4991-47-3Relevant articles and documents
Characterisation of metal carboxylates by Raman and infrared spectroscopy in works of art
Otero, Vanessa,Sanches, Diogo,Montagner, Cristina,Vilarigues, Mrcia,Carlyle, Leslie,Lopes, Joo A.,Melo, Maria J.
, p. 1197 - 1206 (2015/02/19)
This work introduces the complementary use of μ-Raman and μ-Fourier transform infrared (IR) spectroscopy for the detection of specific carbon chains and cations for the identification of metal carboxylates within oil paint microsamples. Metal carboxylates (metal soaps) form naturally when free fatty acids react with metal cations and may also be found as additives or degradation products. Twenty-two metal carboxylates were synthesised, and their spectra assembled in a reference database. Metal salts of cations commonly present in oil paintings were used, including lead, zinc, calcium, cadmium, copper and manganese. The fatty acids selected were the saturated acids palmitic (C1 6:0) and stearic (C18:0) and the polyunsaturated oleic acid (C1 8:1). Azelaic acid (C9 diacid), a product resulting from autoxidation of polyunsaturated acids, was also included. Metal carboxylates were characterised by Raman and IR spectroscopy, and their structures were confirmed by X-ray diffraction. Raman and IR spectroscopy proved to be complementary techniques for a full identification of the metal carboxylates in complex aged paint. Raman enables the differentiation of the carbon chain length in the C-C stretching region (1120-1040 cm-1), and IR distinguishes the metal cation in the COO- stretching absorption region (1650-1380cm-1). Principal component analysis was applied to the spectra in order to facilitate a fast and accurate method to discriminate between the different metal carboxylates and to aide in their identification. Finally, spectra from case studies were successfully projected in the principal component analysis models built, enabling a higher confidence level for the identification of copper palmitate and copper azelate in two 19th-century Portuguese oil paintings.
Compact metal-organic frameworks for anti-corrosion applications: New binary linear saturated carboxylates of zinc
Mesbah, Adel,Jacques, Sophie,Rocca, Emmanuel,Francois, Michel,Steinmetz, Jean
, p. 1315 - 1321 (2011/06/10)
Zinc-based metal-organic frameworks (MOFs), binary zinc carboxylates ZnCnCn′ with Cn and Cn′ = CH3(CH2)n - 2COO-, have been synthesised and characterised for anti-corrosion applications. The crystallographic structures of ZnC10C14 and ZnC 10C16 were determied from synchrotron powder diffraction data and refined by the Rietveld method. Protective coatings on electrogalvanised steel composed of ZnC12C16 have been developed by formulating a particular "carboxylating" bath. The ZnC12C16 coating exhibits better anti-corrosion behaviour than the pure Zn(C16)2 and Zn(C12)2 coatings, according to electrochemical and non-electrochemical measurements. The crystallographic results and corrosion measurements demonstrate the great flexibility of the zinc carboxylate lamellar structures in modifying the insolubility and hydrophobicity of the protective coatings. In addition, the conditions for the ZnC12C16 coating process fulfil the specifications for the surface treatment of zinc. Finally, these new compounds, which can be easily synthesised in water, provide a new and environmentally friendly anti-corrosion treatment for metals. New zinc-based metal-organic frameworks (MOFs), binary zinc carboxylates ZnCnCn′ with Cn and Cn′ = CH3(CH2)n - 2COO-, have been synthesised and characterised for anti-corrosion applications on zinc. The crystallographic structures demonstrate the great flexibility of these MOFs in modifying the insolubility and hydrophobicity of the protective coatings on metals in an aqueous solvent process. Copyright
Melting of saturated fatty acid zinc soaps
Barman,Vasudevan
, p. 22407 - 22414 (2008/10/09)
The melting of alkyl chains in the saturated fatty acid zinc soaps of different chain lengths, Zn(CnH2n-1COO)2; n = 11, 13, 15, and 17, have been investigated by powder X-ray diffraction, differential scanning calorimetry, and vibrational spectroscopy. These compounds have a layer structure with the alkyl chains arranged as tilted bilayers and with all methylene chains adopting a planar, all-trans conformation at room temperature. The saturated fatty acid zinc soaps exhibit a single reversible melting transition with the associated enthalpy change varying linearly with alkyl chain length, but surprisingly, the melting temperature remaining constant. Melting is associated with changes in the conformation of the alkyl chains and in the nature of coordination of the fatty acid to zinc. By monitoring features in the infrared spectra that are characteristic of the global conformation of the alkyl chains, a quantitative relation between conformational disorder and melting is established. It is found that, irrespective of the alkyl chain length, melting occurs when 30% of the chains in the soap are disordered. These results highlight the universal nature of the melting of saturated fatty acid zinc soaps and provide a simple explanation for the observed phenomena.
