Zirconium complexes containing a diarylamido diphosphine ligand: Structural preferences controlled by ligand electronics and sterics

This work describes the preparation of [PNP]ZrX₃ ([PNP]⁻ = [N(o-C₆H₄PⁱPr₂)₂]⁻; X = Cl, Me, CH₂SiMe₃) whose structural preference is found to be a function of the electronic and steric nature of the monodentate ligand X⁻. The reaction of ZrCl₄(THF)₂ with [PNP]Li in toluene at room temperature generates [PNP]ZrCl₃ as a red solid in 60% yield. Alkylation of [PNP]ZrCl₃ with three equivalents of Grignard reagents in diethyl ether at −35 °C produces cleanly [PNP]ZrR₃ (R = Me, CH₂SiMe₃) as yellow crystalline materials. An X-ray diffraction study of [PNP]ZrCl₃ showed it to be a chloride-bridged binuclear species {[PNP]ZrCl₂(μ−Cl)}₂ in which both zirconium atoms are 7-coordinate whereas that of [PNP]ZrMe₃ revealed a mononuclear, 6-coordinate core structure. Interestingly, with the incorporation of more sterically demanding alkyls, [PNP]Zr(CH₂SiMe₃)₃ is a 5-coordinate compound wherein the amido phosphine ligand is κ²-N,P bound to zirconium. The solution structures of these molecules were also assessed by variable-temperature NMR spectroscopy.     

Comprehensive molecular imaging of photolabile surface samples with synchronized dual-polarity time-of-flight mass spectrometry

This work presents the unique features of a novel configuration of a synchronized dual-polarity time-of-flight mass spectrometer for comprehensive surface imaging. Mass spectrometry imaging of surface samples covering positive and negative ion modes is difficult due to rapid signal depletion. This limitation is overcome here by dual-polarity time-of-flight mass spectrometry (DP-TOFMS) via two separate TOF mass analyzers that are installed above a sample surface. The new instrument eliminates the polarity bias characteristic of most mass spectrometers, which is important for the analysis of samples with diverse physical and chemical properties. The experimental results show for the first time that the spatial distribution of positive and negative ions of various photolabile samples can be distinguished, including pigments and conventional matrix-assisted laser desorption/ionization samples. The different positive and negative ion distributions suggest that accurate quantitative information can only be obtained when the entire sample region is examined by DP-TOFMS, which was unfeasible in the past. Such a comprehensive diagnostic method is essential for the molecular imaging of trace compositions in delicate biological tissues, as demonstrated here with a Phyllanthus urinaria leaf that only produced ion signals in the first examination and not in the subsequent measurements.     

大孔炭载Pd催化剂对甲酸氧化的电催化性能

用X射线能量色散谱(EDS)、X射线衍射(XRD)谱、拉曼光谱和电化学技术研究和比较了直接甲酸燃料电池(DFAFC)中Vulcan XC-72炭黑载Pd (Pd/XC)和大孔炭载Pd (Pd/MC)催化剂对甲酸氧化的电催化性能. 循环伏安曲线测量表明甲酸在Pd/XC和Pd/MC催化剂电极上主要氧化峰的峰电位基本相同, 在0.15 V左右, 但在Pd/MC催化剂电极上的峰电流密度比在Pd/XC催化剂上的大30%左右. 计时电流曲线测量表明, 在6000 s时, 在Pd/MC催化剂电极上的峰电流密度比在Pd/XC催化剂上的大38%左右, 这些结果说明Pd/MC催化剂对甲酸氧化的电催化活性和稳定性要好于Pd/XC催化剂. 由于Pd/MC和Pd/XC催化剂的Pd粒子平均粒径和相对结晶度相似, 因此, Pd/MC催化剂电催化性能好的原因只能归结于MC大的孔径和高的石墨化程度引起的高电导率.     

Synchronous high-performance liquid chromatography with a photodiode array detector and mass spectrometry for the determination of citrinin, monascin, ankaflavin, and the lactone and acid forms of monacolin K in red mold rice

The Monascus fermentation product red mold rice (RMR) has been found to contain the cholesterol-lowering agent monacolin K (MK) in both its lactone (MKL) and acid (MKA) forms and the mycotoxin citrinin (CT). The yellow pigments in RMR, namely, monascin (MS) and ankaflavin (AK), have been reported to exhibit antimetastatic and antiangiogenic activities. Currently, MK and these yellow pigments are usually detected in RMR by different analytical methods that are inconvenient, expensive, and time-consuming. The goal of this study was to establish a rapid, synchronous analytical method for determination of the MKA, MKL, MS, AK, and CT levels in RMR. MKA, MKL, MS, AK, and CT were extracted by the same extraction method, then separated by RP-HPLC with a C18 column. The effluent from the column was passed through a photodiode array detector and then introduced directly into a fluorescence detector. The results showed that high recovery rates of MKA, MKL, MS, AK, and CT are possible if RMR powder is extracted with 75% ethanol (10 mL) at 80 degrees C for 30 min. With regard to the optimal conditions of the HPLC, the peaks of MKA, MKL, MS, AK, and CT can be clearly separated from any noise peaks by isocratic elution with a mobile phase comprising 0.05% trifluoroacetic acid in acetonitrile-water (62.5 + 37.5, v/v).     

Green microfluidic devices made of corn proteins

An alternative green microfluidic device made of zein, a prolamin of corn, can be utilized as a disposable environmentally friendly microchip especially in agriculture applications. Using standard soft lithography and stereo lithography techniques, we fabricated thin zein films with microfluidic chambers and channels. These were bonded to both a glass slide and another zein film. The zein film with microfluidic features bonds irreversibly with other surfaces by vapor-deposition of ethanol to create an adhesive layer resulting in very little or no trapped air and small shape distortion. Zein-zein and zein-glass microfluidic devices demonstrated sufficient strength to facilitate fluid flow in a complex microfluidic design that showed no leakage under high hydraulic pressure. Zein-glass microfluidic devices with serpentine mixing design showed successful fluid manipulation as a concentration gradient of Rhodamine B solution was generated. The ease of fabrication and bonding and the flexibility and moldability of zein offer attractive possibilities for microfluidic device design and manufacturing. These devices can include several unit operations with mixing being one of the most commonly used. The zein-based microfluidic devices, made entirely from a biopolymer from agricultural origin, offer alternative environmentally friendly material choices that are less dependent on limited petroleum based polymer resources.     

Transimination reactions in [b-3C-im][NTf2] ionic liquid

Compared to conventional molecular solvents, the ionic liquid [b-3C-im][NTf(2)] was found to promote transimination reactions with up to ～100-fold rate enhancement. This rate effect observed at ambient temperature might be explained by the fact that the ionic liquid displays weak Lewis acidity with very low, if any, nucleophilicity and its imidazolium cation is expected to interact by associating with, and thus electrophilically activating, the C=N bond of the starting imine, leading to increased stabilization of the polar, charged intermediate species and ultimately, rapid product formation. Moreover, the presence of 1 mol% Sc(OTf)(3) in [b-3C-im][NTf(2)] further facilitates the transimination reactions studied.     

Synthesis, crystal structures, luminescent and magnetic properties of homodinuclear lanthanide complexes with a flexible tripodal carboxylate ligand

Six new homodinuclear lanthanide(III) complexes with a flexible tripodal carboxylate ligand (H(3)L), of formulae [Ln(2)L(2)(DMF)(4)]·4DMF (Ln = La (1), Nd (2), Eu (3), Gd (4), Tb (5), Dy (6), DMF = N, N-Dimethylformamide) have been synthesized. Among them, 1, 2, 3, 4, 6 were characterized by single-crystal X-ray diffraction, which crystallized in the monoclinic space group P2(1)/n with a = 13.309(2) ?, b = 27.404(4) ?, c = 16.686(3) ?, β = 105.115(2) and V = 5875.2(17) ?(3) for 1, a = 13.3016(5) ?, b = 27.1952(12) ?, c = 16.6339(7) ?, β = 105.030(2) and V = 5811.3(4) ?(3) for 2, a = 13.2797(10) ?, b = 27.072(2) ?, c = 16.6564(13) ?, β = 104.9390(10) and V = 5785.7(8) ?(3) for 3, a = 13.2855(3) ?, b = 27.0074(6) ?, c = 16.6357(3) ?, β = 104.9790(10) and V = 5766.2(2) ?(3) for 4, a = 13.2837(5) ?, b = 26.9105(10) ?, c = 16.6066(6) ?, β = 104.917(2) and V = 5736.3(4) ?(3) for 6. The crystal structures reveal that these complexes are isostructural, and molecules are connected from 0D to 3D supramolecular structures by hydrogen bonds. All of them were characterized by elemental analysis, IR spectroscopy, XRD and TGA. Unusually, non-luminescent Tb(III) complex was obtained. The photophysical property of the Eu(III) complex and the magnetic property of Gd(III) complex are investigated and discussed in detail.     

Ruthenium-catalyzed oxidation of a carbon-carbon triple bond: facile syntheses of alkenyl 1,2-diketones from alkynes

A new oxidation procedure of alkynes catalyzed by Tp(PPh(3))(CH(3)CN)Ru-Cl is presented, which provides an efficient way to obtain alkenyl 1,2-diketones via ruthenium alkenyl 1,2-diketone intermediates. In contrast, the analogous reactions with Tp(PPh(3))(PhCN)Ru-Cl gave rise to the ruthenium metallacycle complexes.     

High-throughput 3D spheroid culture and drug testing using a 384 hanging drop array

Culture of cells as three-dimensional (3D) aggregates can enhance in vitro tests for basic biological research as well as for therapeutics development. Such 3D culture models, however, are often more complicated, cumbersome, and expensive than two-dimensional (2D) cultures. This paper describes a 384-well format hanging drop culture plate that makes spheroid formation, culture, and subsequent drug testing on the obtained 3D cellular constructs as straightforward to perform and adapt to existing high-throughput screening (HTS) instruments as conventional 2D cultures. Using this platform, we show that drugs with different modes of action produce distinct responses in the physiological 3D cell spheroids compared to conventional 2D cell monolayers. Specifically, the anticancer drug 5-fluorouracil (5-FU) has higher anti-proliferative effects on 2D cultures whereas the hypoxia activated drug commonly referred to as tirapazamine (TPZ) are more effective against 3D cultures. The multiplexed 3D hanging drop culture and testing plate provides an efficient way to obtain biological insights that are often lost in 2D platforms.