Oxidative Cleavage of S–S Bond During the Reduction of Tris(pyridine‐2‐carboxylato)manganese(III) by Dithionite in Sodium Picolinate–Picolinic Acid Buffer Medium

The reduction of tris(pyridine‐2‐carboxylato)manganese(III) by dithionite has been investigated within the temperature window 288–303 K and at pH range 5.22–6.10 in sodium picolinate–picolinic acid buffer medium. The reaction obeys the following stoichiometry: The reaction is described in terms of a mechanism that involves an initial complex formation between S₂O₄^2? and [Mn^III(C₅H₄NCO₂)₃] followed by S–S bond cleavage to give 2HSO₃^? and [Mn^II(C₅H₄NCO₂)₂(H₂O)₂] as the products via the formation of SO₂^●? radical anion. Kinetics and spectrophotometric evidences are cited in favor of the suggested mechanism. Thermodynamic parameters associated with the equilibrium step and the activation parameters with the rate‐determining step have been computed.     

Synthesis and characterization of low bandgap copolymers based on indenofluorene and thiophene derivative

A series of low band gap, highly soluble alternating conjugated copolymers, comprised of 11,11,12,12‐tetrahexylindenofluorene and thiophene derivatives ( P1‐P4 ), were synthesized via Pd‐catalyzed Suzuki coupling reaction with very good yields. Described here are the synthesis, thermal, optical, and electrochemical properties of these new copolymers as potential new active materials for electronic and optoelectronic device applications. P1 and P2 have electron donating non‐π‐substituents with ethylenedioxy and propylenedioxy bridging the 3,3 positions of the cyclopentadithiophene groups; whereas P3 and P4 have electron withdrawing π‐substituents (carbonyl and pyrazine groups on P3 and P4 , respectively). For the main absorptions in UV‐vis spectrum, P1 and P2 displayed more red absorptions in comparison with P3 and P4 . Nevertheless, much suppressed quantum yields are exhibited by P3 and P4 . The behaviors of P3 can be attributed to the significant charge transfer interactions between the π‐substituents and the conjugated polymer backbone that leads to a less allowed optical transition between the ground and the lowest excited state. For P4 , the weak fluoresence might associate with energy transfer from indenofluorene to the low band gap thiophene‐pyrazinethiophene‐thiophene (T‐PT‐T) unit. In comparison with the corresponding polymers containing fluorene instead of indenofluorene, the use of indenofluorene exhibited mixed effects on the optical properties and improved solubility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5044–5056, 2009     

The effect of extragent properties on the distribution of carboxylic acids

It has been established that the generalization of data on the distribution of carboxylic acids between organic and aqueous phases using the multiparameter linear free energy equations is preferential to using the London-Debye-Keesom potentials, which requires nonpolar and polar extragents to be examined separately. The formation of hydrogen bond between the components, which is determined by the basicity of an extragent, was shown to have an effect on the distribution value.     

Bis-chelate tetracarbene palladium(II) complex as an efficient and recyclable catalyst precursor for Heck reaction

A homoleptic Pd(II) complex with two chelating di-N-heterocyclic carbene (NHC) ligands has been synthesized and its square planar molecular geometry has been determined by X-ray diffraction analysis. The complex proved to be an efficient catalyst having exceedingly high turnover number and good reusability in Heck reaction.     

Experimental investigation of slosh dynamics of liquid-filled containers

This paper is concerned with the experimental studies on the sloshing response of liquid-filled containers. A three-dimensional finite element analysis is carried out for the numerical simulation of this problem. The effects of sloshing are computed in the time domain using Newmark's time integration scheme. A simple experimental setup is designed and fabricated in-house to conduct experiments for measuring some of the basic parameters of sloshing. A sensor device is especially developed to record the free-surface wave heights. Each wave height sensor is a capacitance probe that detects the change in level of liquid (water) precisely with no time lag. The sensors are used in conjunction with a signal-processing unit in which the capacitance values are transduced to a voltage signal between 0 V and 10 V. These wave height sensors simultaneously record the slosh wave height near the periphery of the container wall from 16 predetermined locations to give the free-surface profiles of liquid at desired time steps. The experimental results are compared with those obtained from the present theoretical analysis, and good agreements are observed.     

Oxanorbornenes: promising new single addition monomers for the metathesis polymerization

Higher ring-opening metathesis propagation rates of exo-norbornene derivatives over endo derivatives are well established in the literature. Here, we report for the first time that endo-isomers of oxanorbornene derivatives show higher reactivity towards ring-opening metathesis with Grubbs'' 3rd generation catalyst (G3) than the corresponding exo-isomers. A very high selectivity for the reaction of G3 with endo over the exo-isomers could be shown. Furthermore, single molecular addition of the endo-isomers with G3 was observed. On the other hand, pure exo-monomers could successfully be homopolymerized. Mixtures of exo- and endo- monomers, however, prevented the homopolymerization of the exo-monomer. Such mixtures could successfully be copolymerized with cycloalkenes, resulting in alternating copolymers. An oxanorbornadiene derivative could be shown to undergo single addition reactions, exploited in the preparation of mono-end functional ROMP polymers. These could be selectively derivatized via endgroup selective thiol-ene click reactions. A thiol and alcohol end functional ROMP polymer was synthesized, and the efficient end functionalization was confirmed by ¹H NMR spectroscopy and MALDI-ToF spectrometry.

Bridgehead revisited: endo-7-oxa norborneneimide derivatives (green) initiate faster but propagate more slowly than the analogous exo-derivatives (red) in ring-opening metathesis allowing the synthesis of alternating and end functional polymers.     

Excess Molar Volumes and Excess Partial Molar Volumes of Triethylene Glycol Monoethyl Ether–n-Alcohol Mixtures at 25°C

We have measured excess molar volumes V^E _m of binary mixtures of triethylene glycol monoethyl ether with methanol, ethanol, 1-propanol, 1-pentanol, and 1-hexanol over the full range of compositions at 25°C. The measurements were carried out with a continuous-dilution dilatometer. The excess molar volumes V^E _m are negative over the entire range of composition for the systems triethylene glycol monoethyl ether + methanol, + ethanol, and + 1-propanol and positive for the remaining systems, triethylene glycol monoethyl ether + 1-pentanol, and + 1-hexanol. The excess V^E _m increases in the positive direction with increasing chain length of the n-alcohol. The measured excess volumes have been compared to our previous published data with an effort to assess the effects of replacing methyl by ethyl groups and of inserting oxyethylene groups. The results have been used to estimate the excess partial molar volumes V^E _m,i of the components. The behavior of V^E _m and V^E _m,i with composition and the number of carbon atoms in the alcohol molecule is discussed.     

Enhanced Adsorption of Hexavalent Chromium onto Magnetic Calcium Ferrite Nanoparticles: Kinetic,Isotherm, and Neural Network Modeling

Calcium ferrite nanoparticles with super-paramagnetic behavior were synthesized via simple chemical precipitation method for effective removal of hexavalent chromium from aqueous media. The properties of synthesized nanoparticles were studied by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), and vibrating sample magnetometer (VSM) measurements. The ferrite nanoparticles have shown polycrystalline nature and high BET specific surface area (229.83 m²/g) with active functional groups on the surface. The adsorption process follows second-order kinetics with the involvement of intra-particle diffusion and adsorption capacity as much as 124.11 mg/g was determined from the Langmuir isotherm. The thermodynamic analysis revealed that the adsorption process was feasible, spontaneous, and exothermic in nature. A three-layer feed-forward back-propagation artificial neural network (ANN) model was employed to predict the removal (%) of Cr(VI) ions as output. Optimal ANN network (4:8:1) shows the minimum mean squared error (MSE) of 0.00161 and maximum coefficient of determination (R²) of 0.984. The adsorption process is mostly influenced by solution pH and followed by adsorbent dosage, initial Cr(VI) concentration, and contact time as illustrated by sensitivity analysis. With small size and high surface area, biocompatibility, ecofriendly nature, easy magnetic separation, and enhanced adsorption capacity towards Cr(VI), calcium ferrite nanoparticles will find its potential application in wastewater remediation.     

Synthesis of Novel Drug‐Like Small Molecules Based on Quinoxaline Containing Amino Substitution at C‐2

A series of novel “drug‐like” small molecules based on quinoxaline containing amino substitution at C‐2 were synthesized. All these molecules were prepared either via the reaction of 2‐phenyl‐3‐(piperazin‐1‐yl)quinoxaline with acyl bromides or benzyl bromides or various carboxylic acids or via the reaction of 2‐chloro‐3‐phenylquinoxaline with various amines. The structures of these novel compounds were confirmed by spectral analysis. The strategy used is simple and efficient and afforded good yields of quinoxaline derivatives.