Biomedical applications of tannic acid

Tannic Acid (TA) is a naturally occurring antioxidant polyphenol that has gained popularity over the past decade in the field of biomedical research for its unique biochemical properties. Tannic acid, typically extracted from oak tree galls, has been used in many important historical applications. TA is a key component in vegetable tanning of leather, iron gall ink, red wines, and as a traditional medicine to treat a variety of maladies. The basis of TA utility is derived from its many hydroxyl groups and its affinity for forming hydrogen bonds with proteins and other biomolecules. Today, the study of TA has led to the development of many new pharmaceutical and biomedical applications. TA has been shown to reduce inflammation as an antioxidant, act as an antibiotic in common pathogenic bacterium, and induce apoptosis in several cancer types. TA has also displayed antiviral and antifungal activity. At certain concentrations, TA can be used to treat gastrointestinal disorders such as hemorrhoids and diarrhea, severe burns, and protect against neurodegenerative diseases. TA has also been utilized in biomaterials research as a natural crosslinking agent to improve mechanical properties of natural and synthetic hydrogels and polymers, while also imparting anti-inflammatory, antibacterial, and anticancer activity to the materials. TA has also been used to develop thin film coatings and nanoparticles for drug delivery. In all, TA is fascinating molecule with a wide variety of potential uses in pharmaceuticals, biomaterials applications, and drug delivery strategies.

Visualising Iron Gall Ink Underdrawings In 16th Century Paintings In-Situ By Micro-XRF Scanning (MA-XRF) And LED-Excited IRR (LEDE-IRR)

Until today, iron gall ink is classified as an exceptional underdrawing material for paintings. A certain identification is always based on invasive analysis. This article presents a new non-destructive analysis approach using micro-X-ray fluorescence scanning (MA-XRF), LED-excited IRR (LEDE-IRR) using a narrow wavelength-range of infrared radiation (IR) and stereomicroscopy for visualising and identifying iron gall ink underdrawings. To assess possibilities and limits of this non-invasive approach, results were compared to invasive examinations on cross-sections using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX). The approach is tested on panel paintings of Hans Holbein the Elder and Giovanni Battista Cima da Conegliano. The holistic setup could successfully visualise underdrawing lines made with iron gall inks, which formerly remained invisible by means of conventional IRR. For the first time, a direct access to a formerly invisible type of underdrawing is created, allowing to harness the whole iron gall ink underdrawing for interdisciplinary studies.

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

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.

Logwood Writing Inks: History, Production, Forensics, and Use

In the 16th century, the Spanish brought logwood from Mexico to Europe. Its extract was used for textile dyeing. The French introduced the logwood tree to Western Hispaniola, which became Haiti in 1804. Around 1880, Haiti exported most of its logwood to France. In 1847, Runge introduced the black chrome-logwood ink as an alternative for iron-gall ink, because the latter attacked the steel writing nibs. The most important constituents of logwood are hematoxylin and hematein. Due to the profitable import conditions from Haiti, chrome-logwood ink became the cheapest and most commonly used black writing ink in France. This could explain why Vincent van Gogh, during his French period, used it for writing and drawing and why most of the French postcards from the first half of the 20th century, studied in this publication, were written with chrome-logwood ink, while most of the Dutch postcards were written with an iron gall ink.

XRF elemental analysis of inks in South American manuscripts from 1779 to 1825

The Regional Archive of Cusco in Peru guards valuable history collections with exceptional regional and international value dating from the sixteenth century to the present. Historical manuscripts are part of the identity of all people; they constitute a tangible cultural heritage that must be studied, valued, and protected. In this sense, the objective of this research was to identify the chemical compositions of inks and paper, with the goals of setting the background of their originality, identifying relationships between them, and glimpsing antecedents that generated degradation due to the compositions of the inks. This study is the first of its kind in Peru and reveals the chemical elements present in the writing ink, the seal, and the paper of five documents from the late eighteenth and early nineteenth centuries. Duplicate in situ nondestructive analyses were carried out using a hand-held X-ray fluorescence spectrometer under ambient conditions in soil mode, configured with three sequential shots, and energies from zero to 40, 40, and 15 keV, respectively. The elements S and Fe were present as components of iron gall inks. Cu and Zn were less abundant; probably, they provided less corrosion and more color intensity to the inks. The minor elements Pb, As, and especially Ag in all manuscripts differentiate them from European inks of the same period. Additionally, the five documents reflect the same elemental compositions but with different concentrations. This could mean that writers used local raw materials and Spanish ink recipes. Finally, the analyses of standard reference material, SRM 1646a and SRM 196b, gave results with acceptable precision. Graphical Abstract

Beneficial effect of gelatin on iron gall ink corrosion

Iron gall Inks corrosion causes paper degradation (browning, embrittlement) and treatments were developed to tackle this issue. They often include resizing with gelatin to reinforce the paper and its cellulosic fibers (of diameter approx. 10 µm). This work aimed at measuring the distribution of ink components at the scale of individual paper fibers so as to give a better understanding of the impact of gelatin (re-)sizing on iron gall ink corrosion. For this purpose, scanning transmission X-ray microscopy (STXM) was used at the Canadian light source synchrotron (CLS, Saskatoon). This technique combines nano-scale mapping (resolution of 30 nm) and near edge X-ray absorption fine structure (NEXAFS) analysis. Fe L-edge measurements enabled to map iron distribution and to locate iron(II) and iron(III) rich areas. N K-edge measurement made it possible to map gelatin distribution. C K-edge measurements allowed mapping and discrimination of cellulose, gallic acid, iron gall ink precipitate and gelatin. Three fibers were studied: an inked fiber with no size, a sized fiber that was afterwards inked and an inked fiber sprayed with gelatin. Analysis of gelatin and ink ingredients distribution indicated a lower amount of iron inside the treated cellulosic fiber, which may explain the beneficial effect of gelatin on iron gall ink corrosion.

Materials and techniques used for the “Vienna Moamin”: multianalytical investigation of a book about hunting with falcons from the thirteenth century

A multianalytical approach was used to characterize the materials in the “Vienna Moamin”, an outstanding richly illustrated manuscript from the late thirteenth century, which was made in Italy and is now kept in the Kunsthistorisches Museum Wien. The investigations were carried out with a non-invasive approach by using complementary techniques, such as X-ray fluorescence (XRF), reflection Fourier transform infrared spectroscopy (rFTIR), Raman spectroscopy, and fiber optic reflectance spectroscopy (FORS). In addition, XRF scans were performed in two areas which yielded chemical maps showing the elemental distribution. The results revealed that typical materials from the medieval times were applied for the manuscript. Calcium carbonate on the parchment surface indicated a dehairing process with lime and/or whitening with chalk. Two different iron gall inks were detected in the main text and marginal notes, and vermilion was used for rubrication. The color palette included azurite, a green colorant composed of orpiment and indigo, yellow ochre, brown iron oxide pigments, minium, vermilion, brazilwood lake, and carbon black. Moreover, mosaic gold was detected in gold-beige hues. Lead white was identified for white areas and fine decoration lines, as well as in mixture with blue and red pigments for light color shades. No reliable information could be obtained concerning the binding media. Two differing application techniques for gold leaf were detected, which correspond with stylistic differences: either on gypsum or chalk preparation layers. Furthermore, calcium soap contents in certain colors were determined only on one folio with unique characteristics. The XRF scans of two historiated initials revealed that similar materials were applied in both cases and provided further valuable information about the painting technique. The results obtained enabled to gain insights into Italian thirteenth century manuscript production techniques and to characterize the used materials. The investigations showed the importance of scanning XRF for the elucidation of painting techniques, but also the demand of scanning devices utilizing compound specific analytical techniques such as rFTIR.