Similar Structural Dynamics for the Degradation of CH3NH3PbI3 in Air and in Vacuum

We investigate the degradation path of MAPbI₃ (MA=methylammonium) films over flat TiO₂ substrates at room temperature by means of X‐ray diffraction, spectroscopic ellipsometry, X‐ray photoelectron spectroscopy, and high‐resolution transmission electron microscopy. The degradation dynamics is found to be similar in air and under vacuum conditions, which leads to the conclusion that the occurrence of intrinsic thermodynamic mechanisms is not necessarily linked to humidity. The process has an early stage, which drives the starting tetragonal lattice in the direction of a cubic atomic arrangement. This early stage is followed by a phase change towards PbI₂. We describe how this degradation product is structurally coupled with the original MAPbI₃ lattice through the orientation of its constituent PbI₆ octahedra. Our results suggest a slight octahedral rearrangement after volatilization of HI+CH₃NH₂ or MAI, with a relatively low energy cost. Our experiments also clarify why reducing the interfaces and internal defects in the perovskite lattice enhances the stability of the material.     

Study of Electrochemical Oxidation of Xanthohumol by Ultra-Performance Liquid Chromatography Coupled to High Resolution Tandem Mass Spectrometry and Ion Mobility Mass Spectrometry

Electrochemically assisted oxidation off-line combined with UPLC/ESI–MS and ion mobility mass spectrometry enabled us to gain insight into the oxidation mechanisms of xanthohumol. Several types of monomeric oxidation products were identified, i.e., monohydroxylated and dehydrogenated derivatives and related quinones. Besides, high contents of dimers were observed. The structures of four main oxidative condensation products of two xanthohumol molecules were proposed based on combination of retention time, exact mass measurement, fragmentation pattern, data from on-line ion mobility mass spectrometric experiments and with the support of independent electrochemical experiments. To the best of our knowledge, this is the first evidence on formation of xanthohumol dimers. The effect of the pH on the generation of oxidation products was further investigated. The monomeric and dimeric oxidation products are favored at pH of 5.5 and 4.5, respectively.

     

Batch versus Flow Photochemistry: A Revealing Comparison of Yield and Productivity

The use of flow photochemistry and its apparent superiority over batch has been reported by a number of groups in recent years. To rigorously determine whether flow does indeed have an advantage over batch, a broad range of synthetic photochemical transformations were optimized in both reactor modes and their yields and productivities compared. Surprisingly, yields were essentially identical in all comparative cases. Even more revealing was the observation that the productivity of flow reactors varied very little to that of their batch counterparts when the key reaction parameters were matched. Those with a single layer of fluorinated ethylene propylene (FEP) had an average productivity 20 % lower than that of batch, whereas three‐layer reactors were 20 % more productive. Finally, the utility of flow chemistry was demonstrated in the scale‐up of the ring‐opening reaction of a potentially explosive [1.1.1] propellane with butane‐2,3‐dione.     

Overcoming Selectivity and Sensitivity Issues of Direct Inject Electrospray Mass Spectrometry via DAPNe-NSI-MS

Direct inject electrospray mass spectrometry offers minimal sample preparation and a “shotgun” approach to analyzing samples. However, complex matrix effects often make direct inject an undesirable sample introduction technique, particularly for trace level analytes. Highlighted here is our solution to the pitfalls of direct inject mass spectrometry and other ambient ionization methods with a focus on trace explosives. Direct analyte-probed nanoextraction coupled to nanospray ionization mass spectrometry solves selectivity issues and reduces matrix effects while maintaining minimal sample preparation requirements. With appropriate solvent conditions, most explosive residues can be analyzed with this technique regardless of the nature of the substance (i.e., nitroaromatic, oxidizing salt, or peroxide).

Three New Polyoxygenated Steroids from Two Species of the South China Sea Gorgonian Muricella flexuosa and Menella verrucosa Brundin

Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds.     

Synthesis and Biological Evaluation of Several Dephosphonated Analogues of CMP‐Neu5Ac as Inhibitors of GM3‐Synthase

Previous studies demonstrated that reducing the GM3 content in myoblasts increased the cell resistance to hypoxic stress, suggesting that a pharmacological inhibition of the GM3 synthesis could be instrumental for the development of new treatments for ischemic diseases. Herein, the synthesis of several dephosphonated CMP‐Neu5Ac congeners and their anti ‐ GM3‐synthase activity is reported. Biological activity testes revealed that some inhibitors almost completely blocked the GM3‐synthase activity in vitro and reduced the GM3 content in living embryonic kidney 293A cells, eventually activating the epidermal growth factor receptor (EGFR) signaling cascade.     

EXAFS Spectroscopy of the Alkoxide Precursor Zr(O n Bu)4 and its Modification in Solution

Summary. The molecular structure of the transition metal alkoxide Zr(OⁿBu)₄ in toluene and its modification by addition of i-propanol, tetrahydrofurane, and the coordinating ligand pentane-1,3-dione (Hacac) were investigated by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy. Zr(OⁿBu)₄ dissolved in toluene forms dimers. It was proved that cluster size is a function of the number of added equivalents ligand. In contrast, the addition of i-propanol or tetrahydrofurane caused no structural changes observable by EXAFS spectroscopy. A detailed discussion of the structural models is given in terms of possible alternatives and errors within the EXAFS analysis.