Assessment of Raman microscopy coupled with principal component analysis to examine egg yolk–pigment interaction based on the protein CH stretching region (3100–2800 cm⁻¹)

Abstract

This work seeks to identify the slight changes in the characteristic C-H stretching region (3100-2800 cm −1 ) of a protein-based binder and fatty acid esters from egg yolk, which may occur in complex paint samples due to the presence of particular pigments. To date, this protein region -where historic pigments do not show characteristic Raman bands -has not been used to identify possible interactions between painting materials, in spite of its potential due to the mentioned feature. This study is based on the investigation of pure egg yolk model samples and tempera model samples prepared by mixing this binder with some historic pigments (cinnabar, raw Sienna, lead white, gypsum, calcite, azurite, lapis lazuli and smalt) as binary samples. All samples were analyzed in this region by Raman microscopy (RM) coupled with principal component analysis (PCA) for three color groups (red, white and blue) separately. The results show relevant spectral changes in the C-H stretching region of amino acids and polyunsaturated fatty acids esters of the egg yolk binder, particularly in the azurite, lead white and gypsum-based tempera samples. Lesser interactions were discerned in the tempera samples made with smalt, as well as shift in the region of polyunsaturated fatty acid esters of the egg yolk binder in the cinnabar and rawSienna-based tempera paintings. No interactions were recognized between the egg yolk and the pigments calcite and lapis lazuli. The effectiveness of applying RM combined with PCA for identifying interaction processes between binders and pigments is demonstrated.

Overlapping spectral features and new assignment of 2‐propanol in the C–H stretching region

“…[1][2][3] The C-H functional groups such as -CH, -CH 2 , and -CH 3 exist widely in organic and biological molecules, and the vibration spectroscopy in the C-H stretching region of 2800~3100 cm À1 is one of the extensively employed finger regions for analyzing various dynamical processes or imaging in biology and medicine studies. [4][5][6][7][8][9] This benefits from the two main factors that the C-H stretching vibration is highly localized with no insignificant mixing of other vibrational modes and exhibits the large intensity both in IR and Raman measurements. Thus, the C-H stretching spectrum is relatively easy to be obtained and applied subsequently.…”

Discrimination of aged mixtures of lipidic paint binders by Raman spectroscopy and chemometrics

“…Principal component analysis (PCA) on Raman spectra of the proteinaceous materials used in paints proved to be a powerful tool for discriminating between different media on the basis of their Raman spectra, and between naturally and artificially aged protein‐based paint media . The characterization and the study of pigment/proteinaceous binder interaction in tempera by means of PCA have both been recently proposed . Thus, the combined use of multivariate methods and Raman spectroscopy has been shown to be a valid procedure for characterizing both inorganic and organic artistic materials.…”

Estimating the concentrations of pigments and binders in lead‐based paints using FT‐Raman spectroscopy and principal component analysis

“…Lead white has been reported to induce molecular‐level changes to the amino acids present in EY and, as well as forming lead soaps, is also known to accelerate the degradation of the binders, by interacting with them and causing the release of formic acid . To confirm that such interactions were, in part, responsible for the spectral changes occurring with paint composition, we simulated model pigment–binder spectra by averaging the spectra of the pure components in the mixing proportions and projected these onto a PCA score plot formed by analysis of the ‘real’ spectra (this time including the 1 : 1 spectra in the training set; Fig.…”