High‐Valent Technetium Fluorides. Does TcF7 Exist?

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

Does the Surface Matter? Hydrogen‐Bonded Chain Formation of an Oxalic Amide Derivative in a Two‐ and Three‐Dimensional Environment

We report on a multi‐technique investigation of the supramolecular organisation of N,N‐diphenyl oxalic amide under differently dimensioned environments, namely three‐dimensional (3D) in the bulk crystal, and in two dimensions on the Ag(111) surface as well as on the reconstructed Au(111) surface. With the help of X‐ray structure analysis and scanning tunneling microscopy (STM) we find that the molecules organize in hydrogen‐bonded chains with the bonding motif qualitatively changed by the surface confinement. In two dimensions, the chains exhibit enantiomorphic order even though they consist of a racemic mixture of chiral entities. By a combination of the STM data with near‐edge X‐ray absorption fine‐structure spectroscopy, we show that the conformation of the molecule adapts such that the local registry of the functional group with the substrate is optimized while avoiding steric hindrance of the phenyl groups. In the low coverage case, the length of the chains is limited by the Au(111) reconstruction lines restricting the molecules into fcc stacked areas. A kinetic Monte Carlo simulated annealing is used to explain the selective assembly in the fcc stacked regions.     

Cu?Cu2O?TiO2 Nanojunction Systems with an Unusual Electron–Hole Transportation Pathway and Enhanced Photocatalytic Properties

Multicomponent Cu? Cu₂O? TiO₂ nanojunction systems were successfully synthesized by a mild chemical process, and their structure and composition were thoroughly analyzed by X‐ray diffraction, transmission electron microscopy, field‐emission scanning electron microscopy, and X‐ray photoelectron spectroscopy. The as‐prepared Cu? Cu₂O? TiO₂ (3 and 9 h) nanojunctions demonstrated higher photocatalytic activities under UV/Vis light irradiation in the process of the degradation of organic compounds than those of the Cu? Cu₂O, Cu? TiO₂, and Cu₂O? TiO₂ starting materials. Moreover, time‐resolved photoluminescence spectra demonstrated that the quenching times of electrons and holes in Cu? Cu₂O? TiO₂ (3 h) is higher than that of Cu? Cu₂O? TiO₂ (9 h); this leads to a better photocatalytic performance of Cu? Cu₂O? TiO₂ (3 h). The improvement in photodegradation activity and electron–hole separation of Cu? Cu₂O? TiO₂ (3 h) can be ascribed to the rational coupling of components and dimensional control. Meanwhile, an unusual electron–hole transmission pathway for photocatalytic reactions over Cu? Cu₂O? TiO₂ nanojunctions was also identified.     

Ammonia‐Annealed TiO2 as a Negative Electrode Material in Li‐Ion Batteries: N Doping or Oxygen Deficiency?

Improving the chemical diffusion of Li ions in anatase TiO₂ is essential to enhance its rate capability as a negative electrode for Li‐ion batteries. Ammonia annealing has been used to improve the rate capability of Li₄Ti₅O₁₂. Similarly, ammonia annealing improves the Li‐ion storage performance of anatase TiO₂ in terms of the stability upon cycling and the C‐rate capability. In order to distinguish whether N doping or oxygen deficiencies, both introduced upon ammonia annealing, are more relevant for the observed improvement, a systematic electrochemical study was performed. The results suggest that the creation of oxygen vacancies upon ammonia annealing is the main reason for the improvement of the stability and C‐rate capability.     

Thermal Activation of N?H Bonds by Transition‐metal Oxide Cations: Does a Hierarchy Exist in the First Row?

The thermal reactions of first-row transition-metal oxide cations [MO](+) (M=Sc-Ni, Zn) with ammonia have been studied by gas-phase experiments and computational methods. The activation of N-H bonds is brought about by the monoxides of the middle and late 3d metals Mn-Ni and Zn. The two primary reaction channels correspond to dehydration, which leads to [M(NH)](+), and hydrogen-atom abstraction to form [M(OH)](+). Oxygen-atom transfer from [MO](+) to NH(3) to produce neutral or ionized hydroxylamine was observed as a minor channel for some of the late transition-metal oxides. The computational analysis of these reactions, which was aimed at elucidating the reaction mechanisms and to uncover possible periodic trends across the first row, have been performed for the couples [MO](+) /NH(3) (M=Sc-Zn). Dehydration is found to be endothermic for the oxides of scandium to vanadium and exothermic for the other systems. Hydrogen-atom abstraction becomes exothermic starting with [MnO](+) and, finally, oxygen-atom transfer is feasible for the cationic oxides of nickel to zinc.     

Visible‐Light Photocatalysis: Does It Make a Difference in Organic Synthesis?

Visible‐light photocatalysis has evolved over the last decade into a widely used method in organic synthesis. Photocatalytic variants have been reported for many important transformations, such as cross‐coupling reactions, α‐amino functionalizations, cycloadditions, ATRA reactions, or fluorinations. To help chemists select photocatalytic methods for their synthesis, we compare in this Review classical and photocatalytic procedures for selected classes of reactions and highlight their advantages and limitations. In many cases, the photocatalytic reactions proceed under milder reaction conditions, typically at room temperature, and stoichiometric reagents are replaced by simple oxidants or reductants, such as air, oxygen, or amines. Does visible‐light photocatalysis make a difference in organic synthesis? The prospect of shuttling electrons back and forth to substrates and intermediates or to selectively transfer energy through a visible‐light‐absorbing photocatalyst holds the promise to improve current procedures in radical chemistry and to open up new avenues by accessing reactive species hitherto unknown, especially by merging photocatalysis with organo‐ or metal catalysis.     

Use of LC–HRMS in full scan‐XIC mode for multi‐analyte urine drug testing – a step towards a ‘black‐box’ solution?

The influx of new psychoactive substances (NPS) has created a need for improved methods for drug testing in toxicology laboratories. The aim of this work was to design, validate and apply a multi‐analyte liquid chromatography–high‐resolution mass spectrometry (LC–HRMS) method for screening of 148 target analytes belonging to the NPS class, plant alkaloids and new psychoactive therapeutic drugs. The analytical method used a fivefold dilution of urine with nine deuterated internal standards and injection of 2 μl. The LC system involved a 2.0 μm 100 × 2.0 mm YMC‐UltraHT Hydrosphere‐C₁₈ column and gradient elution with a flow rate of 0.5 ml/min and a total analysis time of 6.0 min. Solvent A consisted of 10 mmol/l ammonium formate and 0.005% formic acid, pH 4.8, and Solvent B was methanol with 10 mmol/l ammonium formate and 0.005% formic acid. The HRMS (Q Exactive, Thermo Scientific) used a heated electrospray interface and was operated in positive mode with 70 000 resolution. The scan range was 100–650 Da, and data for extracted ion chromatograms used ± 10 ppm tolerance. Product ion monitoring was applied for confirmation analysis and for some selected analytes also for screening. Method validation demonstrated limited influence from urine matrix, linear response within the measuring range (typically 0.1–1.0 μg/ml) and acceptable imprecision in quantification (CV <15%). A few analytes were found to be unstable in urine upon storage. The method was successfully applied for routine drug testing of 17 936 unknown samples, of which 2715 (15%) contained 52 of the 148 analytes. It is concluded that the method design based on simple dilution of urine and using LC–HRMS in extracted ion chromatogram mode may offer an analytical system for urine drug testing that fulfils the requirement of a ‘black box’ solution and can replace immunochemical screening applied on autoanalyzers. Copyright © 2017 John Wiley & Sons, Ltd.     

In Search of Organic Zeolites – Does Modern Information Retrieval Inevitably Become a ‘Sieving‐the‐Desert' Exercise?

Information retrieval for planning and executing research projects and for publishing results is considered a routine task that is usually neither mentioned explicitly in a scientific publication nor described in any detail. In the information searches for the preceding publication (‘Building an Organic Zeolite from a Macrocyclic TADDOL Derivative or How to Teach an Old Dog New Tricks'), we were confronted with so many problems during retrieval of the desired information about related work that we decided to deviate from this tradition. We had to use the Cambridge Structural Database, the Chemical Abstracts structure and literature databases, and the Beilstein database to the full extent of their contents, indexing, and search facilities to retrieve the necessary information about ‘organic zeolites'. In the process, we found important limitations and deficiencies in any one of these databases, and we had to conceive search procedures that we considered rather unusual even after more than 20 years of experience in searching chemistry databases. The results and, particularly, the problems encountered underline the necessity for enhanced integration of individual compound and property databases and improved standardization as a prerequisite for this.     

Does a Stabilising Interaction Favouring the Z,Z Configuration of ?S‐NSN‐S? Systems Exist?

The existence of the orbital interaction presented in the literature as being the cause for the stabilisation of the Z,Z configuration of Ph-S-N=S=N-S-Ph (1) and its derivatives in the crystal phase, has been investigated. The results of theoretical calculations at the DFT/B3LYP/6-311+G* level of theory suggest that such a stabilising interaction might not exist or be extremely weak and that packing forces must be the main cause of the observed Z,Z configuration in the solid. To reach this conclusion structural and energetic parameters were combined to study the bonding in these -S-N=S=N-S- systems. For the analogous Ph-Se-N=S=N-Se-Ph (2) in particular the isomeric equilibrium in solution found in the variable-temperature 77Se NMR spectrum indicates that, in the gas phase or in solution, the observed Z,Z configuration is not stabilised to a greater extent than the Z,E configuration.     

Photostability Study of Nanoporous TiO2 Film Electrodes in Basic Solutions

The nanoporous TiO2 film electrodes have been prepared by a sol-gel deposition process The photostability of the electrodes in basic solutions has been studied. The results show that the photostability of the electrodes decreases rapidly in strong basic solutions with or without methanol. The reaction of holes to O^2- produces active O^2- atoms and the products O^2- atomsoxidize Ti^3 to Ti^4 on TiO2 film surface and subsurface. This results in the TiO2 film electrodes unstable in basic solutions both without methanol and with too low concentration.     

Do Anti‐Bredt Natural Products Exist? Olefin Strain Energy as a Predictor of Isolability

Bredt’s rule holds a special place in the realm of physical organic chemistry, but its application to natural products chemistry—the field in which the rule was originally formulated—is not well defined. Herein, the use of olefin strain (OS) energy as a readily calculated predictor of the stability of natural products containing a bridgehead alkene is introduced. Schleyer first used OS energies to classify parent bridgehead alkenes into “isolable”, “observable”, and “unstable” classes. OS calculations on natural products, using contemporary forcefield methods, unequivocally predict all structurally verified bridgehead alkene natural products to be “isolable”. Thus, when one assigns the structure of a putative bridgehead alkene natural product, an OS in the “observable” or “unstable” ranges is a red flag for error.     

Towards a universal LC–MS screening procedure – can an LIT LC–MSn screening approach and reference library be used on a quadrupole‐LIT hybrid instrument?

In contrast to libraries with highly reproducible gas chromatography electron ionization mass spectra, current liquid chromatography (LC–MS) libraries are limited to specific instrument types. Therefore, the aim of the study was to prove whether a recently developed linear ion trap (LIT) LC–MSⁿ screening approach and reference library can be transferred to an LC–MS/MS system with a quadrupole‐LIT hybrid mass analyzer using SmileMS, a sophisticated search algorithm. The LIT reference library was built with MS² and MS³ wideband spectra recorded on a ThermoFisher LXQ LIT with electrospray ionization in positive mode and full‐scan data‐dependent acquisition (DDA). Collision parameter optimizations, including different scan types and energies, were performed on an Applied Biosystems QTRAP 4000 system using electrospray ionization in positive mode and full‐scan DDA. Modified library sets were generated to improve the detection of a compound by the used search algorithm. Additionally, 100 authentic human urine samples were screened by both systems for proof of applicability. In the applicability study, 533 compounds were detected by the LXQ and 477 by the QTRAP system using enhanced product ion scan and a modified database. The presented data showed that the LIT screening approach and reference library could be used successfully on a QTRAP instrument with some limitations. These should be overcome by further optimizations regarding DDA settings for better sensitivity and further library modifications to reduce spectra mismatches. Copyright © 2012 John Wiley & Sons, Ltd.     

Do Anti‐Bredt Natural Products Exist? Olefin Strain Energy as a Predictor of Isolability

Bredt’s rule holds a special place in the realm of physical organic chemistry, but its application to natural products chemistry—the field in which the rule was originally formulated—is not well defined. Herein, the use of olefin strain (OS) energy as a readily calculated predictor of the stability of natural products containing a bridgehead alkene is introduced. Schleyer first used OS energies to classify parent bridgehead alkenes into “isolable”, “observable”, and “unstable” classes. OS calculations on natural products, using contemporary forcefield methods, unequivocally predict all structurally verified bridgehead alkene natural products to be “isolable”. Thus, when one assigns the structure of a putative bridgehead alkene natural product, an OS in the “observable” or “unstable” ranges is a red flag for error.     

Does α‐effect exist in E2 reactions? A G2(+) investigation

The gas-phase base-induced bimolecular elimination (E2) reactions at saturated carbon with 13 bases, B(-) + CH3CH2Cl --> BH + CH2=CH2 + Cl(-) (B = HO, CH3O, CH3CH2O, FCH2CH2O, ClCH2CH2O, Cl, Br, FO, ClO, BrO, HOO, HSO, and H2NO), were investigated with the high-level G2(+) theory. It was found that all alpha-bases with adjacent lone pair electrons examined exhibited downward deviations from the correlation line between the overall barriers and proton affinities for the normal bases without adjacent lone pair electrons, indicating the existence of the alpha-effect in the gas phase E2 reactions. The sizes of the alpha-effect for the E2 reaction, DeltaH(alpha)(E2), span a smaller range if the alpha-atoms are on the same column in the periodic table, in contrast to the corresponding S(N)2 reactions, where the DeltaH(alpha)(S(N)2) values significantly decrease from an upper to a lower column. The origin of the alpha-effects in E2 reactions can be interpreted by the favorable orbital interaction between the lone-pair electrons and positively charged anti-bonding orbital. It is worth noticing that the neighboring electron-rich pi lobe instead of lone pair electrons could also cause the alpha-effect in E2 reaction.