排序方式: 共有19条查询结果,搜索用时 15 毫秒
1.
2.
Wolfgang Oppolzer Giovanni Poli Arend J. Kingma Christian Starkemann Grald Bernardinelli 《Helvetica chimica acta》1987,70(8):2201-2214
The 1,4-addition of alkylmagnesium chlorides to conjugated N-enoylsultams and subsequent ‘enolate trapping’ with aq. NH4Cl or MeI/hexamethylphosphoric triamide generated centers of asymmetry at C(β) and/or at C(α) with good to excellent π-face defferentiation as demonstrated by the conversions 1 → 2 , 1 → 4 , and 8 → 9 . This holds also for the regioselective 1,4-addition of EtMgC1 to a dienoylsultam ( 15 → 16 ). Reactive conformations 1 ≠, 8 ≠, 13 , and 14 are postulated in agreement with X-ray evidence which also served for the structure determination of the product 9j . 相似文献
3.
We report six-dimensional quantum dynamics calculations of the dissociative scattering of molecular hydrogen from the copper111 surface. Two potential energy surfaces are investigated and the results are compared with experiment. Our study completes the preliminary work of Somers et al. [Chem. Phys. Lett. 360, 390 (2002)] and focuses on the role of initial vibrational excitation and on isotopic effects. None of the two investigated potential energy surfaces is found satisfactory: the use of neither potential yields reaction and vibrational excitation probabilities and vibrational efficacies that are in close agreement with experiment. In addition to showing the shortcomings of existing potential energy surfaces we point out an inconsistency in the experimental fits for D2. 相似文献
4.
Demkin V. P. Melnichuk S. V. Svetlik M. V. Shchetinin P. P. Kingma H. Van de Berg R. Demkin O. V. Udut E. V. 《Russian Physics Journal》2019,61(12):2264-2267
Russian Physics Journal - Experimental data on electric signal transmission through tissues of the vestibular organ of a guinea pig are presented. Stimulating electrodes are implanted in three... 相似文献
5.
Effect of Leakage Currents on the Formation of Electrical Pulse for the Vestibular Nerve Stimulation
Demkin V. P. Kingma G. Mel’nichuk S. V. Svetlik M. V. Rudenko T. V. Akinina M. D. Suyundukova A. T. 《Russian Physics Journal》2020,62(12):2228-2234
Russian Physics Journal - A theoretical and experimental study was performed of a frequency dependence of the amplitude-phase characteristics of the vestibular nerve stimulation signal and its... 相似文献
6.
A capillary gas chromatographic method with nitrogen-phosphorus detection is used to determine simultaneously 1,3-diaminopropane, putrescine, cadaverine, spermidine and spermine in human erythrocytes. The compounds are isolated by adsorption on silica and converted into their heptafluorobutyryl derivatives. We give quality-control data and (age-dependent) normal values for 48 apparently healthy controls. 相似文献
7.
Demkin V. P. Shchetinin P. P. Melnichuk S. V. Kingma H. Van de Berg R. Pleshkov M. O. Starkov D. N. 《Russian Physics Journal》2018,60(11):2019-2024
Russian Physics Journal - An electric model of current transmission through tissues of the vestibular labyrinth of a patient is suggested. To stimulate directly the vestibular nerve in surgical... 相似文献
8.
Successive treatment of conjugated N-enoylsultams 2 with alkyl Grignard reagents/CuCl and aq. NH4Cl solution generated selectively two stereogenic centers at C(α) and C(β) providing, after flash chromatography and crystallization, acylsultams 5 in high purity. Mild cleavage afforded the recovered sultam auxiliary 1 and enantiomerically pure carboxylic acids 7 . 相似文献
9.
van Loo B Spelberg JH Kingma J Sonke T Wubbolts MG Janssen DB 《Chemistry & biology》2004,11(7):981-990
The enantioselectivity of epoxide hydrolase from Agrobacterium radiobacter (EchA) was improved using error-prone PCR and DNA shuffling. An agar plate assay was used to screen the mutant libraries for activity. Screening for improved enantioselectivity was subsequently done by spectrophotometric progress curve analysis of the conversion of para-nitrophenyl glycidyl ether (pNPGE). Kinetic resolutions showed that eight mutants were obtained with up to 13-fold improved enantioselectivity toward pNPGE and at least three other epoxides. The large enhancements in enantioselectivity toward epichlorohydrin and 1,2-epoxyhexane indicated that pNPGE acts as an epoxyalkane mimic. Active site mutations were found in all shuffled mutants, which can be explained by an interaction of the affected amino acid with the epoxide oxygen or the hydrophobic moiety of the substrate. Several mutations in the shuffled mutants had additive effects. 相似文献
10.
Determination of N-(3-acetamidopropyl)pyrrolidin-2-one, a metabolite of spermidine, in urine by isotope dilution mass fragmentography 总被引:1,自引:0,他引:1
A capillary gas chromatographic method with mass spectrometric detection for the determination of N-(3-acetamidopropyl)pyrrolidin-2-one, the monoacetyl conjugate of isoputreanine-gamma-lactam, in urine has been developed. Using a quantification based on stable isotope dilution mass fragmentography, age-dependent normal values for the urinary excretion of N-(3-acetamidopropyl)pyrrolidin-2-one by 44 apparently healthy control subjects were determined. Quality control data and normal values for 27 adults are given. The method was applied to the monitoring of the chemotherapeutic treatment of two patients with high-grade non-Hodgkin lymphoma. 相似文献