Chiara Riedo

Advances in identification of plant gums in cultural heritage by thermally assisted hydrolysis and methylation.

AbstractPlant gums are present in works of art as binding media for watercolours and adhesives for cellulosic substrates. Thermally assisted hydrolysis and methylation (THM) in combination with analytical pyrolysis coupled to GC/MS has been applied to the characterisation of plant gums typically used in artworks. THM products from standard samples of arabic gum, tragacanth gum and cherry gum were characterised. The main products identified are permethylated and partially methylated aldonic acids, characteristic of specific epimeric sugars. Aldonic acids were formed by alkaline hydrolysis of free reducing sugars and of reducing polysaccharide terminal groups, while methylation occurs during pyrolysis. The presence of these characteristic markers allows gum identification. A systematic analysis of all the parameters that can affect the marker yields was performed. In particular, the influence of pyrolysis temperature, reagent concentration and contact time between tetramethylammonium hydroxide and sample were studied, and different kinds of sample preparation procedures were tested. Some analyses on real watercolours were performed, and gum binders were classified using the peak area ratio of the main monosaccharide markers. FigureClassification of gums on the basis of marker area peaks ratio

Characterization of fresh and aged natural ingredients used in historical ointments by molecular spectroscopic techniques: IR, Raman and fluorescence

Natural organic materials used to prepare pharmaceutical mixtures including ointments and balsams have been characterized by a combined non-destructive spectroscopic analytical approach. Three classes of materials which include vegetable oils (olive, almond and palm tree), gums (Arabic and Tragacanth) and beeswax are considered in this study according to their widespread use reported in ancient recipes. Micro-FTIR, micro-Raman and fluorescence spectroscopies have been applied to fresh and mildly thermally aged samples. Vibrational characterization of these organic compounds is reported together with tabulated frequencies, highlighting all spectral features and changes in spectra which occur following artificial aging. Synchronous fluorescence spectroscopy has been shown to be particularly useful for the assessment of changes in oils after aging; spectral difference between Tragacanth and Arabic gum could be due to variations in origin and processing of raw materials. Analysis of these materials using non-destructive spectroscopic techniques provided important analytical information which could be used to guide further study.

Molecularly imprinted cyclodextrin nanosponges for the controlled delivery of L-DOPA: perspectives for the treatment of Parkinson's disease.

ABSTRACT Background: L-DOPA is an amino acid precursor to the neurotransmitter dopamine that is extensively used as a prodrug for the treatment of Parkinson’s disease. However, L-DOPA is an unstable compound: when exposed to light or added to aqueous solutions, it may degrade, compromising its therapeutic properties. Methods: In this work, a new type of drug-loaded cyclodextrin-based nanosponge, obtained using molecular imprinting, is described for the prolonged and controlled release of L-DOPA. The molecularly imprinted nanosponges (MIP-NSs) were synthesized by cross-linking β-cyclodextrin with 1,1ʹ-carbonyldiimidazole in DMF in the presence of L-DOPA as a template molecule. TGA, DSC and FTIR analyses were performed to characterize the interactions between L-DOPA and the two nanosponge structures. Quantitative NMR spectroscopy was used to determine the amount and the affinity of L-DOPA entrapped in the nanosponges. The in vitro L-DOPA release kinetics from the NSs were quantitatively determined by HPLC analysis. Results: The MIP-NSs show a slower and more prolonged release profile than the non-imprinted nanosponges. No degradation of the L-DOPA hosted in the MIP-NSs was observed after long-term storage at room temperature. Conclusions: The MIP-NSs are a promising alternative for the storage and controlled delivery of L-DOPA.

A multi-analytical approach for the characterization of powders from the Pompeii archaeological site.

AbstractNine black powders found in Pompeii houses in three different types of bronze vessels (cylindrical theca atramentaria, unguentaries, and aryballoi) were characterized in order to assess a correspondence between the composition and the type of vessel and, possibly, to verify if these powders were inks or not. For the compositional characterization, a multi-analytical approach was adopted, which involved the use of scanning electron microscopy–energy dispersive X-ray, Fourier-transformed infrared spectroscopy, Raman, X-ray diffraction, electron paramagnetic resonance spectroscopy, thermogravimetric analysis, gas chromatography coupled with mass spectrometry (GC/MS), and pyrolysis GC/MS. Powders contained in cylindrical theca atramentaria form a homogeneous group, and their organic and inorganic compositions suggest that they were writing inks, while powders contained in unguentaries and aryballoi could have had several different uses, including writing inks and cosmetics. Furthermore, the composition profile of the powders found in cylindrical cases shows that, at 79 ad, in Pompeii, carbon-based inks were still used for writing, and iron gall inks had not been introduced yet. FigurePhotography of the 12724 black powder contained in a cylindrical theca atramentaria.

A round robin exercise in archaeometry: analysis of a blind sample reproducing a seventeenth century pharmaceutical ointment

Chemical analysis of ancient residues of pharmaceutical or cosmetic preparations such as balms or ointments is made problematic by the high complexity of these mixtures, composed of organic and inorganic materials. Consequently, a multi-analytical approach and special caution in the interpretation of the results are necessary. In order to contribute to the improvement of analytical strategies for the characterization of complex residues and to reconstruct ancient medical practices, a replica of a pharmaceutical formulation of the seventeenth century was prepared in the laboratory according to a historically documented recipe. In a round robin exercise, a portion of the preparation was analysed as a blind sample by 11 laboratories using various analytical techniques. These included spectroscopic, chromatographic and mass spectrometric methods. None of the laboratories was able to completely reconstruct the complex formulation, but each of them gave partial positive results. The round robin exercise has demonstrated that the application of a multi-analytical approach can permit a complete and reliable reconstruction of the composition. Finally, on the basis of the results, an analytical protocol for the study of residues of ancient medical and pharmaceutical preparations has been outlined.

Poly(vinylalcohol)-borate hydrogels with improved features for the cleaning of cultural heritage surfaces

Poly(vinylacohol) (PVA) is a versatile polymer capable of forming hydrogels useful in a wide range of applications. Hydrogels based on cross-linking of PVA with borax, and able to incorporate organic solvents, have been used in the field of cultural heritage as tool for cleaning the surfaces. Poly(ethylenoxide) (PEO) has been introduced in the formulations of PVA-borax, with the aim of increasing the gel compatibility with organic solvents and of improving the mechanical properties of the materials. The formulations were investigated with rheological characterization, solvent loss measurements and study of the free water through the determination of the Free Water Index. The PEO molecules do not participate in the formation of the network but have been found to be responsible for a decrement of the storage moduli, explained by a spacing between crosslinks and the partial disentanglement of the PVA chains. At the same time PEO produces in the gel an increase of the apparent relaxation time, thus stabilizing the dispersions and enhancing their ability to maintain the shape. Cleaning tests for removal of an acrylic coating on limestone have been also successfully performed. Graphical abstractPVA/borax hydrogels with acetone were studied with cleaning test and rheological measurements and hypothesis on network structure was proposed.

From Plant Extracts to Historical Textiles: Characterization of Dyestuffs by GC–MS

A gas chromatographic–mass spectrometric procedure for the analysis of dyes from plant extracts was optimized and applied for the detection of components in extracts from 12 dyeing plants native from all over the world. The main marker molecules in each of the dyestuffs, as well as accessory compounds, were successfully separated and identified by means of their electron impact mass spectra, thus demonstrating that a single GC–MS procedure can be conveniently applied to the detection of natural dyes such as flavonoids, neoflavonoids, anthraquinones and tannins. Other constituents of plant extracts, such as organic acids, oils and sugars, that hydrolyse during the extraction process, were also detected and recognized in the same chromatographic run. The GC–MS method was tested on woollen references dyed according to traditional recipes, and on historical wool samples taken from a tapestry of the sixteenth century, and the main dyestuffs used for colouring could be traced even with the low amounts usually available with the archaeometric samples. Besides some limitations, that are addressed, the results show that the GC analysis is a useful tool for quick assessment and control of natural extracts and the application of the technique for the characterization of dyes in historical textiles, in addition or in place of the more widely used procedures that employ liquid chromatography, is encouraged.

Pyrolysis–GC/MS for the identification of macromolecular components in historical recipes

AbstractAnalytical pyrolysis with thermally assisted hydrolysis and methylation was employed to investigate ancient ointments collected from Spanish vessels coming from the sixteenth century pharmacies. The ointments were reproduced on the basis of historical recipes and characterization was made in comparison with real samples. Characteristic markers indicate the presence of beeswax, of animal and plant lipids, and of natural resins. Analyses of old samples are consistent with the modern reproductions and with the analysis of raw materials. Multivariate data analysis was used to discriminate between the different types of lipidic materials, also in connection with their relative amount in the samples. FigureScore plot of principal component analysis performed on data obtained from real samples, reference ointments, and raw materials by means of thermally assisted hydrolysis and methylation

Risk Assessment and Preservative Measures for Volatile Organic Compounds in Museum Showcases

ABSTRACT The first step in preservative measures for artworks in airtight showcases is the exclusion of outgassing from construction materials or, at least, limitation of the emissions to a minimum acceptable level if the volatile organic compounds (VOCs) generated may be qualified as harmless. Once it is ascertained that the objects in the showcases are responsible for VOC emissions, a step forward becomes necessary, implying showcase ventilation with air flowing through active sorbent materials. Solid phase micro-extraction (SPME) followed by GC separation and MS identification has been applied for checking the outgassing characteristics of different types of materials used for the construction of airtight showcases, and the method was found particularly attractive in terms of speed and sensitivity, suitable for measurements in presence of low-emitting materials. Sampling could also be done in the case interiors, thus making possible detection and recognition of emissions from art objects within a case. A comprehensive preventive conservation scheme has been further devised by means of active air circulation within the showcase and functional sorbent materials along the flow, for complete suppression of gaseous compounds. Control of the compounds in the air flow and of their filtration efficacy was achieved by direct sampling, also using SPME fibers. Continuous monitoring of the air quality in the showcases has been developed with insertion of a photoionization detector capable of detecting the VOCs in the air by inducing molecular ionization, and measuring the generated photocurrent. The system is not selective, but gives the total concentration, reaching ppb sensitivity with high-quality data. In addition it includes temperature and humidity sensors, making the whole a useful instrument for environment control.