One-step synthesis of low molecular weight poly(p-phenyleneethynylenevinylene)s via polyaddition of aromatic diynes by catalysis of the [Ru(p-cymene)Cl2]2/AcOH system

pi-Conjugated low molecular weight polymers characterized by regio- and stereoregular alternation of phenylene and ( E)-1-en-3-yne moieties have been synthesized by polyaddition of 1,4-diethynylbenzene or of 2,5-diethynyl-1,4-alkoxybenzene monomers, employing the commercially available di-micro-chlorobis[( p-cymene)chlororuthenium(II)] complex as the metal catalyst source, under homogeneous, atom-economical, amine- and phosphine-free conditions. Bulk materials of poly( p-phenyleneethynylenevinylene) derivatives are obtained with yields larger than 80%, from which polymers readily soluble in chlorinated solvents and in tetrahydrofuran are extracted in 60-75% yields. The polymers with average degrees of polymerization in the range n AV = 4-8 display optical properties in solution similar to those of the higher molecular weights analogues.     

New copper(I) and silver(I) triazolato-complexes: Synthesis, reactivity and catalytic activity in olefin cyclopropanation

A new class of azolate ligands, deriving from the equimolar condensation of 3,5-diamino-1,2,4-triazole with salicylaldehyde (H₃L¹) and o-anisaldehyde (H₃L²) was prepared. In their anionic form, these species act as bridging moieties upon coordination to Cu(I) and Ag(I), giving rise to the formation of dinuclear complexes with the ligand in the typical N,N′-exobidentate conformation. The copper derivative [Cu(H₂L¹)(CH₃CN)]₂ (1) showed attractive reactivity in the replacement of the labile acetonitrile molecules. In particular, it was possible to isolate a dinuclear copper(I)-carbonyl complex [Cu(H₂L¹)(CO)]₂ (4), by substitution of the nitrile with carbon monoxide. Moreover, the reaction of 1 with ethyl diazoacetate (EDA) in CH₂Cl₂ afforded a mono-carbene product, as established by ¹³C NMR data. Finally, the copper derivative 1 proved to be a highly diastereoselective catalyst in olefin cyclopropanation in the presence of ethyl diazoacetate. In the case of internal alkenes a trans:cis ratio of up to 97:3 was reached. The X-ray structure of a dinuclear Ag(I) complex, namely [Ag(H₂L¹)(PPh₃)]₂ (3), obtained by reacting the polymeric [Ag(H₂L¹)]_n (2), with triphenylphosphine, is also reported.     

AgY zeolite as catalyst for the effective three-component synthesis of propargylamines

The preparation of substituted propargylamines via three-component reaction between aldehydes, terminal alkynes, and secondary amines following an environmentally acceptable methodology has been developed. The process has been carried out under solvent-free conditions in the presence of AgY zeolite. The catalyst can be easily recovered and reused for at least four cycles without significant decreases in yield and selectivity.     

Identification and characterization of a new family of catalytically highly active imidazolin-2-ylidenes

A new class of easily accessible and stable imidazolin-2-ylidenes has been synthesized where the side chains are comprised of substituted naphthyl units. Introduction of the naphthyl groups generates C 2 -symmetric ( rac) and C s- symmetric ( meso) atropisomers, and interconversion between the isomers is studied in detail both experimentally and computationally. Complete characterization of the carbenes includes rare examples of crystallographically characterized saturated NHC structures. Steric properties of the ligands and an investigation of their stability are also presented. In catalysis, the new ligands show versatility comparable to the most widely used NHCs IMes/SIMes or IPr/SIPr. Excellent catalytic results are obtained when either the NHC salts (ring-opening alkylation of epoxides), NHC-modified palladium compounds (C-C and C-N cross-couplings), or NHC-ruthenium complexes (ring-closing metathesis, RCM) are employed. In several cases, this new ligand family provides catalytic systems of higher reactivity than that observed with previously reported NHC compounds.     

Conventional and narrow bore short capillary columns with cyclodextrin derivatives as chiral selectors to speed-up enantioselective gas chromatography and enantioselective gas chromatography-mass spectrometry analyses

The analysis of complex real-world samples of vegetable origin requires rapid and accurate routine methods, enabling laboratories to increase sample throughput and productivity while reducing analysis costs. This study examines shortening enantioselective-GC (ES-GC) analysis time following the approaches used in fast GC. ES-GC separations are due to a weak enantiomer-CD host-guest interaction and the separation is thermodynamically driven and strongly influenced by temperature. As a consequence, fast temperature rates can interfere with enantiomeric discrimination; thus the use of short and/or narrow bore columns is a possible approach to speeding-up ES-GC analyses. The performance of ES-GC with a conventional inner diameter (I.D.) column (25 m length x 0.25 mm I.D., 0.15 microm and 0.25 microm d(f)) coated with 30% of 2,3-di-O-ethyl-6-O-tert-butyldimethylsilyl-beta-cyclodextrin in PS-086 is compared to those of conventional I.D. short column (5m length x 0.25 mm I.D., 0.15 microm d(f)) and of different length narrow bore columns (1, 2, 5 and 10 m long x 0.10 mm I.D., 0.10 microm d(f)) in analysing racemate standards of pesticides and in the flavour and fragrance field and real-world-samples. Short conventional I.D. columns gave shorter analysis time and comparable or lower resolutions with the racemate standards, depending mainly on analyte volatility. Narrow-bore columns were tested under different analysis conditions; they provided shorter analysis time and resolutions comparable to those of conventional I.D. ES columns. The narrow-bore columns offering the most effective compromise between separation efficiency and analysis time are the 5 and 2m columns; in combination with mass spectrometry as detector, applied to lavender and bergamot essential oil analyses, these reduced analysis time by a factor of at least three while separation of chiral markers remained unaltered.     

H2S gas interaction with Pt(II)-containing polymetallaynes of selected chain length: an XPS and EXAFS study

The interaction between gaseous H2S and the surface of several metal-containing oligomers, investigated by emission and absorption spectroscopies, is presented and discussed. The polymetallayne trans-{Cl-[Pt(PBu3)2(CC-C6H4-C6H4-CC)]9Pt(PBu3)2Cl} and related model molecules, i.e. the binuclear transition metal dialkynyl bridged Pt(II) square planar complex trans, trans-[ClPt(PBu3)2(CC-C6H4-C6H4-CC)Pt(PBu3)2Cl], the tetranuclear linear oligomer trans-{Cl-[Pt(PBu3)2(CC-C6H4-C6H4-CC)]3Pt(PBu3)2Cl}, the tetranuclear cyclic oligomer cis-[Pt(PBu3)2(CC-C6H4-C6H4-CC)]4, were exposed to hydrogen sulfide and then investigated by X-ray photoelectron (XPS) and X-ray absorption (XAS) spectroscopies, in order to shed light on the gas/polymer interaction associated to the sensing properties of these materials. XPS measurements evidenced the presence of S in the polymetallayne samples exposed to H2S, and the measured S2p binding energy values correlate with H2S adsorbed by means of sulfur atoms chemically bonded to metal atoms, owing to the formation of sulfur-containing adducts. XAS data analysis suggested a square-pyramidal geometry around the transition metal with H2S in the apical position for the pentacoordinated platinum units.     

Electron-rich heteroaromatic conjugated bipyridine based ruthenium sensitizer for efficient dye-sensitized solar cells

A novel heteroleptic ruthenium complex carrying a heteroaromatic-4,4'-pi-conjugated 2,2'-bipyridine [Ru(II)LL'(NCS)(2)] (L = 4,4'-bis[(E)-2-(3,4-ethylenedioxythien-2-yl)vinyl]-2,2'-bipyridine, L' = 4,4'-(dicarboxylic acid)-2,2'-bipyridine) was synthesized and used in dye-sensitized solar cells, yielding photovoltaic efficiencies of 9.1% under standard global AM 1.5 sunlight.     

Stress dependence of paramagnetic point defects in amorphous silicon oxide

Room-temperature red cathodoluminescence (CL) emission (R band) arising from the paramagnetic point-defect population present in amorphous silicon oxide (SiOx) has been characterized with respect to its shift upon applied stress, according to a piezo-spectroscopic (PS) approach. The R band (found at around 630 nm) originates from nonbridging oxygen hole centers (NBOHC; Si-O*) generated in the presence of oxygen-excess sites. It is shown that reliable stress assessments can be obtained in silica glass with a relatively high spatial resolution, provided that appropriate spectroscopic procedures are developed to precisely extract from the CL spectrum the shift upon stress of the R band, isolated from other partly overlapping bands. Macroscopic and microscopic PS calibration procedures are shown to lead to consistent results on silica materials with different chemical characteristics and, thus, with different intrinsic defect populations. In addition, quantitative calibrations of both electron probe size and luminescence emission distribution within the electron probe are given. As an application of the PS technique, the magnitude of the residual stress piled up (mainly due to a thermal expansion mismatch) at a sharp silica/silicon interface has been characterized by taking into account the gradient in defect population developed as a function of distance from the interface. In the Results and Discussion section, brief comments are offered regarding the possible impact of highly spatially resolved stress assessments in silica glass upon the development of new materials and advanced electronic devices.     

Branched peptides as therapeutics

The concept of 'magic bullet', initially ascribed to immunoglobulins by Paul Ehrlich at the beginning of the 20th century and strengthened by the hybridoma technology of Kohler and Milstein in the mid 70s, can nowadays be attributed to different target-specific molecules, such as peptides. This attribution is increasingly valid in light of the explosion of new technologies for peptide library construction and screening, not to mention improvements in peptide synthesis and conjugation and in-vivo peptide stability, which make peptide molecules specific bullets for targeting pathological markers and pathogens. Today, hundreds of peptides are being developed and dozens are in clinical trials for a variety of diseases, demonstrating that the general reluctance towards peptide drugs that existed a decade ago has now been overcome. In spite of this progress, the development of new peptide drugs has largely been limited by their short half-life. Branched peptides such as Multiple Antigen Peptides (MAPs) were invented in the 80s by Tam [Tam, J.P., (1998) Proc. Natl. Acad. Sci. USA, 85, 5409] and have been extensively tested to reproduce single epitopes to stimulate the immune system for new vaccine discovery. In our lab we discovered that MAP molecules acquire strong resistance to proteases and peptidases. This resistance renders MAPs very stable and thus suitable for drug development. Here we report our experience with several MAP molecules in different biotechnological applications ranging from antimicrobial and anti toxin peptides to peptides for tumor targeting.     

Modeling the solvation of peptides. The case of (s)-N-acetylproline amide in liquid water

The structure and properties of (s)-N-acetylproline amide (NAP) in aqueous solution are studied by exploiting a continuum solvation model. The conformational preference of NAP as a function of the environment is discussed as well as data for a number of chiral and non-chiral spectroscopic and response properties (IR/VCD, Raman/VROA, UV/CD, ORD, NMR), whose calculation with the accounting of solvent effects is now possible due to recent developments introduced in the PCM approach. When available, calculated results are compared with experimental data, so as to evaluate the quality of the continuum approach to the solvation of this system.