Structure of onchidione, a bis-γ-pyrone polypropionate from a marine pulmonate mollusk

The chemical investigation of the marine pulmonate Onchidium sp. and of its defensive mucous secretion led us to the isolation of a novel polypropionate, onchidione (4), containing two γ-pyrone rings. The structure of 4 was elucidated by spectroscopic methods, mainly NMR techniques, and secured by X-ray analysis on a single crystal.     

A novel fluoride-sensing scaffold by a peculiar acid-promoted trimerization of 5,6-dihydroxyindole

An unusual rearranged trimer, 2-(2-amino-4,5-dihydroxybenzyl)-6,7-dihydroxy-3-(5,6-dihydroxyindol-3-yl)quinoline (1a), was obtained as the acetyl derivative (1b) by mild acid-promoted polymerization of 5,6-dihydroxyindole at pH 2. Compound 1b proved to be a selective fluoride-sensing compound, transducing F⁻ binding into a distinct absorption at 414 nm and a marked fluorescence enhancement at 489 nm.     

Evidence for an internal field in CdSe/CdS nanorods by time resolved and single rod experiments

In this contribution we report on an optical nonlinearity featuring colloidal seeded grown CdSe/CdS nanorods (NRs). It consists of a photoluminescence (PL) blueshift of single rod spectra with increasing laser power and a transient, power-dependent redshift of the spectra studied by time resolved PL measurement, strictly related to the multicarrier scattering occurring at high excitation density. We attribute this nonlinearity to a photo-induced screening of an internal field, originating from the piezoelectric polarization induced at the core/shell interface.     

Coverage effects on phenol adsorption on Si(1 0 0)2 × 1 as: A first principle calculation

We investigated the adsorption of a 6-dimers Si(1 0 0)2 × 1 surface as a function of coverage and adsorption type (molecular/dissociative) by first principle calculations. In particular, we performed calculations on models with 2, 3, 4 and 6 phenol molecules, corresponding to coverage Θ = 0.34, 0.5, 0.67 and 1. We found that total adsorption energy, when at least one phenol is in a molecular state is lower than the sum of the corresponding singly adsorbed molecules. The dissociative adsorption of multiple molecules, both in parallel and switched configuration is most favoured for a coverage Θ = 0.34 (2.6 eV per adsorbed molecule). This values decreases to 2.0 eV and remains constant till the coverage 1 is reached.The energy barrier for the molecular-to-dissociated transition of a phenol molecule, in presence of another dissociatively adsorbed molecule is ∼0.008 eV and it is similar to the value in case of single adsorption. Possible hydrogen displacements were also considered.     

Dependence of the Nanoscale Composite Morphology of Fe3O4 Nanoparticle-Infused Lysozyme Amyloid Fibrils on Timing of Infusion: A Combined SAXS and AFM Study

Understanding the formation process and the spatial distribution of nanoparticle (NP) clusters on amyloid fibrils is an essential step for the development of NP-based methods to inhibit aggregation of amyloidal proteins or reverse the assembling trend of the proto-fibrillary complexes that prompts pathogenesis of neuro degeneration. For this, a detailed structural determination of the diverse hybrid assemblies that are forming is needed, which can be achieved by advanced X-ray scattering techniques. Using a combined solution small angle X-ray scattering (SAXS) and atomic force microscopy (AFM) approach, this study investigates the intrinsic trends of the interaction between lysozyme amyloid fibrils (LAFs) and Fe₃O₄ NPs before and after fibrillization at nanometer resolution. AFM images reveal that the number of NP clusters interacting with the lysozyme fibers does not increase significantly with NP volume concentration, suggesting a saturation in NP aggregation on the fibrillary surface. The data indicate that the number of non-adsorbed Fe₃O₄ NPs is highly dependent on the timing of NP infusion within the synthesis process. SAXS data yield access to the spatial distribution, aggregation manner and density of NP clusters on the fibrillary surfaces. Employing modern data analysis approaches, the shape and internal structural morphology of the so formed nanocomposites are revealed. The combined experimental approach suggests that while Fe₃O₄ NPs infusion does not prevent the fibril-formation, the variation of NP concentration and size at different stages of the fibrillization process can impose a pronounced impact on the superficial and internal structural morphologies of these nanocomposites. These findings may be applicable in devising advanced therapeutic treatments for neurodegenerative diseases and designing novel bio-inorganic magnetic devices. Our results further demonstrate that modern X-ray methods give access to the structure of—and insight into the formation process of—biological–inorganic hybrid structures in solution.     

Universal algorithm for the analysis of charge distributions in segmented electrodes of gas detectors

A general algorithm to extract the center of gravity of charge distributions generated in a patterned electrode is presented. The results obtained analyzing the data produced by the gas focal plane detector of the MAGNEX spectrometer are discussed. The algorithm is characterized by an unprecedented efficiency and accuracy when dealing with data with small signal-to-noise ratio. A clear recovery of the smooth position distribution from the quantized one obtained with standard algorithms is observed. The optimized algorithm is also able to naturally mitigate the cross-talk phenomena that are quite strong in this kind of compact detectors.