Medium effects on the acid dissociation constants of some diimine heterocyclic bases

The acid dissociation constants of the protonated form of diimine heterocyclic compounds (imidazole, 2-methylimidazole, 2,2-bipyridyl, and 1,10-phenanthroline) were determinedpH-meterically in aqueous media containing different amounts of organic solvents, viz. amphiprotic (methanol, ethanol), dipolar aportic (DMSO), and low basic aprotic (acetonitrile) at 25±0.1 °C. It was observed that by increasing the amount of alcohol orDMSO in the aqueous medium thepK _a, values of the investigated compounds decreased. On the other hand, thepK _a values increased as the amount of acetonitrile in the medium was increased. These results are discussed in terms of various solvent characteristics. It is concluded that solvent effects, viz. differences in stabilization of the free base by dispersion forces and of the proton by its interaction with solvent molecules in amphiprotic or dipolar aprotic solvent-aqueous media relative to that in pure aqueous one, as well as the basicity effect of acetonitrile play a vital role in the ionisation equilibria of the investigated compounds.

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Mediumeffekte auf die Säuredissoziationskonstanten einiger heterocyclischer Diimin-Basen

Zusammenfassung Die Säuredissoziationskonstanten der protonierten Formen der heterocyclischen Dimin-Basen Imidazol, 2-Methylimidazol, 2,2-Bipyridyl und 1,10-Phenanthrolin wurdenpH-metrisch in wäßrigem Medium mit einem Anteil an organischen Lösungsmitteln bei 25±0.1 °C bestimmt. Dabei wurden als amphiprotische Zusätze Methanol und Ethanol, als dipolar aprotisches organisches LösungsmittelDMSO und als aprotisches niederer Basizität Acetonitril ausgewählt. Es wurde beobachtet, daß bei ansteigenden Konzentrationen an Alkohol oderDMSO diepK _a-Werte der untersuchten Verbindungen kleiner werden. Andererseits bewirkt Acetonitril ein Ansteigen derpK _a-Werte. Die Ergebnisse werden mittels verschiedener Lösungsmittelparameter diskutiert. Lösungsmitteleffekte wie Stabilisierung der freien Base mittels Dispersionskräften, Protonwechselwirkungen in den verschiedenen Lösungsmittelgemischen und Basizitätseffekte des Acetonitril spielen dabei eine entscheidende Rolle.

     

UV/Vis spectroscopic behaviour of some new hydroxy azocoumarin derivatives

Summary The UV/Vis spectroscopic behaviour of six new hydroxy azocoumarin compounds in solution has been investigated. The observed bands are assigned to electronic transitions. Azocoumarin compounds exist mainly in the azo form, whereas 6-(2-hydroxy-6-aminonaphthyl-1-azo)-coumarin exhibits an azo-hydrazone tautomeric equilibrium. The solvatochromic behaviour of the azo compounds is investigated by studying their spectra in pure and mixed organic solvents of different characteristics. The longer wavelength band of the azocoumarins inDMF solution is assigned to an intermolecular CT transition.

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UV/Vis-spektroskopisches Verhalten einiger neuer Hydroxyazocumarinderivate

Zusammenfassung Das UV/Vis-spektroskopische Verhalten von sechs neuen Hydroxyazocumarinen in Lösung wurde untersucht. Die beobachteten Banden werden elektronischen Übergängen zugeordnet. Azocumarine liegen hauptsächlich in der Azoform vor, während 6-(2-Hydroxy-6-aminonaphthyl-1-azo)-cumarin eine Azo-Hydrazon-Tautomerie zeigt. Das solvatochrome Verhalten der Azoverbindungen wird durch Messung ihrer Spektren in reinen und gemischten organischen Lösungsmitteln mit unterschiedlichen Eigenschaften studiert. Die bei inDMF gelösten Azocumarinen auftretende langwellige Bande wird einem intermolekularen CT-Übergang zugeordnet.

     

Catalytic effects of galactose oxidase on micelle-forming galactolipids

Catalytic effects of galactose oxidase on the oxidation of beta-D-galactose-carrying lipids with an oligo-ethylene glycol spacer (number of ethylene glycol units (n)=1, 2, 3, 6, 9, 13, and 20) were examined. The affinity of galactose oxidase for the galactose residue in the amphiphile (estimated by the inverse of the Michaelis constant, K(m)) was much higher than those for free D-galactose and small beta-D-galactopyranosides, and dependent on the length of the ethylene glycol spacer. That is, both below and above the critical micellar concentration, the 1/K(m) values decreased with an increase in the n value. The effectiveness of the enzyme, which can be estimated by the k(cat)/K(m) value, showed the same tendency as the 1/K(m) value. These results could be attributed to the role of the nonpolar environment around the galactose residue in the binding by the enzyme. A significant enhancement of the enzymatic oxidation of galactose residue on the liposome surface was also observed.     

Rheology and Permeability of Crosslinked Polyacrylamide Gel

Gels produced by crosslinking polyacrylamide solutions with chromium (III) have been characterized by dynamic rheology studies. To vary the gel strength, different polymer concentrations were used, while keeping the temperature, salinity, and crosslinker concentration constant. Both the loss and storage moduli increased with the polymer concentration for this gel system. The storage modulus at the end of the gelation was used to characterize the gel strength. Steady-state water flow experiments through gel-filled capillary tubes were performed, with the aim of linking the gel strength and flow behavior. The permeability was found to be a function of the water flow rate (velocity) and polymer concentration. Two parameters were used to characterize the flow behavior, intrinsic gel permeability and elasticity index, which are each functions of the polymer concentration. However, only one parameter is needed to fully identify the flow and rheological gel properties, as the elasticity index and storage modulus are linked by a power-law relationship. The loss modulus and intrinsic permeability are correlated with the storage modulus and elasticity index, respectively. A theoretical model for this behavior linking both gel properties based on the dual domain structure was used to demonstrate that the flow and rheological behavior of the gel are indeed related and that the gel strength controls the water permeability. Implications for prediction of flow of water through gels emplaced in a porous medium are discussed.     

Retrievable magnetic copper ferrite nanoparticles: an efficient catalyst for air oxidative cyclization of bisnaphthols

Herein, a green and efficient heterogeneous and photocatalytic system for the oxidation of bisnaphthols in acetonitrile under light-emitting diode will be presented. In this reaction, aerial oxygen and H₂O₂ have been used as oxidant in the presence of copper ferrite nanoparticles and N-hydroxyphthalimide as an organic co-catalyst. Copper ferrite nanoparticles were magnetically separated, the efficiency of which remained nearly unchanged up to five cycles. Magnetic copper ferrite nanoparticles were synthesized by sol–gel method and characterized by XRD, FT-IR, SEM, TEM, VSM and DRS analysis. In this project, both sets of diastereomers were formed.

Graphical abstract

Catalytic system for the oxidation of bisnaphthols.

     

Highly Efficient Method for Synthesis of Bis(Indolyl)Methanes Catalyzed by FeCl3−based Ionic Liquid

A simple and highly efficient green protocol for synthesis of bis(indolyl)methanes was carried out by the reaction of indole with aldehydes and ketones in the presence of FeCl_3?based ionic liquid. These liquids serve as efficient media as well as Lewis acid catalysts.     

Numerical calculation of air entrainment rates due to intake vortices

In the present study, a numerical investigation was performed to estimate air entrainment rates due to intake vortices in different hydraulic conditions. The numerical model was verified with the experimental data. The agreement between numerical and experimental results for air entrainment rates and circulation was good. Regarding formed funnel shape flow pattern in the reservoir towards the horizontal intake, its boundaries at presence of vortices were analyzed. By considering the minimum air entrainment ratio as a new approach, critical submergence was also calculated numerically. Results showed that allowing minimum air entrainment ratio of β = 1 × 10^?5 can cause critical submergence decreases at least about 12%. Moreover, turbulence analysis and discussion were performed in the presence of vortex at the intake. This numerical simulation may be helpful to make a deeper understanding in determining the amount of entrained air and turbulence analysis in the presence of vortex and the critical submergence at horizontal intakes.     

Decoration of copper oxide nanoplatelets with gold nanoparticles by laser ablation in methanol for photodetection applications

In this work, CuO/n-Si and AuNPs-decorated CuO/n-Si heterojunction photodetectors were fabricated by deposition of CuO nanoplatelets and Au nanoparticles NPs decorated CuO nanoplatelets on silicon substrates by laser ablation in methanol. Atomic force microscope AFM, scanning electron microscope SEM and transmission electron microscope TEM were used to study the structural and surface morphology of CuO and AuNPs–CuO. The electrical properties showed that the CuO/Si and AuNPs decorated-CuO/Si showed rectifying behavior. The maximum values of quantum efficiency were about 41 and 78% at 700 nm for CuO/Si and AuNPs–CuO/Si photodetectors, respectively. The I–V characteristics of the photodetectors were measured under UV light.     

All optical 2-bit analog to digital converter using photonic crystal based cavities

A novel design for realizing all optical analog to digital converter will be proposed in this paper. The proposed structure consists of two main parts; a nonlinear 3-channel demultiplexer, followed by an optical coder. The nonlinear demultiplexer will be used to quantize the input analog signal according to its optical intensity and the coder will convert the quantized levels into 2-bit binary codes. The nonlinear demultiplexer will be realized using three nonlinear resonant cavities. At appropriate values of input signal optical intensity one of the cavities can drop the optical beam to its corresponding output port. The proposed structure is capable of supporting maximum sampling rate up to 52 GS/s and total footprint of the structure is about 924 µm².     

Magnetic field dependence of the relative critical current density in γ‐irradiated polycrystalline YBa2Cu3O7

The effect of different doses of γ‐rays on the behavior of the critical current density, J_c in an YBa₂Cu₃O₇ polycrystalline sample has been investigated at high temperatures. The samples were irradiated at room temperature by a ⁶⁰Co γ‐ray source at a dose rate of 0.5 MR/h. J_c was found to increase significantly with after irradiation dose of 10 MR. Further irradiation dose of 50 MR produced a slight and field dependent enhancement of J_c above its values at 10 MR. The most interesting result is that the relative change in the critical current density was found to have a non‐monotonic behavior with the applied magnetic field. These results are discussed in terms of the roles of several mechanisms created by γ‐rays in the regions of the grain boundaries combined with the effect of the magnetic field on these mechanisms. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)