The Many Measures of Molecular Dimensions

In contrast to the high precision with which masses of atoms and molecules can be specified, their external dimensions remain intrinsically fuzzy. Attention is directed to the difference between measurements of interatomic separations within molecules, that in many instances are cited with error bars of +/– 0.002 Å, and the available approximate magnitudes of over-all sizes, needed for estimating packing densities (in solids or liquids). The following account, is a critical examination of the underlying concepts and of the diversity of data in the literature, regarding internal dimensions (bond lengths), overall extensions, cross-sectional areas, and volumes of molecules that may be derived from a variety of experiments. Historical markers of the evolution of the underlying theories and experiments are included.     

Two-dimensional double-quantum 2H NMR spectroscopy in the solid state under OMAS conditions: correlating 2H chemical shifts with quasistatic line shapes.

Solid-state 2H NMR spectroscopy is a well-established and versatile method to study molecular orientation and dynamics in selectively deuterated samples. Herein, we introduce a 2D 2H double-quantum (DQ) NMR experiment performed under fast magic-angle spinning with a slight offset of the magic angle (OMAS). The experiment combines 2H chemical-shift resolution with DQ-filtered quasistatic 2H line shapes. In this way, it is possible to separate 2H resonances and to independently determine 2H quadrupole couplings at multiple sites. While 2H chemical shifts are resolved in the 2H DQ dimension, the quadrupole parameters can be obtained from characteristic line shapes which are reintroduced in the second dimension by the magic-angle offset. The 2D 2H DQ OMAS experiment is demonstrated on L-histidine which was deuterated at multiple sites by recrystallisation from D2O.     

Polymeric Structure and Solid ~(31)P, ~(113)Cd NMR Spectra of Cadmium(II) Dialkyldithiophosphate (Alkyl = n-butyl and i-butyl)

Owing to the particular affinity toward metal ion and changeable dentation, dialkyldithiophosphates are commonly used ligands in preparation of the transition metal complexes with variable structures1. For instances relevant to this work, the IIB metal complexes defined crystallographically so far have provided the examples as follows2-12 (Scheme 1). Scheme 1 The frameworks of IIB metal complexes of dialkyldithiophosphate MMMMMMMMMM a b c d …     

Dense Sphene-type Solid Electrolyte Through Rapid Sintering for Solid-state Lithium Metal Battery

The sphene-type solid electrolyte with high ionic conductivity has been designed for solid-state lithium metal battery. However, the practical applications of solid electrolytes are still suffered by the low relative density and long sintering time of tens of hours with large energy consumption. Here, we introduced the spark plasma sintering technology for fabricating the sphene-type Li_1.125Ta_0.875Zr_0.125SiO₅ solid electrolyte. The dense electrolyte pellet with high relative density of ca. 97.4% and ionic conductivity of ca. 1.44×10^-5 S/cm at 30℃ can be obtained by spark plasma sintering process within the extremely short time of only ca. 0.1 h. Also the solid electrolyte provides stable electrochemical window of ca. 6.0 V(vs. Li⁺/Li) and high electrochemical interface stability toward Li metal anode. With the enhanced interfacial contacts between electrodes and electrolyte pellet by the in-situ formed polymer electrolyte, the solid-state lithium metal battery with LiFePO₄ cathode can deliver the initial discharge capacity of ca. 154 mA·h/g at 0.1 C and the reversible capacity of ca. 132 mA·h/g after 70 cycles with high Coulombic efficiency of 99.5% at 55℃. Therefore, this study demonstrates a rapid and energy efficient sintering strategy for fabricating the solid electrolyte with dense structure and high ionic conductivity that can be practically applied in solid-state lithium metal batteries with high energy densities and safeties.     

制备纳米氧化锌的新方法

以草酸和醋酸锌为原料，用室温固相化学反应首先制备前驱物二水合草酸锌，后者在微波场辐射分解得到产物纳米氧化锌。用XRD，TEM和IR等技术对产物的组成，大小及形貌进行了表征。结果表明：产物纳米氧化锌为粒度分布均匀的球形六角晶系结构，平均粒径约为8nm。     

Molecularly-imprinted polypyrrole-modified stainless steel frits for selective solid phase preconcentration of ochratoxin A

A molecularly-imprinted polymer (MIP) was prepared by electropolymerization of pyrrole (Py) onto a stainless steel frit, using ochratoxin A (OTA) as the template, in order to make a micro solid phase preconcentration (SPP) device. The OTA template was removed with 1% triethylamine (TEA) in methanol. Compared to non-imprinted polypyrrole (PPy), the molecularly-imprinted polypyrrole (MIPPy) enhanced the selective binding of OTA. The percentage recovery improved from 0 to 40% when the OTA sample solution was acidified with 1 M HCl (1% by volume). At a flow rate of 0.2 mL/min, maximum OTA binding was reached in 6 min after a total loading of 3.2 ng OTA. Final elution of the OTA was analyzed by high performance liquid chromatography (HPLC) with fluorescence detection, using 20:80 v/v acetonitrile–ammonia buffer (NH₄Cl/NH₃, 20 mM, pH 9.2) as the mobile phase. The MIPPy-SPP-HPLC results clearly demonstrated that the MIPPy-SPP device afforded selective preconcentration of OTA from red wine samples, at OTA concentration levels as low as 0.05 ppb, prior to HPLC analysis.     

Predicting the shape and structure of face-centered cubic gold nanocrystals smaller than 3 nm.

Although a number of computational studies have examined the relative stability of icosahedral and decahedral gold clusters from 1 to 3 nm in size, few studies have focussed on the variety of face-centered cubic (fcc) nanoparticles in this size regime. In most cases small fcc gold particles are assumed to adopt the truncated octahedral shape, but in light of the fact that the shape and structure of gold nanoparticles is known to vary, the relative stability of fcc polyhedra may change with size. Presented here are results of first-principles calculations investigating the preferred shape of gold particles less than 3 nm in size. Our results indicate that the equilibrium shape of fcc gold nanoparticles less than 1 nm is the cuboctahedron, but this shape rapidly becomes energetically unstable with respect to the truncated octahedron, octahedron and truncated cube shapes as the size increases.     

多嵌段聚醚氨酯脲为基质的新型高分子固态离子导体

本文合成了一系列聚乙二醇型多嵌段聚醚氨酯脲，而且用这类聚醚氨酯甩与高氯酸锂制得了一种新型的高分子固态离子导体复合物。在室温和50℃之间，其电导率比聚环氧乙烷为基质的固体电解质的高一到二个数量级，它还具有优良的综合性能。因此，对于室温薄膜蓄电池来说，这种新型的固体电解质是一类良好的候选材料。     

Sm2O3掺杂CeO2纳米粉体的烧结动力学

对Sm2O3掺杂CeO2纳米粉体的烧结性能进行了研究, 得出等速烧结过程中试样的线收缩率、密度、气孔率随烧结温度的变化规律, 它们随烧结温度的变化均呈"S"型曲线关系, 利用非线性回归了等速烧结过程动力学方程. 结果表明, Sm2O3掺杂CeO2纳米粉体的烧结过程分为3个阶段, 当烧结温度低于1000 ℃时, 线收缩率与密度变化较小, 处于烧结的初期; 在1000～1400 ℃时, 随着烧结温度的升高, 线收缩率与体积密度急剧增大, 材料开始烧结并致密化; 当烧结温度高于1400 ℃时, 线收缩率与体积密度趋于一恒定值, 材料已经致密化. 由归一化速率方程可知, 在T=1225 ℃时, 材料的烧结致密化速率最大.