Deviations from two-dimensionality in classical adsorbed films

The statistical mechanical theory of adsorption is presented as an expansion about the two-dimensional approximation. Two corrections to the latter are additive in the perturbation limit. One contribution, arising from the lateral variation of the substrate potential, has been previously evaluated. The second correction term is due to the particles' mutual interaction when their separation vector is not parallel to the surface. The latter is expressed in terms of the radial distribution function. Its contribution to the deviation from two-dimensionality is shown to be comparable to the first term for the case of a Lennard-Jones model.     

Determination of amphetamine-type stimulants in oral fluid by solid-phase microextraction and gas chromatography-mass spectrometry

A method for the simultaneous identification and quantification of amphetamine (AMP), methamphetamine (MET), fenproporex (FEN), diethylpropion (DIE) and methylphenidate (MPH) in oral fluid collected with Quantisal? device has been developed and validated. Thereunto, in-matrix propylchloroformate derivatization followed by direct immersion solid-phase microextraction and gas chromatography-mass spectrometry were employed. Deuterium labeled AMP was used as internal standard for all the stimulants and analysis was performed using the selected ion monitoring mode. The detector response was linear for the studied drugs in the concentration range of 2-256 ng mL(-1) (neat oral fluid), except for FEN, whereas the linear range was 4-256 ng mL(-1). The detection limits were 0.5 ng mL(-1) (MET), 1 ng mL(-1) (MPH) and 2 ng mL(-1) (DIE, AMP, FEN), respectively. Accuracy of quality control samples remained within 98.2-111.9% of the target concentrations, while precision has not exceeded 15% of the relative standard deviation. Recoveries with Quantisal? device ranged from 77.2% to 112.1%. Also, the goodness-of-fit concerning the ordinary least squares model in the statistical inference of data has been tested through residual plotting and ANOVA. The validated method can be easily automated and then used for screening and confirmation of amphetamine-type stimulants in drivers' oral fluid.     

The effect of topology on the structure and free energy landscape of DNA kissing complexes

We use a recently developed coarse-grained model for DNA to study kissing complexes formed by hybridization of complementary hairpin loops. The binding of the loops is topologically constrained because their linking number must remain constant. By studying systems with linking numbers -1, 0, or 1 we show that the average number of interstrand base pairs is larger when the topology is more favourable for the right-handed wrapping of strands around each other. The thermodynamic stability of the kissing complex also decreases when the linking number changes from -1 to 0 to 1. The structures of the kissing complexes typically involve two intermolecular helices that coaxially stack with the hairpin stems at a parallel four-way junction.     

Establishing the irradiation dose for paper decontamination

Museums, libraries and archives are preserving documents that are slowly degrading due to the inherent ageing of the cellulose substrate or to the technological errors of the past (acid paper, iron gall ink). Beside this, large quantities of paper are rapidly damaged by biological attacks following natural disasters and improper storage conditions.The treatment of paper documents with ionizing radiation can be used for mass decontamination of cultural heritage items but conservators and restaurators are still reserved because of the radiation induced degradation.We conducted a study for establishing the dose needed for the effective treatment of paper documents, taking into account the biological burden and the irradiation effects on paper structure. We used physical testing specific to paper industry and less destructive analytical methods (thermal analysis).Our results show that an effective treatment can be performed with doses lower than 10 kGy. Old paper appears to be less affected by gamma radiation than recent paper but the sampling is highly affected by the non-uniform degree of the initial degradation status. The extent of testing for degradation and the magnitude of acceptable degradation should take into account the biological threat and the expected life time of the paper documents.     

Irradiation effects on canvas oil painting: Spectroscopic observations

“Winter” oil painting, by Romanian contemporary artist George Alexandrescu was used as experimental model for the substantiation of gamma radiation treatment, as the best choice to stop the biological attack of paintings. In this purpose, spectroscopic and colorimetric methods were used to analyse in situ, non-destructively and non-contact, the experimental model before and after ⁶⁰Co gamma irradiation. Chemical structure and colour changes were monitored by FTIR, FT-Raman and Vis reflectance spectroscopy. Negligible Infrared spectral transformations have been observed after irradiation. Furthermore, it was found that gamma irradiation did not induce any significant colour alterations. Insignificant structural and colour changes observed, recommend the use of gamma irradiation in the disinfection of oil paintings.     

Effect of orientation of the peptide-bridge dipole moment on the properties of fullerene-peptide-radical systems

We synthesized two series of compounds in which a nitroxide radical and a fullerene C(60) moiety were kept separated by a 3(10)-helical peptide bridge containing two intramolecular C═O···H-N hydrogen bonds. The direction of the resulting molecular dipole moment could be reversed by switching the position of fullerene and nitroxide with respect to the peptide nitrogen and carbon termini. The resulting fullerene-peptide-radical systems were compared to the behaviors of otherwise identical peptides but lacking either C(60) or the free radical moiety. Electrochemical analysis and chemical nitroxide reduction experiments show that the dipole moment of the helix significantly affects the redox properties of both electroactive groups. Besides providing evidence of a folded helical conformation for the peptide bridge, IR and NMR results highlight a strong effect of peptide orientation on the spectral patterns, pointing to a specific interaction of one of the helical orientations with the C(60) moiety. Time-resolved EPR spectra show not only that for both systems triplet quenching by nitroxide induces spin polarization of the radical spin sublevels, but also that the coupling interaction can be either weak or strong depending on the orientation of the peptide dipole. As opposed to the concept of dyads, the molecules investigated are thus better described as fullerene-peptide-radical systems to stress the active role of the bridge as an important ingredient capable of tuning the system's physicochemical properties.     

Catalytic Antioxidant Activity of Bis-Aniline-Derived Diselenides as GPx Mimics

Herein, we describe a simple and efficient route to access aniline-derived diselenides and evaluate their antioxidant/GPx-mimetic properties. The diselenides were obtained in good yields via ipso-substitution/reduction from the readily available 2-nitroaromatic halides (Cl, Br, I). These diselenides present GPx-mimetic properties, showing better antioxidant activity than the standard GPx-mimetic compounds, ebselen and diphenyl diselenide. DFT analysis demonstrated that the electronic properties of the substituents determine the charge delocalization and the partial charge on selenium, which correlate with the catalytic performances. The amino group concurs in the stabilization of the selenolate intermediate through a hydrogen bond with the selenium.     

Structure and Morphology of SBA-15 Thin Films on Different Substrates

Well-ordered hexagonal mesoporous silica thin films, SBA-15 type, were synthesized with Pluronic P123 and tetraethyl orthosilicate in a diluted ethanol-hydrochloric acid solution. Films deposited on a broad range of distinct substrates by a sol-gel dip-coating method resulted in transparent and adherent samples. Transmission electron microscopy images revealed, predominantly, well-ordered regions of hexagonal arrays of cylindrical mesopores parallel to the substrate. X-ray reflectivity showed similar lattice parameters for all analyzed films, with a (h00) preferred orientation. The films presented diverse shrinkage susceptibilities, which were tested after different polymer removal procedures. Calcined films have 342 m²/g surface area, 0.130 cm³/g pore volume, and 6.8 nm pore diameter. The wetting characteristics of the substrates in water and alcoholic solutions were evaluated. The films showed different structural properties, mostly related to the mean surface roughness of the substrates and to the drying process.     

Ion bunch stacking in a Penning trap after purification in an electrostatic mirror trap

The success of many measurements in analytical mass spectrometry as well as in precision mass determinations for atomic and nuclear physics is handicapped when the ion sources deliver “contaminations”, i.e., unwanted ions of masses similar to those of the ions of interest. In particular, in ion-trapping devices, large amounts of contaminant ions result in significant systematic errors—if the measurements are possible at all. We present a solution for such cases: The ions from a quasi-continuous source are bunched in a linear radio-frequency-quadrupole ion trap, separated by a multi-reflection time-of-flight section followed by a Bradbury–Nielsen gate, and then captured in a Penning trap. Buffer-gas cooling is used to damp the ion motion in the latter, which allows a repeated opening of the Penning trap for a stacking of mass-selected ion bunches. Proof-of-principle demonstrations have been performed with the ISOLTRAP setup at ISOLDE/CERN, both with ¹³³Cs⁺ ions from an off-line ion source and by application to an on-line beam of ¹⁷⁹Lu⁺ ions contaminated with ¹⁶³Dy¹⁶O⁺ ions. In addition, an optimization of the experimental procedure is given, in particular for the number of ion bunches captured as a function of the ions’ lifetimes and the parameters of the experiment .