Trimethoxysilylpolymethacrylate as new material for stone conservation. Porosimetric and colorimetric investigations

Aimed to obtain new materials for the conservation of stone substrates, we report here on the synthesis of a polymer which has been obtained by inducing polymerization on a methacrylate monomer functionalized by alchoxysilane groups. Two lithotypes, the Comiso calcarenite and Mistretta quartzite, stones largely used in artworks of north-eastern Sicily, were treated with the above polymer and its conserving efficacy evaluated in terms of porosimetric features, hydric properties and appearance. The collected data were compared to those provided, under the same experimental conditions, by an ethylmethacrylate/methylmethacrylate copolymer and an alkylalchoxysilane, products widely employed in the protection of stones. Experiments aimed to test the durability of the above polymer against UV artificial ageing are also reported.     

Elemental Analysis of Phytotherapeutic Products by Inductively Coupled Plasma–Tandem Mass Spectrometry

A procedure for the determination of As, Cd, Cr, Ni, Pb, and V in phytotherapy medicines by inductively coupled plasma–tandem mass spectrometry is reported. The use of tandem mass spectrometry with oxygen into an octopole reaction system at various gas flow rates and the combination of on-mass and mass-shift modes was evaluated. Cadmium, Cr, Ni, and Pb were determined as free atomic ions while As and V were determined as the oxides AsO⁺ and VO⁺ in the same run. Samples were prepared by microwave-assisted digestion with dilute nitric acid and hydrogen peroxide. Two plant-certified reference materials (apple leaves and tomato leaves) were used to check the accuracy. For tandem mass spectrometry with 0.5?mL min^?1 O₂, recoveries in the 85–113% were typically obtained and no statistical differences were observed at the 95% confidence level (t-test) in comparison with the certified values. Using these conditions, the limits of detection for the method were 0.01, 0.0002, 0.008, 0.008, 0.003, and 0.002?µg g^?1 for As, Cd, Cr, Ni, Pb, and V, respectively. The procedure was used for the analysis of four phytotherapic drugs and the determined concentrations were up to 0.168?µg g^?1 As, 0.03?µg g^?1 Cd, 0.82?µg g^?1 Cr, 1.18?µg g^?1 Ni, 0.52?µg g^?1 Pb, and 2.4?µg g^?1 V with average precision values of 8% as the relative standard deviation. The found concentrations were compared with limits proposed in official guidelines and, in most cases, the values were below the maximum limits allowed.     

Interferences in Thermospray Flame Furnace AAS: Co and Mn Behavior

ABSTRACT

The effects caused by concomitants [Na(I), K(I), Ca(II), and Mg(II)] on the atomization of cobalt and manganese by thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) were here studied. The main concomitants were chosen according to typical major elements found in foods and beverages. Severe interference effects were caused by all concomitants. The interferences varied from ?101.0% to +360.0% and ?117.5% to +175.5% for Co and Mn, respectively. These data demonstrated a frequently paradoxical situation in spectrochemical analysis, that is, efforts are directed toward the introduction of a higher amount of sample, however, when this condition is attained, there is the manifestation of severe processes of interferences. These interference processes require the application of either previous separation steps or special strategies of calibration.     

Are Heavy Pnictogen-π Interactions Really “π Interactions”?

The noncovalent interactions of heavy pnictogens with π-arenes play a fundamental role in fields like crystal engineering or catalysis. The strength of such bonds is based on an interplay between dispersion and donor/acceptor interactions, and is generally attributed to the presence of π-arenes. Computational studies of the interaction between the heavy pnictogens As, Sb and Bi and cyclohexane, in comparison with previous studies on the interaction between heavy pnictogens and benzene, show that this concept probably has to be revised. A thorough analysis of all the different energetic components that play a role in these systems, carried out with state-of-the-art computational methods, sheds light on how they influence one another and the effect that their interplay has on the overall system. Furthermore, the analysis of such interactions leads us to the unexpected finding that the presence of the pnictogen compounds strongly affects the conformational equilibrium of cyclohexane, reversing the relative stability of the chair and boat-twist conformers, and thus suggesting a possible application of tuneable dispersion energy donors to stabilise the desired conformation.     

Local structure of ball-milled LaNi5 hydrogen storage material by Ni K-edge EXAFS

Local structure of the nanostructured LaNi₅ hydrogen storage alloys, prepared by ball-milling, has been studied using Ni K-edge extended X-ray absorption fine structure spectroscopy. Results indicate that the ball-milling up to 100 h results in the production of nanoparticles characterized by large atomic disorder and slightly reduced unit-cell volume, compared to the bulk LaNi₅. High temperature annealing appears to help in partial recovery of atomic order in the ball-milled samples; however, long-time ball-milled samples retain large disorder even after the high temperature annealing. The results suggest that the large disorder and the reduced unit-cell volume might be causing a higher energy-barrier for the hydride-phase formation in the long time ball-milled LaNi₅ powders.     

Redox-active dirhodium(II,II) species covalently entrapped into a methylmethacrylate backbone

A novel class of polymers was obtained by insertion of dirhodium(II,II) metal systems into a methacrylate backbone; the synthesis was realized by free radical polymerization of an appropriate methacrylate-functionalized dirhodium polymer precursor, namely [Rh2(form)2(MA-COO)2](form =N,N'-di-p-tolylformamidinate)(MA-COO = 2-(methacroyloxy)ethyl-phthalate), with methylmethacrylate (MMA); the new copolymers, in solution, show reversible CO-absorption, connected to the axial reactivity of dirhodium(II,II) species.     

Reactivity of styrene and substituted styrenes in the presence of a homogeneous isospecific titanium catalyst

The isospecific polymerization of several para‐substituted styrenes was performed in the presence of the catalyst dichloro[1,4‐dithiabutanediyl‐2,2′‐bis(4,6‐di‐tert‐butyl‐phenoxy)]titanium activated by methylaluminoxane. All the polymers were highly regioregular and isotactic with narrow molecular weight distributions. The presence of electron‐donating substituents on the aromatic ring had a positive effect on the catalyst activity, whereas electron‐withdrawing substituents affected the polymerization activity negatively. Binary copolymerizations of the various substituted styrenes showed an inversion of the reactivity with respect to that observed in the homopolymerization. These results suggested that the last monomer unit of the polymer chain coordinated to the metal center, influencing the reactivity of the catalyst with respect to the incoming monomer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1486–1491, 2006     

A comparison of two-particle rapidity correlations in antiproton-proton and proton-proton interactions at 31 GeV centre-of-mass energy

We investigated correlations between pairs of charged secondaries produced in antiproton-proton and proton-proton interactions at a centre-of-mass energy of 31 GeV using the pseudorapidity variable η=?ln (tanθ/2). Positive, short-range correlations were observed in both reactions. In the antiproton-proton case, however, there is a stronger correlation at very short range when both particles are produced in the central region and when the charged multiplicity of the event is about 30% higher than the mean. A simple Monte Carlo calculation indicates that quark-antiquark annihilation into two hadronic jets could account for the observed effect.