Combination of DQ and ZQ Coherences for Sensitive Through‐Bond NMR Correlation Experiments in Biosolids under Ultra‐Fast MAS

A double‐zero quantum (DZQ)‐refocused INADEQUATE experiment is introduced for J‐based NMR correlations under ultra‐fast (60 kHz) magic angle spinning (MAS). The experiment records two spectra in the same dataset, a double quantum–single quantum (DQ‐SQ) and zero quantum–single quantum (ZQ‐SQ) spectrum, whereby the corresponding signals appear at different chemical shifts in ω₁. Furthermore, the spin‐state selective excitation (S³E) J‐decoupling block is incorporated in place of the second refocusing echo of the INADEQUATE scheme, providing an additional gain in sensitivity and resolution. The two sub‐spectra acquired in this way can be treated separately by a shearing transformation, producing two diagonal‐free single quantum (SQ‐SQ)‐type spectra, which are subsequently recombined to give an additional sensitivity enhancement, thus offering an improvement greater than a factor of two as compared to the original refocused INADEQUATE experiment. The combined DZQ scheme retains transverse magnetization on the initially polarized (I) spin, which typically exhibits a longer transverse dephasing time (T₂′) than its through‐bond neighbour (S). By doing so, less magnetization is lost during the refocusing periods in the sequence to give even further gains in sensitivity for the J correlations. The experiment is demonstrated for the correlation between the carbonyl (CO) and alpha (CA) carbons in a microcrystalline sample of fully protonated, [¹⁵N,¹³C]‐labelled Cu^II, Zn^II superoxide dismutase, and its efficiency is discussed with respect to other J‐based schemes.     

Improved Multianalyte Determination of the Intense Sweeteners Aspartame and Acesulfame‐K with a Solid Sensing Zone Implemented in an FIA Scheme

Abstract

A multianalyte flow‐through sensor is proposed for the simultaneous determination of aspartame (AS) and acesulfame‐K (AK) in tabletop sweeteners. The procedure is based on the transient retention of AK in the ion exchanger Sephadex DEAE A‐25 placed in the flow‐through cell of a monochannel flow injection analysis (FIA) set‐up using pH 2.70 ortophosphoric acid/sodium dihydrogen phosphate buffer 0.06 M as carrier. In these conditions AS is very weakly retained, which makes it possible to measure the intrinsic ultraviolet (UV) absorbance of first AS and then AK after desorption by the carrier itself. The applicable concentration range, the detection limit, and the relative standard deviation were the following: for AS, from 10 to 100 µg mL^?1; 5.65 µg mL^?1; 3.4% (at 50 µg mL^?1); and for AK, between 40 and 100 µg mL^?1; 11.9 µg mL^?1 and 1.61% (at 50 µg mL^?1). The method was applied and validated satisfactorily for the determination of AS and AK blends in tabletop sweeteners. The results were compared against an HPLC reference method.     

Fabrication of free‐standing TiO2 nanotube membranes with through‐hole morphology

In the present work, we show a simple and robust ex‐situ method to fabricate free‐standing membranes consisting of vertically oriented, both‐side‐open TiO₂ nanotube arrays. In this method, self‐organized TiO₂ nanotube membranes with different thickness ranging from seven to tens of micrometers could be easily separated from the metallic Ti substrate by applying a reverse‐bias voltage at the end of anodization. The stress developing at the TiO₂ nanotubes/Ti interface during H₂ gas generation facilitates the separation of the TiO₂ membranes. This procedure leads to an intact, free‐standing TiO₂ nanotube membrane with closed bottoms. After exposing the TiO₂ membrane to HF vapor, the barrier layer at the closed bottoms was etched away, and then a free‐standing TiO₂ membrane with through‐hole morphology was obtained. The bottom‐opening process is a slow barrier layer thinning process. Meanwhile, it is found that the mean diameter of tube bottoms monotonously decreases with the increasing the etching time.     

Molecular Pair Analysis: C?H⋅⋅⋅F Interactions in the Crystal Structure of Fluorobenzene? And Related Matters

The crystal structure of fluorobenzene is compared with isomorphous crystal structures of molecules of roughly similar shape. The lowest-energy fluorobenzene dimers are identified by theoretical calculations. Molecular pair analysis of the crystal structure of fluorobenzene and of an isomorphous virtual low-energy polymorph of benzene suggests that the important intermolecular interactions in the two structures are closely similar. In particular, the intermolecular C-H...F interactions in the fluorobenzene crystal have approximately the same structure-directing ability and influence on the intermolecular energy as the corresponding C-H...H interactions in benzene. Molecular pair analysis of the isomorphous crystal structures of benzonitrile, alloxan, and cyclopentene-1,2,3-trione indicates that essentially the same crystal structure can be adopted with quite different patterns of pair energies and atom-atom interactions. The question as to whether the packing radius of organic fluorine is larger or smaller than that of hydrogen, is addressed, but not answered.     

学术探讨要凭证据、讲理性，坚持实事求是态度——就“郁达夫死因”的争论质疑铃木正夫先生

为了查找郁达夫的真正死因,日本学者铃木正夫多年来调查采访、并引用大量资料证明自己的观点,这值得肯定;同时,其相关结论并非定论、仍然需要继续深入考证.我国学者罗以民坚持科学实证、独立思考、勇于献疑的精神,令人敬佩.这本来是一个用史实说话的学术探讨过程,而不是一场"口诛笔伐"的意气纠纷.然而,日本记者对铃木正夫的袒护和对中国学者的非理性批评,却造成了不良影响.为此,争论的双方都应当以学者直笔信史的严谨态度,心平气和地摆事实、讲道理,在学术对话中实现互补共进、深化认识,给读者提供一个令人信服的解答.     

Study and modeling of the transport mechanism in a semi insulating GaAs Schottky diode

The current through a metal–semiconductor junction is mainly due to the majority carriers. Three distinctly different mechanisms exist in a Schottky diode: diffusion of carriers from the semiconductor into the metal, thermionic emission–diffusion (TED) of carriers across the Schottky barrier and quantum–mechanical tunneling through the barrier. The insulating layer converts the MS device in an MIS device and has a strong influence on its current–voltage (I–V) and the parameters of a Schottky barrier from 3.7 to 15 eV. There are several possible reasons for the error that causes a deviation of the ideal behavior of Schottky diodes with and without an interfacial insulator layer. These include the particular distribution of interface states, the series resistance, bias voltage and temperature. The GaAs and its large concentration values of trap centers will participate in an increase of the process of thermionic electrons and holes, which will in turn the IV characteristic of the diode, and an overflow maximum value [NT = 3 × 10²⁰] is obtained. The I–V characteristics of Schottky diodes are in the hypothesis of a parabolic summit.     

滴南凸起-阜北斜坡中上侏罗统-下白垩统油气成藏条件分析

作为准噶尔盆地腹部较早开发的地区之一,近年来在滴南凸起下白垩统及白家海凸起-阜北斜坡区的中上侏罗统地层内相继发现了高产油气藏,揭示了该区中上侏罗统-下白垩统具有良好的生、储、盖成藏条件,丰富的圈闭类型和有效的疏导体系。在成藏条件上,东道海子凹陷、阜康凹陷的石炭统、二叠系平地泉组以及侏罗系的八道湾组、三工河组、西山窑组等多套烃源岩为侏罗-白垩系成藏提供了充足的油气,河流、三角洲沉积体系控制下的中上侏罗统头屯河组、齐古组以及下白垩统的清水河组、呼图壁河组分布有多套有效的储盖组合,长期继承性的断裂系统及砂体和不整合面作为油气的疏导体系,在成藏条件分析的基础上总结了滴南凸起-阜北斜坡地区3种油气成藏模式。     

江汉盆地白垩系沉积相与沉积演化

在对江汉盆地露头剖面野外实测、钻井及分析化验资料综合研究的基础上,运用层序地层学、沉积学和测井地质学原理,识别了白垩系层序及沉积相类型、沉积特征。研究表明, 受燕山期幕式构造运动的影响,白垩系可划分为两个构造层序,主要发育冲积扇、辫状河、辫状河三角洲和氧化型湖泊四种主要沉积相类型;早白垩世,由于拉张断陷强度较弱,仅在盆地边缘断裂前缘的局部地区发育一套粒度较粗的冲积扇-辫状河砂砾岩沉积;至晚白垩世,在区域引张力的作用下盆地整体拉伸断陷,从盆缘往盆内方向依次发育冲积扇—辫状河—三角洲—氧化型湖泊沉积,构成一个自下而上粒度由粗变细的沉积序列。