Synthesis, crystal structure and thermal behavior of dimethylgold(III) derivatives of salicylaldimine Schiff bases - Novel precursors for gold MOCVD applications

Dimethylgold(III) complexes with salicylaldimine Schiff bases of general formula Me₂Au(SalN-R) (R = methyl (1), iso-propyl (2), or cyclohexyl (3)) have been synthesized in a single step reaction from dimethylgold(III) iodide [Me₂AuI]₂ and N-substituted salicylaldimines. Single-crystal X-ray studies provide evidence of mononuclear four-coordinated complexes with square-planar coordination geometry. The temperature dependences of saturated vapour pressure of complexes have been studied by the Knudsen effusion method with mass spectrometric analysis of the composition of the gas phase. The thermodynamic parameters of the sublimation process ΔH^o_T and ΔS^o_T have been calculated. Thermal decomposition of the vapour of compounds has been studied by means of high temperature mass spectrometry in a vacuum, and by-products have been determined. All of these complexes show good volatility and thermal stability. For complex 2, which is more volatile and low-melting, pulse MOCVD experiments have been carried out at substrate temperatures lower than 200 °C. The deposited gold nanoparticles (5-15 nm) have been investigated by means of SEM and AFM.     

Benefits of applying combined diffuse reflectance FTIR spectroscopy and principal component analysis for the study of blue tempera historical painting

This paper explores the application of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to the examination of historic blue pigments and blue tempera paintings commonly found on works of art. The discussion is mainly focused on the practical benefits of using this technique joined to principal component analysis (PCA), a powerful multivariate analysis tool. Thanks to the study of several replica samples that contain either pure blue pigments (azurite, lapis lazuli and smalt), or pure binder (rabbit glue) and mixtures of each of the pigments with the binder (tempera samples), different aspects of these benefits are highlighted. Comparative results of direct spectra and multivariate analysis using transmittance-Fourier transform infrared spectroscopy (T-FTIR) are discussed throughout this study. Results showed an excellent ability of PCA on DRIFT spectra for discriminating replica samples according to differing composition. Several IR regions were tested with this aim; the fingerprint IR region exhibited the best ability for successfully clustering the samples. The presence of the binder was also discriminated. Only using this approach it was possible to completely separate all the studied replica samples. This demonstrates the potential benefits of this approach in identifying historical pigments and binders for conservation and restoration purposes in the field of Cultural Heritage.     

PalladiumII and platinumII complexes with heteroditopic 10-(aryl)phenoxarsine (aryl = 2-C6H4OR, R = H, Me, Pr(i)) ligands: solvent-oriented crystallization of cis isomers

The synthesis and characterization of 10-(o-alkoxyphenyl)phenoxarsines 2-ROC6H4As(C6H4)2O (R = H, Me, and Pri, As(C6H4)2O = phenoxarsine) and their platinum(II) and palladium(II) complexes cis-[PtCl2{2-PriOC6H4As(C6H4)2O-kappaAs}2] (1), trans-[PdCl2{2-PriOC6H4As(C6H4)2O-kappaAs}2] (2), cis-[PtCl2{2-HOC6H4As(C6H4)2O-kappaAs}2] (3), cis-[PdCl2{2-HOC6H4As(C6H4)2O-kappaAs}2] (4), cis-[PtI2{2-MeOC6H4As(C6H4)2O-kappaAs}2] (5), and trans-[PdCl2{2-MeOC6H4As(C6H4)2O-kappaAs}2] (6) are reported. The chelate complex cis-[Pt{2-OC6H4As(C6H4)2O-kappaAs,O}2] (7) is also described. The molecular structures of 1-4 and 7 were determined. The short As...O intramolecular interaction found in complexes 1-4 in the solid state was also verified by calculations at the B3LYP/LANL2DZ level for complex 2 and for 10-(o-isopropoxyphenyl)phenoxarsine in the gas phase, and this suggests that the interaction is a characteristic of the ligand rather than a packing effect. Calculations at the B3LYP/LANL2DZ and Oniom(B3LYP/LANL2DZ:uff) levels for complexes 1-4 showed that the solvent plays a crucial role in the crystallization (through geometry constraints) of the kinetically stable cis isomers.     

Photocatalytic hydrogen evolution over mesoporous TiO2/metal nanocomposites

Na⁺ complex with the dibenzo-18-crown-6 ester was used as a template to synthesize mesoporous titanium dioxide with the specific surface area 130–140 m²/g, pore diameter 5–9 nm and anatase content 70–90%. The mesoporous TiO₂ samples prepared were found to have photocatalytic activity in Cu^II, Ni^II and Ag^I reduction by aliphatic alcohols. The resulting metal–semiconductor nanostructures have remarkable photocatalytic activity in hydrogen evolution from water–alcohol mixtures, their efficiency being 50–60% greater than that of the metal-containing nano-composites based on TiO₂ Degussa P25.The effects of the thermal treatment of mesoporous TiO₂ upon its photocatalytic activity in hydrogen production were studied. The anatase content and pore size were found to be the basic parameters determining the photoreaction rate. The growth of the quantum yield of hydrogen evolution from TiO₂/Ag⁰ to TiO₂/Ni⁰ to TiO₂/Cu⁰ was interpreted in terms of differences in the electronic interaction between metal nanoparticles and the semiconductor surface. It was found that there is an optimal metal concentration range where the quantum yield of hydrogen production is maximal. A decrease in the photoreaction rate at further increment in the metal content was supposed to be connected with the enlargement of metal nanoparticles and deterioration of the intimate electron interaction between the components of the metal–semiconductor nanocomposites.     

Can glycans unveil the origin of glycoprotein hormones? - human chorionic gonadotrophin as an example -

Doping with (glyco)protein hormones represent an extremely challenging, analytical problem as nearly all are constitutively present at low concentrations that fluctuate according to circadian or alternative periodical, or external stimuli. Thus the mere concentration in a biological sample is only resolutive when this surpasses extreme values. As the vast majority of these molecules are produced by recombinant DNA technology it is believed that the exogenous molecules could bear the signature of the host cell. In particular, these could comprise structural differences originated from co or post-translational differences. In this study we have employed both proteomics and glycomics strategies to compare recombinant and urinary human chorionic gonadotrophin in order to evaluate this hypothesis. As anticipated the recombinant hormone could be shown to contain N-glycolyl neuraminic acid, a sialic acid that cannot be produced by humans. Furthermore, differences were observed in the overall glycosylation, in particular the presence of abundant hybrid-type glycans that were much less pronounced in the recombinant species. These differences were determined to occur predominantly in the alpha-subunit for which antidoping strategies focussed on these elements could be used for both chorionic gonadotrophin and lutrophin as they share the same alpha-subunit.     

Investigation of iron oxide nanoparticles by capillary zone electrophoresis

The electrophoretic behavior of γ-Fe₂O₃ nanoparticles was studied in aqueous solutions of Na₂SO₄-NaOH (pH 10.8) and of Na₂SO₄-Na₃cit (pH 7.1) as running electrolytes. Two electrophoretic zones (smooth and with spikes) due to colloidal and suspended particles of approximately the same size range were formed during the runs. The suspension stability and size distribution were shown to depend on the composition of electrolyte used for dispersing the solids. The effects of electric field strength, injection time, injection pressure as well as sodium citrate concentration were studied and particle electrophoretic mobilities were calculated. Electron micrographs of particles studied were obtained. Preparation of reference samples based on the colloidal γ-Fe₂O₃ has been discussed.     

Challenges in quantum dot-neuron active interfacing

Semiconductor nanocrystal quantum dots (qdots) are now being explored in applications requiring active cellular interfaces, such as biosensing and therapeutics in which information is passed from the qdot to the biological system, or vice versa, to perform a function. These applications may require surface coating chemistry that is different from what is commonly employed for passive interface applications like labeling (i.e., thick polymer coatings such as poly(ethylene glycol) (PEG)), in which the only concern is nonspecific sticking to cells and biocompatibility. The thick insulating coatings that are generally needed for labeling are generally not suitable for active qdot-cell interface applications. There is currently little data regarding the interactions between viable cells and qdots under physiological conditions. Our initial investigations using mercaptoacetic acid-coated CdS and CdTe qdots as a simple model to interface with neuron cell surface receptors under physiological conditions uncovered two significant technological hurdles: nonspecific binding and endocytosis. Nonspecific binding can be extensive and in general there appears to be greater nonspecific binding for larger particle sizes, but this also depends sensitively on the particle surface characteristics and the type of neuron, possibly indicating a detailed relationship between particle-cell affinity and cell membrane chemistry. More importantly, qdot endocytosis occurs rapidly at physiological temperature for the different nerve cell types studied, within the first five minutes of exposure to both CdS and CdTe qdots, regardless of whether the molecular coatings specifically recognize cell surface receptors or not. As a consequence, new strategies for tagging cell surface recognition groups for long-term active interfacing with cells under physiological conditions are needed, which requires more sophisticated ligands than MAA but also the absence of thick insulating coatings.     

Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 12--aliphatic and alicyclic oximes

One-bond carbon-carbon coupling constants were calculated in a series of nine aliphatic and alicyclic oximes at the SOPPA (second-order polarization propagator approach) level in good agreement with the available experimental data, and several unknown couplings were predicted with high reliability. The experimental difference between J(C,C) of the corresponding carbon-carbon bonds in cis and trans orientations to the nitrogen lone pair is very well reproduced at the SOPPA level, and this provides an additional tool in the configurational assignment at the C=N bond in oximes and related systems.     

Euler Tours of Maximum Girth in K2 n +1 and K2 n ,2 n

Given an eulerian graph G and an Euler tour T of G, the girth of T, denoted by g(T), is the minimum integer k such that some segment of k+1 consecutive vertices of T is a cycle of length k in G. Let g^E(G)= maxg(T) where the maximum is taken over all Euler tours of G.We prove that g^E(K_2n,2n)=4n–4 and 2n–3g^E(K_2n+1)2n–1 for any n2. We also show that g^E(K₇)=4. We use these results to prove the following:1)The graph K_2n,2n can be decomposed into edge disjoint paths of length k if and only if k4n–1 and the number of edges in K_2n,2n is divisible by k.2)The graph K_2n+1 can be decomposed into edge disjoint paths of length k if and only if k2n and the number edges in K_2n+1 is divisible by k.