Uniaxial deformation and orientation of ethylene–tetrafluoroethylene films

This study concerns the thermal and mechanical response of several commercial grades of ethylene – tetrafluoroethylene copolymer films. Differential scanning calorimetry was used to show that, although films have similar degrees of crystallinity and melting temperature, the melting endotherms and crystallisation exotherms differ between materials, suggesting small changes in composition between manufacturers. Films were deformed in tension at a range of temperatures and rates. Selected films were unloaded immediately after stretching, and measurement of the elastic recovery highlighted further differences between materials. Batches of films were pre-drawn uniaxially above the glass transition and immediately quenched. When these materials were subsequently re-drawn below the glass transition temperature, most of them exhibited much improved yield stress, modulus and tensile strength (improving by factors of 5, 5 and 4, respectively at a draw ratio of 3), but a reduced strain to failure. In most of the films, the pre-drawing, as well as the initial orientation of the films, is accounted for by a simple shift in the true strain axis. This is indicative of a material response dominated by entropic network stretch. It also suggests that, in the cases where strain superposition does not work, a different arrangement of crystalline lamellae may be present, limiting the extent to which improved properties can be achieved in some materials.     

Topotactic Synthesis of Phosphabenzene‐Functionalized Porous Organic Polymers: Efficient Ligands in CO2 Conversion

Progress toward the preparation of porous organic polymers (POPs) with task‐specific functionalities has been exceedingly slow—especially where polymers containing low‐oxidation phosphorus in the structure are concerned. A two‐step topotactic pathway for the preparation of phosphabenzene‐based POPs (Phos‐POPs) under metal‐free conditions is reported, without the use of unstable phosphorus‐based monomers. The synthetic route allows additional functionalities to be introduced into the porous polymer framework with ease. As an example, partially fluorinated Phos‐POPs (F‐Phos‐POPs) were obtained with a surface area of up to 591 m² g^?1. After coordination with Ru species, a Ru/F‐Phos‐POPs catalyst exhibited high catalytic efficiency in the formylation of amines (turnover frequency up to 204 h^?1) using a CO₂/H₂ mixture, in comparison with the non‐fluorinated analogue (43 h^?1) and a Au/TiO₂ heterogeneous catalysts reported previously (<44 h^?1). This work describes a practical method for synthesis of porous organic phosphorus‐based polymers with applications in transition‐metal‐based heterogeneous catalysis.     

Phase transfer of CdS nanocrystals mediated by heptamine β-cyclodextrin

A fundamental and systematic study on the fabrication of a supramolecularly assembled nanostructure of an organic ligand-capped CdS nanocrystal (NC) and multiple heptamine β-cyclodextrin ((NH(2))(7)βCD) molecules in aqueous solution has been here reported. The functionalization process of presynthesized hydrophobic CdS NCs by means of (NH(2))(7)βCD has been extensively investigated by using different spectroscopic and structural techniques, as a function of different experimental parameters, such as the composition and the concentration of CD, the concentration of CdS NCs, the nature of the NC surface capping ligand (oleic acid and octylamine), and the organic solvent. The formation of a complex based on the direct coordination of the (NH(2))(7)βCD amine groups at the NC surface has been demonstrated and found responsible for the CdS NC phase transfer process. The amine functional group in (NH(2))(7)βCD and the appropriate combination of pristine capping agent coordinating the NC surface and a suitable solvent have been found decisive for the success of the CdS NC phase transfer process. Furthermore, a layer-by-layer assembly experiment has indicated that the obtained (NH(2))(7)βCD functionalized CdS NCs are still able to perform the host-guest chemistry. Thus, they offer a model of a nanoparticle-based material with molecular receptors, useful for bio applications.     

Nuclear motion effects on the density matrix of crystals: An ab initio Monte Carlo harmonic approach

In the frame of the Born-Oppenheimer approximation, nuclear motions in crystals can be simulated rather accurately using a harmonic model. In turn, the electronic first-order density matrix (DM) can be expressed as the statistically weighted average over all its determinations each resulting from an instantaneous nuclear configuration. This model has been implemented in a computational scheme which adopts an ab initio one-electron (Hartree-Fock or Kohn-Sham) Hamiltonian in the CRYSTAL program. After selecting a supercell of reasonable size and solving the corresponding vibrational problem in the harmonic approximation, a Metropolis algorithm is adopted for generating a sample of nuclear configurations which reflects their probability distribution at a given temperature. For each configuration in the sample the "instantaneous" DM is calculated, and its contribution to the observables of interest is extracted. Translational and point symmetry of the crystal as reflected in its average DM are fully exploited. The influence of zero-point and thermal motion of nuclei on such important first-order observables as x-ray structure factors and Compton profiles can thus be estimated.     

Fluorescence lifetimes and quantum yields of rhodamine derivatives: new insights from theory and experiment

Although lifetimes and quantum yields of widely used fluorophores are often largely characterized, a systematic approach providing a rationale of their photophysical behavior on a quantitative basis is still a challenging goal. Here we combine methods rooted in the time-dependent density functional theory and fluorescence lifetime imaging microscopy to accurately determine and analyze fluorescence signatures (lifetime, quantum yield, and band peaks) of several commonly used rhodamine and pyronin dyes. We show that the radiative lifetime of rhodamines can be correlated to the charge transfer from the phenyl toward the xanthene moiety occurring upon the S(0) ← S(1) de-excitation, and to the xanthene/phenyl relative orientation assumed in the S(1) minimum structure, which in turn is variable upon the amino and the phenyl substituents. These findings encourage the synergy of experiment and theory as unique tool to design finely tuned fluorescent probes, such those conceived for modern optical sensors.     

HPLC-ESI-MS and MS/MS structural characterization of multifucosylated N-glycoforms of the basic proline-rich protein IB-8a CON1+ in human saliva

This study describes the characterization of the glycan moieties and the peptide backbone of six glycoforms of IB-8a CON1(+), a basic proline-rich protein present in human saliva. MS analyses on the intact glycoproteins before and after N-deglycosylation with PNGase F and high-resolution MS/MS sequencing by LTQ Orbitrap XL of peptides and glycopeptides from tryptic digests allowed the structural characterization of the glycan moieties and the polypeptide backbone, as well as to establish the glycosylation site at the asparagine residue at 98th position. Five of the glycoforms carry a biantennary N-linked glycan fucosylated in the innermost N-acetylglucosamine of the core and showing from zero to four additional fucoses in the antennal region. The sixth glycoform carries a monoantennary monofucosylated oligosaccharide. The glycoform cluster was detected on 28 of 71 adult saliva specimens. Level of fucosylation showed interindividual variability with the major relative abundance for the trifucosylated glycoform. Nonglycosylated IB-8a CON1(+) and the variant IB-8a CON1(-), lacking of the glycosylation site, have been also detected in human saliva.     

Intramolecular Direct Dehydrohalide Coupling Promoted by KO(t)Bu: Total Synthesis of Amaryllidaceae Alkaloids Anhydrolycorinone and Oxoassoanine

A transition-metal-free intramolecular dehydrohalide coupling via intramolecular homolytic aromatic substitution (HAS) with aryl radicals has been developed in the presence of potassium tert-butoxide and an organic molecule as the catalyst. The methodology has been applied to a concise synthesis of Amaryllidaceae alkaloids viz. oxoassoanine (1b), anhydrolycorinone (1d), and other related structures. Interestingly, the method also works only in the presence of potassium tert-butoxide.     

Further investigating the determination of phosphorus in plants by INAA using<Emphasis Type="Italic"> bremsstrahlung</Emphasis> measurement

Phosphorus is an essential element for plants and animals, playing a fundamental role in the production of biochemical energy. Despite its relevance, phosphorus is not commonly determined by instrumental neutron activation analysis (INAA), because ³²P does not emit gamma-rays in its decay. There are alternative methods for the determination of phosphorus by INAA, such as the use of beta counting or the measurement of bremsstrahlung originated from the high energy beta particle from ³²P. Here the determination of phosphorus in plant materials by measuring the bremsstrahlung production was further investigated, to optimize an analytical protocol for minimizing interferences and overcoming the poor specificity. Eight certified reference materials of plant matrices with phosphorus ranging between 171 and 5,180 mg kg⁻¹ were irradiated at a thermal neutron flux of 9.5 × 10¹² cm⁻² s⁻¹ and measured with a HPGe detector at decay times varying from 7 to 60 days. Phosphorus solutions added to a certified reference material at three levels were used for calibration. Counts accumulated in the baseline at four different regions of the gamma-ray spectra were tested for the determination of phosphorus, with better results for the 100 keV region. The Compton scattering contribution in the selected range was discounted using an experimental peak-to-Compton factor and the net areas of all peaks in the spectra with energies higher than 218 keV, i.e. Compton edge above 100 keV. Amongst the interferences investigated, the production of ³²P from sulfur, and the contribution of Compton scattering should be considered for producing good results.     

Neutron activation analysis for assessing chemical composition of dry dog foods

Brazil holds the second largest population of domestic dogs in the world, with 33 million dogs, only behind the United States. The annual consumption of dog food in the country is 1.75 million tons, corresponding to the World’s sixth in trade turnover. Dog food is supposed to be a complete and balanced diet, formulated with high quality ingredients. All nutrients and minerals required for an adequate nutrition of dogs are added to the formulation to ensure longevity and welfare. In this context, the present study aimed at assessing the chemical composition of dry dog foods commercialized in Brazil. Thirty-four samples were acquired in the local market of Piracicaba and analyzed by instrumental neutron activation analysis (INAA) to determine the elements As, Br, Ca, Co, Cr, Cs, Fe, K, La, Na, Rb, Sb, Sc, Se, U, and Zn. In general, the concentrations of Ca, Fe, K, Na, and Zn complied with the values required by the Association of American Feed Control Officials (AAFCO). To evaluate the safety of dog food commercialized in Brazil, further investigation is necessary to better understand the presence of toxic elements found in this study, i.e. Sb and U. INAA was useful for the screening analysis of different types and brands of dry dog foods for the determination of both essential and toxic elements.