Kinetics of Oxidation of 4-Oxoacids by <Emphasis Type="Italic">N</Emphasis>-Chlorosaccharin in Aqueous Acetic Acid Medium

The oxidation kinetics of substituted and unsubstituted 4-oxoacids (S) by N-chlorosaccharin (NCSA) have been studied in aqueous acetic acid media. The reaction follows first-order kinetics in each of the 4-oxoacids, NCSA and H⁺. The effect of changes in the electronic nature of the substrate reveals that positive charge develops in the transition state. Based on the kinetic results and product analysis, a suitable mechanism has been proposed for the reaction of NCSA with 4-oxoacids.     

Copolymers and two-layered composites of poly(<Emphasis Type="Italic">o</Emphasis>-aminophenol) and polyaniline

Electroactive conducting copolymers of aniline (ANI) and o-aminophenol (OAP) and two-layered poly(o-aminophenol) (POAP)/polyaniline (PANI) composites were prepared in aqueous acidic solution by electrode potential cycling. Copolymerization was carried out at different feed concentrations of OAP and ANI on a gold electrode. A strong inhibition of electropolymerization was found at a high molar fraction of OAP in the feed. The copolymers showed good adherence on the electrode surface and gave a redox response up to pH=10.0. Two transitions were observed in the in situ conductivities of the copolymers (as with PANI), but the conductivities were lower by 2.5–3 orders of magnitude as compared to PANI. Electrosynthesis of PANI on POAP modified electrodes showed copolymer formation after reaction initiation and finally formation of a PANI layer at the copolymer/solution interface. The ‘memory effect’ of the bilayer structures of both polymers was discussed in terms of protonation/deprotonation and anion consumption taking place during redox processes of both polymers.     

Ligand influence on the electrochemical behavior of some copper(II) thiosemicarbazone complexes

The redox properties of the title mono- and binuclear copper(II) chelates have been investigated by cyclic voltammetry in DMF at a working platinum electrode. The cathodic reduction and anodic oxidation of the investigated chelates produced the corresponding electrochemical Cu^I and Cu^IIIspecies stable only in the voltammetric time scale, The effects of substituents on E_1/2, redox properties and stability towards oxidation of the complexes were related to the electron-withdrawing or releasing ability of the substituents on the C=N¹[H, CH₃ or C₆H₅] and/or N⁴H [H, C₂H₅, C₆H₅ or pClC₆H₄] groups, The electron attracting substituents stabilize the Cu(II) complexes while electron-donating groups favor oxidation to Cu(III). Changes in the E_1/2 for the complexes due to remote substituent effects could be related to changes in basicity of N⁴H.Thus, variation in N⁴1-J has more influence on E_1/2 than changes in C=N¹. The correlation between E_1/2 of the complexes and pK_a of the ligands has been attributed to the spherical potential generated by the electron density of the donor atoms at the antibonding d orbitals.     

Darstellung und Kristallstruktur von LnAl3Br12 (Ln = La,Ce, Pr,Nd, Sm,Gd) und thermischer Abbau zu LnBr3

Preparation and Crystal Structure of LnAl₃Br₁₂ (Ln = La, Ce, Pr, Nd, Sm, Gd) and Thermal Decomposition to LnBr₃ LnAl₃Br₁₂ (Ln = La, Ce, Pr, Nd, Sm, Gd) was prepared in crystalline form for the first time. The crystal structures of LaAl₃Br₁₂, PrAl₃Br₁₂, and NdAl₃Br₁₂ were determined on single crystals by X-ray methods. The isotypic compounds crystallize with trigonal symmetry, space group P 3₁12, Z = 3. A structural comparison to lanthanoide chloroaluminates of equal composition is given and thermal decomposition of LnAl₃Br₁₂ (Ln = Nd) to the corresponding lanthanoide tribromide is described.     

Graphs to chemical structures. 4: Combinatorial enumeration of planted three-dimensional trees as stereochemical models of monosubstituted alkanes

Planted three-dimensional (3D) trees, which are defined as a 3D version of planted trees, are enumerated by means of Fujita’s proligand method formulated in Parts 1–3 of this series [Fujita in Theor Chem Acc 113:73–79, 80–86, 2005; Fujita in Theor Chem Acc 115:37–53, 2006]. By starting from the concepts of proligand and promolecule introduced previously [Fujita in Tetrahedron 47:31–46, 1991], a planted promolecule is defined as a 3D object in which the substitution positions of a given 3D skeleton are occupied by a root and proligands. Then, such planted promolecules are introduced as models of planted 3D-trees. Because each of the proligands in a given planted promolecule is regarded as another intermediate planted promolecule in a nested fashion, the given planted promolecule is recursively constructed by a set of such intermediates planted promolecules. The recursive nature of such intermediate planted promolecules is used to derive generating functions for enumerating planted promolecules or planted 3D-trees. The generating functions are based on cycle indices with chirality fittingness (CI-CFs), which are composed of three kinds of sphericity indices (SIs), i.e., a _d for homospheric cycles, c _d for enantiospheric cycles, and b _d for hemispheric cycles. For the purpose of evaluating c _d recursively, the concept of diploid is proposed, where the nested nature of c _d is demonstrated clearly. The SIs are applied to derive functional equations for recursive calculations, i.e., a(x), c(x ²), and b(x). Thereby, planted 3D-trees or equivalently monosubstituted alkanes as stereoisomers are enumerated recursively by counting planted promolecules. The resulting values are collected up to 20 carbon content in a tabular form. Now, the enumeration problem initiated by mathematician Cayley [Philos Mag 47(4):444–446, 1874] has been solved in such a systematic and integrated manner as satisfying both mathematical and chemical requirements.     

Cellulose microfibrils from banana farming residues: isolation and characterization

Cellulose microfibrils have been prepared from banana rachis using a combination of chemical and mechanical treatments. The morphology and structure of the samples were characterized using transmission electron microscopy, atomic force microscopy, and X-ray diffraction. Fourier-transformed infrared spectroscopy (FTIR) was used to characterize the chemical modifications of the samples after each treatment. Suspensions of bundled or individualized 5-nm-wide microfibrils were obtained after homogenization (PH) whereas an organosolv (PO) treatment resulted in shorter aggregates of parallel cellulose microcrystallites. The sharper rings in the X-ray diffraction pattern of the PO-treated sample suggest a higher crystallinity due to a more efficient removal of hemicelluloses and dissolution of amorphous zones by the acid treatment. Both microfibrils and microcrystals prepared by both methods can be used as reinforcing filler in nanocomposite materials.     

A way of establishing quality of measurements in gas analysis—national and international aspects

Standardising quality of measurements at both the national and international level results in a unity in measurement that may be regarded a synonym of traceability. In gas analysis, the key issue in achieving this aim is production of gaseous reference materials. Establishing a network of secondary measurement standards at gaseous CRM producers’ sites in Ukraine might be interesting for those involved in gas analysis activities. Inevitably, problems concerning the recognition of measuring capabilities of both national metrological institutes and local CRM producers are now an international issue. Thus, the problems of national adoption of international standards, as well as harmonisation between different international documents are currently relevant, and Ukrainian experience may be useful to others in this field. Presented at the 3rd International Conference on Metrology, November 2006, Tel Aviv, Israel.     

New In-situ Sampling and Analysis of the Production of CeO<Subscript>2</Subscript> Powders from Liquid Precursors using a Novel Wet Collection System in a rf Inductively Coupled Thermal Plasma Reactor. Part 1: Reactor System and Sampling Probe

A new reactor and a novel in-situ sampling technique were developed for the study of the synthesis of CeO₂ powders produced from dissolved cerium nitrate salts. The conical reactor minimized particle recirculation and provided a highly symmetrical and undisturbed plasma flow suitable for the analysis of the phenomena affecting the formation of CeO₂ powders. Both a calorimetric study of the reactor and a thermodynamic analysis of CeO₂ formation were conducted. The sampling probe is described and near-isokinetic sampling was achieved. The sampled particles were collected using a miniature wet collection system, i.e. a mist atomizer and a custom-made spray chamber. A numerical simulation of the velocity and temperature fields of the plasma gas in the reactor was done using Fluent. A comprehensive droplet-to-particle formation mechanism presented elsewhere is revisited and expanded based on calorimetry, thermodynamics of CeO₂ formation, numerical simulations and collected particles. No traces of other oxidation states other than CeO₂ were found.     

Preconcentration of Cadmium and Zinc on a Chelating Sorbent and Their Determination by Flame Atomic Absorption Spectrometry

A method is developed for cadmium and zinc preconcentration on a minicolumn packed with a new chelating polymer sorbent. The effects of the test solution pH and volume, the sample matrix composition, the eluent volume, and the sample and eluent flow rates are studied. Zinc and cadmium in the eluate are determined by flame atomic absorption spectrometry. Under optimal conditions, the determined ion recovery is more than 95%. The detection limits (3σ, n = 20) are found to be 15.0 (Cd) and 17.2 (Zn) ng/mL. The developed method is employed for cadmium and zinc determination in samples of seawater and water obtained after oil pumping.     

Flow-injection analysis with a small cylindrical wire type electrode

An amperometric detector with a small thin mercury film electrode is described. The device demonstrates advantageous operational characteristics such as small dispersion (D<2) and “memory effect” (me<0.6%), extensive maximum sample frequency (msf −200 samples/h), and high sensitivity. It has been proven useful in flow-injection analysis at a constant potential under hydrodynamic conditions.