Desarrollo de una celda electroquímica en gel para la evaluación in situ del patrimonio cultural metálico

A lo largo de toda la historia, la humanidad ha tratado de preservar ciertos objetos que por diversos motivos han adquirido un valor y un significado para la sociedad que los ha poseído, constituyendo su patrimonio cultural. En ese esfuerzo por preservar el pasado para las generaciones presentes y futuras, la investigación científica ha ido adquiriendo una relevancia progresiva. La ciencia de la conservación trata de comprender los problemas y aportar soluciones para la conservación del patrimonio, tanto desde el punto de vista tecnológico como estratégico o de sostenibilidad. El adecuado diseño y planificación de las estrategias de conservación de los objetos y colecciones del patrimonio cultural son fundamentales, y deben tener en cuenta las limitaciones tecnológicas y de recursos. El fin de esta tesis ha sido contribuir desde la Ciencia e Ingeniería de Materiales a este objetivo, concretamente en el ámbito del patrimonio cultural metálico, desarrollando una herramienta de diagnóstico del estado de conservación y de los sistemas de protección para este tipo de bienes culturales. El principal problema para la conservación del patrimonio metálico es la corrosión, que tiene lugar por interacción entre el objeto metálico y el medio que lo rodea. Para enfrentarse a este problema, los conservadores de patrimonio metálico cuentan con dos estrategias: el control de las condiciones ambientales –lo que no siempre es posible- o el empleo de recubrimientos protectores, que lo aíslen del medio, que es el método más habitual en la práctica de la conservación. Sin embargo, cualquier método presenta limitaciones, por lo que resulta de gran relevancia el poder evaluar la eficacia y la duración de los sistemas empleados, antes de que aparezcan efectos negativos en el objeto. Así, los recubrimientos habituales en conservación –principalmente ceras y barnices acrílicos- tienen una capacidad protectora bastante limitada y deben ser renovados cada cierto tiempo. Esto conlleva la necesidad de conocer y evaluar el comportamiento de los sistemas aplicados, con especial hincapié en su durabilidad. La espectroscopía de impedancia electroquímica (EIS) es una técnica electroquímica que permite estudiar los procesos de corrosión en los metales en diferentes medios y evaluar la capacidad protectora de los recubrimientos, por lo que a priori resulta una técnica idónea para este propósito. Sin embargo, la aplicación de la EIS a la conservación del patrimonio cultural metálico no es una práctica generalizada, por las dificultades particulares que presenta su aplicación en este campo. Las características propias de los bienes culturales, hacen que en muchos casos los estudios de laboratorio no sean suficientes, y que el objeto no se pueda trasladar, por lo que resulta imprescindible la realización de medidas in situ, directamente sobre la superficie del objeto a conservar. La aplicación de técnicas electroquímicas requiere montar una celda electroquímica, en la que poner en contacto la superficie del material que se va a estudiar con un electrólito líquido y los electrodos auxiliares (electrodo de referencia y contraelectrodo). Esta tarea resulta compleja en el caso de superficies irregulares y no horizontales como las de una escultura. Para dar una solución a este problema, el objetivo de esta tesis ha sido el desarrollo de una celda electroquímica con un electrólito en gel, específicamente diseñada para la realización de medidas in situ sobre patrimonio cultural. Para el diseño se han tenido en cuenta diversos factores relacionados con este tipo de medidas, tales como la forma y tamaño de la celda para facilitar su colocación en la superficie de la obra, la naturaleza, geometría y posición de los electrodos para obtener una señal de calidad, o el tipo de soporte adecuado para lograr una buena estabilidad mecánica. El trabajo se ha estructurado en varios apartados, si bien no recorrido su no ha sido lineal, ya que los avances y dificultades en cada uno de los aspectos o subapartados han contribuido al desarrollo de los demás. El primer paso ha sido comprobar la posibilidad de realizar medidas de impedancia utilizando un electrólito gelificado con agar, abordando cuestiones como la validez, reproducibilidad o repetividad de los resultados. Una vez verificada la obtención de medidas de calidad y comparables a las de un electrólito tradicional, se ha estudiado en mayor detalle la contribución del agar en las medidas, para establecer la concentración más adecuada tanto desde el punto de vista electroquímico como mecánico. En esta misma línea, se ha comparado el comportamiento del agar y de la agarosa, uno de los dos polisacáridos que componen este material, y que es el responsable de las propiedades gelificantes. El siguiente paso ha sido analizar en detalle el comportamiento del sistema completo, incluyendo los electrodos (de referencia y contraelectrodo) para optimizar el diseño. Así, se han estudiado diferentes configuraciones de celda con electrodos de distinta naturaleza y geometría, un factor que ha demostrado su relevancia para minimizar la aparición de artefactos en las medidas al emplearse electrólitos de baja conductividad. En paralelo al desarrollo y estudio de la celda, se han realizado medidas sobre diferentes sustratos para evaluar la aplicabilidad del sistema desarrollado a la resolución de problemas de conservación. Por un lado, se han realizado ensayos de laboratorio sobre probetas de bronce y acero patinable con diversas pátinas y recubrimientos, simulando cuestiones que se abordan habitualmente en la conservación del patrimonio metálico; por otro lado, se han realizado estudios in situ, sobre obra real (principalmente escultura moderna y contemporánea del Museo Arqueológico Nacional, Museo de Escultura de Leganés y colección de escultura del campus de la Universidad Politécnica de Valencia), para comprobar y validar el diseño de la celda en su modo de aplicación final, e ir introduciendo las modificaciones necesarias para solventar las dificultades prácticas que se iban encontrando en diferentes situaciones. Todo ello ha permitido concluir con éxito con el diseño de una celda electroquímica con electrólito en gel, adecuada para la realización de medidas electroquímicas in situ sobre el patrimonio cultural metálico, aportando una nueva herramienta para avanzar en la conservación de este tipo de patrimonio.Along history, mankind has sought to preserve certain objects which, for multiple reasons, have acquired a special value and a meaning for the society that owned them, constituting their cultural heritage. In this effort to preserve the past for the present and future generations, scientific research has gained an increasing relevance. Conservation science aims at understanding problems and provide solutions for the conservation of heritage, both from the technological and sustainable point of view. The proper design and planning of strategies for the conservation of cultural heritage objects and collections is essential, and should take into account both technological and resources limitations. The purpose of this thesis is to contribute through Materials Science and Engineering to this objective, in particular in the field of metallic cultural heritage, developing a tool of diagnosis of the state of conservation and evaluation of protection systems for this type of heritage. The main challenge for the conservation of the heritage metal is corrosion, which takes place because of the interaction between the metal object and its environment. To deal with this problem, metal conservators have two strategies: control of environmental conditions - which is not always possible - or the use of protective coatings to isolate the metal object from the environment, which is the most frequent solution in conservation practice. Nonetheless, any method has certain limitations. For this reason, it is of great importance being able to evaluate the effectiveness and lifespan of protective systems before damage occurs. Common coatings in heritage conservation –mainly waxes and acrylic varnishes- have a quite limited protective ability, and have to be renewed periodically. This entails the need of knowing and evaluating the behavior of applied protective coatings, with particular focus on durability. Electrochemical impedance spectroscopy (EIS) is an electrochemical technique that allows to investigate corrosion mechanisms of metals in different environments and to evaluate the protective properties of coatings. This makes EIS the ideal technique for this purpose. Unfortunately, the use of EIS in metal cultural heritage is not a widespread practice, due to the particular difficulties in applying this technique in heritage objects. The special characteristics of cultural heritage assets make it necessary to carry out on site measurements, directly on the surface of the object to preserve. The use of electrochemical techniques requires mounting an electrochemical cell, in which the surface of the material under study is placed in contact with a liquid electrolyte and the auxiliary electrodes (reference and counter electrode). This is not an easy task for irregular and non-horizontal surfaces as in a sculpture. To overcome this challenge, the objective of this thesis is to develop an electrochemical cell with a gelled electrolyte, specifically designed for conducting in situ electrochemical measurements on cultural heritage. The design has taken into account various factors related to this type of measures, such as the shape and size of the cell to be placed on the surface of the object, the nature, geometry and position of the electrodes to obtain a quality signal, or the fixing system to ensure a good mechanical stability. This work has been structured into several sections, although its progress has not been linear in time, since the advances and difficulties in each of the aspects or subsections have contributed to improve and develop the others. The first step has been checking the possibility of performing impedance measures using an agar gelled electrolyte, addressing issues such as validity, reproducibility, or repeatability of the results. Once verified the quality of measurements, comparable to a traditional electrolyte, detail the contribution of the agar been studied in greater detail, to establish the most appropriate concentration both from the electrochemical and mechanical point of view. With the same purpose the behavior of agar and agarose has been compared. The next step was to analyze in detail the behavior of the entire system, including electrodes (reference and counter electrode) to optimize the design. Thus, we have studied different configurations of cell with electrodes of different nature and geometry, a factor that has shown its relevance to minimize the appearance of artifacts in the measurements when using low-conductivity electrolytes. In parallel to the development and study of the cell, measurements on different substrates have been performed to assess the applicability of the developed system to solve conservation problems. On the one hand, laboratory tests on bronze and weathering steel coupons, with different patinas and coatings were performed, simulating issues usually addressed in metallic heritage conservation; on the other hand, studies have been conducted in situ on real work (mainly modern and contemporary sculpture of the National Archaeological Museum, Museum of Sculpture in Leganes and the sculpture collection at the Polytechnic University of Valencia campus), to check and validate the design of the cell in its final application mode, and to introduce the modifications necessary to solve the practical difficulties that were found in different situations. This has allowed concluding successfully with the design of an electrochemical cell with a gel electrolyte, suitable for carrying out on-site electrochemical measures on metallic cultural heritage, providing a new tool for a better conservation of this kind of heritage.El trabajo que aquí se presenta ha sido financiado por la beca FPI BES-2012-052716 y el proyecto HAR2011-22402 del Plan Nacional de I+D+i 2008-2011 del Ministerio de Ciencia e Innovación, el proyecto HAR2014-54893-R, HAR2014-54893-R, la Comunidad de Madrid y el fondo Social Europeo en el marco del Programa Geomateriales 2 (S2013/MIT 2914), y el proyecto IPERION-CH (European Union H2020, G.A. 654028).Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de MadridPresidente: Juan Carlos Galván Sierra.- Secretario: Antonia Jiménez Morales.- Vocal: Kepa Castro Ortiz de Pined

Heparin and the solubilization of asymmetric acetylcholinesterase

AbstractHeparin solubilizes asymmetric acetylcholinesterase, from chick skeletal muscle and retina, as a 24 S complex which is quantitatively converted to conventional asymmetric molecular forms of the enzyme (A12 and A8, either class I or class II) upon exposure to high salt. The simultaneous presence of salt and heparin in the homogenization medium selectively prevents, however, the release of class II A-forms in both muscle and retina. Heparin may generally act by displacing native proteoglycans involved in the attachment of the enzyme tail to the extracellular matrix, or its neural equivalent, being in turn removed by salt to yield typical asymmetric enzyme forms. Heparin would also appear to displace some other molecules specifically involved in the EDTA-sensitive attachment of class II tailed forms, this effect being antagonized by salt

Making an impact : guidelines on designing and implementing outreach programs for transitional justice

Despite the critical role of outreach programs and the dedication and strategic planning required to implement them effectively, the level of thought and support devoted to outreach work has varied widely among transitional justice institutions. This report offers a definition and systematic consideration of outreach activities, along with practical guidance on the design and implementation of outreach programs

Outreach strategies in international and hybrid courts : report of the ICTJ-ECCC Workshop, Phnom Penh, March 3-5, 2010

This document presents a non‐exhaustive summary of some of the topics discussed at a workshop on outreach organized by ICTJ in collaboration with the Extraordinary Chambers in the Courts of Cambodia (ECCC) from March 3-5, 2010. It first provides a general overview of the ECCC functions and outreach activities. Thereafter, it highlights the main themes that were raised in the presentations and discussion sessions

Prediction of the n‑octanol/water partition coefficients in the SAMPL6 blind challenge from MST continuum solvation calculations

The IEFPCM/MST continuum solvation model is used for the blind prediction of n-octanol/water partition of a set of 11 fragment-like small molecules within the SAMPL6 Part II Partition Coefficient Challenge. The partition coefficient of the neutral species (log P) was determined using an extended parametrization of the B3LYP/6-31G(d) version of the Miertus-Scrocco-Tomasi continuum solvation model in n-octanol. Comparison with the experimental data provided for partition coefficients yielded a root-mean square error (rmse) of 0.78 (log P units), which agrees with the accuracy reported for our method (rmse = 0.80) for nitrogen-containing heterocyclic compounds. Out of the 91 sets of log P values submitted by the participants, our submission is within those with an rmse < 1 and among the four best ranked physical methods. The largest errors involve three compounds: two with the largest positive deviations (SM13 and SM08), and one with the largest negative deviations (SM15). Here we report the potentiometric determination of the log P for SM13, leading to a value of 3.62 ± 0.02, which is in better agreement with most empirical predictions than the experimental value reported in SAMPL6. In addition, further inclusion of several conformations for SM08 significantly improved our results. Inclusion of these refinements led to an overall error of 0.51 (log P units), which supports the reliability of the IEFPCM/MST model for predicting the partitioning of neutral compounds

Kainate-Triggered Currents in Xenopus Oocytes Injected with Chick Retinal Membrane Fragments: Effect of Guanine Nucleotides

PURPOSE. To electrophysiologically characterize ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate receptors in chick retinal membrane fragments, incorporated into Xenopus oocytes by direct microinjection. METHODS. A 6-day retinal membrane suspension was injected into Xenopus oocytes by use of an electronic nanoliter injector. Fifteen to 40 hours after injection, the oocytes were assayed for kainate-elicited inward currents, under voltage-clamp conditions (membrane potential held at Ϫ70 mV). The structural incorporation of the retinal membrane fragments into the oocyte membrane was verified by specific immunofluorescent staining. RESULTS. Chick retinal membrane fragments were efficiently grafted onto Xenopus oocytes after microinjection, with 22.9% Ϯ 7.6% of the oocyte membrane being stained with anti-chick retina antibody. Part of the retinal material was seen as patches of relatively uniform size (292.1 Ϯ 72.3 m 2 ). Bath-applied kainate induced dose-dependent (EC 50 : 64 Ϯ 7 M), nondesensitizing inward currents (15-90 nA) in the chimeric Xenopus oocytes. Sham-injected oocytes did not respond to kainate. Kainate-driven currents were blocked by 6,7-dinitroquinoxaline-2,3-dione (DNQX) and 1-(4-aminopropyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride (GYKI 52466), but not by ␥-D-glutamylaminomethyl sulfonic acid (GAMS) or aminophosphonoheptanoate (AP7), suggesting the involvement of AMPA receptors in the observed responses. Guanine nucleotides (GNs) also blocked kainate currents in a concentration-dependent manner. CONCLUSIONS. An alternative oocyte microinjection technique to analyze the electrophysiological properties of glutamate receptors in chick retinal membranes is described. The results show the functional activity of putative AMPA-preferring receptors from chick retina and confirm, in the chick retinal model, the antagonistic behavior of guanine nucleotides toward glutamate receptors and their potential role as neuropro- These results add to the accumulated evidence on the antagonistic behavior of guanine nucleotides (GNs) at ionotropic glutamate receptors, in very diverse experimental setups, including agonist displacement, electrophysiological recording and neuroprotection paradigms. 21,22 MATERIALS AND METHODS Chick Retinal Membrane Preparation All experiments with animals (chicks, Xenopus, and rabbits) followed our institutional guidelines for care and handling of laboratory animals, in full agreement with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. Six-day-old white leghorn chicks were used as the source of retinal membrane fragments. Lysed membranes, prepared as described, 7 were resuspended in 10 mM HEPES (pH 7.4), containing 140 mM KCl and 20 mM NaCl, at a protein concentration of 2 mg/mL, stored in liquid nitrogen, and thawed and sonicated for 10 seconds in an ice water bath just before injection. A control solution without membranes was similarly processed and used for sham-injected control chicks. Oocyte Preparation and Injection Mature female Xenopus laevis were obtained from the Centre d&apos;Elevage des Xénopes, CRBM (Montpellier, France), and kept in chlorine-free fresh water, at 22°C. Discrete ovary portions were removed from anesthetized frogs 23 and stage-V/VI oocytes 24 were individually dissected and kept, at 15°C to 17°C, in sterile modified Barth&apos;s solution (10 mM HEPES [pH 7.4], 88 mM NaCl, 1 mM KCl, 0.33 mM Ca(NO 3 ) 2 , 0.41 mM CaCl 2 , 0.82 mM MgSO 4 , and 2.4 mM NaHCO 3 ) supplemented with penicillin (100 IU/mL) and streptomycin (0.1 mg/mL). Oocytes were further treated with collagenase (clostridiopeptidase A: EC3.4.24.3; type IA, 0.5 mg/mL; Sigma-Aldrich, St. Louis, MO), for 50 minutes at room temperature, to remove enveloping cells. 25 From th

Protective Coatings for Metals in Scientific—Technical Heritage: The Collection of the Spanish National Museum of Science and Technology (MUNCYT)

This paper presents results on the protective properties of different coatings over metals representative of those found in scientific–technical heritage collections. An examination of several objects in the collection of the Spanish National Museum of Science and Technology have allowed the identification of brass and steel as the most representative metals, and the existence of coatings (mainly shellac and acrylic resins) applied for aesthetic and/or conservation purposes. Based on these findings, brass and steel coupons coated with Paraloid B-44, B-48, B-67, B-72, Incralac, Cosmolloid H80, B-72 + H80 double layer and shellac have been studied to carry out a first screening in order to select the most promising candidates and determine the most appropriate methodology and key factors for the study. Coatings have been aged up to 336 h using cycles of UV light and water condensation. The change in the aspect of the coupons has been assessed via visual examination, optical microscopy and colorimetric measurements, with B-44 and Incralac showing the least change. EIS has been used for a quantitative evaluation of the protective properties and FTIR to measure chemical changes experienced by some coatings, such as B-48 and B-67. These evaluations allowed us to follow, understand and compare the behaviour of the different coatings and substrates after artificial ageing

What remains of the future: sustainability through heritage

Coordinators : Felipe Criado Boado (INCIPIT, CSIC), Blanca Ramírez Barat (CENIM, CSIC).Heritage is increasingly being recognized as a key element for social cohesion, sustainable socioeconomic development and people’s welfare. Resources dedicated to heritage conservation have gone from being considered an expense to being regarded as an investment, with a high revenue. The heritage industry has been an active part of this transformations in recent decades, it has generated employment, contributed to the worldwide expansion of tourism and has become a coveted sign of identity for political communities. Today there is no social or political process that does not use heritage in some way. Hence the actuality of the subject, and the importance of an organization such as the CSIC having research capabilities in this field