A stationary flow of fresh and salt groundwater in a coastal aquifer with nonlinear darcy' law

We study an homogeneous aquifer where fresh and salt water are separated by an interface T. The flow is governed by a nonlinear Darcy' law. Using suitable approximated problems, we prove existence of a solution and establish some properties.     

一种新型噻唑盐的微波辅助合成及对安息香缩合的催化作用

以4-甲基-5-羟乙基噻唑和对氰基氯化苄为原料微波合成一种新型噻唑盐,3-(对氰基苄基)-4-甲基-5-(2-羟乙基)噻唑氯化物,再用此噻唑盐替代VB1作为安息香缩合反应的催化剂,检验其催化性能,发现催化苯甲醛得苯偶姻收率为74.5％、催化糠醛得糠偶姻收率为76.1％,此噻唑盐不仅具有天然VB1的无毒性,且可回收利用;考察了物质的量投料比、反应时间、反应温度及微波反应器功率对此噻唑盐收率的影响;并用HPLC测定产物的纯度,通过熔点、元素分析、IR及LC-MS对噻唑盐性质和及苯偶姻结构进行了表征.     

Novel nano molten salt tetra‐2,3‐pyridiniumporphyrazinato‐oxo‐vanadium tricyanomethanide as a vanadium surface‐free phthalocyanine catalyst: Application to Strecker synthesis of α‐aminonitrile derivatives

Efficient and recyclable novel nano tetra‐2,3‐pyridiniumporphyrazinato‐oxo‐vanadium tricyanomethanide, {[VO(TPPA)][C(CN)₃]₄}, as a vanadium surface‐free phthalocyanine‐based molten salt catalyst was successfully designed, produced and used for the Strecker synthesis of α‐aminonitrile derivatives through a one‐pot three‐component reaction between aromatic aldehydes, trimethylsilyl cyanide and aniline derivatives under neat conditions at 50 °C. This catalyst was well characterized using Fourier transform infrared, UV–visible, X‐ray photoelectron and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction, scanning and high‐resolution transmission electron microscopies, inductively coupled plasma mass spectrometry and thermogravimetric analysis. The catalyst can be simply recovered and reused several times without significant loss of catalytic activity.     

Effects of salicylate 2-hydroxybenzoate on ionic liquid N-hexadecane-N-methylpyrrolidinium bromide

Surface tension, steady-shear viscosity, and antibacterial activity were investigated when salicylate 2-hydroxybenzoate (NaSal) was added to the micellar solution of N-hexadecane-N-methylpyrrolidinium bromide (C₁₆MPB). It was found that for the mixed system, two flat portions appeared on the surface tension curve with the existence of NaSal in the low-concentration range. The equilibrium contact angle of droplets was decreased with the increase of NaSal concentration. In addition, the steady-shear viscosity abruptly increased with the increase of the concentration of mixture, even if the concentration of NaSal is low. However, this high-viscosity solution exhibited temperature-sensitive property, and white precipitate formation below 18°C. Moreover, the bactericidal capability of C₁₆MPB was affected severely by the mixture of high concentration. All of these features could be attributed to the special interactions between C₁₆MPB and NaSal molecules, among which intramolecular hydrogen bonding of NaSal plays a key role, which have been primely demonstrated by the package of Gaussian09 in this work.     

Unusual Salt‐Induced Color Modulation through Aggregation‐Induced Emission Switching of a Bis‐cationic Phenylenedivinylene‐Based π Hydrogelator

The synthesis, hydrogelation, and aggregation‐induced emission switching of the phenylenedivinylene bis‐N‐octyl pyridinium salt is described. Hydrogelation occurs as a consequence of π‐stacking, van der Waals, and electrostatic interactions that lead to a high gel melting temperature and significant mechanical properties at a very low weight percentage of the gelator. A morphology transition from fiber‐to‐coil‐to‐tube was observed depending on the concentration of the gelator. Variation in the added salt type, salt concentrations, or temperature profoundly influenced the order of aggregation of the gelator molecules in aqueous solution. Formation of a novel chromophore assembly in this way leads to an aggregation‐induced switch of the emission colors. The emission color switches from sky blue to white to orange depending upon the extent of aggregation through mere addition of external inorganic salts. Remarkably, the salt effect on the assembly of such cationic phenylenedivinylenes in water follow the behavior predicted from the well‐known Hofmeister effects. Mechanistic insights for these aggregation processes were obtained through the counterion exchange studies. The aggregation‐induced emission switching that leads to a room‐temperature white‐light emission from a single chromophore in a single solvent (water) is highly promising for optoelectronic applications.     

Catalytic oxidative conversion of aldehydes into nitriles using NH3·H2O/FeCl2/NaI/Na2S2O8: A practical approach to febuxostat

A novel approach to convert aldehydes into nitriles using NH₃·H₂O/FeCl₂/NaI/Na₂S₂O₈ has been developed. Both alkyl and aryl nitriles were obtained in good to excellent yields. Electron-withdrawing and electron-donating groups, such as fluoro, chloro, bromo, nitro, ester, cyano, trifluoromethyl and alkoxy were tolerated. Notably, febuxostat and its intermediate, ethyl 2-[3-cyano-4-(2-methylpropoxy)phenyl]-4-methyl-5-thiazolecarboxylate, were obtained in excellent yields.     

A convenient cyclopropanation process of oxindoles via bromoethylsulfonium salt

A practical convenient conversion of oxindoles into the corresponding spirocyclopropyl oxindoles is achieved efficiently using bromoethylsulfonium salt, which is easily prepared on a large scale and is stable crystalline. This reaction of bromoethylsulfonium salt with different substituted unprotected oxindoles proceeded under mild condition and provided moderate yields.     

Mechanisms of ion transport in lithium salt-doped polymeric ionic liquid electrolytes at higher salt concentrations

We used atomistic simulations to study the mechanisms of ion transport in salt-doped polymeric ionic liquid systems at higher salt concentrations. Consistent with the experimental observations, our simulations indicate that at higher salt concentrations, the anion mobilities become lower than that of the lithium cations. Further, the anion mobilities become relatively insensitive to the salt concentration, while the mobilities of lithium increase with increasing salt concentration. We rationalize the results for the anion mobilities by considering the fractions of anions which are exclusively coordinated with the polycations (Type1); co-coordinated with cations and lithium (Type2); and those exclusively coordinated with lithium (Type3). By considering the coordination characteristics of the different types of anions and their hopping motions, we demonstrate that the net anion mobilities results from a compensation effect of the salt concentration dependence of the mobilities of the different anions. With respect to the mobilities of the lithium ions, we demonstrate that the latter moves primarily by a structural diffusion mechanism involving refreshing of the solvation shell during hopping. Further, for the majority of the lithium ions, the solvation shell is shown to be comprised of co-coordinated Type2 anions, and that the number of polycations and the unique polymer chains involved in such coordination decreases with increasing salt concentration. Such changes are shown to weaken the solvation shell around the lithium, thereby facilitating faster ion motion. Together, our results suggest that systems in which the anion which exhibits a stronger coordination to the polycation in comparison to that of the lithium can facilitate higher transference numbers without a concomitant reduction in the mechanical strength.     

Synthesis and Characterization of a Helicene‐Based Imidazolium Salt and Its Application in Organic Molecular Electronics

Herein we demonstrate the synthesis of a helicene‐based imidazolium salt. The salt was prepared by starting from racemic 2‐methyl[6]helicene, which undergoes radical bromination to yield 2‐(bromomethyl)[6]helicene. Subsequent treatment with 1‐butylimidazole leads to the corresponding salt 1‐butyl‐3‐(2‐methyl[6]helicenyl)‐imidazolium bromide. The prepared salt was subsequently characterized by using NMR spectroscopy and X‐ray analysis, various optical spectrometric techniques, and computational chemistry tools. Finally, the imidazolium salt was immobilized onto a SiO₂ substrate as a crystalline or amorphous deposit. The deposited layers were used for the development of organic molecular semiconductor devices and the construction of a fully reversible humidity sensor.