Metastable Ionic Diodes Derived from an Amine‐Based Polymer of Intrinsic Microporosity

A highly rigid amine‐based polymer of intrinsic microporosity (PIM), prepared by a polymerization reaction involving the formation of Tröger’s base, is demonstrated to act as an ionic diode with electrolyte‐dependent bistable switchable states.     

Yb(OTf)3-catalyzed reactions of 5-alkylidene Meldrum's acids with phenols: one-pot assembly of 3,4-dihydrocoumarins, 4-chromanones, coumarins, and chromones

[reaction: see text] The Yb(OTf)3-catalyzed annulation reactions of phenols with 5-alkylidene Meldrum's acids enabled the synthesis of structurally diverse heterocycles in high isolated yields. A series of 4-substituted 3,4-dihydrocoumarins, 2,2-disubstituted 4-chromanones, coumarins, and 2-substituted chromones were readily and efficiently assembled, including the naturally occurring coumarins citropten, scoparone, and ayapin. Addition of phenols to biselectrophilic 5-alkylidene Meldrum's acids proceeded through two distinct multibond-forming modes: Friedel-Crafts C-alkylation/O-acylation and Friedel-Crafts C-acylation/O-alkylation. The regioselectivity of the catalytic annulation reaction was controlled by the degree of substitution on the alkylidene moiety.     

Making the liquid-phase catalytic hydrodechlorination of pce over Pd/C safer

Summary The hydrodechlorination of tetrachloroethylene in methanol (MeOH) over palladium catalysts on activated carbon (Pd/C) at 20°C and atmospheric pressure was rendered safer by using ethanol (EtOH), isopropanol (IPA) or water-alcohol mixtures as solvents. Adding water to MeOH was better than using EtOH or IPA since it resulted in a faster reaction and better stability of Pd/C, which could also be completely reactivated.     

Analysis of DNA relaxation and cleavage activities of recombinant Mycobacterium tuberculosis DNA topoisomerase I from a new expression and purification protocol

Background  

Mycobacterium tuberculosis DNA topoisomerase I is an attractive target for discovery of novel TB drugs that act by enhancing the accumulation of the topoisomerase-DNA cleavage product. It shares a common transesterification domain with other type IA DNA topoisomerases. There is, however, no homology between the C-terminal DNA binding domains of Escherichia coli and M. tuberculosis DNA topoisomerase I proteins.     

Mass spectrometric analysis of the S-layer proteins from Clostridium difficile demonstrates the absence of glycosylation

Like many other bacterial cell surfaces, the cell wall of Clostridium difficile is also encapsulated by a proteinaceous paracrystalline layer, the surface (S)-layer. In many bacterial species, the S-layer proteins (SLPs) have been shown to be glycosylated, whereas in other species glycosylation is absent. Unusually, the S-layer of C. difficile is composed of two distinct proteins, the high-molecular weight (HMW) and low-molecular-weight (LMW) SLPs. Previous investigations have reported that one or both of these SLPs are glycosylated, though no definitive study has been conducted. We have used a variety of mass spectrometric approaches to analyse SLPs from a number of strains of C. difficile for the presence of associated glycans. Analysis of intact SLPs by matrix assisted laser desorption/ionisation time of flight (MALDI-ToF) mass spectrometry demonstrated that the observed molecular masses matched the predicted masses of the LMW and HMW SLPs. Furthermore, analysis of Cyanogen bromide (CNBr) and tryptic peptides displayed no evidence of post-translational modification. In the first in-depth study of its kind, we unequivocally demonstrate that the S-layer proteins from the C. difficile strains investigated are not glycosylated.     

A screening test for heroin based on sequential injection analysis with dual-reagent chemiluminescence detection

A sequential injection analysis procedure with dual-reagent chemiluminescence detection was applied to the screening of street drug seizure samples for the presence of heroin. The chemiluminescence reagents (acidic potassium permanganate and tris(2,2'-bipyridine)ruthenium(III)) were aspirated from either side of a sample aliquot that was sufficiently large to prevent interdispersion of the reagent zones, and therefore two different chemical reactions could be performed simultaneously at either end of the sample zone. The presence of heroin in seizure samples was indicated by a strong response with the tris(2,2'-bipyridine)ruthenium(III) reagent and confirmed by a significant increase in the response with the permanganate reagent when the sample was treated with sodium hydroxide to hydrolyse the heroin to morphine. Nicomorphine (a morphine-derived pharmaceutical) was synthesised and tested under the same conditions. The responses with the permanganate reagent were similar to those for heroin, which supports the proposed chemical basis for the test. However, the responses with tris(2,2'-bipyridine)ruthenium(III) were far lower for nicomorphine than heroin (approximately 5-fold for the samples that had not been hydrolysed).     

Electron delocalization in the metallabenzenes: a computational analysis of ring currents

Many metallabenzene complexes appear to exhibit an enhanced thermodynamic stability which has been attributed to the concept of aromaticity. Analysis of the ring currents induced by a magnetic field, either by direct visualization or by considering nuclear or nucleus-independent chemical shielding values (NMR or NICS), have become useful theoretical tools to characterize the aromaticity of many molecules involving the main group elements. We have analyzed 21 metallabenzenes using variations of these techniques, which take account of the large core and metal orbital contributions which often lead to transition-metal-containing systems exhibiting anomalous shielding values. Analysis of individual orbital contributions to both the ring currents and chemical shielding values based upon the ipsocentric and CSGT (continuous set of gauge transformations) methods has shown that complexes such as the 18 electron Ir or Rh(C 5H 5)(PH 3) 2Cl 2 molecules should be classed as aromatic, whereas the 16 electron complexes such as Os or Ru(C 5H 5)(PH 3) 2Cl 2 should not, despite having the same occupancy of pi-MOs. The differences can be directly attributed to the HOMO/LUMO b 2 in-plane (d xy ) molecular orbital, which, when unoccupied, is available to disrupt the delocalized currents typical of aromatic systems. A range of Pd and Pt metallabenzenes with cyclopentadienyl and phosphine ligands is also discussed as having aromatic and nonaromatic character, respectively.