Maria Elvira Egidia Carbone

Comparative Spectra Illustrating Degradation of CaC2O4⋅H2O During XPS Analysis

Calcium oxalate monohydrate is found as a by-product of environmental damage to stonework of importance in preserving cultural heritage. XPS (X-ray Photoelectron Spectroscopy) was here used to characterize the standard compound, calcium oxalate monohydrate, RPE, chemically synthesized as provided by Carlo Erba Reagents - Cod. 434004. Degradation occurred during analysis and this is described. Repeat XPS acquisitions have allowed us to monitor the spectral changes of calcium oxalate during the whole process of analysis: its degradation was rationalized by considering the effect of x-ray power; UHV exposure; and thermal effects suffered by the powdered sample after its insertion into the spectrometer and, particularly, during spectra acquisition. Measurement of degradation with time enabled extrapolation to yield the primary composition. It was found that samples will completely dehydrate in ultra high vacuum, UHV. Although dehydrated samples are then stable in UHV, during XPS acquisitions degradation of ca...

In Situ Electrochemical–AFM and Cluster-Ion-Profiled XPS Characterization of an Insulating Polymeric Membrane as a Substrate for Immobilizing Biomolecules

The electrochemical oxidation of ortho-aminophenol (oAP) by cyclic voltammetry (CV), on platinum substrates in neutral solution, produces a polymeric film (PoAP) that grows to a limiting thickness of about 10 nm. The insulating film has potential use as a bioimmobilizing substrate, with its specificity depending on the orientation of its molecular chains. Prior investigations suggest that the film consists of alternating quinoneimine and oAP units, progressively filling all the platinum sites during the electrosynthesis. This work concerns the evaluation of the growth orientation of PoAP chains, which until now was deduced only from indirect evidence. Atomic force microscopy (AFM) has been used in situ with an electrochemical cell so that PoAP deposition on a specific area can be observed, thus avoiding any surface reorganization during ex situ transport. In parallel with microscopy, XPS experiments have been performed using cluster ion beams to profile this film, which is exceptionally thin, without damage while retaining molecular information.

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

AbstractThis 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 abstractSynthesis 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