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291.
Wang J Li H Lou B Zu L Guo H Wang W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(16):4321-4332
Chiral (S)-pyrrolidine trifluoromethanesulfonamide has been shown to serve as an effective catalyst for direct Michael addition reactions of aldehydes and ketones with nitroolefins. A wide range of aldehydes and ketones as Michael donors and nitroolefins as acceptors participate in the process, which proceeds with high levels of enantioselectivity (up to 99 % ee) and diastereoselectivity (up to 50:1 d.r.). The methodology has been employed successfully in an efficient synthesis of the potent H(3) agonist Sch 50917. In addition, a practical three-step procedure for the preparation of (S)-pyrrolidine trifluoromethanesulfonamide has been developed. The high levels of stereochemical control attending Michael addition reactions catalyzed by this pyrrolidine sulfonamide, have been investigated by using ab initio and density functional methods. Transition state structures for the rate-limiting C--C bond-forming step, corresponding to re- and si-face addition to the reactive conformation of the key enamine intermediates have been calculated. Analysis of these structures indicates that hydrogen bonding plays an important role in catalysis and that the energy barrier for si-face attack in reactions of aldehydes to form 2R,3S products is lower than that for the re-face attack leading to 2S,3R products. In contrast, the energy barrier for re-face addition is lower than that for si-face addition in reactions of ketones. The computational results, which are in good agreement with the experimental observations, are discussed in the context of the stereochemical course of these Michael addition reactions. 相似文献
292.
Polynuclear Pd(II) and Ni(II) complexes of macrocyclic polyamine 3,6,9,16,19,22‐hexaazatricyclo[22.2.2.211,14]‐triaconta 11,13,24,26(l),27,29‐hexaene (L) in solution were investigated by electrospray ionization mass spectrometry (ESIMS). For methanol solution of complexes M2LX4 (M = Pd(II) and Ni(II), X= Cl and I), two main clusters of peaks were observed which can be assigned to [M2LX3]+ and [M2LX2]2+. When Pd2LCl4 was treated with 2 or 4 mol of AgNO3, it gave rise formation of Pd2LCl2 (NO3)2 · H2O and [Pd2L(H2O)m(NO3)n](4‐n)+, respectively. ESMS spectra show that the dissociation of the former in the ionization process gave peaks of [Pd2LCl2]2+ and [(Pd2LCl2)NO3]+, while dissociation of the later gave the peaks of [Pd2L(CH3CO2)2]2+ and [Pd2L(CH3CO2)2](NO3) + in the presence of acetic acid. Similar species were observed for Pd2LI4 when treated with 4 mol of AgNO3. When [Pd2L · (H2O)m(NO3)n](4‐n)+ reacted with 2 mol of oxalate anions at 40°C, [Pd4L2(C2O4)2(NO3)2]2+ and [Pd4L2(C2O4)2 (NO3)]3+ were detected. This implies the formation of square‐planar molecular box Pd4L2(C2O4)2(NO3)4 in which C2O4? may act as bridging ligands as confirmed by crystal structure analysis. The dissociation form and the stability of complex cations in gaseous state are also discussed. This work provides an excellent example of the usefulness of ESIMS in the identification of metal complexes in solution. 相似文献
293.
Wang Y Chen W Wu J Guo Y Xia X 《Journal of the American Society for Mass Spectrometry》2007,18(8):1387-1395
Because of its good biocompatibility, high surface-to-volume ratio, and distinct surface electrical properties, porous anodic alumina (PAA) membrane has been used to selectively enrich phosphopeptides from a mixture of synthetic peptides and tryptic digest product of beta-casein by a direct MALDI-TOF MS analysis. As we reported previously, PAA membrane has strong incorporation ability to the phosphate anion. Herein, we describe the application of PAA membrane as a selective sampling absorbent for phosphopeptides. The PAA membrane could enrich phosphopeptides with high efficiency and selectivity; for example, the tryptic digest product of beta-casein at a concentration as low as 4 x 10(-9) M can be satisfactorily detected. Compared to that from the nonenriching peptide mixture, the MS signal of the phosphorylated peptides enriched by the PAA membrane is remarkably improved. In addition, acidic peptides have insignificant influence on the enriching process. Results show that the adsorption of phosphate anions on the PAA membrane plays a determining role in achieving highly selective enriching capacity toward phosphopeptides. The feasibility of PAA membranes as specific absorbents for phosphopeptides is also demonstrated. 相似文献
294.
Ranganathan S Guo R Murray RW 《Langmuir : the ACS journal of surfaces and colloids》2007,23(13):7372-7377
Electron-transfer reactions of redox solutes at electrode/solution interfaces are facilitated when their formal potentials match, or are close to, the energy of an electronic state of the electrode. Metal electrodes have a continuum of electronic levels, and redox reactions occur without restraint over a wide span of electrode potentials. This paper shows that reactions on electrodes composed of films of metal nanoparticles do have constraints when the nanoparticles are sufficiently small and molecule-like so as to exhibit energy gaps, and resist electron transfers with redox solutes at potentials within the energy gap. When solute formal potentials are near the electronic states of the nanoparticles in the film, electron-transfer reactions can occur. The electronic states of the nanoparticle film electrodes are reflected in the formal potentials of the electrochemical reactions of the dissolved nanoparticles at naked metal electrodes. These ideas are demonstrated by voltammetry of aqueous solutions of the redox solutes methyl viologen, ruthenium hexammine, and two ferrocene derivatives at films on electrodes of 1.1 nm core diameter Au nanoparticles coated with protecting monolayers of phenylethanethiolate ligands. The methyl viologen solute is unreactive at the nanoparticle film electrode, having a formal potential lying in the nanoparticle's energy gap. The other solutes exhibit electron transfers, albeit slowed by the electron hopping resistance of the nanoparticle film. The nanoparticles are not linked together, being insoluble in the aqueous medium; a small amount of an organic additive (acetonitrile) facilitates observing the redox solute voltammetry. 相似文献
295.
We previously reported the preparation of the salbutamol sulfate pulsatile-release capsules with the pH-sensitive ion exchange resin as the carriers. In the present study, we investigated the pharmacokinetics of the salbutamol sulfate pulsatile-release capsules in beagle dogs. The analysis method was established for the drugs in vivo by HPLC method. The pharmacokinetics parameters of pulsatile-release salbutamol sulfate and reference tablet were AUC(0-24) (ng.h/ml) 1031.8+/-123.1, 1112.6+/-118.24, Cmax (ng/ml) 172.4+/-21.4, 179.3+/-26.1, Tmax (h) 3.8+/-0.6, 1.5+/-0.5, Tlag (h) 2.7+/-0.5, 0.3+/-0.2. The results showed that the test dosage forms was bioequivalent with reference dosage form, and had an obviously pulsatile-release effect. 相似文献
296.
Le Guo Xiaochen Ma Huaquan Fang Xiangqing Jia Prof. Dr. Zheng Huang 《Angewandte Chemie (International ed. in English)》2015,54(13):4023-4027
Catalytic α‐alkylation of esters with primary alcohols is a desirable process because it uses low‐toxicity agents and generates water as the by‐product. Reported herein is a NCP pincer/Ir catalyst which is highly efficient for α‐alkylation of a broad scope of unactivated esters under mild reaction conditions. For the first time, alcohols alkylate unactivated α‐substituted acyclic esters, lactones, and even methyl and ethyl acetates. This method can be applied to the synthesis of carboxylic acid derivatives with diverse structures and functional groups, some of which would be impossible to access by conventional enolate alkylations with alkyl halides. 相似文献
297.
C? H Arylation of olefins by triarylphosphines via C? P bond cleavage has been achieved with either Pd0 or PdII catalysts. A variety of olefins and triarylphosphines are tolerated, and we inferred that both Pd0 and PdII could function directly without pre‐oxidation or pre‐reduction. 相似文献
298.
Stochastic/Controlled Symmetry Breaking of the T8‐POSS Cages toward Multifunctional Regioisomeric Nanobuilding Blocks 下载免费PDF全文
Xiao‐Man Wang Qing‐Yun Guo Shuai‐Yuan Han Jing‐Yi Wang Di Han Prof. Qiang Fu Prof. Wen‐Bin Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(43):15246-15255
Precise synthesis of nanobuilding blocks with accurately positioned functional groups presents a daunting challenge. Herein, a practical synthesis and thorough characterization of a series of T8‐polyhedral oligomeric silsesquioxane (POSS) di‐ and triadducts is reported. Upon addition of triflic acid across the double bonds in octavinylPOSS (V8T8) followed by hydrolysis, the cubic symmetry of the T8‐POSS cage (Oh) is broken into C2v (ortho‐), C2v (meta‐), and D3d (para‐) for diadducts and further to Cs (oom‐), Cs (omp‐), and C3v (mmm‐) for triadducts in a stochastic fashion. Their structures and regioconfigurations have been unambiguously demonstrated by 1H, 13C, and 29Si NMR spectroscopy, as well as MALDI‐TOF mass spectrometry. The assignment of the diadducts was further corroborated by converting each individual diadduct into triadduct(s), the structure of which is controlled by the symmetry of the precursor. Except for the C3v triadduct, they can all be prepared in synthetically useful quantities. The presence of two types of highly reactive and mutually orthogonal functional groups facilitates further modification into complex nanostructures and composite materials. These unique regioisomers provide a versatile platform for constructing giant molecules and Janus silsesquioxanes. 相似文献
299.
Discrete Rectangles,Prisms, and Heterometallic Cages from a Conjugated Cp*Rh‐Based Building Block 下载免费PDF全文
Xu‐Yu Shen Dr. Ying‐Ying Zhang Long Zhang Dr. Yue‐Jian Lin Prof. Guo‐Xin Jin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(47):16975-16981
By carefully selecting an existing synthetic strategy and suitable coordination subunits, constructing desired coordination geometries is no longer that difficult to accomplish. Herein, a new strategy to construct a series of unprecedented structures by using conjugated Cp*Rh‐based complex BN‐OTf (Cp*=η5‐C5Me5) as the building block is proposed. DFT calculations revealed extensive delocalized π bonds in the subunit. With BN‐OTf , rectangular macrocycles TN‐bpy and TN‐bpe were controllably synthesized. Single‐crystal XRD studies confirmed one‐dimensional stacking channels for the tetranuclear structure. Notably, the starting ligand imidazole‐4,5‐dicarboxylate was found to act not only as a tetradentate but also as a hexadentate ligand that can coordinate to further metal ions. Subsequently, [4 Rh+1 M] heterometallic complexes HMZ (M=Cu and Zn) were accessed by chelating borderline hard/soft Lewis acids. With TN‐Linker or HMZ , two routes resulted in the [8 Rh+2 M] heterometallic cages HMC (M=Cu and Zn) with excellent crystallinity and stability. Surprisingly, when BN‐OTf bonded to rhodium itself, triangular prisms TP‐Linker were obtained with high solubility after being linked by bipyridine linkers. Both the X‐ray structure and 1H NMR spectrum confirmed the novel isomerization of the triangular structures. All of the compounds were obtained in high yields and were fully characterized by 1H NMR spectroscopy, elemental analysis, IR spectroscopy, and in most cases single‐crystal X‐ray structure determination. 相似文献
300.
E. J. Gao Y. X. Zhang M. C. Zhu H. Y. Liu Y. Huang M. Zhang M. Su M. J. Guo F. Guan X. N. Gao M. L. Wang 《Russian Journal of Coordination Chemistry》2010,36(11):853-858
The complex [Pd(Bipy)2](Bpcc) · 11H2O has been synthesized and characterized (Bipy = 2,2′-bipyridyl, H2Bpcc = 4,4′-biphenylcarboxylic acid). The supramolecular architecture was constructed through hydrogen bonding and π-π-stacking. The Pd atom is four-coordinated and forms a distorted square geometry. The free H2O molecules form 1D infinite zigzag chains of water cluster, while the water cluster and Bpcc2? form an organic-water framework. 相似文献