Preventing colour fading in artworks with graphene veils.

Modern and contemporary art materials are generally prone to irreversible colour changes upon exposure to light and oxidizing agents. Graphene can be produced in thin large sheets, blocks ultraviolet light, and is impermeable to oxygen, moisture and corrosive agents; therefore, it has the potential to be used as a transparent layer for the protection of art objects in museums, during storage and transportation. Here we show that a single-layer or multilayer graphene veil, produced by chemical vapour deposition, can be deposited over artworks to protect them efficiently against colour fading, with a protection factor of up to 70%. We also show that this process is reversible since the graphene protective layer can be removed using a soft rubber eraser without causing any damage to the artwork. We have also explored a complementary contactless graphene-based route for colour protection that is based on the deposition of graphene on picture framing glass for use when the direct application of graphene is not feasible due to surface roughness or artwork fragility. Overall, the present results are a proof of concept of the potential use of graphene as an effective and removable protective advanced material to prevent colour fading in artworks.

Grafted nanocellulose and alkaline nanoparticles for the strengthening and deacidification of cellulosic artworks.

HYPOTHESIS: Strongly degraded cellulosic artworks usually need deacidification and consolidation. Alkaline nanoparticles are known to be effective in neutralizing the acidity, while cellulose nanocrystals have the potential to be used as compatible and effective strengthening agents. EXPERIMENTS: We have grafted cellulose nanocrystals with oleic acid using a 1'1-carbonyldiimidazole-mediated procedure, to increase their dispersibility in organic solvents, and synthesized Ca(OH)2 or CaCO3 nanoparticles via a solvothermal process. Grafted nanocellulose and alkaline nanoparticles were used to prepare ethanol-based "hybrids". Prior to the application, the physico-chemical properties of nanocellulose dispersions and "hybrids" were studied by rheology and small-angle X-ray scattering. FINDINGS: Cellulose nanocrystals were effectively grafted and stably dispersed in ethanol. It was shown that the use of ethanol as a dispersing medium, and the addition of alkaline nanoparticles act in a synergistic way, increasing the interactions between grafted cellulose nanocrystals, leading to the formation of clusters. These dispersions are thixotropic, a behavior particularly appealing to conservation purposes, since they can be applied in the liquid state, or, when a more confined application is required, they can be applied in a gel-like state. As a result of the application, an improvement in the mechanical properties of paper and an increase of pH were obtained.

The carbonation kinetics of calcium hydroxide nanoparticles: A Boundary Nucleation and Growth description.

HYPOTHESIS: The reaction of Ca(OH)2 with CO2 to form CaCO3 (carbonation process) is of high interest for construction materials, environmental applications and art preservation. Here, the "Boundary Nucleation and Growth" model (BNGM) was adopted for the first time to consider the effect of the surface area of Ca(OH)2 nanoparticles on the carbonation kinetics. EXPERIMENTS: The carbonation of commercial and laboratory-prepared particles' dispersions was monitored by Fourier Transform Infrared Spectroscopy, and the BNGM was used to analyze the data. The contributions of nucleation and growth of CaCO3 were evaluated separately. FINDINGS: During carbonation the boundary regions of the Ca(OH)2 particles are densely populated with CaCO3 nuclei, and transform early with subsequent thickening of slab-like regions centered on the original boundaries. A BNGM limiting case equation was thus used to fit the kinetics, where the transformation rate decreases exponentially with time. The carbonation rate constants, activation energies, and linear growth rate were calculated. Particles with larger size and lower surface area show a decrease of the rate at which the non-nucleated grains between the boundaries transform, and an increase of the ending time of Ca(OH)2 transformation. The effect of temperature on the carbonation kinetics and on the CaCO3 polymorphs formation was evaluated.

Dewetting acrylic polymer films with water/propylene carbonate/surfactant mixtures - implications for cultural heritage conservation.

The removal of hydrophobic polymer films from surfaces is one of the top priorities of modern conservation science. Nanostructured fluids containing water, good solvents for polymers, either immiscible or partially miscible with water, and surfactants have been used in the last decade to achieve controlled removal. The dewetting of the polymer film is often an essential step to achieve efficient removal; however, the role of the surfactant throughout the process is yet to be fully understood. We report on the dewetting of a methacrylate/acrylate copolymer film induced by a ternary mixture of water, propylene carbonate (PC) and C9-11E6, a nonionic alcohol ethoxylate surfactant. The fluid microstructure was characterised through small angle X-ray scattering and the interactions between the film and water, water/PC and water/PC/C9-11E6, were monitored through confocal laser-scanning microscopy (CLSM) and analised both from a thermodynamic and a kinetic point of view. The presence of a surfactant is a prerequisite to induce dewetting of µm-thick films at room temperature, but it is not a thermodynamic driver. The amphiphile lowers the interfacial energy between the phases and favors the loss of adhesion of the polymer on glass, decreasing, in turn, the activation energy barrier, which can be overcome by the thermal fluctuations of polymer film stability, initiating the dewetting process.

Coupling non invasive and fast sampling of proteins from work of art surfaces to surface plasmon resonance biosensing: Differential and simultaneous detection of egg components for cultural heritage diagnosis and conservation.

Despite the wide application of surface plasmon resonance (SPR) to a broad area of interests, from environment to food analysis, from drug discovery to diagnostics, its exploitation in cultural heritage conservation is still unexplored. Water-based highly viscous polymeric dispersions (HVPD) composed by partially hydrolyzed polyvinyl acetate (PVA), borax, and water, were recently developed and successfully applied for the selective removal of surface degradation patinas (i.e. protein materials, natural resins etc.) from paintings of historical and artistic interest. This approach is here coupled for the first time to a SPR biosensor to simultaneously recognize albumen, yolk, or their mixtures in HVPD extracts. Ovalbumin and immunoglobulin Y are selected as analytes for egg white and yolk recognition, respectively. The biosensor was first characterized on standard analytes within the range 0-400mgL(-1) and then on fresh and dried egg albumen and yolk down to 2·10(^4) and 1·10(^5) dilution factors, respectively. Once optimized, the biosensor was combined to the HVPD application on simulated and real art samples for the evaluation of hen egg presence in the extract, i.e. albumen, yolk, or their co-presence in the matrix. For a contemporary 'sacred icon', realized by the traditional egg tempera procedure described by Cennino Cennini, the biosensor successfully distinguished different uses of egg components for the realization of painted and gilded areas, i.e. yolk and albumen, respectively. Finally, a XVIII century italian painting whose the realization technique is unknown, was tested confirming its egg tempera-based realization technique.

Structural characterization of magnesium silicate hydrate: towards the design of eco-sustainable cements.

Magnesium-based cement is one of the most interesting eco-sustainable alternatives to standard cementitious binders. The reasons for the interest towards this material are twofold: (i) its production process, using magnesium silicates, brine or seawater, dramatically reduces CO2 emissions with respect to Portland cement production, and (ii) it is very well suited to applications in radioactive waste encapsulation. In spite of its potential, assessment of the structural properties of its binder phase (magnesium silicate hydrate or M-S-H) is far from complete, especially because of its amorphous character. In this work, a comprehensive structural characterization of M-S-H was obtained using a multi-technique approach, including a detailed solid-state NMR investigation and, in particular, for the first time, quantitative (29)Si solid-state NMR data. M-S-H was prepared through room-temperature hydration of highly reactive MgO and silica fume and was monitored for 28 days. The results clearly evidenced the presence in M-S-H of "chrysotile-like" and "talc-like" sub-nanometric domains, which are approximately in a 1 : 1 molar ratio after long-time hydration. Both these kinds of domains have a high degree of condensation, corresponding to the presence of a small amount of silanols in the tetrahedral sheets. The decisive improvement obtained in the knowledge of M-S-H structure paves the way for tailoring the macroscopic properties of eco-sustainable cements by means of a bottom-up approach.

Nanostructured fluids from degradable nonionic surfactants for the cleaning of works of art from polymer contaminants.

Nanostructured fluids containing anionic surfactants are among the best performing systems for the cleaning of works of art. Though efficient, their application may result in the formation of a precipitate, due to the combination with divalent cations that might leach out from the artifact. We propose here two new aqueous formulations based on nonionic surfactants, which are non-toxic, readily biodegradable and insensitive to the presence of divalent ions. The cleaning properties of water-nonionic surfactant-2-butanone (MEK) were assessed both on model surfaces and on a XIII century fresco that could not be cleaned using conventional methods. Structural information on nanofluids has been gathered by means of small-angle neutron scattering, dynamic light scattering and nuclear magnetic resonance with diffusion monitoring. Beside the above-mentioned advantages, these formulations turned out to be considerably more efficient in the removal of polymer coatings than those based on anionic surfactants. Our results indicate that the cleaning process most likely consists of two steps: initially, the polymer film is swollen by the MEK dissolved in the continuous domain of the nanofluid; in the second stage, surfactant aggregates come into play by promoting the removal of the polymer film with a detergency-like mechanism. The efficiency can be tuned by the composition and nature of amphiphiles and is promoted by working as close as possible to the cloud point of the formulation, where the second step proceeds at maximum rate.

Physicochemical characterization of partially hydrolyzed poly(vinyl acetate)-borate aqueous dispersions.

The dynamic and structural properties of Highly Viscous Polymeric Dispersions (HVPDs), constituted of polyvinyl alcohol obtained from the 75% hydrolysis (75PVA) of polyvinlyl acetate (PVAc) cross-linked with borate ions, were studied as a function of the 75PVA concentration at a constant ratio between the OH groups and the borate ions (OH/B(OH)4(-)). The threshold 75PVA concentration C* necessary for the formation of the three-dimensional network was determined by flow rheology. The oscillating rheology measurements were performed in the linear viscoelastic region; the relaxation spectra calculated from the frequency sweep curves showed only one peak whose width increased upon increasing the 75PVA concentration due to the broadening of the relaxation modes. The dependence of the mean relaxation time τH upon the concentration of 75PVA followed a power law expression (τH ∼ C(x) with x = 1.9) indicating that τH referred to a sticky reptation mechanism and that water was a good solvent for 75PVA as confirmed also by small angle X-rays scattering (SAXS) investigation. The HVPDs were used for the removal of grime layers from the surface of Carlo Carrà (1881-1966) paints decorating the walls of the Palazzo di Giustizia in Milan, Italy.

Magnetic nanoparticle clusters as actuators of ssDNA release.

One of the major areas of research in nanomedicine is the design of drug delivery systems with remotely controllable release of the drug. Despite the enormous progress in the field, this aspect still poses a challenge, especially in terms of selectivity and possible harmful interactions with biological components other than the target. We report an innovative approach for the controlled release of DNA, based on clusters of core-shell magnetic nanoparticles. The primary nanoparticles are functionalized with a single-stranded oligonucleotide, whose pairing with a half-complementary strand in solution induces clusterization. The application of a low frequency (6 KHz) alternating magnetic field induces DNA melting with the release of the single strand that induces clusterization. The possibility of steering and localizing the magnetic nanoparticles, and magnetically actuating the DNA release discloses new perspectives in the field of nucleic-acid based therapy.

Antibacterial activity of silver nanoparticles grafted on stone surface.

Microbial colonization has a relevant impact on the deterioration of stone materials with consequences ranging from esthetic to physical and chemical changes. Avoiding microbial growth on cultural stones therefore represents a crucial aspect for their long-term conservation. The antimicrobial properties of silver nanoparticles (AgNPs) have been extensively investigated in recent years, showing that they could be successfully applied as bactericidal coatings on surfaces of different materials. In this work, we investigated the ability of AgNPs grafted to Serena stone surfaces to inhibit bacterial viability. A silane derivative, which is commonly used for stone consolidation, and Bacillus subtilis were chosen as the grafting agent and the target bacterium, respectively. Results show that functionalized AgNPs bind to stone surface exhibiting a cluster disposition that is not affected by washing treatments. The antibacterial tests on stone samples revealed a 50 to 80 % reduction in cell viability, with the most effective AgNP concentration of 6.7 µg/cm(2). To our knowledge, this is the first report on antimicrobial activity of AgNPs applied to a stone surface. The results suggest that AgNPs could be successfully used in the inhibition of microbial colonization of stone artworks.

Serum thyrotrophin at baseline predicts the natural course of subclinical hyperthyroidism.

OBJECTIVE: Optimal therapeutic strategies for subclinical hyperthyroidism are undecided. Overt disease develops in a minority of cases, but the risk factors for progression remain unclear. We examined whether a baseline thyrotrophin (TSH) predicted progression to overt hyperthyroidism in asymptomatic individuals with subclinical hyperthyroidism. DESIGN, PATIENTS AND MEASUREMENTS: This was a retrospective study of 323 patients with subclinical hyperthyroidism seen in our institution from 2003 to 2010 (mean age 71 years, males 26·9%, females 73·1%, mean follow-up duration 32 months, range 6-93 months). Serum TSH and free thyroxine (FT4) were documented at baseline and during follow-up. After excluding individuals with nonthyroid causes of low TSH, patients were grouped according to initial TSH as: TSH 0·10-0·39 mU/l (grade I) and TSH < 0·10 mU/l (grade II). RESULTS: Only 38 patients (11·8%) developed overt hyperthyroidism with annual progression rates of 0·6-3·7%. Most patients reverted to normal thyroid status (31·6%) or remained subclinically hyperthyroid (56·7%). Progression to frank hyperthyroidism was higher in grade II than in grade I patients (20·3% vs 6·8%, P < 0·001, Chi square test). Kaplan-Meier curves showed faster progression rates in grade II than grade I (P < 0·001, log rank test). In stepwise multivariate Cox regression analysis, TSH < 0·1 mU/l was associated with overt hyperthyroidism (hazard ratio 3·4, confidence interval 1·6-7·0), whereas age, gender, FT4 and aetiological diagnosis were not associated with hyperthyroidism. CONCLUSIONS: Thyrotrophin predicts overt hyperthyroidism in asymptomatic individuals with subclinical hyperthyroidism. Patients with TSH < 0·10 mU/l have a higher risk of progressing to hyperthyroidism than those with TSH 0·10-0·39 mU/l.

Can a random serum cortisol reduce the need for short synacthen tests in acute medical admissions?

BACKGROUND: Short synacthen tests (SSTs) are frequently performed in medical inpatients with suspected adrenocortical insufficiency. The utility of a random or baseline serum cortisol in this setting is unclear. We determined random cortisol thresholds that safely preclude SSTs in acute medical admissions. METHODS: We analysed SSTs in acute non-critically ill general medical patients (n = 166, median age 66, range 15-94 y; men 48%, women 52%). The SST was defined according to the 30-min cortisol as 'pass' (>550 nmol/L) or 'fail' (< or =550 nmol/L). Receiver operating characteristics (ROC) curves were generated to determine the predictive value of the basal cortisol for a failed SST. RESULTS: Of 166 SSTs, a pass was seen in 127 (76.5%) tests, while 39 (23.5%) tests failed the SST. ROC curves showed that no single cut-off point of the baseline cortisol was adequately both sensitive and specific for failing the SST despite a good overall predictive value (area under curve 0.94; 95% confidence interval 0.89-0.98). A basal cortisol <420 nmol/L had 100% sensitivity and 54% specificity for failing the SST, while a basal cortisol <142 nmol/L had 100% specificity and 35% sensitivity. Restricting the SST to patients with a basal cortisol <420 nmol/L would have prevented 44% of SSTs while correctly identifying all patients who failed the SST. CONCLUSION: A baseline serum cortisol may prevent unnecessary SSTs in medical inpatients with suspected adrenocortical insufficiency. However, SSTs are still indicated in patients with random cortisol <420 nmol/L, or where the suspicion of adrenal insufficiency is compelling.

Small-angle neutron scattering of percolative perfluoropolyether water in oil microemulsions.

A water in oil microemulsion system composed of water, surfactant, and oil, the latter two components of perfluoropolyether (PFPE) type, has been studied by small-angle neutron scattering (SANS) with the aim of knowing the microstructure of the system and to have an insight on the connection between microstructure characterization and percolation behavior. In fact, along the dilution line W/S = 11 of the phase diagram, dielectric spectroscopy and conductivity studies revealed a dynamic percolation process taking place approaching and above the dynamic percolation threshold, leading to a system composed of droplet clusters with percolation thresholds varying with temperature from a 0.501 volume fraction of the dispersed phase at 9.3 degrees C to 0.205 at 32.5 degrees C. The SANS experimental spectra of this work have been studied by modeling the microemulsion droplets as adhesive hard spheres. For all of the samples, the surfactant area per polar head has been also measured in the Porod region of the SANS spectra. Geometric and potential parameters as well as the osmotic pressure, the second virial coefficient, and the distance between droplets have been extracted from data as a function of droplets concentration. At low concentration, that is, below percolation thresholds, the droplets behave as hard spheres, whereas at threshold and above, adhesion changes significantly the samples. In fact, for each temperature, the measured size increases versus concentration from 30 to 50 A, and the area per polar head decreases correspondingly, suggesting that a process of dynamic fusion of droplets occurs in the system above threshold, that is, couples of droplets stick and unstick continuously with interdigitation of the surfactant tails.

Evidence of dynamic crossover phenomena in water and other glass-forming liquids: experiments, MD simulations and theory.

In a recent quasi-elastic neutron scattering experiment on water confined in a Portland cement paste, we find that this 3D confined water shows a dynamic crossover phenomenon at T(L) = 227 ± 5 K. The DSC heat-flow scan upon cooling and an independent measurement of specific heat at constant pressure of confined water in silica gel show a prominent peak at the same temperature. We show in this paper that this type of behavior is common to many other glassy liquids, which also show the crossover temperature in coincidence with the temperature of a small specific heat peak. We also demonstrate with MD simulations that the dynamic crossover phenomenon in confined water is an intrinsic property of bulk water, and is not due to the confinement effect. Recently, an extended version of the mode coupling theory (MCT) including the hopping effect was developed. This theory shows that, instead of a structural arrest transition at T(C) predicted by the idealized MCT, a fragile-to-strong dynamic crossover phenomenon takes place instead at T(C), confirming both the experimental and the numerical results. The coherent and incoherent α relaxation times can be scaled with the calculated viscosity, showing the same crossover phenomenon. We thus demonstrated with experiments, simulations and theory that a genuine change of dynamical behavior of both water and many glassy liquids happens at the crossover temperature T(L), which is 10-30% higher than the calorimetric glass transition temperature T(g).

Phospholipid membranes decorated by cholesterol-based oligonucleotides as soft hybrid nanostructures.

DNA monomers and oligomers are currently showing great promise as building blocks for supramolecular arrays that can self-assemble in a fashion preprogrammed by the base pairing code. The design and build-up of hybrid DNA/amphiphilic self-assemblies can expand the range of possible architectures and enhance the selectivity toward a well-specified geometry. We report on the self-assembly properties in aqueous solution of a cholesteryl-tetraethylenglycol single stranded 18-mer oligonucleotide (ON 1TEG-Chol) and on its spontaneous insertion in fluid phospholipid membranes. Up to 500 units of these lipophilic ss-oligonucleotides can be incorporated in the outer leaflet of 350 A radius POPC vesicle. The insertion and hybridization with the complementary oligonucleotide are monitored through light scattering as an increase of hydrodynamic thickness, which is interpreted in terms of average distance between anchoring sites. The conformation of the ss-oligonucleotidic portion is strongly dependent on surface coverage, passing from a quasi-random coil to a more rigid configuration, as concentration increases. Interestingly, conformational details affect in a straightforward fashion the hybridization kinetics. Liposomes with single- and double-strand decorations remain stable within the experimental time window (about one week). The structure represents an example of successful and stable amphiphile/DNA supramolecular hybrid, where a DNA guest is held in a membrane by hydrophobic interactions. The lipophilic oligonucleotide under investigation is therefore a suitable building block that can effectively serve as a hydrophobic anchor in the fluid bilayer to assemble supramolecular constructs based on the DNA digital code.

Small-angle neutron scattering of mixed ionic perfluoropolyether micellar solutions.

Aqueous mixed micellar solutions of perfluoropolyether carboxylic salts with ammonium counterions have been studied by small-angle neutron scattering. Two surfactants differing in the tail length were mixed in proportions n2/n3 = 60/40 w/w, where n2 and n3 are the surfactants with two and three perfluoroisopropoxy units in the tail, respectively. The tails are chlorine-terminated. The mixed micellar solutions, in the concentration range 0.1-0.2 M and thermal interval 20-40 degrees C, show structural characteristics of the interfacial shell that are very similar to ammonium n2 micellar solutions previously investigated; thus, the physics of the interfacial region is dominated by the polar head and counterion. The shape and dimensions of the micelles are influenced by the presence of the n3 surfactant, whose chain length in the micelle is 2 A longer than that of the n2 surfactant. The n3 surfactant favors the ellipsoidal shape in the concentration range 0.1-0.2 M with a 1/2 ionization degree of n2 micelles. The very low surface charge of the mixed micelles is attributed to the increase in hydrophobic interactions between the surfactant tails, due to the longer n3 surfactant molecules in micelles. The closer packing of the tails decreases the micellar curvature and the repulsions between the polar heads, by surface charge neutralization of counterions migrating from the Gouy-Chapman diffuse layer, leading to micellar growth in ellipsoids with greater axial ratios.

Experimental evidence of fragile-to-strong dynamic crossover in DNA hydration water.

We used high-resolution quasielastic neutron scattering spectroscopy to study the single-particle dynamics of water molecules on the surface of hydrated DNA samples. Both H(2)O and D(2)O hydrated samples were measured. The contribution of scattering from DNA is subtracted out by taking the difference of the signals between the two samples. The measurement was made at a series of temperatures from 270 down to 185 K. The relaxing-cage model was used to analyze the quasielastic spectra. This allowed us to extract a Q-independent average translational relaxation time of water molecules as a function of temperature. We observe clear evidence of a fragile-to-strong dynamic crossover (FSC) at T(L)=222+/-2 K by plotting log versus T. The coincidence of the dynamic transition temperature T(c) of DNA, signaling the onset of anharmonic molecular motion, and the FSC temperature T(L) of the hydration water suggests that the change of mobility of the hydration water molecules across T(L) drives the dynamic transition in DNA.

Observation of fragile-to-strong dynamic crossover in protein hydration water.

At low temperatures, proteins exist in a glassy state, a state that has no conformational flexibility and shows no biological functions. In a hydrated protein, at temperatures greater-- similar 220 K, this flexibility is restored, and the protein is able to sample more conformational substates, thus becoming biologically functional. This "dynamical" transition of protein is believed to be triggered by its strong coupling with the hydration water, which also shows a similar dynamic transition. Here we demonstrate experimentally that this sudden switch in dynamic behavior of the hydration water on lysozyme occurs precisely at 220 K and can be described as a fragile-to-strong dynamic crossover. At the fragile-to-strong dynamic crossover, the structure of hydration water makes a transition from predominantly high-density (more fluid state) to low-density (less fluid state) forms derived from the existence of the second critical point at an elevated pressure.