Biorthogonal systems for solving Volterra integral equation systems of the second kind

With the aid of biorthogonal systems in adequate Banach spaces, the problem of approximating the solution of a system of nonlinear Volterra integral equations of the second kind is turned into a numerical method that allows it to be solved numerically.     

Synthesis and luminescence properties of cyclopalladated complexes with S^N and O^N donor ligands

The direct reaction between the hydroxo-complexes [{Pd(μ-OH)(C^N)}(2)] and protonated S^N-donor ligands to yield new dinuclear cyclometallated palladium(ii) complexes containing -NCS- bridging heterocyclic thionates of general formula [{Pd(μ-N^S)(C^N)}(2)] (C^N = 2-(2-pyridyl)phenyl (Phpy) I; = 7,8-benzoquinolyl (Bzq) II; N^S = pyrimidine-2-thionate (Spym) 1, benzoimidazolidine-2-thionate (Sbimid) 2, 1-methylimidazoline-2 thionate (Smeimid) 3) is described. The related mononuclear complexes [Pd(N^S)(C^N)] N^S = 2-aminothiophenolate (Atph) 4) were prepared in a similar way. Photophysical properties were investigated together with those of complexes with related ligands pyridin-2-thionate (Spy) 5 and pyrrole-2-carboxaldehydate (2-pcal) 6. All the compounds absorb intensely below 300 nm via(1)LC transitions located in Bzq or Phpy ligands, and display additional low energy absorptions of mixed (1)MLCT-(1)LC character. In the solid state diffuse reflectance UV-vis spectra, the differences are notable for dinuclear complexes. The complexes under study are quite unusual in terms of luminescence behaviour, since most of them are emissive in solution at room temperature and all display intense emissions in frozen CHCl(3) solution, but also in the solid state at 298 and 77 K. Emission quantum yields are in the range 2.52-0.14%, similar to that of related complexes. Structural characterisation by X-ray diffraction of complexes II3 and II6 confirmed the proposed formula.     

Identification and validation of tetracyclic benzothiazepines as Plasmodium falciparum cytochrome bc1 inhibitors

Here we report the discovery of tetracyclic benzothiazepines (BTZs) as highly potent and selective antimalarials along with the identification of the Plasmodium falciparum cytochrome bc₁ complex as the primary functional target of this novel compound class. Investigation of the structure activity relationship within this previously unexplored chemical scaffold has yielded inhibitors with low nanomolar activity. A combined approach employing genetically modified parasites, biochemical profiling, and resistance selection validated inhibition of cytochrome bc₁ activity, an essential component of the parasite respiratory chain and target of the widely used antimalarial drug atovaquone, as the mode of action of this novel compound class. Resistance to atovaquone is eroding the efficacy of this widely used antimalarial drug. Intriguingly, BTZ-based inhibitors retain activity against atovaquone resistant parasites, suggesting this chemical class may provide an alternative to atovaquone in combination therapy.     

Mesogenic behaviour in some pyrazole and isoxazole derivatives

Abstract

Several aromatic β-diketones with a different number of alkyloxy groups in the aromatic rings and their derived pyrazoles, isoxazoles and thallium (I) complexes have been synthesized. The potential mesomorphic properties of these compounds have been investigated by optical microscopy, DSC and X-ray diffraction. The pyrazoles and isoxazoles with one chain in each aromatic ring are mesogenic, showing smectic A and smectic C mesophases, whereas the pyrazoles and isoxazoles with two chains per ring and the β-diketones and thallium complexes are not. The mesogenic potentiality is shown to be related to the molecular linearity and to the number of alkyloxy groups. To the best of our knowledge, this is the first time liquid crystal properties have been described for pyrazole and isoxazole derivatives.     

New dimeric liquid crystals with chiral flexible spacers

In order to obtain chiral compounds of low molecular weight expected to exhibit mesogenic and ferroelectric properties, the asymmetric carbon was introduced into the central part of the molecule. The series consists of nine chiral dimers in which the chiral flexible spacer derives from S-2-chlorosuccinic acid. The mesomorphic properties of the compounds were studied and all of them were found to be mesogenic. From n = 6 onwards the mesophases were chiral smectic C. Some analogous compounds derived from S-2-chloroglutaric acid were also prepared; these were not found to be mesogenic. The thermal instability of the 2-chlorosuccinic acid derivatives prevented the study of their ferroelectric properties. We attempted to perform this study for several mixtures involving 3-methyladipic acid derivatives and both 2-chlorosuccinic and 2-chloroglutaric acids derivatives. All the mixtures studied show chiral smectic C phases. The mixtures containing 2-chlorosuccinoyl derivatives show thermal instability; however those containing 2-chloroglutaroyl derivatives are stable, but do not show significant values of spontaneous polarization.     

Supermolecular liquid crystals with a six-armed cyclotriphosphazene core: from columnar to cubic phases

New liquid crystals having a non‐conventional structure have been synthesised from a six‐armed cyclotriphosphazene core, [N₃P₃(OC₆H₄OH‐4)₆], which was condensed with polycatenar acids. Reactions were monitored by ³¹P{¹H} and ¹H NMR spectroscopy and the chemical structure of the resulting materials was confirmed by different spectroscopic techniques and mass spectrometry (MALDI‐TOF). Results were in accordance with monodisperse, fully functionalised cyclotriphosphazenes. Thermal and mesomorphic properties were studied by optical microscopy, differential scanning calorimetry and X‐ray diffraction. All of the synthesised phosphazenes, substituted with benzyl ether chains, show a high thermal stability and exhibit mesomorphic properties, which depend on the number and type of alkyl terminal chains located at the periphery of the mesogens. Mesomorphic properties range from Col_h for cph‐A1 and cph‐A2 to a cubic phase detected for cph‐A3 , which has the larger number of alkyl chains. Furthermore, helical order was detected on X‐ray data of cph‐A2 , which has chiral branched chains. Circular dichroism spectra of annealed films at mesophase temperature show a signal attributed to the chiral helical arrangement of the mesogenic chromophores.     

XRD Line Broadening Studies on Mullite

An X-ray diffraction microstructural study on 110, 220, 001 and 111 peaks has been performed on mullite in the temperature range of primary mullite formation in order to monitor nucleation and growth process. Considering the crystallinity of the starting kaolinites, a greater disorder of the kaolinite has been found to enhance the mullite formation. Isothermal growth is related to a decrease in the Al₂O₃ content of mullite.