New advances in homoleptic organotransition-metal compounds: the case of perhalophenyl ligands

Homoleptic derivatives of formula [M(C(6)X(5))(n)](z-) (X = F, Cl) have been prepared and isolated for every first-row transition metal as well as for several of the heavier ones. The stoichiometry attained in each case (n ranging between 2 and 6) can be understood considering the tendency of a given metal ion to compensate its coordinative and electronic unsaturation, while not incurring severe interligand repulsive effects. The molecular structures associated with each stoichiometry seem, in turn, to be governed by electronic rather than steric factors. Most of these [M(C(6)X(5))(n)](z-) compounds are unsaturated, open-shell organometallic species, not fulfilling the 18-electron (or Effective Atomic Number) rule. This behaviour can be attributed to the absence of pi stabilising ligands (such as CO, phosphines, alkenes, alkynes, a variety of substituted aromatic rings, and so on) which are otherwise ubiquitous in organotransition-metal chemistry. The magnetic properties of the [M(C(6)X(5))(n)](z-) species have been determined by EPR spectroscopy and/or bulk magnetisation measurements. Excellent correlation between molecular geometry and magnetic properties (whether diamagnetic or paramagnetic) has been observed. Many of these compounds undergo chemically- or electrochemically-induced electron exchange processes. These redox reactions proceed without alteration in the stoichiometry of the [M(C(6)X(5))(n)](z-) compound, but usually involve a sharp change in the molecular geometry according to the different electron configuration of the interrelated species.     

High molecular weight poly-biphenoxyphosphazene copolymers with cyclic secondary amino groups

The reaction of poly(dichlorophosphazene) [NPCl₂]_n with 2,2′-dihydroxybiphenyl, 2,2′-(OH)C₆H₄-C₆H₄(OH), and then with p-anisidine, p-NH₂C₆H₄OMe, in the presence of K₂CO₃ led to the formation of the chlorine containing phosphazene copolymer {[NP(O₂C₁₂H₈)]_0.75[NP(NHC₆H₄OMe)₂]_0.15[NP(NHC₆H₄OMe)Cl]_0.05[NPCl₂]_0.05}_n (1), which could be isolated and fully characterised. When using cyclic secondary amines instead of aromatic primary amines, namely, HNC₅H₁₀ (piperidine), HNC₄H₈O (morpholine), HNC₄H₈S (thiomorpholine), the reaction gave the functionalized copolymers {[NP(O₂C₁₂H₈)]_0.6[NP(NC₅H₁₀)₂]_0.4}_n (2), {[NP(O₂C₁₂H₈)]_0.65[NP(NC₄H₈O)₂]_0.35}_n (3) and {[NP(O₂C₁₂H₈)]_0.75[NP(NC₄H₈S)₂]_0.25}_n (4), respectively. The broad bands in their ³¹P NMR spectra and the bimodal aspect of their GPC chromatograms suggested they could be forming aggregates in solution.     

Micellar electrokinetic chromatography method for the determination of several natural red dyestuff and lake pigments used in art work

The identification of organic colorants used in artistic paintings is an important information source for reconstructing the working techniques found in a particular work and for defining a programme for the restoration and conservation of the painting. In this work, sodium dodecyl sulfate (SDS) was used as a surfactant in micellar electrokinetic chromatography (MEKC) for separating a broad range of red organic pigments, based on their colouring matters: madder (colouring matters: alizarin, quinizarin and purpurin), cochineal (colouring matter: carminic acid), red sandalwood (colouring matter: santalin), brazilwood (colouring matter: brazilin), lac dye (colouring matter: laccaic acid) and dragon's blood (colouring matter: dracorhodin). The running electrolyte used was 20 mM borax (pH 9), containing 20 mM SDS and 10% acetonitrile as organic modifier. Separation was carried out by applying a +20 kV voltage at the injection end, 25 degrees C and 214 nm/254 nm as detection wavelengths. All colorants were separated within less than 13 min with a good baseline resolution. The method was applied to the analysis of paint samples obtained from the Diocesan Museum of Holy Art of Bilbao.     

New hexamethine–hemicyanine dyes for the development of integrated optochemical sensors

New far-visible absorbing anilino-cyanine dyes have been synthesised for future application as chromoionophores in integrated waveguide absorbance optodes based on bulk optodes. The effect of the heterocycle, of the substitution of the heterocyclic nitrogen and of the type of heptamethine central ring on the pK _a values (4.3–8.2 in ethanol–water solutions and 9.5–11.0 in plasticised PVC membranes), on the spectroscopic characteristics of the dye and on photostability is discussed. pH-selective bulk optodes have been formulated as a first approach to develop ion-selective optodes, and sensitivity, repeatability, lifetime and response time have been determined. The dyes show good analytical behaviour for use as chromoionophores for the development of ion-selective optodes. Reversible (80–87%), fast (tr_90% = 0.94–2.28 min) and pH-sensitive membranes (slopes of 0.09–0.23 ΔAbs·pHdec^–1, absorbance range 0.19–0.53) have been obtained. Moreover, they exhibit good spectroscopic features for employment with integrated optochemical sensors: absorption maxima of the acidic species in plasticised PVC membranes matched those of 650–670-nm LEDs, high molar absorption coefficients ( L mol^–1 cm^–1 and L mol⁻¹ cm⁻¹) and fluorescence. Absorption spectra of the acidic and basic structures of one of the synthesised chromoionophores at different pKa values. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Chemical Analysis at Atomic Resolution of Isolated Extended Defects in an Oxygen‐Deficient,Complex Manganese Perovskite

A general approach to the structural and analytical characterization of complex bulk oxides that exploits the advantage of the atomic spatial resolution and the analytical capability of aberration‐corrected microscopy is described. The combined use of imaging and spectroscopic techniques becomes necessary to the complete characterization of the oxygen‐deficient colossal magnetoresistant La_0.56Sr_0.44MnO_2.5‐related perovskite. In this compound, the formation of isolated (La/Sr)O and MnO rock‐salt‐type planar defects are identified from atomically resolved High Angle Annular Dark Field (HAADF) images. The location of the oxygen atomic columns from Annular Bright Field (ABF) images indicates edge‐sharing MnO₆ octahedra in the MnO planes and the study performed by Electron Energy Loss Spectroscopy (EELS) reveals different Mn oxidation states derived from the corner‐ or edge‐sharing MnO₆ octahedra environment.     

Modelling multiple-simultaneous impact problems with a nonlinear smooth approach: pool/billiard application

Nonlinear Dynamics - Smooth approaches are able to model reasonably well contact/impact events between two bodies, showing some peculiarities when dealing with certain geometries and arising...     

Evaluation of online carbon isotope dilution mass spectrometry for the purity assessment of synthetic peptide standards

We present a novel method for the purity assessment of peptide standards which is applicable to any water soluble peptide. The method is based on the online ¹³C isotope dilution approach in which the peptide is separated from its related impurities by liquid chromatography (LC) and the eluent is mixed post-column with a continuous flow of ¹³C-enriched sodium bicarbonate. An online oxidation step using sodium persulfate in acidic media at 99 °C provides quantitative oxidation to ¹²CO₂ and ¹³CO₂ respectively which is extracted to a gaseous phase with the help of a gas permeable membrane. The measurement of the isotope ratio 44/45 in the mass spectrometer allows the construction of the mass flow chromatogram. As the only species that is finally measured in the mass spectrometer is CO₂, the peptide content in the standard can be quantified, on the base of its carbon content, using a generic primary standard such as potassium hydrogen phthalate. The approach was validated by the analysis of a reference material (NIST 8327), and applied to the quantification of two commercial synthetic peptide standards. In that case, the results obtained were compared with those obtained using alternative methods, such as amino acid analysis and ICP-MS. The results obtained proved the value of the method for the fast, accurate and precise mass purity assignment of synthetic peptide standards.     

Synthesis of N-aryl imidazoles catalyzed by copper nanoparticles on nanosized silica-coated maghemite

A magnetically recoverable catalyst consisting of copper nanoparticles (CuNPs) on nanosized silica-coated maghemite is presented. The catalyst has been prepared under mild conditions by mixing the magnetic support with a freshly prepared suspension of CuNPs obtained by fast reduction of anhydrous CuCl₂ with lithium sand and a catalytic amount of DTBB (4,4′-di-tert-butylbiphenyl) as electron carrier. This copper-based catalyst has shown to be very efficient in the N-(hetero)arylation of imidazole using (hetero)aryl bromides and iodides as arylating agents under ligand-free conditions. The catalyst is easily recovered by means of an external magnet and can be reutilized in three N-arylation cycles without apparent loss of catalytic activity.     

The Nucleoside Uridine Isolated in the Gas Phase

Herein we present the first experimental observation of the isolated nucleoside uridine, placed in the gas phase by laser ablation and characterized by Fourier transform (FT) microwave techniques. Free from the bulk effects of their native environments, anti/C2′‐endo‐g+ conformation has been revealed as the most stable form of uridine. Intramolecular hydrogen bonds involving uracil and ribose moieties have been found to play an important role in the stabilization of the nucleoside.