Tris(2,4,6-trichloro-3,5-dinitrophenyl)methyl radical: a new stable coloured magnetic species as a chemosensor for natural polyphenols

2 pages, 3 figures, 1 table.-- PMID: 12610972 [PubMed].-- Available online Nov 25, 2002.We report the synthesis, electron paramagnetic resonance and electrochemical properties of a novel stable radical of the TTM series. Its strong electron acceptor ability has been tested with (–)-epicatechin, a natural polyphenolic antioxidant.Financial support for this work from the MEC (Spain) through project BQU2000-0789-C02-02 and PPQ2000-0688-C05-03.Peer reviewe

Copper(ii) complexes of macrocyclic and open-chain pseudopeptidic ligands: synthesis, characterization and interaction with dicarboxylates

This journal is © The Royal Society of Chemistry. Mono- and dinuclear Cu(ii) complexes were prepared with pseudopeptidic open chain and macrocyclic ligands, respectively. They were characterized by UV-vis spectroscopy, EPR, HRMS and X-ray diffraction. The Cu(ii) cation is coordinated by two amines and two deprotonated amides, in a slightly distorted square planar coordination geometry. The complexes interact with several substituted dicarboxylates, as shown by UV-vis titrations and EPR experiments. The interaction of both mono- and dinuclear complexes with very similar dicarboxylates of biological interest (malate and aspartate) resulted in strikingly different outcomes: in the first case a ternary complex [ligand⋯metal⋯dicarboxylate] was obtained almost quantitatively, while in the latter, the Cu(ii) displacement to form Cu(Asp)2 was predominant

Selective control of the radical-scavenging activity of poly(phenols) in aqueous media in terms of their electron-donor properties, using a stable organic radical as chemical sensor

The tri-potassium salt of tris(2,3,5,6-tetrachloro-4- hydroxysulphonylphenyl)methyl radical, 3K + TSPTM 3-, is a good chemical sensor of the radical-scavenging activity of poly(phenols) in aqueous media. Its water solubility and its stability at all pH values facilitates the study of the influence of the pH of the medium on the activity of poly(phenols). The radical-scavenging activity of three flavonoids of the catechol and pyrogallol type and the activity of catechol, pyrogallol and methyl gallate at pH values 7 and 8 which are close to physiological pH value (7.4) have been measured. This radical species reacts exclusively by an electron transfer mechanism against the reducing poly(phenols). Therefore, the experiments to determine the radical-scavenging activity of poly(phenols) with 3K + TSPTM 3- are related to their ionization potentials (IP). As IP is a function of the pH of the medium, the electron donor ability of a poly(phenol) depends on the acidity or basicity of the fluid in question. The radical-scavenging activity of poly(phenols) 1-6 is higher at pH 8 than at pH 7. 3K + TSPTM 3- is able to discriminate between catecholic and pyrogallolic moieties of poly(phenols) in water solutions by taking measurements at different pH values. By adjusting the pH of the medium 3K + TSPTM 3- will easily detect those moieties (e.g. pyrogallol) most prone to elicit prooxidant effects. © 2012 Elsevier B.V. All rights reserved.Financial support for this research from the MCI (Spain) through projects AGL2009-12374-C03-03/ALI and CTQ2009-13797 is gratefully acknowledged. J.A.M. gratefully acknowledges the Spanish Foreign Office Department for a pre-doctoral grant (AECI).Peer Reviewe

Reducing activity of polyphenols with stable radicals of the TTM series. Electron transfer versus H-abstraction reactions in flavan-3-ols

4 pages, 2 figures, 2 schemes, 2 tables.-- PMID: 15548081 [PubMed].-- Printed version published Nov 25, 2004.A new method to test the antioxidant activity of polyphenols by electron transfer reactions to a stable organic free radical, tris(2,4,6-trichloro-3,5-dinitrophenyl)methyl radical (HNTTM), is reported. Therefore, the activity of the natural flavanols, (−)-epicatechin, and two synthetic derivatives, 4β-(S-cysteinyl)epicatechin and 4β-(2-aminoethylthio)epicatechin, can be differentiated by their capacity to transfer hydrogen atoms to 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and to transfer electrons to HNTTM.Financial support for this research from the Spanish Ministry of Science and Technology through Project PPQ2003-06602-C04-01.Peer reviewe

An EPR analysis of β-dimerization in α-blocked pyrroles in oxidant conditions

Electron paramagnetic resonance (EPR) analysis of neutral and acidic solutions of 2,5-dimethyl-1-phenylpyrrol (1) and meta-, para-, and ortho-bis(2,5-dimethylpyrrol-1-yl)benzenes (4–6) in the presence of Tl(III) trifluoroacetate as oxidant reveals the poor stability of their generated monomeric radical cations which dimerize through C(β)[BOND]C(β) bond formation. EPR spectra of the monomeric radical cations 4•+, 5•+, and 6•+ coincide with that of 1•+, suggesting that the unpaired electron in these charged species is confined in one of the pyrrolic rings. The very twisted angles between pyrrolic and phenyl planes due to steric hindrance in the X-ray analysis of the molecular structure of 4 confirm the absence of extended conjugation in the π-system.Financial support from the MeI (Spain) through project AGL2009-12374-C03-03/ALI is gratefully acknowledged. We also thank the EPR service of the Centre d'Investigació I Desenvolupament (CSIC) for recording the spectra.Peer reviewe

A tri(potassium sulfonate) derivative of perchlorotriphenylmethyl radical (PTM) as a stable water soluble radical-scavenger of the hydroxyl radical more powerful than 5,5-dimethyl-1-pyrroline-N-oxide

The tripotassium salt of tris(2,3,5,6-tetrachloro-4-hydroxysulfonylphenyl) methyl radical (3 K+ TSPTM3-) reacts in water with hydroxyl radical very fast with a rate constant (k = 2.4 × 1011 M-1 s-1) much higher than that of the reaction of hydroxyl radical with the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) (k = 3.4 × 109 M-1 s-1). The reaction affects the radical character of the molecule and is monitored by electron paramagnetic resonance (EPR). The hydroxyl radical scavenging is established by the characterization of the resulting water-soluble product as the dipotassium salt of 4-[bis(2,3,5,6-tetrachloro-4-hydroxysulfonylphenyl)methylene]-2,3,5,6- tetrachlorocyclohexa-2,5-dien-1-one (2). © 2013 The Royal Society of Chemistry.Financial support for this research from the Spanish Ministry of Science and Innovation through projects AGL2009-12374- C03-03/ALI and CTQ2009-13797 is gratefully acknowledged. J.A.M. gratefully acknowledges the Spanish Foreign Office Department for a pre-doctoral grant (AECI).Peer Reviewe

High electron transfer capacity of thio-derivatives of tea catechins measured using a water soluble stable free radical and their effects on colon cancer cells

The antiradical capacity of cysteamine- and cysteine-flavan-3-ol derivatives of green tea catechins bearing the pyrogallol moiety was evaluated using two stable triphenylmethyl radicals, the tri-potassium salt of a tris(4-hydroxysulfonyltetrachlorophenyl)methyl radical (K3TSPTM) and a tris(2,4,6-trichloro-3,5-dinitrophenyl)methyl radical (HNTTM), as chemosensors in a buffer solution at pH 7 and in the CHCl3-MeOH mixture (2:1, v/v), respectively. The different results obtained using HNTTM or K 3TSPTM lie in the chemical nature of these radicals and, therefore, in their reduction potentials, and in the solvent used in the experiments. The K3TSPTM radical was selectively sensitive to the pyrogallol moiety in water like TNPTM was in organic solvents, and as a chemosensor is closer to the biological processes by using aqueous media as solvent. The new radical is a useful tool to detect highly reactive phenolic positions that are also the most biologically active as shown by the results on the viability and apoptosis of the colon adenocarcinoma cell line HT-29. © 2013 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.Financial support from the MCI (Spain) through projects AGL2009-12374-C03-03/ALI, SAF2008-00164 and CTQ2009-13797, the Instituto de Salud Carlos III and European Regional Development Fund (ISIII-RTICC, RD06/0020/0046), the Generalitat de Catalunya (2009SGR1308, 2009CTP 00026, and Icrea Academia award 2010 granted to M.C.), and the European Commission (Etherpaths Project KBBE-Grant Agreement 222639) is gratefully acknowledged. J.A.M. gratefully acknowledges the Spanish Foreign Office Department for a pre-doctoral grant (AECI).Peer Reviewe

Synthesis of a new stable and water-soluble tris(4-hydroxysulfonyltetrachlorophenyl)methyl radical with selective oxidative capacity

A new stable organic free radical of the PTM (perchlorotriphenylmethyl) series very soluble in water is reported. This free radical is sensitive to electron transfer processes, and the selectivity of these reactions in the presence of ascorbic acid, pyrogallol, and catechol as reducing species is described. The electron paramagnetic resonance spectrum and the electrochemical behavior are also presented.Financial support for this research from the MCI (Spain) through project AGL2009-12374-C03-03/ALI is gratefully acknowledged. J.A.M. gratefully acknowledges the Spanish Foreign Office Department for a predoctoral grant. We also thank the EPR service of the Advanced Research Institute of Catalunya (CSIC) (Spain) for recording the EPR spectra and the scientific-technical services of the University of Barcelona for recording the mass spectra.Peer reviewe

EPR/Spin-trapping study of free radical intermediates in the photolysis of trifluoromethyl ketones with initiators

Photolysis of trifluoromethyl ketones (TFMKs) 1a–1e versus the non-fluorinated ketones 2a–2b in the presence of radical initiators by electron paramagnetic resonance spectroscopy has been studied for the first time. The transient radicals generated after irradiation of the ketones were identified by trapping with 2-methyl-2-nitrosopropane (MNP) and 2,4,6-tri-tert-butylnitrosobenzene (TTBNB) as spin traps. TTBNB is a powerful, particularly useful spin trap in these kinds of processes producing anilino and nitroxyl spin adducts due to the ambivalent reactivity on the N and O atoms. In the presence of t-butylperoxide, short-chain TFMKs, such as 1,1,1-trifluoroacetone (1d) and hexafluoroacetone (1e), give rise to detection of the elusive trifluoromethyl radical. In contrast, long-chain TFMKs did not provide clues to prove formation of the trifluoromethyl radical but instead to radicals derived by abstraction of one α-methylene proton to the carbonyl. Although TFMKs are quite stable to photodegradation in the absence of initiator, methyl ketone 2b and phenyl ketone 3 produce radicals resulting from abstraction of a γ-hydrogen to the carbonyl group.We gratefully acknowledge CSIC for an Associated Unit UdL-CSIC fellowship to E. Rosa and CICYT (projects AGL 2006-13489-C02-01, AGL 2006-12210-C03-02 and PPQ2003-06602-C04-01) for financial support.Peer reviewe