The effect of functionalization on structure and electrical conductivity of multi-walled carbon nanotubes

Nanosized powders of Ti-Nb oxide core-shell nanocrystals with atomic ratios of Nb/Ti = 0.11, 0.25, and 0.38 have been prepared by two preparation routes. The first route was co-precipitation, followed by␣annealing, using NbCl₅ as a source of Nb. The second route was coating of pure TiO₂ nanocrystals by Nb-isopropoxide in liquid medium, followed by impregnation of the Nb into the nanoparticles by annealing. Both methods yielded anatase nanocrystals with a Nb-rich shell and a core, which had much lower Nb loadings. The anatase structure solid solution (with Nb incorporated) was stable under annealing up to 760°C. The particle size remained within the nanometric scale (<50 nm) under heat-treatment up to 760°C. It has been shown that the fabricated powders can be redispersed in aqueous media by simple ultrasound treatment, resulting in nanosized dispersions. Using a variety of analytical techniques, including depth profiling of single nanocrystallites by AES combined with sputtering by Ar ions, the mechanism of the core-shell structure creation was studied. It is proposed that the formation of the core-shell structure is governed by solubility limitations in the co-precipitation route and by solubility and diffusion limitations in the coating-incorporation route.     

The many levels pairing Hamiltonian for two pairs

We address the problem of two pairs of fermions living on an arbitrary number of single-particle levels of a potential well (mean field) and interacting through a pairing force in the framework of the Richardson equations. The associated solutions are classified in terms of a number v_l, which reduces to the seniority v in the limit of a large pairing strength G and yields the number of pairs not developing a collective behaviour, their energy remaining finite in the G limit. We express analytically, through the moments of the single-particle levels distribution, the collective mode energy and the two critical values G_cr⁺ and G_cr^- of the coupling which can exist on a single-particle level with no pair degeneracy. Notably G_cr⁺ and G_cr^-, when the number of single particle levels goes to infinity, merge into the critical coupling of a one-pair system G_cr (when it exists), which is not envisioned by the Richardson theory. In correspondence of G_cr, the system undergoes a transition from a mean-field- to a pairing-dominated regime. We finally explore the behaviour of the excitation energies, wave functions and pair transfer amplitudes versus G finding out that the former, for G > G_cr^-, come close to the BCS predictions, whereas the latter display a divergence at G_cr, signaling the onset of a long-range off-diagonal order in the system.     

Direct continuous supercritical fluid extraction as a novel method of wine analysis. Comparison with conventional indirect extraction and implications for wine variety identification

Direct supercritical fluid extraction (SFE) of wines with carbon dioxide was compared to SFE of the sorbent used for solid-phase extraction of the same wine samples (SPE-SFE). Compared to SPE-SFE, the direct SFE results in amore specific and representative gas chromatographic fingerprint of the wine sample. The multivariate statistical processing of the direct SFE-GC data provides a clear-cut and sharp discrimination among the individual wine varieties while the discrimination based on the SPE-SFE-GC data is relatively poor. This finding reflects the adverse effects of additional analyte-sorbent interactions and sorption/desorption steps involved in SPE-SFE.     

Bottlebrush‐shaped copolymers with cellulose diacetate backbone by a combination of ring opening polymerization and ATRP

Graft copolymers with cellulose diacetate (CDA) backbone and both the poly(ε‐caprolactone) and polystyrene, or poly(butyl acrylate) or PMMA grafts were prepared by two‐step process. First, ε‐caprolactone (CL) was polymerized by ring‐opening polymerization (ROP) initiated with CDA, partly funcionalized with 2‐bromo‐isobutyryl groups (degree of functionalization was 0.5). The p(CDA‐g‐CL) copolymers were used in the second step as polyfunctional macroinitiators of ATRP of the vinyl monomer, giving densely grafted copolymers with polyester and PSt, or PBuA, or PMMA grafts. The prepared copolymers were characterized by SEC, some of them also by FTIR spectroscopy and atomic force microscopy (AFM). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 564–573, 2008     

Liquid chromatography coupled to quadruple time‐of‐flight tandem mass spectrometry for microcystin analysis in freshwaters: method performances and characterisation of a novel variant of microcystin‐RR

Cyanobacteria, also called blue‐green algae, occur worldwide within water blooms in eutrophic lakes and drinking water reservoirs, producing several biotoxins (cyanotoxins). Among these, microcystins (MCs) are a group of cyclic heptapeptides showing potent hepatotoxicity and activity as tumour promoters. So far, at least 89 MCs from different cyanobacteria genera have been characterised. Herein, ion trap, matrix‐assisted laser desorption/ionisation time‐of‐flight (MALDI‐ToF) and quadruple time‐of‐flight (Q‐ToF) mass spectrometry (MS)‐based methods were tested and compared for analysing MCs in freshwaters. Method performances in terms of limit of detection, limit of quantification, mean recoveries, repeatability, and specificity were evaluated. In particular, a liquid chromatography/electrospray ionisation (LC/ESI)‐Q‐ToF‐MS/MS method was firstly described to analyse MCs in freshwaters; this technique is highly selective and sensitive, and allowed us to characterise the molecular structure of an unknown compound. Indeed, the full structural characterisation of a novel microcystin variant from a bloom of Planktothrix rubescens in the Lake Averno, near Naples, was attained by the study of the fragmentation pattern. The new cyanotoxin was identified as the 9‐acetyl‐Adda variant of microcystin‐RR. Copyright © 2009 John Wiley & Sons, Ltd.     

Electrospun Mats from Styrene/Maleic Anhydride Copolymers: Modification with Amines and Assessment of Antimicrobial Activity

New antimicrobial microfibrous electrospun mats from styrene/maleic anhydride copolymers were prepared. Two approaches were applied: (i) grafting of poly(propylene glycol) monoamine (Jeffamine® M‐600) on the mats followed by formation of complex with iodine; (ii) modification of the mats with amines of 8‐hydroxyquinoline or biguanide type with antimicrobial activity. Microbiological screening against S. aureus, E. coli and C. albicans revealed that both the formation of complex with iodine and the covalent attachment of 5‐amino‐8‐hydroxyquinoline or of chlorhexidine impart high antimicrobial activity to the mats. In addition, S. aureus bacteria did not adhere to modified mats.

     

Analysis of multiple mycotoxins in beer employing (ultra)-high-resolution mass spectrometry

The objective of the presented study was to develop and optimize a simple, high-throughput method for the control of 32 mycotoxins (Fusarium and Alternaria toxins, aflatoxins, ergot alkaloids, ochratoxins, and sterigmatocystin) in beer. Due to the broad range of their physicochemical properties, the sample preparation step was simplified as much as possible to avoid analyte losses. The addition of acetonitrile to beer samples enabled precipitation of abundant matrix components. The clean-up efficiency was controlled by ambient mass spectrometry employing a direct analysis in real time (DART) ion source. For determination of analytes, ultra-high-performance liquid chromatography hyphenated with high-resolution mass spectrometry utilizing an orbitrap (U-HPLC-orbitrapMS) or time-of-flight (TOFMS) technology was used. Because of significantly better detection capabilities of the orbitrap technology, the U-HPLC-orbitrapMS method was chosen as a determinative step and fully validated. To compensate matrix effects, matrix-matched calibration was employed. The lowest calibration levels for most of the target mycotoxins ranged from 1 to 8 μg L(-1) beer and the recoveries of analytes were in range from 86 to 124%.     

Polyisoprenylated benzophenone derivatives from the fruits of Garcinia cambogia and their absolute configuration by quantum chemical circular dichroism calculations

Three new tetracyclic polyisoprenylated xanthones, named oxy-guttiferones M, K2, and I, along with oxy-guttiferone K and guttiferone M, have been isolated from the fruits of Garcinia cambogia. Their structures were elucidated by MS and NMR spectroscopic experiments. The absolute configurations of oxy-guttiferone K, taken as a model of tetracyclic xanthones, and guttiferone M, as a model of polyisoprenylated benzophenones, have been determined by comparison of their experimentally measured circular dichroism (CD) curves with the TDDFT-predicted curves.     

Automated preparation of carbon-11 ethanol and carbon-11 butanol for human studies using positron emission tomography

An automated continuous flow process has been developed for the synthesis of¹¹C-ethanol and¹¹C-butanol. These alcohols were synthesized via the same route. The reaction of¹¹CO₂ with methylmagnesium bromide or with n-propylmagnesium chloride, followed by a lithium aluminum hydride reduction and hydrolysis produced respectively¹¹C-ethanol and¹¹C-butanol. Preparation can be completed in 25 min. In each case the radiochemical purity, as determined by high pressure liquid chromatography /HPLC/ was greater than 98%. Biological quality control shows that the products are suitable for human use. The process has been completely automated to limit radiation exposure to personnel, reduce preparation time, and increase reproducibility.