Nitric oxide (NO) is a ubiquitous signaling molecule in a variety of physiological and pathological process in living organisms. A two-photon probe, i.e., 2-acetyl-6-dialkylaminonaphthalene as the reporter and an o-diaminobenzene as the reaction site for NO, linked by prolinamide (ANO1), has been synthesized. Based on the experimental study, five other two-photon probes have been designed by substituting the naphthalene fluorophore in ANO1 with the luciferin analogue (ANO2), pyrene (substitution at 1,6-position, ANO3, and 2,7-position, ANO3’), fluorene (ANO4), and boron-dipyrromethene (ANO5) units. DFT/TDDFT studies have been conducted on both experimental two-photon probe ANO1 and designed ANOn (n=2–5). Our results indicated that for designed probes, both absorption and emission spectra show red shifts compared with ANO1. The one- and two-photon absorption band positions as well as the emission wavelength do have no significant change for each probe before and after reaction with NO. However, the fluorescence intensities are enhanced after reaction with NO. ANO3 and ANO4 have large two-photon absorption cross sections. Furthermore, analysis of molecular orbitals is exhibited to interpret the photoinduced electron transfer mechanism between the donor and acceptor.
Catalytic behavior of metal-free Hydroxyl group (OH) functionalized single nitrogen (N-Gra(OH)16), and triple nitrogen (N3-Gra(OH)16) doped graphene surface are investigated in the 4e- reduction pathway under oxygen reduction reaction (ORR) process. The thermodynamical parameters indicate the reaction to be highly exothermic and feasible with the N-Gra(OH)16 and N3-Gra(OH)16 as catalysts. However, N3-Gra(OH)16 shows better catalytic properties than N-Gra(OH)16. First, all reactive species (*O2, *OOH, *O, and *OH) chemisorb via a covalent bond on the N3-Gra(OH)16, which is essential for the efficient reaction kinetics. Secondly, the product H2O is physisorbed on the N3-Gra(OH)16, required for the uninterrupted reaction cycle. Categorically, the N3-Gra(OH)16 shows excellent catalytic activity due to a higher number of nitrogen atoms which has a lowered EHOMO-LUMO gap, concomitantly increasing the surface’s reactivity. Besides the above, the barrier energies are comparable with platinum (Pt) catalyst. Our results show that the N3-Gra(OH)16 surface is the most suitable catalyst for ORR activity.
Sulforaphane is the plant active substance with the best anticancer effect and antioxidant found in vegetables. In this paper, based on density functional theory(DFT), the B3LYP/6-311G+(d,p) theoretical level was used to optimize the molecular structure of sulforaphane in gas phase. On the basis of optimization, the first 30 excited states of molecule in methanol were calculated by time-density functional theory(TD-DFT) in SMD solvent model. To analy the excited states of sulforaphane molecule by calculate UV spectrum and hole-electron. Finally, we predicted the active sites of sulforaphane molecule by calculating frontier orbital and fukui function. The results show that: In the UV spectrum, the absorption peaks at 204.4602 and 336.5590nm are the absorption bands of hetero atomic groups of conjugate molecules, which are generated by n-π* transition and belong to R absorption band. According to hole-electron analysis, S0→S18 is the local excitation, and S0→S7, S0→S25 and S0→S29 are the charge transfer excitation. In addition, the O and S atoms on sulfuryl group of sulforaphane are the site of electrophilic reaction; the C and S atoms on the cyanide group are sites of nucleophilic reaction. This study provides a theoretical basis for better understanding the antioxidant and anticancer mechanisms of sulforaphane.
A set of new rasagiline derivatives is presented. They were designed to be antioxidant compounds with the potential to be used for treating neurodegenerative disorders. They are expected to be multifunctional molecules that can help reduce oxidative stress, which is thought to contribute to neurodegenerative disorders. The CADMA-Chem computational protocol was used to produce rasagiline derivatives and to evaluate their likeliness as oral drugs and antioxidants. Three of them were identified as the most promising ones. They are proposed to be better free radical scavengers than rasagiline. In addition, they are expected to keep the parent's molecule neuroprotective capability. Hopefully, the results presented here would promote further experimental and theoretical investigations on these compounds.
Magnesium-based hydrogen storage material (MgH2) has attracted much attention due to its high hydrogen storage density (7.6 wt%). However, the high hydrogen dissociation enthalpy and slow hydrogen dissociation rate in bulk Mg hinder its wide application in the efficient hydrogen storage. In the present work, we study the hydrogen adsorption and desorption reactions of MgmHn (m = 1-6) nanoclusters using density functional theory (DFT). From the global search for the configurations of MgmHn nanoclusters, we found not only stable saturated MgmHn (n = 2m) nanoclusters, but four hydrogen-enriched MgmHn (n:m>2:1) nanoclusters, Mg3H7, Mg4H9, Mg5H11, Mg6H13, with the hydrogen storage density higher than 8.3 wt%. The electronic-structure calculations indicate that the stability of the hydrogen-enriched cluster gets relatively higher for larger nanocluster. The ab initio dynamics simulations shows that all hydrogen-enriched clusters have very fast hydrogen dissociation rates, which is promising for the hydrogen dissociation at ambient temperature and pressure. This work provides insights into the hydrogen storage mechanism of nano-magnesium materials.
Ab initio calculations were carried out to understand the effect of electron donating groups (EDG) and electron withdrawing groups (EWG) at the C5 position of cytosine (Cyt) and saturated cytosine (H2Cyt) of the deamination reaction. Geometries of the reactants, transition states, intermediates, and products were fully optimized at the B3LYP/6-31G(d,p) level in the gas phase as this level of theory has been found to agree very well with G3 theories. Activation energies, enthalpies, and Gibbs energies of activation along with the thermodynamic properties (ΔE, ΔH, and ΔG) of each reaction were calculated. A plot of the Gibbs energies of activation (ΔG‡) for C5 substituted Cyt and H2Cyt against the Hammett σ-constants reveal a good linear relationship. In general, both EDG and EWG substituents at the C5 position in Cyt results in higher ΔG‡ and lower σ values compared to those of H2Cyt deamination reactions. C5 alkyl substituents (−H, −CH3, −CH2CH3, −CH2CH2CH3) increase ΔG‡ values for Cyt, while the same substituents decrease ΔG‡ values for H2Cyt which is likely due to steric effects. However, the Hammett σ-constants were found to decrease for both the Cyt and H2Cyt. Both ΔG‡ and σ values decrease for the substituents Cl and Br in the reaction Cyt, while ΔG‡ values increase and σ decrease in the reaction H2Cyt. This may be due to high polarizability of bromine which results in a greater stabilization of the transition state in the case of bromine compared to chlorine. Regardless of the substituent at C5, the positive charge on C4 is greater in the TS compared to the reactant complex for both the Cyt and H2Cyt. Moreover, as the charges on C4 in the TS increase compared to reactant, ΔG‡ also increase for the C5 alkyl substituents (-H, −CH3, −CH2CH3, −CH2CH2CH3) in Cyt, while ΔG‡ decrease in H2Cyt. In addition, analysis of the frontier MO energies for the transition state structures shows that there is a correlation between the energy of the HOMO‒LUMO gap and activation energies.
Hydrogen is regarded as one of the most potential sustainable energy sources in the future. applications including transportation. Still, the event of materials for its storage is difficult notably as a fuel in vehicular transport. Nanocones are a promising hydrogen storage material. Silicon, germanium, and tin carbide nanocones have recently been proposed as promising hydrogen storage materials. In the present study, we have investigated the hydrogen storage capacity of iC,GeC and SnC nanocones functionalized with Ni. The functionalized Ni a are found to be adsorbed on iCNC,GeCNC and SnCNC with an adsorption energy of -5.56, -6.70 and -4.25 eV. The functionalized iCNC,GeCNC and SnCNC bind up to seven, six and four molecules of hydrogen with the adsorption energy of (-0.34, -0.35 and -0.26 eV) and an average desorption temperature of around 434, 447 and 332K (ideal for fuel cell applications). The SiC, GeC, and SnC nanocones systems exhibit a maximum gravimetric storage capacity of 12.51, 7.78 and 4.08 wt%. We suggested that Ni- SiCNC and Ni- GeCNC systems can act as potential H2 storage device materials because of their higher H2 uptake capacity as well as there with strong interaction adsorbed hydrogen molecules than Ni- SnCNC systems. The hydrogen storage reactions are characterized in terms of the charge transfer, the partial density of states (PDOS), frontier orbital band gaps, isosurface plots, and electrophilicity are calculated for the functionalized and hydrogenated SiC,GeC and SnC nanocones.
On pure and metal, non-metal, co-doped rutile TiO2, DFT simula- tions are performed. For the stability study of doped materials, the defect formation energies of non-metal (S), metal (Fe), and metal and non-metal (Fe/S) co-doped materials are determined. A Ti- rich environment is preferable over an O-rich environment. With values of 2.98 eV, 2.18 eV, 1.58 eV, and 1.40 eV, the bandgap for pristine, S-doped, Fe-doped, and Fe/S co-doped materials is found to be direct. The effective masses (m*) and ratios (R) of charge carriers are also examined, and it is discovered that Fe/S co-doped material has the lowest charge carrier recombination rate. The maximum static dielectric constant is found in the Fe/S co-doped material. Doped material’s absorption spectra shifted into the vis- ible region. Additionally, using SCAPS-1D simulation software, a complete solar cell device study using these materials as ETL is performed for the first time. The absorber layer and the ETL settings have been tweaked to perfection. Current-voltage (IV) characteristics, quantum efficiency (QE), capacitance-voltage (CV) characteristics, and capacitance-frequency (Cf) character- istics are provided for optimize solar cells.When the smallest degree of defect for each layer is taken into account, the solar cell with Fe/S co-doped ETL has the highest efficiency of 34.27%.
The oxygen electroreduction mechanism on the V- and Nb-doped nitrogen-codoped (6,6)armchair carbon nanotube with incorporated MN4 fragment has been studied using the ωB97XD and PBE density functional theory approaches. The metal center in MN4 fragment and the adjacent NC=CN double bond (C2 site) of the support have been revealed as active centers. The metal active centers turned out to be irreversibly oxidized at the first step of ORR affording stable O*, 2O*, or O*HO* adsorbates depending on the applied electrode potential U, that makes them no longer active in ORR. Therefore, the C2 site comes at the forefront in ORR catalysis. Among the metal oxidized forms M(O)N4–, M(O)(O)N4– and M(O)(OH)N4–CNT, the C2 site of the latter turned out to be most active for 4e dissociative ORR. For both metals the last protonation/electron transfer step, HO* + H* = H2O, is the rate-limiting step. The alternative hydrogen peroxide formation is not only thermodynamically less favorable but also kinetically slower than the 4e dissociative ORR route on the C2 site of model M(O)(OH)N4–CNT catalyst.
Density functional calculations have been carried out to investigate the possibility of trapping of noble gas dimers by cyclocarbon dimer. Parallel-displaced conformation of the cyclocarbon dimer is found to be the minimum energy structure. Non-covalent interaction is found to hold the noble gas dimers. The lighter noble gases (He, Ne) posses repulsive interactions, the heavier one (Ar, Kr) are held by attractive interactions forming genuine bonds. Each of the noble gas atoms in turn forms non-covalent interaction with the cyclocarbon monomers. The bond dissociation energy of the noble gas dimers dramatically increases inside the cyclocarbon dimer. Energy decomposition analysis reveals that dispersion plays the major role towards the stabilization energy.
Interactions of antimony-oxide clusters with trypanothione have been modelled to understand their inhibitory activity against leishmaniasis. Trypanothione is essential for the survival of leishmania parasites because it is responsible for maintaining their cellular thiol-disulfide redox regulation. Density functional theory (DFT) calculations show that the SbV oxide clusters form hydrogen bonds from the oxygens to the amine and carboxyl group of the trypanothione. The reaction between trypanothione and the SbV oxide cluster does not break the S-S bond of trypanothione, whereas the reaction with antimony-oxide clusters containing at least one SbIII atom leads to dissociation of the S-S bond of both the oxidized and the reduced form of trypanothione suggesting that antimony-oxide clusters with at least one SbIII atom may destroy trypanothione that is vital for the parasite metabolism.
Spectrum graph theory not only facilitate comprehensively reflflect the topological structure and dynamic characteristics of networks, but also offer signifificant and noteworthy applications in theoretical chemistry, network science and other fifields. Let Ln (8, 4) represent a linear octagonal-quadrilateral network, consisting of n eight-member ring and n four-member ring. The M¨obius graph Qn(8, 4) is constructed by reverse identifying the opposite edges, whereas cylinder graph Q’n (8, 4) identififies the opposite edges by order. In this paper, the explicit formulas of Kirchhoffff indices and complexity of Qn(8, 4) and Q‘n (8, 4) are demonstrated by Laplacian characteristic polynomials according to decomposition theorem and Vieta’s theorem. In surprise, the Kirchhoffff index of Qn(8, 4)(Q’n (8, 4)) is approximately one-third half of its Wiener index as n → ∞.
Geometries and electronic properties of selfassembled (InN)12n (n=1-9) nanosheets or nanowires are investigated at the PBE1PBE level. The growth patterns of semiconductor InN nanocrystal are revealed. Relative stabilities of (InN)12n (n=1-9) are studied. The even-numbered (InN)12n (n is even) nanoclusters have stronger stabilities than the neighboring odd-numbered (InN)12n ones. The particular stable geometries are assigned as the (InN)48 nanosheet for selfassembled film nanomaterials. The calculated energy gaps exhibit even-odd oscillation and reveal that (InN)12n (n=1-9) semiconductor nanoclusters are apparently good optoelectronic or energy nanomaterials; Furthermore, (InN)12n nanoclusters with energy gaps at the visible regions have potential applications in microelectronic and optoelectronic nanodevices. The slightly varied energy gaps for (InN)12n nanowires reveals they maintain individual (InN)12 properties. The calculated charge-transfers for (InN)12n (n=1-9) reflect that their ionic bonding enhances the stabilites of nanoclusters and that ionic bonding in (InN)12n (n=1-9) nanoclusters exists with covalent.
A new class of materials was identified as Cu20Nb monolayer clusters, which hosts strong correlation electrons. Direct observation show maps of electron wave function patterns, where the symmetry, brightness and size of features was directly related to the position of a Nb atom in Cu lattice, around which the electron was bound. Using the Fourier transform (FT) of the fractal dimension of the AFM images, these clusters present quasi-particle interference (QPI), which reveals a unique picture of electron waves and the trapping of further electrons in the lattice. Furthermore, density functional theory (DFT) calculations validated electronic features of the clusters with remarkable accuracy. DFT calculations also revealed differences between the lowest unoccupied energy (LUMO) and the highest occupied energy (HOMO), and these phase gaps evolved in the ground state. These phenomena provide evidence that electron correlation stimulates electronic bands to pseudo-gap states. Indeed, our experiments pave the way for realizing unconventional superconductivity in zero-dimension materials.
Singlet and triplet spin state energies for three-dimensionalHooke atoms, i .e. electrons in a quadratic confinement, with even number of electrons (2, 4, 6, 8, 10) is discussed using Full-CI and CASSCF type wavefunctions with a variety of basis sets and considering perturbative corrections up to second order. The effect of the screening of the electron-electron interaction is also discussed by using a Yukawa-type potential with different values of the Yukawa screening parameter (λee =0.2, 0.4, 0.6, 0.8, 1.0). Our results show that the singlet state is the ground state for 2 and 8 electron Hooke atoms, whereas the triplet is the ground spin state for 4, 6 and 10 electron systems. This suggests the following Auf bau structure 1s < 1p < 1d with singlet ground spin states for systems in which the generation of the triplet implies an inter-shell one electron promotion, and triplet ground states in cases when there is a partial filling of electrons of a given shell. It is also observed that the screening of electronelectron interactions has a sizable quantitative effect on the relative energies of both spin states, specially in the case of 2 and 8 electron systems, favouring the singlet state over the triplet. However, the screening of the electron-electron interaction does not provoke a change in the nature of the ground spin state of these systems. By analyzing the different components of the energy, we have gained a deeper understanding of the effects of the kinetic, confinement and electron-electron interaction components of the energy.
In thiswork,we have computed and implemented one-body integrals concerning gaussian confinement potentials over gaussian basis functions. Then, we have set an equivalence between gaussian and Hooke atoms and we have observed that, according to singlet and triplet state energies, both systems are equivalent for large confinement depth for a series of even number of electrons n = 2, 4, 6, 8 and 10. Unlike with harmonic potentials, gaussian confinement potentials are dissociative for small enough depth parameter; this feature is crucial in order to model phenomena such as ionization. In this case, in addition to corresponding Taylor series expansions, the first diagonal and sub-diagonal Padé approximant were also obtained, useful to compute the upper and lower limits for the dissociation depth. Hence, this method introduces new advantages compared to others.
This work reports on a novel computational approach to the efficient evaluation of one-electron coupling coefficients as they are required during spin-adapted electronic structure calculations of the configuration interaction type. The presented approach relies on the equivalence of the representation matrix of excitation operators in the basis of configuration state functions and the representation matrix of permutation operators in the basis of genealogical spin eigenfunctions. After the details of this connection are established for every class of one-electron excitation operator, a recursive scheme to evaluate permutation operator representations originally introduced by Yamanouchi and Kotani is recapitulated. On the basis of this scheme we have developed an efficient algorithm that allows the evaluation of all nonredundant coupling coefficients for systems with 20 unpaired electrons and a total spin of S = 0 within only a few hours on a simple Desktop-PC. Furthermore, a full-CI implementation that utilizes the presented approach to one-electron coupling coefficients is shown to perform well in terms of computational timings for CASCI calculations with comparably large active spaces. More importantly, however, this work paves the way to spin-adapted and configuration driven selected configuration interaction calculations with many unpaired electrons.
A search has been conducted, employing ab initio molecular orbital theory, for potential tetrel-bonded complexes between the fluorinated methanes methyl fluoride, difluoromethane and fluoroform, and the related hydrides ammonia, water, hydrogen fluoride, phosphine, hydrogen sulfide and hydrogen chloride. Eleven such complexes have been identified, six containing CH3F and five CH2F2. The complexes are typically less strongly bound than their hydrogen-bonded counterparts, and the interaction energies vary in a consistent way with the periodic trend of the electron donors. The intermolecular separations and changes of the relevant intramolecular bond lengths, the wavenumber shifts of the critical vibrational modes, and the extents of charge transfer for the atoms most closely involved in the interactions correlate, by and large, with the strengths of interaction.