Kinetics and Thermodynamics of Solvolysis of a Cationic and an Anionic Chlorocobalt (III) Complex in Water–Ethanol Mixtures

Rate constants and derived thermodynamic activation parameters are reported for solvolysis of trans-[Co(3Mepy)₄Cl₂]⁺ and [Co(CN)₅Cl]^3– ions in water-rich mixtures of water with ethanol at various temperatures and are analyzed by initial- and transition-state contributions. The variation of enthalpies and entropies of activation with solvent composition show extrema in composition ranges where the physical properties of the mixtures, influenced by changes in solvent structures, also show extrema. From the application of a free-energy cycle to the process of the initial state going to the transition state, it is concluded for the solvolysis of both complexes that the Co(III) species in the transition state is more stable in water + ethanol mixtures than in the initial state.     

Equilibrium geometry and gas‐phase proton affinity of 2‐thiouracil derivatives

The ground‐state geometries of uracil, 6‐hydroxy‐uracil, and 6‐hydroxy‐, 6‐amino‐, 6‐methyl‐, 6‐trifluoro‐, and 6‐phenyl‐2‐thiouracil were optimized at the Hartree–Fock level. The molecular structures were fully optimized using the 6‐31G and 6‐31G* basis sets. The effect of substituents on the geometry and electronic structural features of 2‐thiouracils were examined. The perturbation effects of the OH and NH₂ groups are by far more pronounced on the geometric features and the dipole moment magnitude and direction of 2‐thiouracil. The potential energy per atom criteria was used to compare the relative tightness of binding in the studied series. Proton affinity and deprotonation enthalpy on each of the possible sites in 2‐thiouracil and its derivatives have been calculated at the 6‐31G/MP2 level of theory. The obtained results show that thiouracils behave as bases where they possess a high tendency to abstract protons. Substituents in the 6‐position have the general effect of enhancing the basicity strength of the thiocabonyl site in the order Ph < CH3 ≈ NH2 < OH. The CF3 group has the effect of reducing considerably the basicity strength and enhances the acidity strength at both N1 and N3. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Synthesis and efficiency of 5-(2-hydroxyphenylazo)-indazoles as new reagents for the determination of vanadium

Summary Four azo compounds based on 5-aminoindazole have been synthesized and characterized by elemental analysis as well as different spectroscopic techniques. The potentiality of the prepared compounds as new chromophoric reagents for the spectrophotometric determination of VO ₂ ⁺ was studied by extensive investigation of optimum conditions favouring the formation of the coloured complexes. The effect of interfering ions on the determination of VO ₂ ⁺ was investigated.Beer's law is obeyed in the concentration range of 1.0–12 µg/ml. The detection limits are 0.8, 0.9, 0.7, and 1.1 µg/ml using reagent1a,1b,1c, and1d, respectively. The standard deviations of the proposed method are 0.098, 0.111, 0.089, and 0.078. The molar absorptivities are 5.8, 6.7, 6.1, and 8.2×10³l·mol^–1·cm^–1 for1a–d, respectively, whereasSandell sensitivities are found to be 0.0187, 0.0163, 0.0174, and 0.0146 µg·cm^–2 using the same reagents. The ability of using these reagents as metallochromic reagents in complexon III titrations was also studied.

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Synthese und Leistungsfähigkeit von 5-(Hydroxyphenylazo)-indazolen als neue Reagentien zur Bestimmung von Vanadium

Zusammenfassung Vier von 5-Aminoindazol abgeleitete Azoverbindungen wurden synthetisiert und mittels Elementaranalyse sowie mit Hilfe verschiedener spektroskopischer Techniken charakterisiert. Die Einsatzmöglichkeiten der Verbindungen als Reagentien zur spektrophotometrischen Bestimmung von VO ₂ ⁺ wurde durch ausführliche Untersuchungen zur Ermittlung der optimalen Bedingungen für die Ausbildung der gefärbten Komplexe ausgetestet. Der Einfluß von Fremdionen auf die Ergebnisse wurde ebenfalls untersucht. DasBeer'sche Gesetz wird im Konzentrationsbereich von 1.0–12µg/ml befolgt. Die Nachweisgrenzen liegen bei 0.8, 0.9, 0.7 und 1.1 µg/ml für die Reagentien1a–d. Die entsprechenden Standardabweichungen betragen 0.098, 0.111, 0.089 und 0.078. Die Komplexe zeigen molare Extinktionen von 5.8, 6.7, 6.1 und 8.2×10³l·mol^–1·cm^–1 und Empfindlichkeiten nachSandell von 0.0187, 0.0163, 0.0174 und 0.0146 für die jeweiligen Verbindungen1a–d. Die Verwendungsmöglichkeit der neuen Verbindungen als metallochrome Reagentien bei Titrationen mit Komplexon III war ebenfalls Gegenstand der Untersuchungen.

     

Solochrome Green V as a new analytical reagent

Summary The acid-base properties of Solochrome Green V have been studied with the object of testing its use as a metal indicator or colorimetric reagent. The pK values of the three steps of ionisation of the free acid were evaluated. The dye has proved to be a suitable indicator in EDTA titrations of zinc and manganese as well as a colorimetric reagent for the microdetermination of zinc. The method is highly sensitive that by its application 0.05 ppm Zn can be determined with fair accuracy.     

Glow discharge in microfluidic chips for visible analog computing

Here we present a novel visible analog computing approach for solving a wide class of shortest path problems. Using a microfluidic chip for computation, based on the lighting up of a glow discharge, the solution to maze search problems, the solution of a network shortest path and k-shortest paths problems and the practical application of finding the shortest paths between several landmarks from a street map are presented. The solution and visible display (in real time) for these problems shows only a small difference in practical problem solving time among problems with varying differences in size.     

Synthesis and Some Reactions of Quinoxalinecarboazides

Chlorination of ethyl(quinoxalin‐2(1H)one)‐3‐carboxylate 1 gave ethyl (2‐chloroquinoxaline)‐3‐carboxylate 2 ;thionation of 1 by P₂S₅ or 2 by thiourea yielded the same product 3 . Reaction of chloro compound 2 or thiocompound 3 with hydrazine hydrate gave pyrazolylquinoxaline 4 . The reaction of ester 1 with thiourea or hydrazine hydrate afforded pyrimido quinoxaline 5 or carbohydrazide 6 ; the reaction of 6 with carbon disulfide in basic medium followed by alkylation afforded oxadiazoloquinoxaline derivatives 7, 8a,b . Carboazide 9 was produced by reaction of 5 with nitrous acid. Compound 9 on heating in an inert solvent, with or without amines, in alcohols or hydrolysis in H₂O undergoes Curtius rearrangments to yield 10‐13 . Reaction of 13 with thiosemicarbazide gave triazoloquinoxaline 14 which on reaction with alkylhalides or hydrazine hydrate yielded 15a‐c while hydrolysis of 13 gave 3‐aminoquinoxalinone 16 which was used as an intermediate to produce 17‐20 .     

Improved light uniformity and SNR employing new LED distribution pattern for indoor applications in VLC system

In this paper, a new LED arrangement design using 16 LED array in an indoor VLC system is introduced. The performance of the proposed design is investigated and compared with other different (previously introduced) designs using the same number of LED arrays. Our aim is to increase light uniformity and decrease power and SNR fluctuations across the room without increasing number of LED arrays. The received power and SNR were calculated to evaluate the system performance, while the root mean square delay spread was calculated to analyze the intersymbol interference impact on the system performance. The power standard deviation (STD) was calculated as well to measure uniformity of distributed power. The received power fluctuations under our proposed LED lamp arrangement were reduced from 4.46 to 0.93 dBm, the STD is decreased from 1.01 to 0.23, and the SNR fluctuations were reduced from 9 to 1.8 dB leading to almost identical communication across the entire room with high quality.     

Diminishing the Gap Between GC-Selective and Universal Detection by Capped Pd Nanoparticles

A simple Pd²⁺ ligand exchanger was prepared and applied for isolation of aromatic heterocyclic sulfur compounds (S-PAHs) from petroleum condensate oil. The ligand exhibited excellent isolation efficiency and selectivity towards S-PAHs. The chromatograms of pre-isolated S-PAHs recorded by universal flame ionization (FID) and mass spectrum (MS) detections are similar to selective sulfur atomic emission detector chromatograms, indicated from traces or absence of hydrocarbons in FID and MS chromatograms. Nitrogen adsorption, electronic microscope, and X-ray diffraction techniques were employed to confirm the formation of capped Pd²⁺ nanoparticle dispersion within the silica framework. The results obtained revealed that Pd²⁺ ions exist as dispersed capped nanoparticles sized between 69 and 79 nm that can be rationalized for their enhanced isolation selectivity towards the S-PAH fraction of petroleum condensate oil.     

Reassignment of the structures of condensation products of α-keto α′-formylarylhydrazones with ethyl cyanoacetate: a novel route to ethyl 5-arylazo-2-hydroxynicotinates

The condensation of α-keto α′-formylarylhydrazones with ethyl cyanoacetate afforded ethyl 5-arylazo-2-hydroxy-6-aryl (or alkyl) nicotinates. The structures of the reaction products could be established based on X-ray crystal structure determination.     

MHD of a fractional viscoelastic fluid in a circular tube

We investigate the effect of a transverse magnetic field on the unsteady flow of a generalized second grade fluid through a porous medium in a circular tube. Using fractional partial differential equations, we are able to describe the velocity and stress fields of the flow. We also obtain exact analytic solutions of these differential equations in terms of the Fox’s H-function.