The Structure of [HSi9]3− in the Solid State and Its Unexpected Highly Dynamic Behavior in Solution

We report on the first unambiguous detection of the elusive [HSi₉]^3? anion in solutions of liquid ammonia by various ²⁹Si and ¹H NMR experiments including chemical exchange saturation transfer (CEST). The characteristic multiplicity patterns of both the ²⁹Si and ¹H resonances together with CEST and a partially reduced ¹H,²⁹Si coupling constant indicate the presence of a highly dynamic Si₈ entity and a Si?H moiety with slow proton hopping. Theoretical calculations corroborate both reorganization of Si₈ on the picosecond timescale via low vibrational modes and proton hopping. In addition, in a single‐crystal X‐ray study of (K(DB[18]crown‐6))(K([2.2.2]crypt))₂[ HSi₉ ]?8.5 NH₃, the H atom was unequivocally localized at one vertex of the basal square of the monocapped square‐antiprismatic cluster. Thus experimental studies and theoretical considerations provide unprecedented insight into both the structure and the dynamic behavior of these cluster anions, which hitherto had been considered to be rigid.     

Optimization of Aqueous Stability versus π-Conjugation in Tetracationic Bis(triarylborane) Chromophores: Applications in Live-Cell Fluorescence Imaging

The stability of tetracationic triarylboranes in dilute aqueous solution was investigated by tuning the steric demand of the linker in a (para-(N,N,N-trimethylammonio)xylyl)₂B–(linker)–B(para-(N,N,N-trimethylammonio)xylyl)₂ structure. With increasing steric bulk of the linker, namely 1,4-phenylene, 2,2′′′-(3,3′′′-dimethyl)-5,2′:5′,2′′:5′′,5′′′-quaterthiophene, 9,10-anthracenylene, and 4,4′′′-(5′-(3,5-dimethylphenyl))(5′′-(3′′′,5′′′-dimethylphenyl))-2′,2′′-bithiophene, the stability of the compounds increased. The anthracene-based chromophore, compound 3M is water-stable for at least 48 h, is nontoxic to cells and exhibits an exceedingly high fluorescence quantum yield of 0.86 in water making it an ideal candidate for confocal live-cell imaging of lysosomes.     

Improved Synthesis of Indirubin Derivatives by Sequential Build‐Up of the Indoxyl Unit: First Preparation of Fluorescent Indirubins

Indirubin, present in extracts of Isatis tinctoria and some other plant species, has promising cytotoxicity against a variety of cell lines by inhibition of cyclin‐dependent kinases. Chemical synthesis of its derivatives relies on the combination of isatins and 2,3‐dihydro‐1H‐indol‐3‐one (‘indoxyl’) derivatives and usually yields indigo as well as other by‐products. Inspection of the hydrolysis of the long‐known condensation products of 2‐thioxothiazolidin‐4‐one with isatins gave useful hints for an improved synthesis of indirubins: this reaction does not yield quinoline derivatives but 2‐(2,3‐dihydro‐2‐oxo‐1H‐indol‐3‐ylidene)‐2‐sulfanyl acetic acids. By substitution of the sulfanyl group in this oxindoles with anilines and straightforward cyclization under Nazarov conditions, a broad variety of indirubins substituted in the indoxyl ring system are thus available, usually in very good purity and yield. Use of naphthylamines in this reaction sequence yields various fluorescent substances with λ_fl at ca. 630 nm.     

The challenges in reliable determination of degradation rates and lifetime in polymer electrolyte membrane fuel cells

The durability of polymer electrolyte membrane fuel cells (PEMFCs) needs to be further improved to cope with application requirements and economic competitiveness. This article highlights the challenges in the reliable determination of degradation rates and lifetime. The reliable evaluation of performance degradation rates is fundamental to quantify and benchmark durability and to allow comparisons between PEMFC durability tests performed using different materials or in different laboratories. The use of efficient recovery procedures enables the discrimination of reversible and irreversible voltage losses and facilitates the understanding of recovery mechanisms. In the end, recent contributions about lifetime diagnoses and prediction are presented, which are promising to be implemented in PEMFC applications.     

Three kinds of normative behaviour: minimal requirements for feedback models

We present an analysis for modelling social norms. In social psychology three different normative behaviours have been identified: obedience, conformity and compliance. We show that this triad is a useful conceptualisation of normative behaviour and that current models only ever deal with conformity and obedience two, neglecting compliance. We argue that this is a result from modelling having so far focussed too much on agent behaviour rather than agent knowledge and that cognitive models of normative behaviour are needed to capture this third and arguably most interesting normative behaviour.     

Bioavailability and biotransformation of sulforaphane and erucin metabolites in different biological matrices determined by LC–MS–MS

The food-related isothiocyanate sulforaphane (SFN), a hydrolysis product of the secondary plant metabolite glucoraphanin, has been revealed to have cancer-preventive activity in experimental animals. However, these studies have often provided inconsistent results with regard to bioavailability, bioaccessibility, and outcome. This might be because the endogenous biotransformation of SFN metabolites to the structurally related erucin (ERN) metabolites has often not been taken into account. In this work, a fully validated liquid chromatography tandem mass spectrometry (LC–MS–MS) method was developed for the simultaneous determination of SFN and ERN metabolites in a variety of biological matrices. To reveal the importance of the biotransformation pathway, matrices including plasma, urine, liver, and kidney samples from mice and cell lysates derived from colon-cancer cell lines were included in this study. The LC–MS–MS method provides limits of detection from 1 nmol L^?1 to 25 nmol L^?1 and a mean recovery of 99 %. The intra and interday imprecision values are in the range 1–10 % and 2–13 %, respectively. Using LC–MS–MS, SFN and ERN metabolites were quantified in different matrices. The assay was successfully used to determine the biotransformation in all biological samples mentioned above. For a comprehensive analysis and evaluation of the potential health effects of SFN, it is necessary to consider all metabolites, including those formed by biotransformation of SFN to ERN and vice versa. Therefore, a sensitive and robust LC–MS–MS method was validated for the simultaneous quantification of mercapturic-acid-pathway metabolites of SFN and ERN.

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Graphical Abstract Biotransformation of sulforaphane and erucin metabolites in mice and cell culture