Stabilization of ortho-quinone methides by a bis(sulfonium ylide) derived from 2,5-dihydroxy-[1,4]benzoquinone

The zwitterionic intermediates (2a) in the oxidation of ortho-alkylphenols (1) and bis(sulfonium ylide) 3 form reasonably stable 2:1-complexes (4), in which the ortho-quinone methide (oQM) moieties are not present in quinoid form with the exocyclic in-plane methylene group, but as zwitterionic, aromatic conformer having an out-of-plane exocyclic methylene group. The complex 7 derived from the α-tocopherol model compound PMC (5) was comprehensively characterized. As exemplarily demonstrated, the adducts can be advantageously employed in organic synthesis as ‘stabilized oQMs’.     

Configurationally stable longitudinally twisted polycyclic aromatic compounds

Two strategies for the synthesis of configurationally stable twisted polycyclic aromatic compounds (PACs) were pursued. The first approach employed dissymmetrically positioned 1-naphthyl substituents to bias the direction of twist in highly substituted PACs. 2,3-Bis(1-naphthyl)-1,4-diphenyltriphenylene (7) was prepared, and its meso cis-dinaphthyl and enantiomeric trans-dinaphthyl isomers were resolved by preparative supercritical fluid chromatography (SFC) on chiral supports. Similarly, several naphthyl-substituted derivatives of the more highly twisted 9,10,11,12,13,14-hexaphenylbenzo[b]triphenylene (2) were prepared. Of these, 10-(1-naphthyl)-9,11,12,14-tetraphenylbenzo[b]triphenylene (13) was resolved by SFC on a chiral support. The pure enantiomers of trans-7 showed moderately large specific rotations ([alpha]D(25) = -330 and +320 degrees), but the specific rotations for the enantiomers of 13 were unexpectedly small ([alpha]D(25) = -23 and +23 degrees). Computational studies suggest that the latter result is due to presence of a minor conformation of 13 possessing a larger rotation of opposite sign than the major conformation. Both 7 and 13 showed strong circular dichroism and moderately strong circularly polarized luminescence. A byproduct of these syntheses was 9,10,19,21-tetraphenyldiphenanthro[9,10-b:9,10-h]carbazole (15), a very crowded carbazole that exhibits an 81 degree end-to-end twist but is not resolvable. In the second approach, the large, twisted, polycyclic aromatic ligand 9,10,11,12,13,14-hexaphenylbenzo[h]naphtho[2,3-f]quinoline (21, an aza-2) was used to prepare the chiral, cyclometallated iridium(III) complex 4. The ligand 21 was prepared via an unusually stable benzannulated norbornadienone, for which the free energy of activation for decarbonylation was a remarkable 33.5 kcal/mol. The iridium complex 4 proved to be configurationally stable and resolvable by analytical HPLC on chiral supports, but the low solubility of 4 prevented its resolution on a preparative scale. A much more soluble dibutyl analogue of 4 (complex 28) was then prepared, but it was not resolvable on any of the available media.     

Cyclometalated iridium(III) Aquo complexes: efficient and tunable catalysts for the homogeneous oxidation of water

A series of bis-phenylpyridine, bis-aquo iridium(III) complexes is herein shown to robustly and efficiently catalyze the oxidation of water to dioxygen in the presence of a sacrificial oxidant. Through substitution on the cyclometalating ligands of these complexes, it is shown that a broad range of oxidation potentials can be achieved within this class of catalyst. Parallel, dynamic monitoring of oxygen evolution, made possible by equipping reaction vessels with pressure-voltage transducers, facilitates correlation of these complexes' ionization potentials with their respective activity toward water oxidation. The importance of these catalysts lies in (A) their ability to oxidize water in a purely aqueous medium, (B) their simplicity of design, (C) their durability, and (D) the ease with which they can be tuned to accommodate the electrochemical needs of photosensitizers in hypothetical photochemical water oxidation and full artificial photosynthetic schemes.     

Solid-state characterization and dissolution properties of ezetimibe–cyclodextrins inclusion complexes

The objectives of this research were to prepare and characterize inclusion complex of Ezetimibe (EZE) with cyclodextrins (β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HPβ-CD)) and to study the effect of complexation on the dissolution rate of EZE, a water insoluble drug. Phase solubility curve was classified as A _P -type for both cyclodextrins, indicating the 2:1 stoichiometric ratio for β-CD–EZE and HPβ-CD – EZE inclusion complexes. The inclusion complexes in the molar ratio of 2:1 (β-CD–EZE and HPβ-CD–EZE) were prepared by various methods such as kneading, coevaporation and physical mixing. The molecular behaviors of drug in all samples were characterized by fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) studies. The results of these studies indicated that complex prepared by kneading and coevaporation methods showed inclusion of the EZE molecule into the cyclodextrins cavities. The highest improvement in in-vitro dissolution profiles was observed in complex prepared with hydroxypropyl-β-cyclodextrin using co-evaporation method. Mean dissolution time and similarity factor indicated significant difference between the release profiles of EZE from complexes and physical mixtures and from pure EZE.     

Development of a Creatinine Sensor Based on a Molecularly Imprinted Polymer‐Modified Sol‐Gel Film on Graphite Electrode

An electrochemical creatinine sensor based on a molecularly imprinted polymer (MIP)‐modified sol‐gel film on graphite electrode was developed. The surface coating of MIP over sol‐gel was advantageous to obtain a porous film with outwardly exposed MIP cavities for unhindered selective rebinding of creatinine from aqueous and biological samples. A fast differential pulse, cathodic stripping voltammetric response of creatinine can be obtained after being preanodized the sensor in neutral medium containing appropriate amount of creatinine at +1.8 V versus SCE for 120 s. A linear response over creatinine concentration in the range of 1.23 to 100 μg mL^?1 was exhibited with a detection limit of 0.37 μg mL^?1 (S/N=3).     

Synthetic,spectroscopic and thermal aspects of some heterochelates

The present article describes the synthesis, structural features and thermal studies of heterochelates of the type [M(SB)(benen)(H₂O)]·nH₂O [where H₂SB=(Z)-2-(2,2,2-trifluoro-1-(5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)ethylideneamino)benzoic acid, benen=bis(benzylidene)ethylenediamine and M=Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and VO(IV)]. The Schiff base (H₂SB) have been characterized on the basis of elemental analysis, IR, ¹H and ¹³C NMR. The heterochelates have been characterized on the basis of elemental analyses, magnetic measurements, solid state conductivity measurements, IR, reflectance spectra, and thermal studies. The FAB mass spectrum of [Co(SB)(benen)(H₂O)] has been carried out. The kinetic parameters such as order of reaction (n) and the energy of activation (E _a) have been reported using Freeman-Carroll method. The pre-exponential factor (A), the activation entropy (ΔS ^#), the activation enthalpy (ΔH ^#) and the free energy of activation (ΔG ^#) have been calculated.     

Individually addressable microelectrode array for monitoring oxygen and nitric oxide release

We have fabricated a six individual addressable gold working electrode microarray. The device is wirebonded to an eight-pin DIL package that can be easily interconnected to an external multi-channel potentiostat. A polyion complex film coating on the electrode surface provides a suitable coating for the growth of cells. The responses of oxygen and nitric oxide were assessed on uncoated and coated devices using electroanalytical methods. The film coating reduced the diffusion current by approximately 20% in both cases. No changes in the electrochemical mechanism were observed. Simultaneous recordings were obtained for 2 h in the presence of the cells, thus the device is stable for the duration of the bioanalytical measurements. Measurements were conducted to study the simultaneous changes in oxygen and nitric oxide levels in cultured fibroblast cells in the presence of growth hormones that cause cell proliferation. Increases in oxygen consumption of the cells were coupled with increases in nitric oxide levels when in the presence of the growth hormones. Use of a biological detergent to cause an oxidative burst resulted in a large increase in the current for potentials set to detect nitric oxide and oxygen.     

Detecting conserved secondary structures in RNA molecules using constrained structural alignment

Constrained sequence alignment has been studied extensively in the past. Different forms of constraints have been investigated, where a constraint can be a subsequence, a regular expression, or a probability matrix of symbols and positions. However, constrained structural alignment has been investigated to a much lesser extent. In this paper, we present an efficient method for constrained structural alignment and apply the method to detecting conserved secondary structures, or structural motifs, in a set of RNA molecules. The proposed method combines both sequence and structural information of RNAs to find an optimal local alignment between two RNA secondary structures, one of which is a query and the other is a subject structure in the given set. The method allows a biologist to annotate conserved regions, or constraints, in the query RNA structure and incorporates these regions into the alignment process to obtain biologically more meaningful alignment scores. A statistical measure is developed to assess the significance of the scores. Experimental results based on detecting internal ribosome entry sites in the RNA molecules of hepatitis C virus and Trypanosoma brucei demonstrate the effectiveness of the proposed method and its superiority over existing techniques.     

Aluminium complexes with thio-phosphorus ligands: syntheses and characterisations of [Al(2)(CyPS(3))(2)(CyPHS(2))(2)] and [Al(S(2)PPh(2))(3)

The novel aluminium complexes [Al(2)(CyPS(3))(2)(CyPHS(2))(2)] and [Al(S(2)PPh(2))(3)] have been prepared as potential models for alumino-thiophosphonate based materials; [Al(2)(CyPS(3))(2)(CyPHS(2))(2)] is the first example of a primary dithiophosphinate to be characterised in the solid state.