Analytical Investigation of Iron-Based Stains on Carbonate Stones: Rust Formation, Diffusion Mechanisms, and Speciation.

In cultural heritage, unaesthetic stains on carbonate stones due to their close contacts with metals are of concern for the preservation of sculptures, monumental facades and archeological finds of various origin and antiquities. Rust stains made up of various oxidized iron compounds are the most frequent forms of alteration. The presence of ferric iron on rust-stained marble surfaces was confirmed in previous studies and oriented the choice of the best cleaning method (based on complexing agents specific for ferric ions). However, the composition of rust stains may vary along their extension. As the corrosion of the metallic iron proceeds, if the oxygen levels in the surroundings are low and there are no conditions to favor the oxidation, ferrous ions can also diffuse within the carbonate structure and form a variety of intermediate compounds. In this study, the iron stains on archeological marbles were compared with those artificially produced on Carrara marbles and Travertine samples. The use of integrated techniques (optical and scanning electron microscopy as well as Mössbauer and XPS spectroscopy) with complementary analytical depths, has provided the overall information. Rust formation and diffusion mechanisms in carbonates were revealed together with the evolution of iron speciation and identification of phases such as ferrihydrite, goethite, maghemite, nanomagnetite, and hematite.

The Bio-Patina on a Hypogeum Wall of the Matera-Sassi Rupestrian Church "San Pietro Barisano" before and after Treatment with Glycoalkaloids.

The investigation focused on the deterioration of the walls in the hypogeum of "San Pietro Barisano" rupestrian church, located in the Matera-Sassi (Southern Italy), one of the UNESCO World Heritage sites. The study evaluated the biocide activity of a mixture of natural glycoalkaloids (GAs) extracted from the unripe fruit of Solanum nigrum and applied to clean a hypogeum wall surface in the church affected by bio-patinas. The analyzed bio-patina, collected before treatment and, at pre-established times, after treatment, showed changes in chemical composition detected by XPS, accompanied by visible discoloration and biological activity variation. The biocidal action of the glycoalkaloids mixture, directly employed on the wall surface, was effective after about four weeks for most bio-patina colonizers but not for the fungal species that can migrate and survive in the porosities of the calcarenite. Consequently, the cleaning procedure requires the integration of fungicidal actions, combined with the consolidation of the surfaces, to obtain complete bioremediation and avoid subsequent biological recolonization. SEM images and associated microanalysis of pretreated bio-patina have revealed the biocalcogenity of some autochthonous microorganisms, thus preluding to their eventual isolation and reintroduction on the wall surface to act as consolidants once the bio-cleaning phase has been completed.

Validation of an Analytical Method for Nitrite and Nitrate Determination in Meat Foods for Infants by Ion Chromatography with Conductivity Detection.

Nitrate and nitrite as sodium or potassium salts are usually added to meat products to develop the characteristic flavor, to inhibit the growth of microorganisms (particularly Clostridium botulinum), and effectively control rancidity by inhibiting lipid oxidation. However, both nitrate and nitrite ions need to be monitored for ensuring the quality and safety of cured meats. In this work, for the first time the content of nitrite and nitrate ions in homogenized meat samples of baby foods was determined by a validated method based on ion chromatography (IC) coupled with conductivity detection. Recoveries of nitrate and nitrite ions in meat samples were not lower than 84 ± 6%. The detection limits of nitrate and nitrite were 0.08 mg L-1 and 0.13 mg L-1, respectively. Five commercial samples of homogenized meat, namely lamb, rabbit, chicken, veal, and beef, for infant feeding were investigated; while nitrite content was below the detection limit, nitrate ranged from 10.7 to 21.0 mg kg-1. The results indicated that nitrate contents were below the European (EU) fixed value of 200 mg kg-1, and an acceptable daily intake of 3.7 mg kg-1 was estimated.

Interactions between elastin-like peptides and an insulating poly(ortho-aminophenol) membrane investigated by AFM and XPS.

This investigation was undertaken to explore the mutual recognition of the pentapeptide (ValGlyGlyValGly)n, a hydrophobic elastin-like peptide (ELP), suspended in deionized water in monomer (n = 1) and trimer (n = 3) forms and the outer surface of a very thin, insulating polymer, poly(ortho-aminophenol) (PoAP), electrochemically grown on a platinum foil by cyclic voltammetry in a neutral medium (phosphate-buffered saline, I = 0.1M) immersed in the suspension. As a prior task, the proved propensity of the ValGlyGlyValGly sequence, at the given minimal length (three or more repeats), to self-assemble into amyloid-like fibrils when solubilized in an aqueous environment was considered within the framework of testing PoAP surfaces for the specific detection of amyloid precursors. From our knowledge of the chemical structure and physical properties of both biomacromolecule families obtained in previous studies, we focused on the efficacy of the binding sites offered to ELP fibrils by PoAP in its as-prepared form or properly modified either by postsynthesis oxidation or by adsorption/entrapping of ELP monomer(s) with or without protecting terminal groups. Consistent with all methods of preparation, the best surfaces, recognizable by the trimer fibrils, are those modified to carry a larger number of carbonyls, particularly by entrapment of ELP monomer(s) during PoAP electrosynthesis using an imprinting-inspired method. The degree of attachment of fibrillar aggregates, detected by atomic force microscopy and X-ray photoelectron spectroscopy, provides unequivocal evidence of the cooperative forces involving PoAP-ELP interactions. The results obtained suggest the prospect of using the proposed Pt/PoAP/ELP systems as biodetectors in Alzheimer disease. Graphical abstract Synthesis steps of Pt/PoAP/ELP electrodes for amyloid detection. AFM = Atomic Force Microscopy, CV = Cyclic Voltammetry, ELPs = Elastin like Peptides, PoAP = Poly ortho-Aminophenol, Pt = Platinum, XPS = X-ray Photoelectron Spectroscopy.

Structural characterization and biological properties of the amyloidogenic elastin-like peptide (VGGVG)3.

The peculiar and unique properties of elastin are due to the abundance of hydrophobic residues and of repetitive sequences as XGGZG (X, Z=V, L or A). Unexpectedly, these sequences not only provide elasticity to the whole protein, but are also able to form amyloid-like fibrils. Even though amyloid fibrils have been associated for a long time to the development of serious disorders as Alzheimer's disease, recent evidence suggests that toxicity may be related to oligomeric species or to pre-fibrillar intermediates, rather than to mature fibrils. In addition, a number of studies highlighted the potential of "bio-inspired" materials based on amyloid-like nanostructures. The present study has been undertaken with the aim to characterize a chemically synthesized elastin-like peptide (VGGVG)3. Structural and biological features were compared with those of peptides as poly(VGGVG) and VGGVG that, having the same amino acid sequence, but different length and supramolecular structure have been previously investigated for their amyloidogenic properties. Results demonstrate that a minimum sequence of 15 amino acids is sufficient to aggregate into short amyloid-like fibrils, whose formation is however strictly dependent on the specific VGGVG repeated sequence. Moreover, in the attempt to elucidate the relationship among aggregation properties, fibers morphology and biocompatibility, 3T3 fibroblasts were grown in the presence of VGGVG-containing elastin-like peptides (ELPs) and analyzed for their ability to proliferate, attach and spread on ELPs-coated surfaces. Data clearly show that amyloid-like fibrils made of (VGGVG)3 are not cytotoxic at least up to the concentration of 100 µg/ml, even after several days of culture, and are a good support for cell attachment and spreading.

XPS characterization of (copper-based) coloured stains formed on limestone surfaces of outdoor Roman monuments.

Limestone basements holding bronzes or other copper alloys artefacts such as sculptures, decorations and dedicatory inscriptions are frequently met both in modern and ancient monuments. In outdoor conditions, such a combination implies the corrosion products of the copper based alloy, directly exposed to rainwater, will be drained off and migrate through the porous surfaces, forming stains of different colours and intensities, finally causing the limestone structures to deteriorate.In this work we have analysed samples from two modern limestone monuments in Rome, the Botticino surfaces of the 'Vittoriano' (by G.Sacconi, 1885-1911- Piazza Venezia) and the travertine basement of the 'Statua dello Studente' (by A.Cataldi, 1920- University city, La Sapienza), and focussed our investigation on the chemical composition of the copper-stained zones using XPS (X-ray Photoelectron Spectroscopy) as a surface-specific technique.Based on observations reporting on the structure and bonding at the calcite surfaces we have identified copper complexes and mixed calcium/copper carbonates associated with the stains, as well as the chemical state of other elements therein included, and related the compositional changes with differences in chromatic characteristics and sampling locations.

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.

Electrosynthesized, non-conducting films of poly(2-naphthol): electrochemical and XPS investigations.

Advanced biosensors are frequently based on electrosynthesized polymeric films. In this context, the electrosynthesis mechanism underlying the electrochemical oxidation of 2-naphthol (2-NAP) in phosphate buffer at pH 7 on Pt electrodes has been investigated. The voltammetric behaviour suggested the formation of a non-conducting polymer (poly(2-NAP)) through an irreversible electrochemical process complicated by 2-NAP adsorption and fast electrode passivation. Repeat experiments showed the passive films to be strongly adherent to the Pt surface with thicknesses of approximately 10 nm, as estimated by in-situ electrochemical quartz crystal microbalance (EQCM) measurements and by X-ray photoelectron spectroscopy (XPS). The polymer structure was then investigated by XPS, which gave evidence of the presence of naphthalene rings bonded through poly(oxide) groups (C-O-C) and of quinonoid groups, probably present as the ends of polymeric chains. The polymer repeat unit and terminal groups derived by XPS analysis are in accordance with electrochemical results and with synthesis routes reported for phenol-derived compounds in aqueous solution. XPS also gave evidence of a large excess of oxygen, probably arising from water molecules entrapped by the polymeric chains, as suggested by angle-resolved XPS and thermal treatment of poly(2-NAP)/Pt film under ultra-high vacuum (UHV).