Superstructure in RE2-xFe4Si14-y (RE = Y, Gd-Lu) characterized by diffraction, electron microscopy, and Mössbauer spectroscopy

Ternary rare-earth iron silicides RE(2-x)Fe4Si(14-y) (RE = Y, Gd-Lu; x approximately equal to 0.8; y approximately equal to 4.1) crystallize in the hexagonal system with a approximately equal to 3.9 A, c approximately equal to 15.3 A, Pearson symbol hP20-4.9. Their structures involve rare-earth silicide planes with approximate compositions of "RE1.2Si1.9" alternating with beta-FeSi2-derived slabs and are part of a growing class of rare-earth/transition-metal/main-group compounds based on rare-earth/main-group element planes interspersed with (distorted) fluorite-type transition-metal/main-group element layers. The rare-earth silicide planes in the crystallographic unit cells show partial occupancies of both the RE and Si sites because of interatomic distance constraints. Transmission electron microscopy reveals a 4a x 4b x c superstructure for these compounds, whereas further X-ray diffraction experiments suggest ordering within the ab planes but disordered stacking along the c direction. A 4a x 4b structural model for the rare-earth silicide plane is proposed, which provides good agreement with the electron microscopy results and creates two distinct Fe environments in a 15:1 ratio. Fe-57 M?ssbauer spectra confirm these two different iron environments in the powder samples. Magnetic susceptibilities suggest weak (essentially no) magnetic coupling between rare-earth elements, and resistivity measurements indicate poor metallic behavior with a large residual resistivity at low temperatures, which is consistent with disorder. First-principles electronic-structure calculations on model structures identify a pseudogap in the densities of states for specific valence-electron counts that provides a basis for a useful electron-counting scheme for this class of rare-earth/transition-metal/main-group compounds.     

Experimental and theoretical investigations of the sulfite-based polyoxometalate cluster redox series: alpha- and beta-[Mo(18)O(54)(SO(3))(2)](4-/5-/6-)

The synthesis, isolation and structural characterization of the sulfite polyoxomolybdate clusters alpha-(D(3h))(C(20)H(44)N)(4){alpha-[Mo(18)O(54)(SO(3))(2)]}CH(3)CN and beta-(D(3d))(C(20)H(44)N)(4){beta-[Mo(18)O(54)(SO(3))(2)]}CH(3)CN is presented. Voltammetric studies in acetonitrile (0.1 M Hx(4)NClO(4), Hx(4)N=tetra-n-hexylammonium) reveal the presence of an extensive series of six one-electron reduction processes for both isomers. Under conditions of bulk electrolysis, the initial [Mo(18)O(54)(SO(3))(2)](4-/5-) and [Mo(18)O(54)(SO(3))(2)](5-/6-) processes produce stable [Mo(18)O(54)(SO(3))(2)](5-) and [Mo(18)O(54)(SO(3))(2)](6-) species, respectively, and the same reduced species may be produced by photochemical reduction. Spectroelectrochemical data imply that retention of structural form results upon reduction, so that both alpha and beta isomers are available at each of the 4-, 5-, and 6-redox levels. However, the alpha isomer is the thermodynamically favored species in both the one- and two-electron-reduced states, with beta-->alpha isomerization being detected in both cases on long time scales (days). EPR spectra also imply that increasing localization of the unpaired electron occurs over the alpha- and beta-[Mo(18)O(54)(SO(3))(2)](5-) frameworks as the temperature approaches 2 K where the EPR spectra show orthorhombic symmetry with different g and hyperfine values for the alpha and beta isomers. Theoretical studies support the observation that it is easier to reduce the alpha cluster than the beta form and also provide insight into the driving force for beta-->alpha isomerization in the reduced state. Data are compared with that obtained for the well studied alpha-[Mo(18)O(54)(SO(4))(2))](4-) sulfate cluster.     

Structure-function correlations in Iron(II) tris(pyrazolyl)borate spin-state crossover complexes

Iron(II) poly(pyrazolyl)borate complexes have been investigated to determine the impact of substituent effects, intramolecular ligand distortions, and intermolecular supramolecular structures on the spin-state crossover (SCO) behavior. The molecular structure of Fe[HB(3,4,5-Me3pz)3]2 (pz = pyrazolyl ring), a complex known to remain high spin when the temperature is lowered, reveals that this complex has an intramolecular ring-twist distortion that is not observed in analogous complexes that do exhibit a SCO at low temperatures, thus indicating that this distortion greatly influences the properties of these complexes. The structure of Fe[B(3-(cy)Prpz)4]2.(CH3OH) ((cy)Pr = cyclopropyl ring) at 294 K has two independent molecules in the unit cell, both of which are high spin; only one of these high-spin iron(II) sites, the site with the lesser ring-twist distortion, is observed to be low-spin iron(II) in the 90 K structure. A careful evaluation of the supramolecular structures of these complexes and several similar complexes reported previously revealed no strong correlation between the supramolecular packing forces and their SCO behavior. Magnetic and M?ssbauer spectral measurements on Fe[B(3-(cy)Prpz)4]2 and Fe[HB(3-(cy)Prpz)3]2 indicate that both complexes exhibit a partial SCO from fully high-spin iron(II) at higher temperatures, respectively, to a 50:50 high-spin/low-spin mixture of iron(II) below 100 K. These results may be understood, in the former case, by the differences in ring-twisting and, in the latter case, by a phase transition; in all complexes in which a phase transition is observed, this change dominates the SCO behavior. A comparison of the M?ssbauer spectral properties of these two complexes and of Fe[HB(3-Mepz)3]2 with that of other complexes reveals correlations between the M?ssbauer-effect isomer shift and the average Fe-N bond distance and between the quadrupole splitting and the average FeN-NB intraligand dihedral torsion angles and the distortion of the average N-Fe-N intraligand bond angles.     

The malonyl transferase activity of type II polyketide synthase acyl carrier proteins

Acyl carrier proteins (ACPs) play a fundamental role in directing intermediates among the enzyme active sites of fatty acid and polyketide synthases (PKSs). In this paper, we demonstrate that the Streptomyces coelicolor (S. coelicolor) actinorhodin (act) PKS ACP can catalyze transfer of malonate to type II S. coelicolor fatty acid synthase (FAS) and other PKS ACPs in vitro. The reciprocal transfer from S. coelicolor FAS ACP to a PKS ACP was not observed. Several mutations in both act ACP and S. coelicolor FAS ACP could be classified by their participation in either donation or acceptance of this malonyl group. These mutations indicated that self-malonylation and malonyl transfer could be completely decoupled, implying that they were separate processes and that a FAS ACP could be converted from a non-malonyl-transferring protein to one with malonyl transferase activity.     

Symmetry-breaking substitutions of [Re(CN)8]3- into the centered, face-capped octahedral clusters (CH3OH)24M9M'6(CN)48 (M = Mn, Co; M = Mo, W)

The diamagnetic complex [Re(CN)8]3- is shown to react with Mn2+ ions in methanol to generate the centered, face-capped octahedral cluster (CH3OH)24Mn9Re6(CN)48, which is structurally analogous to (CH3OH)24Mn9Mo6(CN)48. Related reactions involving stoichiometric mixtures of octacyanometalate complexes generate the substituted species (CH3OH)24Mn9Mo5Re(CN)48, (CH3OH)24Co9Mo5Re(CN)48, (CH3OH)24Mn9Mo3Re3(CN)48, (CH3OH)24Mn9W5Re(CN)48 and (CH3OH)24Co9W5Re(CN)48, in which the O(h) symmetry of the cluster core is broken. Reassessment of the magnetic properties of the Mn9Mo6(CN)48 cluster confirm that it possesses a ground state spin of S = 39/2, but does not exhibit single-molecule-magnet behavior. Lowering the symmetry of the molecule by substitutions of ReV at one or three of the MoV sites does not lead to an overall increase in the magnetic anisotropy, as probed by ac magnetic susceptibility measurements. A similar result occurs for the other substituted species, with the important exception of the new single-molecule magnet (CH3OH)24Co9W5Re(CN)48, for which the spin reversal barrier is significantly reduced relative to that observed previously in (CH3OH)24Co9W6(CN)48.     

石松碱的合成方法综述

石松碱是第一个被发现的石松生物碱类化合物, 其较好的生物活性引起了合成工作者的兴趣. 较全面地介绍了石松碱的各种合成路线, 并对其做了简单分析.     

One-step immobilization of alkanethiol/glycolipid vesicles onto gold electrode: amperometric detection of Concanavalin A

Functionalized vesicles composed of glycolipid and alkanethiol lipids have been immobilized onto gold surface through one-step self-assembly to construct an electrochemical biosensor for Concanavalin A (Con A) detection. Incorporation of alkanethiol lipid molecules into the vesicles allows for firm attachment of the vesicles onto a gold surface to form a sensing interface. At the same time, the introduction of alkanethiol lipid avoids cumbersome organic syntheses of sulfur-containing compound, making the biosensor greater applied prospect. Through the recognition of Con A by glycolipid which was immobilized on the surface of electrode, a decrease of electrochemical signal was observed. This decrease was restored when the electrode was immersed in a stronger binding solution such as glucose. The repeated usability of the novel sensor is excellent.     

聚丙烯酸修饰咔唑的电化学聚合及表征

合成了侧链带有咔唑的N-丙烯酰氧己基咔唑(MACZ),通过自由基聚合得到聚N-丙烯酰氧己基咔唑(PMACZ),在四氢呋喃含10%三氟化硼乙醚与四氟化硼四丁基胺的混合电解质溶液中,直接阳极氧化PMACZ获得自支撑交联网状的聚(聚N-丙烯酰氧己基咔唑)(PPMACZ)薄膜.PPMACZ薄膜具有良好的氧化还原性和热稳定性,电导率为1.34×10-5S·cm-1.1HNMR和红外光谱表明PMACZ二次聚合反应发生在咔唑单元的3,6位上,荧光光谱表明PPMACZ薄膜是一种良好的蓝色发光材料.     

(S)-(+)-N-取代吡咯烷甲醇衍生物的合成及晶体结构

从L-α-脯氨酸出发,经过酯化、N-烷基化、与格氏试剂反应合成了6个未见文献报道的(S)-(+)-N-取代吡咯烷甲醇衍生物3a～3f,其结构经IR,1HNMR和元素分析测定确证.并用X射线单晶衍射法测定了化合物(S)-(+)-1-[N-(5-氯-2-噻唑甲基)-2-吡咯烷基]-1,1-二苯基甲醇(3e)的晶体结构.晶体为单斜晶系,空间群为P2(1),a=0.8737(14)nm,b=0.9098(14)nm,c=1.2180(17)nm,α=90.00°,β=92.55(3)°,γ=90.00°,V=0.9671(3)nm3,Z=2,Dc=1.3217g/cm3,F(000)=404,R=0.0584,wR=0.1335.     

Schiff碱类锌(Ⅱ)配合物的合成、晶体结构及发光性能

本文合成了2个新的Schiff碱锌配合物Zn(C13H10NO)2(1)和Zn(C14H12NO)2(2),测定了它们的晶体结构。结果表明,配合物1属三斜晶系,空间群P1,晶胞参数a=0.9495(2)nm,b=1.0758(2)nm,c=1.2343(3)nm,α=68.318(2)°,β=67.882(3)°,γ=78.316(3)°,V=1.0824(4)nm3,Z=2,Dc=1.405Mg·m-3,F(000)=472,μ=1.160mm-1;配合物2属单斜晶系,空间群C2/c,晶胞参数a=2.1845(5)nm,b=0.87905(19)nm,c=1.1988(3)nm,β=96.563(3)°,V=2.2870(9)nm3,Z=4,Dc=1.411Mg·m-3,F(400)=1008,μ=1.102mm-1。研究了它们在甲醇、乙醇溶液中的发光行为,结果表明这两个配合物在溶液中发光为金属离子微扰下配体的n-π*的发光。