Assessment of density functional theory optimized basis sets for gradient corrected functionals to transition metal systems: the case of small Nin (n<or=5) clusters

Density functional calculations have been performed for small nickel clusters, Ni(n), Ni(n) (+), and Ni(n)(-) (n相似文献   

Reliability of fibres in solid-phase microextraction for routine analysis of the headspace of aromatic and medicinal plants

This article evaluates the HS-SPME recovery repeatability, intermediate precision and their performance over time when applied to HS-SPME sampling for quality control of medicinal and aromatic plants. Experiments were carried out on two sets of fibres coated with two different coatings and belonging to different lots (i.e 100 microm polydimethylsyloxane (PDMS) and Carboxen/divinylbenzene/PDMS 50/30 microm, l: 1 cm (CAR/DVB/PDMS)) and on chamomile (Matricaria chamomilla L.), sage (Salvia lavandulifolia Vahl.) and a standard solution containing 3-hexanol, isoamyl acetate, 1,8-cineole and menthol in diisobutyl phthalate. The performance of each set of fibres was evaluated by determining a group of complementary statistical parameters including: (i) repeatability of the absolute areas of each marker from each matrix with each fibre; (ii) intra-fibre repeatability of the total absolute areas of the markers of each matrix obtained with each fibre of each set; (iii) inter-fibre intermediate precision of the total absolute areas of the markers of each matrix obtained with all fibres of each set; and (iv) analysis of variance by one-way ANOVA with Fisher and Tukey tests. The influence of the number of analyses on fibre effectiveness (fibre life-time) was studied by linear regression analysis (LRA). The results proved that HS-SPME can successfully be used for routine control analysis of aromatic ad medicinal plants since both types of fibres showed good repeatability and intermediate precision of analytes recovery and consistency over time. Unlike data previously reported by other authors, CAR/DVB/PDMS coated fibres gave better results than those coated with PDMS. The fibre-life seemed mainly to be influenced by the number and conditions of samplings and nature of the matrix investigated.     

Supra-molecular association and polymorphic behaviour in systems containing bile acid salts

A wide number of supra-molecular association modes are observed in mixtures containing water and bile salts, BS, (with, eventually, other components). Molecular or micellar solutions transform into hydrated solids, fibres, lyotropic liquid crystals and/or gels by raising the concentration, the temperature, adding electrolytes, surfactants, lipids and proteins. Amorphous or ordered phases may be formed accordingly. The forces responsible for this very rich polymorphism presumably arise from the unusual combination of electrostatic, hydrophobic and hydrogen-bond contributions to the system stability, with subsequent control of the supra-molecular organisation modes. The stabilising effect due to hydrogen bonds does not occur in almost all surfactants or lipids and is peculiar to bile acids and salts. Some supra-molecular organisation modes, supposed to be related to malfunctions and dis-metabolic diseases in vivo, are briefly reported and discussed.     

On the ground state of Pd13

First-principles electronic structure calculations within a gradient corrected density functional formalism have been carried out to investigate the electronic structure and magnetic properties of Pd(13) clusters. It is shown that a bilayer ground-state structure that can be regarded as a relaxed bulk fragment is most compatible with the experimental results from Stern-Gerlach measurements. An icosahedral structure, considered to be the ground state in numerous previous studies, is shown to be around 0.14 eV above the ground state. A detailed analysis of the molecular orbitals reveals the near degeneracy of the bilayer or icosahedral structures is rooted in the stabilization by p- or d-like cluster orbitals. The importance of low-lying spin states in controlling the electronic and magnetic properties of the cluster is highlighted.     

Palytoxin in seafood by liquid chromatography tandem mass spectrometry: investigation of extraction efficiency and matrix effect

Blooms of Ostreopsis spp. have been recently reported along the Mediterranean coasts of Spain, France, Italy, and Greece posing serious risks to human health. Occurrence of Ostreopsis spp. may result in palytoxin contamination of seafood and, in order to prevent sanitary risks, the need exists to develop efficient extraction procedures to be coupled to rapid and sensitive monitoring methods of palytoxin-like compounds in seafood. In the present study, the best conditions for both extraction of palytoxin from seafood and palytoxin quantification by using liquid chromatography tandem mass spectrometry (LC-MS/MS) were investigated. Three seafood matrices (mussels, sea-urchins, and anchovies) were selected and five different extraction systems were tested, namely: the official protocol for extraction of lipophilic toxins and various aqueous methanol or acetonitrile solutions (MeOH/H₂O 1:1, MeOH/H₂O 8:2, MeCN/H₂O 8:2 and MeOH 100%). Extraction with MeOH/H₂O 8:2 provided the best results in terms of accuracy and matrix interference on LC-MS/MS detection of palytoxin. Accuracy and intra-day reproducibility (n = 3) were evaluated for all the selected matrices but only for mussels at three spiking concentration levels, including the provisional limit proposed by the Community Reference Laboratory for marine biotoxins (250 μg kg⁻¹). Limits of quantitation of palytoxin in mussels, sea-urchins and anchovies tissues were calculated using matrix-matched standards; taking into account extraction efficiency of MeOH/H₂O 8:2, they resulted to be 228, 343, and 500 μg kg⁻¹, respectively.     

Intact protein separation by chromatographic and/or electrophoretic techniques for top-down proteomics

Mass spectrometry used in combination with a wide variety of separation methods is the principal methodology for proteomics. In bottom-up approach, proteins are cleaved with a specific proteolytic enzyme, followed by peptide separation and MS identification. In top-down approach intact proteins are introduced into the mass spectrometer. The ions generated by electrospray ionization are then subjected to gas-phase separation, fragmentation, fragment separation, and automated interpretation of mass spectrometric and chromatographic data yielding both the molecular weight of the intact protein and the protein fragmentation pattern. This approach requires high accuracy mass measurement analysers capable of separating the multi-charged isotopic cluster of proteins, such as hybrid ion trap-Fourier transform instruments (LTQ-FTICR, LTQ-Orbitrap). Front-end separation technologies tailored for proteins are of primary importance to implement top-down proteomics. This review intends to provide the state of art of protein chromatographic and electrophoretic separation methods suitable for MS coupling, and to illustrate both monodimensional and multidimensional approaches used for LC-MS top-down proteomics. In addition, some recent progresses in protein chromatography that may provide an alternative to those currently employed are also discussed.     

Nucleophilic substitutions in the isoindole series as a valuable tool to synthesize derivatives with antitumor activity

A novel synthetic approach to the synthesis of 3-substituted isoindoles through nucleophilic substitution of 3-halo derivatives by charged carbon, and neutral nitrogen, oxygen, and sulfur nucleophiles, assisted by a 1-acyl group, is reported. Aryl-thio-isoindoles, obtained through a direct nucleophilic substitution with sulfur nucleophiles, showed cytotoxic activity, with GI₅₀ values from micromolar to sub-micromolar concentrations, against the total number of cell lines investigated.     

Synthesis of the new ring system pyrrolizino[2,3-b]indol-4(5H)-one

Derivatives of the new ring system pyrrolizino[2,3-b]indol-4(5H)-one were prepared in four steps starting from substituted benzonitriles bearing a functionalized amino group in the adjacent position. The unsubstituted- and the dimethoxy-pyrrolizinoindolones 5a and 5b exhibited modest activity against the HL-60(TB) human leukemia cell line, whereas the N-methylated dimethoxy-pyrrolizinoindolone 6b showed to be selective against MOLT-4 leukemia, A549/ATCC, HOP-92, and NCI-H460 non-small cell lung cancer, and CAKI-1 renal cancer cell lines.     

Evolution of the protein corona of lipid gene vectors as a function of plasma concentration

The concept that the effective unit of interest in the cell-nanomaterial interaction is the particle and its corona of associated proteins is emerging. Here we investigate the compositional evolution of the protein corona of 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) cationic liposomes (CLs) and DOTAP/DNA lipoplexes over a wide range of plasma concentrations (2.5-80%). The composition of the hard corona of lipoplexes is quite stable, but that of CLs does evolve considerably. We show that the protein corona of CLs is made of both low-affinity and competitive-binding proteins whose relative abundance changes with the plasma concentration. This result may have deep biological implications for the application of lipid-based gene vectors both in vitro and in vivo.     

Reverse mode operation polymer dispersed liquid crystal with a positive dielectric anisotropy liquid crystal

The development of electrically activated chromogenic materials is important for their potential applications in smart windows. Several previous works have reported on reverse mode operation polymer dispersed liquid crystals (PDLCs) based on negative dielectric anisotropy liquid crystals. They have a transparent OFF state, which turns opaque after the application of a suitable external electric field. Nevertheless, these devices have some limitations such as the use of large amount of expensive liquid crystals with peculiar physical‐chemical properties. In addition, a good matching between the refractive index of liquid crystal and the polymer matrix one is required. The main result of this work is the achievement of reverse mode operation devices prepared with a positive dielectric anisotropy liquid crystal and characterized by a high OFF state transmittance obtained by the onset of high intensity built‐in DC electric fields in a direct mode operation PDLC, which allows the OFF state homeotropic alignment of liquid crystal directors. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011