New insight from MALDI-TOF MS and multivariate data analysis on the botanical origin of polysaccharide-based paint binders in ancient Egypt.

Polysaccharide-based materials of plant origin are known to have been used as binding media in paint and ground layers of artifacts from ancient Egypt, including wall paintings, cartonnages and sarcophagi. The use of gums from Acacia, Astragalus and Prunus genera has been suggested in the literature on the basis of their qualitative or quantitative monosaccharide profile after complete chemical hydrolysis. The introduction of partial enzymatic digestion of the polysaccharide material, followed by analysis of the released oligosaccharides by matrix assisted laser desorption ionization-time-of-flight mass spectrometry, has proved effective in discriminating among gums from different genera, as well as among species within the Acacia genus. In this study, the previously built Acacia database was expanded, principal component analysis (PCA) was used to aid in grouping of the samples, and data interpretation was refined following a modified acacieae taxonomy. Application of the analytical strategy to investigate the paint binders in artworks from ancient Egypt allowed qualitative discrimination of gums at a species level, and provided new insights into the artists' material choices.

Encapsulation of phenolic acids into cyclodextrins: A global statistical analysis of the effects of pH, temperature and concentrations on binding constants measured by ACE methods.

Affinity capillary electrophoresis was used for the simultaneous measurement of the pKa values and of the binding constants relative to the encapsulation of naturally occurring phenolic acids (rosmarinic and caffeic acids) with cyclodextrins. A thorough study as a function of pH and temperature was coupled to a detailed statistical analysis of the resulting experimental data. A step-by-step curve fitting process was sufficient for obtaining individual binding constant for each experimental condition, but the influence of temperature remained unclear. A quantitative and qualitative gain was then obtained by supplementing this initial analysis with global multiparameter optimization. This leads to the estimation of both entropy and enthalpy of reaction and to the full description of the binding reactions as a function of pH and temperature. The encapsulation was shown to be very sensitive to pH and temperature, with optimal complexation occurring at low pH and low temperature, gaining up to a factor of 3 by cooling from 36 to 15°C, and up to a factor of 10 by lowering the pH from 7 to 2.

Characterization of surface materials on African sculptures: new insights from a multi-analytical study including proteomics.

Multiple analytical techniques were used to characterize materials from the surfaces of two African sculptures in the collection of the Art Institute of Chicago: a Bamana power object (boli), and a Yoruba wooden sculpture of a female figure. Surface accretions on objects such as these have received relatively little scientific attention to elucidate their composition and function, in part because they are made with complex mixtures of natural materials, which are often unfamiliar and poorly represented in the scientific literature on artists' materials. For this reason, a complement of techniques including Fourier transform infrared spectroscopy and pyrolysis gas chromatography mass spectrometry were applied, along with shotgun proteomics to better understand the nature and biological origin, down to the species level, of the proteinaceous materials. The results highlighted the presence of diverse materials including plant resins, oils, polysaccharides, and inorganic (clay or earth) compounds. In particular, mass spectrometry-based proteomics provided new insights on proteinaceous components, allowing us to identify the presence of sacrificial blood, and more specifically, blood from chicken, goat, sheep and dog. This new scientific evidence supports and supplements knowledge derived from curatorial and field work studies, and opens new doors to understanding the objects' significance and history of use.

The inclusion complex of rosmarinic acid into beta-cyclodextrin: A thermodynamic and structural analysis by NMR and capillary electrophoresis.

This work focuses on the characterization of the rosmarinic acid (RA)-ß-cyclodextrin (CD) complex in aqueous solution by (1)H NMR (1D- and 2D-ROESY), completed with studies by capillary electrophoresis (CE). From the (1)H NMR data, the stoichiometry of the complex was determined by a Job's plot and the binding constant was estimated from a linear regression (Scott's method). At pH 2.9, the results showed that RA binds CD with a 1:1 stoichiometry and a binding constant Kb of 445 (±53) M(-1) or 465 (±81) M(-1) depending on the CD protons (H-5 or H-3) selected for the evaluation. The Kb value was also calculated from the CD-induced chemical shifts of each RA proton in order to collect information on the structure of the complex. The pH dependence of Kb revealed that the RA carboxylic form displays the highest affinity for CD. An investigation by capillary electrophoresis fully confirmed these results. 2D ROESY analysis provided detailed structural information on the complex and showed a strong correlation between H-3 and H-5 of CD and most RA protons. In conclusion, RA, an efficient phenolic antioxidant from rosemary with a marketing authorization, spontaneously forms a relatively stable inclusion complex with CD in water.