Dendrimer-conjugated magnetic nanoparticles for removal of zinc (II) from aqueous solutions

Dendrimers are novel nanostructure materials that possess a unique three-dimensional molecular configuration. They have high adsorption capacities of heavy metals. Dendrimer-conjugated magnetic nanoparticles (Gn-MNPs) combining the superior adsorbent of dendrimers with magnetic nanoparticles (MNPs) have been developed for effective removal and recovery of Zn(II). In this study, the Gn-MNPs were synthesized, characterized, and examined as reusable adsorbents of Zn(II). Characterization conducted by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and elemental analysis revealed that dendrimers were successfully coated onto the surface of MNPs made of magnetite (Fe₃O₄). The pH effect studies indicate the Zn(II) adsorption with Gn-MNPs is a function of pH. The adsorption efficiency increases with increasing pH. At pH less than 3, Zn(II) is readily desorbed. Hence, the Gn-MNPs can be regenerated using the diluted HCl aqueous solution (0.1 M) where Zn(II) can be recovered in a concentrated form. It was found that the Gn-MNPs underwent 10 consecutive adsorption–desorption processes still retained the original removal capacity of Zn(II). The adsorption data were fitted well with both Langmuir and Freundlich isotherms. The maximum adsorption capacity determined by the Langmuir model is 24.3 mg/g at pH 7 and 25°C. A synergistic effect between the complexation reaction and the electrostatic interaction may account for the overall performance of Gn-MNPs.     

An approach to the core skeleton of lancifodilactone F

Two cycloaddition reactions were utilized for the construction of the 5,6,7-tricyclic skeleton of lancifodilactone F and buxapentalactone. A [2+2] ketene cycloaddition reaction was first used to set their adjacent all-carbon quaternary centers at the 5,6-ring junction. An arene-olefin meta-photocycloaddition reaction was then used to install the 6- and 7-membered rings concurrently.     

Repurposing Iron- and 2-Oxoglutarate-Dependent Oxygenases to Catalyze Olefin Hydration

Mononuclear nonheme iron(II) and 2-oxoglutarate (Fe/2OG)-dependent oxygenases and halogenases are known to catalyze a diverse set of oxidative reactions, including hydroxylation, halogenation, epoxidation, and desaturation in primary metabolism and natural product maturation. However, their use in abiotic transformations has mainly been limited to C−H oxidation. Herein, we show that various enzymes of this family, when reconstituted with Fe(II) or Fe(III), can catalyze Mukaiyama hydration—a redox neutral transformation. Distinct from the native reactions of the Fe/2OG enzymes, wherein oxygen atom transfer (OAT) catalyzed by an iron-oxo species is involved, this nonnative transformation proceeds through a hydrogen atom transfer (HAT) pathway in a 2OG-independent manner. Additionally, in contrast to conventional inorganic catalysts, wherein a dinuclear iron species is responsible for HAT, the Fe/2OG enzymes exploit a mononuclear iron center to support this reaction. Collectively, our work demonstrates that Fe/2OG enzymes have utility in catalysis beyond the current scope of catalytic oxidation.     

Synthesis of dinitrosyl iron complexes (DNICs) with intramolecular hydrogen bonding

HSCH₂CONHCH₃ and HSCH₂CON(CH₃)₂ containing a peptide bond are prepared for the synthesis of DNICs with/without intra-molecular hydrogen bonding, respectively. The IR ν(NO) bands of [(NO)₂Fe(SCH₂CONHCH₃)₂]⁻ (2) appears at 1751, 1700 cm⁻¹. In complex 2, the presence of intramolecular [NH?S] hydrogen bonding was verified by the observation of IR spectroscopy with N−H stretching frequency 3334 cm⁻¹ (CDCl₃) and subsequently confirmed by single-crystal X-ray diffraction showing N−S distance of 2.94 Å. Complex 2 displays the rhombic EPR spectrum with g₁ = 2.039, g₂ = 2.031 and g₃ = 2.013 at in frozen H₂O. Complexes 2 and 3 rapidly release NO when exposed to light. The time needed for photolysis reactions of 2 is two times faster than that of 3 in less polar solvent. Representative time courses for the photolability of 2 and 3 in THF display the NO-off ability: 2 > 3.     

Resolution enhancement of digital laser scanning fluorescence microscopy with a dual-lens optical pickup head

The resolution of the cell fluorescence image captured by a digital laser scanning microscopy with a modified dual-lens BD-ROM optical pickup head is enhanced by image registration and double sample frequency. A dual objective lens of red (655 nm) and blue (405 or 488 nm) laser sources with numerical apertures of 0.6 and 0.85 is used for sample focusing and position tracking and cell fluorescence image capturing, respectively. The image registration and capturing frequency are based on the address-coded patterns of a sample slide. The address-coded patterns are designed as a string of binary code, which comprises a plurality of base-straight lands and grooves and data-straight grooves. The widths of the base-straight lands, base-straight grooves, and data-straight grooves are 0.38, 0.38, and 0.76 μm, respectively. The numbers of sample signals in the x-direction are measured at every intersection point by intersecting the base intensity of the push–pull signal of the address-coded patterns, which has a minimum spacing of 0.38 μm. After taking a double sample frequency, the resolution of the measured cell fluorescence image is enhanced from 0.38 μm to the diffraction limit of the objective lens.     

Sequential electrochemical oxidation of alternating benzene-furan oligomers

Electrochemical oxidation of pentaaryl 2 containing two furan moieties occurs sequentially to give diketone 8 after two-electron transfer. Further oxidation with another two-electron transfer gives the corresponding tetraketone 9. Radical cation intermediate is detected by absorption spectroscopy. The radical intermediates of different regiochemistry have been shown to exhibit different oxidation potentials as revealed by the differential pulse voltammetry.     

Stochastic design optimization of asynchronous flexible assembly systems

This paper presents the application of the stochastic quasigradient method (SQG) of Ermoliev and Gaivaronski to the performance optimization of asynchronous flexible assembly systems (AFAS). These systems are subject to blocking and starvation effects that make complete analytic performance modeling difficult. A hybrid algorithm is presented in this paper which uses a queueing network model to set the number of pallets in the system and then an SQG algorithm is used to set the buffer spacings to obtain optimal system throughput. Different forms of the SQG algorithm are examined and the specification of optimal buffer sizes and pallet numbers for a variety of assembly systems with ten stations are discussed. The combined Network-SQG method appears to perform well in obtaining a near optimal solution in this discrete optimization example, even though the SQG method was primarily designed for application to differentiable performance functionals. While a number of both theoretical and practical problems remain to be resolved, a heuristic version of the SQG method appears to be a reasonable technique for analyzing optimization problems for certain complex manufacturing systems.     

非线性异方差分层模型及其参数估计

提出了一类非线性异方差分层模型,研究了其固定效应和方差分量的极大似然估计问题.主要采用了期望条件最大化算法(Expectation Conditional Maximization Algorithm)和蒙特卡罗积分法(Monte-Carlo integration method).对于随机效应和模型误差的方差-协方差矩阵,本文既考虑了一般的非结构化形式,也考虑了诸如自回归(AR(1))和复合对称等的结构化形式.仿真模拟的结果显示本文提出的模型及参数估计方法表现良好.此外,本文还将该类模型和估计方法应用到中国官方经济数据上,得到了一些有意义的结论.     

Differentially protected benzenediboronic acids: divalent cross-coupling modules for the efficient synthesis of boron-substituted oligoarenes

On the basis of the boron-masking strategy, new divalent cross-coupling modules have been designed for the efficient synthesis of boron-substituted oligoarenes. The modules, i.e., monoprotected o-, m-, and p-benzenediboronic acid derivatives, undergo highly selective Suzuki-Miyaura coupling with sp2 iodides, bromides, chlorides, and triflates, affording coupling products in which the protected boronyl groups are left intact.