Schematic of UV-vis absorption maxima (at 275 and 570 nm) measured in TA-Fe complexes at different Fe2+ concentrations. The positions of the polyphenol-iron complex bands (ν1, ν2 and ν3) and the differences between the position of the ν1 and ν2 bands extracted from the corresponding Raman spectra of the polyphenol-iron complexes recorded at pH 7 (at pH 5 for SA - Fe Complex) .
INTRODUCTION/INTRODUCCIÓN
Las tintas ferrogálicas
Algunos ejemplos del uso de tinta de hiel de hierro que se han utilizado a lo largo de la historia humana: (a) Los cuadernos de Leonardo da Vinci b) Los bocetos de Rembrandt. Algunas de las investigaciones previas sobre el compuesto de ácido tánico, que forma parte de la tinta IGI, se ven en los textos de Guibourt [17].
Teoría del color: las causas del color
La longitud de onda (λ) de la luz absorbida depende de la diferencia de energía entre los estados excitado y fundamental de la molécula. Imágenes esquemáticas de (a) electrones de valencia en la molécula de carbono, la capa externa de electrones contiene 4 electrones disponibles; (b) hibridación del orbital en los anillos de la molécula de benceno;
Estructuras de las tintas ferrogálicas propuestas en la bibliografía
Las celdas resaltadas en azul reflejan lo que a priori serían las causas del color de las tintas con hiel de hierro estudiadas en esta tesis. El efecto de la goma arábiga, un componente utilizado en la fabricación de tintas para impartir viscosidad a la tinta, no se ha abordado en profundidad en estos estudios previos.
Estado del arte
Este estudio fue posible gracias al uso de la espectroscopia Raman mediante transformada de Fourier (FT-Raman), que utiliza una fuente de excitación láser de infrarrojo cercano, es decir, el láser que permite atenuar la fluorescencia característica de los colorantes (natural). Esta técnica se basa en la mejora de la señal Raman mediada por metales plasmónicos nanoestructurados [58].
Introducción a la espectroscopía vibracional
Para que la transición sea Raman activa, debe haber un cambio en la polarizabilidad de la molécula durante las vibraciones. Esto significa que la nube de electrones de la molécula debe sufrir un cambio de posición.
OBJECTIVES OF THE THESIS
The main objective of this thesis is to understand and define a relationship between the structure of the selected phenolic compounds and the chemical reactions and processes characteristic of iron gall inks (IGIs) analyzed with spectroscopic techniques. In particular, we look for specific reaction points in the structure of the phenolic molecules, which have particular reactivity towards the metal ions (especially with iron), and as a result, it is possible to define them as structural and spectral markers for sensitive and spectral markers. selective detection, identification and characterization of polyphenols and thus for IGIs. Since we have experimented with a significant lack of the scientific papers on systematic investigation and spectroscopic characterization, especially by means of Raman and SERS spectroscopy, of gallic acid and other structurally similar phenolic compounds and their complexation with various transition metal ions, we also plan to perform basic research dedicated to their vibrational characterization.
To carry out the spectroscopic study of the selected polyphenolic compounds (pyrogallol (PY), gallic acid (GA), tannic acid (TA) and spray acid (SA)) by means of UV-visible absorption, IR and Raman spectroscopies. To prepare and carry out spectroscopic study of the complexes formed by the interaction of the selected polyphenolic compounds and iron(II) and copper(II) ions by means of UV-visible absorption, IR and Raman spectroscopies feed. To carry out studies of the effect of various factors such as solvent, base (support), metal, pH, time (aging) on the formation of IGIs.
MATERIALS AND METHODS
- Chemicals
- Preparation of complexes and sampling
- Preparation and characterization of metal nanoparticles
- Historical Manuscripts
- Measurement of the pH on historical manuscripts
- Instrumentation
The phenolic compounds and their reagents have been selected on the basis of the generally known composition of. It is worth noting that the molecular structure of gallic acid and pyrogallol can be found in the structure of the tannic acid molecule. These NPs were shown to be more efficient in the intensification of the electric field compared to the spherical NPs [77].
Above (on previous page): Visual appearance of the metal colloids prepared in this thesis. Don Emilio Castelar y Ripoll was a Spanish republican politician and president of the First Spanish Republic.). The mixed basis sets 6-311+G* + LANL2DZ (Los Alamos National Laboratory 2 double ζ) were used for Fe complex calculations.
RESULTS AND DISCUSSION
UV-visible absorption spectra
These colorless compounds do not show absorption properties in the visible region of the electromagnetic spectrum. UV-vis absorption spectra of 10-5 M aqueous solutions of the studied polyphenolic compounds, pyrogallol (PY), gallic acid (GA), tannic acid (TA) and spray acid (SA), measured at pH 7. In the case of SA, the latter can observed as slightly red-shifted (to 261 nm) due to methyl substitution of the two of three phenolic hydroxyl groups, Figure 15d, i.e.
The images above show the colors of solutions/suspensions of molecules and their corresponding metal complexes. In particular, a new broad band appearing at longer wavelength is attributed to ligand–metal charge transfer (LMCT) from the polyphenol to the Fe3+ center of the complex. However, this shift can also be caused by a change in the stoichiometry of the ligand interaction with Fe3+ after ionization of the OH group [88].
Vibrational spectra
This is not the case for the region corresponding to the C=O and C=C stretching vibrations ((C=O) and (C=C)) seen in the 1710-1530 cm-1 region, where there are some similarities found among these molecules, with the exception of PY which does not have a (C=O) functional group. The Raman spectrum of the PY molecule differs the most (compared to the other three molecules) especially in the intensity of the observed bands (Figure 31a). A similar metal effect was also observed in the case of the GA-Fe complex (Figure 33e and g) as well as for PY and SA (Figure 34).
The position of the ν(Fe−O) bands may change due to the different molecular environment of this bond. In contrast, a negligible sensitivity to pH variation is observed in the case of the SA−Fe complex (Figure 40d). Fluorescence emission variation of the 2000 cm−1 (~724 nm) band for the polyphenol-Fe (a) and polyphenol-Cu (b) complexes (blue bars) recorded in solution (gray bars).
SERS spectra
The corresponding SERS spectra of the analyzed polyphenols (Figure 50 and Figure 51) show significant changes compared to the Raman spectra of polyphenols both in the solid state (Figure 31) and in aqueous or ethanol solution (Figure 33 and Figure 34) . At first sight, the adsorption of acidic polyphenols (GA and SA) on Ag nanoparticles promotes the ionization of carboxylate groups which can be concluded from the weakening of the bands at 1688 and 1687 cm-1, for SA and GA, respectively, in solution (Figure 50c and Figure 51a). In conclusion, the SERS spectra of the analyzed polyphenols show significant differences compared to the Raman spectra.
Inset plot: comparison of the 3 band in the SERS and normal Raman of the TA-Fe complex. In the case of the IGI prepared with a higher relative concentration of gum arabic (Figure 52c and d), i.e. This demonstrates the gain of the citrate/Fe linker in the adsorption of these polyphenols on the silver surface.
Analysis of Historical Manuscripts
Finally, the clear changes in the Fe-O region are related to the formation of new Fe-O bonds after the degradation process of the original organic compounds. This process leads to the reorganization of the iron complexes and the formation of new metal coordination spheres. The analysis of the Fe-O spectral region may be more useful in the comparative study.
On previous page) (a) pH data obtained from the samples of Figure 65 and the reference sample, water. In addition, all the inks in the manuscripts lowered their pH above the pH of water (pH ~ 6.4). Raman spectra measured at different points of the Castelar letters analyzed at the Museo Arqueológico Nacional de Madrid (MAN).
CONCLUSIONS/CONCLUSIONES
This is a negative effect in the case of using IGIs, as it induces a progressive degradation of the paper. In addition, it was demonstrated that the pH decreases even more with time after the deposition of the complex on the paper. The formation of the complex leads to fluorescence quenching, and this is a positive effect for the Raman study of these complexes, since polyphenols show a strong fluorescence emission that overlaps the Raman signal.
The presence of gum arabic in IGI ink seems primordial to induce a protection of the polyphenol, preventing oxidation and acidification due to the formation of H-bonds between hydroxyl groups of the polyphenol and the polysaccharide. The analysis of historical manuscripts by Raman revealed the keys to the interpretation of the aging effect of iron gall ink, which consists in the oxidation and hydrolysis of polyphenols together with a change in the coordination pattern of the iron. The analysis of manuscripts from the end of the XIX century and the beginning of the XX revealed the presence of modern synthesized dyes that were added to IGI ink.
Ponce et al., "Opheldering van de Fe (III) gallaatstructuur in historische ijzergalinkt", Anal. Shah, "Tip-Enhanced Raman Spectroscopy (TERS) for in Situ Identi fication of Indigo and Iron Gall Ink on Paper", 2014. Jurašeková, "Vibrational Study (Raman, SERS, and IR) of Plant Gallnut Polyphenols Related to the Fabrication van Iron Gall Inks,” Mol.
Ponce et al., “Structure elucidation of Fe(III) gallate in historical iron gall ink,” Anal. Shah, "Tip-enhanced raman spectroscopy (TERS) for in situ identification of indigo in iron gall ink on paper," J. Kočar, "Evaluation of a method for treat iron gall ink corrosion on paper," Cellulose, vol.
FUNDING AND DIFFUSION
Funding
This work is supported by the research grant provided by the Grants Agency of the Ministry of Education, Science, Research and Sports of the Slovak Republic (VEGA by the grant of the Faculty of Sciences, P.
Diffusion
XXVII RNE - XI CIE, XXVII Nailian nga Espektroskopiko a Miting - XI Iberiano nga Espektroskopiko a Kongreso, Libro dagiti Abstrakto, p. Ti nauneg nga estruktural a panaganalisar kadagiti landok a komplikado ti tanniko nga asido ken dagiti dadduma pay a mainaig a polipenol a kas naipalgak babaen dagiti espektroskopikon a tekniko. Maika-5 nga edision dagiti Sientipiko a Seminar ti IOSA, IOSA Student Chapter CSIC, Madrid, Espania, 12 Disiembre 2018 (oral a presentasion).
Raman and surface-enhanced Raman scattering analysis of iron gallic inks in ancient manuscripts from Spain and Slovakia, ISA 2018, 42nd Int. Noninvasive microraman and SERS analysis of colored materials in paper artefacts of cultural and historical significance. ALMA 2017, 6th ALMA Interdisciplinary Conference and 2nd CrysAC Workshop: Painting as Story, Book of Abstracts, p.