Vibrational Study (Raman, SERS, and IR) of Plant Gallnut Polyphenols Related to the Fabrication of Iron Gall Inks

Abstract

FT-Raman, FTIR, and SERS spectra of the structurally related gallnut polyphenols tannic acid, gallic acid, pyrogallol, and syringic acid are reported in this work aiming at performing a comparative assignation of the bands and finding specific marker features that can identify these compounds in complex polyphenol mixtures. Tannic and gallic acids are the principal components in oak gallnuts, and they can be found in iron gall inks. The different functional groups existing in these molecules and their spatial distribution lead to slight changes of the vibrations. The Raman spectra are dominated by bands corresponding to the ring vibrations, but the substituents in the ring strongly affect these vibrations. In contrast, the FTIR spectra of these molecules are dominated by the peripheral oxygen-containing substituents of the aromatic ring and afford complementary information. SERS spectroscopy can be used to analyze trace amounts of these compounds, but the spectra of these polyphenols show strong changes in comparison with the Raman spectra, indicating a strong interaction with the metal. The most significant modification observed in the SERS spectra of these compounds is the weakening of the benzene 8a ring vibration and the subsequent intensification of the 19a mode of the benzene ring. This mode is also more intense in the FTIR spectra, and its intensification in the SERS spectra could be related to a drastic change in the molecular polarizability associated with the interaction of the polyphenol with the metal in Ag NPs.

Analysis of Iron Complexes of Tannic Acid and Other Related Polyphenols as Revealed by Spectroscopic Techniques: Implications in the Identification and Characterization of Iron Gall Inks in Historical Manuscripts

“…In a previous work, the vibrational characterization of these four molecules was performed. 30 UV–vis absorption spectroscopy was also employed to follow the changes in color and perform an analysis of the metal–ligand interaction. This investigation was conducted by measuring the Raman and UV–vis absorption spectra of these polyphenols at different conditions: in solution and deposited on paper, at different pH, and evaluating the effect of the pH, aging, and stoichiometric proportions between iron and polyphenols.…”

“…In a previous work, the vibrational characterization of these four molecules was performed . UV–vis absorption spectroscopy was also employed to follow the changes in color and perform an analysis of the metal–ligand interaction.…”

Interpol questioned documents review 2019–2022

“…The article by Espina et al focused on using different spectroscopic methods (Raman, SERS, and IR) in order to differentiate structurally related gallnut polyphenols tannic acid, gallic acid, pyrogallol, and syringic acid, components in iron gall inks [ 419 ]. The different functional groups existing in these molecules and their spatial distribution led to slight changes in their spectra.…”

Differentiation of advanced generation mutant wheat lines: Conventional techniques versus Raman spectroscopy

“…Change (from com to ml, shift, and/or intensity) Assignment Reference 823 Decrease g(CO 2 ), histidine solid, isoleucine solid, valine solid/equatorial anomeric H (a-anomers and a-glycosides) (Synytsya et al, 2003;Zhu et al, 2011) 849 850 -decrease Cg-twist, Cϵ-wag, Cb-wag, lysine solution, tryptophan solid/Me-Pec (Synytsya et al, 2003;Zhu et al, 2011) 864 Decrease g(CH), gallic acid (Espina et al, 2022) 1,137 Increase C-N and C-O stretching, valine solution (Fasman et al, 1978;Zhu et al, 2011) 1,153 1,150 -increase Skeletal C-O and C-C vibration, glycosidic bonds and pyranoid ring, acetylated pectates (Synytsya et al, 2003) 1,188 1,185 -increase n(C-O-H) next to aromatic ring + s (CH), carotenoids/phenylalanine solid (Zhu et al, 2011;Morey et al, 2021) 1,224 1,222 n(C-N) + C-C + d(C-H), histidine solid (Mesu et al, 2005;Zhu et al, 2011) 1,241 Decrease d(CH), n(ring), n(CO), pyrogallol (Espina et al, 2022) 1,374 1,377 dsym(CH3(CO)), 1,8-cineol (Schulz and Baransca, 2007) 1,437 1,434 d(CH2), a-bisabolol/tyrosine solid (Schulz and Baransca, 2007;Zhu et al, 2011) 1,443 Decrease n(ring), d(OH), gallic acid/arginine solid, histidine solution (Zhu et al, 2011;Espina et al, 2022) 1,491 Decrease Aromatic ring stretch, asymmetric, lignin (Agarwal and Reiner, 2009) 1,516 1,519 -increase n(ring), d(C-OH), d(CH)/b-carotene/glycine solid (Zhu et al, 2011;Jehlic ̌ka et al, 2014;Espina et al, 2022) 1,582 Decrease Stretching vibrations of CO 2 − , isoleucine solid, leucine solid (Zhu et al, 2011) 1,630 Decrease Aromatic and aliphatic -C=C-, C=O stretching, benzene ring/serine solid (Schulz and Baransca, 2007;Zhu et al, 2011) 1,668 Decrease n(0,0), collagen solid, amide-I (Fermandjian et al, 1972;Zhu et al, 2011) 1,697 Decrease CO stretching (Schulz and Baransca, 2007) defense system in plants has emerged as a frequently preferred breeding criterion in recent years (Chen al., 2011;…”