Electronic, spectroscopic, and ion-sensing properties of a dehydro[m]pyrido[14]- and [15]annulene isomer library

An isomeric series of dehydro[m]pyrido[n]annulenes incorporating strained 1,4-buta-1,3-diyne units have been synthesized, where m = 2, n = 14 (1a-d); m = 2, n = 15 (2a,b); and m = 3, n = 15 (3). The number of pyridine rings and annulene ring π-electrons are denoted by m and n, respectively. The X-ray crystal structures of 1b and 1c confirmed their cyclic formulation. All macrocycles were found to be luminescent chromophores with differing isomer-dependent proton and metal ion-sensory emission responses, which appear collectively as analyte-specific color patterns. Within the series studied, 1a was singular in displaying the highest luminescence quantum yield and sharing the strongest emission energy and molar absorption changes upon protonation and Hg(II) binding. Spectroscopic and electrochemical results were supported by density functional theory calculations in showing 1a, 2a, and 3 to be low bandgap materials with lowest unoccupied molecular orbitals delocalized over the 1,4-di(pyridin-4-yl)buta-1,3-diyne bridges that provide a pathway for electronic communication between the nitrogens. Overall, the investigations suggest that 1a, 2a, and 3 would be excellent ligands for the construction of novel conjugated hybrid metallosupramolecular nanostructures, polymers, and ion-sensory systems.     

Dual-channel spectral subtraction algorithms based speech enhancement dedicated to a bilateral cochlear implant

In this paper, two speech enhancement algorithms (SEAs) based on spectral subtraction (SS) principle have been evaluated for bilateral cochlear implant (BCI) users. Specifically, dual-channel noise power spectral estimation algorithm using power spectral densities (PSD) and cross power spectral density (CPSD) of the observed signals was studied. The enhanced speech signals were obtained using either Dual Channel Non Linear Spectral Subtraction ‘DC-NLSS’ or Dual-Channel Multi-Band Spectral Subtraction ‘DC-MBSS’ algorithms. For performance evaluation, some objective speech assessment tests relying on Perceptual Evaluation of Speech Quality (PESQ) score and speech Itakura-Saito (IS) distortion measurement were performed to fix the optimal number of frequency band needed in DC-MBSS algorithm. In order to evaluate the speech intelligibility, subjective listening tests were assessed with 50 normal hearing listeners using a specific BCI simulator and with three deafened BCI patients. Experimental results, obtained using French Lafon database corrupted by an additive babble noise at different Signal-to-Noise Ratios (SNR), showed that DC-MBSS algorithm improves speech understanding better than DC-NLSS algorithm for single and multiple interfering noise sources.     

Ligand exchange method for determination of mole ratios of relatively weak metal complexes: a comparative study

Ligand exchange method is introduced as an alternative to Job’s and mole ratio methods for studying the stoichiometry of relatively weak metal complexes in solutions. The method involves adding varying amounts of a ligand (L) to an excess constant amount of a colored complex (MX) with appropriate stability and molar absorptivity. The absorbance of each solution is measured at the λ_max of the initial complex, MX, and plotted against the concentration of the studied ligand, L. If the newly formed complex ML does not absorb at the λ_max of the initial complex, then attenuation of the absorbance of the initial complex on adding varying quantities of the investigational ligand gives an inverse calibration line that intersects with the calibration curve of initial complex at a given point. If a line parallel to the ordinate is drawn from this point to the x-axis, the ratio of the two parts of the x-axis to the left and to the right (α/β) gives the metal to ligand molar ratio in the complex formed, ML. The new method has been applied to the study of the composition of iron (III) complexes with three bisphosphonate drugs: alendronate, etidronate, and ibandronate. The mole ratio was found to be 1:1 with the three investigated bisphosphonates and results were further confirmed by Job’s and mole ratio methods. The ligand exchange method is simpler, quicker, easier to perform and more accurate than Job’s and mole ratio methods for studying weak and relatively weak complexes.

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ACTIVATED NITRILES IN HETEROCYCLIC SYNTHESIS: NOVEL SYNTHESIS OF PYRROLO[1,2-c]IMIDAZOLE AND PYRANO[2,3-d]IMIDAZOLE DERIVATIVES

Abstract

Several new pyrrolo[1,2-ylidene ethyl cyanoacetate (lc, d) with each of (2) and (11) afforded the 5-ylidene-2-thiohydantoins (Sa, b), (Wn. b) respectively. Compounds Sn, b react with each of malononitrile and ethyl cyanoacet-ate to give the corresponding pyrroloimidazole derivatives (h,b) and (an, b) respectively. The structure of the isolated products were established by elemental analyse and spectral data studies.     

Stability analysis of a polymer film casting problem

The polymer cast film process consists of stretching a molten polymer film between a flat die and a drawing roll. Drawing instabilities are often encountered and represent a drastic limitation to the process. Newtonian fluid film stretching stability is investigated using two numerical strategies. The first one is a ‘tracking’ method, which consists of solving Stokes equations in the whole fluid area (extrusion die and stretching path) by finite elements. The interface is determined to satisfy a kinematic equation. A domain decomposition meshing technique is used in order to account for a flow singularity resulting from the change in the boundary conditions between the die flow region and the stretching path region. A linear stability method is then applied to this transient kinematic equation in order to investigate the stability of the stationary solution. The second method is a direct finite element simulation in an extended area including the fluid and the surrounding air. The time‐dependent interface is captured by solving an appropriate level‐set function. The agreement between the two methods is fair. The influence of the stretching parameters (Draw ratio and drawing length) is investigated. For a long stretching distance, a critical Draw ratio around 20 delimitating stable and unstable drawing conditions is obtained, and this agrees well with the standard membrane models, which have been developed 40 years ago. When decreasing the stretching distance, the membrane model is no longer valid. The 2D models presented here point out a significant increase of the critical Draw ratio, and this is consistent with experimental results. Copyright © 2015 John Wiley & Sons, Ltd.     

Chromium-Assisted Oxidations with Sodium Perborate by Phase Transfer Catalysis

Oxidation by sodium perborate of selected alcohols and unsaturated compounds to ketones and acids was achieved at 60–80°C in the presence of catalytic amounts of chromium(VI) oxide and methyltridecylammonium chloride.