210 research outputs found
Crystal structures of a bis(cyclopentadienyl)(Z)-enyne framed manganese(I)-rhenium(I) complex and its [Co2(CO)8] adduct
No full textThe X-ray structural determination of the manganese(I)-rhenium(I) complex [(OC)3Mn{eta-5-C5H4)(Z)CH = CHC = C(eta-5-C5H4)}Re(CO)3] 1 has been carried out. The structural data show that the (Z)-enyne linkage between the two cyclopentadienyl rings, despite the conjugation that would keep the ligand framework coplanar, allows twisting of the two cyclopentadienylmetal units. Because of this characteristic the Mn Re interatomic distance (6.1 angstrom) is much shorter than in similar bis(cyclopentadienyl)-linked heterobimetallic complexes. Reaction of 1 with [Co2(CO)8] affords quantitatively the corresponding dicobalt tetragonal pyramidal adduct [(OC)3Mn{eta-5-C5H4)(Z)CH = CHC-(OC)3Co-Co(CO)3-C-(eta-5-C5H4)}Re(CO)3]2 the X-ray structure of which has been determined. The presence of the dicobalt unit on the triple bond heavily affects the carbon chain connecting the two cyclopentadienyl rings, and the metal centres are at a larger distance than in 1. Crystal data: 1, triclinic, space group P1BAR, a = 6.546(1), b = 11.066(2), c = 13.451 (3) angstrom, alpha = 96.06(2), beta = 100.46(2), gamma = 96.31 (1)-degrees, R(F) = 0.0466, R'(F) = 0.0542 for 2710 observed reflections with F > 4.0-sigma(F); 2, triclinic, space group P1BAR, a = 9.825(3), b = 11.853(4), c = 13.662(3) angstrom, alpha = 109.41 (2), beta = 1 04.36(2), gamma = 99.16(2)-degrees, Z = 2, R(F) = 0.0325, R'(F) = 0.0352 for 5913 observed reflections with F > 4.0-sigma(F)
A new frontier in the metal-catalyzed cross-coupling reaction field. The palladium-promoted metal-carbon bond formation. Scope and mechanism of a new tool in organometallic synthesis
No full textThe synthetic uses and the investigation of the reaction mechanism of the Pd-catalyzed metal/carbon bond-formation process are accounted. Preparations of simple s-metal metal acetylides of typeM/C/C/R (M/Fe, Ru, Mo, W; R/H, Alkyl, Ph), homo and heterobimetallic complexes of type M/C/C/Thiop/C/C/M? (Thiop/2,5-thiophene; M, M?/Fe, Ru, Mo, W), polymetallaacetylide tethers of type M/C/C/Thiop/C/C/M?(h5-Cp)/C/C/Thiop/C/C/(h5-Cp)M?/C/C/Thiop/C/C/M (M/Re, Mn;M?/Fe), and metallaacetylide polymers of type [/M/C/C/Ar/C/C/]n (Ar/2,5-thiophene, 1,4-phenylene) are reported. By the use of properly designed model substrate principal intermediates (i.e. oxidative addition, transmetalation) involved in the catalytic cycle have been isolated and fully characterized. Kinetic and spectroscopic studies of the reaction mechanism have evidenced that,
depending from the reaction conditions, the transmetalation step may proceed by two pathways: (i) in concentrated solutions of the complex of oxidative addition (/104 M), the reaction proceeds through formation of a highlyreactive solvent-coordinate species (dissociative mechanism). These results are showing clear analogies with mechanistic studies of the carbon/carbon coupling process, thus with the use of these model substrates, a unique opportunity to investigate factors
affecting the metal/carbon bond formation reaction is offered, as well as the possibility to shed light on unclear aspects of the carbon/carbon coupling itself, a phenomenon of paramount importance in synthetic organic chemistry
Design, Synthesis and Optoelectronic Properties of Aminoacid Derivatives of Poly(arylene ethynylene) Platforms: Hybrid Bio-Synthetic Systems for Sensoring Applications
No full textBy means of the modular construction of a large series of poly(arylene ethynylene)s (PAEs) employing Pd-promoted synthetic routes, molecular models of type A-C equivalent to C-B-C equivalent to C-A and B-C equivalent to C-A-C equivalent to C-B, and polymers of type [-C equivalent to C-A-] n and [-C equivalent to C-A-C equivalent to C-B-](n) carrying a variety of aminoacidic side arms, have been prepared and fully characterized towards their application as sensing materials. The introduction of different aminoacidic groups as side substituents on the conjugated backbone may allow the tuning of the recognition ability of the receptor site towards given analytes. The luminescent sensing properties of these materials towards metal ions were investigated. The flexibility of the synthetic route allows tuning of binding activity, molecular recognition and opto- and electro- properties of the materials, as well as the responses upon exposure to metal ions. All compounds showed high selectivity towards Hg(II) ions, and a signal amplification in Hg(II) detection was observed for the polymeric compound in comparison with small molecule analogues. Further functionalization of aminoacid substituted PAEs with ferrocene moieties allows the electrochemical sensing by change in the oxidation potential of Fe(II)/Fe(III) redox couple, and its dependence with the interaction of aminoacidic side arms with given analytes
Chemical Composition and Antioxidant Activity of Cannabis sativa L. 'Futura 75' Essential Oil: Effect of the Distillation Time.
No full textIn the last decades, there is an increasing interest in the cultivation of industrial hemp, Cannabis sativa L. with low content of delta9-tetrahydrocannabinol (THC), the psychotropic agent, due to its use in different field, among them food, cosmetic and pharmaceutical industry [1]. In particular, have been investigated C. sativa extracts with high content of cannabidiol (CBD), that is a molecule showing different pharmacological activities, including an antitumoral action [2]. At the same time, characterization studies of the hemp essential oil (EO) were conducted and its antioxidant and antimicrobial activity was shown [3,4,5].
The aim of this work was to explore the effect of the distillation time on the chemical composition and the antioxidant properties of the EOs obtained by steam distillation from C. sativa cv. Futura 75, cultivated in the Abruzzo Region.
Dried inflorescence, provided by a local farm and preserved in vacuum bags until distillation, were subjected to steam distillation at two, four and six hours, affording EOs with 0,13%, 0,16% and 0,26% yield, respectively. The chemical composition of the obtained EOs was determined by GC-MS analysis, and was compared with the volatile fraction composition of dried inflorescences matrix, carried out by solid phase microextraction (SPME) coupled to GC-MS technique. EOs at different time contain the same main compounds, but with different relative abundance.
The EOs were evaluated for the total phenolic content (TPC) by Folin-Ciocâlteu method, and for the antioxidant activity (AOC) by TEAC/ABTS, FRAP and DPPH assays.
EOs distilled at more time showed higher yield, TPC and AOC, with four and six hours more similar to each other, and more performing than two hours one
Response of a Pt-polyyne membrane in surface acoustic wave sensors: Experimental and theoretical approach
No full textA surface acoustic wave (SAW) sensor, based on a polymeric sensitive membrane, has been realized for sensor applications and materials characterization. A platinum-containing rigid-rod organometallic polymer [-Pt(PPh3)(2)(-C=C-pC(6)H(2)(2,5-OC16H33)(2)-C=C-)](n) (Pt-P-HDOB), obtained by the reaction of cis-[Pt(PPh3)(2)Cl-2] with 1,4-diethynyl-2,5-dihexadeciloxybenzene (HDOB) by means of the recently assessed "Extended one pot" polymerization route, was here studied. The chemical structure and chain length of Pt-P-HDOB polymer were defined by spectroscopic techniques and gel permeation chromatography measurements. The acoustic characterization of the Pt-P-HDOB film was developed with the aid of the perturbation theory applied to different polymer-coated-piezoelectric substrates and the shear modulus of Pt-P-HDOB film have been estimated. A SAW delay line has been implemented on ZnO/Si substrate and a thin polymeric film has been spin deposited on the device surface to realize a chemical sensor. The sensor has been exposed to different chemicals and its response has been measured for different chemical concentrations. High sensitivity and reproducibility of the sensor response to relative humidity and methanol vapors were found. (C) 2003 American Institute of Physics
Use of the extended one-pot (EOP) procedure for the preparation of ethynylated thiophene derivatives and related palladium-ethynylthiophene organometallic oligomers
No full textThe palladium-catalyzed coupling (Stille coupling) of 2,5-diiodothiophene (1) with tributyl(ethynyl)tin forms the 2,5-bis(ethynyl)thiophene (3) and tributyltin iodide as side product (step 1). Addition of lithium diisopropylamide (LDA) to this mixture causes deprotonation of the bis-alkyne and its reaction with the tin halide present in the medium to form the 2,5-bis[(tributyltin)ethynyl]thiophene (4) (step 2). To this mixture was subsequently added trans-dichlorobis(tri-n-butylphosphine)palladium (5), and the corresponding trans-bis(tri-n-butylphosphine)-mu- [2,5-bis(ethynyl)thiophene]palladium oligomer (6) was obtained (step 3). Alternatively, the same route can be directed toward the formation of ethynylated thiophene oligomers: after formation of the 2,5-bis[(tributyltin)ethynyl]thiophene (4) (step 2), addition of 2-iodothiophene (8) or 2-iodo-5-(trimethylsilyl)thiophene (10) led to the formation of 2,5-bis(2-thienylethynyl)thiophene (9) (step 3) and [2-trimethylsilyl(ethynyl)thiophene]-2,5-bisethynylthiophene (11) (step 3') respectively. The latter can be easily desilylated to obtain the [2-(ethynyl)thiophene]-2,5-bisethynylthiophene (13), while treatment of 9 with sec-BuLi/I-2 formed the 2,5-[2,2'-(5,5'-diiodo)bisthienyl]bisethynylthiophene (12). Through a sequence of transformations similar to steps 1-3, the oligo(iodo)ethynylthiophene 12 has been connected to the bis(tri-n-butylphosphine)palladium moiety to form the trans-bis(tri-n-butylphosphine)-,u-[2,2'-bis(ethynyl)thiophenel-2,5-bisethynylthiophene]palladium polymer (15). To compare the advantages of the above extended one-pot (EOP) procedures over classical routes, polymers 6 and 15 were also prepared by the copper-catalyzed reaction of trans-dichlorobis(tri-n-butylphosphine)palladium (5) with 2,5-bis(ethynyl)thiophene (3) and [2-(ethynyl)thiophene]-2,5-bisethynylthiophene (13)
An Efficient One-Pot Access to Poly(arylene ethynylene) Homopolimers: Use of the Bu3Sn-Moiety as Recyclable carrier to Introduce the Ethynyl Unit into the Chain
No full textMechanism of the palladium-catalyzed metal-carbon bond formation. A dual pathway for the transmetalation step
No full textChemical Composition and Antioxidant Activity of Thyme, Hemp and Coriander Extracts: A Comparison Study of Maceration, Soxhlet, UAE and RSLDE Techniques
No full textAppropriate and standardized techniques for the extraction of secondary metabolites
with interesting biological activity from plants are required. In this work, a comparison of dierent
conventional and unconventional extraction techniques (maceration—M, Soxhlet—S, ultrasound
assisted extraction—UAE, and rapid solid-liquid dynamic extraction—RSLDE) was investigated.
Bioactive compounds were extracted from Thymus vulgaris L. (thyme), Cannabis sativa L. (industrial
hemp) and Coriandrum sativum L. (coriander) and chemically characterized for their volatile fraction
and polyphenolic content by means of gas chromatography-mass spectrometry (GC-MS) and high
performance liquid chromatography-ultraviolet (HPLC-UV). Linalool (48.19%, RSLDE) and carvacrol
(21.30%, M) for thyme, caryophyllene (54.78%, S) and humulene (14.13%, S) for hemp, and linalool
(84.16%, RSLDE) for coriander seeds were the main compounds among terpenes, while thyme
was the richest source of polyphenols with rosmarinic acid (51.7 mg/g dry extract-S), apigenin
(7.6 mg/g dry extract-S), and luteolin (4.1 mg/g dry extract-UAE) being the most abundant. In order
to shed light on their potential as natural food preservatives, the biological activity of the extracts
was assessed in terms of antioxidant activity (2,20-azino-bis(3-ethylbenzothiazoline-6-sulphonic
acid—ABTS ̇+, ferric reducing antioxidant power—FRAP, 2,2-diphenyl-1-picrylhydrazyl—DPPH ̇
assays) and phenolic content (Folin–Ciocâlteu method). For thyme, Soxhlet extracts showed best
performances in FRAP and ABTS ̇+ assays (74 mg TE/g dry extract and 134 mg TE/g dry extract,
respectively), while Soxhlet and RSLDE extracts recorded similar activity in DPPH ̇ (107–109 mg
TE/g dry extract). For hemp and coriander, indeed, RSLDE extracts accounted for higher antioxidant
activity as evidenced by FRAP (80 mg TE/g dry extract and 18 mg TE/g dry extract, respectively)
and ABTS ̇+ (557 mg TE/g dry extract and 48 mg TE/g dry extract, respectively) assays. With respect
to DPPH ̇, the best results were observed for UAE extracts (45 mg TE/g dry extract and 220 mg
TE/g dry extract, respectively). Our findings suggest that all the investigated techniques are valid
extraction methods to retain bioactive compounds and preserve their activity for application in food
and pharmaceutical formulations. Among them, the innovative RSLDE stands out for the slightly
higher antioxidant performances of the extracts, coupled with the facility of use and standardization
of the extraction process
Preparation of Models and Oligomers of Metal Alkynyls. NMR, GPC and X-Ray Structural Characterization of Building Blocks for the Construction of Molecular Devices
No full textA systematic study has been carried out for the use of the palladium-based Extended One Pot (EOP) synthetic protocol toward the preparation of metal alkynyl oligomers of general formula [/C/C/Ar/C/C/M(L)m /]n (M/Pt, Pd). Model compounds of type trans-M(PBu3)2(C/CC6H5)2 have been prepared by the reaction of tributyltinethynylbenzene with trans-M(PBu3)2Cl2, in the absence of palladium catalysis, since the presence of catalytic Pd(PPh3)4 yields reaction mixtures containing starting material, product and intermediate complex trans-MCl(PBu3)2(C/CC6H5). Palladium catalysis has been used for the formation of the bistinacetylide compounds Bu3Sn/C/C/Ar/C/C/SnBu3 (Ar/C6H4; bis(2,5-n-octyloxy)C6H4). Subsequent coupling of these compounds with MCl2(PBu3)2 in the absence of palladium catalyst yields metal alkynyl oligomers. Comparison of 31P-NMR and gel
permeation chromatography (GPC) analyses indicates that the GPC technique represents a reliable method to estimate polymer chain lengths for polymers bearing branched aromatic spacers, in spite of the rigid-rod shape of the polymer backbone. Single crystal X-ray determinations of model compounds demonstrate the essential role of side substituents in the aromatic ring to control
the supramolecular order and, as a consequence, the optoelectronic properties of materials
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