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731.
An efficient diversity-oriented strategy has been developed for the solution-phase parallel synthesis of di- and trisubstituted pyrrole libraries. Methyl esters 1 were effectively converted to 1,2-di- and 1,2,5-trisubstituted pyrroles 5 and 6 in three steps. Treatment of ester 1 with vinylmagnesium bromide in the presence of copper (I) cyanide yielded the corresponding homoallylic ketone 2, which was subjected to ozonolysis or Tsuji-Wacker oxidation to yield the respective cyclization precursors 3 and 4 after aqueous workup. Compounds 3 and 4 were condensed without further purification with a primary amine to afford the desired 1,2-di- or 1,2,5-trisubstituted pyrroles 5 and 6 in good yield and purity. 相似文献
732.
Castagnola M Rossetti DV Inzitari R Vitali A Lupi A Zuppi C Cabras T Fadda MB Podda I Petruzzelli R Giardina B Messana I 《Electrophoresis》2003,24(10):1612-1619
Binding of Zn(2+) to bacitracin A(1) was studied by capillary electrophoresis in water/2,2,2-trifluoroethanol (70/30 v/v) at different apparent pH values in order to estimate the association constant of metal, the acidic dissociation constants and the Stokes radii of both free and bounded peptide in apolar environment. The Stokes radii of the free peptide species were compared with those in aqueous solution, as obtained in a recent study performed by our group, indicating that apolar environment stabilizes bacitracin A(1) in a conformational structure with the lateral chain of apolar amino acids exposed on the external surface. This conformation of the macrocyclic dodecapeptide is ready to interact with Zn(2+) ion, as pointed out by the strong increase of the association constant measured in water/2,2,2-trifluoroethanol with respect to the value obtained in aqueous solution. In addition, whereas Zn(2+) ion binding in aqueous solution provides a sensible reduction of peptide Stokes radius, no sensible variations following to ion binding were observed in hydro-organic solution. The present results suggest that the apolar environment, rather than the metal ion binding, could be responsible for the conformational transition that brings bacitracin A(1) towards its biologically active structure.* 相似文献
733.
Pineschi M Del Moro F Crotti P Di Bussolo V Macchia F 《The Journal of organic chemistry》2004,69(6):2099-2105
A novel regiodivergent kinetic resolution of a series of allylic epoxides with alkylzinc reagents is described. Results demonstrate the potential of chiral copper-phosphoramidite catalysts for enantiomer differentiation of allylic epoxides, allowing a chiral catalyst-stereoregulated synthesis of cyclic allylic and homoallylic alcohols with high optical purities. 相似文献
734.
In this paper we deal with the limit behaviour of the bounded solutions uε of quasi-linear equations of the form
of Ω with Dirichlet boundary conditions on σΩ. The map a=a(x,ϕ) is periodic in x, monotone in ϕ, and satisfies suitable coerciveness
and growth conditions. The function H=H(x,s,ϕ) is assumed to be periodic in x, continuous in [s,ϕ] and to grow at most like
|ξ|p. Under these assumptions on a and H we prove that there exists a function H0=H0(s,ϕ) with the same behaviour of H, such that, up to a subsequence, (uε) converges to a solution u of the homogenized problem -div(b(Du)) + γ|u|p-2u = H0(u,Du) + h(x) on Ω, where b depends only on a and has analogous qualitative properties. 相似文献
735.
An exact solution of Einstein's equations describing the gravitational wave associated to a ring of massless particles is presented. It has been obtained by boosting the Kerr metric along the axis of symmetry, and considering the limit in which the speed of the boost tends to the velocity of light. 相似文献
736.
In this paper we study the gauge invariance of the time-dependent Ginzburg-Landau equations through the introduction of a model which uses observable variables. We observe that the various choices of gauge lead to a different representation of such variables and therefore to a different definition of the weak solution of the problem. With a suitable decomposition of the unknown fields, related to the choice of London gauge, we examine the Ginzburg-Landau equations and deduce some energy estimates which prove the existence of a maximal attractor for the system. 相似文献
737.
In this paper we study a new variant of the minimum energy broadcast (MEB) problem, namely the probabilistic MEB (PMEB). The objective of the classic MEB problem is to assign transmission powers to the nodes of a wireless network is such a way that the total energy dissipated on the network is minimized, while a connected broadcasting structure is guaranteed by the assigned transmission powers. In the new variant of the problem treated in this paper, node failure is taken into account, aiming at providing solutions with a chosen reliability level for the broadcasting structure. Three mixed integer linear programming formulations for the new problem are presented, together with efficient formulation-dependent methods for their solution. Computational results are proposed and discussed. One method emerges as the most promising one under realistic settings. It is able to handle problems with up to fifty nodes. 相似文献
738.
Valeria Amendola Michela Di Casa Luigi Fabbrizzi Maurizio Licchelli Carlo Mangano Piersandro Pallavicini Antonio Poggi 《Journal of inclusion phenomena and macrocyclic chemistry》2001,41(1-4):13-18
Fluorescence switches are molecular systems containing a light-emitting fragment whose activity can be quenched/revived reversibly, at will,through an external parameter, i.e., a change of pH or the variation of the redox potential.Fluorescence switches can be static (the emission of the fluorophore isswitched ON/OFF by a bistable covalently linked control unit) or dynamic(the change in fluorescence is accompanied by an oriented molecular motion). Of the latterclass of switches, we will consider the cases (i) of a metal scorpionate and (ii) ofsystems in which a metal is reversibly translocated between two nonequivalent compartmentsof a ditopic ligand. 相似文献
739.
Guillermo E. Eliçabe Walter F. Schroeder Gloria L. Frontini Valeria Pettarin 《Particle & Particle Systems Characterization》2007,24(3):163-172
In this work a light scattering apparatus for the study of heterogeneous liquid systems of evolving morphology is presented. A Fraunhofer configuration consisting of a linear array of photodiodes is used to detect the light scattered by thin samples illuminated by a He‐Ne laser light. Temperature control is available. The instrument is tested with the polymerization induced phase separation of a thermosetting polymer formulated with a divinylester resin copolymerized with styrene and modified with poly(methylmethacrylate). The system is successfully modeled as an arrangement of particles growing in size and number, and varying in composition. The ability of the experimental setup to provide results that can be quantitatively analyzed is checked using microspherical polystyrene standards. Different samples with nominal sizes of 0.5, 1 and 2 μm are used in different combinations of sample thickness and concentration. The analysis of the light scattering spectra is performed using inverse techniques to estimate the particle size distribution of the microspheres. The results agree with previous knowledge of the parameters of the samples. 相似文献
740.
Abdulkarim A. Amirov Yogesh A. Chaudhari Subhash T. Bendre Ksenia A. Chichay Valeria V. Rodionova Dibir M. Yusupov Zairbek M. Omarov 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(4):63
Multiferroic BiFe1?xZn x O3 ceramics were prepared by solution combustion method. Their structure, magnetoelectric, dielectric, magnetic, thermal characteristics were studied. The magnetic M(T) and heat capacity C p (T) measurements demonstrate an antiferromagnetic to paramagnetic phase transition (T N ) around 635 K. The anomaly on the temperature dependence of the dielectric constant near T N was observed, which could be induced by the magnetoelectric coupling between electric and magnetic ordering. The magnetoelectric behavior was also confirmed by the linear relation between Δε and M2, which is in the agreement of the Ginzburg-Landau theory for the second-order phase transition. 相似文献