Self-assembly of a nucleotide-calixarene hybrid in a triangular supramolecule

The self-assembly of a thymine nucleotide-calixarene hybrid (1) in CDCl₃ as a solvent was investigated. FT-IR, ESI-MS, ¹H and DOSY-NMR spectra evidenced that compound 1 (ammonium or sodium salt) self-assembles in a triangular trimeric supramolecule by thymine-thymine hydrogen bonding. The saline form is crucial for the arrangement in the cyclic trimer as the protonation of the nucleotide phosphate groups leads the assembly toward a dimeric species.     

Electronic states of a single layer of pentacene: standing-up and flat-lying configurations

The electronic properties of a single layer (SL) of pentacene molecules are investigated by high-resolution UV photoemission and near-edge X-ray absorption spectroscopy in different configurations of the SL, either standing up on an aromatic self-assembled monolayer or planar on a bare Cu(001) substrate. The weakly interacting pentacene molecules in the standing-up SL present a semiconducting character, and the empty states distribution reflects that of gas-phase pentacene, while the planar pentacene-Cu system shows a metallic interface with redistribution of the empty molecular states. The highest-occupied molecular orbital lineshape in the weakly interacting SL shows a double structure, attributed to two nonequivalent molecules in the ordered configuration.     

Gas chromatography-mass spectrometry characterization of the varnish and glue of an ancient 18th century double bass

A GC-MS investigation is conducted on the double bass "Panormus", property of Conservatorio di Musica "Vincenzo Bellini" in Palermo. The most important components of the varnish (fatty acids) and of the glue (proteinaceous amino acids), with which the musical instrument was treated in the past, are determined. The analyses are carried out by prior derivatization of fatty acids by acidic methanol and of amino acids by acidic methanol and trifluoroacetic anhydride (TFAA). Analytes identification is achieved by direct comparison with several reference materials and the use of a digitized library.     

Interaction of lipophilic gemcitabine prodrugs with biomembrane models studied by Langmuir-Blodgett technique

The stability and bioavailability of anticancer agents, such as gemcitabine, can be increased by forming prodrugs. Gemcitabine is rapidly deaminated to the inactive metabolite (2('),2(')-difluorodeoxyuridine), thus to improve its stability a series of increasingly lipophilic gemcitabine prodrugs linked through the 4-amino group to valeroyl, lauroyl, and stearoyl acyl chains were synthesized. Studies of monolayer properties are important to improve understanding of biological phenomena involving lipid/gemcitabine or lipid/gemcitabine derivative interactions. The interfacial behavior of monolayers constituted by DMPC plus gemcitabine or lipophilic gemcitabine prodrugs at increasing molar fractions was studied at the air/water interface at temperatures below (10 degrees C) and above (37 degrees C) the lipid phase transition. The effect of the hydrophobic chain length of gemcitabine derivatives on the isotherm of pure DMPC was investigated by surface tension measurement, and the results are reported as molar fractions as a function of mean molecular area per molecule. The results show that the compounds interact with DMPC producing mixed monolayers that are subject to an expansion effect, depending on the prodrug chain length. The results give useful hints of the interaction of these prodrugs with biological membranes and increase knowledge on the incorporation site of such compounds, as a function of their lipophilicity, in a lipid carrier; they may lead to improved liposomal formulation design.     

Calorimetric evaluation of the interaction and absorption of eicosapentaenoic acid by biomembrane models

The interaction of eicosapentaenoic acid, a polyunsaturated fatty acid belonging to the omega-3 class, with biomembrane models represented by multilamellar or unilamellar vesicles made of dimyristoylphosphatidylcholine was monitored by means of differential scanning calorimetry technique. The calorimetric analysis of vesicle prepared in the presence of increasing molar fraction of eicosapentaenoic acid was carried out to show its maximum interaction with biomembrane models evaluating the effects of eicosapentaenoic acid on the biomembrane models thermotropic parameters (transition temperature and enthalpy variation). Furthermore, in order to detect the influence of the presence of hydrophilic or lipophilic media on the entity of the compound absorption by the biomembrane models, kinetic experiments were carried out.The results indicate that eicosapentaenoic acid strongly interacts with the biomembrane models depressing the transition temperature and the enthalpy variation. Eicosapentaenoic acid is absorbed by the biomembrane models and the absorption is affected by the used medium; in fact a bigger absorption happens in the presence of a lipophilic medium.     

Regioselective O-alkylations and acylations of polyphenolic substrates using a calix[4]pyrrole derivative

The 10α,20α-bis(4-nitrophenyl)-calix[4]pyrrole 2 can act as a topologically selective protecting group in the O-alkylation and acylation of polyphenolic polycyclic aromatic compounds thanks to the regioselective formation of phenolate-type complexes. Remarkably, the host-guest interaction with the anionic reagents is sufficiently strong and kinetically slow to produce a high degree of selectivity.     

A sinapic acid–calix[4]arene hybrid selectively binds Pb over Hg and Cd

The binding affinity for Pb²⁺, Cd²⁺ and Hg²⁺ of the sinapic acid–calix[4]arene hybrid 2, having four sinapyl pendants at the upper rim, has been investigated via an UV–Vis study. Compound 2 has better complexing ability than the monomeric p-phenetidine derivative 1. This highlights that the clustering of sinapyl units in a basket-like structure, dictated by the calixarene scaffold, greatly enhances the complexing properties. Ligand 2 forms complexes even with Hg²⁺, which is not complexed by 1 at all; the complexes formed by 2 with Pb²⁺ and Cd²⁺ are much stronger than the analogous complexes formed by 1. The UV–Vis investigation shows that the hybrid 2 markedly favors Pb²⁺ over Cd²⁺ and Hg²⁺. Information on the structural properties of the complex species was obtained by ¹H NMR spectroscopy. NMR data show that all three metal ions are placed into the cavity consisting of the calixarene scaffold and the sinapyl pendants, though their binding affects the coordinating regions to a different extent.     

Chemical waves

In our paper we try to describe the basic concepts of chemical waves and spatial pattern formation in a simple way. We pay particular attention to self-organisation phenomena in extended excitable systems. These result in the appearance of travelling waves, spiral waves, target patterns, Turing structures or more complicated structures called scroll waves, which are three-dimensional systems. We describe the most famous oscillating reaction, the Belousov-Zhabotinsky (BZ) reaction, in greater detail. This is because it is of great interest in both physical chemistry and in studies on the evolution and sustenance of self-organising biological systems.     

An independent component analysis-based approach on ballistocardiogram artifact removing

Interest about simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) data acquisition has rapidly increased during the last years because of the possibility that the combined method offers to join temporal and spatial resolution, providing in this way a powerful tool to investigate spontaneous and evoked brain activities. However, several intrinsic features of MRI scanning become sources of artifacts on EEG data. Noise sources of a highly predictable nature such as those related to the pulse MRI sequence and those determined by magnetic gradient switching during scanning do not represent a major problem and can be easily removed. On the contrary, the ballistocardiogram (BCG) artifact, a large signal visible on all EEG traces and related to cardiac activity inside the magnetic field, is determined by sources that are not fully stereotyped and causing important limitations in the use of artifact-removing strategies. Recently, it has been proposed to use independent component analysis (ICA) to remove BCG artifact from EEG signals. ICA is a statistical algorithm that allows blind separation of statistically independent sources when the only available information is represented by their linear combination. An important drawback with most ICA algorithms is that they exhibit a stochastic behavior: each run yields slightly different results such that the reliability of the estimated sources is difficult to assess. In this preliminary report, we present a method based on running the FastICA algorithm many times with slightly different initial conditions. Clustering structure in the signal space of the obtained components provides us with a new way to assess the reliability of the estimated sources.     

Simultaneous EEG-fMRI acquisition: how far is it from being a standardized technique?

Simultaneous EEG–fMRI is a powerful tool to study spontaneous and evoked brain activity because of the complementary advantages of the two techniques in terms of temporal and spatial resolution. In recent years, a significant number of scientific works have been published on this subject. However, many technical problems related to the intrinsic incompatibility of EEG and MRI methods are still not fully solved. Furthermore, simultaneous acquisition of EEG and event-related fMRI requires precise synchronization of all devices involved in the experimental setup. Thus, timing issue must be carefully considered in order to avoid significant methodological errors.

The aim of the present work is to highlight and discuss some of technical and methodological open issues associated with the combined use of EEG and fMRI. These issues are presented in the context of preliminary data regarding simultaneous acquisition of event-related evoked potentials and BOLD images during a visual odd-ball paradigm.