Bismuth(III) Flavonolates: The Impact of Structural Diversity on Antibacterial Activity,Mammalian Cell Viability and Cellular Uptake

A series of homoleptic and heteroleptic bismuth(III) flavonolate complexes derived from six flavonols of varying substitution have been synthesised and structurally characterised. The complexes were evaluated for antibacterial activity towards several problematic Gram-positive (Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococcus (VRE)) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria. The cell viability of COS-7 (monkey kidney) cells treated with the bismuth flavonolates was also studied to determine the effect of the complexes on mammalian cells. The heteroleptic complexes [BiPh(L)₂] (in which L=flavonolate) showed good antibacterial activity towards all of the bacteria but reduced COS-7 cell viability in a concentration-dependent manner. The homoleptic complexes [Bi(L)₃] exhibited activity towards the Gram-positive bacteria and showed low toxicity towards the mammalian cell line. Bismuth uptake studies in VRE and COS-7 cells treated with the bismuth flavonolate complexes indicated that Bi accumulation is influenced by both the substitution of the flavonolate ligands and the degree of substitution at the bismuth centre.     

Lithium–Bromide Exchange versus Nucleophilic Addition of Schiff's base: Unprecedented Tandem Cyclisation Pathways

By exploring lithium–bromide exchange reactivity of aromatic Schiff's bases with tert-butyllithium (tBuLi), we have revealed unprecedented competitive intermolecular and intramolecular cascade annulation pathways, leading to valuable compounds, such as iso-indolinones and N-substituted anthracene derivatives. A series of reaction parameters were probed, including solvent, stoichiometry, sterics and organolithium reagent choice, in order to understand the influences that limit such ring-closing pathways. With two viable reactivity options for the organolithium on the imine; namely, nucleophilic addition or lithium–bromide exchange, a surprising competitive nature was observed, where nucleophilic addition dominated, even under cryogenic conditions. Considering the most commonly used solvents for lithium–bromide exchange, tetrahydrofuran (THF) and diethyl ether (Et₂O), contrasting reactivity outcomes were revealed with nucleophilic addition promoted in THF, while Et₂O yielded almost double the conversion of cyclic products than in THF.     

The Phase-Transfer Catalyzed Synthesis of Bis(4-Aryloxy-3-Nitrophenyl) Sulfones

Ten bis(4-aryloxy-3-nitrophenyl) sulfones were synthesized via a phase-transfer catalyzed, nucleophilic displacement reaction involving phenoxides and bis(4-chloro-3-nitrophenyl) sulfone.     

Conformational landscapes of bimesogenic compounds and their implications for the formation of modulated nematic phases

ABSTRACT

The twist-bend phase (N_TB) is most commonly observed in materials with a gross-bent shape: dimers; bent-cores; bent-oligomers. We had suggested previously that the bend-angle of such systems effectively dictates the relative thermal stability of the N_TB phase. However, our earlier paper relied on the use of a single energy-minimum conformer and so failed to capture any information about flexibility and conformational distribution. In the present work, we revisit our hypothesis and examine a second set of dimers with varying linking groups and spacer composition. We have improved on our earlier work by studying the conformational landscape of each material, allowing average bend-angles to be determined as well as the conformer distribution. We observe that the stability of the N_TB phase exhibits a strong dependence not only on the Boltzmann-weighted average bend-angle (rather than just a static conformer), but also on the distribution of conformers. To a lesser extent, the flexibility of the spacer appears important. Ultimately, this work satisfies both theoretical treatments and our initial experimental study and demonstrates the importance of molecular bend to the N_TB phase.     

Three‐dimensional imaging of chemical phase transformations at the nanoscale with full‐field transmission X‐ray microscopy

The ability to probe morphology and phase distribution in complex systems at multiple length scales unravels the interplay of nano‐ and micrometer‐scale factors at the origin of macroscopic behavior. While different electron‐ and X‐ray‐based imaging techniques can be combined with spectroscopy at high resolutions, owing to experimental time limitations the resulting fields of view are too small to be representative of a composite sample. Here a new X‐ray imaging set‐up is proposed, combining full‐field transmission X‐ray microscopy (TXM) with X‐ray absorption near‐edge structure (XANES) spectroscopy to follow two‐dimensional and three‐dimensional morphological and chemical changes in large volumes at high resolution (tens of nanometers). TXM XANES imaging offers chemical speciation at the nanoscale in thick samples (>20 µm) with minimal preparation requirements. Further, its high throughput allows the analysis of large areas (up to millimeters) in minutes to a few hours. Proof of concept is provided using battery electrodes, although its versatility will lead to impact in a number of diverse research fields.     

Sensitized Lanthanide‐Ion Luminescence with Aryl‐Substituted N‐(2‐Nitrophenyl)acetamide‐Derived Chromophores

The syntheses of the two tetraazamacrocyclic ligands L1 and L2 bearing a [(methoxy‐2‐nitrophenyl)amino]carbonyl chromophore, i.e., an N‐(methoxy‐2‐nitrophenyl)acetamide moiety, together with their corresponding lanthanide‐ion complexes are described. A combined spectroscopic (UV/VIS, ¹H‐NMR), structural (X‐ray), and theoretical (DFT) investigation revealed that the absorption properties of the chromophores were dictated by the extent of electronic delocalisation, which in turn was determined by the position of the MeO substituent at the aromatic ring. X‐Ray crystallographic studies showed that when attached to the macrocycle, both isomeric forms of the N‐(methoxy‐2‐nitrophenyl)acetamide unit can participate in coordination, via the C?O, to an encapsulated potassium cation. Luminescence measurements confirmed that such a binding mode also exists in solution for the corresponding lanthanide complexes (q ca. ≤1), with the para‐MeO derivative allowing longer wavelength sensitization (λ_ex 330 nm).     

A luminescent rhenium(I) complex of 2,7-dimethyl-1,8-naphthyridine: synthesis,spectroscopy and X-ray crystal structure

2,7-Dimethyl-1,8-naphthyridine (L¹) reacts with pentacarbonylchlororhenium in toluene or chloroform to give the target complex fac-{ReCl(CO)₃(L¹)}. X-ray crystallographic data were obtained for fac-{ReCl(CO)₃(L¹)}. The structural and ¹H NMR data suggest that the ligand coordinates to the rhenium in a bidentate fashion in both solid and solution states. The complex was also found to be luminescent in both solution and solid states. The fluxionality of the ligand in solution causes ligand-centred emission to be observed in solution, whereas only ³MLCT emission was observed in the solid state. Although the complex was air-stable, the lability of L¹ was studied in ¹H NMR experiments where CD₃OD induced complete ligand dissociation over the course of 24 h, and also in reaction of fac-{ReCl(CO)₃(L¹)} with one equivalent of 2,2′-bipyridine in chloroform which resulted in quantitative ligand exchange. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The meaning of Ramanujan now and for the future

December 22, 2010 marks the 123th anniversary of Ramanujan’s birth. In this paper we pay homage to this towering figure whose mathematical discoveries so affected mathematics throughout the twentieth century and into the twenty-first.     

Partitions with initial repetitions

A variety of interesting connections with modular forms, mock theta functions and Rogers- Ramanujan type identities arise in consideration of partitions in which the smaller integers are repeated as summands more often than the larger summands. In particular, this concept leads to new interpretations of the Rogers Selberg identities and Bailey＇s modulus 9 identities.