Emilios Patsalides

Methods for testing antioxidant activity

Antioxidant activity has been assessed in many ways. The limitation of many newer methods is the frequent lack of an actual substrate in the procedure. The combination of all approaches with the many test methods available explains the large variety of ways in which results of antioxidant testing are reported. The measurement of antioxidant activities, especially of antioxidants that are mixtures, multifunctional or are acting in complex multiphase systems, cannot be evaluated satisfactorily by a simple antioxidant test without due regard to the many variables influencing the results. Several test procedures may be required to evaluate such antioxidant activities. A general method of reporting antioxidant activity independent of the test procedure is proposed.

Gas chromatography of some oxovanadium(IV) tetradentate β-ketoamine chelates

Abstract The gas chromatographic elution behaviour is reported, for the first time, for the oxovanadium(IV) chelates of seven tetradentate β-ketoamines on a non-polar column. Interaction with Chromosorb W as support is shown to be appreciably greater than with Chromosorb 750. Detection limits using the Chromosorb 750 support and flame ionization detection are less than nanogram amounts of elemental vanadium. The separation of copper and nickel from vanadium complexes is demonstrated.

Comparison of the liquid and gas chromatography of five classes of metal complexes

The chromatographic behaviour (GC and/or LC) of metal complexes of five ligand types (various salicylaldimines and Schiff bases, a fluorinated β-diketone and β-dithione and a hexadentate macrocycle) is reported. Metal ions included the lanthanides, transition metals, platinum, palladium, and zinc. Dissociation and thermal instabilities were seen as the main limitations in the chromatography of such derivatives. These effects were minimised by the use of selected multidentate or macrocyclic ligands. If the latter have suitable chromophore properties, they may be useful precolumn derivatizing reagents for trace metal analysis by LC. Diastereoisomers of oxovanadium(IV) complexes of tetradentate Schiff bases were resolved by both GC and LC.

Chromatographic and other properties of novel tetradentate tetraketo schiff base and chelates : Further evidence of isomerism in bidentate ketoenamines

Abstract The synthesis and characterisation of a new class of tetradentate Schiff bases obtained from the condensation of oxalyl chloride and the bidentate Schiff base 4- aminopent-3-en-2-one and its analogues are reported, together with their copper(II) and nickel(II) complexes. Data are presented from studies including gas chromatography, spectroscopy (infrared, mass and 1 H NMR), thermal analysis, cyclic voltammetry and measurements of dipole moments. In the chelates, the 1,2-dicarbonyl group at the bridge lowers their thermal stability, reverses the direction of the dipole moment with little change in magnitude, and gives rise to reversible electrochemical oxidation and reduction. Differences between chelates and the corresponding ligands are discussed in terms of electron delocalisation in the dicarbonyl bridge. Chromatographic and spectroscopic evidence supports the existence of structural isomers in the unsymmetrical tetraketo compounds, and, hence, in the original bidentate Schiff bases used in their synthesis.

Hexamethylmelamine: a study of solvation and crystallisation

Dielectric, electro-optic, and spectroscopic properties of hexamethylmelamine (HMM) are examined in various solvents. The study is an extension of earlier work relating the dielectric characteristics of solvent to the habit of HMM crystals, a factor of importance to the effectiveness of pulmonary administration of this drug in the treatment of human small-call lung carcinoma. In solution HMM is confirmed to be non-dipolar though abnormally large atomic polarisation is found. The optical polarisability anisotropy correlates with an extensively delocalised π-system involving the triazine ring and the exocyclic nitrogens. Interactions between HMM and cyclohexane, dioxane, and benzene are weak and not sterically defined—each of these solvents yields predominantly ‘compact’ crystal forms of HMM. In hexafluorobenzene definitive evidence is provided for strongly favoured stereospecific face-to-face HMM–C6F6 interactions. Needle-shaped crystals obtained from this solvent very rapidly become opaque and friable. Thermal analysis indicates an unstable 1 : 1 HMM–C6F6 adduct. This was confirmed by X-ray crystal structure determination which showed that HMM and C6F6 alternate in infinite columns, suggestive of a π–π interaction between the rings. The study provides an important correlation, based on experiment, between the statistically preferred HMM–C6F6 configuration in solution and that found for the crystalline adduct when isolated.

Kerr constants and dielectric polarisations of amides and thioamides in water and dioxane solutions

Measurements of dielectric polarisations and electric birefringences are reported for simple amides and thioamides in dilute aqueous and dioxane solutions. Interpretation of the exerimental data is made according to the Onsager, Block–Walker modified Onsager, and Lorentz models for the internal static field. The derived solute polarisability anisotropies from water are in fair concordance with those from dioxane provided the Onsager model is used. Combining refractivity and optical anisotropy data, polarisability tensor elements are derived for the solutes in water which are reasonably close to those in dioxane.

Dehydrogenation at the ethane bridge in transition metal chelates of tetradentate Schiff bases

Dehydrogenation has been induced, under mild conditions aided by palladized carbon, in the copper(II), nickel(II), palladium(II), and oxovanadium(IV) chelates of the tetradentate Schiff base 4,4′-(ethane-1,2-diyldiimino)bis(pent-3-en-2-one); the new compounds are readily distinguished from their parent compounds by column or layer chromatography.