A quantitative approach to the recycling of alpha-tocopherol by coantioxidants

A systematic investigation is reported on the regeneration of alpha-tocopherol (alpha-TOH) in homogeneous solution by coantioxidants in order to better understand the mechanism and the factors responsible for the effectiveness of this process. The current availability of thermochemical data concerning the reactants involved in the regeneration reactions, as well as a large number of the kinetic constants for the various reactions involved, allowed us to rationalize the experimental observations collected so far. Three limiting cases have been considered. The first case is that of a coantioxidant irreversibly regenerating alpha-TOH, where the effectiveness of the recycling process depends on the magnitude of the rate constant k(r). The second case is that of a coantioxidant reversibly recycling alpha-TOH, where regeneration can only be observed if the bond dissociation enthalpy value of the coantioxidant is lower or at least close to that of the O-H bond of alpha-tocopherol. The third case is that of a catechol derivative (chosen as a model compound for polyphenolic antioxidants), where recycling of alpha-TOH is feasible even though the BDE value is significantly higher than that of vitamin E. In this case, the driving force for the recycling process is the removal of the semiquinone radical from the catechol derivative by the alpha-tocopheroxyl radical, which makes the regeneration of alpha-TOH practically irreversible.     

Mild metal-free syn-stereoselective ring opening of activated epoxides and aziridines with aryl borates

A conceptually new, simple and practical method for the syn-nucleophilic displacement of aryl and vinyl epoxides and aryl aziridines with (substituted) phenols, using aryl borates as activating nucleophiles under neutral conditions, is reported.     

Chemoselective hydrogenation catalysts: Pt on mesostructured CeO2 nanoparticles embedded within ultrathin layers of SiO2 binder

Pt on mesostructured CeO(2) nanoparticles embedded within ultrathin layers of highly structured SiO(2) binder shows highest activity reported with 80% selectivity for the chemoselective hydrogenation of crotonaldehyde. Characterization by transmission electron microscopy (TEM), CO adsorption, and X-ray photoelectron spectroscopy (XPS) show the presence of small Pt metal particles, preferentially located on CeO(2) (70%) together with the formation of Pt-CeO(2-x) sites at the interface between Pt and CeO(2) (4 nm) nanoparticles. These sites are able to polarize the carbonyl group and facilitate the selective hydrogenation of this with respect to the double bond.     

CERTAIN SINGLET OXYGEN QUENCHERS AFFECT THE PHOTOREACTION BETWEEN 8-MOP and DNA

The effect of certain chemicals known as singlet oxygen quenchers on the photoreaction between 8-MOP and DNA has been studied in vitro; sodium azide, l,4-diazabicyclo-(2,2,2)-octane, p-carotene and dimethylsolfoxide (used as a solvent) appeared to be capable of reducing significantly the 8-MOP ability to induce both monoadducts and cross-links in DNA. Therefore, these chemicals seem to be not useful in studying the singlet oxygen implication in the induction of biological effects of 8-MOP sensitization.     

First observation of the hyperfine structure of an excited quintet state in liquid solution

After pulsed photoexcitation of a new fullerene-linked bisnitroxide, a well resolved transient EPR spectrum is detected which is assigned to an excited quintet spin state generated by spin coupling of the nitroxides and the fullerene excited triplet.     

Quasi-classical trajectories study of the chemisorption of H2 on the Pt(111) surface: effect of surface motion

The effect of energy exchange on the dynamics of the chemisorption of H₂ on Pt (111) is studied within a LEPS potential quasi-classical trajectories treatment. The Einstein model is assumed for the solid. The rigidity of the surfaces is shown to be an acceptable approximation.     

A mixed‐ligand quinazoline‐based Ni(II) Schiff base complex: Synthesis,characterization, crystal structure,antimicrobial investigation and catalytic activity for the synthesis of 2H–indazolo[2,1‐b]phthalazine‐triones

A tridentate Schiff base ligand, (E)‐3‐((2‐hydroxy‐3‐methoxybenzylidene)amino)‐2‐methylquinazolin‐4(3H)‐one [HL], and its mixed‐ligand Ni(II) complex [Ni(L)(imi)], were synthesized and fully characterized using elemental analysis, FT‐IR, UV–Vis and ¹HNMR spectroscopy techniques. The structure of the synthesized ligand and complex was determined with single crystal X‐ray diffraction method. In the complex, a square planner geometry was observed around the Ni(II) central atom coordinated with the donor atoms of the Schiff base ligand and one nitrogen of imidazole group. In addition, the catalytic activity of the complex on the three‐component condensation of hydrazine hydrate with phthalic anhydride and dimedone to obtain 2H–indazolo[2,1‐b]phthalazine‐triones was investigated. Furthermore, in‐vitro antimicrobial studies were performed that indicated the great antibacterial activities of the Ni(II) complex against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus cereus bacteria.     

Conjugated Azoalkenesi Part III. Synthesis of Sone Phosphorous Azoalkenes

Recently, some of us reviewed the synthes is and chemical reactions of conjugated azoalkenes.¹ Emphasis was placed on the fact that these derivatives represent at the same time interesting products and useful intermediates in organic chemistry. In fact, conjugated azoolefins undergo a wide range of 1,4-additions, (3+2)- and (4+2)-cycloadditions allowing various functionalizations of the carbon atom adjacent to the carbonyl group, and the construction of many types of interesting five - and six-membered heterocycles, such as widely substituted pyrrole and pyridazine rings. These relevant synthetic objectives appear not to be smoothly obtained by other procedures. In addition, many of the compounds produced from conjugated azoalkenes can profitably be employed in the preparation of natural, pharmaceutical, and phytopharmaceutical products.¹     

Electrolytic Oxidation of Thiocyanate and Selenocyanate Salts and the Photoelectrochemical Effect.

New photosensitive materials can be obtained by electrochemical oxidation of thiocyanate and selenocyanate salts. Using (K,Na)SCN eutectic melt, the formation of an electrodic deposit, with photoelectrochemical properties, has already been reported by us. To improve the photoelectrochemical characteristics of the deposit, futher investigations were carried out in the following sistems: selenocyanate ammoniate, KSCH-Acetamide eutectic mixture and KSCN ethylene carbonate solution:. Attempts to obtain a massive deposit in the ammoniate solution were unsuccessful due to ammonia oxidation. Measurements performed on the other KSCN systems show that temperature is a parameter of remarkable importance. In fact, lowering the temperature one obtains a decrease on formation of parathiocyanogen on behalf of the polytrithiocyanogen, the species that gives rise to the photoeffect.