Sonochemical degradation of triclosan in water and wastewater

The sonochemical degradation of 5 μg l⁻¹ triclosan, a priority micro-pollutant, in various environmental samples (seawater, urban runoff and influent domestic wastewater) as well as in model solutions (pure and saline water) was investigated. Experiments were conducted with a horn-type sonicator operating at 80 kHz frequency and a nominal applied power of 135 W, while solid-phase microextraction coupled with gas chromatography–electron capture detector (SPME/GC–ECD) was employed to monitor triclosan degradation. The latter followed pseudo-first order kinetics with the rate constant being (min⁻¹): 0.2284 for seawater > 0.1051 for 3.5% NaCl in deionised water > 0.0597 for centrifuged urban runoff  0.0523 for untreated urban runoff > 0.0272 for deionised water > 0.0063 for wastewater influent. SPME/GC–ECD and SPME coupled with gas chromatography–mass spectrometry (SPME/GC–MS) were also used to check for the formation of chlorinated and other toxic by-products; at the conditions in question, the presence of such compounds was not confirmed.     

Protein‐Specific,Multicolor and 3D STED Imaging in Cells with DNA‐Labeled Antibodies

Photobleaching is a major challenge in fluorescence microscopy, in particular if high excitation light intensities are used. Signal‐to‐noise and spatial resolution may be compromised, which limits the amount of information that can be extracted from an image. Photobleaching can be bypassed by using exchangeable labels, which transiently bind to and dissociate from a target, thereby replenishing the destroyed labels with intact ones from a reservoir. Here, we demonstrate confocal and STED microscopy with short, fluorophore‐labeled oligonucleotides that transiently bind to complementary oligonucleotides attached to protein‐specific antibodies. The constant exchange of fluorophore labels in DNA‐based STED imaging bypasses photobleaching that occurs with covalent labels. We show that this concept is suitable for targeted, two‐color STED imaging of whole cells.     

Polyelectrolyte-compression forces between spherical DNA brushes

Optical tweezers are employed to measure the forces of interaction within a single pair of DNA-grafted colloids, dependent on the molecular weight of the DNA chains, and the concentration and valence of the surrounding ionic medium. The resulting forces are short range and set in as the surface-to-surface distance between the colloidal cores reaches the value of the brush height. The measured force-distance relation is analyzed by means of a theoretical treatment that quantitatively describes the effects of compression of the chains on the surface of the opposite-lying colloid. Quantitative agreement with the experiment is obtained for all parameter combinations.     

Organic–inorganic bonding in chitosan–silica hybrid networks: Physical properties

Novel biomaterials are needed for bone tissue repair with improved mechanical performance compared to classical bioceramics. The objective of this work was to characterize a hybrid filler material, which is capable to coat as a thin film porous scaffolds improving their mechanical properties for bone tissue engineering. The hybrid filler material is a blend of chitosan and silica network formed through in situ sol–gel using tetraethylortosilicate and 3‐glycidoxypropyltrimethoxysilane (GPTMS) as silica precursors. The hypothesis was that the epoxy ring of GPTMS could react with the amino groups of chitosan in acidic media while it is also reacting the siloxane groups of hydrolyzed silica precursors. The formation of the hybrid organic–inorganic network was assessed by different physical techniques revealing changes in molecular mobility and hydrophilicity upon chemical reaction. Finally, the cytotoxicity of the samples was also evaluated by MTT assay. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1391–1400     

Insights into the Cascade Reaction of CO and Heteroallenes Mediated by Dinitrogen Hafnocene Complexes: The Indirect Effect of Nitride's Nucleophilicity

A DFT mechanistic exploration of the reactivity of the dinitrogen hafnocene complex, [{(η⁵‐C₅H₂‐1,2,4‐Me₃)₂Hf}₂(μ₂‐N₂)], towards mixtures of CO/CO₂ and CO/OCNtBu is reported. The crucial role of the nitride intermediate is highlighted, as well as the importance of the bridging mode of the cyanate ligand between the two Hf metal atoms throughout the process. Interestingly, the CO₂ addition to the nitride intermediate occurs through an outer‐sphere transition state, whereas the addition of the heteroallene is governed by the steric congestion imposed by cyclopentadienyl ligands.     

A convergent approach to batzelladine alkaloids. Total syntheses of (+)-batzelladine E, (−)-dehydrobatzelladine C,and (+)-batzelladine K

We recently reported a convergent strategy to access the polycyclic guanidinium alkaloid (+)-batzelladine B via an aldol addition–retro-aldol–aza-Michael addition cascade. Here we describe the application of this approach toward the total syntheses of (+)-batzelladine E, (?)-dehydrobatzelladine C, and (+)-batzelladine K. The identification of suitable methods to functionalize a common tropane core by electrophilic alkynylation and nucleophilic 1,2-addition were essential to generalizing this approach. We provide evidence for the intermediacy of an acylallene species in the cascade reaction.     

A facile and effective synthesis of lipophilic 2,6-diketopiperazine analogues

Adamantane and cyclooctane lipophilic 2,6-diketopiperazines (2,6-DKPs) have been prepared by a simple and effective method, including the synthesis of the corresponding iminodiacetic amido-ester derivatives and their intramolecular cyclization. In this method, the key step of the imide formation was accomplished by a novel base-induced cyclization protocol, which involved the treatment of amido-ester 2,6-DKP precursors with potassium bis(trimethylsilyl)amide. Moreover, the cyclization methodology used allowed the synthesis of the respective 1-functionalized 2,6-DKPs in one pot and in excellent yields when the same primary amido-esters were treated with the previous base and the intermediate potassium imidate salts were then reacted with the electrophile benzyl bromoacetate. Hydrogenolysis of the benzyl 2,6-diketopiperazine acetates afforded the respective carboxylic acids, which constitute versatile intermediates in the synthesis of peptidomimetics and other bioactive molecules concerning our pharmacological studies.     

Darobactin B Stabilises a Lateral-Closed Conformation of the BAM Complex in E. coli Cells

The β-barrel assembly machinery (BAM complex) is essential for outer membrane protein (OMP) folding in Gram-negative bacteria, and represents a promising antimicrobial target. Several conformational states of BAM have been reported, but all have been obtained under conditions which lack the unique features and complexity of the outer membrane (OM). Here, we use Pulsed Electron-Electron Double Resonance (PELDOR, or DEER) spectroscopy distance measurements to interrogate the conformational ensemble of the BAM complex in E. coli cells. We show that BAM adopts a broad ensemble of conformations in the OM, while in the presence of the antibiotic darobactin B (DAR-B), BAM′s conformational equilibrium shifts to a restricted ensemble consistent with the lateral closed state. Our in-cell PELDOR findings are supported by new cryoEM structures of BAM in the presence and absence of DAR-B. This work demonstrates the utility of PELDOR to map conformational changes in BAM within its native cellular environment.