Adsorption of Rare Earth Ion La(Ⅲ) on Yunnan Bowl Tea Surface from Aqueous Solution

The adsorption characteristics of rare earth ion La(Ⅲ) on Yunnan bowl tea surface from aqueous solution and effects of various surfactants on the adsorption were studied. It was found that Yunnan bowl tea can adsorb strongly La(Ⅲ) and pH may affect drastically the adsorption amount of La(Ⅲ). The adsorption law of La(Ⅲ) on Yunnan bowl tea surface follows the Langmuir equation. The maximum adsorption amount of La(Ⅲ) can reach 15 mg·g (-1). A comprehensive adsorption model is suggested according to the experimental results.

Addition Mechanisms of Phenol toward Formaldehyde under Acidic Condition: a Theoretical Investigation

The reaction mechanisms of phenol with formaldehyde in the first and second addition at the ortho- and para-position in acid solution were theoretically investigated at the PW91/DNP level with solvent effects included. The reaction of phenol with protonated methanediol firstly forms an adduct intermediate, via a SN2 mechanism with a water molecule as the leaving group. From the adduct intermediate, there are two reaction channels involving a proton transfer to form the addition products. One is that a proton directly transfers via a four-membered ring transition state with a notable energy barrier （Four-member mechanism）. Another mechanism involving a water molecule as catalyst to mediate the proton transfer （WCP mechanism）, is a barrierless process, indicating that the formation of the adduct intermediate, the first reaction step, is rate-limiting. The reaction products are free hydroxymethyl phenols and/or hydroxybenzy carbocation （HOC6H4CH2＋） which plays an important role in the following formation of methylene and methylene ether linkages. The second addition reactions between formaldehyde and hydroxymethyl phenol at all possible reaction sites of the phenol ring in acid solution were also investigated and discussed.

Initial atmospheric corrosion of zinc in presence of Na_2SO_4 and (NH_4)_2SO_4

Initial atmospheric corrosion of zinc in the presence of Na2SO4 and (NH4)2SO4 was investigated via quartz crystal microbalance(QCM) in laboratory at relative humidity(RH) of 80% and 25 ℃. The results show that both Na2SO4 and (NH4)2SO4 can accelerate the initial atmospheric corrosion of zinc. The combined effect of Na2SO4 and (NH4)2SO4 on the corrosion of zinc is greater than that caused by (NH4)2SO4 and less than that caused by Na2SO4. Fourier transform infrared spectroscopy(FTIR), X-ray diffractometry(XRD) and scanning electron microscopy(SEM) were used to characterize the corrosion products of zinc. (NH4)2Zn(SO4)2, Zn4SO4(OH)6·5H2O and ZnO present on zinc surface in the presence of (NH4)2SO4 while Zn4SO4(OH)6·5H2O and ZnO are the dominant corrosion products on Na2SO4-treated zinc surface. Probable mechanisms are presented to explain the experimental results.

Apoptotic Effects of Hypocrellin A on HeLa Cells

Hypocrellin A（ HA）, a photosensitive perylenequinone compound of Hypocrella bambusae, inhibited the proliferation of several tumor cell lines. Human cervical cancer cells, HeLa ceils, were used as a model to elucidate the molecular mechanisms of HA-induced tumor cell death. The results show that HA can induce the oligonucleosomal fragmentation of DNA in HeLa cells and also can increase the expression of apoptosis inducer Bax mRNA and that it decreases the expression of apoptosis suppressor, Bcl-2 mRNA, in mitochondria. It can be concluded from the data that HA-induced apoptosis is related to the balance between Bcl-2 and Bax gene expressions.

DFT Study on the Os^+-catalytic Reduction Reaction of N_2O with H_2 in the Gas Phase

The Os＋-catalytic reduction of N2O by H2 in gas phase has been theoretically investigated with B3LYP method.The reaction mechanisms on the sextet and quartet surfaces were found to be similar.The calculated sextet potential energy profiles show that the two reactions involved in the catalytic cycle,Os＋ ＋ N2O → OsO＋ ＋ N2 and OsO＋ ＋ H2 → Os＋ ＋ H2O,have barriers of 28.3 and 123.3 kJ/mol,respectively.In contrast,the reactions on the quartet surfaces are energetically much more favorable.These results rationalize the experimentally observed low catalytic reactivity of sextet（ground-state） Os＋.Further,the crossing between the sextet and quartet surfaces are also suggested and qualitatively discussed.

Theoretical Study on the Reaction of Thymine with Iodomehane in the Water Phase

The reaction mechanisms of carcinogenic methylating agent iodomethane （MeI） with keto and enol tautomers of thymine （K- and E-thymine） were studied by using the B3LYP/6-311＋G （d, p） method in water phase. The solvent effects were examined using the polarizable continuum model （PCM）. Specifically, PCM single-point calculations at the same level of theory were performed in acetone and CCl4 that represent a range in nonpolarity. The calculated results show that the reaction of K-thymine with MeI is a two-step mechanism, whereas that of E-thymine is a one-step mechanism. Our calculations reveal that K-thymine is appreciably more stable than the enol form in the water phase or in the two solvents. The K- and E-form reaction barriers are 135.6 and 222.1 kJ/mol, respectively in water phase. These findings indicate that the reactions mentioned above could not occur efficiently in biological media in the absence of catalyst. Our conclusions are in agreement with the previous studies on the reactions of guanine with methyl chloride and methyl bromide.

2D-QSARs of 1-Alkoxymethyl-5-alkyl-6-naphthylmethyl Uracils as HEPT Analogues with Anti-HIV-1 Activity

The two-dimensional Quantitative Structure-Activity Relationship （2D-QSAR） models have been developed to estimate and predict the inhibitory activities of a series of HEPT analogues against HIV-1 by using quantum chemical parameters and physicochemical parameters. The best model of three parameters yields r = 0.908, r^2A = 0.800 and s = 0.467 based on stepwise multiple regression （SMR） method. The stability of the model has been verified by t-test, and the results show that the model has perfect robustness. The predictive power of QSAR models has been tested by Leave-One-Out （LOO） and Leave-Group（regularly random set）-Out（LGO） procedure Cross-Validation methodology. The r^2cv of 0.755 and r^2pred of 0.759 were obtained, respectively.

Methyl and methane elimination in the gas phase reaction of zirconium atom with 2-butyne:A DFT study

The mechanisms for CH3- and CH_4-elimination in the gas phase reaction of ground-state Zr with 2-butyne has been investigated in detail using B3LYP method.For the elimination of CH3,two mechanisms which are similar to those previously found for the reactions of Y and Zr with propyne are identified.The mechanism for the elimination of CH_4 was revealed as：Zr ＋ CH3C≡CCH_3→π-complex→TS（H-migration）→HZr-（H2CCC）-CH3→TS（C-C insertion）→（H2CCC）-HZr-CH3→TS（H-migration）→CH4＋ ZrC3H2.

Theoretical Study on the Dehydrogenation Reaction of H_2S by VS^+ (~3Σ^-)

The dehydrogenation reaction of H2S by the ^3Σ^- ground state of VS^＋： VS^＋ ＋ H2S → VS2^＋ ＋ H2 has been studied by using Density Functional Theory （DPT） at the B3LYP/DZVP level. It is found that the reaction proceeds along two possible pathways （A and B） yielding two isomer dehydrogenation products VS2^＋-1 （^3B2） and VS2^＋-2 （^3A1）, respectively. For both pathways, the reaction has a two-step-reaction mechanism that involves the migration of two hydrogen atoms from S2 to V^＋, respectively. The migration of the second hydrogen via TS3 and that of the first via TS4 are the rate-determining steps for pathways A and B, respectively. The activation energy is 17.4 kcal/mol for pathway A and 22.8 kcal/mol for pathway B relative to the reactants. The calculated reaction heat of 9.9 kcal/mol indicates the endothermicity of pathway A and that of -11.9 kcal/mol suggests the exothermicity of pathway B.

Theoretical Study of the Photochemical Reaction Mechanism of Bicyclo[4.1.0]heptane

The photochemical reaction of bicyclo[4.1.0]heptane was studied at the complete active space SCF（CASSCF） level with a 6-31G^＊ basis set. A muhireference MP2 algorithm that has been implemented in the Gaussian program was used to correct the energetics for the dynamic correlation. Starting from the Franck-Condon excitation of bicyclo [ 4.1.0 ] heptane, the reaction is via two bonds＇ breakage to give rise to 1,6-heptdiene. One internal conversion （IC） and two intersystem crossing points（ISC） were located and are discussed separately. The reaction proceeds to its own characteristic product on the ground state.

The Nature of Bonding in WC and WN

The nature of bonding in the title compounds has been studied by using CASSCF and FOCI techniques. The ground states of WC and WN are found to be 3Δ and 4∑- state arising primarily from:...1(22(21(41(13(1 and ...1(22(21(41(23(1 configuration respectively. WC shows a strong character of covalent bond while WN have obvious character of ionic bond and the dissociation energy of WN is larger than that of WC (6.15 and 5.41 eV respective).

The Nature of Bonding in PtC and PtN

The nature of bonding in the title compounds has been studied by using CASSCF and FOCI techniques. The ground states of PtC and PtN are found to be (1)Sigma (+) and (2)Pi state arising primarily from:... 1 sigma (2)2 sigma (2)1 pi (4)1 delta (4)3 sigma (2) and...1 sigma (2)2 sigma (2)1 pi (4)1 delta (4)3 sigma (2)2 pi (1) configuration respectively and both of which form triple bond tone sigma, two pi bonds), but the bond of PtC is much stronger than that of PtN.

Theoretical study on the reaction of VS^+(~3∑^-,~1Γ)with CO

Two possible reaction mechanisms of VS^＋（^3∑^-, 1^Г） with CO in the gas phase have been studied by using B3LYP/TZVP and CCSD（T）/6-311＋G （3df, 3pd） methods： the O/S exchange reaction （VS^＋＋CO→VO^＋＋CS） and the S-transfer reaction （VS^＋ ＋ CO → V^＋ ＋ COS）. The two reactions proceed via two-step and one-step mechanism, respectively. The barriers of the triplet and singlet PESs are 30.6 and 50.9 kcal/mol, respectively, for O/S exchange reaction and 7.3 and 50.2 kcal/mol, respectively, for the S-transfer reaction. The results indicate that the triplet ground state reaction is more favorable, and the S-transfer reaction is more favorable than the O/S exchange reaction, which is in good agreement with the experimental observation.

Theoretical Study on the Triplet-sensitized Photolysis of 2,5-Dimethylfuran

In the present work, the triplet-sensitized photolysis of 2,5-dimethylfuran has been investigated with the complete active space SCF （CASSCF） molecular orbital method. Two different reaction routes through diradical and carbene intermediates respectively have been systematically studied, and the reaction via carbene intermediate is the major part well compatible with experiment. Geometries of minima and transition states on S0T1 surface were fully optimized at the CAS level with a 6-31G^＊ basis set. A multireference MP2 algorithm that has been implemented in Gaussian was used to correct the energetics for dynamic correlation. Four intersystem crossing points have been located and discussed, and two of them are efficient. Our computation indicates that the reaction must occur on the triplet-excited state.

Theoretical Study on Photoisomerization of 2-Methylfuran to 3-Methylfuran

In the present work, the photoisomerization of 2-methylfuran to 3-methylfuran is investigated with the complete active space SCF （CASSCF） molecular orbital method. Geometries of minima and transition states on the excited and ground states are fully optimized at the CAS level with a 6-3 IG＊ basis set. A multireference MP2 algorithm that has been implemented in Gaussian is used to correct the energetics for dynamic correlation. The topology and reaction funnels of the singlet, triplet （S0, T1, T2） and potential energy surfaces have been characterized along the reaction coordinates corresponding to the mechanism. The reaction proceeds via two diradical intermediates, one intermediate product and four transition states. The two diradical S 1/T2 and T1/S0 energy surface crossing points are located along the reaction path and a T1/T2 conical intersection is also located. From this point the reaction soon returns to T1 surface. It is the most reasonable that the intersystem crossing from T1 to S0 takes place.

Initial atmospheric corrosion of Zinc sprayed with NaCl

Regularities of the initial atmospheric corrosion of zinc sprayed with different amount of NaCl exposed to air at 80% relative humidity and 25 ℃ were investigated via quartz crystal microbalance in laboratory. The results show that NaCl can accelerate the corrosion of zinc. Mass gain of zinc increases with the exposure time increasing, which can be correlated by using exponential decay function. The relationship between mass gain and amount of NaCl sprayed at a certain exposure time follows a quadratic function. Meanwhile, Fourier transform infrared spectroscopy, X ray diffraction, scanning electron microscopy and electron dispersion X ray analysis were used to characterize the corrosion surface and products. Zn 5(OH) 8Cl 2·H 2O and ZnO are the dominant corrosion products, which unevenly distribute on the surface of zinc in the presence of NaCl. A probable mechanism is simply presented to explain the experimental results.

COS Activation by Zr^+ in the Gas Phase:A Case of Two-state Reactivity Process

To elucidate the mechanisms of Zr ＋ reacting with COS,both the quartet and doublet potential energy surfaces （PESs） for reactions of Zr ＋ （4 F,2 D） with COS in the gas phase have been investigated in detail by means of density functional method （B3LYP）.To obtain more accurate results,the coupled cluster single-point calculations （CCSD（T）） using B3LYP optimized geometries were performed.For the C-O bond activation,the calculated results indicate that both the quartet and doublet states proceed via an insertion-elimination mechanism.For the C-S bond activation,the quartet reaction has an insertion-elimination mechanism,but the doublet reaction is a direct abstraction of the sulfur atom by Zr ＋.The C-S bond activation is found to be energetically more favorable than the C-O bond activation.It is found that the reaction of the 4 F gound state of Zr ＋ to yield ZrO ＋ is spin-forbidden （Zr ＋ （4 F） ＋ COS （1 Σ） → ZrO ＋ （2） ＋ CS （1 Σ）） and the crossing points were approximately determined.All the results have been compared with the existing experimental and theoretical data.

Theoretical Study of the Reactivity of Mn^+ with CS_2

The reactions of Mn＋（7S,5S） with CS2 have been studied at the B3LYP/TZVP level on both septuplet and quintet potential energy surfaces（PESs）.The overall energies have been refined at the CCSD（T） level.The calculated results indicate that the reactions of Mn＋（7S,5S） with CS2 proceed via an insertion-elimination mechanism.Calculations show that the quintet reaction is more favorable than the septuplet under high energy conditions.The spin-forbidden reaction Mn＋（7S） ＋ CS2 → MnS＋（5Π） ＋ CS proceeds through a septuplet-quintet surface and the crossing seam is approximately determined.All results have been compared with the existing experimental and theoretical data.

Theoretical Study on the Gas Phase Reaction of Au^+ with CS_2

The reaction of Au＋（1S,3D） with CS2 has been investigated at the B3LYP and CCSD（T） levels of theory.The identified reaction pathways revealed that the experimentally observed products,AuS＋ and AuCS＋,can be produced by the insertion of Au＋ into C-S bond.The calculated energetics shows that the reactions on singlet surface lead to excited-state products,AuS＋（1Σ） ＋ 1CS and AuCS＋（1Σ） ＋ 1S,and have notable energy barriers,whereas the reactions on triplet surface producing the ground state products of AuS＋（3Σ） ＋ 1CS and AuCS＋（1Σ） ＋ 3S are energetically much more favorable.This result suggests that the minor formations of AuS＋ and AuCS＋ observed in the previous experiment under room-temperature condition should result from the reactions of excited-state Au＋（3D） with CS2.Further,the possibility for singlet-triplet surface crossing was also discussed by approximately determining the crossing region.

A computational study on the gas phase reaction of Os^+ with N_2O

The reaction of Os^＋ （^6D, ^4F） with N20 has been investigated at B3LYP/TZVP and CCSD（T）/6-311＋G^＊ levels of theory. The mechanisms corresponding to O-atom and N-atom transfer reactions have been revealed. It was found that on the sextet reaction surface both the O-atom and N-atom transfer reactions undergo through direct-abstraction mechanism, leading to the formation of OsO^＋ and OsN^＋, whereas on quartet surface the two reactions undergo through O-N bond or N-N bond insertion mechanism. The calculated energetics shows that the reactions on the sextet surface have notable energy barriers, whereas the reactions on quartet surface are barrierless. ？2009 Xiao Guang Xie. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.