Synthesis, X-ray structure and properties of a new nitrite-bound copper(II) complex with 2-(3,5- dimethylpyrazol-1-ylmethyl)pyridine in a CuN4(O) coordination

Synthesis and characterization of a nitrite-bound copper(II) compound [CuL⁴)₂(ONO)]ClO₄ have been achieved (L⁴ = 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine]. The bidentate ligand L⁴ provides a pyridine and a pyrazole donor site; however, they are separated by a methylene spacer. The complex has been structurally characterized and it belongs to only a handful of complexes having nitrito-bound mononuclear copper(II) centre. The metal atom has a distorted square pyramidal geometry with the copper atom displaced from the equatorial plane by 0.25 Å. In MeCN solution the green complex exhibits a broad ligand-field transition at 655 nm with a shoulder at 675 nm and in dichloromethane-toluene glass (80 K) it exhibits an EPR spectral feature characteristic of the unpaired electron in the d_x²−y² orbital. Variable-temperature (80–300 K) magnetic susceptibility measurements in the solid state as well as room temperature measurement in MeCN solution reveal mononuclear magnetically dilute copper(II) centre. When examined by cyclic voltammetry (MeCN solution) it displays electrochemically irreversible Cu^II---Cu^I response [cathodic peak potential, E_pc (V vs saturated calomel electrode (SCE)): −0.32]. An oxidative response is observed at 1.14 V, probably due to bound-nitrite oxidation and is partially removed to generate a solvated complex at the electrode surface. The latter species gives rise to reversible Cu^II---Cu^I redox response [ ].     

Stability of AQUO-organic silver iodide sol

Summary The coagulation concentration for silver iodide sol, both in presence of pyridine and dioxane, increases for mono- and bivalent coagulating electrolyte. In presence of a mixture of pyridine and dioxane in equal volume, the coagulation concentration assumes an intermediate value, which is nearer to dioxane. However, in presence of dioxane more bivalent electrolyte is needed than in presence of pyridine. If a bivalent coagulating electrolyte is added to a sol containing a mixture of pyridine and dioxane, the amount of electrolyte required to coagulate is less than pyridine and greater than dioxane. Thus silver iodide sol is more stable toward mono- and bivalent coagulating electrolytes. The degree of stabilization increases with the decrease of the dielectric constant of the dispersing medium. The intermediate values for dioxane pyridine mixture is accountable by the fact that dioxane acts as a solvent for pyridine. The PH value of the sol increases up to the coagulation point. Beyond this, there is an abrupt decrease. When the particles settle down completely a rise in PH is again noted on the further addition of electrolytes. The increase in the electrical conductance is more significant after coagulation. These changes have been explained by adsorption of the ions and due to the release of ions from the electrical double layer.

---

Zusammenfassung Die Koagulationskonzentration für Silberjodidsol in Gegenwart von Pyridin und Dioxan steigt für ein- und zweiwertige Elektrolyte an. In Gegenwart einer Mischung zu gleichen Volumen erh?lt man mittlere Werte, n?her denen zu Dioxan. Für Koagulation in Gegenwart von Dioxan ist jedoch mehr zweiwertiger Elektrolyt notwendig als in Gegenwart von Pyridin. Bei Koagulation mit zweiwertigem Elektrolyt verbraucht ein Sol mit der Mischung von Pyridin und Dioxan weniger als für Pyridin und mehr als für Dioxan. Daher ist das Silbersol gegenüber ein- und zweiwertigen Elektrolyten stabiler. Der Grad der Stabilisierung w?chst mit abnehmender Dielektrizit?tskonstante des Dispersionsmediums. Die Zwischenwerte der Dioxan-Pyridin-Mischungen lassen sich verstehen durch die Tatsache, da? Dioxan als L?sungsmittel für Pyridin wirkt. Der PH-Wert des Sols w?chst bis zum Koagulationspunkt, darüberhinaus erfolgt ein steiler Abfall. Wenn die Teilchen vollst?ndig absetzen, ist bei weiterer Zugabe von Elektrolyt ein erneuter Anstieg im PH feststellbar. Der Anstieg der elektrolytischen Leitf?higkeit wird nach der Koagulation ausgepr?gter. Diese ?nderungen lassen sich durch Ionenadsorption und Freiwerden von Ionen aus der elektrischen Doppelschicht erkl?ren.

---

---

Our thanks are due to Prof. R. C. Mehrotra for providing all the facilities for this work and to Prof. S. Ghosh of Allahabad University for helpful discussions. Thanks are also due to the University Grants Commission, Government of India, for the award of a research scholarship to one of us (V. K. S.).     

Spectrophotometric determination of traces of selenium(IV) in various environmental samples using the flow-injection technique (FIT)

A simple, sensitive, and rapid flow-injection spectrophotometric method was developed for the determination of trace amounts of selenium(IV). The method is based on the oxidation reaction of 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) by selenium(IV) followed by the coupling reaction with chromotropic acid (4.5-dihydroxy naphthalene-2.7-disulphonic acid) in a basic medium (phosphate buffer, pH 10.5) to give a pink derivative with λ_max 530 nm that is stable for more than 7 days at 35°C. The reaction and flow conditions of the full experimental design were optimized. A detection limit (2s) of 0.25 μg/L Se(IV) was obtained at a sampling rate of 10 samples per hour. Beer’s law is obeyed for a Se(IV) concentration range of 0.05–0.5 μg/mL at the wavelength of maximum absorption. The detailed study of various interference ions indicates that the method is highly selective. The method was successfully applied to the determination of traces of selenium(IV) in various water samples. The results obtained were in good agreement with those obtained by the reported methods at the 95% confidence level. The text was submitted by the authors in English.     

Kinetics of substitution of aquo ligands fromcis-diaquo-bis-(biguanide) cobalt(III) and chromium(III) ions by aspartic acid in ethanol—water mixtures

The kinetics of substitution of aqua ligands fromcis-diaqua-bis(biguanide)cobalt(III) and chromium(III) ions by aspartic acid in EtOH–H₂O media have been studied spectrophotometrically in the 30 to 45°C range. We propose the following rate law for the anation

Silica-alumina supported transition metal oxide catalyst for alkylation of aromatic compounds

Titanium oxide on silica-alumina support is described to be an efficient regenerable catalyst for alkylation of aromatic compounds with alkyl halides, alcohols and olefins, and the reaction is proposed to be initiated by the protonated metal active species present in the catalyst.     

On the characterization of electrified interface

Summary Estimation of zeta potential from experimental data on electroosmotic and electrophoretic effects for Zeokarb 225 (Na⁺ form)/methanol-water system has been made and discussed. Results indicate that zeta potentials estimated from electroosmotic flux and electrophoretic mobility are not in agreement and vary with applied potential difference in a linear manner. Reasons for the variation of zeta potential with electrical field have been discussed. It has been argued that zeta potentials estimated from electroosmotic data are more reliable in comparison to the values obtained from electrophoretic data.With 2 figures and 2 tables     

Solution- and solid-phase synthesis of natural product-like tetrahydroquinoline-based polycyclics having a medium size ring

A solid-phase synthesis of tetrahydroquinoline-derived polycyclic 4, having a medium size ring with an enamide functionality, was achieved from tetrahydroquinoline derivative 3 in five steps with overall 40-45% yield. An enantiopure, tetrahydroquinoline-derived beta-amino ester, 1, was converted into compound 2 that has a free phenolic hydroxyl group as an anchoring site for solid-phase synthesis. The solid-phase worked well for this sequence, in which the synthesis of the unsaturated eight-membered enamide lactam was obtained by a ring-closing metathesis approach. Compound 4 is a novel, natural product-like polycyclic derivative that could further be utilized in library generation for developing small molecule chemical probes.     

A Sensitive Spectrophotometric Determination of Nitrite in Water and Soil

A highly sensitive spectrophotometric method for the determination of nitrite in water and soil has been developed. The reaction of nitrite with acidified potassium iodide to liberate iodine which oxidizes leuco‐crystal violet (LCV) to form crystal violet having absorption maxima at 590 nm forms the bases of this method. In aqueous medium the system obeys Beer's law in the range of 0.1 to 1.0 μg per 25 mL (0.004–0.04 ppm), while in an extractive system the range is 0.025–0.25 μg in 100 mL (0.00025–0.0025 ppm). The molar absorptivity and Sandell's sensitivity were found to be 1.54 × 10⁶ 1 mol^?1 cm^?1 and 44 pg cm^?2, respectively.     

Nucleation of β-hairpin structure in a pyrrole amino acid containing peptide

Synthesis and conformational studies of two short peptides containing pyrrole amino acids (1, Paa), Boc-Paa-Paa-d-Pro-Gly-Xaa-Paa-Paa-OMe (2: Xaa=Ala; 3: Xaa=Val), were carried out in which it was established that replacement of Ala in 2 with a Val residue helps peptide 3 to adopt a well-defined β-hairpin conformation in a nonpolar solvent, like CDCl₃.