“…At intermediate chain length, the energy difference between type A and type B structures is so small that both types seem to co-exist, as reported by Mesbah and François for C11 chains. 31 This transition from optimal coordination to optimal chain packing is highly similar to the structural transition reported for lead soaps, 32,33 where the lead ions switch from hemidirected to holodirected coordination around an alkyl chain length of nine carbons. Figure 3.Illustration of various methods for the analysis of IR microscopy data.…”
The formation of crystalline zinc soaps (zinc salts of fatty acids) in oil paint layers is a common sign of paint degradation. In this study, we have used infrared spectroscopy to systematically identify differences in structure and composition of crystalline zinc soap phases, and report data analysis methods for structure attribution in challenging oil paint samples. Supported by reported crystal structures, it was possible to distinguish two distinct types of zinc soap geometry: a highly symmetrical packing for long-chain saturated soaps (type B) and an alternating packing for zinc soaps with short, unsaturated, or dicarboxylic chains (type A). These two types of packing can be identified by a single or split asymmetric COO stretch vibration band. With this new information, we studied the structure and composition of zinc soaps formed in a zinc white model paint and in a cross-section from the painting Equations in Space by Lawren Harris. Using non-negative matrix factorization, band integration and band position maps, it was possible to clearly identify zinc azelate in the model paint and map its spatial distribution. The same methods showed that the paint cross-section contained both types of zinc soap structure within the same paint layer, with the less symmetrical structure appearing only at the interface with the ground layer. The results give valuable information on the internal chemistry of oil paint layers, and the demonstrated methods can find widespread application for in-depth analysis of infrared microscopy data.
“…At intermediate chain length, the energy difference between type A and type B structures is so small that both types seem to co-exist, as reported by Mesbah and François for C11 chains. 31 This transition from optimal coordination to optimal chain packing is highly similar to the structural transition reported for lead soaps, 32,33 where the lead ions switch from hemidirected to holodirected coordination around an alkyl chain length of nine carbons. Figure 3.Illustration of various methods for the analysis of IR microscopy data.…”
The formation of crystalline zinc soaps (zinc salts of fatty acids) in oil paint layers is a common sign of paint degradation. In this study, we have used infrared spectroscopy to systematically identify differences in structure and composition of crystalline zinc soap phases, and report data analysis methods for structure attribution in challenging oil paint samples. Supported by reported crystal structures, it was possible to distinguish two distinct types of zinc soap geometry: a highly symmetrical packing for long-chain saturated soaps (type B) and an alternating packing for zinc soaps with short, unsaturated, or dicarboxylic chains (type A). These two types of packing can be identified by a single or split asymmetric COO stretch vibration band. With this new information, we studied the structure and composition of zinc soaps formed in a zinc white model paint and in a cross-section from the painting Equations in Space by Lawren Harris. Using non-negative matrix factorization, band integration and band position maps, it was possible to clearly identify zinc azelate in the model paint and map its spatial distribution. The same methods showed that the paint cross-section contained both types of zinc soap structure within the same paint layer, with the less symmetrical structure appearing only at the interface with the ground layer. The results give valuable information on the internal chemistry of oil paint layers, and the demonstrated methods can find widespread application for in-depth analysis of infrared microscopy data.
“…It should be noted that it is expected that there is some variations in the peak position and intensity of ν sym and ν asym for different PbX NCs due to differences in the lead carboxylate bonding angle and variation in the Pb–O bond distance. 44,47,49…”
For colloidal semiconductor
nanocrystals (NCs), the knowledge of
the chemical structure and the size-dependent optical properties is
of crucial importance, both from a practical and fundamental perspective.
Here, we report the basic properties of PbTe NCs in order to complement
the already existing knowledge on PbS and PbSe NCs. The band gap versus
NC diameter (sizing) curve was determined by combining transmission
electron microscopy with absorption spectroscopy; the energy of the
primary optical absorption follows 1/d dependence
with the diameter. The lead content of the NCs was determined with
inductive coupled plasma optical emission spectrometry and the relative
tellurium content with energy-dispersive X-ray spectroscopy. Combining
these results yields a relation for the intrinsic absorption coefficient,
which is independent of the NC size at 3.1 eV. The PbTe NCs are stabilized
by Pb(oleate)2, but different from PbS NCs, oleate is predominantly
bound in a chelating bidentate coordination. Besides that, we analyzed
the structure of the aliphatic chains on all lead chalcogenide NCs
and showed that the aliphatic chains are partly crystalline near the
core and more liquid-like at the solvent side.
“…These data are consistent with a previous study that showed there is a partial melting of the aliphatic chains before the phase change. 32,78 These deuterium NMR experiments demonstrate that qualitatively, even though PA and LP mixed with linseed oil are similar to the pure materials in some parts of the material by NMR analysis, portions of the sample in the mixtures are dynamically different from the pure materials. In particular, the existence of molecular rotational mobility in some parts of the sample suggests that fatty acids may have the rotational (and likely translational) freedom to migrate through a linseed oil matrix to…”
Section: Deuterium Nmr Studies Of the Local Mobility Of Fatty Acid mentioning
confidence: 87%
“…X-ray diffraction analysis of single crystals of lead octanoate, lead nonanoate, and lead azelate confirm that the local site symmetry in those materials had the expected local structures predicted by the NMR parameters. 4,27,32,66 Although none of the coordination environments around the lead centers are perfectly spherically symmetric, the diffraction data display a more nearly symmetric environment around the lead center in the lead nonanoate crystal than in the lead octanoate crystal. This is consistent with the observation of two 207 Pb different NMR spans, one "narrow" (~730-750 ppm) and one "wide" (~2,600-2,700 ppm), for these materials.…”
mentioning
confidence: 88%
“…10,[23][24][25][26][27][28][29][30][31] Structural information about carboxylates related to soap formation determined by powder and single-crystal X-ray diffraction has been reported for Pb, Zn, and Cu soaps. 4,27,32,33 Micro-X-ray fluorescence (XRF) has been particularly useful for analyzing the elemental distribution in Pb soap protrusions. The use of a micron-sized beam in XRF mapping, with scanning of the X-ray photon energy, allows micro-X-ray absorption near-edge structure (micro-XANES) spectroscopy across the Pb-M 4 and M 5 edges that permits differentiation of Pb pigments and Pb soaps.…”
Heavy metal carboxylate or soap formation is a widespread deterioration problem affecting oil paintings and other works of art bearing oil‐based media. Lead soaps are prevalent in traditional oil paintings because lead white was the white pigment most frequently chosen by old masters for the paints and in some cases for the ground preparations, until the development of other white pigments from approximately the middle of the 18th century on, and because of the wide use of lead‐tin yellow. In the latter part of the 19th century, lead white began to be replaced by zinc white. The factors that influence soap formation have been the focus of intense study starting in the late 1990s. Since 2014, nuclear magnetic resonance (NMR) studies have contributed a unique perspective on the issue by providing chemical, structural, and dynamic information about the species involved in the process, as well as the effects of environmental conditions such as relative humidity and temperature on the kinetics of the reaction(s). In this review, we explore recent insights into soap formation gained through solid‐state NMR and single‐sided NMR techniques.
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