Coinage metal complexes of a boron-substituted soft scorpionate ligand

An improved synthesis of lithium phenyltris(methimazolyl)borate, Li[PhTm(Me)], (methimazole = 1-methylimidazole-2-thione) is described, and the structure of the methanol-solvated [Li(OHMe)4][PhTm(Me)] has been determined. The syntheses and characterization of complexes [M(PhTm(Me))(PR3)] (M = Cu, Ag, Au; R = Et, Ph;) are reported, and the complexes [Cu(PhTm(Me))(PPh3)], [Ag(PhTm(Me))(PEt3)] and [Au(PhTm(Me))(PEt3)] are crystallographically characterized, showing a progression from pseudo-tetrahedral geometry (copper, S3P coordination) to trigonal planar geometry (silver, S2P coordination) to linear geometry (gold, SP coordination). In addition, the copper(I) and silver(I) triphenylphosphine complexes of the adventitiously formed phenylhydrobis(methimazolyl)borate ligand, [M(PhBm(Me))(PPh3)], have been crystallographically characterized, showing both species to have a trigonal planar primary coordination sphere, with a secondary M...H-B interaction. Finally, reaction of copper(II) chloride with Li[PhTm(Me)] results in formation of a compound analyzing as [Cu(II)(PhTm(Me))Cl], although its extreme insolubility and marked instability have precluded its complete characterization. Attempts to prepare this by ultra-slow diffusion of the reactants through solvent blanks has led to isolation of a mixed-valence copper(I/II) methimazolate cluster, [Cu(I)10Cu(II)2(mt)12Cl2] and a copper(I) dimeric complex [Cu2(PhTm(Me))2], indicating that copper(II) ions oxidatively decompose the phenyltris(methimazolyl)borate anion.     

Asymmetric multicomponent [C+NC+CC] synthesis of highly functionalized pyrrolidines catalyzed by silver(I)

[reaction: see text] Highly functionalized pyrrolidines are obtained in a single chemical step via a mild, efficient, and selective Ag(I)-catalyzed asymmetric [C+NC+CC] coupling process. Oppolzer's camphorsultam enables the desired reaction cascade and provides a reliable means to control the developing stereochemistry and purify the products. This three-component reaction provides unprecedented access to structurally diverse pyrrolidines for both target- and diversity-oriented syntheses.     

Influence of primary-level and primary-frequency ratios on human distortion product otoacoustic emissions

The combined influence of primary-level differences (L1-L2) and primary-frequency ratio (f2/f1) on distortion product otoacoustic emission (DPOAE) level was investigated in 20 normal-hearing subjects. DPOAEs were recorded with continuously varying stimulus levels [Neely et al. J. Acoust. Soc. Am. 117, 1248-1259 (2005)] for the following stimulus conditions: f2= 1, 2, 4, and 8 kHz and f2/f1=1.05 to 1.4; various L1-L2, including one individually optimized to produce the largest DPOAE. For broadly spaced primary frequencies at low L2 levels, the largest DPOAEs were recorded when L1 was much higher than L2, with L1 remaining relatively constant as L2 increased. As f2/fl decreased, the largest DPOAEs were observed when L1 was closer to L2 and increased as L2 increased. Optimal values for L1-L2 and f2 f1 were derived from these data. In general, average DPOAE levels for the new L1-L2 and f2/f1 were equivalent to or larger than those observed for other stimulus combinations, including the L1-L2 described by Kummer et al. [J. Acoust. Soc. Am. 103, 3431-3444 (1998)] and those defined by Neely et al. in which L1-L2 was evaluated, but f2/f1 was fixed at 1.2.     

Hydrogen-mediated aldol reductive coupling of vinyl ketones catalyzed by rhodium: high syn-selectivity through the effect of tri-2-furylphosphine

[reaction: see text]. Catalytic hydrogenation of methyl vinyl ketone (MVK) and ethyl vinyl ketone (EVK) in the presence of diverse aldehydes at ambient temperature and pressure using tri-2-furylphosphine-ligated rhodium catalysts enables formation of aldol products with high levels of syn-diastereoselectivity. A progressive increase in diastereoselectivity is observed upon sequential replacement of phenyl residues for 2-furyl residues (Ph3P, FurPh2P, Fur2PhP, Fur3P). Hydrogen-labile functional groups, including alkynes, alkenes, benzylic ethers, and nitroarenes, remain intact under the coupling conditions.     

Photocaged morpholino oligomers for the light-regulation of gene function in zebrafish and Xenopus embryos

Morpholino oligonucleotides, or morpholinos, have emerged as powerful antisense reagents for evaluating gene function in both in vitro and in vivo contexts. However, the constitutive activity of these reagents limits their utility for applications that require spatiotemporal control, such as tissue-specific gene disruptions in embryos. Here we report a novel and efficient synthetic route for incorporating photocaged monomeric building blocks directly into morpholino oligomers and demonstrate the utility of these caged morpholinos in the light-activated control of gene function in both cell culture and living embryos. We demonstrate that a caged morpholino that targets enhanced green fluorescent protein (EGFP) disrupts EGFP production only after exposure to UV light in both transfected cells and living zebrafish (Danio rerio) and Xenopus frog embryos. Finally, we show that a caged morpholino targeting chordin, a zebrafish gene that yields a distinct phenotype when functionally disrupted by conventional morpholinos, elicits a chordin phenotype in a UV-dependent manner. Our results suggest that photocaged morpholinos are readily synthesized and highly efficacious tools for light-activated spatiotemporal control of gene expression in multiple contexts.     

Asymmetric synthesis of substituted 1-aminocyclopropane-1-carboxylic acids via diketopiperazine methodology

Diketopiperazinespirocyclopropane 12 is prepared in > 98% d.e. via the conjugate addition of a phosphorus ylide to (6S)-N,N'-bis(p-methoxybenzyl)-3-methylenepiperazine-2,5-dione 2. Deprotection and hydrolysis of adduct 12 and subsequent peptide coupling demonstrate the applicability of this methodology to the asymmetric synthesis of 1-aminocyclopropane-1-carboxylic acids for incorporation into novel peptides. A model for the high level of diastereofacial selectivity observed in the cyclopropanation reaction is presented. A highly selective asymmetric approach (> 98% d.e.) to (S)-[2,2-(2)H2]-1-aminocyclopropane-1-carboxylic acid 29 is also reported via a deuterated sulfur ylide addition to acceptor 2.     

Determination of the effective charge on muonium during its reaction in aqueous solution

The rate of reaction of muonium atoms with solutes of either charge is unaffected by the addition of a high concentration of an inert salt, therefore the effective charge on the muonium at the point of reaction is essentially zero.     

YBa2Cu3Ox超导体的光谱研究

能带是决定固体特性的头等重要的因素。我们用光谱方法对单相YBa₂Cu₂O_x高T。超导体进行了研究,测量了样品的反射-吸收谱、Raman光谱和荧光光谱.其350和500nm吸收带以及390nm,560nm荧光峰来自晶格中Cu⁺发光中心,是跃迁过程¹A_1g(3d¹⁰)-¹E_g和~3E_g(3d⁹4s¹)。其720nm和860nm荧光峰来自Cu²⁺发光中心,是由于自由离子光谱项²D在八面体晶场、正交晶系晶场中分裂为5个能级之间的跃迁。此外,还有一些光谱可能来自晶格中Cu³⁺发光中心,其481cm^-1和551cm^-1声子对说明了312cm^-1处声子对与电子系统是强耦合。     

相对论性核与乳胶(Ag)碰撞中灰粒子的系统研究 *

用描写相对论性核 核碰撞的LUCIAE模型和相应的事件产生器系统地研究了 1 4.6 ,6 0和 2 0 0AGeV的O核、2 0 0AGeV的Si和S核以及 1 1 .6AGeV的Au核与乳胶 (Ag)碰撞中灰粒子产生的平均多重数、多重数分布以及角分布 3个物理量同入射能量、射弹质量及碰撞中心度间的关系 ,还研究了再散射在灰粒子产生机制中的作用 .LUCIAE的这些研究结果与相应的EMU0 1乳胶实验结果都相一致 .     

算术级数中的陈景润定理 *

设N为一充分大的偶数且q≥ 1 ,(l_i,q) =1 (i=1 ,2 ) ,l₁+l₂ ≡N(modq) .证明了方程N =p+P₂ ,p≡l1(modq) ,P₂ ≡l₂ (modq)对区间 1 ,N^1/37中除了ON^1/37log^-5 N个例外的整数q ,都有无穷多解 ,其中p是素数 ,P₂ 为一至多有2个素因子的殆素数 .