On the mean square of the error term for the asymmetric two-dimensional divisor problems(II)

Let Δ(a, b; x) denote the error term of the asymmetric two-dimensional divisor problem. In this paper we shall study the relation between the discrete mean value ${\sum_{n\leq T} \Delta^2(a,b;n)}$ and the continuous mean value ${\int_1^T\Delta^2(a,b;x)dx}$ .     

波尔共振仪相位差测量方法的改进

介绍了波尔共振仪研究机械受迫振动的幅频特性和相频特性的用途，阐述了频闪法测定相位差和利用脉冲电路改进相位差测量的方法，给出了改进方案电路方框图及各点波形图并分析了数字显示相位差的理论依据．     

聚丙烯表面接枝PNIPAAm膜Ⅱ.表面特性和温度响应性研究

通过吸水率和接触角测定研究了聚N 异丙基丙烯酰胺 (PNIPAAm)接枝膜的温度敏感特性 .尽管非交联型接枝膜和交联型接枝膜的吸水特性没有显著差别 ,但是交联组分的引入确实在一定程度上延缓了接枝膜的失水趋势 ,同时也有利于接枝膜亲水性的提高 .对接枝膜进行接触角研究发现 ,在某临界温度以下 ,接触角随时间的变化表征了探测水滴与膜表面之间的相互作用过程 .为了消除接触角测定过程中水份蒸发造成的影响 ,建立了接触角修正算法和修正经验关系式 ,并发展了一种适合于温度敏感性接枝膜LCST测定的变温实时接触角测定方法 .提出了接枝膜与水滴相互作用过程分为两个阶段的模型 ,并得到交联型PP接枝膜表面性能发生明显变化的临界接枝率为 0 6mg cm2 左右     

硒预防原发性肝癌的研究进展

综述了从八十年代以来，在肝癌高发区进行的微量元素硒与肝癌关系的研究，包括流行病学、动物实验和防治应用等方面。     

溶剂辅助蒸馏-气相色谱-串联质谱法分析酿酒葡萄中的游离态萜烯类化合物

应用气相色谱-串联质谱联用技术(GC-MS/MS)和溶剂辅助蒸馏技术(SAFE)对4种酿酒葡萄中的游离态萜烯类化合物进行了研究。采用恒温振荡法浸提葡萄中的成分,溶剂辅助蒸馏法除去不挥发性成分,提取液经氮吹浓缩后进行GC-MS/MS分析。实验中优化了SAFE条件(循环水浴温度、样品流量)。通过NIST05a谱库检索、标准品的保留指数（RI值）对比及参考文献的RI值对比分析，在4种葡萄中共鉴定出30种萜烯类化合物,其中包括10种单萜烯类化合物、18种倍半萜烯类化合物、1种二萜烯类化合物以及1种三萜烯类化合物。在蛇龙珠葡萄中检出了28种萜烯类化合物,在梅鹿辄、赤霞珠和品丽珠葡萄中分别检出了16，17和16种萜烯类化合物。在蛇龙珠葡萄中检出了17种倍半萜烯类化合物,远多于其他3种酿酒葡萄。通过半定量分析，发现在赤霞珠葡萄中单萜烯类化合物含量较高,在蛇龙珠葡萄中倍半萜烯化合物含量较高。实验结果表明,该方法适用于酿酒葡萄中游离态萜烯类成分的定性和定量分析。     

Dehydrogenation of iron amido-borane and resaturation of the imino-borane complex

We report on the first isolation and structural characterization of an iron phosphinoimino-borane complex Cp*Fe(η²-H₂B NC₆H₄PPh₂) by dehydrogenation of iron amido-borane precursor Cp*Fe(η¹-H₃B–NHC₆H₄PPh₂). Significantly, regeneration of the amido-borane complex has been realized by protonation of the iron(ii) imino-borane to the amino-borane intermediate [Cp*Fe(η²-H₂B–NHC₆H₄PPh₂)]⁺ followed by hydride transfer. These new iron species are efficient catalysts for 1,2-selective transfer hydrogenation of quinolines with ammonia borane.

Dehydrogenation of an amido-borane iron complex provides an imino-borane complex. Regeneration of the amido-borane precursor was achieved by protonation of the imino-borane followed by hydride transfer to the amino-borane intermediate.

Because of relevance to H₂ storage^1–10 and hydrogenation catalysis,^11–15 metal amine-borane complexes^16–18 and their dehydrogenated forms, such as amino-boranes^20–22 and imino-boranes⁴ are arising as a significant family in organometallic chemistry. In transition metal-catalyzed dehydrocoupling of amine-boranes and related transfer hydrogenations, the interactions between the metal and the borane fragment are essential to dehydrogenation and the consequent transformations.^16–20 Specifically, amino-borane complexes containing a M–H₂B NR₂ moiety are the primary dehydrogenated species and are often identified as a resting point in the catalysis (Scheme 1a).^20–22 Management of reversible dehydrogenation–regeneration reactions on a M–BH₂ NR₂ platform could provide a strategy with which to design efficient catalysts capable of operating sustainable syntheses.Open in a separate windowScheme 1Schematic representation of metal-based amine-borane dehydrogenation.Wider exploration of metal amino-borane chemistry is challenging since M–H₂B NH₂ species are very reactive toward H₂ release. In 2010, Aldridge et al. reported the isolation of [(IMes)₂Rh(H)₂(η²-H₂B NR₂)] and [(IMes)₂Ir(H)₂(η²-H₂B NR₂)] from the metal-catalyzed dehydrogenation of R₂HN·BH₃.^21a At the same time, Alcaraz and Sabo-Etienne reported the preparation of (PCy₃)₂Ru(H)₂(η²-H₂B NH_nMe_2−n) (n = 0–2) complexes^22a by the dehydrogenation of amine-boranes with the corresponding ruthenium precursors. Subsequently, a straightforward synthesis of Ru, Rh, and Ir amino-borane complexes by reaction of H₂B NR₂ (R = iPr or Cy) with the bis(hydrogen) complexes of M(H)₂(η²-H₂)₂(PCy₃)₂ or [CpRu(PR₃)₂]⁺ fragments was developed.^21b,22b Turculet et al. have shown that the ruthenium-alkoxide complex is able to activate H₃B·NHR₂ producing hydrido ruthenium complex.²³ Notably, Weller and Macgregor found that dehydrocoupling of ammonia-borane by [Ph₂P(CH₂)₃PPh₂Rh(η⁶-C₆H₅F)] affords a μ-amino-borane bimetallic Rh complex, in which the simplest H₂B NH₂ moiety is trapped on a rhodium dimer.^20aAlthough iron-catalyzed dehydrocoupling of amine-boranes has attracted great interest,^24–29 iron amine-borane complexes, their dehydrogenated derivatives, and especially the catalysis relevant to organic synthesis are largely unexplored. Recently, Kirchner et al. reported a pincer-type iron complex generated by protonation of the borohydride iron complex (PNP)Fe(H)(η²-BH₄) with ammonium salts.³⁰ Inspired by earlier research on M–H₂B NR₂ chemistry, we intended to establish the reversible conversions of amino-borane complexes and their dehydrogenated forms in a synthetic piano-stool iron system. Herein, we report dehydrogenation of iron amido-borane complex Cp*Fe(η¹-H₃B–NHC₆H₄PPh₂) (2) (Cp* = Me₅C₅⁻) to the imino-borane complex Cp*Fe(η²-H₂B NC₆H₄PPh₂) (3), and resaturation of the imino-borane by stepwise protonation and hydride transfer (Scheme 1b). This new class of iron species is capable of catalyzing 1,2-selective transfer hydrogenation of quinolines with H₃N·BH₃.To synthesize the iron amido-borane complex, a new monomer, the iron tetrahydridoborate precursor Cp*Fe(η²-BH₄)(NCMe) (1), was prepared in situ by the reaction of [Cp*Fe(NCMe)₃]PF₆ with Bu₄NBH₄ in acetonitrile at room temperature for 5 min. Such ferrous borohydrides have been documented only rarely,³¹ since they are prone to form polynuclear iron borate clusters.^32,33 The ¹¹B NMR spectrum of the reaction solution shows a quintet at δ 15.4 (J_BH = 88 Hz) for the BH₄⁻ ligand of 1, and this stands in contrast to the signal at δ −32.0 observed for Bu₄NBH₄. Upon storing the reaction mixture at −30 °C overnight, single crystals suitable for X-ray diffraction were obtained. Crystallographic analysis confirmed the structure of 1 as a piano-stool iron tetrahydridoborate compound (ESI, Fig. S1^†).Addition of phosphinoamine ligand 1,2-Ph₂PC₆H₄NH₂ to a solution of 1 in acetonitrile caused an instantaneous color change from deep blue to dark brown (Scheme 2). ESI-MS studies indicated the production of the iron amido-borane compound (2) with m/z = 481.1793 (calcd m/z = 481.1770), which was isolated in 87% yield. NMR spectra showed a boron resonance at δ −17.5, and a phosphorus resonance at δ 85.9. The ¹H NMR spectrum exhibits a characteristic hydride signal at δ −13.98, which is assigned to the bridging hydride Fe–H–B. Owing to exchange between the hydrogen atoms at the boron,³⁴ the terminal B–H resonances in the ¹H NMR spectrum are very broad and are obscured by the distinct Cp* signals. To assign the B–H hydride signals, the deuterated compound Cp*Fe(D₃B–NHC₆H₄PPh₂) (d-2) was synthesized from Cp*Fe(BD₄)(NCMe). In addition to the Fe–D–B signal at δ −13.98, the ²H NMR spectrum of d-2 displayed discrete peaks at δ 2.23 and 0.19 for the terminal B–D hydrides (Fig. 1).Open in a separate windowFig. 1 ²H NMR spectra for dehydrogenation of d-2 to d-3.Open in a separate windowScheme 2Synthetic route to imino-borane complex.When a C₆H₆ solution of 2 was held at 50 °C for 6 h the dehydrogenated imino-borane compound (3) was produced in 92% yield. The ESI-MS spectrum of 3 has a strong peak at m/z 479.1626 (calcd m/z = 479.1637) which can be compared to the peak at m/z = 481.1793 for 2. The isotopic distributions match well with the calculated values (see Fig. S3^†). GC analysis shows that the reaction produced H₂ nearly quantitatively (see Fig. S4^†). In solution, the ³¹P NMR spectrum of 3 displays a sharp signal at δ 71.9, in contrast to the peak at δ 85.9 for 2. The ¹¹B resonance shifts significantly, from δ −17.5 for 2 to δ 42.7 for 3 (Fig. S16^†), and is particularly diagnostic of a three-coordinate boron atom.^21,35 This result indicates the B N double bond character in the dehydrogenated form of the amido-borane complex. In the ¹H NMR spectrum, the Fe–H–B signal was observed at δ −17.91 with the integral of 2H, and no characteristic signal for a terminal B–H hydride was found. To confirm the formation of an imino-borane compound, the hydrogen decoupling was also carried out with compound d-2 and monitored by ²H NMR spectra. Only a deuterium signal was observed at δ −17.91 for Fe–D–B, indicating the formation of d-3 (Fig. 1). When the dehydrogenation was conducted in a J-Young tube in C₆D₆, a characteristic triplet corresponding to HD appeared at δ 4.43 (J_HD = 45 Hz) in the ¹H NMR spectrum (Fig. S18^†).³⁶The structures of 2 and 3 were verified by X-ray crystallographic analysis (Fig. 2). Consistent with NMR spectroscopic analysis, the BH₃ moiety in 2 is stabilized by one of the B–H bonds binding at the Fe–NH unit to form an Fe–H–B–N four-membered metallacycle. This metal–ligand cooperative binding mode increased the B–H bond length in the bridging B–H(1) bond to 1.362 Å vs. 1.129 Å and 1.121 Å for the two terminal B–H bonds. The B–N bond length of 1.545(3) Å in 2 is slightly shorter than that in H₃B·NH₃ (d_B–N = 1.58(2) Å).³⁷ Crystallographic analysis of 3 confirmed an imino-borane complex with a Cp*Fe(η²-H₂B NC₆H₄PPh₂) framework. After dehydrogenation of 2, striking structural changes were observed. The N atom has been become detached from Fe, while the BH₂ fragment acts as a bis(σ-borane) ligand coordinated to the metal center.^21–23 The B–N bond distance of 1.455(5) Å in 3 is shorter by 0.09 Å than that in 2, and is close to that reported for the cyclic trimer borazine (1.4355(21) Å).³⁸ Combined with the NMR results, the B–N bond length in 3 suggests some double bond character.^21,22 As the imino-borane fragment is tethered in the coordination sphere, the boron center adopts a quasi-tetrahedral geometry, and the B–N bond appears to be partially sp³ hybridized. Dehydrogenation of the amido-borane complex also caused the decrease of the Fe⋯B distances from 2.223(3) Å to 2.026(4) Å which is shorter than the sum of the covalent radii of Fe and B atom (2.16 Å), indicating that the borane and the metal are bonded.Open in a separate windowFig. 2Solid-sate structure (50% probability thermal ellipsoids) of (a) complex 2 and (b) 3. For clarity, hydrogen atoms of Cp* and phenyl rings are omitted.Notably, the amido-borane compound 2 can be regenerated by stepwise protonation of 3 and transfer of a hydride (Scheme 3). Complex 3 reacts readily with H(Et₂O)₂BAr^F₄ in C₆H₅F. The reaction solution was analyzed by ESI-MS spectroscopy, which showed an ionic peak at m/z = 480.1726 (calcd m/z = 480.1715), suggesting the formation of [3H]⁺. Alternatively, the reaction of complex 2 with H(Et₂O)₂BAr^F₄ unambiguously provides [3H]⁺ and produces H₂. X-ray crystallographic analysis reveals that the resulting cationic complex [3H]⁺ exhibits a similar framework to its imino-borane precursor (3). The BH₂ moiety retains a binding mode of the bis(σ-BH₂) fashion (Fig. 3). In contrast, the B–N distance in [3H]⁺ (1.586(6) Å) is extended by 0.13 Å and the [3H]⁺ framework becomes much less compact than that of 3. Probably due to the fluxional structure of the seven-membered Fe–P–C–C–N–B(H) ring, the solution of [3H][BAr^F₄] gives broad ¹H NMR resonances even at −60 °C. The phosphorus resonance arose at δ 72.0 as a singlet when the solution sample was cooled to −40 °C (Fig. S20 and S21^†).Open in a separate windowFig. 3Solid-state structures of (a) complex [3H]⁺ and (b) [3H(PPh₃)]⁺. For clarity, counterion [BAr^F₄]⁻, hydrogen atoms of Cp* and phenyl rings have been omitted.Open in a separate windowScheme 3Conversions of iron imino-borane, amino-borane and amido-borane complexes.In [3H]⁺, the boron is coordinatively unsaturated, as manifested by its interaction with a σ-donor. For instance, treatment of 2 with [HPPh₃][BAr^F₄] (pK^MeCN_a = 7.6)³⁹ provides a Ph₃P-stabilized borane complex, [3H(PPh₃)]⁺ (m/z = 742.2620, calcd m/z = 742.2626). The ¹H NMR spectrum of [3H(PPh₃)]⁺ exhibits an NH resonance at δ 4.68, suggesting that protonation occurred at the N site. The distinctive upfield hydride signal for Fe–H–B is observed at δ −15.58. In the ³¹P NMR spectrum, two phosphorus signals at δ 78.90 and −1.26 correspond to the Fe–P and the B–P resonances, respectively. The ¹¹B signal at δ −13.72 indicates a tetracoordinated boron, which is further confirmed by crystallographic analysis of [3H(PPh₃)]⁺ (Fig. 3). In the solid-sate structure, a Ph₃P molecule is bound to the B center (d_B–P = 1.982(4) Å), leading to the formation of a new Fe–H–B–N four-membered metallacycle. As a amido-borane complex, [3H(PPh₃)]⁺ has a B–N bond length of 1.527(5) Å, somewhat shorter than 1.545(3) Å in 2.After attaching a proton at the N atom, we subsequently explored restoration of the original borane moiety. Treatment of freshly prepared [3H][BAr^F₄] in fluorobenzene with catecholborane-NEt₃ adduct (δ_B = 10.56, J_HB = 142.4 Hz)⁴⁰ results in the regeneration of 2, as evidenced by the NMR spectra (Fig. S29 and S30^†). The ¹H NMR spectrum of the reaction mixture displays a characteristic hydride signal at −13.97 ppm, indicating the recovery of the iron amido-borane complex. On the other side, concomitant formation of the borenium ion (δ_B = 13.86) was also observed in the ¹¹B NMR spectrum, which agrees with the hydride transfer from the organohydride reagent to [3H]⁺. It was interesting that the ion [3H]⁺ is stable towards 5,6-dihydrophenanthridine and Hantszch ester. These results indicate that the hydride-donating ability (ΔG_H⁻) of 2 is in the range of 55–59 kcal mol⁻¹.⁴¹ The reactive nature of the hydride in 2 was demonstrated by the reaction with [HPPh₃][BAr^F₄], which produces [3H(PPh₃)]⁺ and releases H₂ (Scheme 3).1The metal amine-borane complexes and their dehydrogenated derivatives are implicated throughout the catalytic cycle of amine-borane dehydrogenation. We found both the iron complexes 2 and 3 are efficient catalysts for H₃N·BH₃ dehydrogenation at room temperature. In the presence of 1 mol% catalyst, a THF solution of H₃N·BH₃ (1.0 mmol) generates about 2.2 equivalent of H₂ within 6 h based on GC quantification (Fig. S33^†). More importantly, such catalytic dehydrocoupling systems allow for selective transfer hydrogenation of quinolines to dihydroquinolines, which are valuable synthons leading to many bio-active compounds.⁴² For instance, addition of methyl-6-quinolineacetate (4) to the catalytic system containing one equiv. of H₃N·BH₃ and 1 mol% of 3 gave 1,2-dihydro-methyl-6-quinolineacetate (5) in excellent yield within 6 h (eqn (1)). The outcome of this reaction was unaffected by switching the catalyst from 3 to 2, or by use of excess reducing agent or by an increase in the reaction temperature (Table S1^†).     

用霍耳传感器测量扭摆周期

本文介绍二种开关型霍耳传感器在扭摆周期测定中的应用 ,给出了部分传感器参数和安装接线图     

环形HYLTE喷管叶片的简化设计及加工方法

 在不影响喷管性能的前提下,将环形HYLTE喷管叶片分解为4个1/4圆环,经过进一步简化设计后,得到只有3个截面中心共面的内部管道的1/4环形叶片。提出了两种环形HYLTE喷管叶片的加工方法：真空钎焊的方法和嵌铸的方法,并对两种方法进行了比较。对于真空钎焊的方法,进行了验证加工,测试结果表明喷管叶片焊接处气密性良好,力学性能优良,可在较高温度下正常工作。嵌铸的方法在一体化加工方面优势明显,可作为环形喷管加工的备选方法。     

金刚石膜/多孔硅复合材料的性能表征

提出了一种新颖的多孔硅表面钝化技术,即采用微波等离子体辅助的化学气相沉积（MPCVD）方法在多孔硅上沉积金刚石薄膜。采用原子力显微镜（AFM）、扫描电子显微镜（SEM）、X射线衍射仪（XRD）、拉曼光 谱仪和荧光分光度计对多孔硅及金刚石膜的表面形貌、结构和发光特性进行了表征。结果表明采用微波等离子体化学气相沉积法可在多孔硅基片上形成均匀、致密、性能稳定且对可见光具有全透性的金刚石膜。金刚石膜与多孔硅的复合,大大稳定了多孔硅的发光波长和强度,同时增强了多孔硅的机械强度。     

Isolated Square‐Planar Copper Center in Boron Imidazolate Nanocages for Photocatalytic Reduction of CO2 to CO

Photocatalytic reduction of CO₂ to value‐added fuel has been considered to be a promising strategy to reduce global warming and shortage of energy. Rational design and synthesis of catalysts to maximumly expose the active sites is the key to activate CO₂ molecules and determine the reaction selectivity. Herein, we synthesize a well‐defined copper‐based boron imidazolate cage (BIF‐29) with six exposed mononuclear copper centers for the photocatalytic reduction of CO₂. Theoretical calculations show a single Cu site including weak coordinated water delivers a new state in the conduction band near the Fermi level and stabilizes the *COOH intermediate. Steady‐state and time‐resolved fluorescence spectra show these Cu sites promote the separation of electron–hole pairs and electron transfer. As a result, the cage achieves solar‐driven reduction of CO₂ to CO with an evolution rate of 3334 μmol g^?1 h^?1 and a high selectivity of 82.6 %.