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Ab initio study regarding the evaluation of the antioxidant character of cyanidin, delphinidin and malvidin

100%
Pop R., Ştefănut M., Căta A., Tănasie C., Medeleanu M.
Open Chemistry
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2012
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vol. 10
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issue 1
180-186
EN
A theoretical study regarding the evaluation of the antioxidant character of three of the most wide-spread anthocyanidins (cyanidin, delphinidin and malvidin) was carried out at ab initio level. Different parameters (bond dissociation enthalpy, ionization potential, proton affinity, and electron transfer enthalpy) were computed for each OH group of the compounds in order to predict their antioxidant capacity. Several molecular descriptors based on frontier molecular orbital theory (hardness, electrophilicity, frontier charge density) were also calculated, as well as the atomic charges corresponding to the O atoms of the hydroxyl groups.
2
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Ab initio study of hydrogen bond complexes of ring compounds containing the H2N-C=Y moiety with water

100%
Liu T., Liu G.-D., Yu Z.-Y.
Open Chemistry
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2010
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vol. 8
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issue 5
1117-1126
EN
Ab initio calculations, including natural charge population and natural resonance theory analyses, have been carried out to study the two-way effects between hydrogen bonds (H-bonds) and the intramolecular resonance effect by using the H-bonded complexes of ring compounds containing the H2N-C=Y moiety (C=Y bond is contained in the six-membered or five-membered rings) with water as models. The amino groups in the four monomers of ring compounds (FAYs, Y represents the heavy atoms in the substituent groups, =CH, =N, =SiH, and =P, respectively) can all serve as H-bond donors (HD) and H-bond acceptors (HA) to form stable H-bonded complexes with water. The HD H-bond and resonance effect enhance each other (positive two-way effects) whereas the HA H-bond and resonance effect weaken each other (negative two-way effects). The resonance effect in FAY(1) (C=Y bond is contained in the six-membered rings) is weaker than that in formamide, and those in FAY(2) and FAY(3) (C=Y bonds are contained in the five-membered rings). The two-way effects between H-bond and resonance effect exist in the H-bonded complexes of ring compounds containing the H2N-C=Y moiety with water. [...]
3
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The intermolecular interactions in the aminonitromethylbenzenes

100%
Kruszynski R., Sieranski T.
Open Chemistry
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2011
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vol. 9
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issue 1
94-105
EN
The intermolecular non-covalent interactions in aminonitromethylbenzenes namely 2-methyl-4-nitroaniline, 4-methyl-3-nitroaniline, 2-methyl-6-nitroaniline, 4-amino-2,6-dinitrotoluene, 2-methyl-5-nitroaniline, 4-methyl-2-nitroaniline, 2,3-dimethyl-6-nitroaniline, 4,5-dimethyl-2-nitroaniline and 2-methyl-3,5-dinitroaniline were studied by quantum mechanical calculations at RHF/311++G(3df,2p) and B3LYP/311++G(3df,2p) level of theory. The calculations prove that solely geometrical study of hydrogen bonding can be very misleading because not all short distances (classified as hydrogen bonds on the basis of interaction geometry) are bonding in character. For studied compounds interaction energy ranges from 0.23 kcal mol−1 to 5.59 kcal mol−1. The creation of intermolecular hydrogen bonds leads to charge redistribution in donors and acceptors. The Natural Bonding Orbitals analysis shows that hydrogen bonds are created by transfer of electron density from the lone pair orbitals of the H-bond acceptor to the antibonding molecular orbitals of the H-bond donor and Rydberg orbitals of the hydrogen atom. The stacking interactions are the interactions of delocalized molecular π-orbitals of the one molecule with delocalized antibonding molecular π-orbitals and the antibonding molecular σ-orbital created between the carbon atoms of the second aromatic ring and vice versa. [...]
4
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Conformational study on the structures and energies of the weakly bound complexes of AlCl3 with diatomic molecules

100%
Jimenez-Fabian I., Jalbout A., Boutalib A.
Open Chemistry
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2007
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vol. 5
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issue 4
1007-1018
EN
In this work we present the results of high level ab initio calculations on weakly bound complexes of aluminium trichloride and hydrogen halides, HX, halogens, X2 and diatomic interhalogens, XY (where X, Y = F, Cl, Br). Based upon these calculations we have predicted that all structures in the staggered conformation (except for Cl3AlFH and Cl3AlClH) are stable minima while those in the eclipsed configurations are transition state structures. In the XH complexes the strength of interaction with the Cl3Al group is FH > ClH > BrH. In the case of X2 species it is Br2 > F2 > Cl2, and finally in the XY (YX) group it is: FBr > ClBr > FCl > BrCl > BrF > ClF. [...]
5
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A G2(MP2) theoretical study of substituent effects on H3BNHnCl3−n (n= 3-0) donor-acceptor complexes

88%
Anane H., Houssame S., Guerraze A., Guermoune A., Boutalib A., Jarid A., Nebot-Gil I., Tomás F.
Open Chemistry
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2008
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vol. 6
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issue 3
400-403
EN
The complexation energies of H3BNHnCl3−n (n= 3-0) complexes and the proton affinities of NHnCl3−n compounds have been computed at the G2(MP2) level of theory. G2(MP2) results show that the successive chlorine substitution on the ammonia decreases both the basicity of the NHnCl3−n ligands and the stability of H3BNHnCl3−n complexes. The findings are interpreted in terms of the rehybridisation of the nitrogen lone-pair orbital. The NBO partitioning scheme shows that the variation of the N-H and N-Cl bond lengths, upon complexation, is due to variation of “s” character in these bonds. [...]
6
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The role of F A1:Ag+ defects in laser light generation and coadsorption of CO and halogen atoms at the KCl and KBr surface sites. First principles calculations

63%
Abdelrazik S., Shalabi A.
Open Physics
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2007
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vol. 5
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issue 4
611-636
EN
FA1:Ag+ color center at the low coordination (100) and (110) surface sites of KCl and KBr thin films play an important role in providing tunable laser oscillation and adsorbatesubstrate interactions. Double-well potentials at this site are investigated using ab initio molecular electronic structure calculations. The calculated Stokes shifted (optical transition bands), opticaloptical conversion efficiencies, the probability of orientational destruction, exciton (energy) transfer and Glasner-Tompkins empirical rule suggest that laser light generation is sensitive to (i) the lattice anion, (ii) the coordination number of surface ions, and (iii) the choice of the basis set centered on the anion vacancy. The adsorbate-substrate interactions were found to be dependent on the electronegativity of the adatom and on the lattice anion. Optimised geometries and the coadsorption of CO and (F, Cl, Br, I) on KCl and KBr (100) crystals are presented. Calculated chemisorption energies for CO on the (halogen atom/defect free sites of KCl and KBr (100) crystals) showed that the coadsorption of halogen atom tends to block other adsorbate-substrate interactions at the nearest neighbour sites. Thus if halogen atom coverage increases, the CO prefers to be adsorbed on the K+ site of the KCl and KBr (100) surfaces and on KBr relative to KCl.
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