Paper preservation by poly(cyclohexene oxide) deposition – an XPS study

Paper was preserved by deposition of poly(cyclohexene oxide) polymerised in situ by a photoinitiated cationic process. The efficiency of the deposition, as function of parameters such as the used catalytic system and the reaction time, has been evaluated by detection of uncovered cellulose present at the sample surface determined by means of X-ray photoelectron spectroscopy. The percentage of uncovered cellulose detected was ranging from 1 to 40%.     

Scaling behavior of the thermopower of the archetypal heavy-fermion metal YbRh2Si2

We reveal and explain the scaling behavior of the thermopower S/T exhibited by the archetypal heavy-fermion (HF) metal YbRh₂Si₂ under the application of magnetic field B at temperature T. We show that the same scaling is demonstrated by different HF compounds such as β-YbAlB₄ and the strongly correlated layered cobalt oxide [BiBa_0.66K_0.36O₂]CoO₂. Using YbRh₂Si₂ as an example, we demonstrate that the scaling behavior of S/T is violated at the antiferromagnetic phase transition, while both the residual resistivity ρ₀ and the density of states, N, experience jumps at the phase transition, causing the thermopower to make two jumps and change its sign. Our elucidation is based on flattening of the single-particle spectrum that profoundly affects ρ₀ and N. To depict the main features of the S/T behavior, we construct a T –B schematic phase diagram of YbRh₂Si₂. Our calculated S/T for the HF compounds are in good agreement with experimental facts and support our observations.     

Amplified Spontaneous Emission Threshold Dependence on Determination Method in Dye-Doped Polymer and Lead Halide Perovskite Waveguides

Nowadays, the search for novel active materials for laser devices is proceeding faster and faster thanks to the development of innovative materials able to combine excellent stimulated emission properties with low-cost synthesis and processing techniques. In this context, amplified spontaneous emission (ASE) properties are typically investigated to characterize the potentiality of a novel material for lasers, and a low ASE threshold is used as the key parameter to select the best candidate. However, several different methods are currently used to define the ASE threshold, hindering meaningful comparisons among various materials. In this work, we quantitatively investigate the ASE threshold dependence on the method used to determine it in thin films of dye-polymer blends and lead halide perovskites. We observe a systematic ASE threshold dependence on the method for all the different tested materials, and demonstrate that the best method choice depends on the kind of information one wants to extract. In particular, the methods that provide the lowest ASE threshold values are able to detect the excitation regime of early-stage ASE, whereas methods that are mostly spread in the literature return higher thresholds, detecting the excitation regime in which ASE becomes the dominant process in the sample emission. Finally, we propose a standard procedure to properly characterize the ASE threshold, in order to allow comparisons between different materials.     

Cyclobishelicenes: Shape-Persistent Figure-Eight Aromatic Molecules with Promising Chiroptical Properties

Cyclobis[n]helicenes (n=3 or 5) are chiral D₂-symmetric π-conjugated macrocycles with stable lemniscular, or figure-eight, shapes. The conformational analysis of five different cyclobis[n]helicenes revealed that these molecules can only exist as their lemniscular conformers with high barriers to enantiomerization (>200 kJ mol⁻¹). The enantiomers of a cyclobis[5]helicene were resolved by HPLC and their unusual chiroptical properties were attributed to the inherent chirality of their macrocyclic figure-eight.     

Characterization of additives in plastics: From MS to MS10 multistep mass analysis and theoretical calculations of tris(2,4‐di‐tert‐butylphenyl)phosphate

In the analysis by electrospray (+) of an extract of hemp sprouts put in a polypropylene vial, we found a large contamination of a plastic additive. It was characterized by multiple‐stage MSⁿ experiments (MS ÷ MS¹⁰) and identified as tris(2,4‐di‐tert‐butylphenyl)phosphate, also known with the synonyms F32IRS6B46, oxidized Naugard 524, and others. The MS² ÷ MS⁷ spectra are characterized by consecutive eliminations of six isobutene molecules from the tert‐butyl moieties, some of them also occurring in the ion source. The first three are calculated to occur preferentially from the ortho positions, whereas eliminations from the para positions are estimated to be less favored at about 5–6 kcal/mol in each step. Once the first three isobutene molecules are eliminated, the remaining three are lost from the tert‐butyl moieties in para positions (MS⁵ ÷ MS⁷), yielding protonated triphenylphosphate, whose structure has been confirmed by the MS² spectrum of triphenylphosphate standard: the latter spectrum is almost superimposable with the MS⁸ spectrum of the analyte under investigation. MS⁸ and MS⁹ spectra show main losses of water and C₆H₄ molecules. The MS¹⁰ spectrum of precursor ions at m/z 215 shows the gas‐phase addition of water and methanol and ions at m/z 168, attributable to the loss of a phosphorus oxide radical. Density functional theory (DFT) calculations (Becke 3LYP [B3LYP] 6‐311+G(2d,2p)) have been used to evaluate structure and stability of different ionic and neutral species involved in the decomposition pathways and to calculate thermochemical data of the decomposition reactions. This multistep mass analysis combined with theoretical calculations resulted to be particularly useful and effective, yielding chemical, thermochemical, and mechanistic data of significant utility in the structural characterization and identification of the unknown analyte as well as to define its gas‐phase reactivity under a multistep low‐energy collision‐induced dissociation regime.     

Characterization and differentiation of heterocyclic isomers. Part 3. Study of high internal energy ions produced by electron ionization mass spectrometry on 3-methyl-1,2- and 2-methyl-1,3-thiazolopyridines

The eight members of two classes of heterocyclic isomers, namely 3-methyl-1,2-, 1a-d and 2-methyl-1,3-thiazolopyridines 2a-d have been characterized by mass spectrometry under electron ionization. High internal energy ions formed in the source have been studied by low and high resolution mass spectrometry. The data show remarkable differences among the various components of each class depending on the position of the nitrogen in the pyridine ring. Furthermore, by comparing the mass spectra of members of series 1 with those of their corresponding isomers belonging to series 2 , it is still possible to obtain evidence for different behaviors in the fragmentation pathways. It seems to exclude the occurrence of inter-conversion phenomena from one isomer into another, as well as conversion to a common intermediate before fragmentation. This also suggests that each member of series 1 and 2 retains its own structure after electron ionization. The data obtained on a double focusing instrument equipped with electrostatic and magnetic analyzers have been compared with those obtained on a mass spectrometer with an ion trap as the analyzer.     

Total reflection X ray fluorescence in environmental and geochemical studies: unveiling solute provenance in streams during a rain episode

Rural population uses water for irrigation, animal watering and for their own consumption, therefore water contamination is a major concern and a priority for its inhabitants. Unveiling the presence and source of contaminants can help to understand the dynamic of pollutants and therefore define management politics to address the issue. One way to elucidate the origin of contaminants in surface water is by studying rain episodes, relating water discharge with changes in solute concentration. Total Reflection x‐ray Fluorescence (TXRF) was used as the main analytical technique. The study was based on the analysis of samples originating from a Pampean stream (Buenos Aires, Argentina). Solutes (As, P, Ca, Fe, K, Zn, Br) were monitored before, during and after a storm event. During the monitoring it was observed that As was diluted at the beginning of the episode and concentration increased slowly after the rain ceased. The pattern of As is consistent with Ca, K and Fe behavior, revealing a groundwater source. Instead, P concentration increased in the early hours, it was diluted later and finally increased. This behavior indicates that the source of this analyte is superficial and sub superficial water, implying a runoff origin. The simultaneous determination of these analytes by TXRF allowed comparing solute behavior under the same episode, allowing reveal their provenance. Copyright © 2016 John Wiley & Sons, Ltd.     

Microwave-assisted cycloaddition of diisopropyl diazomethylphosphonate to electron-deficient alkenes: synthesis of multifunctionalized phosphonopyrazolynes and phosphonopyrazoles

An efficient method for the synthesis of functionalized phosphonopyrazolines has been developed. The procedure involved the microwave-assisted cycloaddition of diisopropyl diazomethylphosphonate to dipolarophiles, such as α,β-unsaturated-nitriles and -esters, performed in neat conditions. By oxidative aromatization the phosphonopyrazolines, thus obtained, were converted into the corresponding phosphonopyazoles. Alternatively, phosphonopyazoles could be obtained by a one-pot, two step procedure directly from dipolarophiles, thus avoiding the isolation of the intermediate pyrazolines. Full spectroscopic characterization of the compounds has been also reported.