Following our recent study on triazane, we present a follow-up study on the thermodynamic properties of triazane’s unsaturated
analog, triazene. We predict optimized structural parameters, vibrational frequencies, enthalpies of formation, enthalpies
of combustion, specific enthalpies of combustion, and proton affinities. Our results indicate that the cis form of triazene
has a specific enthalpy of combustion of −15.2 kJ g−1 and the trans form has a specific enthalpy of combustion of −14.7 kJ g−1.
Figure Structures of cis- and trans-triazane, N3H3相似文献
Following our recent studies of the thermodynamic properties of azaspiropentane and borospiropentane, in consideration of
their usefulness as new potential high energy materials, we follow up with ab initio calculations on the thermodynamic properties
of azaborospiropentanes. Properties reported in this study include optimized structural parameters, vibrational frequencies,
enthalpies of formation, specific enthalpies of combustion, proton affinities, and hydride affinities. Our results indicate
that azatriborospiropentane gives off most energy when combusted, as evidenced by its specific enthalpy of combustion of about
−52 kJ per gram.
Figure Optimized geometry for R-azatriborospiropentane (10)
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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
The structure and stability of endohedral X@C20F20 complexes (X = H−, F−, Cl−, Br−, H, He) have been computed at the B3LYP level of theory. All complexes in Ih symmetry were found to be energy minimum structures. H−@C20F20 and F−@C20F20 complexes have negative inclusion energies, while other complexes have positive inclusion energies. Similarity between C20F20 and C20H20 has been found for X = H and He. On the basis of the computed nucleus independent chemical shift values at the cage center,
both C20F20 and C20F20 are aromatic.
Figure Endohedral X@C20F20 complexes 相似文献
Effective force fields for Ni-C interactions developed by Yamaguchi and Maruyama for the formation of metallofullerenes are
modified to simulate the catalyzed growth of single-wall carbon nanotubes on Nin clusters with n >20, and the reactive empirical bond order Brenner potential for C-C interactions is also revised to include the effect of
the metal atoms on such interactions.
Figure Force field parameters for carbon-metal interactions obtained from DFT calculations in small clusters. 相似文献
Theoretical investigation of Pt(0)-olefin organometallic complexes containing tertiary phosphine ligands was focused on the
strength of platinum-olefin electronic interaction. DFT theoretical study of electronic effects in a substantial number of
ethylene derivatives was evaluated in terms of the Pt-olefin binding energy using MP2 correlation theory. Organometallics
bearing coordinated olefins with general formula (R1R2C = CR3R4)Pt(PH3)2 [R = various substituents] had been selected, including olefins containing both electron-donor substituents as well as electron-withdrawing
groups. The stability of the corresponding complexes increases with a strengthening electron-withdrawal ability of the olefin
substituents.
Figure Representation of (CH2 = CHR)Pt(PPh3)2 and the stability chart 相似文献
Dipeptidyl peptidase IV (DPP-IV) deactivates the incretin hormones GLP-1 and GIP by cleaving the penultimate proline or alanine
from the N-terminal (P1-position) of the peptide. Inhibition of this enzyme will prevent the degradation of the incretin hormones
and maintain glucose homeostasis; this makes it an attractive target for the development of drugs for diabetes. This paper
reports 3D-QSAR analysis of several DPP-IV inhibitors, which were aligned by the receptor-based technique. The conformation
of the molecules in the active site was obtained through docking methods. The QSAR models were generated on two training sets
composed of 74 and 25 molecules which included phenylalanine, thiazolidine, and fluorinated pyrrolidine analogs. The 3D-QSAR
models are robust with statistically significant r2, q2, and values. The CoMFA and CoMSIA models were used to design some new inhibitors with several fold higher binding affinity.
Figure The CoMFA contours around molecule D1T155 (a) steric contours - favored (green); disfavored (yellow) (b) electrostatic contours
- electropositive (blue); electronegative (red) 相似文献
The Nafion, Dow and Aciplex systems – where the prime differences lies in the side-chain length – have been studied by molecular
dynamics (MD) simulation under standard pressure and temperature conditions for two different levels of hydration: 5 and 15
water molecules per (H)SO3 end-group. Structural features such as water clustering, water-channel dimensions and topology, and the dynamics of the hydronium
ions and water molecules have all been analysed in relation to the dynamical properties of the polymer backbone and side-chains.
It is generally found that mobility is promoted by a high water content, with the side-chains participating actively in the
H3O+/H2O transport mechanism. Nafion, whose side-chain length is intermediate of the three polymers studied, is found to have the
most mobile polymer side-chains at the higher level of hydration, suggesting that there could be an optimal side-chain length
in these systems. There are also some indications that the water-channel network connectivity is optimal for high water-content
Nafion system, and that this could explain why Nafion appears to exhibit the most favourable overall hydronium/water mobility.
Figure The simulation box for Aciplex with 5 water molecules per sulphonate end-group (yellow spheres). The polymer backbone is black;
while side-chains are brown. The water-channel iso-surfaces are represented as blue clouds 相似文献
The structures and stabilities of square–hexagon alternant boron nitrides (BxNx, x=12–36) vs their tube isomers containing octagons, decagons and dodecagons have been computed at the B3LYP density functional level of theory with the correlation-consistent cc-pVDZ basis set of Dunning. It is found that octagonal B20N20 and B24N24 tube structures are more stable than their square–hexagon alternants by 18.6 and 2.4 kcal mol−1, respectively, while the square–hexagon alternants of other cages are more stable. Trends in stability as a function of cluster size are discussed.Figure The octagonal B20N20 and B24N24 tube structures are more stable than their square-hexagon alternant cagesDedicated to Professor Dr. Paul von Ragué Schleyer on the occasion of his 75th birthday 相似文献
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
Structure-based 3D-QSAR studies were performed on 20 thiazoles against their binding affinities to the 5-HT3 receptor with comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). The thiazoles were initially docked into the binding pocket of a human 5-HT3A receptor homology model, constructed on the basis of the crystal structure of the snail acetylcholine binding protein (AChBP), using the GOLD program. The docked conformations were then extracted and used to build the 3D-QSAR models, with cross-validated values 0.785 and 0.744 for CoMFA and CoMSIA, respectively. An additional five molecules were used to validate the models further, giving satisfactory predictive values of 0.582 and 0.804 for CoMFA and CoMSIA, respectively. The results would be helpful for the discovery of new potent and selective 5-HT3 receptor antagonists.
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
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
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
Twelve H-bonded supersystems constructed between the adenine tautomers and methanol, ethanol, and i-propanol were studied
at the B3LYP and MP2 levels of theory using 6-311G(d,p) and 6-311++G(d,p) basis functions. The thermodynamic parameters of
the complex formations were calculated in order to estimate the exact stability of the supersystems. It was proven that the
calculated energy barriers of the alcohol-assisted proton transfers are about 60% lower than those of the intramolecular proton
transfers in adenine found earlier (Gu and Leszczynski in J Phys Chem A 103:2744–2750, 1999).
Figure H-bonded complex between i-propanol and adenine 相似文献
Umpolung catalysis is studied by a sequence of model reactions (CPCM in THF, B3LYP/6-31G*) with different aldehydes and catalysts. We involved addition of the catalyst to the aldehyde and 1,2-H-migration to form a carbanionic d1-species, which is the crucial intermediate according to the Lapworth- and Breslow-mechanisms. Cyanide, N-methylthiazol-2-ylidene, and a glycol-based phosphite perform as umpolung catalysts, formaldehyde, acetaldehyde, benzaldehyde, and acrolein are substrates in this study. In these aldehyde substrates, alkyl-substitution disfavors but π-conjugation favors formation of the carbanionic d1-intermediate. The nucleophilic carbene, N-methylthiazol-2-ylidene, is the strongest umpolung catalyst, while the phosphite is about as active as cyanide.
Figure Transitions structure for the umpolung of formaldehyde with a glycol phosphinite catalyst
Dedicated to Professor Dr. Paul von Ragué Schleyer on the occasion of his 75th birthday 相似文献
We present the results of simulations of a CCl4 monolayer adsorbed on a graphite surface. The CCl4 molecule was represented either by a shapeless superatom or by its atomic sites. The simulations were carried out over a
large range of temperatures, from 20 K up to 340 K. We address the following problems: (1) the influence of molecular shape
on the structure and stability of phases (particularly at low temperatures), and (2) the influence of the graphite corrugation
on layer stability and mechanism of phase transitions. In particular, we discuss the possibility and conditions of the appearance
of hexatic phase in the system.
Figure Temperature dependence of Φ6 order parameter for CCl4 monolayer adsorbed onsmooth and corrugated surfaces, in the spherical Lennard Jones (LJ) approximation.For comparison, the
order parameter calculated for MacDonald’s five-site potential is also presented 相似文献
3D-QSAR and molecular docking analysis were performed to explore the interaction of estrogen receptors (ERα and ERβ) with
a series of 3-arylquinazolinethione derivatives. Using the conformations of these compounds revealed by molecular docking,
CoMFA analysis resulted in the first quantitative structure-activity relationship (QSAR) and first quantitative structure-selectivity
relationship (QSSR) models predicting the inhibitory activity against ERβ and the selectivity against ERá. The q2 and R2 values, along with further testing, indicate that the obtained 3D-QSAR and 3D-QSSR models will be valuable in predicting
both the inhibitory activity and selectivity of 3-arylquinazolinethione derivatives for these protein targets. A set of 3D
contour plots drawn based on the 3D-QSAR and 3D-QSSR models reveal modifications of substituents at C2 and C5 of the quinazoline
which my be useful to improve both the activity and selectivity of ERβ/ ERα. Results showed that both the steric and electrostatic
factors should appropriately be taken into account in future rational design and development of more active and more selective
ERβ inhibitors for the therapeutic treatment of osteoporosis.
Figure Structures of ERβ binding with compounds 1aar, 1ax and 1aag obtained from molecular docking 相似文献
An accurate comparison of the interaction of furan, pyrrole, and thiophene with different gaseous analytes is vital not only for understanding the sensing mechanism of corresponding polymers but also for rational design of new materials. In the present study, DFT calculations at (M05-2X/Aug-cc-PVDZ) have been performed to investigate the interaction behavior of furan, pyrrole, and thiophene (as models for their corresponding polymers) with different analytes (NH3, CO2, CO, N2H4, HCN, H2O2, H2S, CH4, CH3OH, SO2, SO3, H2O). The interaction of heterocycles with analytes is illustrated by changes in geometric, energetic, and electronic properties. SAPT calculations were performed for energy decomposition analysis to study the contribution of non-covalent components of the total interaction energy for each complex. Analysis of energetic and electronic properties reveals that all heterocycles are highly sensitive to SO3. The results suggest that sensing ability of polypyrrole is higher than polyfuran and polythiophene for all analytes.
Three of the most frequent antitubercular agents employed against Mycobacterium tuberculosis are: Rifampicin, Isoniazid and
Pyrazinamide. It has been proven that the use of these antitubercular agents together, shortens the treatment period from
12–18 months to 6 months [1]. In this work we use a new Density Functional Theory chemistry model called CHIH-DFT (Chihuahua-Heterocycles-Density Functional
Theory) that reflects the mixture of Hartree Fock exchange and DFT exchange, according to a mixing parameter based on empirical
rules suited for heterocyclic systems. This new chemistry model was used to calculate the molecular structure of these antitubercular
compounds, as well as their infrared, UV spectra, chemical reactivity and electronic properties. The UV and infrared spectra
were obtained by experimental techniques. The calculated molecular structure, UV and IR spectra values from CHIH-DFT were
compared with experimentally obtained values and theoretical studies. These results are in good agreement with experimental
and theoretical studies. We also predicted using the relative electrophilicity and relative nucleophilicity concepts as defined
by Roy et al. [2] the chemical active sites for the three antitubercular compounds as well as their electronegativity, ionization potential,
electron affinity, hardness, dipole moment, EHOMO-ELUMO gap energy, etc.
相似文献