A femtosecond fluorescence upconversion study is reported for HBO in solution, as well as for HBO... more A femtosecond fluorescence upconversion study is reported for HBO in solution, as well as for HBO incorporated in DNA. The typical time for the excited-state intramolecular proton-transfer reaction of the syn-enol tautomer in solution and in DNA has been determined to be 150 fs. In addition, the lifetimes of the keto, the anti-enol and the ‘solvated enol’ tautomer forms were determined in protic solvents, aprotic solvents and DNA. Picosecond rise and decay components in the fluorescence transients with characteristic times between 3 and 25 ps are also observed and attributed to the effects of vibrational cooling.
... Email: Dr. Osama K. Abou-Zied (abouzied@squ.edu.om). *Correspondence: Dr. Osama K. Abou-Zied,... more ... Email: Dr. Osama K. Abou-Zied (abouzied@squ.edu.om). *Correspondence: Dr. Osama K. Abou-Zied, Department of Chemistry, Faculty of Science, Sultan Qaboos University, PO Box 36, Postal Code 123, Muscat (Sultanate of Oman), Fax: (+968) 2414-1469. Publication History. ...
International Journal of Nanomedicine, Jun 1, 2019
It has been indicated that NPs may change the amyloidogenic steps of proteins and relevant cytoto... more It has been indicated that NPs may change the amyloidogenic steps of proteins and relevant cytotoxicity. Therefore, this report assigned to explore the impact of ZVFe NPs on the amyloidogenicity and cytotoxicity of α-synuclein as one of the many known amyloid proteins. Methods: The characterization of α-synuclein at amyloidogenic condition either alone or with ZVFe NPs was carried out by fluorescence, CD, UV-visible spectroscopic methods, TEM study, docking, and molecular modeling. The cytotoxicity assay of α-synuclein amyloid in the absence and presence of ZVFe NPs was also done by MTT, LDH, and flow cytometry analysis. Results: ThT fluorescence spectroscopy revealed that ZVFe NPs shorten the lag phase and accelerate the fibrillation rate of α-synuclein. Nile red and intrinsic fluorescence spectroscopy, CD, Congo red adsorption, and TEM studies indicated that ZVFe NP increased the propensity of α-synuclein into the amyloid fibrillation. Molecular docking study revealed that hydrophilic residues, such as Ser-9 and Lys-12 provide proper sites for hydrogen bonding and electrostatic interactions with adsorbed water molecules on ZVFe NPs, respectively. Molecular dynamics study determined that the interacted protein shifted from a natively discorded conformation toward a more packed structure. Cellular assay displayed that the cytotoxicity of α-synuclein amyloid against SH-SY5Y cells in the presence of ZVFe NPs is greater than the results obtained without ZVFe NPs. Conclusion: In conclusion, the existence of ZVFe NPs promotes α-synuclein fibrillation at amyloidogenic conditions by forming a potential template for nucleation, the growth of αsynuclein fibrillation and induced cytotoxicity.
Journal of environmental chemical engineering, Oct 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
International Journal of Nanomedicine, Jul 1, 2019
Aim: Nanoparticles (NPs) have been receiving potential interests in protein delivery and cell the... more Aim: Nanoparticles (NPs) have been receiving potential interests in protein delivery and cell therapy. As a matter of fact, NPs may be used as great candidates in promoting cell therapy by catalase (CAT) delivery into high oxidative stress tissues. However, for using NPs like SiO 2 as carriers, the interaction of NPs with proteins and mesenchymal stem cells (MSCs) should be explored in advance. Methods: In the present study, the interaction of SiO 2 NPs with CAT and human MSCs (hMSCs) was explored by various spectroscopic methods (fluorescence, circular dichroism (CD), UV-visible), molecular docking and dynamics studies, and cellular (MTT, cellular morphology, cellular uptake, lactate dehydrogenase, ROS, caspase-3, flow cytometry) assays. Results: Fluorescence study displayed that both dynamic and static quenching mechanisms and hydrophobic interactions are involved in the spontaneous interaction of SiO 2 NPs with CAT. CD spectra indicated that native structure of CAT remains stable after interaction with SiO 2 NPs. UV-visible study also revealed that the kinetic parameters of CAT such as Km, Vmax, Kcat, and enzyme efficiency were not changed after the addition of SiO 2 NPs. Molecular docking and dynamics studies showed that Si and SiO 2 clusters interact with hydrophobic residues of CAT and SiO 2 cluster causes minor changes in the CAT structure at a total simulation time of 200 ps. Cellular assays depicted that SiO 2 NPs induce significant cell mortality, change in cellular morphology, cellular internalization, ROS elevation, and apoptosis in hMSCs at higher concentration than 100 µg/mL (170 µM). Conclusion: The current results suggest that low concentrations of SiO 2 NPs induce no substantial change or mortality against CAT and hMSCs, and potentially useful carriers in CAT delivery to hMSC.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Apr 1, 2018
The ability of human serum albumin (HSA) to bind medium-sized hydrophobic molecules is important ... more The ability of human serum albumin (HSA) to bind medium-sized hydrophobic molecules is important for the distribution, metabolism, and efficacy of many drugs. Herein, the interaction between pyrene, a hydrophobic fluorescent probe, and HSA was thoroughly investigated using steady-state and time-resolved fluorescence techniques, ligand docking, and molecular dynamics (MD) simulations. A slight quenching of the fluorescence signal from Trp214 (the sole tryptophan residue in the protein) in the presence of pyrene was used to determine the ligand binding site in the protein, using Förster's resonance energy transfer (FRET) theory. The estimated FRET apparent distance between pyrene and Trp214 was 27 Å, which was closely reproduced by the docking analysis (29 Å) and MD simulation (32 Å). The highest affinity site for pyrene was found to be in subdomain IB from the docking results. The calculated equilibrium structure of the complex using MD simulation shows that the ligand is largely stabilized by hydrophobic interaction with Phe165, Phe127, and the nonpolar moieties of Tyr138 and Tyr161. The fluorescence vibronic peak ratio I 1 /I 3 of bound pyrene inside HSA indicates the presence of polar effect in the local environment of pyrene which is less than that of free pyrene in buffer. This was clarified by the MD simulation results in which an average of 5.7 water molecules were found within 0.5 nm of pyrene in the binding site. Comparing the fluorescence signals and lifetimes of pyrene inside HSA to that free in buffer, the high tendency of pyrene to form dimer was almost completely suppressed inside HSA, indicating a high selectivity of the binding pocket toward pyrene monomer. The current results emphasize the ability of HSA, as a major carrier of several drugs and ligands in blood, to bind hydrophobic molecules in cavities other than subdomain IIA which is known to bind most hydrophobic drugs. This ability stems from the nature of the amino acids forming the binding sites of the protein that can easily adapt their shape to accommodate a variety of molecular structures.
The incorporation of gold nanorod-modified TiO2 nanoparticles (TiO2/AuNRs) along with cobalt-imid... more The incorporation of gold nanorod-modified TiO2 nanoparticles (TiO2/AuNRs) along with cobalt-imidazolate frameworks (ZIF-67) into the photoanode of dye-sensitized solar cells resulted in a notable enhancement in energy conversion efficiency.
Abstract Photoluminescence (PL) quenching of nanoassemblies of CuInS2/ZnS quantum dots (CIS QDs) ... more Abstract Photoluminescence (PL) quenching of nanoassemblies of CuInS2/ZnS quantum dots (CIS QDs) and rhodamine 560 molecules (Rh560) is spectroscopically investigated by steady-state and femtosecond-to-nanosecond time-resolved techniques. Fluorescence lifetime measurements of CIS QDs show a bi-exponential decay (time constants ca. 650 ns and 210 ns) that are assigned to the radiative recombination of delocalized CB electrons with localized holes, presumably associated with Cu-related defect sites. A trapped electron recombines nonradiatively with the localized hole. That means, electron trapping is the first step in the nonradiative recombination pathway in CIS QDs. The traps are of surface origin and are likely associated with unpassivated dangling bonds. In this work, we controlled the trap density by varying the amount of Rh560 on the QD surface and monitoring the electron trapping in different time scales. Transient absorption measurements of the CIS-Rh560 assemblies resolved the fast component of electron trapping that occurs in tens to hundreds of picoseconds, while fluorescence lifetime measurements resolved the slow components of trapping that occur in hundreds of nanoseconds. Unlike the case of more traditional CdSe/ZnS QDs, the PL lifetime of CIS QDs approaches the typical time scale of fluorescence intermittency. As a result, the excited state of CIS QDs is vulnerable to the blinking process. In the CIS-Rh560 assembly, trapping of CB electrons increases with dye loading which eventually prolongs the dark (or dim) period and therefore reduces the fluorescence quantum yield of CIS QDs. The appearance of short lifetime components (ca. 0.5–6.9 ns) in the QD-dye assembly hints that Auger quenching process and/or electron-phonon coupling seems to play a major role in the PL quenching process.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Feb 1, 2022
Carbon nanoparticles (CNPs) are getting wide attention due to their fluorescence and low level of... more Carbon nanoparticles (CNPs) are getting wide attention due to their fluorescence and low level of toxicity compared to other semiconducting photoluminescent materials. CNPs show strong 'solvatochromism', and the emission mechanism is still under discussion. Florescent carbon in the form of films would tremendously increase its potential for applications. In this work, we report for the first time the fluorescent emission characteristics of carbon films formed by aggregation of CNPs. Films of carbon were grown on glass substrates by using a novelCold Vapour Deposition System. We have performed a detailed comparative study of the emission spectra of film and CNPs (prepared using the microwave synthesis method) in various solvents. A qualitative model based on solvatochromism of CNPs is used to understand the emission pathways in the film.
A femtosecond fluorescence upconversion study is reported for HBO in solution, as well as for HBO... more A femtosecond fluorescence upconversion study is reported for HBO in solution, as well as for HBO incorporated in DNA. The typical time for the excited-state intramolecular proton-transfer reaction of the syn-enol tautomer in solution and in DNA has been determined to be 150 fs. In addition, the lifetimes of the keto, the anti-enol and the ‘solvated enol’ tautomer forms were determined in protic solvents, aprotic solvents and DNA. Picosecond rise and decay components in the fluorescence transients with characteristic times between 3 and 25 ps are also observed and attributed to the effects of vibrational cooling.
... Email: Dr. Osama K. Abou-Zied (abouzied@squ.edu.om). *Correspondence: Dr. Osama K. Abou-Zied,... more ... Email: Dr. Osama K. Abou-Zied (abouzied@squ.edu.om). *Correspondence: Dr. Osama K. Abou-Zied, Department of Chemistry, Faculty of Science, Sultan Qaboos University, PO Box 36, Postal Code 123, Muscat (Sultanate of Oman), Fax: (+968) 2414-1469. Publication History. ...
International Journal of Nanomedicine, Jun 1, 2019
It has been indicated that NPs may change the amyloidogenic steps of proteins and relevant cytoto... more It has been indicated that NPs may change the amyloidogenic steps of proteins and relevant cytotoxicity. Therefore, this report assigned to explore the impact of ZVFe NPs on the amyloidogenicity and cytotoxicity of α-synuclein as one of the many known amyloid proteins. Methods: The characterization of α-synuclein at amyloidogenic condition either alone or with ZVFe NPs was carried out by fluorescence, CD, UV-visible spectroscopic methods, TEM study, docking, and molecular modeling. The cytotoxicity assay of α-synuclein amyloid in the absence and presence of ZVFe NPs was also done by MTT, LDH, and flow cytometry analysis. Results: ThT fluorescence spectroscopy revealed that ZVFe NPs shorten the lag phase and accelerate the fibrillation rate of α-synuclein. Nile red and intrinsic fluorescence spectroscopy, CD, Congo red adsorption, and TEM studies indicated that ZVFe NP increased the propensity of α-synuclein into the amyloid fibrillation. Molecular docking study revealed that hydrophilic residues, such as Ser-9 and Lys-12 provide proper sites for hydrogen bonding and electrostatic interactions with adsorbed water molecules on ZVFe NPs, respectively. Molecular dynamics study determined that the interacted protein shifted from a natively discorded conformation toward a more packed structure. Cellular assay displayed that the cytotoxicity of α-synuclein amyloid against SH-SY5Y cells in the presence of ZVFe NPs is greater than the results obtained without ZVFe NPs. Conclusion: In conclusion, the existence of ZVFe NPs promotes α-synuclein fibrillation at amyloidogenic conditions by forming a potential template for nucleation, the growth of αsynuclein fibrillation and induced cytotoxicity.
Journal of environmental chemical engineering, Oct 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
International Journal of Nanomedicine, Jul 1, 2019
Aim: Nanoparticles (NPs) have been receiving potential interests in protein delivery and cell the... more Aim: Nanoparticles (NPs) have been receiving potential interests in protein delivery and cell therapy. As a matter of fact, NPs may be used as great candidates in promoting cell therapy by catalase (CAT) delivery into high oxidative stress tissues. However, for using NPs like SiO 2 as carriers, the interaction of NPs with proteins and mesenchymal stem cells (MSCs) should be explored in advance. Methods: In the present study, the interaction of SiO 2 NPs with CAT and human MSCs (hMSCs) was explored by various spectroscopic methods (fluorescence, circular dichroism (CD), UV-visible), molecular docking and dynamics studies, and cellular (MTT, cellular morphology, cellular uptake, lactate dehydrogenase, ROS, caspase-3, flow cytometry) assays. Results: Fluorescence study displayed that both dynamic and static quenching mechanisms and hydrophobic interactions are involved in the spontaneous interaction of SiO 2 NPs with CAT. CD spectra indicated that native structure of CAT remains stable after interaction with SiO 2 NPs. UV-visible study also revealed that the kinetic parameters of CAT such as Km, Vmax, Kcat, and enzyme efficiency were not changed after the addition of SiO 2 NPs. Molecular docking and dynamics studies showed that Si and SiO 2 clusters interact with hydrophobic residues of CAT and SiO 2 cluster causes minor changes in the CAT structure at a total simulation time of 200 ps. Cellular assays depicted that SiO 2 NPs induce significant cell mortality, change in cellular morphology, cellular internalization, ROS elevation, and apoptosis in hMSCs at higher concentration than 100 µg/mL (170 µM). Conclusion: The current results suggest that low concentrations of SiO 2 NPs induce no substantial change or mortality against CAT and hMSCs, and potentially useful carriers in CAT delivery to hMSC.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Apr 1, 2018
The ability of human serum albumin (HSA) to bind medium-sized hydrophobic molecules is important ... more The ability of human serum albumin (HSA) to bind medium-sized hydrophobic molecules is important for the distribution, metabolism, and efficacy of many drugs. Herein, the interaction between pyrene, a hydrophobic fluorescent probe, and HSA was thoroughly investigated using steady-state and time-resolved fluorescence techniques, ligand docking, and molecular dynamics (MD) simulations. A slight quenching of the fluorescence signal from Trp214 (the sole tryptophan residue in the protein) in the presence of pyrene was used to determine the ligand binding site in the protein, using Förster's resonance energy transfer (FRET) theory. The estimated FRET apparent distance between pyrene and Trp214 was 27 Å, which was closely reproduced by the docking analysis (29 Å) and MD simulation (32 Å). The highest affinity site for pyrene was found to be in subdomain IB from the docking results. The calculated equilibrium structure of the complex using MD simulation shows that the ligand is largely stabilized by hydrophobic interaction with Phe165, Phe127, and the nonpolar moieties of Tyr138 and Tyr161. The fluorescence vibronic peak ratio I 1 /I 3 of bound pyrene inside HSA indicates the presence of polar effect in the local environment of pyrene which is less than that of free pyrene in buffer. This was clarified by the MD simulation results in which an average of 5.7 water molecules were found within 0.5 nm of pyrene in the binding site. Comparing the fluorescence signals and lifetimes of pyrene inside HSA to that free in buffer, the high tendency of pyrene to form dimer was almost completely suppressed inside HSA, indicating a high selectivity of the binding pocket toward pyrene monomer. The current results emphasize the ability of HSA, as a major carrier of several drugs and ligands in blood, to bind hydrophobic molecules in cavities other than subdomain IIA which is known to bind most hydrophobic drugs. This ability stems from the nature of the amino acids forming the binding sites of the protein that can easily adapt their shape to accommodate a variety of molecular structures.
The incorporation of gold nanorod-modified TiO2 nanoparticles (TiO2/AuNRs) along with cobalt-imid... more The incorporation of gold nanorod-modified TiO2 nanoparticles (TiO2/AuNRs) along with cobalt-imidazolate frameworks (ZIF-67) into the photoanode of dye-sensitized solar cells resulted in a notable enhancement in energy conversion efficiency.
Abstract Photoluminescence (PL) quenching of nanoassemblies of CuInS2/ZnS quantum dots (CIS QDs) ... more Abstract Photoluminescence (PL) quenching of nanoassemblies of CuInS2/ZnS quantum dots (CIS QDs) and rhodamine 560 molecules (Rh560) is spectroscopically investigated by steady-state and femtosecond-to-nanosecond time-resolved techniques. Fluorescence lifetime measurements of CIS QDs show a bi-exponential decay (time constants ca. 650 ns and 210 ns) that are assigned to the radiative recombination of delocalized CB electrons with localized holes, presumably associated with Cu-related defect sites. A trapped electron recombines nonradiatively with the localized hole. That means, electron trapping is the first step in the nonradiative recombination pathway in CIS QDs. The traps are of surface origin and are likely associated with unpassivated dangling bonds. In this work, we controlled the trap density by varying the amount of Rh560 on the QD surface and monitoring the electron trapping in different time scales. Transient absorption measurements of the CIS-Rh560 assemblies resolved the fast component of electron trapping that occurs in tens to hundreds of picoseconds, while fluorescence lifetime measurements resolved the slow components of trapping that occur in hundreds of nanoseconds. Unlike the case of more traditional CdSe/ZnS QDs, the PL lifetime of CIS QDs approaches the typical time scale of fluorescence intermittency. As a result, the excited state of CIS QDs is vulnerable to the blinking process. In the CIS-Rh560 assembly, trapping of CB electrons increases with dye loading which eventually prolongs the dark (or dim) period and therefore reduces the fluorescence quantum yield of CIS QDs. The appearance of short lifetime components (ca. 0.5–6.9 ns) in the QD-dye assembly hints that Auger quenching process and/or electron-phonon coupling seems to play a major role in the PL quenching process.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Feb 1, 2022
Carbon nanoparticles (CNPs) are getting wide attention due to their fluorescence and low level of... more Carbon nanoparticles (CNPs) are getting wide attention due to their fluorescence and low level of toxicity compared to other semiconducting photoluminescent materials. CNPs show strong 'solvatochromism', and the emission mechanism is still under discussion. Florescent carbon in the form of films would tremendously increase its potential for applications. In this work, we report for the first time the fluorescent emission characteristics of carbon films formed by aggregation of CNPs. Films of carbon were grown on glass substrates by using a novelCold Vapour Deposition System. We have performed a detailed comparative study of the emission spectra of film and CNPs (prepared using the microwave synthesis method) in various solvents. A qualitative model based on solvatochromism of CNPs is used to understand the emission pathways in the film.
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