I. Osman

Assessment of Committed Effective Dose due to consumption of Red Sea coral reef fishes collected from the local market (Sudan)

An assessment of Committed Effective Dose (CED) due to consumption of Red Sea fish containing (210)Po and (137)Cs was performed for 23 different marine fish samples collected from the local market at Port Sudan. The fish were classified according to their feeding habits into three categories: carnivores, herbivores, and omnivores. Measured activity concentrations of (210)Po were found in the ranges 0.25-6.42 (carnivores), 0.7-5 (omnivores) and 1.5-3.8 (herbivores) Bq/kg fresh weight. In the same study, activity concentrations of Cs-137 were determined to be in the ranges 0.1-0.46 (carnivores), 0.09-0.35 (omnivores) and 0.09-0.32 (herbivores) Bq/kg fresh weight, which were several times lower than those of (210)Po. Appropriate conversion factors were used to derive the CED, which was found to be 0.012, 0.01 and 0.01 (microSv/yr) in carnivores, omnivores and herbivores, respectively, for (137)Cs. This contributes about 0.4% of the total dose exclusively by ingestion of fish. For (210)Po, it was found to be 3.47, 4.81 and 4.14 (microSv/yr) in carnivores, omnivores and herbivores, respectively, which represents 99.6% of the total dose (exclusively by ingestion of fish). The results of CED calculations suggest that the dose received by the Sudanese population from the consumption of marine fish is rather small and that the contribution of (137)Cs is negligible compared to (210)Po.

Selective Solvent-Assisted Linker Exchange (SALE) in a Series of Zeolitic Imidazolate Frameworks

Solvent-assisted linker exchange (SALE) has recently emerged as an attractive strategy for the synthesis of metal-organic frameworks (MOFs) that are unobtainable via traditional synthetic pathways. Herein we present the first example of selective SALE in which only the benzimiadazolate-containing linkers in a series of mixed-linker zeolitic imidazolate frameworks (ZIF-69, -78, and -76) are replaced. The resultant materials (SALEM-10, SALEM-10b, and SALEM-11, respectively) are isostructural to the parent framework and in each case contain trifluoromethyl moieties. We therefore evaluated each of these materials for their hydrophobicity in condensed and gas phases. We expect that selective SALE will significantly facilitate the design of improved, and potentially complex, MOF materials with new and unusual properties.

A computational study of the nonlinear optical properties of carbazole derivatives: theory refines experiment

Abstract The nonlinear optical (NLO) properties of N-ethyl dicyanocarbazole (1), N-ethyl cyanoethylacetatecarbazole (2), and N-ethyl dimethylacetatecarbazole (3) are studied with traditional hybrid and long-range corrected (LC) density functional theory (DFT) methods. The carbazoles are predicted to have planar structures with a high degree of π-conjugation and charge transfer, resulting in measurable NLO responses. The DFT data here calculated allow us to refine and correct previously reported experimental hyperpolarizabilities for these compounds. Experimental UV–vis absorption bands (related to hyperpolarizabilities estimated via solvatochromism) are also accurately reproduced by LC-DFT when using gap fitting schemes. The effects of different functionals on the HOMO–LUMO energy gaps and eventually on the total hyperpolarizabilities are discussed.

Nonlinear optical properties of DPO and DMPO: a theoretical and computational study

The gas phase properties of the Z- and E-isomers of 4-(p-N,N-dimethyl-aminophenylmethylene)-2-phenyl-5-oxazolone (DPO) and 4-(2,5-dimethoxyphenylmethylene)-2-phenyl-5-oxazolone (DMPO) are studied using traditional hybrid and long-range-corrected density functional theories (LC-DFT). Excellent agreement is found between the optimized molecular geometries and the experimental crystal structures. Our calculations predict both DPO and DMPO to have significant nonlinear optical (NLO) susceptibilities. These results are compared with data for the prototypical NLO chromophore p-nitroaniline, and the effect of the range separation parameter on LC-DFT hyperpolarizabilities is also analyzed.

A density functional theory investigation of the electronic structure and spin moments of magnetite

Abstract We present the results of density functional theory (DFT) calculations on magnetite, Fe3O4, which has been recently considered as electrode in the emerging field of organic spintronics. Given the nature of the potential applications, we evaluated the magnetite room-temperature cubic phase in terms of structural, electronic, and magnetic properties. We considered GGA (PBE), GGA + U (PBE + U), and range-separated hybrid (HSE06 and HSE(15%)) functionals. Calculations using HSE06 and HSE(15%) functionals underline the impact that inclusion of exact exchange has on the electronic structure. While the modulation of the band gap with exact exchange has been seen in numerous situations, the dramatic change in the valence band nature and states near the Fermi level has major implications for even a qualitative interpretation of the DFT results. We find that HSE06 leads to highly localized states below the Fermi level while HSE(15%) and PBE + U result in delocalized states around the Fermi level. The significant differences in local magnetic moments and atomic charges indicate that describing room-temperature bulk materials, surfaces and interfaces may require different functionals than their low-temperature counterparts.

Experimental and theoretical assignment of the vibrational spectra of triazoles and benzotriazoles. Identification of IR marker bands and electric response properties

The FTIR spectra of a series of 1H- and 2H- 1,2,3- and 1,2,4- triazoles and benzotriazoles were measured in the solid state. Assignments of the observed bands were facilitated by computation of the spectra using the density functional B3LYP method with the 6-311++G** basis set. The theoretical spectra show very good agreement with experiment. Rigorous normal coordinate analyses have been performed, and detailed vibrational assignment has been made on the basis of the calculated potential energy distributions. Several ambiguities and contradictions in the previously reported vibrational assignments have been clarified. “Marker bands” characterize the triazole ring were identified. The effect of substituents, the nature of the characteristic “marker bands” and quenching of intensities of some bands are discussed. Comparison of the topology of the charge density distribution, and the electric response properties of the 1H-, and 2H- isomers of both 1,2,3- and 1,2,4 triazole have been made using the quantum theory of atoms-in-molecules (QTAIM) by calculating the Laplacian of the electron density (∇2ρ(r)). Analysis of the contour plots and relief maps of ∇2ρ(r) reveals that 1,2,3- and 1,2,4-triazoles show completely different topological features for the distribution of the electron density. Thus, while the 1,2,3-isomer is a very polar molecule, the 1,2,4-isomer is much more polarizable. Bonding characteristics show also different features. This would thus underlie the different features of their vibrational spectra. The reported vibrational assignment can be used for further spectroscopic studies of new drugs and biological compounds containing the triazole ring.

Towards Understanding the Decomposition/Isomerism Channels of Stratospheric Bromine Species: Ab Initio and Quantum Topology Study

The present study aims at a fundamental understanding of bonding characteristics of the C–Br and O–Br bonds. The target molecular systems are the isomeric CH3OBr/BrCH2OH system and their decomposition products. Calculations of geometries and frequencies at different density functional theory (DFT) and Hartree–Fock/Møller–Plesset (HF/MP2) levels have been performed. Results have been assessed and evaluated against those obtained at the coupled cluster single-double (Triplet) (CCSD(T)) level of theory. The characteristics of the C–Br and O–Br bonds have been identified via analysis of the electrostatic potential, natural bond orbital (NBO), and quantum theory of atoms in molecules (QTAIM). Analysis of the electrostatic potential (ESP) maps enabled the quantitative characterization of the Br σ-holes. Its magnitude seems very sensitive to the environment and the charge accumulated in the adjacent centers. Some quantum topological parameters, namely ∇2ρ, ellipticity at bond critical points and the Laplacian bond order, were computed and discussed. The potential energy function for internal rotation has been computed and Fourier transformed to characterize the conformational preferences and origin of the barriers. NBO energetic components for rotation about the C–Br and O–Br bonds as a function of torsion angle have been computed and displayed.

Prediction of the linear and nonlinear optical properties of tetrahydronaphthalone derivatives via long-range corrected hybrid functionals

The linear and nonlinear optical (NLO) properties of methoxybenzylidene (1) and thiophen-2-ylmethylidene (2) tetrahydronaphthalone derivatives are studied using long-range corrected density functional theory (LC-DFT). The calculated hyperpolarisabilities indicate that both compounds have measurable NLO properties (approximately one to two times the hyperpolarisability of p-nitroaniline). Charge-transfer indices and time-dependent DFT calculations suggest that the NLO properties are a result of a charge-transfer excitation, which is typical in conjugated donor–acceptor structures. The ultraviolet–visible spectra of 1 and 2 are also predicted using gap-fitting schemes, and these data are used to assess how accurately the hyperpolarisabilities of 1 and 2 could be estimated by the solvatochromic method.

Gas-Phase Thermal Tautomerization of Imidazole-Acetic Acid: Theoretical and Computational Investigations.

The gas-phase thermal tautomerization reaction between imidazole-4-acetic (I) and imidazole-5-acetic (II) acids was monitored using the traditional hybrid functional (B3LYP) and the long-range corrected functionals (CAM-B3LYP and ωB97XD) with 6-311++G** and aug-cc-pvdz basis sets. The roles of the long-range and dispersion corrections on their geometrical parameters, thermodynamic functions, kinetics, dipole moments, Highest Occupied Molecular Orbital–Lowest Unoccupied Molecular Orbital (HOMO–LUMO) energy gaps and total hyperpolarizability were investigated. All tested levels of theory predicted the preference of I over II by 0.750–0.877 kcal/mol. The origin of predilection of I is assigned to the H-bonding interaction (nN8→σ*O14–H15). This interaction stabilized I by 15.07 kcal/mol. The gas-phase interconversion between the two tautomers assumed a 1,2-proton shift mechanism, with two transition states (TS), TS1 and TS2, having energy barriers of 47.67–49.92 and 49.55–52.69 kcal/mol, respectively, and an sp3-type intermediate. A water-assisted 1,3-proton shift route brought the barrier height down to less than 20 kcal/mol in gas-phase and less than 12 kcal/mol in solution. The relatively high values of total hyperpolarizability of I compared to II were interpreted and discussed.

Optical properties and fluorescence quenching of carbazole containing (D–π–A) push–pull chromophores by silver nanoparticles: a detailed insight via an experimental and theoretical approach

(4Z)-4-[(9-Ethyl-9H-carbazol-3-yl)methylidene]-2-phenyl-1,3-oxazol-5(4H)-one (ECPO) was prepared by the one-pot multi-component reaction of 9-ethyl-9H-carbazole-3-carbaldehyde, hippuric acid, anhydrous sodium acetate and acetic anhydride under microwave irradiation. The structure of ECPO was confirmed by elemental analysis and spectral studies (1H and 13C NMR, FT-IR) and theoretically by Density Functional Theory (DFT). The experimental and simulated electronic absorption and fluorescence spectra of ECPO have been studied in solvents of different polarities. They are in good agreement with each other. The data were used to study solvatochromic properties such as excitation coefficient, Stokes shift, oscillator strength, transition dipole moment, and fluorescence quantum yield. The wavelength maxima showed red shifts with increasing solvent polarity from n-hexane to DMSO. ECPO undergoes solubilization in different micelles and may be used as a probe for determining the critical micelle concentration (CMC) of CTAB and SDS. The interaction of colloidal silver nanoparticles (AgNPs) with ECPO dye was studied in ethanol and ethylene glycol using steady state fluorescence quenching measurements. The Stern–Volmer quenching rate constant (Ksv) was calculated to be 5.28 × 107 M−1 and 3.48 × 107 M−1 in ethanol and ethylene glycol, respectively. ECPOs highly promising NLO character was complemented by NBO investigation.