ABSTRACT
In this study, the interaction between the neurotransmitter epinephrine and small gold nanoclusters (AunNCs) with n = 6, 8, and 10 is described by density functional theory calculations. The interaction of Au6, Au8, and Au10 nanoclusters with epinephrine is governed by Au-X (X = N and O) anchoring bonding and Au···H-X conventional hydrogen bonding. The interaction mechanism of epinephrine with gold nanoclusters is investigated in terms of electronic energy and geometrical properties. The adsorption energy values for the most favorable configurations of Au6NC@epinephrine, Au8NC@epinephrine, and Au10NC@epinephrine were calculated to be -17.45, -17.86, and -16.07 kcal/mol, respectively, in the gas phase. The results indicate a significant interaction of epinephrine with AunNCs and point to the application of the biomolecular complex AunNC@epinephrine in the fields of biosensing, drug delivery, bioimaging, and other applications. In addition, some important electronic properties, namely, the energy gap between HOMO and LUMO, the Fermi level, and the work function, were computed. The effect of aqueous media on adsorption energy and electronic parameters for the most favorable configurations was also studied to explore the influence of physical biological conditions.
ABSTRACT
First-principles calculations based on density functional theory were utilized to evaluate whether an iron atom decorated B40 borospherene can be employed as a catalyst for converting methane (CH4) to methanol (CH3OH) in the presence of N2O or O2 molecule. Geometry optimizations indicated that N2O and O2 are both chemisorbed on the Fe atom of the catalyst, whereas CH4 is physisorbed. Using N2O as the oxidant, the oxidation of CH4 begins with N2O decomposition on the catalyst, which has an activation barrier of 0.50 eV. The CH4 molecule then combines with the activated O atom remained on the Fe to form the CH3OH molecule. However, the oxidation of CH4 with O2 requires an activation barrier as high as 1.91 eV, implying that this process is unlikely to occur under normal conditions. These novel results are anticipated to help in the design and modeling of noble-metal free catalysts for CH4 oxidation.
ABSTRACT
This study focused on the theoretical viability of Ngn@C24N24 (Ng = Ne, Ar, Kr, Xe, and Rn; n = 1, 2) complexes using density functional theory at the computational level of ωB97X-D/def2-TZVP. Thermodynamic and kinetic stabilities of these complexes have been evaluated by calculating the interaction energy of Ng atoms encapsulated C24N24 cage (ΔEint), and the corresponding dissociation energy barrier (ΔG), respectively. The obtained results predict that although these complexes are thermodynamically unstable compared to their dissociation into free Ng atoms and the bare C24N24 cage, but once formed, they are protected by the activation energy barrier of the corresponding dissociation process. Furthermore, natural population analysis (NPA) and topological analysis of the electron density have been employed to investigate the nature of Ng-Ng and Ng-cage interactions. The results demonstrate that these interactions are highly significant compared to similar cases in the free state; and the amounts of energy of the interaction gradually increases as the Ng atom becomes heavier. Surprisingly in the Kr2@C24N24 complex the Kr-Kr bond is somewhat covalent in nature relative to non-bonded interaction in Kr2 free dimer.
Subject(s)
Fullerenes , Porphyrins , Porosity , ThermodynamicsABSTRACT
Systematic density functional theory (DFT) calculations using the TPSSh functional and the def2-TZVP basis set were carried out to identify the global energy minimum structure of the Li2FeB14 cluster. Keeping the double ring tubular shape of FeB14, capping of two Li atoms leads to a teetotum form at a low spin state, in which the Fe atom is endohedrally covered by two B7 strings, and both Li atoms are attached to Fe along the C7 axis at both sides. Calculated results show that strong electrostatic interactions between 2Li+ and Fe2- arising from Li electron transfer upon doping particularly provide a key driving force for stabilizing this charge-transfer structure. The bonding pattern of the teetotum can be understood from the hollow cylinder model (HCM). TD-DFT calculations demonstrate that this cluster can also be regarded as a useful material for transparent optoelectronic devices. Furthermore, the Li2FeB14 superatom can be used as a building block for making boron-based nanowires with metallic character. Replacement of Li atoms by Mg atoms was also found to lead to nanowires.
ABSTRACT
A systematic exploration of the potential energy surface through evolutionary search algorithms was carried out to identify the most stable B27Sc2+ structure. A nearly perfect boron box was found featuring a triple ring tubular shape with high D9h symmetry formed by three B9 strings connected with each other and the box is capped by an Sc-Sc dimer. Each Sc atom is placed at the centre of a B9 terminal string along the C9 axis. The shapes of the MOs of the B27+ triple ring are reproduced by eigenstates of a simple model of a particle on a hollow cylinder (HCM). The resulting MOs demonstrate that only the set of radial-MOs of the B27+ skeleton significantly interact with MOs of a stretched Sc2 dimer. This structure is representative of a new fruit can-type of shape in the family of doped boron clusters.
ABSTRACT
Based on the local Shannon entropy concept in information theory, a new measure of aromaticity is introduced. This index, which describes the probability of electronic charge distribution between atoms in a given ring, is called Shannon aromaticity (SA). Using B3LYP method and different basis sets (6-31G**, 6-31+G** and 6-311++G**), the SA values of some five-membered heterocycles, C(4)H(4)X, are calculated. Significant linear correlations are observed between the evaluated SAs and some other criteria of aromaticity such as ASE, Lambda and NICS indices. According to the obtained relationships, the range of 0.003 < SA < 0.005 is chosen as the boundary of aromaticity/antiaromaticity. Using B3LYP/6-31+G** level of theory, the Shannon aromaticities for a series of mono-substituted benzene derivatives are calculated and analyzed. It is found that the least standard deviation between the aromaticities and the best linear correlation with the Hammett substituent constants are observed for the new index in comparison with the other indices. Also the values of the new index are evaluated for some substituted penta- and heptafulvenes, which successfully predict the order of aromaticity in these compounds. Applying this index to some non-benzonoids, linear and angular polyacenes also give satisfactory results and prove to be quite suitable for determining the local aromaticity of different rings in polyaromatic hydrocarbons.
ABSTRACT
By calculating the energies of neutral and different ionic forms (M2+, M+, M, M-, and M2-) of 32 elements (using B3LYP/6-311++G** level of theory) and taking energy (E) to be a Morse-like function of the number of electrons (N), the electrophilicity values (omega) are calculated for these atoms. The obtained electrophilicities show a good linearity with some commonly used electronegativity scales such as Pauling and Allred-Rochow. Using these electrophilicities, the ionicities of some diatomic molecules are calculated, which are in good agreement with the experimental data. Therefore, these electrophilicities are introduced as a new scale for atomic electronegativity, chi(omega)0. The same procedure is also performed for some simple polyatomic molecules. It is shown that the new scale successfully obeys Sanderson's electronegativity equalization principle and for those molecules which have the same number of atoms, the ratio of the change in electronegativity during the formation of a molecule from its elements to the molecular electronegativity (Delta chi/chi omega) is the same.
