Physico-chemical characterization of protein-pigment interactions in tempera paint reconstructions: casein/cinnabar and albumin/cinnabar

In this work, we characterized paint reconstructions using ovalbumin and casein as binders, and cinnabar (HgS) as a pigment, before and after artificial ageing. Egg and casein are common paint binders that were used historically in the technique of tempera painting. Despite extensive research on the identification of proteinaceous binders in paintings, there is a substantial lack of knowledge regarding the ageing pathway of their protein content, and their chemical interaction with inorganic pigments. Thermogravimetric analysis, infrared spectroscopy and size-exclusion chromatography (SEC) were used to reveal the physico-chemical processes involved in the ageing of proteins in paintings. Taken together, the three techniques highlighted that proteins are subject to both cross-linking and hydrolysis upon ageing, and to a lesser extent, to oxidation of the side chains. Mercury–protein interactions were also revealed using a cold vapour generation atomic fluorescence spectrometer mercury-specific detector coupled to SEC. The study clearly showed that HgS forms stable complexes with proteins and acts as a sensitizer in cross-linking, hydrolysis and oxidation.     

An isoperimetric inequality for the Wiener sausage

Let (ξ(s)) _{s?≥ 0} be a standard Brownian motion in d?≥ 1 dimensions and let (D _s ) _{s ≥?0} be a collection of open sets in ${\mathbb{R}^d}$ . For each s, let B _s be a ball centered at 0 with vol(B _s ) =?vol(D _s ). We show that ${\mathbb{E}[\rm {vol}(\cup_{s \leq t}(\xi(s) + D_s))] \geq \mathbb{E}[\rm {vol}(\cup_{s \leq t}(\xi(s) + B_s))]}$ , for all t. In particular, this implies that the expected volume of the Wiener sausage increases when a drift is added to the Brownian motion.     

New Metal–Organic Framework Solids Built from Barium and Isoelectronic Chelidamic and Chelidonic Acids

Abstract  

Two new Ba(II) metal–organic framework solids bearing the chelidamate [Ba₂(C₇H₃NO₅)₂(μ-H₂O)(H₂O)₆]·2H₂O (1) and chelidonate [Ba(C₇H₂O₆)(H₂O)] (2) ligands were synthesized and characterized by IR, elemental, thermal, photoluminescent and X-ray diffraction analyses. In complex 1 the chelidamate dianion exists in two tautomeric forms, in which the enol form exhibits unprecedented (К¹, К¹) (К¹) (К², К², μ₂, μ₂)-μ₇ heptadentate coordination while the keto form with (К¹, К¹)(К²)-μ₄ tetradentate mode. It is a 2D polymer in which the first and second dimensions are satisfied by carboxylate oxygens while the third is by the combination of hydrogen bonds and π–π stacking of aromatic rings. There are two independent barium ions (Ba1, Ba2) in complex 1 that are nine coordinated, but their coordination environment is different. Complex 2 is a 3D polymer and the organic linker, 4-oxo-pyran-2,6-dicarboxylate (chelidonate) anion exhibits denticity as seven with barium having the similar nine coordination.     

First chemical evidence of royal purple as a material used for funeral treatment discovered in a Gallo�CRoman burial (Naintr��, France, third century AD)

Violet-purple residues collected from a Gallo-Roman burial dated back to the second half of the third century A.D. and excavated at Naintré (France) were chemically investigated by multi-analytical methodology involving the use of Raman spectroscopy, direct exposure-mass spectrometry (DE-MS) and high-performance liquid chromatography (HPLC-UV-visible). Little is known about funeral treatment and rituals during Roman times. Retrieving valuable information on these by chemical analysis of organic residues was thus a key aspect of this work. Analyses demonstrated the presence of the very precious purple colorant obtained from shellfish glands commonly known as Tyrian or royal purple and its exceptional preservation. Chemical investigation and archaeological evidence have shown that purple was widely spread after the deposition of the body for burial. These results are the earliest chemical evidence of purple colorant used during funeral rituals (not as textile dye) and enabled us to highlight new aspects of funeral practices in Roman times.     

Discovering the composition of ancient cosmetics and remedies: analytical techniques and materials

This article reviews the analytical techniques and procedures used in the study of ancient cosmetics, therapeutic chemicals, and remedies found in historical and archaeological sites. Well consolidated techniques based on molecular and atomic spectroscopy, for example FT-IR, Raman, SEM-EDX, and XRD, and analytical procedures based on high-performance chromatography and mass spectrometry, for example GC–MS and HPLC–MS are reviewed. The advantages of recently introduced techniques based on synchrotron radiation and on direct mass spectrometric techniques are also discussed. The possibility of extracting information about composition, preparation techniques, and the degradation processes of ancient cosmetics, pharmaceutics, and ritual balms is analysed by use of several case studies.     

Unimolecular rearrangements of ketene-O,O-acetals and fragmentations occurring in the gas phase

Gas phase skeletal rearrangements of regioisomeric 3‐cyano‐2‐methoxy‐3a‐alkylfuro[2,3‐b]‐ and [3,2‐b]indoles were evidenced by product ions [M ? 32]^+?, consistent with loss of methanol, on electron ionization in their mass spectra. The rearranged products occurring in gas phase were demonstrated to have elemental composition and fragmentation properties identical to those of authentic samples of 2‐indolyl cyanomalonates. Isotopic labeling experiments support the formation mechanism of the [M ? 32]^+? ion. Additional thermal gas‐phase reaction products were characterized by comparison with an authentic sample. Copyright © 2011 John Wiley & Sons, Ltd.     

Analytical pyrolysis with in situ thermally assisted derivatisation, Py(HMDS)-GC/MS, for the chemical characterization of archaeological birch bark tar

An analytical method based on pyrolysis in the presence of hexamethyldisilazane followed by gas chromatographic/mass spectrometric analysis, Py(HMDS)-GC/MS, was used for the first time to study birch bark tar, an adhesive that has been used since the Palaeolithic period. Py(HMDS)-GC/MS enabled us to obtain information simultaneously both on polymerised and solvent soluble fractions of birch bark tar. A very particular chromatographic pattern was obtained, which was mainly characterised by the presence of homologous series of linear saturated and unsaturated monocaboxylic fatty acids, and homologous series of straight-chain alkenes and alkanes. The pattern can be linked to suberin and suberan, which are known to be present in birch barks. In addition, lupane-type triterpenoids were also revealed. Py(HMDS)-GC/MS was initially applied to a reference material, and was then used to study the archaeological adhesives from a wooden spindle recovered in a Gallo-Roman burial (3rd century AD) and from the golden sheath of a Thracian dagger (8th-7th centuries BC) recovered in Belogradets (Bulgaria).