Chemistry

Single phased, polycrystalline mixed metal
oxides, La1-xSrxFeO3- (x = 0.0, 0.2, 0.3, 0.5) have been prepared
via the thermal decomposition of mixed metal acetylacetonate
precursors. The precursors were synthesized at 55 °C by
coprecipitation and decomposed at 450 oC to give multi-phased
lanthanum strontium ferrite nanoparticles which were further
calcined at 1000 oC to obtain the single-phased perovskite
ferrites. The decomposition temperature of the precursors was
determined by thermogravimetric analysis (TGA). The
perovskite ferrites were then characterized by X-ray diffraction
(XRD), scanning electron microscopy (SEM) and energy
dispersive spectroscopy (EDS). SEM and XRD analyses showed
that the particles of the ferrites were spherical and nano-sized
with structures ranging from orthorhombic to rhombohedral as
the Sr content increased. For x = 0.0, 0.2, and 0.3
(orthorhombic), the average FeO bond length and the unit cell
volume decreased with increasing Sr content.
Magnetic properties were investigated at room temperature
(27 °C) using a vibrating sample magnetometer and the
hysteresis loops showed that all the compositions exhibit antiferromagnetic ordering with a weak ferromagnetic interaction
related to their structures. Increasing coercive fields were also
observed with increasing Sr content.

The chelating ability of juglone and two of its derivatives towards Fe2+ion and the antioxidant activity (AOA) of the resulting chelates and complexes (in the presence of H2O and CH3OH as ligands) in gas phase is reported via bond dissociation enthalpy, ionization potential, proton dissociation enthalpy, proton affinity, and electron transfer enthalpy. The DFT/B3LYP level of theory associated with the 6-31+G(d,p) and 6-31G(d) Pople-style basis sets on the atoms of the ligands and the central Fe(II), respectively, was used. Negative chelation free energies obtained revealed that juglone derivatives possessing the O-H substituent (L2) have the greatest ability to chelate Fe2+ion. Apart from1B, thermodynamic descriptors of the AOA showed that the direct hydrogen atom transfer is the preferred mechanism of the studied molecules. NBO analysis showed that the Fe-ligand bonds are all formed through metal to ligand charge transfer. QTAIM studies revealed that among all the Fe-ligand bonds, ...

The sensitivity of pure and doped X 12 N 12 (X = B and Al) fullerene-like nano-cages (FLNs) toward the anti-cancer drug temozolomide (TMZ) is probed herein at DFT/M06-2X-D3/6-311G(d,p) theoretical level in both gas phase and water. A noticeable affinity of the FLNs toward TMZ was observed along with the negative gas-phase adsorption energies −1.37 and −2.09 eV for the most stable configurations of pure B 12 N 12 and Al 12 N 12 pristines, respectively. Considerable charge transfer from TMZ to the FLNs was also revealed via NBO analysis and the Hirshfeld atomic charges, making the dipole moment vector of the molecular complexes to be oriented from the nano-cages to the TMZ moiety. Furthermore, a percentage decrease in the HOMO-LUMO energy gap (Δ E g ) of 38.09 and 17.72% was obtained for the B 12 N 12 and Al 12 N 12 nano-cages, respectively. The percentage change in Δ E g was found to be reduced upon doping and solvation of the FLNs. Finally, a recovery time in vacuum ultraviolet ligh...

Herein is presented a density functional theory (DFT) study of reactivity and structural properties of transition metal complexes of the Schiff base ligand 2,2′(1E,1′E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(phenylmethan-1-yl-1-ylidene)dibenzoic acid (hereafter denoted EDA2BB) with Cu(II), Mn(II), Ni(II), and Co(II). The quantum theory of atoms-in-molecules (QTAIM), conceptual DFT, natural population analysis (NPA), and molecular electrostatic potential (MEP) methods have been used. Results have revealed a distorted octahedral geometry around the central metal ion in each gas phase complex. In the DMSO solvent, a general axial elongation of metal-oxygen bonds involving ancillary water ligands has been observed, suggestive of loosely bound water molecules to the central metal ion that may be acting as solvent molecules. Weak, medium, and strong intramolecular hydrogen bonds along with hydrogen-hydrogen and van der Waals interactions have been elucidated in the complexes investi...

The emergence of artemisinin-resistant variants of Plasmodium falciparum necessitates the urgent search for novel antimalarial drugs. In this regard, an in silico study to screen antimalarial drug candidates from a series of benzimidazolethiosemicarbazone hybrid molecules with interesting antiplasmodial properties and explore their falcipain-2 (FP2) inhibitory potentials has been undertaken herein. FP2 is a key cysteine protease that degrades hemoglobin in Plasmodium falciparum and is an important biomolecular target in the development of antimalarial drugs. Pharmacokinetic properties, ADMET profiles, MM/GBSA-based binding free energies, reaction mechanisms, and associated barrier heights have been investigated. DFT, molecular dynamics simulation, molecular docking, and ONIOM methods were used. From the results obtained, four 4 N-substituted derivatives of the hybrid molecule (E)-2-(1-(5-chloro-1H-benzo[d]imidazol-2-yl)ethylidene)hydrazine-1-carbothioamide (1A) denoted 1B, 1C, 1D, and 1E are drug-like and promising inhibitors of FP2, exhibiting remarkably small inhibitory constants (5.94 × 10-14 − 2.59 × 10-04 n M) and favorable binding free energies (−30.32 to −17.17 kcal/mol). Moreover, the ONIOM results have revealed that 1B and possibly 1C and 1D may act as covalent inhibitors of FP2. The rate-determining step of the thermodynamically favorable covalent binding mechanism occurs across a surmountable barrier height of 24.18 kcal/mol in water and 28.42 kcal/mol in diethyl ether. Our findings are useful for further experimental investigations on the antimalarial activities of the hybrid molecules studied.

Ground state geometries, spectral (IR and UV-Vis) properties, analysis of frontier molecular orbitals (FMOs), natural bond orbital (NBO) analysis and molecular electrostatic potential (MEP) surfaces of three transition metal complexes [Cu(AOYP)2(OH2)2] (A), [Ni(AOYP)2(OH2)2] (B) and [Zn-(AOYP)2(OH2)2] (C), have been studied theoretically by the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) methods. AOYP is the oxadiazole ligand 2-(5-amino-[1,3,4]-oxadiazol-2-yl)phenol. The geometries of these complexes were initially optimized using two basis sets: LAN2DZ and a generic basis set, the latter of which was selected for subsequent analysis. The stability of the complexes arising from intramolecular interactions and electron delocalization was estimated by natural bond orbital (NBO) analysis. The NBO results showed significant charge transfer from lone pair orbitals on the AOYP donor atoms O19, O21, N15 and N36 to central metal ions in the complexes, as well as to the benzene and oxadiazole rings. The electronic spectrum of (A) showed bands at 752 and 550 nm mainly attributable to ligand-tometal charge transfer (LMCT) transitions, and a band at 446 nm assigned to a d-d transition. The electronic spectrum of (B) consisted of bands at 540, 463 and 395 nm mainly due to d-d transitions. Calculated electronic bands for (C) occurred at 243, 238 and 235 nm, arising from intraligand charge transfer (ILCT) transitions within AOYP. A good agreement in terms of band positions was found between experimental and calculated absorption spectra of the complexes.

Recent studies have shown that 4-methoxyacetophenone thiosemicarbazone (MAPTSC) and its complexes with some transition metal chlorides are potent antimicrobial agents. To deepen the understanding of their structure-activity relationships necessary for rational drug design, their structural and spectral properties, along with thione-thiol tautomerism of MAPTSC, have been studied herein using the density functional theory (DFT). From our results, the thione tautomer of MAPTSC is more stable than the thiol counterpart in ethanolic solution, and thione-to-thiol tautomerization is highly precluded at ambient temperature (25°C) by a high barrier height ≈46.41 kcal/mol. MAPTSC can therefore exist as a mixture of the thione (major) and thiol (minor) tautomers in ethanolic solution at room and higher temperatures. Conformational analysis has revealed five possible conformers of the thione tautomer, of which two are stable enough to be isolated at 25°C. Based on our computed values of MAPTSC-...

Nonlinear optical (NLO) properties of organic and metal-organic materials are of considerable interest to emerging optoelectronic and photonic technologies. Much work has been carried out on the former materials but the latter ones have received less attention till date. Herein, a density functional theory (DFT) study on the combined effects of transition metal chelation and solvent polarity on the first hyperpolarizability (βtot) of 4-methoxyacetophenone thiosemicarbazone (MAPTSC) is reported. MAPTSC exhibits a tautomeric form with higher optical nonlinearity rendering its NLO response in polar solvents potentially switchable. Our results have revealed significant modifications of the first hyperpolarizability of MAPTSC upon complexation with different transition metal chlorides in the presence of solvents with varying dielectric constants. Therefore, its second-order NLO response is highly tunable by the synergy of transition metal chelation and solvent polarity. MAPTSC and its Zn...

The chelation ability of divalent Mg, Ca, Fe, Co, Ni, Cu, Zn, and monovalent Cu ions by neutral and anionic forms of juglone has been investigated at DFT/B3LYP/6-31+G(d,p) level of theory in gas and aqueous phases. It is noteworthy that only the 1 : 1 stoichiometry was considered herein. The effects of these metals on the radical scavenging activity of neutral juglone were evaluated via the usual descriptors of hydrogen atom transfer. According to our results, metal chelation by the two forms of juglone was spontaneous and exothermic in both media. Based on the binding energies, Cu(II) ion showed the highest affinity for the ligands. QTAIM analyses identified the metal-ligand bonds as intermediate type interactions in all the chelates, except those of Ca and Mg. It was also found that the chelates were better radical scavengers than the ligands. In the gas phase, the scavenging activity of the compounds was found to be governed by direct hydrogen atom transfer, the Co(II) chelate be...

Thiosemicarbazones (TSCs) possess significant antimalarial properties believed to be linked to the inhibition of major cysteine proteases, such as falcipain-2, in Plasmodium falciparum. However, the binding modes of TSCs to the active site of these enzymes are not clear. As a result of this, the nature of the bonding interactions between the active site of falcipain-2 and different derivatives of acetophenone thiosemicarbazone (APTSC) and propiophenone thiosemicarbazone (PPTSC) acting as inhibitors, have been studied herein via topological analyses of electron density. Derivatives of APTSC and PPTSC are well known to possess inhibitory effects against Plasmodium falciparum. Equilibrium geometries of the inhibitor–active site complexes in the aqueous phase have been obtained via dispersion-corrected density functional theory (DFT-D3) calculations. In-depth analyses of the covalent and noncovalent interactions in these complexes have been performed using the quantum theory of atoms in...

This work reports on the density functional theory (DFT) and its time-dependent extension (TD-DFT) study of the structural, electronic, and charge transport properties of 2-(5-mercapto-1,3,4-oxadiazol-2-yl) phenol (MODP) and some of its transition M2+ complexes (M = Fe, Co, Cu, Ni, Zn, Pd, Pt). Reorganization energy, integral charge transfer, mobility, open circuit voltage, and electronic properties of these compounds have been calculated by employing the global hybrid functional PBE0 in conjunction with the Karlsruhe basis set def2-TZVP. Results show that MODP and its transition metal complexes are good electron donors for organic solar cells (OSC) owing to their relatively higher HOMO and LUMO energies compared to the prototypical (6, 6)-phenyl-C61-butyric acid methyl ester (PCBM). Energy gaps ranging between 2.502 and 4.455 eV, energy driving forces (∆EL-L) ranging between 2.08 and 2.44 eV, and large open circuit voltages ( V OC ) ranging from 1.12 to 2.05 eV were obtained. The r...

The nonlinear optical (NLO) properties of ethyl 4-[( E )-(2-hydroxy-4-methoxyphenyl)methyleneamino]benzoate (EMAB) and some of its derivatives are investigated herein using the density functional theory (DFT) and time-dependent (TD)-DFT methods. The density functionals B3LYP, CAM-B3LYP, M06-2X and ω B97XD, and basis sets 6-31 + G**, 6-311 + + G** and Def2-TZVPP have been used. From the results, EMAB and its substituted derivatives studied are promising candidates for NLO materials. In all cases, the static first and second hyperpolarizabilities (31.7–86.5 × 10 −30 and 84.4–273 × 10 −36 electrostatic units (esu), respectively) and the frequency-dependent NLO properties are found to be significantly larger (about 43–103 and 28–76 times greater) than those of the NLO prototypical molecule, para -nitroaniline. Furthermore, the maximum absorption wavelengths of the molecules fall within the UV region of the electromagnetic spectrum. Relative to EMAB, the derivatives have shown improved t...

This study reports the nonlinear optical (NLO) properties of the exohedral adsorption of N-(4-methoxybenzylidene) isonicotinohydrazone (INH) onto B12N12 and Al12N12 nanocages. All ground state computations were performed using the density functional theory (DFT) method at the B3LYP-D3/6-311G(d,p) level of theory in the gaseous phase. Excited state computations were achieved via the time-dependent density functional theory (TD-DFT) at the CAM-B3LYP/6-311G(d,p) level of theory. Molecular electrostatic potential (MEP) analysis of INH reveals the presence of three preferential interaction sites: the O-atom of carbonyl (site 1), the N-atom of pyridine (site 2), and the N-atom of the azomethine group (site 3). The highest interaction energy values for the adsorption of INH onto the B12N12 and Al12N12 were −43.560 and −52.724 kcal·mol−1, respectively, indicating a chemisorption process. The computed Gibbs free energy change (ΔGad) and adsorption enthalpy change (ΔHad) values for all comple...

This study examines the adsorptive removal of cadmium from aqueous solutions using chemically modified avocado seed activated carbon (ASAC). The prepared adsorbent was characterized using FTIR, Boehm titration, iodine number, pHpzc, proximate analysis and surface area, respectively. A two-level, four-factor central composite design (CCD) in response surface methodology (RSM) was utilized to optimize the effect of the four process variables namely initial concentration (100-200 mgL-1), adsorbent dosage (0.10-1.0 g), pH (3-8) and contact time (10-180 min) on cadmium removal from aqueous solution. Based on the design, a total of 30 adsorption experiments were performed and a quadratic model was developed linking the process factors to the response. Analysis of variance (ANOVA) was applied to assess the adequacy of the model. From the analysis, the model's coefficient of determination (R 2) of 0.9730 and F-value of 38.55 are indicative that the model is adequate and can be used to navigate the design space. The optimum conditions of initial concentration (200 mgL-1), adsorbent dose (0.1 g), pH (3.37) and contact time (100 min) were obtained from the desirability function. The adsorption equilibrium data were best described by the Jovanovic model. Finally, the pseudo second order kinetic model described the cadmium adsorption process best.

Raffia Palm (Raphia Hookeri) fruit epicarp biomass waste was used for the preparation of activated carbon by chemical activation using ZnCl2. The surface characteristics of the adsorbent were determined by Fourier transform infrared spectroscopy, Boehm titration, iodine number and bulk density. Later on, the Raphia hookeri fruit epicarp activated carbon (RHFE-AC) was employed for Direct Red 81 (DR81) dye colour removal from aqueous solutions. The experiment made up of 15 runs was setup with the help of Box-Behnken design to modelled and optimized the effects of the primary operating parameters such as adsorbent dosage (0.1-2 g), solution pH (2-10), and contact time (10-60 min), while the initial DR81 dye concentration was fixed at 100 mg/L. Analysis of variance showed that the suggested quadratic model successfully explained the experimental data with a correlation coefficient of R 2 =0.9997 and adjusted R 2 =0.9993. The optimum pH, contact time, and adsorbent dosage were determined to be 2, 60 min, and 1.73 g respectively. The predicted % removal acquired from the RSM under optimal conditions was 78.82%. A confirmatory test of the optimal conditions supported the validity of the model yielding a % removal of 80.21%. The adsorption equilibrium data were best described by the Langmuir isotherm with R 2 =0.96584 and the pseudo-second order kinetic model fitted the experimental data best. The study showed the pertinence of RHFE-AC utilized in batch mode for the removal of dyes.

Activated carbon from avocado (Persea Americana) seeds, obtained by chemical activation using H 3 PO 4 acid i.e. avocado seed activated carbon (ASAC) was used for the removal of phenol from aqueous solution. Samples were characterized by FTIR, Boehm, pHpzc, iodine number, surface area, and proximate analysis. Batch adsorption studies were performed in order to evaluate the maximum adsorption capacity of phenol by ASAC at 27 o C. optimal conditions from equilibrium studies stood at: adsorbent dose of 1g, pH of 7 and contact time of 120 min for all the different initial concentrations of adsorbate used. The Langmuir isotherm model best represented the equilibrium data with monolayer adsorption capacities of 7.94 mg/g, 15.36 mg/g, and 19.79 mg/g respectively for 100ppm, 200ppm, and 300ppm initial adsorbate concentrations. Kinetic studies revealed that the adsorption process followed a pseudo-second order model and the mechanism of the sorption process is controlled by film diffusion of the adsorbate into the adsorbent. In order to examine the main factors (pH, adsorbent dosage and contact time) and their interactions for the uptake of phenol, a 2 3 full factorial design was used. The optimization of factors to obtain maximum adsorption was carried out by using main factors and their interactions, normal probability plot, Analysis of Variance (ANOVA) and Pareto chart.

Activated carbons from raphia hookeri fruit epicarps obtained by chemical activation using ZnCl 2 (CAZn), H 3 PO 4 (CAH) and KOH (CAK) were utilized for the removal of lead (II) ion from aqueous solution. Samples were characterized by FTIR, Boehm method, pHpzc, iodine number, bulk density and surface area. Batch adsorption experiments were performed to study the effects of contact time, solution pH, adsorbent mass and initial adsorbate concentration at 27 o C. Optimal conditions from equilibrium studies were as follows: contact times of 80 minutes for CAZn and CAH and 100 minutes for CAK, pH = 6 for all samples, adsorption capacities of 66.37 mg/g for CAZn, 56.30 mg/g for CAH and 28.0 for CAK. Adsorption was modeled using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. Equilibrium data were best represented by Langmuir isotherm model with monolayer adsorption capacities of 72.62 mg/g, 58.62 mg/g and 12.16 mg/g for CAZn, CAH and CAK respectively. Adsorption kinetics was via pseudo-first order, pseudo-second order, Elovich and intra-particle diffusion models. Kinetic studies revealed that the adsorption process followed pseudo-second order model. Raphia hookeri based activated carbons (CAZn and CAH) are shown to be promising materials for the adsorption of lead(II) ions from aqueous solutions.

This study examines the adsorptive removal of cadmium from aqueous solutions using chemically modified avocado seed activated carbon (ASAC). The prepared adsorbent was characterized using FTIR, Boehm titration, iodine number, pHpzc, proximate analysis and surface area, respectively. A two-level, four-factor central composite design (CCD) in response surface methodology (RSM) was utilized to optimize the effect of the four process variables namely initial concentration (100-200 mgL-1), adsorbent dosage (0.10-1.0 g), pH (3-8) and contact time (10-180 min) on cadmium removal from aqueous solution. Based on the design, a total of 30 adsorption experiments were performed and a quadratic model was developed linking the process factors to the response. Analysis of variance (ANOVA) was applied to assess the adequacy of the model. From the analysis, the model's coefficient of determination (R 2) of 0.9730 and F-value of 38.55 are indicative that the model is adequate and can be used to navigate the design space. The optimum conditions of initial concentration (200 mgL-1), adsorbent dose (0.1 g), pH (3.37) and contact time (100 min) were obtained from the desirability function. The adsorption equilibrium data were best described by the Jovanovic model. Finally, the pseudo second order kinetic model described the cadmium adsorption process best.

Two photocatalysts Pt, N co-doped TiO 2 (Pt-N-TiO 2) and Pt, N co-doped TiO 2 associated with Raphia Hooker epicarp activated carbon (Pt-N-TiO 2 /RHEAC) were synthesized via the sol-gel method. The as-prepared photocatalysts were characterized for their surface areas via the BET method, pore size distribution via the BJH method, and bandgap energy using diffuse reflectance spectroscopy. Both photocatalysts exhibited mesoporous structures with cylindrical pore structures having mean pore diameters of 27.86nm and 37.09nm and bandgap energies of 3.05eV and 2.83eV for Pt-N-TiO 2 and Pt-N-TiO 2 /RHEAC respectively. Taguchi design was employed for the optimization and modeling of the process parameters which were dye concentration, amount of catalyst, irradiation time, and pH. The photodegradation efficiencies of methylene blue removal by both catalysts were 77.58% and 83.38% for Pt-N-TiO 2 and Pt-N-TiO 2 /RHEAC respectively under optimum conditions. Furthermore, the mathematical models developed exhibited high correlation coefficients (R 2) of 96.23% and 97.38% for the photodegradation efficiencies by Pt-N-TiO 2 and Pt-N-TiO 2 /RHEAC respectively between the predicted and the experimental response characteristics. This was an indication that both models could be effectively utilized in predicting the response characteristics at the optimum process parameters level. The amount of catalyst and dye concentration were the only process parameters that contributed meaningfully to MB removal.

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.