The structure,magnetic and spectral properties of 4-acetylpyridine N-oxide complexes of copper(II) propionates

The synthesis and characterization of CuX₂L; (X = CH₃CH₂COO^?, ClCH₂CH₂COO^?, CH₃CHClCOO^? or CH₃CCl₂COO^?; and L = 4-acetylpyridine N-oxide) is reported. The characterization of these compounds was based on electronic, infrared and EPR spectra, as well as magnetic measurements over the temperature range. Several correlations between the spectral and magnetic data as well as pK_a values of the respective acids were found and discussed. On the basis of spectral and magnetic data the structures of the compounds are discussed.     

Imidazole-based excited-state intramolecular proton-transfer materials: synthesis and amplified spontaneous emission from a large single crystal

We have synthesized a novel class of imidazole-based excited-state intramolecular proton-transfer (ESIPT) materials, i.e., hydroxy-substituted tetraphenylimidazole (HPI) and its derivative HPI-Ac, which formed large single crystals exhibiting intense blue fluorescence and amplified spontaneous emission (ASE). Transparent, clear, and well-defined fluorescent single crystals of HPI-Ac as large as 20 mm x 25 mm x 5 mm were easily grown from its dilute solution. From the X-ray crystallographic analysis and semiempirical molecular orbital calculation, it was deduced that the four phenyl groups substituted into the imidazole ring of HPI and HPI-Ac allowed the crystals free from concentration quenching of fluorescence by limiting the excessive tight-stacking responsible for intermolecular vibrational coupling and relevant nonradiative relaxation. Fluorescence spectral narrowing and efficient ASE were observed in the HPI-Ac single crystal even at low excitation levels attributed to the intrinsic four-level ESIPT photocycle.     

Ghost orbitals in semiempirical methods. Estimation of basis set superposition error

Based on the all-valence ZDO SCF approximation a procedure for estimating the basis set superposition error (BSSE ) in semiempirical CNDO /INDO methods has been proposed. The results of the calculation show that the BSSE effect may improve the results obtained from the standard CNDO /INDO supermolecule calculation. The estimated BSSE effect enables one to explain some recently reported artificial structures for water and ethylene dimers.     

Identification of thiols by means of mercurated fluorescein

A method is proposed for the identification of thiols by examination of their complexes with tetra-acetoxymercurifluorescein (TMF). It is based on the determination of the fluorescence intensity as a function of pH and exciting wavelength, and of absorbance as a function of pH at 465 and 510 mmu. The relative fluorescence of the complexes does not depend on the wavelength of the exciting light in the range 460-500 mmu. The presence of a carboxyl group in the thiol molecule results in a strong increase of fluorescence with increasing pH and an exciting wavelength > 500 mmu.     

Circular dichroism of 9,10-dihydrophenanthrene derivatives reveals both the absolute configuration and conformation: a novel approach to Mislow's helicity rule

The absolute configuration and the conformation of 9,10-trans-disubstituted 9,10-dihydrophenanthrenes, known chiral metabolites of phenanthrene-9,10-oxide, have been determined by circular dichroism. The absolute configuration assignment is based on the sign of the long-wavelength Cotton effect (A-band), which is conformation invariant and originates from benzylic chirality. This provides a new interpretation of the Mislow biphenyl-helicity rule for the case of the 9,10-dihydrophenanthrene chromophore. The sign of the B-band Cotton effect reflects the conformation of the biphenyl chromophore in 9,10-dihydrophenanthrenes. It is shown that the origin of chiroptical properties of 9,10-dihydrophenanthrenes is closely related to those of 5,6-trans-disubstituted 1,3-cyclohexadienes.     

Colorimetric determination of palladium (II) by means of promazine hydrochloride

In acetate buffer medium palladium(II) ions form with promazine hydrochloride (PM) two complexes: an orange one of a formula [Pd(C₁₇H₂₀N₂S)]²⁺ (λ_max = 460 nm, ε = 4.5 × 10³, at 20 °C and pH = 2) and a violet one of a formula [Pd(C₁₇H₂₀N₂S)₂]²⁺ (λ_max = 540 nm, ε = 8.8 × 10³ at 20 °C and pH = 2).The values for instability constants determined by Bjerrum's method amount to pK₁ = 3.95; pK₂ = 3.07; pβ₁ = 3.95; pβ₂ = 7.02, respectively.A colorimetric method of the determination of palladium(II) has been elaborated. The method consists in a measurement of the absorbance of the violet complex of palladium(II) with promazine hydrochloride at λ = 540 nm. The method permits the determination of 2–17 μg Pd/ml with an error of ±2%. The time of the determination is 20 min. Iron(III), Ce(IV), Pt(IV), V(V), Cr(VI), and HNO₃ interfere with the determination.     

Dissociative recombination cross section and branching ratios of protonated dimethyl disulfide and N-methylacetamide

Dimethyl disulfide (DMDS) and N-methylacetamide are two first choice model systems that represent the disulfide bridge bonding and the peptide bonding in proteins. These molecules are therefore suitable for investigation of the mechanisms involved when proteins fragment under electron capture dissociation (ECD). The dissociative recombination cross sections for both protonated DMDS and protonated N-methylacetamide were determined at electron energies ranging from 0.001 to 0.3 eV. Also, the branching ratios at 0 eV center-of-mass collision energy were determined. The present results give support for the indirect mechanism of ECD, where free hydrogen atoms produced in the initial fragmentation step induce further decomposition. We suggest that both indirect and direct dissociations play a role in ECD.     

Thermal decompositions of zinc(II) benzenedicarboxylates

The thermal decompositions of zinc(II)benzenedicarboxylates were studied in air atmosphere at a heating-rate of 10 deg min^–1. Zinc phthalate and isophthalate were dehydrated in one step and next decomposed directly to ZnO. Zinc terephthalate was dehydrated in two steps and then decomposed directly to ZnO.

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Zusammenfassung Bei einer Aufheizgeschwindigkeit von 10°-min^–1 wurde die thermische Zersetzung von Zink(II)benzoldikarboxylat in Luft untersucht. Zinkphtalat und -isophtalat wird zunächst in einem Schritt dehydratisiert und anschließend zu ZnO zersetzt. Zinkterephtalat wird vor der endgültigen Zersetzung zu ZnO in zwei Schritten dehydratisiert.

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Electric and sorption properties of controlled pore glasses

A series of controlled pore glasses (CPG) was made from the same raw glass by means of different chemical and thermal treatments. BET specific area, selectivity of cesium adsorption in relation to sodium, ionosorption capacity under dynamic conditions of these CPG were measured and potentiometric titrations carried out. ₀ vs. pH curves show i.e.p. and c.i.p. values similar to those for silica. KOH treatment leads to increase of BET specific surface but ionosorption capacity is decreased.