binding sites of the complex were also estimated and the calculations show that the 7-HQ probe binds only in subdomain IIA. The change in the fluorescence intensity of HSA in the presence of the probe indicates that the 7-HQ molecule selectively interacts with the Trp-214 residue which results in partial unmasking of the fluorescence due to the Tyr-263 residue (located in the same site). A much stronger fluorescence from Tyr-263 is observed when HSA is chemically unfolded by 6.0 M GdnHCl. 7- HQ is found to still bind in subdomain IIA in the unfolded state of HSA and causes a reduction in the fluorescence intensities of both Trp-214 and Tyr-263. The present results propose 7-HQ as a useful photophysical probe in studying binding sites in proteins and exploring their hydrophobic environment.

Proceedings Article | 22 February 2008 Paper

Steady-state and time-resolved fluorescence investigation of 2-pyridone and 3-pyridone in solution and their specific binding to human serum albumin

Osama K. Abou-Zied, Othman I. K. Al-Shihi

Proceedings Volume 6867, 68670K (2008) https://doi.org/10.1117/12.762218

KEYWORDS: Luminescence, Absorption, Molecules, Energy transfer, Proteins, Absorbance, Binary data, Hydrogen, Time resolved spectroscopy, Picosecond phenomena

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2-pyridone (2Py) and 3-pyridone (3Py) were examined in different solvents and their binding to human serum albumin (HSA) was studied using steady-state spectroscopy and time-resolved fluorescence. Solvation of 2Py and 3Py by water was examined in binary mixtures of 1,4-dioxane and water. Analysis of the absorption and fluorescence data reveals the solvation of the hydrogen bonding center in 2Py by one water molecule and in 3Py by three water molecules. A zwitterionic tautomer of 3Py is formed in water and shows distinct absorption peaks from the absorption of the neutral tautomer. Fluorescence of 3Py was observed in polar solvents only, whereas 2Py is fluorescent in polar and nonpolar solvents. The absorption and fluorescence spectra of 2Py in different solvents indicate less solute-solvent interaction in nonpolar solvents. This observation was confirmed by the measured longer fluorescence lifetime of 2Py in cyclohexane compared to that in water. The mechanism of binding of 2Py and 3Py as probe ligands to HSA was investigated by following the intensity change and lifetime of HSA fluorescence after excitation at 280 nm. The presence of 2Py and 3Py causes a reduction in the fluorescence intensity and lifetime of HSA. This observation indicates that subdomain IIA binding site (Sudlow site I) is the host of the probes and the reduction in the fluorescence of HSA is due to energy transfer from the Trp-214 residue to the probe in each case. The distance between Trp-214 and each of the probes was calculated using Förster theory for energy transfer to be 1.99 nm for HSA/2Py and 2.44 nm for HSA/3Py. The shorter distance in the former complex indicates more efficient energy transfer than in the latter. This was confirmed by estimating the quenching rate constant (k_q) in each complex. k_q was calculated to be 1.44 x 10¹² M^-1s^-1 for HSA/2Py and 3.45 x 10¹¹ M^-1s^-1 for HSA/3Py. The calculated distances and the k_q values indicate a static quenching mechanism operative in the two complexes. The binding constants were estimated to be K = (3.4 ± 0.4) x 10⁴ M^-1 for the HSA/2Py complex and K = (2.3 ± 0.3) x 10⁴ M^-1 for the HSA/3Py complex. The number of binding sites of HSA was calculated to be one in both complexes. The latter results, along with the quenching results, indicate that both probes, 2Py and 3Py, bind only in Sudlow site I in subdomain IIA.

Proceedings Article | 14 February 2007 Paper

Steady-state spectroscopy of new biological probes

Osama K. Abou-Zied

Proceedings Volume 6449, 64490L (2007) https://doi.org/10.1117/12.703269

KEYWORDS: Luminescence, Absorption, Molecules, Hydrogen, Spectroscopy, Binary data, Cadmium sulfide, Environmental sensing, Molecular spectroscopy, Proteins

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