Computational Study of the Stability of Nanotube Fragments

Extremely short (<1 nm) fragments of zig‐zag carbon nanotubes are studied with ab‐initio techniques to determine their geometric and electronic structure as well as their magnetic susceptibility. It is found that for lengths of a few carbon–carbon bonds, each fragment can be viewed as composed of crowns, that is, zig‐zag rings of carbon atoms along the circumference of the tube. In this case, two kinds of electronic structures are found, depending on whether the number of carbon atoms in each crown is even or odd. Systems comprising three or more crowns either have a high spin ground state or involve a charge transfer across the length of the fragment. Conjugation changes qualitatively when the length of the fragment approaches and surpasses its girth. Indications regarding the predicted chemical stability and electronic response are provided and interpreted in terms of current densities induced within each crown by a magnetic field along the tube axis.     

Mild Oxidative Conversion of Nitroalkanes into Carbonyl Compounds in Ionic Liquids

Basic hydrogen peroxide and sodium perborate were found to be cheap and efficient alternatives for the conversion of primary and secondary nitro to carbonyl compounds (Nef reaction) in ionic liquids.     

Mercaptothiacalixarenes Steer 24 Copper(I) Centers to form a Hollow‐Sphere Structure Featuring Cu2S2 Motifs with Exceptionally Short Cu⋅⋅⋅Cu Distances

Tetramercaptotetrathiacalix[4]arene ( LH₄ ) can be used as a coordination platform to bind four Cu^I ions at the thiolate and thioether S atoms. Donor ligands such as phosphanes can stabilize the resulting [LCu₄] units, which then remain monomeric ( [(Ph₃PCu)₄L] ). In the absence of donor ligands, they aggregate, providing a hexamer ( [LCu₄]₆ ) in high yields, with a hollow‐sphere structure formed by an unprecedented Cu₂₄S₄₈ cage that is surrounded by the organic framework of the calixarene chalices. Preliminary NMR experiments with regard to the host‐guest chemistry in solution showed that the compound represents a polytopic host for acetonitrile and methane.     

Small‐angle X‐ray scattering as a useful supplementary technique to determine molecular masses of polyelectrolytes in solution

Determination of molecular masses of charged polymers is often nontrivial and most methods have their drawbacks. For polyelectrolytes, a new possibility for the determination of number‐average molecular masses is represented by small‐angle X‐ray scattering (SAXS) which allows fast determinations with a 10% accuracy. This is done by relating the mass to the position of a characteristic peak feature which arises in SAXS due to the local ordering caused by charge‐repulsions between polyelectrolytes. Advantages of the technique are the simplicity of data analysis, the independency from polymer architecture, and the low sample and time consumption. The method was tested on polyelectrolytes of various structures and chemical compositions, and the results were compared with those obtained from more conventional techniques, such as asymmetric flow field‐flow fractionation, gel permeation chromatography, and classical SAXS data analysis, showing that the accuracy of the suggested method is similar to that of the other techniques. © 2016 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1913–1917     

Determination of volatile organic compounds in the dried leaves of Salvia species by solid-phase microextraction coupled to gas chromatography mass spectrometry

Salvia spp. are used throughout the world both for food and pharmaceutical purposes. In this study, a method involving headspace solid-phase microextraction combined with gas chromatography–mass spectrometry was developed, to establish the volatiles profile of dried leaves of four Iranian Salvia spp.: Salvia officinalis L., Salvia leriifolia Benth, Salvia macrosiphon Boiss. and two ecotypes of Salvia reuterana Boiss. A total of 95 volatiles were identified from the dried leaves of the five selected samples. Specifically, α-thujone was the main component of S. officinalis L. and S. macrosiphon Boiss. (34.40 and 17.84%, respectively) dried leaves, S. leriifolia Benth was dominated by β-pinene (27.03%), whereas α-terpinene was the major constituent of the two ecotypes of S. reuterana Boiss. (21.67 and 13.84%, respectively). These results suggested that the proposed method can be considered as a reliable technique for isolating volatiles from aromatic plants, and for plant differentiation based on the volatile metabolomic profile.     

Molecular Recognition and Visual Detection of G‐Quadruplexes by a Dicarbocyanine Dye

The interactions of a dicarbocyanine dye 3,3′‐diethylthiadicarbocyanine, DiSC₂(5) , with DNA G‐quadruplexes were studied by means of a combination of various spectroscopic techniques. Aggregation of excess dye as a result of its positive charge is promoted by the presence of the polyanionic quadruplex structure. Specific high‐affinity binding to the parallel quadruplex of the MYC promoter sequence involves stacking of DiSC₂(5) on the external G‐tetrads; the 5′‐terminal tetrad is the favored binding site. Significant energy transfer between DNA and the dye in the UV spectral region is observed upon DiSC₂(5) binding. The transfer efficiency strongly depends on the DNA secondary structure as well as on the G‐quadruplex topology. These photophysical features enable the selective detection of DNA quadruplexes through sensitized DiSC₂(5) fluorescence in the visible region.     

Delivery of Thyronamines (TAMs) to the Brain: A Preliminary Study

Recent reports highlighted the significant neuroprotective effects of thyronamines (TAMs), a class of endogenous thyroid hormone derivatives. In particular, 3-iodothyronamine (T1AM) has been shown to play a pleiotropic role in neurodegeneration by modulating energy metabolism and neurological functions in mice. However, the pharmacological response to T1AM might be influenced by tissue metabolism, which is known to convert T1AM into its catabolite 3-iodothyroacetic acid (TA1). Currently, several research groups are investigating the pharmacological effects of T1AM systemic administration in the search of novel therapeutic approaches for the treatment of interlinked pathologies, such as metabolic and neurodegenerative diseases (NDDs). A critical aspect in the development of new drugs for NDDs is to know their distribution in the brain, which is fundamentally related to their ability to cross the blood–brain barrier (BBB). To this end, in the present study we used the immortalized mouse brain endothelial cell line bEnd.3 to develop an in vitro model of BBB and evaluate T1AM and TA1 permeability. Both drugs, administered at 1 µM dose, were assayed by high-performance liquid chromatography coupled to mass spectrometry. Our results indicate that T1AM is able to efficiently cross the BBB, whereas TA1 is almost completely devoid of this property.     

Two-phase damage modeling of concrete affected by alkali–silica reaction under variable temperature and humidity conditions

In the present work the concrete affected by alkali–silica reaction (ASR) is represented as a two-phase material made of a solid skeleton and a wet expanding gel, which exerts a pressure capable of severely damaging the concrete surrounding the reactive sites. Both the effects of temperature and humidity conditions on the kinetic of the chemical reaction and on the final value of the consequent expansion are included in the proposed model. The mechanical degradation induced by the ASR is described by a phenomenological isotropic damage model. The constitutive model, implemented in a finite element code, is used for the analyses of structures made of reactive concrete in the presence of temperature and moisture gradients. Firstly the temperature and humidity fields are obtained through uncoupled heat and moisture transport analyses and then the chemo-mechanical analysis is performed starting from the values of temperature and humidity preliminary calculated.     

New polymer matrix system for phosphorescent organic light‐emitting diodes and the role of the small molecular co‐host

A new matrix system for phosphorescent organic light‐emitting diodes (OLEDs) based on an electron transporting component attached to an inert polymer backbone, an electronically neutral co‐host, and a phosphorescent dye that serves as both emitter and hole conductor are presented. The inert co‐host is used either as small molecules or covalently connected to the same chain as the electron‐transporting host. The use of a small molecular inert co‐host in the active layer is shown to be highly advantageous in comparison to a purely polymeric matrix bearing the same functionalities. Analysis of the dye phosphorescence decay in pure polymer, small molecular co‐host film, and their blend lets to conclude that dye molecules distribute mostly in the small molecular co‐host phase, where the co‐host prevents agglomeration and self‐quenching of the phosphorescence as well as energy transfer to the electron transporting units. In addition, the co‐host accumulates at the anode interface where it acts as electron blocking layer and improves hole injection. This favorable phase separation between polymeric and small molecular components results in devices with efficiencies of about 47 cd/A at a luminance of 1000 cd/m². Investigation of OLED degradation demonstrates the presence of two time regimes: one fast component that leads to a strong decrease at short times followed by a slower decrease at longer times. Unlike the long time degradation, the efficiency loss that occurs at short times is reversible and can be recovered by annealing of the device at 180 °C. We also show that the long‐time degradation must be related to a change of the optical and electrical bulk properties. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013