Kyriakos Papadopoulos

Development and validation of a chemiluminogenic method for the evaluation of antioxidant activity of hydrophilic and hydrophobic antioxidants

A sensitive and simple procedure is described for evaluating the antioxidant activity of 21 known hydrophilic and hydrophobic compounds by using the chemiluminogenic reaction of lucigenin with hydrogen peroxide. The method was validated for linearity, limit of detection, precision, additivity and ruggedness and compared to the DPPH method. Furthermore, the IC(50) values of all compounds were calculated and compared by both methods and results are discussed on the basis of structure-antioxidant activity relationship. Among hydrophilic antioxidants, phenolic compounds with adjacent hydroxyl groups (gallic acid, caffeic acid, pyrocatechol, (+/-)-catechin, oleuropein) were found to be efficient antioxidants in chemiluminescence method with IC(50) values at the sub-micromolar range, while phenolic compounds without adjacent hydroxyl groups (p-coumaric acid, BHT, BHA, resorcinol) exhibited weak activity with IC(50) values>10microM. Alpha-tocopherol was the most efficient hydrophobic antioxidant (IC(50)=6.7microM) while oleic and linoleic acids were found to be very poor antioxidants (IC(50)>300microM). Finally the method was applied to the estimation of antioxidant activity of complex samples such as olive oils. To the best of our knowledge, this is the first time that total antioxidant activity can be determined directly in olive oil and not in aqueous extracts.

Flow-Based Methods with Chemiluminescence Detection for Food and Environmental Analysis: A Review

This paper presents an overview of flow-based methods in food and environmental analysis using chemiluminescence (CL) detection covering the period from 2005 to the present. The review discussses both automated flow methods of analysis [such as flow-injection analysis (FIA), sequential-injection analysis (SIA) and their variants] and separation techniques [liquid chromatography (LC) and capillary electrophoresis (CE) coupled to CL detection]. The most widely used CL reactions are presented together with representative applications in food and environmental analysis (determination of naturally occurring compounds, contaminants, additives as well as determination of inorganic and organic compounds).

Luminescent Methods in the Analysis of Untreated Edible Oils: A Review

The present review describes the application of luminescent methods in the analysis of edible oils without any pretreatment such as extraction prior to analysis. Emphasis has been given to applications of chemiluminescence and fluorescence assays for determining quality parameters of edible oils, such as oxidative stability, antioxidant activity, and lipid hydroperoxides content, as well as classification or adulteration of vegetable oils.

Modified DPPH and ABTS Assays to Assess the Antioxidant Profile of Untreated Oils

This research dwells on two widely used spectrophotometric methods, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays, which assess the free radical scavenging activity (RSA) of natural samples and standard compounds. In particular, these assays were modified in order to simplify the evaluation of RSA of untreated edible oils, as well as to assess the antioxidant profile of oils’ hydrophilic and lipophilic extracts with the same analytical procedure. A thorough study highlighted the effect of solvents on the DPPH and ABTS methods and resulted in selecting 2-propanol and an ethanol/1-butanol solvent mixture as the reaction solvent for the DPPH method and the ABTS method, respectively. The developed methods were used to evaluate the RSA of 12 antioxidant compounds and 8 edible oils. Then, the contribution of lipophilic and hydrophilic extracts to the total RSA of oils was estimated. The obtained results demonstrate the applicability of the method to routine edible oil analysis.

Novel Ru(II) sensitizers bearing an unsymmetrical pyridine-quinoline hybrid ligand with extended π-conjugation: synthesis and application in dye-sensitized solar cells

Heteroleptic ruthenium(II) sensitizers DV42 and DV51, encompassing a novel unsymmetrical pyridine-quinoline hybrid ligand with extended π-conjugation, were synthesized, characterized, and utilized in nanocrystalline dye-sensitized solar cells. Due to the extended conjugation of DV42 and DV51, the absorption of the corresponding sensitized TiO2 films extends into the red spectral range, shifted by 30-40 nm relative to the absorption of TiO2 films sensitized with the standard Z907 ruthenium(II) dye. Contact angle measurements of DV42- and DV51-sensitized TiO2 films suggest that these films are hydrophilic with contact angle values commonly observed upon sensitization with the standard N3 ruthenium(II) dye. Electrochemical studies of the novel ruthenium(II) dyes show that their first oxidation potentials lie well below the I(-)/I3(-) redox potential allowing easy regeneration. The excited-state oxidation potentials of both dyes lie above the TiO2 conduction band, permitting efficient electron injection from the excited dye molecules into the semiconductor conduction band. Liquid electrolyte dye-sensitized solar cells incorporating DV42- or DV51-sensitized TiO2 photoelectrodes afford overall power conversion efficiencies of 3.24 or 4.36% respectively. These efficiencies are up to 56% of the power conversion efficiencies attained by TiO2 photoelectrodes sensitized by the benchmark Z907 ruthenium(II) dye under similar experimental conditions.

Evaluation of antioxidant activity of hydrophilic and lipophilic compounds in edible oils by a novel fluorimetric method.

A novel fluorimetric method is described for the evaluation of the antioxidant activity of hydrophilic and lipophilic compounds and complex natural products such as edible oils. The method is based on the measurement of fluorescence emission intensity of N-methylacridone produced during the reaction of lucigenin with hydrogen peroxide. The presence of antioxidants in the sample inhibits the concentration of N-methylacridone and reduces the fluorescence intensity. The method was fully validated and applied to a variety of hydrophilic and lipophilic compounds as well as to various types of edible oils and their corresponding hydrophilic and lipophilic extracts. Results were compared to those derived from a lucigenin based chemiluminescent method and the Folin-Ciocalteau method for total phenols. The differences in total antioxidant activity of edible oils of various origins and the effect of heating on total antioxidant activity was further studied and discussed.

Evaluation of food antioxidant activity by photostorage chemiluminescence

A sensitive and simple method for measuring antioxidant activity was developed, based on antioxidant-dependant quenching of the chemiluminescence (CL) generated from photolyzed acridine and methanolic potassium hydroxide. This method was used to evaluate the antioxidant activity of food additives by measuring the inhibition of CL at a gradient of antioxidant concentrations. Adipic, tartaric, citric, ascorbic, malic, fumaric and 6-hydroxy-2,5,7,8-tetramethyl-2-carboxylic acid (Trolox) were employed as antioxidants. The method is more suitable for lipophilic compounds.

Radiochemiluminescence of acridones and alkyl acridities

Abstract Acridone and 9-benzylacridine in dialkylated amides are radiolyzed to novel acridan derivatives which emit light upon addition of strong bases regenerating acridone. The chemiluminescence quantum yields are as high as 2.4 × 10 −2 for acridone, while for the 9-benzylacridine 3.1 × 10 −3 einstein mol −1 . The acridone quantum yield is higher than those of most classical chemiluminescent reactions. The radiolysis and chemiluminescence mechanisms are discussed. The radiochemiluminescence reactions constitute prospective radiation dosemeters.

Chemiluminescence in organized molecular assemblies: lucigenin derivatives containing long alkyl chains in micellar media

Abstract The chemiluminescent reaction of five N,N ′-dilakyl-9,9′-biacridinium nitrates, C 1 , C 4 , C 6 , C 10 and C 12 , with hydrogen peroxide in alkaline aqueous and micellar solutions is reported. The chemiluminescence and chemiexcitation yields in these media are reported together with the chemical yields and the fluorescence quantum yields of the long chain N -alkylacridones, the primary emitters, in cationic, anionic and non-ionic micellar media. Based on the chemiluminescence profiles the reaction rate constants and chemiluminescence intensities are reported.

Green asymmetric synthesis: β-amino alcohol-catalyzed direct asymmetric aldol reactions in aqueous micelles.

The ability of chiral β-amino alcohols to catalyze the direct asymmetric aldol reaction was evaluated for the first time in aqueous micellar media. A family of cheap and easily accessible β-amino alcohols, obtained in one step from naturally occurring amino acids, was shown to successfully catalyze the asymmetric aldol reaction between a series of ketones and aromatic aldehydes. These aldol reactions furnished the corresponding β-hydroxy ketones with up to 93% isolated yield and 89% ee. (S)-2-phenylglycinol and Triton X-100 proved to be the best organocatalyst and surfactant, respectively.