Non-invasive detection of lead carboxylates in oil paintings by in situ infrared spectroscopy: How far can we go?

This paper demonstrates the efficacy of portable mid-infrared spectroscopy as a diagnostic tool for revealing the presence of lead carboxylates on artworks, in situ, without sampling. Samples of cerussite and hydrocerussite - the main components of lead white - were separately mixed with linseed oil, and artificially aged in two steps. Their compositional changes have been monitored over time by infrared spectroscopy in two investigation modes: absorption (benchtop instrument) and reflection (portable instrument), and by XRD spectroscopy. Each component of lead white showed different behavior depending on aging conditions, giving important information about the degradation products which are found in real cases. The accordance of results obtained in both modalities demonstrates that portable FT-MIR is a reliable technique for individuating and identifying lead carboxylates directly on paintings. Examples of the efficacy of this application are provided, by studying paintings from the 17th and 18th centuries.

Preparation Of Zirconium Diphosphonate-Phosphites With A Narrow Distribution Of Mesopores

The presence of H3PO3 in the synthesis of zirconium diphosphonates in dimethylsulfoxide, other than the expected dilution of the pillars, which in turn gives rise to a certain degree of microporosity, may also induce the formation of a high percentag. of mesopores. E.g., compounds with high surface area(300–500 m2 /g) of which 60–70% is due to mesopores with diameters 20–40 Å and the remaining is due to micropores, were obtained. It was furthermore found that the distribution of the mesopores was fairly narrow. Compounds with micropores <3 Å and mesopores of 20–30 Å behave in practice as pure and narrow mesoporous solids;they are therefore of great interest as new molecular inorgano-organic sieves.

Zirconium Organic Diphosphate-Diphosphonates With Tilted Rigid Pillars

The H2O3PCH(C6H4)2CH2PO3H2 and H2O3PO(C6H4)2OPO3H2 acids were synthesizedT and used to obtain new pillared zirconium phosphonates and organic phosphates in which the pillars are tilted with respect to the layers. The Zr(O3PCH2(C6H4)2CH2PO3) and Zr(O3PO(C6H4)2OPO3) obtained have a good thermal resistance and the distance between the inorganic α-layers joined by the organic pillars is 14.7 and 13.8 Å, respectively. Structural models suggest that the biphenyl groups in the solids are tilted at 140° and 137° with respect to the perpendicular at the layer plane. Solid solutions of the two derivatives over the whole range of composition have also been obtained; the distance between the α-layers changes from 14.7 to 13.8 Å in a continuous way as the diphosphate groups replace the diphosphonate ones, allowing us to suppose a variation of the tilting angles. Attempts to remove the phosphoester in the mixed derivatives by hydrolytic attack, and to replace some pillars with phosphite groups are described.

Shaping Solid-State Supramolecular Cavities: Chemically Induced Accordionlike Movement of gamma-Zirconium Phosphate Containing Polyethylenoxide Pillars

The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space.

Mechanism of the Topotactic Formation of gamma-Zirconium Phosphate Covalently Pillared with Diphosphonate Groups

The topotactic reaction of gamma-ZrPO(4)[O(2)P(OH)(2)].2H(2)O (gamma-ZrP) with benzenediphosphonic acid was examined in water and in acetone-water mixtures. This reaction was found to take place in water only on the external surface of the microcrystals, and pillared compounds were never obtained, even after very long reaction times. On the contrary, covalently pillared compounds were quickly obtained in acetone-water mixtures. The mechanism of the latter topotactic reaction was investigated by determining the rate of the phosphate groups released and the rate of the benzenediphosphonates taken up by gamma-ZrP over a long time (50 days). These data showed that pillared derivatives of gamma-ZrP can be obtained because colloidal dispersions of exfoliated lamellae are formed in acetone-water mixtures. The diphosphonate group acts initially as a monovalent species, replacing only one dihydrogen phosphate group on the surface of the exfoliated gamma-lamellae. The colloidal and partially derivatized lamellae thus formed can interact with each other by forming polylamellar pillared systems. When the number of pillared lamellae exceeds a given value (usually 5-6), flocculation of the colloidal gamma-ZrP takes place. Topotactic reactions between packets of pillared lamellae may also continue in the flocculated system. Therefore, the average number of the pillared lamellae slowly increases over time.