Metal-free N-iodosuccinimide-catalyzed mild oxidative C-H bond amination of benzoxazoles

A facile, efficient, and mild protocol for the synthesis of aminobenzoxazoles has been developed using direct oxidative C-H bond amination of benzoxazoles with secondary or primary amines. The reaction was performed using catalytic amount of N-iodosuccinimide and aqueous hydrogen peroxide as a green oxidant and in the absence of transition metals. Reaction proceeds smoothly at ambient temperature and requires shorter reaction time to furnish excellent yield of the desired products. Various cyclic, acyclic, and functionalized aliphatic amines were well tolerated under optimized reaction conditions and provided good to excellent yield of the respective aminobenzoxazoles.     

SG3左半定义域上的Dirichlet边值问题

调和函数在SG₃上的Dirichlet边值问题是分形分析领域的重要研究内容之一。考虑通过垂直切割自相似图形SG₃,得到SG₃上的特定定义域。对于边界值为Cantor集的新的自相似图形,试图探讨在该定义域上的性质。在研究SG₃左半定义域上的Dirichlet边值问题的过程中,借助SG₃上的二元有理点的调和函数值和正则导数求解格林函数。进一步,运用调和函数的有限能以及弱公式化等方法,最终得到了SG₃左半定义域上的格林函数表达式及其相应的定理。     

Green synthesis and physical properties of crystalline silica engineering nanomaterial from rice husk (agriculture waste) at different annealing temperatures for its varied applications

Crystalline nano silica (SiO₂) was synthesized using a cost-effective eco-friendly method from agricultural waste material like rice husk. Polymer nanocomposite has been prepared using the sol-gel technique from crystalline nano silica using PVA as a polymer binder. Thermal analysis measurement is employed to investigate thermal stability. The XRD analysis shows the crystalline nature of silica is revealed to have characteristic peaks of SiO₂. The particle size was evaluated using Schererr's formula and found to be in the range of 21–31 nm. FTIR measurement shows the presence of O–Si–O (silane) bond formation. The PL measurement shows broad excitation prominently in the visible region. In the XRD pattern, a major peak of the Nanocomposite is observed at an angular position of 19.5° degree, which is more prominent than that of the PVA with the addition of 0.2 wt percent Nano silica to the PVA composite. SEM provides information on homogeneous distribution. This could be beneficial in terms of higher mechanical qualities as well as multifunctional properties. By hydrogen bonding, the PVA molecules are strongly linked to each SiO₂ nanoparticle as measured by FTIR. The stability of materials is confirmed by Zeta Potential and DLS. In the photoluminescence property of SiO₂-PVA crystalline Nano silica composite is excited using a radiation wavelength of 200 nm. The indirect bandgap was determined to be 4.28 eV which could be attributed to the 1100 °C annealing temperature. Such materials may be used as a semiconductor material obtained from a direct natural source, rice husk. Thus, in the present research structural, physical, and optical properties of crystalline nano silica and its polymer composite are explored, which leads us to prepare technological grads material from agricultural waste for varied applications including Agriculture to medical science.     

金属圆柱腔体中使用非均一背景增强微波断层成像

针对基于圆柱金属腔体的微波断层成像系统,提出了一种利用非均一背景增强系统获取目标信息能力的方法.该方法通过在腔体内放置已知物体构成非均一背景,这样不但能利用背景的先验信息,而且可以增加等效辐射源对目标进行探测.首先,利用矩量法计算圆柱金属腔体内非均一背景的格林函数和离散积分算子,并对离散积分算子进行奇异值谱和条件数分析,在理论上证明该方法的可行性;然后,利用基于有限元的对比源逆成像法对均一背景、有耗非均一背景和无耗非均一背景三种情况进行仿真研究;最后对仿真结果进行了误差分析和比较.仿真结果表明,该方法可以提高反演收敛速度和结果准确度,有耗非均一背景略优于无耗非均一背景.该方法可以在不改变硬件系统和算法的情况下得到更准确的反演结果,可应用于医学成像与工业无损探测.     

First-principles modelling of scanning tunneling microscopy using non-equilibrium Green’s functions

The investigation of electron transport processes in nano-scale architectures plays a crucial role in the development of surface chemistry and nano-technology. Experimentally, an important driving force within this research area has been the concurrent refinements of scanning tunneling microscopy (STM) techniques. The theoretical treatment of the STM operation has traditionally been based on the Bardeen and Tersoff–Hamann methods which take as input the single-particle wave functions and eigenvalues obtained from finite cluster or slabs models of the surface-tip interface. Here, we present a novel STM simulation scheme based on non-equilibrium Green’s functions (NEGF) and Wannier functions which is both accurate and very efficient. The main novelty of the scheme compared to the Bardeen and Tersoff–Hamann approaches is that the coupling to the infinite (macroscopic) electrodes is taken into account. As an illustrating example we apply the NEGF-STM method to the Si(001)-(2×1):H surface with sub-surface P doping and discuss the results in comparison to the Bardeen and Tersoff–Hamann methods.     

Microwave-assisted synthesis of azetidines in aqueous media

Simple azetidines are synthesized in good to excellent yields and high purity via cyclization of 3-(ammonio)propyl sulfates derived from primary amines and the cyclic sulfate of 1,3-propanediol. A feature of this methodology includes the accelerated synthesis of azetidines in water under the influence of microwave-assisted heating.     

Green synthesis of colloidal silver nanoparticles using natural rubber latex extracted from Hevea brasiliensis

Colloidal silver nanoparticles were synthesized by an easy green method using thermal treatment of aqueous solutions of silver nitrate and natural rubber latex (NRL) extracted from Hevea brasiliensis. The UV–Vis spectra detected the characteristic surface plasmonic absorption band around 435 nm. Both NRL and AgNO₃ contents in the reaction medium have influence in the Ag nanoparticles formation. Lower AgNO₃ concentration led to decreased particle size. The silver nanoparticles presented diameters ranging from 2 nm to 100 nm and had spherical shape. The selected area electron diffraction (SAED) patterns indicated that the silver nanoparticles have face centered cubic (fcc) crystalline structure. FTIR spectra suggest that reduction of the silver ions are facilitated by their interaction with the amine groups from ammonia, which is used for conservation of the NRL, whereas the stability of the particles results from cis-isoprene binding onto the surface of nanoparticles. Therefore natural rubber latex extracted from H. brasiliensis can be employed in the preparation of stable aqueous dispersions of silver nanoparticles acting as a dispersing and/or capping agent. Moreover, this work provides a new method for the synthesis of silver nanoparticles that is simple, easy to perform, pollutant free and inexpensive.     

离子液体--一种新型的绿色化学反应介质

离子液体是室温下表现为液体的离子化合物,近年来被开发成为一种新型绿色化学反应介质。本文简要介绍了离子液体的特点、发展历史、制备、应用等方面,并对其应用前景做了展望。我们阳信,在不久的将来,离子液体会成为绿色化学工程技术中的一枝新秀。     

Nickel nanoparticle-catalyzed facile and efficient one-pot synthesis of polyhydroquinoline derivatives via Hantzsch condensation under solvent-free conditions

Polyhydroquinoline derivatives have been prepared efficiently in a one-pot synthesis via Hantzsch condensation using nanosized Nickel (Ni) as a heterogeneous catalyst. The present method does not involve any hazardous organic solvents or catalysts. The smaller size of Ni (80 ± 0.5 nm) having a higher surface to volume ratio has promising features for the reaction response such as the shortest reaction time, excellent product yields, simple work-up procedure, and purification of products by non-chromatographic methods.     

Profiling fatty acids in vegetable oils by reactive pyrolysis-gas chromatography with dimethyl carbonate and titanium silicate

A novel methodology in on-line pyrolysis-gas chromatography (Py-GC) for the fast analysis of fatty acids in vegetable oils with minimal sample treatment and the use of non-toxic reagents is described. Pyrolysis at 500 degrees C for 10 s of sub-microgram quantity of vegetable oil dissolved in dimethyl carbonate (DMC) and in the presence of nanopowder titanium silicon oxide resulted in the production of fatty acid methyl esters (FAMEs) as unique products. Pyrolysis performed by means of a resistively heated filament pyrolyser interfaced to a GC-MS apparatus enabled the direct analysis of evolved FAMEs. The DMC/Py-GC-MS analysis was tested on soybean, coconut, linseed, walnut and olive oil and the results compared to the classical BF(3)-methanol as reference methodology. The DMC method exhibited a lower precision and was biased towards lower levels of polyunsaturated fatty acids (PUFA) in comparison to the BF(3)-methanol method, but was more advantageous in terms of reduced sample treatment, waste generation and risk factors of employed chemicals.