Electronic energy transfer and collection in luminescent molecular rods containing ruthenium(II) and osmium(II) 2,2':6',2"-terpyridine complexes linked by thiophene-2,5-diyl spacers

The electronic absorption spectra, luminescence spectra and lifetimes (in MeCN at room temperature and in frozen n-C3H7CN at 77 K), and electrochemical potentials (in MeCN) of the novel dinuclear [(tpy)Ru(3)Os(tpy)]4+ and trinuclear [(tpy)Ru(3)Os(3)Ru(tpy)]6- complexes (3 = 2,5-bis(2,2':6',2'-terpyridin-4-yl)thiophene) have been obtained and are compared with those of model mononuclear complexes and homometallic [(tpy)Ru(3)Ru(tpy)]4+, [(tpy)Os(3)Os(tpy)]4+ and [(tpy)Ru(3)Ru(3)Ru(tpy)]6+ Complexes. The bridging ligand 3 is nearly planar in the complexes, as seen from a preliminary X-ray determination of [(tpy)Ru(3)Ru(tpy)][PF6]4, and confers a high degree of rigidity upon the polynuclear species. The trinuclear species are rod-shaped with a distance of about 3 nm between the terminal metal centres. For the polynuclear complexes, the spectroscopic and electrochemical data are in accord with a significant intermetal interaction. All of the complexes are luminescent (phi in the range 10(-4)-10(-2) and tau in the range 6-340 ns, at room temperature), and ruthenium- or osmium-based luminescence properties can be identified. Due to the excited state properties of the various components and to the geometric and electronic properties of the bridge, Ru --> Os directional transfer of excitation energy takes place in the complexes [(tpy)Ru(3)Os(tpy)]4+ (end-to-end) and [(tpy)Ru(3)Os(3)Ru(tpy)]6+ (periphery-to-centre). With respect to the homometallic case, for [(tpy)Ru(3)Os(3)Ru(tpy)]6+ excitation trapping at the central position is accompanied by a fivefold enhancement of luminescence intensity.     

Binuclear wirelike dimers based on ruthenium(II)-bipyridine units linked by ethynylene-oligothiophene-ethynylene bridges

The syntheses, structural characteristics, electrochemical behavior, ground-state spectra, photophysical properties, and transient absorption (TA) spectra in CH(3)CN solvent are reported for binuclear [(bpy)(2)Ru(bpy-E(T)(n)()E-bpy)Ru(bpy)(2)](4+) complexes, Ru(bpyT(n)bpy)Ru, where the Ru-based units are connected by alternating 3,4-dibutylthiophene (DBT')/thiophene (T') fragments linked via ethynyl groups (E) to bpy ligands at the 5-position (bpy is 2,2'-bipyridine). The ligand bpyT(3)bpy represents a module containing DBT'/T'/DBT' subunits, and bpyT(5)bpy accounts for a DBT'/T'/DBT'/T'/DBT' pattern. The syntheses and electrochemical and spectroscopic (emission and TA) properties in CH(2)Cl(2) solvent of the bpyT(n)()bpy ligands are likewise reported. The behavior of the Ru(bpyT(n)bpy)Ru dimers has been compared to that of the bpyT(n)bpy ligands and to that of a related mononuclear complex, [(bpy)(2)Ru(bpy-E-DBT')](2+), Ru(bpyDBT'). For the dimeric complexes, the electrochemical results show that the first reduction step takes place at the bpy ligand(s) bearing an ethynylene group, the first oxidation step is thiophene-centered, and further oxidation involves the metal centers, which are only weakly interacting. The photophysical and TA results for the Ru(bpyT(n)bpy)Ru dimers account for the presence of low-lying oligothiophene-centered (3)pi,pi levels, while higher-lying metal-ligand charge transfer ((3)MLCT) levels are thermally accessible only for the case of Ru(bpyT(3)bpy)Ru; the possible role of charge separation (CS) levels (from oxidation at the thiophene bridge and reduction at one of the coordinated bpy's) is also discussed.     

Nitroarene catalyzed oxidation with sodium percarbonate or sodium perborate as the terminal oxidant

A new catalytic oxidation method for the preparation of aromatic carboxylic acids from methyl aryl ketones is reported. The method is an alternative to the haloform reaction; it is benign and affords the desired product without production of any harmful side products. The catalytic cycle is based on the use of an electron-deficient nitroarene as catalyst with either of the two cheap and green oxidants sodium percarbonate or sodium perborate. The method gives a good yield (87%) and shows excellent selectivity when the model substrate (acetophenone) is oxidized. A series of benzoic acids of industrial interest were prepared by means of this method.     

Positive\partial \bar \partial - closed currents and non-Kähler geometrycurrents and non-Kähler geometry

In this paper some new results on positive \(\partial \bar \partial - closed\) currents are applied to modifications \(f:\bar M \to M\) . The main result in this topic is that every smooth proper modification of a compact Kähler manifoldM is balanced. Moreover, under suitable hypotheses on the map, the Kähler degrees of \(\bar M\) corresponds to homological properties of the exceptional set of the modification. More examples ofp-Kähler manifolds are discussed in the last section of the paper.     

Role of secondary structure in the asymmetric acylation reaction catalyzed by peptides based on chiral C alpha-tetrasubstituted alpha-amino acids

In a recent series of papers, Miller and co-workers were able to show that His(pi-Me)-based, terminally protected peptides are potent catalysts of the asymmetric acyl transfer reaction, useful for the kinetic resolution of alcohols. In a structure-supporting solvent, one of the most active compounds, an Aib-containing tetrapeptide, is folded in a doubly intramolecularly H-bonded beta-hairpin motif incorporating a type-II' beta-turn conformation. In this work, we have expanded the study of the Miller tetrapeptide by examining a set of analogues and shorter sequences (dipeptide amides), characterized by chiral C(alpha)-tetrasubstituted alpha-amino acids of diverging bulkiness and optical configuration. Peptide synthesis in solution, conformational analysis by FT-IR absorption and (1)H NMR techniques, and screening of catalytic activity as well have been performed. Our results confirm the close relationship between the beta-hairpin 3D-structure and the catalytic activity of the peptides. A tetrapeptide analogue slightly more selective than the Miller compound has been found. However, the terminally protected, industrially more appealing, dipeptide amides are poorly effective.     

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.     

Ultrastructural Damages to H1N1 Influenza Virus Caused by Vapor Essential Oils

Influenza viruses are transmitted from human to human via airborne droplets and can be transferred through contaminated environmental surfaces. Some works have demonstrated the efficacy of essential oils (EOs) as antimicrobial and antiviral agents, but most of them examined the liquid phases, which are generally toxic for oral applications. In our study, we describe the antiviral activity of Citrus bergamia, Melaleuca alternifolia, Illicium verum and Eucalyptus globulus vapor EOs against influenza virus type A. In the vapor phase, C. bergamia and M. alternifolia strongly reduced viral cytopathic effect without exerting any cytotoxicity. The E. globulus vapor EO reduced viral infection by 78% with no cytotoxicity, while I. verum was not effective. Furthermore, we characterized the EOs and their vapor phase by the head-space gas chromatography–mass spectrometry technique, observing that the major component found in each liquid EO is the same one of the corresponding vapor phases, with the exception of M. alternifolia. To deepen the mechanism of action, the morphological integrity of virus particles was checked by negative staining transmission electron microscopy, showing that they interfere with the lipid bilayer of the viral envelope, leading to the decomposition of membranes. We speculated that the most abundant components of the vapor EOs might directly interfere with influenza virus envelope structures or mask viral structures important for early steps of viral infection.     

Stereoselective Epoxidation of Cyclic Dienes and Trienes by Dioxiranes

Epoxides are essential building blocks in organic chemistry. The epoxidation of unsubstituted cyclic dienes 2 , 3 , 4 and triene 5 using dimethyldioxirane ( 1a ) and its trifluoro analog 1b methyl(trifluoromethyl)dioxirane has been investigated. The excellent yields obtained (90–98%) are accompanied by outstandingly high diastereoselectivities (90–98%). Interpretation of results based upon the early idea that polar groups can direct the dioxirane attack by dipole–dipole interaction provides a likely rationale, along with a more generalized mechanistic view.     

Convenient Esterification of Carboxylic Acids by SN2 Reaction Promoted by a Protic Ionic-Liquid System Formed in Situ in Solvent-Free Conditions

The reaction of esterification of benzoic acid with benzyl chloride was chosen as a model reaction to study the esterification by S_N2 promoted by tertiary amine as deprotonating agent. The use of ionic liquid (IL) 1,3-dimethylimidazolium methanesulfonate [MMIm][OMs] as reaction medium has proven to give quantitative yield of the ester, but interestingly the reaction does occur even in solvent-free conditions, where the acid + the amine form a liquid system (a protic IL) in situ. This last methodology was extended to several carboxylic acids in conditions of atom economy (i.e., without excess of any reagent), giving moderately good yields of esters (54–78%) recovered by weight in pure form.     

Evaluation of low-dose irradiation on microbiological quality of white carrots and string beans

The minimally processed food provided the consumer with a product quality, safety and practicality. However, minimal processing of food does not reduce pathogenic population of microorganisms to safe levels. Ionizing radiation used in low doses is effective to maintain the quality of food, reducing the microbiological load but rather compromising the nutritional values and sensory property. The association of minimal processing with irradiation could improve the quality and safety of product. The purpose of this study was to evaluate the effectiveness of low-doses of ionizing radiation on the reduction of microorganisms in minimally processed foods. The results show that the ionizing radiation of minimally processed vegetables could decontaminate them without several changes in its properties.