On the mechanism of the copper-catalyzed enantioselective 1,4-addition of grignard reagents to alpha,beta-unsaturated carbonyl compounds

The mechanism of the enantioselective 1,4-addition of Grignard reagents to alpha,beta-unsaturated carbonyl compounds promoted by copper complexes of chiral ferrocenyl diphosphines is explored through kinetic, spectroscopic, and electrochemical analysis. On the basis of these studies, a structure of the active catalyst is proposed. The roles of the solvent, copper halide, and the Grignard reagent have been examined. Kinetic studies support a reductive elimination as the rate-limiting step in which the chiral catalyst, the substrate, and the Grignard reagent are involved. The thermodynamic activation parameters were determined from the temperature dependence of the reaction rate. The putative active species and the catalytic cycle of the reaction are discussed.     

Einige Methoden zur Bestimmung des Hydroxylamins

Ohne Zusammenfassung     

THE SIMULATION AND OPTIMIZATION OF GRADIENT ELUTION HPLC

The movement of a particular component along an HPLC column is studied on the ba-sis of equilibrium equations. Numerical simulation of multi--step gradient elution HPLC isperformed by means o? a personal computer program. The location x, as a fraction of thecolumn length, for a given time t o? each compound is calculated, the velocity and corre-sponding acceleration are given as well. Diagrams for x,dx/dt and d~2x/dt~2 versus t display themovement process of the different components along the HPLC column during gradient elu-tion. The prediction of the retention time and peak width, and the optimization for the multi-step gradient elution HPLC are all based on such simulation and the molecular structure ofthe. components is separated as well.     

Reactions of mer(exo)‐ and mer(endo)‐[Co(dien)(dapo)X]2+ Isomers (X=OH,Cl, ONO2, N3)

Properties indirectly determined, or alluded to, in previous publications on the titled isomers have been measured, and the results generally support the earlier conclusions. Thus, the common five‐coordinate intermediate generated in the OH^?‐catalyzed hydrolysis of exo‐ and endo‐[Co(dien)(dapo)X]²⁺ (X=Cl, ONO₂) has the same properties as that generated in the rapid spontaneous loss of OH^? from exo‐ and endo‐[Co(dien)(dapo)OH]²⁺ (40±2% endo‐OH, 60±2% exo‐OH) and an unusually large capacity for capturing (R=[CoN₃]/[CoOH][]=1.3; exo‐[CoN₃]/endo‐[CoN₃]=2.1±0.1). Solvent exchange for spontaneous loss of OH^? from exo‐[Co(dien)(dapo)OH]²⁺ has been measured at 0.04 s^?1 (k₁, 0.50M NaClO₄, 25°) from which similar loss from the endo‐OH isomer may be calculated as 0.24 s^?1 (k₂). The OH^?‐catalyzed reactions of exo‐ and endo‐[Co(dien)(dapo)N₃]²⁺ result in both hydrolysis of coordinated via an OH^?‐limiting process =153 M ^?1 s^?1; =295 M ^?1 s^?1; K_H=1.3±0.1 M ^?1; 0.50M NaClO₄, 25.0°) and direct epimerization between the two reactants =33 M ^?1 s^?1; =110 M ^?1 s^?1; 1.0M NaClO₄, 25.0°). Comparisons are made with other rapidly reacting Co^III‐acido systems.     

PHOTOREACTIVATION IN THE EXTREME HALOPHILIC ARCHAEBACTERIUM Halobacterium cutirubrum

Abstract— Photoreactivation in the extreme halophilic archaebacterium Halobacterium cutirubrum was studied both in vivo and in vitro. Cells irradiated with ultraviolet (UV)-fluences up to 350 J/m² could be completely photoreactivated, indicating very efficient repair of pyrimidine dimers in UV-irradiated DNA. Dark repair is apparently absent in Halobacterium since liquid holding under non-growth conditions did not influence the survival of UV-irradiated cells, while cells remained completely photoreactivable with no change in the kinetics of photoreactivation. Experiments with Halobacterium isolates of different carotenoid content indicated that carotenoids do not influence either UV-inactivation or photoreactivation. Small differences in the rates of UV-inactivation and photoreactivation could be assigned to the occurrence of gas vesicles. Flash experiments and the temperature dependence of photoreactivation indicated an enzymatical reaction. This was confirmed by in vitro experiments with partially purified photoreactivating enzyme. The in vivo action spectrum of photoreactivation showed a main band in the 400-470 nm region with a maximum at 440 nm. Comparison with action spectra of other microorganisms classified the Halobacterium enzyme as a 8-hydroxy-5-deazaflavin type photoreactivating enzyme.     

On the experimental feasibility of continuous-variable optical entanglement distillation

Entanglement distillation aims at preparing highly entangled states out of a supply of weakly entangled pairs, using local devices and classical communication only. In this note we discuss the experimentally feasible schemes for optical continuous-variable entanglement distillation that have been presented in [D.E. Browne, J. Eisert, S. Scheel, and M.B. Plenio, Phys. Rev. A 67, 062320 (2003)] and [J. Eisert, D.E. Browne, S. Scheel, and M.B. Plenio, Annals of Physics (NY) 311, 431 (2004)]. We emphasize their versatility in particular with regards to the detection process and discuss the merits of the two proposed detection schemes, namely photo-detection and homodyne detection, in the light of experimental realizations of this idea becoming more and more feasible. The text was submitted by the authors in English.     

香菇多糖L-2A的结构表征

从香菇子实体中提取纯化得到香菇多糖级分L-2A,利用紫外光谱、红外光谱、凝胶渗透色谱和气相色谱分析其结构特征.香菇多糖L-2A糖含量为90.14%;重均分子量是2.03×10 5道尔顿;具有D-葡萄吡喃糖构型,单糖组成主要是由吡喃型葡萄糖组成;香菇多糖L-2A多糖含有o-糖苷键,且主要是o-Ser连接方式;具有与刚果红结合的螺旋结构.香菇多糖L-2A为首次从香菇子实体中分离得到.     

The coherent scattering function of the reptation model: Simulations compared to theory

We present results of Monte Carlo simulations measuring the coherent structure function of a chain moving through an ordered lattice of fixed topological obstacles. Our computer experiments use chains up to 320 beads and cover a large range of wave vectors and a time range exceeding the reptation time. For additional information we also measured the coherent structure function of internal pieces of the chain. We compare our results i) to the predictions of the primitive chain model, ii) to an approximate form resulting from Rouse motion in a coiled tube, and iii) to our recent evaluation of the full reptation model. i) The primitive chain model can fit the data for times , where T ₂ is the Rouse time of the chain. Besides some phenomenological amplitude factor this fit involves the reptation time T ₃ as a second fit parameter. For the chain lengths measured, the asymptotic behavior is not attained. ii) The model of Rouse motion in a tube, which we have criticized before on theoretical grounds, is shown to fail also on the purely phenomenological level. iii) Our evaluation of the full reptation model yields an excellent fit to the data for both total chains and internal pieces and for all wave vectors and all times, provided specific micro-structure effects of the MC dynamics are negligible. Such micro-structure effects show up for wave vectors of the order of the inverse segment size and enforce the introduction of some phenomenological, wave-vector-dependent prefactor. For the dynamics of the total chain our data analysis based on the full reptation model shows the importance of tube length fluctuations. Universal (Rouse-type) internal relaxation, however, is unimportant. It can be observed only in the form of the diffusive motion of a short central subchain in the tube. Finally, we present a fit formula which in a large range of wave vectors and chain lengths reproduces the numerical results of our theory for the scattering from the total chain.Received: 9 July 2003, Published online: 11 November 2003PACS: 83.10.Kn Reptation and tube theories - 82.35.Lr Physical properties of polymers - 83.10.Rs Computer simulation of molecular and particle dynamics