The possibility that stable complexes may be formed between alpha particles (He2+) and small molecules is investigated using QCISD quantum mechanical calculations. Implications for their presence in the
terrestrial atmosphere and/or in interstellar space are discussed.
Figure Optimized structure of a stable H2OHe2+ complex 相似文献
Second group metal dimers can replace the carbon atom in benzene to form metallabenzene (C5H6M2) compounds. These complexes possess some aromatic character and promising hydrogen adsorption properties. In this study, we investigated the aromatic character of these compounds using aromaticity indices and molecular orbital analysis. To determine the nature of interactions between hydrogen and the metallic center, variation-perturbational decomposition of interaction energy was applied together with ETS-NOCV analysis. The results obtained suggest that the aromatic character comes from three π orbitals located mainly on the C5H5? fragment. The high hydrogen adsorption energy (up to 6.5 kcal mol?1) results from two types of interaction. In C5H6Be2, adsorption is controlled by interactions between the empty metal orbital and the σ orbital of the hydrogen molecule (Kubas interaction) together with corresponding back-donation interactions. Other C5H6M2 compounds adsorb H2 due to Kubas interactions enhanced by H2–π interactions.
A computational investigation of the sulfur-containing heterocyclic components (substituted thietanes and 1,2-dithiolanes)
of Mustela anal sac secretions has been carried out. A cluster analysis of the chemical compositions of Mustela anal sac volatiles reveals little similarity with established phylogenetic relationships between members of the genus. Ab initio calculations [MP2/6–311++G(2df,2p)//B3LYP/6–311++G**] show the lowest-energy C5H10S isomeric thietane to be 2,2-dimethylthietane, which is also the most abundant of the Mustela thietanes. Similarly, 3,3-dimethyl-1,2-dithiolane is the lowest-energy C5H10S2 compound. 2-n-Propylthietane is the highest-energy C6H12S compound, but the most abundant Mustela C6H12S compound produced, whereas cis-2-ethyl-4-methylthietane, the lowest-energy C6H12S thietane, has never been observed in Mustela anal sac secretions. A molecular docking analysis of the Mustela sulfur-containing heterocycles into both porcine and bovine odorant binding proteins reveals the interactions of the docked
ligands with the proteins to be largely hydrophobic, and have binding energies generally lower than typical odorant molecules
such as linalool or eugenol.
Figure Mustela anal sac volatile components, 2,2-dimethylthietane and cis-3,4-dimethyl–1,2-dithiolane. 相似文献
Quantum chemical calculations at the B3LYP/6-31G* level of theory have been carried out on 20 celastroid triterpenoids to
obtain a set of molecular electronic properties and to correlate these with cytotoxic activities. The cytotoxic activities
of these compounds can be roughly correlated with electronic effects related to nucleophilic addition to C(6) of the compounds:
The energies of the frontier molecular orbitals (EHOMO and ELUMO), the HOMO-LUMO energy gap, the dipole moment, the charge on C(6), and the electrophilicity on C(6).
Figure LUMO of Pristimerin. 相似文献
The geometries of three isomers of the C2H4O···2HF tri-molecular heterocyclic hydrogen-bonded complex were examined through B3LYP/aug-cc-pVDZ calculations. Analysis
of structural parameters, determination of CHELPG (charge electrostatic potential grid) intermolecular charge transfer, interpretation
of infrared stretching modes, and Bader’s atoms in molecules (AIM) theory calculations was carried out in order to characterize
the hydrogen bonds in each isomer of the C2H4O···2HF complex. The most stable structure was determined through the identification of hydrogen bonds between C2H4O and HF, (O···H), as well as in the hydrofluoric acid dimer, (HFD–R···HFD). However, the existence of a tertiary interaction (Fλ···Hα) between the fluoride of the second hydrofluoric acid and the axial hydrogen atoms of C2H4O was decisive in the identification of the preferred configuration of the C2H4O···2HF system.
Figure Geometries of three isomers of the C2H4O···2HF tri-molecular heterocyclic hydrogen-bonded complex 相似文献
The tautomerization mechanism the isolated and monohydrated forms of two Schiff bases 1 and 2, and the effect of solvation
on the proton transfer from enol-imine form to the keto-enamine form have been investigated using the B3LYP hybrid density
functional method at the 6-31G** basis set level. The barrier heights for H2O-assisted reactions are significantly lower than that of unassisted tautomerization reaction in the gas phase. Nonspecific
solvent effects have also been taken into account by using the continuum model (IPCM) of four different solvent. The tautomerization
energies and the potential energy barriers are decreased by increasing solvent polarity.
Figure The tautomerization mechanism the isolated and monohydrated forms of two Schiff bases 1 and 2, and the effect of solvation
on the proton transfer from enol-imine form to the keto-enamine form have been investigated using the B3LYP hybrid density
functional method at the 6-31G** basis set level 相似文献
Based on experimental evidence and DFT studies, a probable cyclization route to 1,3,5-thiadiazinanes-2-thiones in aqueous
medium is proposed. Experimental facts suggest the formation of a {[hydroxymethyl (substituted) carbamothioyl] sulfanyl}methanol
intermediate via reaction of dithiocarbamate (DTC) and formaldehyde. Nucleophilic addition of glycine to this intermediate
generates an adduct that undergoes intramolecular heterocyclization via an SN2 reaction. Computational calculations predict an active role of water in the reaction mechanism that promotes intramolecular
cyclization.
Figure Energy profile of the proposed reaction mechanism for the synthesis of thiadiazinane-2-thione ring 11 in aqueous medium from
a (hydroxymethylcarbamothioyl)sulfanylmethanol intermediate, 9相似文献
The electric dipole transitions between pure spin and mixed spin electronic states are calculated at the XMC-QDPT2 and MCSCF levels of theory, respectively, for different intermolecular distances of the C6H6 and O2 collisional complex. The magnetic dipole transition moment between the mixed-spin ground (“triplet”) and the first excited (“singlet”) states is calculated by quadratic response at MCSCF level of theory. The obtained results confirm the theory of intensity borrowing and increasing the intensity of electronic transitions in the C6H6?+?O2 collision. The calculation of magnetically induced current density is performed for benzene molecule being in contact with O2 at the distances from 3.5 to 4.5 Å. The calculation shows that the aromaticity of benzene is rising due to the conjugation of π-MOs of both molecules. The C6H6?+?O2 complex becomes nonaromatic at the short distances (r?<?3.5 Å). The computation of static polarizability in the excited electronic states of the C6H6?+?O2 collisional complex at various distances supports the theory of red solvatochromic shift of the a?→?X band.
A series of [XN5]− (X=O, S, Se, Te) compounds has been examined with ab initio and Density Functional Theory (DFT) methods. The five-membered nitrogen ring series of structures are global minima and may exist or be characterized due to their significant dissociation barriers (29.7–32.7 kcal mol−1). Nucleus-independent chemical shifts (NICS) criteria and the presence of (4n+2) π-electrons confirmed that the five-membered nitrogen ring in their structures exhibits characteristics of aromaticity. Thus, the strong stability of the five-membered nitrogen ring structures may be attributed partially to their aromaticity.
相似文献
Eight H-bonded complexes between serotonin (5-hydroxy-tryptamine) and water/hydrogen peroxide were studied at the B3LYP and
HF levels of theory, using the 6-31+G(d) basis set. A thermodynamic analysis was performed in order to find the most stable
complex. The calculated bonding parameters showed that the most stable H-bonded complex is formed between serotonin and hydrogen
peroxide by means of the intermolecular H-bond –H2N...H–OOH.
Fig. a Theoretical study of the hydrogen-bonded supersystems serotonin-water/hydrogen peroxide 相似文献
The unusual T-shaped X–H...π hydrogen bonds are found between the B=B double bond of the singlet state HB=BH and the acid
hydrogen of HF, HCl, HCN and H2C2 using MP2 and B3LYP methods at 6-311++G(2df,2p) and aug-cc-pVTZ levels. The binding energies follow the order of HB=BH...HF>HB=BH...HCl>HB=BH...HCN>HB=BH...H2C2. The hydrogen-bonded interactions in HB=BH...HX are found to be stronger than those in H2C=CH2...HX and OCB≡BCO...HX. The analyses of natural bond orbital (NBO) and the electron density shifts reveal that the nature
of the T-shaped X–H...π hydrogen-bonded interaction is that much of the lost density from the π-orbital of B=B bond is shifted
toward the hydrogen atom of the proton donor, leading to the electron density accumulation and the formation of the hydrogen
bond. The atoms in molecules (AIM) theory have also been applied to characterize bond critical points and confirm that the
B=B double bond can be a potential proton acceptor.
The unusual T-shaped X–H...π hydrogen bonds are found between the B=B double bond of the singlet state HB=BH and the acid
hydrogen of HF, HCl, HCN and H2C2相似文献
As a follow-up study to our study on tetrazane (N4H6), we present computed thermodynamic properties of triazane (N3H5). Calculated properties include optimized geometries, infrared vibrations, enthalpy of formation, enthalpy of combustion,
and proton affinities. We have also mapped the potential energy surface as the molecule is rotated about the N-N bond. We
have predicted a specific enthalpy of combustion for triazane of about -20 kJ g−1.
Figure Schematic diagram of the dielectric barrier discharge (left) and typical temporal profiles of voltage and current, as obtained
from the simulations (right) 相似文献
The protomeric tautomerizm and conformation of the 2-methyl-4-pyridin-2′-yl-1,5-benzodiazepine molecule were investigated,
and its three neutral tautomers (B1,B2,B3) and their rotamers (C1,C2,C3) were considered. Full geometry optimizations were carried out at the HF/6-31G* and B3LYP/6-31G* levels in gas phase and
in water. The tautomerization processes in water (ɛ = 78.54) were studied by using self-consistent reaction field theory.
The calculation showed that the boat conformation is dominant for the seven-membered diazepine ring in all of the structures,
even with different double bond positions. The calculated relative free energies (ΔG) showed that the tautomer C1 was the most stable structure, and its conformer B1 was the second most stable in the gas phase and in water.
Figure 2-Methyl-4-pyridin-2′-yl-1,5-benzodiazepine 相似文献
The applicability of the recently developed PM6 method for modeling various properties of a wide range of organic and inorganic
crystalline solids has been investigated. Although the geometries of most systems examined were reproduced with good accuracy,
severe errors were found in the predicted structures of a small number of solids. The origin of these errors was investigated,
and a strategy for improving the method proposed.
Figure Detail of Structure of Dihydrogen Phosphate in KH2PO4 (upper pair) and in (CH3)4NH2PO4. (Footnote): X-ray structures on left, PM6 structure on right.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
Methylidencyclopropabenzene (MCPB) 1 and Fulvalenes 2–4 are molecules of special interest due to the relation between structure and aromaticity. The aim of this work was to analyze
this relation and to quantify the aromaticity in 1–4 using different methods. Magnetic properties are directly related with aromaticity; here we studied the magnetic susceptibility
and the anisotropy of the magnetic susceptibility. Nucleus indepedent chemical shift (NICS) and the anisotropy of the induced
current density (ACID) were also employed. Tools of very different nature, geometric indexes HOMA and Bird, were determinated
too for 1–4. All of these measures were found to be in agreement.
Figure Both spatial NICS and ACID plot allow to show the aromaticity/antiaromaticity of a ring 相似文献
The catalytic pyrolysis pathways of carbonyl compounds in coal were systematically studied using density functional theory (DFT), with benzaldehyde (C6H5CHO) employed as a coal-based model compound and ZnO, γ-Al2O3, and CaO as catalysts. The results show that the products of both pyrolysis and catalytic pyrolysis are C6H6 and CO. However, the presence of any of the catalysts changes the reaction pathway and reduces the energy barrier, indicating that these catalysts promote C6H5CHO decomposition.
Graphical abstract The presence of catalysts changes the reaction pathway and the energy barrier decreases in the order Ea (no catalyst)> Ea (CaO)> Ea (γ-Al2O3)> Ea (ZnO), indicating that these catalysts promote C6H5CHO decomposition.
A 3D QSAR analysis has been performed on a series of 67 benzodiazepine analogues reported as γ-secretase inhibitors using
molecular field analysis (MFA), with G/PLS to predict steric and electrostatic molecular field interaction for the activity.
The MFA study was carried out using a training set of 54 compounds. The predictive ability of model developed was assessed
using a test set of 13 compounds ( as high as 0.729). The analyzed MFA model has demonstrated a good fit, having r2 value of 0.858 and cross validated coefficient, value as 0.790. The analysis of the best MFA model provided insight into possible modification of the molecules for better
activity.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
Effects of explicit consideration of charges displaced from atomic sites due to atomic orbital hybridization called hybridization-displaced
charges (HDC) on dipole moments and surface molecular electrostatic potentials of certain radicals and their complexes with
closed-shell molecules have been studied. HDC were computed for several radicals and their complexes at the B3LYP/6–31G**
level of theory. At this level, HDC consist of three point charges associated with hydrogen atoms and seven point charges
associated with heavy atoms belonging to the second row of the periodic table. HDC are so calculated that the contribution
of each atom to the component of molecular dipole moment arising due to atomic orbital hybridization is preserved. It is found
that dipole moments and electrostatic potentials of the systems studied here can be obtained with a significantly improved
accuracy using a combination of Mulliken charges and HDC over that obtained by Mulliken charges only.
Figure Surface MEP map of H2O-HO· radical complex obtained using Mulliken charges combined with HDC 相似文献