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Theoretical study of photoreactions between oxidized pterins and molecular oxygen
摘要： Pterins are low molecular weight heterocyclic compounds that are widely distributed in living organisms, primarily in the form of reduced coenzyme forms. Oxidized pterins are present in the cells for the most part as oxidation products of tetrahydropterins and dihydropterins. Oxidized pterins are known to cause DNA photodamage under UV-irradiation. Photosensitization of oxidized pterins may cause oxidative stress in the human skin depigmentation disorder vitiligo. There have been made attempts to use oxidized pterins as sensitizers in photodynamic therapy (PDT) of cancer. The photoreactions between a set of six pterin compounds and molecular oxygen were explored using density functional theory, a time-dependent formalism for excited states (TD-DFT) and a continuum COSMO model to include the effects of H2O solvation. Both acid and base forms of pterins were taken into consideration. The computed singlet and triplet excitation energies are in agreement with the experimental data. We showed that compounds with the most electronegative lateral substituent (formyl, carboxyl) at C6 position have the highest value of both S0 and T1 state ionization potential. We conclude that pterin molecules do participate in photoreactions with molecular oxygen. Oxidized pterins are able to generate singlet oxygen and may also produce superoxide-anion radicals indirectly through autoionization reactions. Direct electron transfer reactions between pterins and oxygen were also studied.
关键词： TDDFT,DFT,Pterins,Singlet oxygen,Triplet states
更新于2025-09-23 15:23:52
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Synthesis, crystal structure, vibrational and optical properties of a new Bi(III) halide complex: (C9H13N2O2)2Bi2Cl8
摘要： A new Bi(III) halide complex, (C9H13N2O2)2Bi2Cl8, was successfully grown by slow evaporation method. The structure of this hybrid compound was determinated by single crystal X-ray diffraction and further characterized by IR and RAMAN spectra, UV-Visible, luminescence and DFT calculations. This compound crystallizes in the monoclinic system P21/n space group with the following lattice parameters: a = 10.2036 (4), b = 9.8723 (4), c = 14.5920 (6) ?, ? = 99.899 (4)°, V = 1448.01 (10) ?3 and Z =2. The crystal structure of this compound was solved by direct methods and refined to R = 0.038 (wR = 0.079), based on 4118 unique observed reflections. The crystal structure consists of a 1-(2-furoyl)piperazinium cation and discrete (0D) anion built up of edge-sharing bioctahedra which are linked by bifurcated N-H…Cl and N-H…O hydrogen bonds to build up the whole molecular packing. The optical properties of this compound were studied by UV–Vis, luminescence spectroscopy and by Time Dependent Density Functional Theory studies. The vibrational properties of this compound were investigated by Infrared and Raman spectroscopy and compared with the calculated ones. The nature and amount of contacts in the crystal packing were investigated by means the Hirshfeld surfaces. Ab-initio and DFT calculations were also performed on whole compound and on reduced model: bis(μ2-chloro)-diaqua-hexachloro-di-bismuth.
关键词： luminescence,X-Ray diffraction,Vibrational studies,Bismuthates,DFT calculations
更新于2025-09-23 15:23:52
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Investigations on the quantum chemical studies and physico-chemical properties of an opto-electronic material 1-Allyl-2-Aminopyridine-1-ium bromide
摘要： In the present work, the dual approach of quantum chemical studies and experimental characterizations of the title compound 1-Allyl-2-Aminopyridine-1-ium bromide (1A2APB) were carried out for the first time. The molecular geometry of 1A2APB was optimized by density functional theory (DFT) using B3LYP/6-311++G (d,p) basis set. The optimized geometric structural parameters were compared with the experimental findings and discussed. The dipole moment (μ) and first hyperpolarizability (β) were calculated to predict the NLO behavior. The frontier molecular orbital (FMO), molecular electrostatic potential (MESP), Mulliken atomic charge and thermodynamic properties were investigated to get a better insight of the molecular properties. Stability of the compound arising from hyper-conjugative interactions, intra-molecule re-hybridization and charge delocalization within the molecule were analyzed using NBO analysis. Further, 1A2APB was synthesized and good quality single crystals were grown by slow evaporation technique. Studies such as microanalysis and powder XRD were performed to ascertain material composition and phase respectively. The various characteristic functional groups were identified through FT-IR spectroscopic analyses. The NLO efficiency was measured to be about greater than 5 times that of standard KDP. Thermal behaviors were explored by the simultaneous TG/DTA-DSC thermograms. The UV–Vis–NIR spectral data and fluorescence spectrum were recorded to explore the optical transmission and emission properties respectively. The dielectric properties were evaluated as a function of frequency at various temperatures. The photoconducting nature was analyzed through photoconductivity measurement. The Vicker’s microhardness test was performed at room temperature from which the mechanical stability was analyzed through the classical Meyer’s relation.
关键词： Photoconductivity,Powder XRD analysis,DFT calculations,Organic materials,Non-linear optics,Crystal growth
更新于2025-09-23 15:23:52
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Using First-Principles Calculations in CALPHAD Models to Determine Carrier Concentration of the Binary PbSe Semiconductor
摘要： PbSe is a promising thermoelectric that can be further improved by nanostructuring, band engineering, and carrier concentration tuning; therefore, a firm understanding of the defects in PbSe is necessary. The formation energies of point defects in PbSe are computed via first-principles calculations under the dilute-limit approximation. We find that under Pb-rich conditions, PbSe is an n-type semiconductor dominated by doubly-charged Se vacancies. Conversely, under Se-rich conditions, PbSe is a p-type semiconductor dominated by doubly-charged Pb vacancies. Both of these results agree with previously performed experiments. Temperature- and chemical potential-dependent Fermi levels and carrier concentrations are found by enforcing the condition of charge neutrality across all charged atomic and electronic states in the system. The first-principles-predicted charge-carrier concentration is in qualitative agreement with experiment, but slightly varies in the magnitude of carriers. To better describe the experimental data, a CALPHAD assessment of PbSe is performed. Parameters determined via first-principles calculations are used as inputs to a five-sublattice CALPHAD model that was developed explicitly for binary semiconductors. This five sublattice model is in contrast to previous work which treated PbSe as a stoichiometric compound. The current treatment allows for experimental carrier concentrations to be accurately described within the CALPHAD formalism. In addition to the five-sublattice model, a two-sublattice model is also developed for use in multicomponent databases. Both models show excellent agreement with the experimental data and close agreement with first-principles calculations. These CALPHAD models can be used to determine processing parameters that will result in an optimized carrier concentration and peak zT value.
关键词： CALPHAD,first-principles,DFT,defect chemistry,Thermoelectrics
更新于2025-09-23 15:23:52
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Theoretical studies on the mechanical and electronic properties of 2D and 3D structures of Beryllium-Oxide graphene and graphene nanobud
摘要： In the present study, ab initio-based density functional theory (DFT) calculations were used to determine the effects of certain phenomena that can occur in the synthesis of Beryllium-Oxide (BeO) few-layer sheets, such as various types of defects, attaching nanocages onto the surface of graphene and attaching layers to each side of it on the mechanical and electronic properties of BeO graphene sheets. We also used the density of states (DOS) calculations to obtain a better understanding of the electronic properties of the studied nanostructures. In the first step, we calculated Young’s modulus for the pristine BeO graphene sheet that was found to be equal to 1.110 TPa. Next, the effect of small and large defects on the mechanical properties of the BeO graphene-like structure was examined, and we found that extracting one Be atom resulted in a lower Young’s modulus compared to that obtained after extracting one oxygen atom (1.087 TPa versus 1.104 TPa), demonstrating that Be had a greater effect on the stability and mechanical strength of BeO graphene than did oxygen. The same trend was found when comparing three atom vacancies with two missing Be atoms to those with two missing oxygen atoms. Furthermore, the effect of circular and rectangular shape defects was investigated, and the obtained results demonstrated that the increase in the diameter of defects with both shapes significantly decreased Young’s modulus and band gap energy values. Additionally, due to the number of detached atoms in shape defects which are more than those of small defects, this type of defect had a more destructive effect on the structure’s stability so that it decreased the Young’s modulus more than small defects. Moreover, the mechanical properties of the BeO graphene nanobud structure were determined in terms of placing different numbers of Be12O12 nanocages onto the graphene surface, and a similar decreasing trend was observed for Young’s modulus. Finally, we considered the mechanical properties of the bi- and three-layer BeO graphene-like structures and found that increasing the number of layers reduced Young’s modulus slightly. For both of the latter phenomena of attaching nanocages and layers, the band gap energy decreased.
关键词： BeO Graphene,Multi-layer,DFT,Defect,Young’s Modulus,Graphene Nanobud
更新于2025-09-23 15:23:52
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Effect of acceptor moieties on static and dynamic first hyperpolarizability of azobenzene chromophores
摘要： The effect of acceptor on static and dynamic first hyperpolarizability, β, of trans- and cis-isomers of azochromophores AAB-DCV and AAB-TCV is studied. Calculations were performed by MP2 and DFT with three density functionals: M06-2X, CAM-B3LYP and ωB97X-D in gas phase and chloroform. Dynamic first hyperpolarizabilities were calculated by TD-DFT at 1.165 and 0.65 eV. The first hyperpolarizability values for trans-isomers are approximately three times greater than those for cis-isomer; solvent effect is essential comprising 2.7 and 3.2 times growth for static values for AAB-DCV and AAB-TCV, respectively, the corresponding dynamic estimations for βtot(2ω) being slightly smaller (2.2 and 2.6 times).
关键词： Dynamic characteristics,MP2,Azochromophore,Solvent effect,Acceptor effect,First hyperpolarizability,Density functional theory,TD-DFT
更新于2025-09-23 15:23:52
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New Coumarin-benzoxazole derivatives: Synthesis, photophysical and NLO properties
摘要： In this work, a series of novel D-π-A structure coumarin-benzoxazole derivatives have been synthesized. The third-order NLO properties of the coumarin derivatives in DMSO are investigated by Z-scan measurement, and the photophysical properties of the compounds are studied through experimental and theoretical calculation methods. The results showed that the introducing specific functional groups at multiple active sites of coumarin reduced the π-π intermolecular stacking, while the formation of push-pull structure decreased E-gap of entire molecule. The excellent third-order NLO responses based on chromophore 4c with maximum nonlinear absorptive coefficients is 50.64 × 10-13 esu and the largest second-order NLO hyperpolarizability is 7.12 × 10-30 esu. Experimental results have also been confirmed through DFT, TDDFT and ZINDO calculations. Our results indicate that the coumarin fluorescent dyes are promising candidate materials for NLO applications.
关键词： ZINDO calculation,DFT,Fluorescent,Third-order nonlinear,Coumarin derivatives
更新于2025-09-23 15:23:52
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Synthesis, characterization and DFT analysis of new phthalocyanine complexes containing sulfur rich substituents
摘要： Nine new tetrasubstituted metallophthalocyanines (MPc) bearing sulfur rich substituents on peripheral positions were synthesized and fully characterized. The new MPc compounds contain Co2+, Ni2+ and Cu2+. The photochemical and electrochemical properties of the new molecules were investigated. In addition to this investigation, a comparative study took place on the effect of the type of terminal ligand on properties of the MPc compound. Theoretical studies (DFT) were, also carried out in order to support the corresponding experimental results.
关键词： Cobalt,Copper,Nickel,Microwave synthesis,Phthalocyanines,DFT calculations
更新于2025-09-23 15:23:52
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A triple alkoxo bridged dinuclear cobalt(III) complex mimicking phosphatase and showing ability to degrade organic dye contaminants by photocatalysis
摘要： A dinuclear cobalt(III) complex, [(N3)L1CoIIIL2CoIIIL1] (1), has been synthesized and characterized {H2L1 = 2-((1-hydroxybutan-2-ylimino)methyl)-4-bromophenol and HL2 = 2-amino-1-butanol}. Single crystal X-ray diffraction analysis confirmed its structure. Extended supra-molecular architectures were generated in the complex through weak noncovalent interactions. The energetic features of significant supramolecular interactions have been investigated using DFT calculation and further corroborated with NCI plot index computational tool. The complex has been found to mimic the role of phosphatase enzyme efficiently by transforming 4-nitrophenylphosphate to 4-nitrophenolate at room temperature. The reaction follows Michaelis–Menten enzymatic reaction kinetics with turnover numbers of ~1.4 s-1 in aqueous DMF (98% DMF, v/v) medium. The complex also acts as an efficient photocatalyst for degradation of organic pollutants. Methylene blue (MB), a widely used dye in various industries, was selected as a model pollutant in aqueous media to evaluate the photocatalytic effectiveness of the complex.
关键词： DFT calculation,phosphatase mimicking activity,Photocatalytic degradation of methylene blue (MB),Cobalt(III),Crystal structure
更新于2025-09-23 15:23:52
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H-complexes in the “4-n-alkoxybenzoic acid: 4-pyridyl 4′-n-alkoxybenzoate” system. IR spectroscopy and quantum chemical calculations
摘要： IR spectra of individual 4-n-dodecyloxybenzoic acid (A) and 4-pyridyl 4'-n-dodecyloxybenzoate (B) compounds as well as IR spectra of 2A:1B and 1A:1B systems were recorded. For the assignment of the experimental vibrational spectra a series of quantum chemical calculations of DFT(B97-D)/6-311++G** level was carried out. Hydrogen-bonded complexes of types A···A, A···B, as well as various trimers that can be formed at different component ratios in system A-B were simulated. The geometric structure of these complexes was optimized and the vibrational frequencies were calculated. The conclusions on the molecular organization of system A-B for different ratios of the components A and B were based on the interpretation of IR spectra and the analysis of calculated thermodynamic characteristics of self-assembly processes. Thus, it is determined that the system A consists of cyclic A···Acycl dimers; in 1A:1B system the H-complexes of A···B type are formed. In the 2A:1B system in the process of self-assembly, instead of the complexes A···A···B and A···B···A of stoichiometric composition, the complexes A···B and A···Acycl are formed in the ratio 2:1. These results are confirmed by the dilatometric method data.
关键词： thermodynamic characteristics,4-pyridyl 4'-n-alkoxybenzoate,DFT,IR spectra,self-assembly,4-n-alkoxybenzoic acid,hydrogen bonded complexes
更新于2025-09-23 15:23:52