Rehab M. I. Elsamra

Alexandria University

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Mamdouh S. Masoud

Alexandria University

Shaun A. Carl

KU Leuven

Jozef Peeters

KU Leuven

Sokaina Saad Hemdan

University of Benghazi

Zachary J. Buras

Massachusetts Institute of Technology

Ahmed M. Ramadan

Helwan University

William H. Green

Massachusetts Institute of Technology

Minh Tho Nguyen

Van Lang University

Gehan M. El Zokm

National Institute of Oceanography and Fisheries

Mohamed A. Okbah

National Institute of Oceanography and Fisheries

Cooperative Institutions

KU Leuven

Alexandria University

Massachusetts Institute of Technology

Centre National de la Recherche Scientifique

Tunis El Manar University

Tunis University

King Khalid University

University of Central Florida

National Institute of Oceanography and Fisheries

Royal Belgian Institute for Space Aeronomy

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Experimental and theoretical study of the reaction of the ethynyl radical with nitrous oxide, C2H + N2O

Physical Chemistry Chemical Physics (2012)

Vinh Sơn Nguyễn Rehab M. I. Elsamra Jozef Peeters Shaun A. Carl Minh Tho Nguyen

We investigated the rate constants and reaction mechanism of the gas phase reaction between the ethynyl radical and nitrous oxide (C2H + N2O) using both experimental methods and electronic structure calculations. A pulsed-laser photolysis/chemiluminescence technique was used to determine the absolute rate coefficient over the temperature range 570 K to 836 K. In this experimental temperature range, the measured temperature dependence of the overall rate constants can be expressed as: k(T) (C2H + N2O) = 2.93 × 10−11 exp((−4000 ± 1100) K/T) cm3 s−1 (95% statistical confidence). Portions of the C2H + N2O potential energy surface (PES), containing low-energy pathways, were constructed using the composite G3B3 method. A multi-step reaction route leading to the products HCCO + N2 is clearly preferred. The high selectivity between product channels favouring N2 formation occurs very early. The pathway corresponds to the addition of the terminal C atom of C2H to the terminal N atom of N2O. Refined calculations using the coupled-cluster theory whose electronic energies were extrapolated to the complete basis set limit CCSD(T)/CBS led to an energy barrier of 6.0 kcal mol−1 for the entrance channel. The overall rate constant was also determined by application of transition-state theory and Rice–Ramsperger–Kassel–Marcus (RRKM) statistical analyses to the PES. The computed rate constants have similar temperature dependence to the experimental values, though were somewhat lower.

Nitrous oxide

Potential energy surface

Transition state theory

Atmospheric temperature range

10.1039/c2cp40367f

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Citations (9)

Reactive sulfide dynamic models for predicting metal hazardous in sediments of two northern Egyptian Lakes

Marine Pollution Bulletin (2023)

Gehan M. El Zokm Mamdouh S. Masoud Essam Kh. El-Shorbagi Rehab M. I. Elsamra Mohamed A. Okbah

10.1016/j.marpolbul.2023.114694

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Citations (4)

Pulsed laser photolysis and quantum chemical-statistical rate study of the reaction of the ethynyl radical with water vapor

The Journal of Chemical Physics (2005)

Shaun A. Carl Hue Minh Thi Nguyen Rehab M. I. Elsamra Minh Tho Nguyen Jozef Peeters

The rate coefficient of the gas-phase reaction C2H+H2O→products has been experimentally determined over the temperature range 500–825K using a pulsed laser photolysis-chemiluminescence (PLP-CL) technique. Ethynyl radicals (C2H) were generated by pulsed 193nm photolysis of C2H2 in the presence of H2O vapor and buffer gas N2 at 15Torr. The relative concentration of C2H radicals was monitored as a function of time using a CH* chemiluminescence method. The rate constant determinations for C2H+H2O were k1(550K)=(2.3±1.3)×10−13cm3s−1, k1(770K)=(7.2±1.4)×10−13cm3s−1, and k1(825K)=(7.7±1.5)×10−13cm3s−1. The error in the only other measurement of this rate constant is also discussed. We have also characterized the reaction theoretically using quantum chemical computations. The relevant portion of the potential energy surface of C2H3O in its doublet electronic ground state has been investigated using density functional theory B3LYP∕6-311++G(3df,2p) and molecular orbital computations at the unrestricted coupled-cluster level of theory that incorporates all single and double excitations plus perturbative corrections for the triple excitations, along with the 6-311++G(3df,2p) basis set [(U)CCSD(T)∕6-311++G(3df,2p)] and using UCCSD(T)∕6-31G(d,p) optimized geometries. Five isomers, six dissociation products, and sixteen transition structures were characterized. The results confirm that the hydrogen abstraction producing C2H2+OH is the most facile reaction channel. For this channel, refined computations using (U)CCSD(T)∕6-311++G(3df,2p)∕∕(U)CCSD(T)∕6-311++G(d,p) and complete-active-space second-order perturbation theory/complete-active-space self-consistent-field theory (CASPT2/CASSCF) [B. O. Roos, Adv. Chem. Phys. 69, 399 (1987)] using the contracted atomic natural orbitals basis set (ANO-L) [J. Almlöf and P. R. Taylor, J. Chem. Phys.86, 4070 (1987)] were performed, yielding zero-point energy-corrected potential energy barriers of 17kJmol−1 and 15kJmol−1, respectively. Transition-state theory rate constant calculations, based on the UCCSD(T) and CASPT2/CASSCF computations that also include H-atom tunneling and a hindered internal rotation, are in perfect agreement with the experimental values. Considering both our experimental and theoretical determinations, the rate constant can best be expressed, in modified Arrhenius form as k1(T)=(2.2±0.1)×10−21T3.05exp[−(376±100)∕T]cm3s−1 for the range 300–2000K. Thus, at temperatures above 1500K, reaction of C2H with H2O is predicted to be one of the dominant C2H reactions in hydrocarbon combustion.

Hydrogen atom abstraction

Coupled cluster

Bond-dissociation energy

10.1063/1.1861887

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Citations (33)

Direct Kinetic Measurements of Reactions between the Simplest Criegee Intermediate CH₂OO and Alkenes

The Journal of Physical Chemistry A (2014)

Zachary J. Buras Rehab M. I. Elsamra Amrit Jalan Joshua Middaugh William H. Green

The simplest Criegee Intermediate (CH2OO), a well-known biradical formed in alkene ozonolysis, is known to add across double bonds. Here we report direct experimental rate measurements of the simplest Criegee Intermediate reacting with C2–C4 alkenes obtained using the laser flash photolysis technique probing the recently measured B1A′ ← X1A′ transition in CH2OO. The measured activation energy (298–494 K) for CH2OO + alkenes is Ea ≈ 3500 ± 1000 J mol–1 for all alkyl substituted alkenes and Ea = 7000 ± 900 J mol–1 for ethene. The measured Arrhenius pre-exponential factors (A) vary between (2 ± 1) × 10–15 and (11 ± 3) × 10–15 cm3 molecule–1 s–1. Quantum chemical calculations of the corresponding rate coefficients reproduce qualitative reactivity trends but overestimate the absolute rate coefficients. Despite the small Ea's, the CH2OO + alkene rate coefficients are almost 2 orders of magnitude smaller than those of similar reactions between CH2OO and carbonyl compounds. Using the rate constants measured here, we estimate that, under typical atmospheric conditions, reaction with alkenes does not represent a significant sink of CH2OO. In environments rich in C═C double bonds, however, such as ozone-exposed rubber or emission plumes, these reactions can play a significant role.

10.1021/jp4118985

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Citations (89)

Solvatochromism, Hydrogen Bonding Induced Charge Transfer, and Influence of pH on Electronic Absorption Spectra of Murexide

Journal of Applied Spectroscopy (2024)

Sokaina Saad Hemdan Mamdouh S. Masoud Rehab M. I. Elsamra

Solvatochromism

10.1007/s10812-024-01824-7

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Solvent, substituents and pH effects towards the spectral shifts of some highly colored indicators

Journal of the Serbian Chemical Society (2017)

Mamdouh S. Masoud Rehab M. I. Elsamra Sokaina Saad Hemdan

The solvatochromic responses of six indicators namely Sudan orange, Alizarin yellow R, Aurin tricarboxylic acid, Alizarin yellow GG, Titan yellow and Eriochrome black-T, dissolved in seven solvents of different polarities, have been measured at room temperature. The UV/Vis absorption spectral shifts were analyzed by the multiple linear regression analysis and Kamlet?Taft equation. The observed solvatochromism was found to depend on the presence of the donor and acceptor substituents in the conjugated systems of the indicator and the physical properties of the solvent molecules. The pH effects on the wavenumbers of the absorption band maxima of some indicators with different constituents at room temperature were discussed and the mechanism of ionization was explained. The dissociation constants (pKa) of the investigated compounds were precisely assessed and the existence of the individual predominant ionic species was assigned by constructing distribution diagrams at different pH ranges.

Solvatochromism

Alizarin

Dissociation constant

10.2298/jsc170204032m

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Citations (29)

Synthesis, Ligating Properties, Thermal Behavior, Computational and Biological Studies of Some Azo-transition Metal Complexes

Research Square (Research Square) (2022)

Mamdouh S. Masoud Sokaina Saad Hemdan Rehab M. I. Elsamra

Abstract Synthesis of new Fe(III), Co(II), Ni(II), and Cu(II) complexes of two azo ligands; 1-(phenyldiazenyl) naphthalene-2-ol (sudan orange R, HL 1 ), and sodium 2-hydroxy-5-[(E)-(4-nitrophenyl) diazenyl]benzoate (alizarin yellow GG, HL 2 ) have been reported. Stoichiometries of 1:2 and 1:3 (M:L) of the synthesized complexes were approved by total-reflection X-ray fluorescence technique (TXRF) and by elemental analyses. Complexes geometry of octahedral and square planar types were characterized by various spectroscopic, thermal, and magnetic moment measurements. Notably, bidentate coordination was the common binding mode of the ligands under investigation. The ESR spectroscopy showed that Cu(II) complexes are of different isotropic and rhombic symmetries accompanied by the existence of Cu-Cu ions interaction. TGA, DTA and DSC techniques supported the multi-stage thermal decomposition mechanisms, where the thermal breakdown is ended by the formation of metal oxide in most cases. Moreover, optimization of the structure and chemical reactivity modeling using the density functional theory (DFT) method with the B3LYP/6–31 basis set, showed that metal complexes are more biologically active than their precursor ligands. The calculated lipophilicity character for metal complexes is in the range 33.8–37.5 eV. Furthermore, nucleophilic and electrophilic regions on the surface of the ligands have been mapped aiming to prove the preferable sites of interaction with the metal ions. Docking results revealed high scoring energy for [Fe(HL 2 ) 3 ].H 2 O complex and moderate inhibition strength of [Cu(L 1 ) 2 ].H 2 O complex versus 1bqb, 3t88 and 4esw proteins. Ultimately, the extent of biological effectiveness was endorsed experimentally against four microbial strains. The results are guidelines for toxicological investigations.

Octahedral molecular geometry

10.21203/rs.3.rs-1668924/v1

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Theoretical and experimental investigation of the C2H+SO2 reaction over the range T=295–800K

Chemical Physics Letters (2011)

Saartje Swinnen Rehab M. I. Elsamra Vinh Sơn Nguyễn Jozef Peeters Shaun A. Carl

Atmospheric temperature range

Negative temperature

Buffer gas

Potential energy surface

10.1016/j.cplett.2011.07.098

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Citations (5)

Green synthesis of nanostructured zinc oxide by Ocimum tenuiflorum extract: characterization, adsorption modeling, cytotoxic screening, and metal ions adsorption applications

Biomass Conversion and Biorefinery (2023)

Rehab M. I. Elsamra Mamdouh S. Masoud Alyaa A. Zidan Gehan M. El Zokm Mohamed A. Okbah

Abstract Nano-ZnO was synthesized by the reduction of Zn (CH 3 COO) 2 .2H 2 O salt using the extract of Ocimum tenuiflorum leaves. The generated ZnO NPs were characterized by FT-IR, XRD, SEM, and EDX techniques. FT-IR results approved the characteristic peaks, the formation of ZnO bonds, and the morphology changes after the adsorption of Cd 2+ and Pb 2+ from solutions. The outlined data of the XRD pointed to the formation of a hexagonal wurtzite structure. SEM images showed the spherical nature of the synthesized particles with an average diameter of 19 nm. Moreover, the best conditions for the adsorption of Cd 2+ and Pb 2+ by ZnO NPs were evaluated and fitted to isotherm and kinetic models. Short contact time of ~ 20 min and a small sorbent dosage of 40 mg were sufficient conditions for attaining maximum Pb 2+ adsorption capacity. Based on the modeling parameters, the adsorption follows pseudo-second-order kinetics where ZnO and metal ions are involved in the rate-determining step. Two important applications were thoroughly studied. The nanoparticles significantly removed Pb 2+ and Cd 2+ contaminants from real environmental water samples collected from different locations in Egypt. Additionally, the cytotoxic activity results provided perfect evidence for the higher efficacy of the synthesized ZnO NPs as an anticancer agent against Panc-1, PC-3, and CACO-2 cell lines with IC 50 of 1.70, 3.67, and 5.70 μgml −1 , respectively, compared to cisplatin (IC 50 = 3.57, 5.09, and 7.75 μgml −1 ). Furthermore, a low cytotoxic effect was observed on the normal human lung cell line (MRC-5, IC 50 = 22.40 μgml −1 ). The data can be used as a preliminary study for anticancer drug design after further clinical investigations. Graphical Abstract

Wurtzite crystal structure

10.1007/s13399-022-03709-1

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Citations (14)

Measurements of laminar burning speeds in ammonia and hydrogen-air mixtures for gas turbines

AIAA SCITECH 2022 Forum (2023)

Louis Yovino Gihun Kim Ritesh Ghorpade Rehab M. I. Elsamra Subith Vasu

Major research in sustainable energy is directed at understanding the combustion phenomena of advanced aerospace fuels and their exhaust emissions. Ammonia as a hydrogen carrier provides promising benefits to mitigate fossil fuel scarcity and greenhouse gas emissions. Here, ammonia and hydrogen mixtures are ignited in a spherical chamber to understand their flame characteristics and laminar burning speeds across a range of equivalence ratios. Identifying key combustion parameters like the laminar burning speed supports the development of advanced, sustainable gas turbine systems for alternative fuels.

10.2514/6.2023-1823

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