Potentiometric acid-base properties of the chloroazoxine S dyes

The pK_a of the sulfonic group in the Azoxine S dye o-, m-, and p-chloro derivatives and the parent 7-phenylazo-8-hydroxyquinoline-5-sulfonic acid was determined potentiometrically. The indicators were prepared, obtained in the acid form by percolation through a cation exchange resin, and titrated with NaOH. The pK_a amounts to 3.69, 4.25, 3.65, and 3.71, respectively. Interpretation of the pK_a values is given.     

Spectral investigation of the intramolecular charge-transfer in some aminotriazole Schiff bases

3-Amino-1,2,4-triazole Schiff bases were reported to contain intramolecular charge-transfer. The enhancing and depressing effects were remarkable as the substituent was changed from electron-donating to electron-withdrawing groups. The path of the resonating delocalization was reversed in the case of the p-NO2 group. To validate these results we effectively used Weinhold et al's natural bond orbital analysis to assess the UV and FT-IR spectrophotometric monitoring of the change reflected in this phenomenon when the substituent in the benzene ring is altered. The NBO analysis was simulated by ab inito computations at the HF/6-31G(d) level of theory, in order to properly detect any possible presence of a hydrogen bond association. The changes occurring in electron occupancies of double-centered bonds, antibonding orbitals and in lone-pair orbitals appraised the results, as did the s and p character listings of the two-centered bonds and the simultaneous changes occurring in the geometric parameters of the molecules in question. Contrary to its normal preference, in these molecules the nitrogen used sp2 hybrid orbitals for its interaction, housing its electron lone-pair in the third p hybrid orbital. Furthermore, NBO analysis reflected the presence of a very soft intramolecular hydrogen association (C-H?π), labelled by UV and FT-IR assignments, between the benzene and triazole rings in all Schiff bases but p-N(Me)2. The n-π* stabilization energy decreased in the order: p-OH>p-OCH3>p-Cl>p-CH3>H>p-NO2>o-OH. The relation between the band position and Hammett substitution constant is interpreted in relation to the molecular structure.     

Density functional theory assessment of the thermal degradation of diclofenac and its calcium and iron complexes

Thermogravimetric analyses of diclofenac sodium, its Ca²⁺ and Fe³⁺ complexes manifested a decreasing trend of the onset decomposition temperatures at which these compounds dissociated. The drop in the temperature was metal ion dependent; the sodium salt showed thermal stability up to 245 °C, whereas the complexes started their degradation processes at temperatures starting from 90 °C. While G* for the cleavage of the acetate moiety in the sodium salt was 63.76 kJmol⁻¹, it was 82.06 and 140.57 kJmol⁻¹ in the cases of Ca²⁺ and Fe³⁺, respectively. However, their complete fusion took place at 187.65, 150.34 and 98.77 °C, respectively, displaying a reversed trend which is probably indicative of some catalytic part on the binding metals.

Using the Gaussian 98 W package of programs, ab initio molecular orbital treatments were applied to diclofenac and its Ca²⁺ and Fe³⁺ metal complexes to study their electronic structure at the atomic level. The thermochemistry of diclofenac sodium was followed through the TG fragmentation peak temperatures using the density functional theory calculations at the 6-31G(d) basis set level. The FT-IR data were in good agreement with the theoretically calculated values.

Single point calculations at the B3LYP/ 6-311G(d) level of theory, were used to compare the geometric features, energies and dipole moments of these compounds to detect the effect of the binding metal ions on the thermal dissociation of their diclofenac complexes.     

Radiolysis of NTA complexes with U(VI), Fe(III) and Ni(II)

The radiolysis of NTA complexes with U(VI), Fe(III) and Ni(II) has been studied spectrophotometrically at different pH values, at different doses of⁶⁰Co gamma-radiation. The absorbed doses were measured using the Fricke dosimeter. A clear relation between the radiolytic degradation of the complexes and the ligand concentration was observed. The G values were computed and compared with that of G(OH).