TiO_2负载的纳米铑簇合物催化丙酮酸乙酯不对称氢化反应的研究

研究了辛可尼定作手性修饰剂修饰的负载型纳米铑簇保物催化剂（0.5% Rh/PVP-TiO_2）催化丙酮酸乙酯不对称氧化反应，在该反应中手性修饰剂辛可尼 定不仅具有对产物生成的手性诱导作用，而且对反应具有明显加速作用；在优化反 应条件后，反应的TOF和对映选择性分别可以达到58.0 min~(-1)和61.9% e.e.。     

Enantioselective hydrogenation of ethyl pyruvate catalyzed by alumina support rhodium modified with quinine

Alumina supported rhodium catalyst using cinchonidine as a stabilizer exhibited excellent performance in the asymmetric hydrogenation of ethyl pyruvate with the addition of quinine. Quinine as a chiral modifier can not only induce the enantioselectivity, but also greatly accelerate the reaction. Under the optimum conditions: 293 K, 7.0 MPa of hydrogen pressure and 4.6 × 10⁻³ mol/L of quinine concentration in THF, TOF of Rh/2(cinchonidine)-γ-Al₂O₃ as catalyst and ee value of (R)-ethyl lactate can achieve 894 h⁻¹ and 71.6% ee, respectively.     

Enantioselective electrocatalytic hydrogenation of ethyl pyruvate on carbon supported Pd electrodes

The electrocatalytic hydrogenation of ethyl pyruvate to yield S-ethyl lactate over palladium supported on carbon felt electrodes modified with cinchonidine has been found to yield an enantiomeric excess of 13%. The effect of electrode potential, ethyl pyruvate concentration and cinchonidine have been investigated. The experimental results reported in the present study are in good agreement with the previously reported heterogeneous enantioselective hydrogenation using molecular hydrogen at high pressure. The electrocatalytic driven reaction avoids the dissociation of molecular hydrogen and thus the use of high pressure hydrogen.     

易分离的高效纳米铂氢化催化剂

近年来纳米贵金属的优异催化性能得到了人们的关注,但是纳米粒子在使用、贮藏过程中存在团聚现象。在制备过程中加入稳定剂可以延缓其团聚,但给纳米粒子的分离带来了困难。有献报道利用水溶性表面活性剂聚乙二醇(PEG)的乙二醇链段可以稳定Rh纳米粒子,可是因其分子量过     

Identification of catalyst surface species during asymmetric platinum-catalysed hydrogenation in a "supercritical" solvent

In situ attenuated total reflection infrared spectroscopy studies during the enantioselective hydrogenation of ethyl pyruvate in "supercritical" ethane over a chirally modified Pt/Al(2)O(3) catalyst show the preferential adsorption of ethyl pyruvate as cis-conformer and indicate a hydrogen bond interaction of this species with the co-adsorbed modifier cinchonidine.     

Surface Raman characterization of cinchonidine-modified polycrystalline platinum in ethanol: effects of temperature and comparison with 10,11-dihydrocinchonidine

The adsorption of the chiral modifier cinchonidine on platinum in ethanol as a function of temperature has been studied with surface-enhanced Raman spectroscopy (SERS). The temperature range chosen was from 30 to 70 °C, within which both the activity and selectivity of cinchonidine-modified Pt catalysts have been shown to change dramatically. Platinum surfaces were modified with 260 μM cinchonidine in ethanol, and examined both in pure ethanol and in the modifying solution itself. Adsorbed cinchonidine under pure ethanol was found to partially desorb as the temperature was raised, accompanied by an increase in the average tilt of the quinoline group with respect to the surface. In contrast, the presence of solution-phase cinchonidine resulted in an increase in the cinchonidine surface coverage and average tilt as temperature was raised. In a previous study [J. Mol. Catal. A 212 (2004) 277] we showed that hydrogen causes a dramatic enhancement in the SERS response of adsorbed cinchonidine. This was attributed to a conversion of cinchonidine to 10,11-dihydrocinchonidine on the Pt surface and a more flat orientation of the quinoline group. In both pure ethanol and in 260 μM cinchonidine, the presence of hydrogen causes a significant decrease in the alkaloid SERS bands at temperatures above 40 °C. In addition, the average tilt of the quinoline group increases significantly at these elevated temperatures. The temperature-dependence of 10,11-dihydrocinchonidine adsorption was also investigated, and is almost identical to that observed for cinchonidine in the presence of hydrogen. This lends further support to the conclusion that cinchonidine is being hydrogenated on the Pt surface in the presence of hydrogen. The significant changes observed on the cinchonidine-modified Pt surface above 40 °C correlate well with reported decreases in enantioselectivity and turn-over frequency at similar temperatures during ethyl pyruvate hydrogenation.     

手性修饰的介孔树脂材料负载铂催化剂上丙酮酸乙酯的不对称氢化反应

采用氯铂酸和二氯四氨合铂为前体通过浸渍法分别制备了介孔树脂材料FDU-14负载的质量分数为5%的铂催化剂Pt/FDU-14, 并利用XRD, TEM, N₂气吸附和CO化学吸附等手段对催化剂进行了表征. 考察了经过手性分子辛可尼定修饰后的Pt/FDU-14催化剂在丙酮酸乙酯不对称氢化反应中的催化性能. 以氯铂酸为前体制备的Pt/FDU-14催化剂因其具有较小的铂粒子和较高的分散度而表现出较高的活性, 乙酸溶剂中的初始活性(TOF)可以达到21902 mol/(mol?h); 而以二氯四氨合铂为前体制备的Pt/FDU-14催化剂则具有较强的手性诱导能力, 乙酸溶剂中(R)-(+)-乳酸乙酯的光学选择性可以达到81.4% e.e.. 更重要的是, 由于FDU-14具有较强的疏水性, Pt/FDU-14催化剂在水溶剂中也表现出较高的催化性能, 并且还可以重复使用10次以上.     

The first case of competitive heterogeneously catalyzed enantioselective hydrogenation of ketones

In competitive racemic hydrogenation of methyl benzoylformate (MBF) + ethyl pyruvate (EP) binary mixture over Pt/Al(2)O(3): k(MBF) > k(EP), but in competitive enantioselective hydrogenation k(MBF) < k(EP); the phenomenon verified for the first time is dependent on the adsorption strength of the surface complexes of various compositions (MBF-Pt, EP-Pt, MBF-CD-Pt, EP-CD-Pt, CD = cinchonidine).     

亲水性高分子稳定的纳米铂催化丙酮酸乙酯不对称氢化

贵金属纳米粒子因其优异的催化性能而在近年得到人们的重视．纳米粒子因表面积大而需要加入稳定剂以防止其团聚或次级粒子的产生．贵金属Pt纳米粒子经过生物碱辛可尼丁或合成不对称诱导剂的修饰后作为多相不对称催化剂，催化丙酮酸酯不对称加氢已经成为一种模型反应，检验催化     

On the conformational stability and dimerization of phosphotransferase enzyme I from Escherichia coli

The activity of enzyme I (EI), the first protein in the bacterial PEP:sugar phosphotransferase system, is regulated by a monomer–dimer equilibrium where a Mg²⁺-dependent autophosphorylation by PEP requires the homodimer. Using inactive EI(H189A), in which alanine is substituted for the active-site His189, substrate binding effects can be separated from those of phosphorylation. Whereas 1 mM PEP (with 2 mM Mg²⁺) strongly promotes dimerization of EI(H189A) at pH 7.5 and 20 °C, 5 mM pyruvate (with 2 mM Mg²⁺) has the opposite effect. A correlation between the coupling of N- and C-terminal domain unfolding, measured by differential scanning calorimetry, and the dimerization constant for EI, determined by sedimentation equilibrium, is observed. That is, when the coupling between N- and C-terminal domain unfolding produced by 0.2 or 1.0 mM PEP and 2 mM Mg²⁺ is inhibited by 5 mM pyruvate, the dimerization constant for EI(H189A) decreases from >10⁸ to <5 × 10⁵ or 3 × 10⁷ M⁻¹, respectively. With 2 mM Mg²⁺ at 15–25 °C and pH 7.5, PEP has been found to bind to one site/monomer of EI(H189A) with K_A′10⁶ M⁻¹ (ΔG′=−33.7±0.2 kJ mol⁻¹ and ΔH=+16.3 kJ mol⁻¹ at 20 °C with ΔC_p=−1.4 kJ K⁻¹ mol⁻¹). The binding of PEP to EI(H189A) is synergistic with that of Mg²⁺. Thus, physiological concentrations of PEP and Mg²⁺ increase, whereas pyruvate and Mg²⁺ decrease the amount of dimeric, active, dephospho-enzyme I.     

丙酮酸乙酯多相不对称催化加氢反应的初始过渡期研究

采用奎宁修饰的Pt/Al2O3为催化剂,研究了在常压下,乙酸溶剂中丙酮酸乙酯的不对称加氢反应.考察了奎宁修饰剂浓度、反应温度、预修饰时间、底物起始浓度及氧的加入对内酮酸乙酯不对称氢化反应初始过渡期(ITP)特征的影响.结果表明,在不对称氢化反应的初期,存在对映选择性随底物转化率的增加而不断升高的现象(即ITP现象),反应条件的变化能不同程度地改变ITP特征,在奎宁修饰催化剂时加入O2能明显提高催化剂对产物的对映选择性,改善ITP现象.ITP特征取决于反应起始阶段反应体系中各组分在催化剂表面的相互作用及达到平衡的速度,其实质是手性修饰型催化剂表面的重排过程.     

手性修饰的介孔碳材料MPC-61负载铂催化剂上α-酮酸酯的不对称氢化反应

采用氯铂酸乙醇溶液和氯铂酸水溶液为前体,通过浸渍法制备了介孔碳材料MPC-61负载Pt质量分数分别为4%和10%的Pt/MPC-61催化剂,并利用XRD,TEM,N2吸附-脱附和CO化学吸附等手段对催化剂进行了表征.考察了经过手性分子辛可尼定修饰后的Pt/MPC-61催化剂在丙酮酸乙酯不对称氢化反应中的催化性能.以氯铂...     

Carbonization of alumina-based catalysts in propionitrile ammonolysis

Summary The asymmetric hydrogenation of ethyl 2-acetoxyacrylate (EtA) by cinchonidine modified Pd/Al2O3 and Pt/Al2O3 catalyst is described (ee up to 60 &percnt;). This is the first example of asymmetric hydrogenation of an enol esters in heterogenized conditions.     

Particle size effect on enantioselective hydrogenation of ethyl pyruvate over alumina-supported platinum catalyst

The effect of platinum particle size on the enantioselective hydrogenation of ethyl pyruvate to ethyl lactate in the liquid phase was studied using a series of Pt/γ-Al₂O₃ catalysts modified with cinchonidine.The catalysts containing 5 wt.% platinum were prepared by the incipient wetness technique with H₂PtCl₆ as precursor.Reduction at different temperatures, redispersion in air and sintering were employed to change the platinum dispersion from 0.27 to 0.6, corresponding to a particle size range of 1.7–4.0 nm.Within this particle size range, activity (expressed as initial turnover frequency) and enantioselectivity were higher for the larger particles. However, an increase in selectivity was not observed when the platinum particle size was increased by sintering. This indicates that the method applied for particle size control has an influence on the performance of the catalysts.     

Pungency evaluation of onion cultivars from the Venezuelan West-Center region by flow injection analysis-UV-visible spectroscopy pyruvate determination

A flow injection analysis (FIA) method was developed for the determination of pyruvate in onion cultivars (Allium cepa L.) from the West-Center region of Venezuela. The reference Schwimmer and Weston (1961) (J. Agric. Food Chem. 9 (1961) 301) Batch method was modified and adapted to FIA conditions. The formation kinetic of the 2,4-dinitrophenylhydrazine (DNPH)–pyruvate complex was evaluated at room temperature and at 37 °C. It was demonstrated the suitability of the chromopher formation at room temperature. The optimal values for the FIA parameters were: sample injection volume 3 mL, flow rate 6 mL min⁻¹, reactor length 1.5 m, sodium hydroxide concentration 1.0 mol L⁻¹ and hydrochloric acid concentration 0.5 mol L⁻¹. The working calibration range was extended from 80 mg L⁻¹ (Batch method) to 700 mg L⁻¹ with the FIA set up. The sample dilution step is thus avoided, simplifying the whole analysis process. The pungency in representative samples of the cultivars Yellow granex 438, Ultra Hybrid and Red onion “Sangre de Toro” was evaluated by the flow injection analysis (FIA)–pyruvate method and the results were compared to the reference Batch pyruvate method and to the taste panel test. Non-significant differences were found at the 95% of confidence level between the FIA method and the Batch reference method. Correlation coefficient when comparing the FIA results to the taste panel test was r² = 0.8353. Significant differences (P < 0.05) were found in the pungency of the cultivars, the Ultra Hybrid having the highest pungency. The pungency order from minor to major was: Red onion, Texas Grano 438 and Ultra Hybrid.     

介孔修饰MCM-41负载Pt纳米催化剂高对映选择性催化酮不对称加氢(英文)

Catalysts containing metal nanotubes were prepared by the adsorption of platinum metal nano-tubes onto functionalized and modified silica surfaces(MCM-41 and fumed silica).(3- Chloropro-pyl)trimethoxysilane and cinchonidine were used for functionalization and modification, respec-tively. Potassium chloroplatinate was used as the metal precursor to impregnate platinum metal nanotubes on the pretreated functionalized and modified silica surfaces. The solid catalysts were characterized by ESEM, TEM, EDAX, and XPS. The MCM-41 supported platinum nanotube catalyst showed 98% to ~100% enantioselectivity towards the hydrogenation of a range of pharmaceuti-cally important chemicals such as methyl pyruvate, ethyl pyruvate, and acetophenone with nearly full conversion.     

High enantioselectivity in the asymmetric hydrogenation of ketones by a supported Pt nanocatalyst on a mesoporous modified MCM-41 support

Catalysts containing metal nanotubes were prepared by the adsorption of platinum metal nano‐tubes onto functionalized and modified silica surfaces (MCM‐41 and fumed silica). (3‐Chloropro‐pyl)trimethoxysilane and cinchonidine were used for functionalization and modification, respec‐tively. Potassium chloroplatinate was used as the metal precursor to impregnate platinum metal nanotubes on the pretreated functionalized and modified silica surfaces. The solid catalysts were characterized by ESEM, TEM, EDAX, and XPS. The MCM‐41 supported platinum nanotube catalyst showed>98%to~100%enantioselectivity towards the hydrogenation of a range of pharmaceuti‐cally important chemicals such as methyl pyruvate, ethyl pyruvate, and acetophenone with nearly full conversion.     

Heterogeneous asymmetric reactions, 14. Epicinchona alkaloids in the enantioselective hydrogenation of ethyl pyruvate over Pt/alumina. What determines the sense of enantioselection?

The enantioselective hydrogenation of ethyl pyruvate to (R)-and (S)-ethyl lactate over Pt/Al₂O₃ catalyst was investigated using epiquinine (42% ee) and epiquinidine (22% ee) as modifiers and the results were compared with those found for quinine (85% ee) and quinidine (81% ee). The experimental results show that the sense of enantioselection is determined by the conformation of the entire alkaloid, and the structure of the intermediate is a 1∶1 complex of the pyruvate and the ‘anti open’ conformer of the cinchona alkaloid.     

Role of axial ligand on the electronic structures of active intermediates in cytochrome P-450, peroxidase and catalase

DFT method (B3LYP) with 6-31G^* basis set was utilized in the computation of a fully optimized structure, net atomic charges and spin densities of the intermediate of cytochrome P-450-oxoiron(IV) porphyrin cation radical, compound I – in the presence of axial ligand such as thiolate (SMe⁻) imidazole (IM), phenoxide (OPh⁻), methoxide (OMe⁻) and chloride (Cl⁻). The results show doublet states in compound I are about 2–4 kcal/mol more stable than quartet states for all aforementioned ligands, and the doublet state is the ground state in all cases. However, electron donor ability of the ligands are in the order of SMe⁻ > IM > OMe⁻ > OPh⁻ > Cl⁻. Also the active oxidant intermediate of cytochrome P-450 between different mesomeric structures select sulfur oxygen radical type structure and can be viewed as (RS^↓)Fe^↑(IV)(O^↑)(Por). In horseraddish peroxidase (HRP) and peroxidase with histidine axial ligand π cation radical character of porphyrin ring is preferred (Im)Fe^↑(IV)(O^↑)(Por^↓). For the ligands such as OMe⁻, OPh⁻ and Cl⁻ oxidation mainly took place on the iron and the active intermediate can be viewed as (L)Fe^↑(V)(O)(Por) with one unpaired electron localized on the iron.     

Theoretical investigation of the enantioselective hydrogenation of α-ketoesters over pt/alumina modified with cinchonidine

Enantioselective hydrogenation of α-ketoesters with cinchona-modified platinum catalysts has been studied theoretically in order to rationalize the interaction between the chiral modifier and the substrate. The structure of the probable transition complex has been calculated for the system methyl pyruvate (substrate)–cinchonidine (modifier) using quantum chemistry techniques at both ab initio and semiempirical levels and molecular mechanics. The calculations indicate that crucial interaction occurs via hydrogen bonding of the quinuclidine nitrogen and the oxygen of the α-carbonyl moiety of methyl pyruvate and confirm earlier experimental evidence that the quinuclidine nitrogen of the cinchonidine is involved in the interaction leading to enantiodifferentiation. The resulting complex, which resembles to a half-hydrogenated state of the substrate, is shown to be a possible transition state for the enantioselective hydrogenation of α-ketoesters. © 1994 John Wiley & Sons, Inc.