多胺基烷基酰胺生成机理的量子化学研究

用量子化学方法研究了丙酸与多乙烯多胺缩合反应机理。采用AM1方法全优化计算了丙酸多胺盐及其质子化盐的几何构型、电子结构以及酸催化下的亲核加成和消除反应的机能曲线,求得该两步反应的活化能分别为6.258kJ/mol和206.15kJ/mol。消除反应是速度控制步骤。发现质子化后丙酸羰基碳原子上的净电荷增大,前线分子轨道能级差减小,前线分子轨道间相互作用增强,表明酸催化大大增强反应活性。     

Insight into the reaction mechanism of CH2SH with HO2: A density functional theory study

Density functional theory was adopted in this work to reveal the reaction mechanism of CH₂SH with HO₂. Reaction rate constants were computed from 200 to 2000 K using the transition state theory combined with Wigner and Eckart tunneling correction. Moreover, localized orbital locator, atoms in molecules and Mayer bond order analyses were used to study the essence of chemical bonding evolution. Eleven singlet paths and three triplet ones are located on the potential surface (PES). The results show that the main products on the singlet PES are ¹CH₂S and H₂O₂, whereas on the triplet PES they are CH₃SH + ³O₂, which are coincident with the similar reaction of CH₃S and HO₂. This conclusion is also supported by rate constant calculation results. Interestingly, all the possible paths are involved in the hydrogen transfer. The results have provided underlying insights to the analogous reactions and further experimental studies.     

Insight into vulcanization mechanism of novel binary accelerators for natural rubber

A novel TU derivative, N-phenyl-N′-(у-triethoxysilane)-propyl thiourea(STU), is prepared and its binary accelerator system is investigated in detail. Compared to the control references, the optimum curing time of NR compounds with STU is the shortest, indicating a more nucleophilic reaction occurs. The Py-GC/MS results present that the phenyl isothiocyanate fragment still remains in the NR/STU compounds with or without extracting treatment, but no silane segment can be found in the vulcanizate with extracting treatment. Vibrations of C=S, NH and aromatic ring in FTIR experiments and a new methyne carbon peak, as well as the peaks of phenyl group of STU, in the solid state 13C-NMR experiments are found in the NR/STU vulcanizate with extracting treatment. Moreover, the crosslinking density of vulcanizates with STU evolves to lower level, indicating the sulfur atom of STU does not contribute to the sulfur crosslinking. Therefore, a new vulcanization kinetic mechanism of STU is propounded that the thiourea groups can graft to the rubber main chains as pendant groups by chemical bonds during the vulcanization process, which is in accordance with the experimental observations quite well.     

Mechanistic Insight into Ethanol Dehydration over SAPO-34 Zeolite by Solid-state NMR Spectroscopy

The reaction mechanism of ethanol dehydration over SAPO-34 zeolite is investigated by using solid-state NMR spectroscopy. SAPO-34 zeolites with different Si contents are prepared and their acidities are characterized by NMR experiments. The higher content of stronger Brønsted acid sites is correlated to the higher Si content. The adsorption of ethanol on the Brønsted acid sites in SAPO-34 leads to the formation of frustrated Lewis pairs(FLPs). Surface ethoxy species is observed by the dehydration of the FLP sites at room temperature, which can be further converted into ethene products. The decomposing of diethyl ether over Brønsted acid sites is responsible for the formation of ethoxy species at higher reaction temperatures. Triethyloxonium ions are formed in the reaction. A plausible reaction mechanism is proposed for the dehydration of ethanol over SAPO-34.     

A nucleophilic 1,3-rearrangement leading to 3,4-disubstituted 3,4-dihydroquinolines

A new nucleophilic 1,3-rearrangement is observed when treating 2-methoxyquinolino-3-lithium with an α-C substituted deoxybenzoin,and this rearrangement yielded an unusual 3,4-disubstituted 3,4-dihydroquinoline.Several similar reactions were designed and executed to investigate this novel 1,3-rearrangement,and a mechanism involving a nucleophilic addition and a following 1,3-rearrangement with an unusual dearomatization on the quinoline ring is proposed.     

Insight into catalytic mechanism of papain-like cysteine proteinases

We studied the role of D158 in papain-like cysteine proteinases by using subtilisin Carlsberg, and its chemically modified analog thiolsubtilisin, by applying the proton inventory (PI) method and also by taking into account the pH profiles of the kcat/Km parameter. In the case of thiolsubtilisin, we estimated large inverse solvent isotope effects for kcat/Km, as in papain, whereas for subtilisin we found "dome-shaped" PI, suggesting a completely different mechanism. Finally, the kinetic behavior of thiolsubtilisin presented similarities as well as differences, compared to papain, suggesting a possible role for D158 as part of a catalytic triad in papain-like cysteine proteinases.     

Theoretical study on the mechanism of OH + HCNO reaction

A detailed mechanistic study of the OH + HCNO reaction, in which the products P _i with i=1, 2, . . . ,7 are involved, is carried out by means of CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPVE computatio-nal method to determine a set of reasonable pathways. It is shown that P ₆ (CO + H₂NO) and P ₃ (HNO +HCO) are the major product channels with a minor contribution from P ₅ (NO + H₂CO), whereas the other channels for P ₁ (H₂O + NCO), P ₂ (NH₂ + CO₂), P ₄ (HCN + HO₂) and P ₇(CO + H₂ + NO) are less favorable. All these theoretical results are in harmony with experimental facts.     

Insight into the catalytic thermal decomposition mechanism of ammonium perchlorate

Journal of Thermal Analysis and Calorimetry -     

Insight into the inversion mechanism of an inverse polymer emulsion

A study of the mechanism of inversion of inverse polymer emulsions showed that the likely key step in the inversion process is the swelling of polymer particles caused by added water diffusing through the oil phase. Therefore, we propose that inversion occurs as a result of polymer particle crowding caused by water diffusion and subsequent droplet rupture that results in the release of the polymer into the water phase.     

Synthesis of 2-phenoxyl-2-oxo-1,4,2-oxazaphosphinanes from a three component reaction

Abstract

A one-pot synthetic strategy was developed for the synthesis of heterocyclic 1,4,2-oxazaphosphinanes via a three component Kabachnik-Fields reaction of 2-aminophenol, diphenyl H-phosphonate and carbonyl compounds. Through this newly developed method, 12 organophosphorus heterocycles and 2 related chrysin derivatives were synthesized with high yields. The target compounds were characterized by ¹H, ³¹P and 13C NMR and MS.     

Insight into the sequence-specific elements leading to increased DNA bending and ligase-mediated circularization propensity by antitumor trabectedin

Journal of Computer-Aided Molecular Design - DNA curvature is the result of a combination of both intrinsic features of the double helix and external distortions introduced by the environment and...     

烯酰基-辅酶A水合酶催化机理的理论研究

采用DFT方法研究了烯酰基-辅酶A （ECH）催化的4-（N,N-二甲氨基）-肉桂酰-辅酶A （DAC-CoA）和巴豆酰基-辅酶A （Crotonyl-CoA）水合反应.计算表明：水合反应以分步机理进行,经历一个烯醇负离子中间体.Glu164残基作为唯一的催化碱/酸参与水合反应,而Glu144虽然没有直接参与反应,但是它能通过氢键作用诱使水分子以合适的朝向活化底物.Crotonyl-CoA底物的水加成活性高于DAC-CoA.Ala98和Gly141与底物羰基之间的氢键作用既有利于底物的准确结合,也能有效稳定反应中形成的过渡态和中间体.另外,Glu144和Glu164周围的氢键网络对于合理维持活性位点排布进而有效促进底物活化也很重要.     

Insight into the combustion mechanism of nitroglycerin/nano-aluminum composite materials

Structural Chemistry - The ReaxFF-lg is used to simulate the thermal decomposition of the pure nitroglycerin (NG) and nitroglycerin/nano-Al (NG/Al) systems. The simulation results show that the...     

Insight into the mechanism of transient trapping in micellar electrokinetic chromatography

Transient trapping is a new mechanism of on-line sample concentration and separation that has recently been presented. It involves the injection of a short length of micellar solution in front of the sample, making it similar to sweeping in partial-filling MEKC. Here, we examine the mechanism of transient trapping by the use of computer simulations and compare it to sweeping in MEKC for the two analytes, sulforhodamine B and 101. The simulation results confirm the mechanism for concentration and separation originally proposed. The mechanism for concentration is similar to sweeping since the analytes are picked and accumulated by the micelles that penetrate the sample zone. The mechanism for separation is however quite unique since the concentrated analytes are trapped for a few seconds on the sample/micelle boundary before they are released as the concentration of micelle is reduced as it undergoes electromigration dispersion and the analytes separate down a micelle gradient. Simulation results suggested that a significant contribution of band broadening arises from the micelle gradient, with shallower gradients resulting in broader peaks. However, this is offset by an increase in selectivity, such that resolution was enhanced even though the peaks are broader. Transient trapping analysis with similar resolution to those obtained by sweeping MEKC could be achieved in 1/10 of the time and 1/4 of the capillary length, which results in a 2-3 times increase in sensitivity.     

Insight into the reaction mechanism of the conversion of methylbutynol on silica-alumina

The conversion of methylbutynol (MBOH) over commercially available silicaalumina solids was studied. The formation of 3-methyl-3-butene-2-one (MIPK) was explained in terms of the cooperative action of both Br?nsted acidic and coordinatively unsaturated surface sites. With increasing silica content the number of defect sites decreases and well ordered silica-alumina is formed.     

Mechanistic Insight into Hydroboration of Imines from Combined Computational and Experimental Studies

Boron Lewis acid-catalyzed and catalyst-free hydroboration reactions of imines are attractive due to the mild reaction conditions. In this work, the mechanistic details of the hydroboration reactions of two different kinds of imines with pinacolborane (HBpin) are investigated by combining density functional theory calculations and some experimental studies. For the hydroboration reaction of N-(α-methylbenzylidene)aniline catalyzed by tris[3,5-bis(trifluoromethyl)phenyl]borane (BAr^F₃), our calculations show that the reaction proceeds through a boron Lewis acid-promoted hydride transfer mechanism rather than the classical Lewis acid activation mechanism. For the catalyst- and solvent-free hydroboration reaction of imine, N-benzylideneaniline, our calculations and experimental studies indicate that this reaction is difficult to occur under the reaction conditions reported previously. With a combination of computational and experimental studies, we have established that the commercially available BH₃ ⋅ SMe₂ can serve as an efficient catalyst for the hydroboration reactions of N-benzylideneaniline and similar imines. The hydroboration reactions catalyzed by BH₃ ⋅ SMe₂ are most likely to proceed through a hydroboration/B−H/B−N σ-bond metathesis pathway, which is very different from that of the reaction catalyzed by BAr^F₃.     

Photoredox Reaction of Naphthoquinone C-Glycoside Revisited: Insight into Stereochemical Aspect

Insights into the naphthoquinone photoredox reactions have been gained from the reactions of a C-glycosyl naphthoquinone. The retentiveness comes from the balance of the lifetime of intermediary zwitterionic species relative to the conformational change to bring about the stereo-mutating C−C bond rotation.