A comparative study on the antioxidant properties of tetrahydrocurcuminoids and curcuminoids

Several curcuminoids and tetrahydrocurcuminoids (THCs), bearing various hydroxyl and/or methoxy groups on their benzene rings, have been synthesized to study their antioxidant and hydrogen donating capacities using the DPPH method at 25 °C in methanol. The results show that the tetrahydrocurcuminoids are in general much more efficient than their curcuminoid analogs if they include a phenol group in meta- or para-position of the linking chain and a neighboring phenol or methoxy group. This efficiency gain of THCs by comparison to curcuminoids was attributed to the presence of benzylic hydrogens involved in the oxidation process of these compounds and not to the beta-diketone moiety in the chain.     

A comparative study of phytochemical metabolites and antioxidant properties of Rhodiola

Rhodiola crenulata (RC) and Rhodiola fastigiata (RF) are representative species of Rhodiola with well-accepted health benefits; the roots are the medicinal part. However, prior to this study, the differences in phytochemicals between these two species and different parts of the same species remained unclear. Using LC-ESI-MS/MS, HS-SPME-GC–MS, chemical and sensory analyses, volatile compounds and non-volatile compounds, and antioxidant activities of the roots of Rhodiola crenulata and Rhodiola fastigiata and four parts (roots, leaves, flowers, and above-ground stems) of RC were investigated. The volatile compounds and non-volatile compounds of RC roots exhibited upregulation overall compared to those of RF roots, and the odorousness, phenolic content, and antioxidant activity were more pronounced in the RC roots. The phenolic content and antioxidant activity of roots and leaves, alongside the odorousness of roots and flowers, were more significant among the four parts of RC, and the RC roots and RC flowers exhibited similar odorousness. Comparison of non-volatile differential metabolites between RC roots and RC leaves showed upregulations of saccharides and phospholipids, and minor upregulations of flavonoids and phenylpropanoids in the roots; in addition, amino acids, organic acids, and vitamins were upregulated in the leaves. These results revealed the following: 1) RC roots are superior to RF roots regarding volatile compounds and non-volatile compounds, and antioxidant activity; 2) it is more favorable to select RC roots for exploiting volatile compounds compared with RC flowers in consideration of the biomass available; 3) in terms of non-volatile compounds, and antioxidant ability, RC leaves are also of great value in addition to RC roots, though these two parts show distinct characteristics.     

A comparative study of DFT and traditional ab initio methodologies on the OsO4 molecule

The performance of different conventional ab initio methodologies and density functional procedures is compared through its application to the theoretical calculation of the bond distance and harmonic vibrational frequencies of the OsO₄ molecule. The problem of the basis set is first considered, with up to nine different basis sets being tested in calculations using the hybrid Becke3LYP density functional, and the most appropriate basis set is used in the comparison of Hartree–Fock, post‐Hartree–Fock, and density functional methods. The post‐Hartree–Fock methods analyzed are MP2, CISD, and CCSD(T), and the density functionals tested are SVWN, BLYP, BPW91, and Becke3LYP. The results show that for this particular system density functional methods perform better than do HF‐based methods with the exception of CCSD(T), which gives the best overall results. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 544–551, 2000     

Methane and carbon dioxide adsorption on edge-functionalized graphene: A comparative DFT study

With a view towards optimizing gas storage and separation in crystalline and disordered nanoporous carbon-based materials, we use ab initio density functional theory calculations to explore the effect of chemical functionalization on gas binding to exposed edges within model carbon nanostructures. We test the geometry, energetics, and charge distribution of in-plane and out-of-plane binding of CO(2) and CH(4) to model zigzag graphene nanoribbons edge-functionalized with COOH, OH, NH(2), H(2)PO(3), NO(2), and CH(3). Although different choices for the exchange-correlation functional lead to a spread of values for the binding energy, trends across the functional groups are largely preserved for each choice, as are the final orientations of the adsorbed gas molecules. We find binding of CO(2) to exceed that of CH(4) by roughly a factor of two. However, the two gases follow very similar trends with changes in the attached functional group, despite different molecular symmetries. Our results indicate that the presence of NH(2), H(2)PO(3), NO(2), and COOH functional groups can significantly enhance gas binding, making the edges potentially viable binding sites in materials with high concentrations of edge carbons. To first order, in-plane binding strength correlates with the larger permanent and induced dipole moments on these groups. Implications for tailoring carbon structures for increased gas uptake and improved CO(2)/CH(4) selectivity are discussed.     

A comparative DFT study of tetracyanoquinodimethane and its difluoro and tetrafluoro analogs

The optimized molecular structures, harmonic vibrational wavenumbers and corresponding vibrational assignments, frontier molecular orbitals and UV data of 7,7,8,8-tetracyanoquinodimethane, 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane were computed using quantum mechanical code. Calculations were carried out at Becke-3-Lee-Yang-Parr (B3LYP) functional with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) using the 6–311++G (d,p) basis set. The theoretical results were successfully compared with some of the available experimental data. The influence of fluorine on the structural, vibrational and electronic properties were investigated. The addition of fluorine reduces both the electrical and optical band gaps. The findings of this research can be useful for analogs of the molecules studied which have potential applications in the design of organic semiconductors for electronic devise applications.     

Theoretical elucidation on the antioxidant mechanism of curcumin: a DFT study

[reaction: see text] Bond dissociation enthalpies (BDEs) for the curcumin-related compounds have been calculated using density functional theory (DFT) methods. It was found that the antioxidant mechanism of curcumin was a H-atom abstraction from the phenolic group, not from the central CH2 group in the heptadienone link. Curcumin, methylcurcumin, and half-curcumin had similar O-H BDEs, indicating that the two phenolic groups in curcumin were independent of each other.     

A comparative DFT study of substrates and products of industrial enzyme nitrile hydratase

Nitrile hydratase (NHase) is a metalloenzyme used in industrial biotechnology for a large scale production of common chemicals. NHases convert nitriles to the corresponding amides. Although the structures of some forms of NHases containing nonheme low spin Fe(III) or low spin noncorrinoid Co(III) are known, neither a catalytic mechanism nor the reasons of high selectivity towards aromatic ligands are recognized. Optimized geometries, molecular electrostatic potential maps and infrared spectra of commercially important aromatic substrates of the NHase (nicotinonitrile, o‐, m‐, p‐methylbenzonitrile) and the corresponding products (nicotinamide, o‐, m‐, p‐methylbenzamid) were investigated using the density functional theory method with the B3LYP functional and the 6‐31G(d,p) basis set. Calculated hypothetical intrinsic reaction paths indicate that benzimidic acids may be involved as intermediates. This study elucidates differences in the electronic properties of substrates and products of NHases, provides an insight into the molecular basis of the catalytic reaction and helps to explain varying enzymatic activities of microbial NHases. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

A comparative DFT study of oxygen reduction reaction on mononuclear and binuclear cobalt and iron phthalocyanines

The oxygen reduction reaction (ORR) catalyzed by mononuclear and planar binuclear cobalt (CoPc) and iron phthalocyanine (FePc) catalysts is investigated in detail by density functional theory (DFT) methods. The calculation results indicate that the ORR activity of Fe-based Pcs is much higher than that of Co-based Pcs, which is due to the fact that the former could catalyze 4e^- ORRs, while the latter could catalyze only 2e^- ORRs from O₂ to H₂O₂. The original high activities of Fe-based Pcs could be attributed to their high energy level of the highest occupied molecular orbital (HOMO), which could lead to the stronger adsorption energy between catalysts and ORR species. Nevertheless, the HOMO of Co-based Pcs is the ring orbital, not the 3d Co orbital, thereby inhibiting the electron transfer from metal to adsorbates. Furthermore, compared with mononuclear FePc, the planar binuclear FePc has more stable structure in acidic medium and more suitable adsorption energy of ORR species, making it a promising non-precious electrocatalyst for ORR.     

A comparative study of the optical properties of TbRhGe and DyRhGe

In this paper, experimental and theoretical optical properties of TbRhGe and DyRhGe have been reported and compared. Our measurements by the ellipsometric method in the wavelength range 0.22–15 μm revealed significant differences in energy positions of the interband peaks in the spectral functions of these ternary compounds. The electronic structure of TbRhGe and DyRhGe calculated within the LSDA + U method was used to obtain theoretical optical conductivity, which is in good agreement with the experimental one. Further analysis allowed us to track changes in interband transitions related to the rare-earth 4f and rhodium 4d states, which are responsible for the observed differences in optical properties of TbRhGe and DyRhGe compounds.     

用密度泛函理论研究多氯代菲醌的结构和热力学性质

使用Gaussian 03程序,采用密度泛函理论(DFT)在B3LYP/6-31G*水平上对136个多氯代9,10-菲醌(PCPQ)系列化合物进行全优化和振动分析,得到各分子在298.15K、101.3kPa状态下的优势构型.结合Gaussian 03程序的输出文件,计算了PCPQ化合物在200K至1 000K的摩尔恒压热容(Cp,m).用SPSS13.0对Cp,m与温度进行多元线性回归.结果表明:氯原子取代模式对PCPQ化合物的扭角A(C4-C9-C10-C5)有很大的影响;与此同时,Cp,m与T,T-1和T-2之间有着很好的相关性(r2=1.00).     

DFT study on electronic properties of single- and double-shell icosahedral fullerenes

Multi-shell fullerenes are widely studied for their interesting properties although comparative studies on single- and multi-shell structures remain scarce. In this work, important electronic features of single- and double-shell icosahedral fullerenes as a function of their sizes were calculated in the framework of the density functional theory. Fully optimized structures were used to get the gap between the highest occupied molecular and the lowest unoccupied molecular orbital (H-L gap), electronegativity, softness and density of the electronic states. This work shows that the H-L gap of the single-shell fullerenes decreases nonlinearly as the nanoparticles size increases, whereas for the double-shell fullerenes an opposite trend is obtained. A decrease of the H-L gap is found going from single- to double-shell fullerenes with similar external sizes, up to a diameter of 3.13 nm. The electron density of states revealed that isolated peaks give way to more dense electronic states for nanoparticles with diameters above 2 nm.     

Crystal structures and electronic properties of BaC_2 isomers by theoretical study based on DFT

Band structures and electronic properties of two BaC2 isomers were calculated by using density func-tional theory(DFT) properly.The ionic bond features are all typical between cation(Ba) and anion clusters(C2) in both structures of the isomers.However,a much stronger covalent bond exists in anion clusters which can be seen by inspecting the electron distribution contour that has a dull bell like shape between two carbon atoms.The shortest distance between Ba2 and C22? and the bond length in anion clusters are different in these isomers of BaC2,which are 0.2945 nm and 0.1185 nm for the structure with the I4/mmm space group and 0.2744 and 0.1136 nm with the C2/c type,respectively.Band structures were clarified by combining the DOS to indicate the ionic bonding features more clearly.Population analysis provided further evidence on these ideas.Thermodynamical calculation results reveal that the transition temperature of these two polymorphs of BaC2 locates near 132 K,which is consistent with the recent experimental results.     

Effect of substituents on the absorption properties of three pyridylindolizine derivatives: A DFT and TDDFT study

Ground state properties and the UV–Vis absorption spectra of three recently synthesized pyridylindolizine derivatives have been studied by using density functional theory (DFT) and its time-dependent counterpart TDDFT. Performances of the two widely used hybrid functionals, B3LYP and PBE0, and of four different basis sets have been compared. The two functionals yield absorption spectra which have very similar shapes and characteristics but the excitations calculated with PBE0 are obtained at slightly shorter wavelengths. Basis sets affect the appearances of the calculated absorption spectra only little. Independent of the solvent polarity, simulation of the solvent effects by COSMO induces only slight changes into the ground state properties compared to those calculated in the gas-phase and into the absorption spectra.     

DFT study on the structural and electronic properties of Pt-doped boron nitride nanotubes

First-principles calculations based on density functional theory were carried out to investigate the structural and electronic properties of Pt substitution-doped boron nitride (BN) nanotubes. The electronic and structural properties were studied for substituted Pt in the boron and the nitrogen sites of the (BN) nanotube. The band gap significantly diminishes to 2.095 eV for Pt doping at the B site while the band gap diminishes to 2.231 eV for Pt doping at the N site. The band density increases in both the valence band and the conduction band after doping. The effects of the hardness and softness group 17 (halogen elements) were calculated by density functional theory (DFT).     

DFT study on the effects of substituents on the structure and properties of dithiophosphate collectors

The structures and properties of seven substituted dithiophosphate (DTP) collectors containing three types of functional groups (O₂PS₂, C₂PS₂, and N₂PS₂) were studied using density functional theory. The collectors studied were dibutyl dithiophosphate (DNBDTP), diisobutyl dithiophosphate (DIBDTP), dibutoxyethyl dithiophosphate (DBOEDTP), xylenol dithiophosphate (DMPDTP), diisobutyl dithiohypophosphite (3418A), diphenylamine dithiophosphate (DTADTP), and dicyclohexylamine dithiophosphate (DCADTP). The structural analysis showed that the P S bond lengths in the C₂PS₂ and N₂PS₂ types are longer than those in the O₂PS₂ type, indicating that the strength of the P S bond is weaker in the former two. The frontier molecular orbital studies showed that the energy differences between the highest occupied molecular orbitals (HOMO) of 3418A (C₂PS₂ type) and DCADTP (N₂PS₂ type) and the lowest unoccupied molecular orbital (LUMO) of galena are significantly lower than those of the other collectors, suggesting that C₂PS₂ type and N₂PS₂ type with cyclohexane could enhance the interaction with galena. Using the Fukui function to calculate the nucleophilicity and electrophilicity of the sulfur atom indicated that the S atom exhibits nucleophilicity, especially in DMPDTP and DTADTP, which contain benzene rings, and the S atom exhibits strong nucleophilicity without electrophilicity. However, due to the lack of contribution from S atoms to the LUMO orbitals, the S atoms in these two compounds are not participate in any LUMO reactions. The adsorption results demonstrated that 3418A (C₂PS₂ type) and DCADTP (N₂PS₂ type) exhibit the strongest adsorption on Pb²⁺ ions, while DMPDTP (C₂PS₂ type) and DTADTP (O₂PS₂ type) which contain benzene rings, as well as DBOEDTP (C₂PS₂ type) which does not contain a benzene ring, exhibit weaker interaction compared to the other compounds. These are consistent with the results of the frontier molecular orbital and electrophilic nucleophilicity calculations.     

DFT study of conformational and spectroscopic properties of yatakemycin

Molecular structure and conformational preferences of yatakemycin, a novel and exceptionally potent antitumor agent, have been investigated using the density functional theory (DFT) formalism. From the relative stability of various possible conformations, it is found that two conformers are nearly isoenergetic and markedly more stable than the others in the gas phase. To test the effect of polar mediums, the relative energies have been recalculated using the self-consistent reaction field method. Thus, the most stable conformer of the isolated molecule in the gas phase is expected to be still more preferred in solution. The molecular structure of yatakemycin has also been studied by means of its spectroscopic properties. The DFT results satisfactorily reproduce the experimental data and corroborate the reliability of the structural characterization advanced for yatakemycin. The lowest-energy electronic transitions have been interpreted with time-dependent DFT calculations. Notably, the strong IR band observed at 2852 cm(-1) is unambiguously assigned to the O-H stretching of the (C7)O-H...O(C12) fragment, linked by a strong intramolecular H-bond, and may be viewed as a distinctive fingerprint of yatakemycin. Furthermore, the calculated set of NMR chemical shifts of carbonyl carbon atoms and indole protons, the most sensitive to stereoelectronic factors, is consistent with experiment. The effects of both protonation and oxidation on the geometry of the most stable conformer have also been studied. With reference to yatakemycin's DNA alkylation properties, the structure of the yatakemycin-adenine adduct has been theoretically modeled and found to be consistent with experimental spectroscopic evidence.     

A comparative study on the preparation methods and properties of coal-based fluorescent carbon nanoparticles

Fluorescent carbon nanoparticles (FCNPs) have broad application prospects in the fields of bioimaging, ion detection, and photocatalysis. In this paper, coal-based FCNPs were prepared by using mixed acid oxidation, hydrogen peroxide etching, and organic solvent extraction methods (marked as FCNPs-AO, FCNPs-HE, and FCNPs-OS, respectively), and the structures and properties of the as-prepared products were compared. It was found that the coal-based FCNPs obtained by three kinds of methods are all aromatic structural nanomaterials linked with oxygen-containing groups. Among them, FCNPs-AO is a kind of hollow annular spherical particles and FCNPs-HE and FCNPs-OS are solid spherical particles. These FCNPs not only have similar fluorescence properties as traditional quantum dots, but also can be photoexcited to generate photogenerated electrons and holes, and it can also suppress the recombination of photogenerated electrons and holes by using its own surface defects. In particular, the electron transport capability of the FCNPs-AO is stronger than that of FCNPs-HE and FCNPs-OS because of its lower charge transfer impedance, so it can be excited to generate more photogenerated electrons and has the best photogenerated carrier separation efficiency.     

A DFT study on the geometry,spectroscopic properties,and tautomerization of the local anaesthetic drug prilocaine

The prilocaine is a significant amino amide local anaesthetic. This drug can exist as three possible tautomers. Herein, by using density functional theory (DFT), and handling the solvent effects with the PCM model, the structure, energetic behavior, kinetics and mechanism of tautomerization, as well as the natural bond orbital analysis (NBO) of the prilocaine are reported. P1 is the most stable tautomer of the prilocaine, which can be tautomerized to two other tautomers via the intramolecular-proton transfer. Good agreement between the calculated NMR chemical shifts and IR vibrational frequencies with the experimental values approves the suitability of the optimized geometry for the prilocaine. A large HOMO-LUMO energy gap implies a high stability of the prilocaine.