Solvophobically Driven Complexation of Adamantyl Mannoside with β-Cyclodextrin in Water and Structured Organic Solvents

The effects of solvent and temperature on the complexation of adamantyl mannoside with β-cyclodextrin and 6-O-monotosyl-6-deoxy-β-cyclodextrin were explored experimentally and by means of molecular dynamics simulations. Efficient binding was observed only in hydrogen-bonded solvents, which indicated solvophobically driven complexation. The stability of the inclusion complex was considerably higher in aqueous media. A pronounced temperature dependence of Δ_rH^○ and Δ_rS^○, resulting in perfect enthalpy–entropy compensation, was observed in water. The complexation thermodynamics was in line with classical rationale for the hydrophobic effect at lower temperatures and the nonclassical explanation at higher temperatures. This finding linked cyclodextrin complexation thermodynamics with insights regarding the effect of temperature on the hydration water structure. The complexation enthalpies and entropies were weakly dependent on temperature in organic media. The signs of Δ_rH^○ and Δ_rS^○ were in accordance with the nonclassical hydrophobic (solvophobic) effect. The structures of the optimized product corresponded to those deduced spectroscopically, and the calculated and experimentally obtained values of Δ_rG^○ were in very good agreement. This investigation clearly demonstrated that solvophobically driven formation of cyclodextrin complexes could be anticipated in structured solvents in general. However, unlike in water, adamantane and the host cavity behaved solely as structure breakers in the organic media explored so far.     

pH-Dependent Slipping and Exfoliation of Layered Covalent Organic Framework

Layered/two-dimensional covalent organic frameworks (2D COF) are crystalline porous materials composed of light elements linked by strong covalent bonds. Interlayer force is one of the main factors directing the formation of a stacked layer structure, which plays a vital role in the stability, crystallinity, and porosity of layered COFs. The as-developed new way to modulate the interlayer force of imine-linked 2D TAPB-PDA-COF (TAPB = 1,3,5-tris(4-aminophenyl)benzene, PDA = terephthaldehyde) by only adjusting the pH of the solution. At alkaline and neutral pH, the pore size of the COF decreases from 34 Å due to the turbostratic effect. Under highly acidic conditions (pH 1), TAPB-PDA-COF shows a faster and stronger turbostratic effect, thus causing the 2D structure to exfoliate. This yields bulk quantities of an exfoliated few/single-layer 2D COF, which was well dispersed and displayed a clear Tyndall effect (TE). Furthermore, nanopipette-based electrochemical testing also confirms the slipping of layers with increase towards acidic pH. A model of pH-dependent layer slipping of TAPB-PDA-COF was proposed. This controllable pH-dependent change in the layer structure may open a new door for potential applications in controlled gas adsorption/desorption and drug loading/releasing.     

Controlling the Length of Cooperative Supramolecular Polymers with Chain Cappers

The design and the characterization of supramolecular additives to control the chain length of benzene-1,3,5-tricarboxamide (BTA) cooperative supramolecular polymers under thermodynamic equilibrium is unraveled. These additives act as chain cappers of supramolecular polymers and feature one face as reactive as the BTA discotic to interact strongly with the polymer end, whereas the other face is nonreactive and therefore impedes further polymerization. Such a design requires fine tuning of the conformational preorganization of the amides and the steric hindrance of the motif. The chain cappers studied are monotopic derivatives of BTA, modified by partial N-methylation of the amides or by positioning of a bulky cyclotriveratrylene cage on one face of the BTA unit. This study not only clarifies the interplay between structural variations and supramolecular interactions, but it also highlights the necessity to combine orthogonal characterization methods, spectroscopy and light scattering, to elucidate the structures and compositions of supramolecular systems.     

meso-Diazacorrphycenes: Neighboring Effect of Two Nitrogen Atoms

The neighboring effect of two adjacent heteroatoms influences the structures and properties of heterocyclic compounds. Herein, we demonstrated that the introduction of two adjacent sp² nitrogen atoms into a porphyrinic skeleton significantly enhanced its Brønsted basicity due to the repulsive interaction between two lone pairs on the nitrogen atoms. Palladium- and copper-templated ring closure of dichlorobis(dipyrrin) with hydrazine hydrate provided meso-diazacorrphycene palladium and copper complexes in good yields. The structural, magnetic, and electrochemical properties of the diazacorrphycene complexes were investigated experimentally and theoretically to elucidate the effect of the meso-nitrogen atoms.     

Magnetic field as a means to identify initiating reaction in oxidation of organic substances with molecular oxygen

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Two-Stage Seebeck Effect in Charged Colloidal Suspensions

We discuss the peculiarities of the Seebeck effect in stabilized electrolytes containing the colloidal particles. Its unusual feature is the two stage character, with the linear increase of differential thermopower as the function of colloidal particles concentration n⊙ during the first stage (“initial state”) and dramatic drop of it at small n⊙ during the second one (“steady state”). We show that the properties of the initial state are governed by the thermo-diffusion flows of the mobile ions of the stabilizing electrolyte medium itself and how the colloidal particles participate in the formation of the electric field in the bulk of the suspension. In its turn, we attribute the specifics of the steady state thermoelectric effect the massive colloidal particles undergoing slow thermal diffusion and the break down of their electro-neutrality in the vicinity of electrodes.     

利用静电场中光电离效率谱精确确定1,3-二乙氧基苯分子的电离能

电离能是原子和分子的重要的特性参数,在光物理和光化学过程中起着重要作用,精确电离能对相关研究具有重要意义.电离能是调试零动能光谱信号的重要参考数据,在判断异构物数量和分子构型方面也起着关键作用.1,3-二乙氧基苯是一种重要的苯的衍生物,实验证实在超声分子束中包含两种旋转异构物Ⅰ(downup)和Ⅲ(down-down).它们的精确电离能还未见文献报道.本文采用直线式飞行时间质谱仪测量了静电场中1,3-二乙氧基苯光电离效率曲线,通过不同电场强度下测量的电离能(Stark效应)对场强的平方根线性拟合给出了两种异构物Ⅰ和Ⅲ精确的电离能分别为(62419±2)cm^–1和(63378±2)cm^–1.相对于通常的脉冲电场加速机制和零动能光谱测量的电离能,精确度大约分别由(±10)cm^–1和(±5)cm^–1提高到(±2)cm^–1.分析和讨论了不同方法测量的物理机制和优缺点.     

Synthesis of nanoscale zero‐valent iron modified graphene oxide nanosheets and its application for removing tetracycline antibiotic: Response surface methodology

Nowadays, pharmaceutical antibiotics are known as a serious class of pollutants. Therefore, it is important to develop effective methods for removing these pollutants from aqueous media. Different methods were applied for this purpose, and among these methods, chemical reduction by a cheap and eco‐friendly nanocatalyst is the most efficient and simplest method. In this research, based on graphene oxide supported by zero‐valent iron in mono‐, bi‐, and tri‐metallic systems, various nanocomposites were synthesized and used to degrade tetracycline as a model antibiotic from aqueous media. An investigation was carried out on the synergic effect among graphene oxide and the nano zero‐valent iron‐based tri‐metallic system as well as removal efficiencies. It was found that higher degradation efficiency is yielded by graphene oxide supported by Fe/Cu/Ag tri‐metallic system. The maximum synergic effect occurs at an acidic medium. The Brunauer–Emmett–Teller, Fourier transform spectroscopy, scanning electron microscopy‐energy dispersive X‐ray analysis, transmission electron microscopy, and X‐ray diffraction analysis were used to characterize the synthesized nanocomposites, which has successfully proved the loading of nanoscale Fe/Cu/Ag tri‐metallic on a graphene oxide support. The central composite design was used to model and optimize all involved variables affecting antibiotic removal efficiency. The consequences illustrated the optimum condition regarding the removal of 50 ppm of tetracycline, for the nanocomposites dose of 3.0 mg ml^?1, the contact time of 30 min, and pH of 2, was achieved using the simplex non‐linear optimization method. Moreover, antibiotic adsorption kinetic models were also investigated. Finally, the tetracycline removal from aqueous media at different concentrations, 25, 50, and 75 ppm, was successful by applying the proposed nanocomposite, and the results showed tetracycline removal efficiencies of above 70%.     

Spreading of Oil Droplets Containing Surfactants and Pesticides on Water Surface Based on the Marangoni Effect

Oil droplets containing surfactants and pesticides are expected to spread on a water surface, under the Marangoni effect, depending on the surfactant. Pesticides are transported into water through this phenomenon. A high-speed video camera was used to measure the movement of Marangoni ridges. Gas chromatography with an electron capture detector was used to analyze the concentration of the pesticide in water at different times. Oil droplets containing the surfactant and pesticide spread quickly on the water surface by Marangoni flow, forming an oil film and promoting emulsification of the oil–water interface, which enabled even transport of the pesticide into water, where it was then absorbed by weeds. Surfactants can decrease the surface tension of the water subphase after deposition, thereby enhancing the Marangoni effect in pesticide-containing oil droplets. The time and labor required for applying pesticides in rice fields can be greatly reduced by using the Marangoni effect to transport pesticides to the target.     

Bi4Ge3O12:Er3+晶体中的高阶混合效应对EPR g因子的影响

通过对角化364×364完全能量矩阵的理论方法,对掺杂在Bi₄Ge₃O₁₂晶体中的Er³⁺的Stark能级和EPR参数进行了研究,同时,定量分析了高阶晶体场混合效应和J-J混合效应对EPR g因子的影响。研究结果表明:对Er³⁺来说,最主要的J-J混合效应来源于多重态谱项²K_15/2,其对EPR g因子的贡献约占2.5%,而最主要的高阶晶体场混合效应来源于第一激发多重态⁴I_13/2和基态多重态⁴I_15/2之间的晶体场混合,其对各向异性g因子中g_⊥的贡献大致是g_//的两倍(即g_⊥约占 0.21%,g_//约占0.092%),其他更高阶的晶体场混合和J-J混合效应可以忽略不计。因此,对于Er³⁺掺杂的络合物系统来说,只考虑基态多重态⁴I_15/2对EPR g因子的贡献应该是一个很好的近似。