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1.
The acid-catalyzed models on reaction mechanisms of pinacol rearrangement of propylene glycol conversion to propanal and propanone have been investigated using the density functional method at 298.15 K. Thermodynamic quantities of activation steps of four water-addition models were obtained. The number of added water interacting with the transition states of three concerted pathways has obviously affected the product ratio. The relative energetic profiles of the conversion reactions of all solvation models have been comparatively displayed. Estimation of the percent ratio of product composition computed from activation free energies of each acid-catalyzed reaction model was carried out. The percent ratios of propanal and propanone were decreased as the number of added water increased. 相似文献
2.
Thawatchai Tuntulani Praput Thavornyutikarn Sirilux Poompradub Nongnuj Jaiboon Vithaya Ruangpornvisuti Narongsak Chaichit Zouhair Asfari Jacques Vicens 《Tetrahedron》2002,58(52):10277-10285
Tripodal aza crown ether calix[4]arenes, 5a, 5b, 6a and 6b, have been synthesized. The structure of protonated 5a was elucidated by X-ray crystallography to be a self-threaded rotaxane. Complexation studies of 5a and 5b towards anions using Na+ as countercation were carried out by 1H NMR titration in dimethylsulfoxide-d6 and the mixture of chloroform-d and methanol-d4, respectively. Ligands 5a and 5b were able to form 1:1 complexes with Br−, I− and NO3− and the complexation stability varied as follows: NO3−>I−>Br−. The effect of countercation on anion complexation was also investigated. The results showed that the association constants of 5a towards Br− in the presence of various cations varied as K+>Bu4N+>Na+. The enhancement in anion complexation ability of 5a may result from the rearrangement of the tripodal ammonium unit in the presence of K+. The neutral forms, 6a and 6b, were able to form complexes with transition metal ions such as Co2+, Ni2+, Cu2+ and Zn2+. The stability of the complexes followed the sequence: Ni2+2+Cu2+Zn2+. Compounds 6a and 6b may, therefore, potentially be used as either transition metal ion or anion receptors that can be controlled by pH of the solution. 相似文献
3.
Waranyu PipornpongRaina Wanbayor Vithaya Ruangpornvisuti 《Applied Surface Science》2011,257(24):10322-10328
The adsorption energies for physisorption and the most stable chemisorption of CO2 on the neutral charge of perfect anatase [TiO2] (0 0 1) are −9.03 and −24.66 kcal/mol on the spin-unpolarized and −12.98 and −26.19 kcal/mol on the spin-polarized surface. The small activation barriers of 1.67 kcal/mol on the spin-unpolarized surface and of 6.66 kcal/mol on the spin-unpolarized surface were obtained. The adsorption mechanism of CO2 on the oxygen vacancy defect [TiO2 + VO] surface of anatase TiO2 using density functional theory calculations was investigated. The energetically preferred conversion of CO2 to CO was found either on the spin-unpolarized or spin-polarized surfaces of oxygen vacancy defect surface [TiO2 + VO] as photocatalyst. 相似文献
4.
Vithaya Ruangpornvisuti 《Structural chemistry》2007,18(6):977-984
The structure optimizations of picolinaldehyde N-oxide thiosemicarbazone (Hpiotsc), 2-benzoylpyridine semicarbazone (H2BzPS),
their imino tautomers and their complexes with Ni(II), Cu(II), and Zn(II) were carried out using DFT calculations. The structures
of Hpiotsc and H2BzPS ligands, transition states of their tautomerizations were obtained at the B3LYP/6-31+G(d,p) level and
their thermodynamic properties were derived from the frequency calculations at the same level of theory. The B3LYP/LANL2DZ-optimized
structures of Hpiotsc and H2BzPS complexes with Ni(II), Cu(II), and Zn(II), and the thermodynamic properties of their complexations
derived from the B3LYP/LANL2DZ-frequency calculations were obtained. The B3LYP/LANL2DZ-optimized geometrical parameters for
the [Ni(Hpiotsc)2]2+, [Cu(Hpiotsc).Cl2], and [Zn(Hpiotsc).Cl2] complexes show good agreement with their corresponding X-ray crystallographic data. 相似文献
5.
This report describes a new spectrophotometric method capable of determining low levels of
-glutamate. The assay is based on substrate cycling between
-glutamate dehydrogenase (GlDH) and the novel enzyme
-phenylglycine aminotransferase (
-PhgAT). In this system, GlDH converts
-glutamate to 2-oxoglutarate with concomitant reduction of NAD+ to NADH. The 2-oxoglutarate is recycled to
-glutamate in a transamination reaction catalyzed by
-PhgAT using
-4-hydroxyphenylglycine as an amino donor, which is converted to 4-hydroxybenzoylformate. Both NADH and 4-hydroxybenzoylformate strongly absorb UV light at 340 nm (340nm=6.22×103 and 8.90×103 l mol−1 cm−1, respectively). The signal amplification effect of the cycling reactions is thus further enhanced by the combined absorption of the two accumulating reaction products. The standard calibration curve for
-glutamate was linear from 0.2 to 20 μM, with a detection limit of 0.14 μM. Food samples can be significantly diluted before subjected to the assay, thus reducing the effects of interfering substances. Because of the unique substrate specificity of
-PhgAT,
-glutamate could be selectively determined in the presence of other common amino acids at relatively high concentrations. The assay was satisfactorily applied to measure
-glutamate in various kinds of food products. The procedure is simple, rapid, accurate, and should be easily automated. 相似文献
6.
Siwinee Tetasang Somchai Keawwangchai Banchob Wanno Vithaya Ruangpornvisuti 《Structural chemistry》2012,23(1):7-15
The structures of mono- and di-podal pyrrolic amides functionalized (5,5) single-walled carbon nanotubes (SWCNTs) and their
complexes with fluoride, chloride, and bromide ions were obtained using the two-layered ONIOM(MO:MO) and density functional
theory (DFT) methods. The binding energies between halide ions and all the receptors and their charge transfers were obtained
using DFT method. The computational results indicate that the pyrrolic amide functionalized on the SWCNT affects to the density
of state and energy gap of SWCNT. All the free receptors, mono-, di-podal pyrrolic amides and the functionalized SWCNT forming
the strongest complexes were found. 相似文献
7.
Vithaya Ruangpornvisuti 《International journal of quantum chemistry》2009,109(2):275-284
The structures of nitrosothiol isomers were obtained by geometry optimizations using the density functional theory calculations. Two cis‐isomeric, 2 trans‐isomeric, and 1 zwitterionic species of the HSNO isomers were found and the most stable species is the trans‐isomer. Energetics, thermodynamic properties, rate constants, equilibrium constants of all transformation reactions, and their energy profiles were obtained. Decomposition of the HSNO trans‐isomer to nitric oxide was investigated and its rate constant was obtained. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 相似文献
8.
Sirichai Piyaauksornsak Totsaporn Tangthongkul Raina Wanbayor Banchob Wanno Vithaya Ruangpornvisuti 《Structural chemistry》2009,20(5):767-780
The structures of 8,8′-bis(3-phenylthioureidomethyl)-2,2′-binaphthalene (1), 8,8′-bis(3-butylthioureidomethyl)-2,2′-binaphthalene (2) and their complexes with anionic guests such as carboxylate ions (acetate, oxalate, malonate, succinate, glutarate, adipate,
pimelate, suberate, and azelate), inorganic oxygen-containing anions (nitrate, sulfate, bicarbonate, hydrogen phosphate, and
dihydrogen phosphate), and halide ions (fluoride, chloride, and bromide) were obtained using the ONIOM approach. The binding
abilities of receptors 1 and 2 to anionic species in terms of binding energy, thermodynamic properties, and selectivity coefficient were obtained at the
ONIOM(B3LYP/6-31G(d):AM1) and BSSE-corrected B3LYP/6-31G(d)//ONIOM(B3LYP/6-31G(d):AM1) levels of theory. The multipoint hydrogen
bonding between receptors (either the receptor 1 or 2) and anionic guests were found. The hydrogen phosphate is the most preferable ion to bind with either the receptor 1 or 2. 相似文献
9.
The optimized structures of all isomers of HBI, HBO, HBT, HPyBI, HPyBO, and HPyBT compounds were obtained using the potential
energy surface method at the B3LYP/6-311++G(d,p) level of theory. Four isomers and three transition states of their transformations
for each compound of HBO, HBT, HPyBO, and HPyBT and two isomers and one transition state for each HBI and HPyBI compounds
were found. Energetics, thermodynamic properties, rate constants, and equilibrium constants of their transformations were
determined.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
Wanbayor R Deák P Frauenheim T Ruangpornvisuti V 《The Journal of chemical physics》2011,134(10):104701
First principles density functional theory calculations were carried out to investigate the adsorption and oxidation of CO on the positively charged (101) surface of anatase, as well as the desorption of CO(2) from it. We find that the energy gain on adsorption covers the activation energy required for the oxidation, while the energy gain on the latter is sufficient for the desorption of CO(2), leaving an oxygen vacancy behind. Molecular dynamics simulations indicate that the process can be spontaneous at room temperature. The oxidation process described here happens only in the presence of the hole. The possibility of a photocatalytic cycle is discussed assuming electron scavenging by oxygen. 相似文献