Group IV organometallic complexes are promising systems for C-H bond activation. We are interested in the C-H bond activation of the CH2 positions of the adamantyl group, since these positions are particularly hard to activate and to functionalize. As a potential platform for activation of that important alkyl group, we consider the alkyl bonded to the cyclopentadienyl in a substituted bis-cyclopentadienyl group IV metal diphenyl complex. The mechanism proposed in the classic paper reporting such activation using Zr(IV) (Erker and Mühlenbernd, 1987) involves an η2-benzyne complex intermediate. This current work reports a computational analysis of the problem through Density Functional Theory (DFT). We found that the two-step mechanism proposed for activation of C(Me)2-Ph or tert-Bu groups using Zr(IV) is indeed confirmed by DFT and that it can be extended to Ti and Hf. We further found that the system can be successfully extended to the adamantyl group. The first step involves formation of the benzyne complex, which can also be described as a metallacyclopropene. In the second step, the cyclopentadienyl-bound alkyl is activated in the coordination sphere of the metal via proton transfer to the bound benzyne, which, if the metallacyclopropene description is chosen, resembles a σ-bond metathesis. The C-H bond activation of adamantyl through this approach is thermodynamically and kinetically feasible. Selective α-CH bond activation should be achievable with Ti (under thermodynamic control), and selective γ-CH bond activation with Zr (under kinetic or thermodynamic control).
E,E-2,4-hexadienal is probably a precursor of secondary organic aerosol (SOA) and plays an important role in the atmospheric chemistry. Its main degradation routs are the reactions with OH, Cl, NO3 as well as photolysis. Atmospheric hydroxyl radical, as the most important oxidant, generally controls the removal of volatile organic compounds (VOCs) in the atmosphere. Thus, the quantum chemical calculations are used to investigate the reaction mechanism of E,E-2,4-hexadienal with hydroxyl radical, which would give better understanding for the main degradation products. The reaction paths of E,E-2,4-hexadienal with OH radical have been calculated accurately at the BMC-CCSD//M06-2X/6-311G (d, p) level at atmospheric pressure and room temperature. There are six hydrogen abstraction and four carbon addition paths at the first stages of this reaction. Due to the low energy barrier and reaction exotherm, the ten paths would contribute to the total reaction. Furthermore, the peroxy (RO2) and alkoxy (RO) radicals from the most important adduct IM1(CH3CHOHCHCH=CHCHO) would be formed in the atmospheric environment. The reaction mechanism of the peroxy radical (CH3CHOHCHO2CH=CHCHO) with NO, NO2, HO2, and self-reaction have been studied by using the same quantum chemical methods. And the reaction paths of alkoxy radical (CH3CHOHCHOCH=CHCHO) have been also originally studied. The subsequent reactions play a key role in the cycling of atmospheric radicals, production of ozone, and SOA formation. What’s more, the reaction mechanism of this study accords with the reported experimental observations.
Interatomic potentials laid at the heart of molecular physics. They are a bridge between the spectroscopic and structural properties of molecular systems. In this paper, a century-old review from 1920 to 2020, of functional forms used to analytically represent potential energy as a function of interatomic distance for diatomic systems is presented. With such a purpose fifty functions were selected. For all of them, motivation and the main mathematical features are discussed. Our goal is to provide a chronological pathway to the reader, even with little knowledge on the subject, to understand how to calculate each parameter that composes the interatomic potentials, as well as obtain spectroscopic constants from them. Comparative evaluation for the N2, CO, and HeH+ systems in their ground electronic states are also presented.
Abstract: The orbital, ground and excited state energies of many electron atoms confined by an impenetrable spherical cavity with radius R are calculated using Quantum Genetic Algorithm (QGA) approach and Hartree-Fock Roothaan (HFR) theory. The important properties such as static and dynamic polarizability, oscillator strength and static pressure are investigated as perturbative. The results reveal that cavity radius and impurity charge have played an important role on the polarizability, the oscillator strength and pressure of the system. In addition, it is seen that when cavity radius is extremely large, all energies and the other physical parameters approach the energies and physical parameters of unconfined atom. As the dot radius decreases, the polarizability of system because of the strong spatial confinement decreases, but the pressure exerting on the system as the cavity radius R is shrunk increases. In addition, as the impurity charge increases, the magnitude of the oscillator strength decreases. Keywords: Orbital energy, static and dynamic polarizability, oscillator strength, pressure, many electron quantum dots.
Isoprene (2-methyl-1, 3-butadiene (C5H8)) is one of the most prominent and abundant non-methane hydrocarbon existing in the lower level of the troposphere. In this work, possible reaction mechanism of chlorine (Cl) radical initiated isoprene and its subsequent reactions are investigated using quantum chemical methods. The calculated thermodynamic result shows that the reaction of isoprene with the Cl radical at the terminal C=C bond position plays an important role to predict the end products. The calculated rate coefficient for the reaction between isoprene and Cl radicals (Cl addition at C1, C3, C4 and C5 positions) is found to be 4.89⨯10-11, 6.91⨯10-10, 1.63⨯10-10 and 8.12⨯10-10 cm3/molecule/sec at 298K. The branching ratio and atmospheric lifetime have been calculated from the reaction rate coefficient values of isoprene+Cl. The reaction force analysis predicts Cl radical addition at the terminal C=C bond position plays a dominant role by structural rearrangement. The kinetic and thermodynamic results reveal that the electrophilic addition of Cl radical to the terminal carbon atom plays the dominant role in the marine boundary. Further, the subsequent reaction of Cl-isoprene adduct radical helps for the development of ozone layer during daytime.
Electrochemotherapy is an effective strategy for the treatment of solid tumors by exposing tumor cells to electric fields to enhance the bioactivity of non-permeable or low permeable anticancer drugs, such as cisplatin. To understand the improved efficiency of cisplatin in electrochemotherapy, the effects of oriented external electric fields (OEEFs) on the geometric structures and relevant electronic properties of cisplatin have been systemically investigated by density functional theory (DFT) computations in this work. Our results reveal that the presence of positive OEEFs on cisplatin can not only weaken its Pt-Cl bonds, but also enhance the intramolecular charge transfer in it, which effectively accelerates the critical hydrolysis step involved in the mechanism of its biological activity. Moreover, the positive OEEFs can facilitate the attack of the singly aquated cis-[Pt(NH3)2(H2O)Cl]+ on DNA, and enlarge the dipole moments and water solubility of cisplatin and its aquated product. Consequently, this work provides a deeper insight into the higher efficacy of electrochemotherapy than traditional chemotherapy from a molecular point of view.
The time-dependent density functional theory (TD-DFT) was used to calculate the vibronic absorption spectrum of berberine (BER) in an aqueous solution. The best agreement with the experimental spectrum gives the O3LYP functional. Functionals with long-range correction showed poor agreement with experiment. The molecular orbitals of BER involved in the electronic transition during light absorption in the visible spectral region have been obtained. The dipole moments and atomic charges of the ground and excited states of the BER molecule have been calculated. Maps of BER electron density and electrostatic potential have been drawn. A significant photoinduced electron transfer from the outer di-oxygen five-membered heterocycle to the center of the BER chromophore has been found. According to our calculations, vibronic coupling and Boltzmann distribution play a significant role in the absorption spectrum of BER.
Organic conductive polymers have great significance due to their wide range of applications in optoelectronics and material sciences. In this study, pyrrole-benzothiadiazole/benzoselenadiazole based type green polymers were undertaken computational work to investigate the solubility of polymers. Structural, electronic, and optical properties of eight different polymers were predicted using DFT and TD-DFT at B3LYP/6-31G level on semi-empirical PM6-optimized geometries. It has been shown that the calculation results of synthesized green polymers are in great agreement with the experimental results. Alkylated 4,7-di(1H-pyrrol-2-yl)benzo-[c][1,2,5]thiadiazole (PB1) and 4,7-di(1H-pyrrol-2-yl)benzo[c][1,2,5]selenadiazole (PB7) monomers were studied to investigate the effect of alkyl chains on their electronic and optical properties. Butyl substituted more soluble polymers were shown to have low electronic energy gaps (1.27-1.55 eV). Moreover, the electronic energy gap values of the studied polymeric structures are in the appropriate range of technological applications (1.24-2.18 eV). The approach utilized in this study can be used to design new semi-conducting polymers.
Accurate restricted Hartree-Fock (RHF) wave-functions are used to investigate information theoretic properties of the model problem of two interacting electrons confined within an infinite spherical potential of radius R. Benchmark quality calculations are performed to characterise this system via a range of information measures as a function of the tunable parameter R, across the full electron correlation regime (low to high correlation; small R to large R). Both the Shannon information entropy and a statistical complexity measure provide quantitative insight regarding the onset of the formation of a ‘Wigner molecule’ state for this system.
Bulk SiC phases with tetrahedral arrangements have been identified several decades ago, and have been widely studied due to their potential applications. Until recently, Yaghoubi et al.’s experimental results (Chem. Mater. 2018, 30, 7234) showed that the graphitic SiC with few SiC layers stacking is stable. In this work, we further explore the potential application of graphitic SiC as the Na-ion battery anode via the first-principle simulation. Our results reveal that the theoretical capacity of graphitic SiC reaches up to 1339.44 mAh/g, which is almost the highest among the already known Na-ion battery anodes. Together with the low diffusion barrier, moderate open circuit voltage and excellent electronic conductivity during the sodiation, we propose that the graphitic SiC is a promising material as Na-ion battery anode. More importantly, we find that the intercalation strength of Na ions into C-based multi-layer materials (or the corresponding theoretical capacity, the operation voltage) could be enhanced by increasing the amount of covalent components in Na‒C bonds, which could be realized via doping by atom (such as Li, Be, B, Al, Si or P) with lower electronegativity than that of C atom.
Photovoltaic properties of the natural dyes of chlorophylls consist of Chl a, Chl b, Chl c2, Chl d, Phe a, Phe y and Mg-Phe a, were studied in the gas phases and water. The extension of the π-conjugated system, the substitution of the central Mg2+ and proper functional groups in the chlorophyll structures can amplify the charge transfer and photovoltaic performance. Chl a shows more favorable dynamics of charge transfer than other studied chlorophylls. Chl d, Phe a, Phe y and Mg-Phe a, have a greater rate of the exciton dissociation in comparison with Chl a, Chl b, and Chl c2 originated from a lower electronic chemical hardness, a lower exciton binding energy, and a bigger electron-hole radius. As a result, better efficiencies of the light-harvesting and energy conversion of the chlorophylls mainly appear in the Soret band. The LHE values of the chlorophylls in water show that solvent favorably affects the ability of light-harvesting of the photosensitizers. Finally, based on the energy conversion efficiency, Chl a, Phe a, and Mg-Phe a, are proposed as the best candidates for using in the dye-sensitized solar cells.
A systematic benchmark of phosphorus and fluorine NMR chemical shifts predictions at six different density functional theory (DFT) / the gauge-including atomic orbital (GIAO) methods was conducted. Two databases were compiled: one consists of 35 phosphorus-containing molecules, which cover the most common intra-molecular bonding environments of trivalent and pentavalent phosphorus atoms; the other is composed of 46 fluorine-containing molecules. The characteristics of each DFT/GIAO method with different solvent models were demonstrated in details. The application of linear regression between the calculated isotropic shielding constants and experimental chemical shifts was applicable to improve the prediction accuracy. And, the best methods with the SMD and CPCM implicit solvent models for 31P chemical shifts predictions, are able to yield a root-mean-square deviation (RMSDs) of 5.58 ppm and 5.42 ppm, respectively; for 19F, the corresponding lowest prediction errors with these two applied solvent models are 4.43 ppm and 4.12 ppm. The developed scaling factors fitted from linear regression are applicable to enhance the chance of successful structural elucidations of phosphorus or fluorine-containing compounds, as an efficient complement to 13C, 1H, 11B and 15N chemical shifts predictions.
Density functional theory (DFT) calculations were conducted to investigate mechanistic details of ethanol-to-butadiene conversion reaction over MgO or ZnO catalyst. We evaluated the Lewis acidity and basicity of MgO and ZnO and found that ZnO had the stronger Lewis acidity and basicity compared with those of MgO. Potential energy surfaces (PESs) of ethanol-to-butadiene conversion, which included relevant transition states (TSs) and intermediates, were computed in detail following the generally accepted mechanism reported in the literature, where such mechanism included ethanol dehydrogenation, aldol condensation, Meerwein-Pondorf-Verley (MPV) reduction and crotyl alcohol dehydration. DFT results showed that ethanol dehydrogenation was the rate limiting step of overall reaction when the reaction was catalyzed by MgO. Also, DFT results showed that ethanol dehydrogenation occurred more easily on ZnO compared with MgO where such a result correlated with the stronger Lewis acidity of ZnO. In addition, we computed ethanol dehydration which generates ethylene, one of the major undesired side reaction products for butadiene formation. DFT results showed that ZnO favored dehydrogenation over dehydration while MgO favored dehydration.
In our work, the formation energies, band structures, densities of states, effective masses and optical absorption properties of pure BiOBr and 3d transition metals-doped BiOBr have been calculated using DFT+U method. Ti, V, Fe, Cr, Co, Ni and Cu doping can induce impurity energy levels, originating from spin-up or -down orbits of 3d TMs, within the forbidden band of BiOBr, but Sc, Mn and Zn atoms only change the electronic delocalization in the valence bandor conduction band region of BiOBr. Furthermore, with introduction of 3d TMs atoms, there exist the redshift phenomena for optical absorption band edge of BiOBr to different extents. The photo response priority order, structural stability and recombination probability of photoinduced carriers for 3d TMs-doped BiOBr are summarized. Our theoretical findings should well explain the experimental observations in the previous literatures, and provide promising prediction and significant guidance for the well-construction of BiOBr-based photocatalyst systems.
This work presents analytical and numerical results for the position- and momentum-space information entropies, of the 1s2-state of helium-like ions, using different interaction potentials. The potentials that we used are the Yukawa potential (YP), and the exponential-cosine-screened Coulomb potential (ECSCP). The investigated studies allow us to relate the position-space information with the momentum-space information of Shannon and Fisher, as well as Shannon entropy power, and the Fisher-Shannon information product, through different famous relations. The calculation is done using the one-electron charge density of entangled two-parameter wave function. On one hand, the results that are presented for ten members in the helium isoelectronic sequence demonstrate with precision the effect of correlation on bare charge distributions. On the other hand, it leads to some very important results for both the correlated and uncorrelated values of the informatic entropies. Analytical formula for the momentum-space information entropies are given. The effect of the nuclear charge and the screening parameter on the information expressions has been studied for both potentials. Detailed computational and numerical values and characteristics of these information quantities, as a function of the screening parameter, are reported here for the ﬁrst time. New inequality has been proposed with Fisher’s total value to measure the correlation of two electrons.
The emission of carbon dioxide in large amounts is commonly believed to be the main cause of global climate changes. Development of CO2 capture processes is still a big current challenge. Some anions have been studied for the gas sequestration process due their great affinity to CO2. In this work, electronic structure calculations were performed at the MP2/aug-cc-pvtz level to compute the interaction between 20 anions and CO2. A CBS scheme, using extrapolated energies, was also employed for both gas phase and solvent calculations. The reactions between the anions and CO2 were therefore studied in four different conditions (gas phase, toluene, tetrahydrofuran and water). The trends observed for the reaction thermodynamics with the MP2 method is similar to that observed previously with the B3LYP-D3 and M06-2X functionals. The reactions in the gas phase are highly exothermic and do not involve any activation energy. The solvent effect reduces the exothermicity and induces an intrinsic activation barrier. The negative charge is dispersed in the adduct, leading to a weaker interaction in a polar solvent. Then, increasing the medium polarity, the energy difference between the adduct and the reactants decreases. We also observed a limit for solvent stabilization in the low dielectric constant range. For example, the results obtained with tetrahydrofuran are closer to those obtained with water than to those obtained with toluene. Considering both the thermodynamics of the reaction and the differential solvent effects, we were able to indicate anions derived from alkyl sulfides as the most convenient for CO2 sequestration among the set here considered.
A systemic investigation of the substitution and cooperative effects on the P…N π-hole pnicogen bond were performed via theoretical calculations. The structural and energetic properties of the binary complexes between a series of substituted benzonitrile and PO2F have been examined to study the substitution effect. The stability of the binary complexes increases in the order of CN
Due to it is potential application in the field of high energy density materials, how to stabilize cyclopentazolate anion (cyclo-N5-) has attracted many interests theoretically and experimentally. Therefore, a series of ion salts containing [cyclo-N5]- were synthesized and studied. The instability of [cyclo-N5]- is caused by the five lone pairs of electrons localized on five neighbored N atoms. In this work, we expect if the [cyclo-N5]- can be stabilized by the coordination with acidic ligands, by weakening the multi repulsion from the lone pairs to stabilize the [cyclo-N5]-. The two compounds of [N5(BH3)5]-, and [N5(AgCN)5]- have been designed and compared based on the Lewis acid-base theory. [N5(H2O)5]- is designed to evaluate the effect of hydrogen bond in the stabilization. For all the structures, we study the bonding properties and thermal stabilities based on the analysis of electronic structures and Car-Parrinello molecular dynamics (CPMD) simulations. The results indicate it is a effective method to stabilize [cyclo-N5]- by introducing the Lewis acid. Our insights on [cyclo-N5]- compounds with high thermal stability under ambient conditions will provide a new idea for the research and synthesis of new high energetic [cyclo-N5]- series compounds.