Synthesis and coordination properties of new macrocyclic ligands: equilibrium studies and crystal structures

The synthesis and characterization of two new macrocyclic ligands, the bis-macrocyclic compound 2,6-bis(1,4,13-triaza-7,10-dioxacyclopentadec-1-ylmethyl)phenol (L) and 38-methoxy-1,4,13,16,19,28-hexaaza-7,10,22,25-tetraoxatricyclo[14.14.7.1(32,36)]octatriconta-32,34,Delta(36,38)-triene (L1) are reported. Equilibrium studies of basicity and coordination properties toward metal ions such as Cu(II), Zn(II), Cd(II) and Pb(II) were performed for ligand by potentiometric measurements in aqueous solution (298.1 +/- 0.1 K, I= 0.15 mol dm(-3)). L behaves as a hexaprotic base (logK(1)= 10.93, logK(2)= 9.70, logK(3)= 8.79, logK(4)= 8.05, logK(5)= 6.83, logK(6)= 2.55). All metal ions form stable mono- and dinuclear complexes: logK(MLH(-1))= 25.61 for Cu(II), 15.37 for Zn(II), 12.58 for Cd(II) and 13.79 for Pb(II); logK(M(2)LH(-1))= 31.61 for Cu(II), 23.38 for Zn(II), 24.49 for Cd(II) and 23.68 for Pb(II). All these dinuclear species show a great tendency to add the OH(-) group: the equilibrium constant for the addition reaction was found to be logK(M(2)LH(-1)OH)= 4.77 for Cu(II), 5.66 for Zn(II), 2.8 for Cd(II) and 3.18 for Pb(II). In the case of Ni(II), kinetic inertness prevents the possibility of solution studies. The dinuclear solid adducts [Ni(2)H(-1)L(N(3))(3)].EtOH and [Cu(2)H(-1)L(N(3))](ClO(4))(2) were characterized by X-ray analysis.     

The relative permittivity of 1,2-ethanediol+2-methoxyethanol+water ternary mixtures

The relative permittivities for the ternary 1,2-ethanediol (component 1) + 2-methoxyethanol (2) + water (3) solvent system have been measured for 66 mixtures covering the whole mole fraction composition 0X₁/X₂/X₃ 1 range at –10, –5 and 0 °C. The experimental data were used to test some empirical relations stating the dependence of = (X₁, X₂, X₃). A comparison between the calculated and experimental data show that these equations can be usefully employed to predict values in correspondence of the experimental data gaps.     

Fibrazioni di una classe di near-field regolari di dimensionet+1 sul nucleo

Il contenuto di questo lavoro consiste nel mostrare che le fibrazioni dei near-field regolari di dimensionet+1 sul nucleo , quando , si ottengono da fibrazioni regolari con una operazione di scambio fra alcuni sistemi di matrici, che generalizza il procedimento di sostituzione di regoli con regoli opposti di quadriche rigate nel caso di dimensione due sul nucleo.     

The role of esterification on detection of protonated and deprotonated peptide ions in matrix assisted laser desorption/ionization (MALDI) mass spectrometry (MS)

Esterification was used to investigate how introduction of aliphatic chains within the peptide structure affects the MALDI response of ions analyzed in both polarity regimes. In binary mixtures containing equimolar amounts of a peptide with its correspondent alkyl ester, derivatization of the carboxylic groups has the tendency to increase MALDI detection of the modified protonated peptide ions. This positive effect on ion yield is more pronounced when longer alcohols are employed. In negative mode, the situation is antithetic and esterification produces a deleterious effect on the ion yield of the corresponding deprotonated species. From the data reported here we postulate that modifications of the acidic character of peptides prevent formation of anionic species under MALDI analysis. Furthermore, suppression of the formation pathway for anions alters the overall number of molecules which can undergo protonation. This results in an increased ion yield for the protonated esters.     

New Dolabellane Derivatives from the Brown Alga Dictyota pardalis

Reinvestigation of the brown alga Dictyota pardalis f. pseudohamata CRIBB led to the crystallization of 1 and to the isolation of the two new dolabellane derivatives 2 and 3 . X-Ray analysis of 1 and 2 , together with detailed 1D-and 2D-NMR studies on 2 and 3 , allowed their structures to be elucidated as (1R*,3S*,7S*,11R*,4Z)-dolabella-4,8(17), 12(18)-triene-3,7-diol ( 1 ), (1R*,3S*,4S*,7S*,8S*,11R*,14R*,12E)-3,4:7,8-diepoxydolabe11-12-ene-14, 18-diol ( 2 ), and (1R*,3S*,4S*,7S*,8S*,11R*,14R*)-3,4:7,8-diepoxy-l,4,8,12,12-pentamethylbicyclo[9. 3. 0]tetra-decan-14-ol( 3 ).     

Ceramic Foams from a Preceramic Polymer and Polyurethanes: Preparation and Morphological Investigations

Open-cell ceramic foams were obtained from a preceramic polymer (silicone resin) and blown polyurethanes. The preceramic polymer, which is crosslinked by condensation of silanol groups, was dissolved in CH2Cl2 and added to a liquid polyol containing the surfactant and the amine catalyst. Isocyanate was then added to the mixture and the foam was obtained through a twofold blowing mechanism (physical and chemical blowing). The morphology of the expanded polyurethane, which can be flexible or semirigid, characterized the final structure of the ceramic foam. The materials obtained were pyrolyzed in a nitrogen flux at temperatures of 1000–1200°C, thus allowing for the polymer-to-ceramic transformation to occur in the preceramic polymer. The ceramic foams produced in this way consisted of an amorphous silicon oxycarbide ceramic (SiOC). They presented a density ranging from 0.1 to 0.3 g/cm3. The average pore diameter ranged from 200 to 400 m and they possessed 80 to 90% open porosity.     

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.     

Fast solid-phase extraction-gas chromatography-mass spectrometry procedure for oil fingerprinting. Application to the Prestige oil spill

A rapid and simple fractionation procedure using solid-phase extraction (SPE) cartridges was developed for an accurate determination of aliphatic and polycyclic aromatic hydrocarbons in petroleum residues and further application in chemical fingerprinting of oil spills by gas chromatography-mass spectrometry (GC-MS). Among the adsorbents evaluated, SiO2/C3-CN exhibited the best selectivity, providing, by elution with n-hexane (4 ml) and n-hexane-CH2Cl2 (1:1) (5 ml), two well-resolved aliphatic and aromatic hydrocarbon fractions, with recoveries of 97 +/- 7.2 and 99.7 +/- 13.9%, respectively. The SPE fractionation procedure was compared with the conventional silica-alumina adsorption chromatography showing similar results but practical advantages in terms of reproducibility, analysis time, solvent reduction and cost. Moreover, is particularly suitable for routine analysis with a high sample throughput. The developed methodology was tested in the characterization of fuel-oil samples collected along the Spanish north-west coast, after the Prestige oil spill accident.     

Unexpected and expeditious entry into trifluoromethyl aziridines from substituted beta-dicarbonyl compounds

[Reaction: see text]. One-pot aziridinations were obtained starting from substituted 2,2,2-trifluoroethyl beta-dicarbonyl compounds with nosyloxycarbamates in the presence of an excess of CaO as base. The unexpected ring closure reaction takes place at room temperature, leading to the N-protected alpha-trifluoromethyl aziridines with good yields. The reaction pathway seems to be influenced by the choice of the base.