Neluta Ibris

Nanoparticles and thin film formation in ultrashort pulsed laser deposition of vanadium oxide.

The ultrashort pulsed laser deposition of vanadium oxide thin films has been carried out by a frequency-doubled Nd:glass laser with a pulse duration of 250 fs. The characteristics of the plasma produced by the laser-target interaction have been studied by ICCD imaging and optical emission spectroscopy. The results confirm that an emitting plasma produced by ultrashort laser pulses is formed by both a primary and a secondary component. The secondary component consists of particles with a nanometric size, and their composition and spatial angular distribution influence the deposited films. In fact, these films, analyzed by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, and atomic force microscopy, are formed by the aggregation of a large number of nanoparticles whose composition is explained by a model based on equilibrium thermal evaporation from particles directly ejected from the target. On these basis, the presence in the films of a mixture of V(2)O(5) and VO(2) is discussed.

Investigating by circular dichroism some amyloidogenic elastin-derived polypeptides.

Tamburro and coworkers have demonstrated that some elastin-derived polypeptide sequences are able to give rise, in vitro, to amyloid-like fibers. The biological relevance of this finding could be explained by the recent detection of some amyloidogenic material found in arteries of old patients affected by atherosclerosis and demonstrated to be elastin derived. In this context, the comprehension of the mechanism responsible for the amyloid-like fibrillogenesis of elastin-derived sequences is of crucial importance for the design of drugs that could inhibit the amyloidogenic process. To gain further insights into the elastin amyloidogenic process, we studied the polypeptide sequences encoded by Exon 7 and Exon 32 of the human tropoelastin gene, and we demonstrated that only Exon 32 is able to aggregate in amyloid-like fibers. Vis-UV Thioflavin T circular dichroism (CD) spectroscopy rapidly and unambiguously detected the amyloidogenic propensity of the polypeptides. To gain additional insights into the aggregation mechanism of elastin-derived amyloidogenic peptides, we carried out the kinetics of EX32 amyloid-like aggregates by using ThT dye. CD spectroscopy was also used for investigating the secondary structure of the polypeptides, thus giving useful insights into the conformations involved in amyloid-like fiber formation. Furthermore, complementary techniques such as fluorescence spectroscopy, spectral shift, and binding Congo red UV assays as well as atomic force microscopy were also used to confirm the amyloidogenic behavior of the studied polypeptides.

Li+ distribution into V2O5 films resulting from electrochemical intercalation reactions

We studied interface effects of thin film V2O5 electrodes on top of indium tin oxide (ITO) glass for Li intercalation by means of a combination of methods: depth-profiling by secondary ion mass spectroscopy (SIMS), electrochemical insertion-extraction of lithium ions by slow-scan cyclic voltammetry (SSCV) and by potentiostatic intermittent titration technique (PITT). We show that the Li+ distribution inside the oxide film is always far from homogeneous, and that different diffusion paths (parallel to interfaces as well as perpendicular to them) have to be considered in experiments with electrodes having areas of few cm2. The exposed edge formed when cutting out coupons from the coated glass plate supporting the V2O5 electrode plays a significant role in the process, because it exposes the V2O5-ITO interface to the electrolyte.

Molecular and supramolecular studies on polyglycine and poly-L-proline

Elastin is a cross-linked protein, whose soluble precursor is tropoelastin, responsible for resilience and elastic recoil in vertebrate tissues. Glycine and proline are among the most repeated amino acids in tropoelastin primary structure, the high flexible glycine being present 222 times and the more constrained proline being present 96 times. In order to deeper investigate the role of glycine and proline residues in elastin, we studied the molecular and supramolecular structures of polyglycine and poly-L-proline homopolypeptides as significant sequences for the protein. As a matter of fact, up to now, if few conformational studies are accessible only for poly-L-proline homopolypeptide in solution and for polyglycine homopolypeptide in the solid state, limited supramolecular studies are available for both homopolypeptides. Given the self-aggregation properties of these homopolypeptides, we investigated the aggregation mechanism by turbidimetry measurements together with Congo red birefringence assay, ThT fluorescence spectroscopy, and atomic force microscopy and transmission electron microscopy studies. At molecular level, we show the dominance of the cross-β structure for polyglycine fibrils while for poly-L-proline aggregates PPII conformation prevails. At supramolecular level, the results show that polyglycine is able to self-aggregate into amyloid-like fibres while poly-L-proline aggregates by following a specific pathway ranging from protofibrils to fibrils. These findings suggest that the self-aggregation properties of elastin are influenced by tropoelastin primary structure thus explaining why glycine-rich elastin-derived polypeptide sequences are amyloidogenic (Gly-effect) while proline-rich elastin-derived polypeptide sequences (Pro-effect) are able to coacervate.

Factors influencing charge capacity of vanadium pentoxide thin films during lithium ion intercalation/deintercalation cycles

The intercalation of vanadium pentoxide by lithium ions leads to a change in optical properties, a process that is of value in thin-film electrochromic devices. In this study, films of V2O5, deposited on indium tin oxide (ITO) glass coupons by a sol-gel process, were challenged by increasing numbers of charge-discharge cycles ranging from 72 to 589 full cycles. The samples were characterized by x-ray photoelectron spectroscopy (XPS) and then examined in the deintercalated state by time-of-flight secondary ion mass spectroscopy (SIMS). XPS enabled measurement of the thickness and composition of the solid-electrolyte interface and provided evidence of the residual V4+ concentration within the top few nanometers of the surface. The SIMS profile gave direct information on the thickness of the films and on the thickness loss caused by rinsing the samples after the electrochemical exposure. Determination, by SIMS, of the concentration of lithium ions has enabled a correction to be made for the amount of inactiv...