Luis Juliá

Cysteinyl-flavan-3-ol conjugates from grape procyanidins. Antioxidant and antiproliferative properties.

New bio-based antioxidant compounds have been obtained by depolymerisation of grape polymeric flavanols in the presence of cysteine. Their preparation and purification, as well as their antiradical/antioxidant and antiproliferative properties are reported. 4beta-(S-cysteinyl)epicatechin 5, 4beta-(S-cysteinyl)catechin 6 and 4beta-(S-cysteinyl)epicatechin 3-O-gallate 7 were efficiently purified from the crude depolymerised mixture by cation-exchange chromatography and preparative reversed-phase chromatography. The new compounds were more efficient than the underivatised (-)-epicatechin 1 as scavengers of the 1,1-diphenyl-2-picrylhydrazyl free radical (DPPH) and weak growth inhibitors of human colon carcinoma HT29 cells. The order of antiradical and antiproliferative efficiency was 7 >5 approximately 6 >1, the same for both assays.

Taking advantage of the radical character of tris(2,4,6-trichlorophenyl)methyl to synthesize new paramagnetic glassy molecular materials.

This paper describes the synthesis of the novel bis[4-(N-carbazolyl)-2,6-dichlorophenyl](2,4,6-trichlorophenyl)methyl radical (2*) and tris[4-(N-carbazolyl)-2,6-dichlorophenyl]methyl radical (3*). A Friedel-Crafts reaction on [4-(N-carbazolyl)-2,6-dichlorophenyl)bis(2,4,6-trichlorophenyl]methyl radical (1*), 2*, and 3* leads to the introduction of acyl chains in the 3- and 6-positions of the carbazolyl moiety without impairment of the radical character of the molecule to give radicals 5*, 6*, and 7*. All of these novel radical adducts are thermally stable, 5* and 6* being amorphous solids by differential scanning calorimetry. Electron paramagnetic resonance spectra of them show a multiplet at low temperature due to the electron-coupling with six aromatic hydrogens. They show electrochemical amphotericity being reduced and oxidized to their corresponding stable anionic and cationic species, respectively. These radical adducts have luminescent properties covering the red spectral band of the emission with high intensities.

All-Organic Discotic Radical with a Spin-Carrying Rigid-Core Showing Intracolumnar Interactions and Multifunctional Properties**

The ability of liquid crystals (LCs) to rearrange and thus modify their physical properties as a response to an external stimulus, such as light incidence, temperature changes, or the application of an electrical or magnetic field, is a useful feature for technological applications. Discotics are especially interesting from the point of view of the development of semiconductor devices because of their ability to form onedimensional superstructures that allow free electric charges to migrate. This feature has been recognized as an attractive property for the construction of light-emitting diodes, photovoltaic cells, and field-effect transistors. In particular, carbazole derivatives play an important role as organic materials for electronic applications. However, not many carbazole-containing discotic LCs have been reported to date. 3, 4] The development of spin systems with LC properties is particularly interesting in the field of magnetism because of the possibility of altering the magnetic properties through the phase transition, or the modulation of the magnetic response by external fields. Some calamitic all-organic radical LCs containing 2,2,6,6-tetramethylpiperidine-N-oxide and 2,2,5,5tetramethyl-1-pyrrolidine-N-oxide as spin sources, 21,22] which can be ordered into a variety of LC nematic or layered phases, can be found in the literature. However, there is only one example of a disk-like all-organic radical that has the spin-supporting unit introduced into the disk-like triphenylene core as a lateral chain-bonded moiety. With this in mind, we have developed a new discotic allorganic LC with a radical rigid core based on the tris[4-(Ncarbazolyl)-2,6-dichlorophenyl]methyl aromatic system. Free radicals of the tris(2,4,6-trichlorophenyl)methyl (TTM) series are very persistent species both in the solid state and in solution owing to the presence of the very bulky polychlorophenyl substituents around the trivalent carbon atom. In particular, radical adducts based on carbazolyl TTM radical exhibit electrochemical amphotericity and remarkable luminescent properties into the visible range of the electronic spectrum. 26, 27] To the best of our knowledge, the radical adduct presented herein is the first disk-like LC with the magnetic spin source placed in the center of the rigid discotic core.

Radical Scavenging of White Tea and Its Flavonoid Constituents by Electron Paramagnetic Resonance (EPR) Spectroscopy

White tea (WT) presents high levels of catechins, which are known to reduce oxidative stress. WT is the least processed tea, unfermented and prepared only from very young tea leaves. The subject of this paper is the use of the spin trap method and electron paramagnetic resonance (EPR) spectroscopy as the analytical tool to measure, for the first time, the radical scavenging activity of WT and its major catechin components, epicatechin (EC), epicatechin-3-gallate (ECG), epigallocatechin (EGC), and epigallocatechin-3-gallate (EGCG), against the methoxy radical, using ferulic acid as antioxidant pattern. The antioxidant activity has been measured by the decrease of the intensity of the spectral bands of the adduct DMPO-OCH3 in the EPR with the amount of antioxidant in the reactive mixture. Tea leaves and buds were extracted with waterless methanol. It has been proved that tea compounds with more antiradical activity against methoxy radical are those with the gallate group, EGCG and ECG.

Two functionalized free radicals of the tris(2,4,6-trichlorophenyl)methyl radical series. Synthesis, stability and EPR analysis

Tris(2,4,6-trichlorophenyl)carbenium hexachloro-antimonate (2), (2,6-dichloro-4-hydroxyphenyl)bis(2,4,6-trichlorophenyl)methyl radical (4) and its methyl ether derivative 5 have been synthesized and isolated as crystalline solids. In contrast to 5, radical 4 is not very stable in air, and the disappearance of 4 by aerial oxidation has been monitored by UV-vis spectroscopy. The EPR spectra of 4 and 5 are reported and commented upon.

Charge Transfer States in Stable Neutral and Oxidized Radical Adducts from Carbazole Derivatives

In this paper we report the spectral properties of the stable radical adducts 1(•)-3(•), which are formed by an electron donor moiety, the carbazole ring, and an electron acceptor moiety, the polychlorotriphenylmethyl radical. The molecular structure of radical adduct 1(•) in the crystalline state shows a torsion angle of approximately 90° between the phenyl and the carbazole rings due to steric interactions. They exhibit a charge transfer band in the visible range of the electronic spectrum. All of them are chemically oxidized with copper(II) perchlorate to the respective cation species, which show a strong charge transfer band into the near-infrared region of the spectrum. Radical adducts 1(•)-3(•) and the corresponding stable oxidized species 1(+)-3(+) are real organic mixed-valence compounds due to the open-shell nature of their electronic structure. Charge transfer bands of the cation species are stronger and are bathochromically shifted with respect to those of the neutral species due to the greater acceptor ability of the positively charged central carbon atom of the triphenylmethyl moiety. The cationic species 1(+)-3(+) are diamagnetic, as shown by the absence of a signal in the EPR spectrum in acetonitrile solution at room temperature, but they show an intense and unique band in frozen solutions (183 K).

Oxidant activity of tris(2,4,6-trichloro-3,5-dinitrophenyl)methyl radical with catechol and pyrogallol. Mechanistic considerations.

The reducing activity of simple polyphenols (PhOH), catechol and pyrogallol, is tested in different solvents in front of tris(2,4,6-trichloro-3,5-dinitrophenyl)methyl (HNTTM) radical, a stable organic free radical of the TTM series. HNTTM radical is very active in electron-transfer reactions to give a very stable anion. The standard potential for the reduction of HNTTM radical by cyclic voltammetry in different solvents is E(o) = 0.60 +/- 5 V vs SCE. In hydroxylic solvents, the electron transfer is a very rapid process and the electron-donating species is the ionized PhO(-), whereas in nonpolar solvents, it is suggested that the electron transfer is facilitated by the formation of an intermediate complex between HNTTM and PhOH.

(2,6-Dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl radical. Synthesis, magnetic behaviour and crystal structure

Abstract (2,6-Dichlorophenyl)bis(2,4,6-trichlorophenyl)methyl radical ( 2 ) has been prepared through a reaction sequence of five stages obtaining four new intermediate compounds 1–4 . Assignment of the structures of these compounds have been completely ascertained by means of their 1 H NMR spectra. The new persistent radical 2 has been characterized by EPR spectra and magnetic susceptibility measurements. The X-ray structural analysis of 2 shows that it adopts a propeller-like conformation with the phenyl rings twisted around their bonds to trivalent carbon. Magnetic susceptibility of 2 is characteristic of a paramagnet with a weak antiferromagnetic interaction at low temperatures (Weiss constant, Θ = −1.8 K).

Perchlorophenyl-germanium compounds. Crystal and molecular structure of perchlorotriphenylgermane

Abstract The synthesis of the first pentachlorophenyl derivatives of organo-germanium compounds, perchlorotriphenylgermane ( 1 ), tris(pentachlorophenyl)germane( 2 ) and bromotris(pentachlorophenyl)germane ( 4 ), are reported; hydrolysis of 1 and 4 under neutral conditions gives tris(pentachlorophenyl)germanol ( 3 ). The structure of the germane 1 has been established by X-ray crystallography.

An unusual cyclization reaction in the chemistry of perchloroorganic compounds of silicon and germanium. Synthesis and crystal structure of perchloro(2,2′-biphenylene)diphenyl-silane and -germane

Abstract The reactions of SiCl 4 and GeCl 4 (or Ph Cl ) 3 SiCl and (Ph Cl ) 3 GeCl where Ph Cl denotes Cl 5 C 6 ) with Ph Cl MgCl give perchloro(2,2′-biphenylene)diphenyl-silane ( 2 ) and -germane ( 3 ), respectively. The structure of both strained compounds have been determined by X-ray crystallography of their benzene solvates. The photobromination of germane 3 with Br 2 results in cleavage of one germanium-biphenylene bond to give the highly crowded bromo(2-(2′-bromooctachlorobiphenyl))bis(pentachlorophenyl)germane ( 4 ).