Development and optimisation of protocols for surface cleaning of cultural heritage metals

The conservation and valorisation of cultural heritage is of fundamental importance for our society, since it is witness to the legacies of human societies. In the case of metallic artefacts, because corrosion is a never-ending problem, the correct strategies for their cleaning and preservation must be chosen. Thus, the aim of this project was the development of protocols for cleaning archaeological copper artefacts by laser and plasma cleaning, since they allow the treatment of artefacts in a controlled and selective manner. Additionally, electrochemical characterisation of the artificial patinas was performed in order to obtain information on the protective properties of the corrosion layers. Reference copper samples with different artificial corrosion layers were used to evaluate the tested parameters. Laser cleaning tests resulted in partial removal of the corrosion products, but the lasermaterial interactions resulted in melting of the desired corrosion layers. The main obstacle for this process is that the materials that must be preserved show lower ablation thresholds than the undesired layers, which makes the proper elimination of dangerous corrosion products very difficult without damaging the artefacts. Different protocols should be developed for different patinas, and real artefacts should be characterised previous to any treatment to determine the best course of action. Low pressure hydrogen plasma cleaning treatments were performed on two kinds of patinas. In both cases the corrosion layers were partially removed. The total removal of the undesired corrosion products can probably be achieved by increasing the treatment time or applied power, or increasing the hydrogen pressure. Since the process is non-invasive and does not modify the bulk material, modifying the cleaning parameters is easy. EIS measurements show that, for the artificial patinas, the impedance increases while the patina is growing on the surface and then drops, probably due to diffusion reactions and a slow dissolution of copper. It appears from these results that the dissolution of copper is heavily influenced by diffusion phenomena and the corrosion product film porosity. Both techniques show good results for cleaning, as long as the proper parameters are used. These depend on the nature of the artefact and the corrosion layers that are found on its surface.

Tortoiseshell or Polymer? Spectroscopic Analysis to Redefine a Purported Tortoiseshell Box with Gold Decorations as a Plastic Box with Brass

The study and preservation of museum collections requires complete knowledge and understanding of constituent materials that can be natural, synthetic, or semi-synthetic polymers. In former times, objects were incorporated in museum collections and classified solely by their appearance. New studies, prompted by severe degradation processes or conservation-restoration actions, help shed light on the materiality of objects that can contradict the original information or assumptions. The selected case study presented here is of a box dating from the beginning of the 20th century that belongs to the Portuguese National Ancient Art Museum. Museum curators classified it as a tortoiseshell box decorated with gold applications solely on the basis of visual inspection and the information provided by the donor. This box has visible signs of degradation with white veils, initially assumed to be the result of biological degradation of a proteinaceous matrix. This paper presents the methodological rationale behind this study and proposes a totally non-invasive methodology for the identification of polymeric materials in museum artifacts. The analysis of surface leachates using 1H and 13C nuclear magnetic resonance (NMR) complemented by in situ attenuated total reflection infrared spectroscopy (ATR FT-IR) allowed for full characterization of the object s substratum. The NMR technique unequivocally identified a great number of additives and ATR FT-IR provided information about the polymer structure and while also confirming the presence of additives. The pressure applied during ATR FT-IR spectroscopy did not cause any physical change in the structure of the material at the level of the surface (e.g., color, texture, brightness, etc.). In this study, variable pressure scanning electron microscopy (VP-SEM-EDS) was also used to obtain the elemental composition of the metallic decorations. Additionally, microbiologic and enzymatic assays were performed in order to identify the possible biofilm composition and understand the role of microorganisms in the biodeterioration process. Using these methodologies, the box was correctly identified as being made of cellulose acetate plastic with brass decorations and the white film was identified as being composed mainly of polymer exudates, namely sulphonamides and triphenyl phosphate.

NEW METAL-BASED MICELLES AS ANTICANCER AGENTS

Cancer is a leader cause of death worldwide. One of the problems associated with the current chemotherapeutic options is the noxious side effects caused by the lack of selectivity. In this frame, our research group has been committed to the development of a new Ru and Fe macrometallodrugs.[1] The data obtained so far shows that these compounds present an intrinsic selectivity towards cancer cells (relatively to healthy cells) due to the incorporation of polymeric ligands that promote a passive targeting through the cancer cell membrane. These results prompted us to the development of new macrometallodrugs bearing bioessential metals such as Fe, Zn and Co. We used a ‘M(bipy) 3 ’ scaffold (bipy = 2,2’-bipyridine derivatives) for the synthesis of the new compounds due to the promising cytotoxicity results observed for related compounds.[2] As polymeric ligands we have chosen the polylactide-co-polyethylene glycol amphiphilic copolymer that is able to self-assemble into micelles in water, keeping the metal center hidden, like a Trojan horse. We will present the synthesis and characterization of the new compounds and some preliminary data on their ability to form stable micelles (Figure 1).