Simple extended constant capacitance surface complexation models have been developed to represent the adsorption of polyaromatic dyes (9-aminoacridine, 3,6-diaminoacridine, azure A and safranin O) to kaolinite, and the competitive adsorption of the dyes with Cd. The formulation of the models was based on data from recent publications, including quantitative adsorption measurements over a range of conditions (varying pH and concentration), acid-base titrations and attenuated total reflectance-Fourier transform infrared spectroscopic data. In the models the dye molecules adsorb as aggregates of three or four, forming outer-sphere complexes with sites on the silica face of kaolinite. Both electrostatic and hydrophobic interactions are implicated in the adsorption processes. Despite their simplicity, the models fit a wide range of experimental data, thereby supporting the underlying hypothesis that the flat, hydrophobic, but slightly charged silica faces of kaolinite facilitate the aggregation and adsorption of the flat, aromatic, cationic dye molecules.

The strong adsorption to kaolinite of four polyaromatic, cationic dyes (9-aminoacridine, 3,6-diaminoacridine, azure A and safranin O), which adsorb much less to alumina or silica, was investigated by means of acid-base titrations, measurements of adsorption at varying pH and dye concentration, and by ATR-FTIR spectroscopy. The four dyes adsorb to kaolinite to similar extents, with little change over the pH range 3–10, but at higher pH (above the pKas of the dyes) the adsorption of 9-aminoacridine and 3,6-diaminoacridine decreases, that of azure A increases, and that of safranin O stays approximately constant. Although the dyes adsorb to kaolinite much more strongly than metal ions do, titration and spectroscopic data show that there is only limited chemical interaction between the adsorbed dyes and the kaolinite surface. The results indicate that electrostatic interaction between the dye molecules and the kaolinite surface is necessary for adsorption, but that hydrophobic interactions also contribute. It is proposed that the relatively hydrophobic silica faces of kaolinite, which carry low-density permanent negative charge, facilitate aggregation and adsorption of the positively charged, flat, aromatic dye molecules.

The competitive adsorption to kaolinite between Cd(II) and four polyaromatic dyes (9-aminoacridine, 3,6-diaminoacridine, azure A and safranin O) was studied in 5 mM KNO3 at 25°C. Under these conditions, Cd adsorbs to the silica face of kaolinite between about pH 4 and 6.5, but at higher pH, adsorbed Cd is progressively relocated to the crystal edges. In the presence of dye, less Cd adsorbed to kaolinite below pH 7. If sufficient dye was added to saturate the kaolinite surface, Cd adsorption was totally suppressed up to ∼pH 6. At higher pH, Cd followed the characteristic pattern for edge adsorption. In separate experiments 9-aminoacridine and azure A displaced pre-adsorbed Cd from kaolinite. The displacement curves were initially linear, with one Cd ion being displaced for every 13 dye molecules adsorbed at pH 5.5, and one Cd ion for every 35 dye molecules at pH 7.5. The interpretation of these results is that the dyes bind to kaolinite much more strongly than Cd(II) does, but only to the silica face.

Recent analysis of the wool textiles from the famous Egtved oak coffin burial in Denmark indicated that the wool had been obtained from beyond Denmark. Was this an isolated case or evidence of a large-scale wool trade in the Danish Bronze Age? To investigate the broader pattern of wool provenance, textile manufacturing and trade practices, strontium isotope and organic dye analyses were conducted on textiles from a variety of selected burial contexts. Strontium isotope analysis revealed that at least 75 per cent of the Bronze Age wool samples originated outside present-day Denmark. Results also showed no evidence for the use of organic dyes, thereby supporting the hypothesis that no dyestuffs were used in Nordic Bronze Age textile production. These results challenge extant interpretations of Scandinavian Bronze Age textile provenance, and demonstrate the complexity of exchange networks in wool textiles during this period.

The use of nonallergic, nontoxic, and eco-friendly natural dyes has become a matter of significant importance due to increased environmental awareness on the need to avoid hazardous synthetic dyes. This study was to determine the staining properties of the dye extract of Lonchocarpus cyanescens on histomorphology of the testis. Freshly cut leaves of L. cyanescens obtained from Akpan Ifia Inan village in Ikono local government area of Akwa Ibom state (latitude 5° 10′ 12″ N; longitude 7° 48′ 0″ E) were put into a plastic jar and boiling water was poured to cover the leaves. It was covered and left for an hour. The liquid was strained and potassium hydroxide was added to the dye water mixture to reach a pH of 9. A whisk was used to mix air into the liquid, and the mixuture was then allowed to sit until the blue indigo had settled to the bottom of the container. The dye was diluted with 70% ethanol to a concentration of 0.1 g/mL and was used to stain sections of testes. Its potential for use as a counterstain was also investigated. The testes sections were stained in shades of blue. The dye overshadowed the colors of haematoxylin and eosin. Preliminary phytochemical screening of L. cyanescens revealed that it contains alkaloids, saponins, flavonoids, and tannins.

Biologically and chemically modified nanoparticles are gaining much attention as a new tool in cancer detection and treatment. Herein, we demonstrate that an alizarin red S (ARS) dye coating on TiO2 nanoparticles enables visible light activation of the nanoparticles leading to degradation of neighboring biological structures through localized production of reactive oxygen species. Successful coating of nanoparticles with dye is demonstrated through sedimentation, spectrophotometry, and gel electrophoresis techniques. Using gel electrophoresis, we demonstrate that visible light activation of dye-TiO2 nanoparticles leads to degradation of plasmid DNA in vitro. Alterations in integrity and distribution of nuclear membrane associated proteins were detected via fluorescence confocal microscopy in HeLa cells exposed to perinuclear localized ARS-TiO2 nanoparticles that were photoactivated with visible light. This study expands upon previous studies that indicated dye coatings on TiO2 nanoparticles can serve to enhance imaging, by clearly showing that dye coatings on TiO2 nanoparticles can also enhance the photoreactivity of TiO2 nanoparticles by allowing visible light activation. The findings of our study suggest a therapeutic application of dye-coated TiO2 nanoparticles in cancer research; however, at the same time they may reveal limitations on the use of dye assisted visualization of TiO2 nanoparticles in live-cell imaging.

This article discusses recent scientific research performed by the author in understanding the composition of archaeological purple pigments and dyes from molluskan sources, which were primarily used for the dyeing of royal and priestly textiles, as also cited in the Bible. Towards this end, the high-performance liquid chromatography (HPLC) method has been applied to the qualitative and quantitative multi-component fingerprinting of purple pigments extracted from various Muricidae mollusks inhabiting the Mediterranean waters. The results show that the colorants in these purple pigments belong to three chemical groups: the indigoids (of major importance), the indirubinoids, and the isatinoids. Application of this analytical method to purple pigments and dyes on archaeological artifacts from the ancient Near and Middle East has lead to a number of breakthroughs and discoveries made by this laboratory. These include the following: decipherment of the optimal method by which the ancients practiced purple-dyeing by completely natural means; first HPLC analysis of a raw unprocessed purple archaeological snail pigment and the resulting identification of a dibrominated indirubin in this pigment; discovery of the purple pigment as the sole paint pigment on a 2,500 royal marble jar from the Persian King Darius I; and the discovery that a 2,000 year old miniscule fabric found atop the Judean Desert palatial fortress of Masada belonged to the royal purple mantle of King Herod I and is the first Biblical Argaman dye found in ancient Israel.

Coinage metals nanoparticles have been widely used in last decade for enhancing the Raman signal of a variety of compounds. Several preparation methods have been proposed, including chemical reduction of gold or silver salts with sodium citrate, hydroxylamine or sodium borohydride, microwave-assisted reduction with glucose, Tollens mirror, electrodeposition, vacuum evaporation and pulsed-laser deposition.

In this work, gold and silver nanoparticles were prepared by chemical reduction with sodium citrate and hydroxilmanine, characterized by UV-Vis spectroscopy and High Resolution Transmission Electronic Microscopy and tested as SERS substrate. Carminic acid, cochineal, axiote, muitle and zacatlaxcalli SERS spectra were recorded at different pH. Natural dyes samples were prepared by extraction from its natural sources, following traditional recipes. Although differs for each dye, best results were achieved by performing SERS experiments at pH neutral to basic.

This paper discuss the presence of powdered glass and quartz integrated in the red lake layers of two paintings attributed to the Sevillian painter Bartolome Esteban Murillo that belongs to the Guadalajara’s Regional Museum’s art collection. A laboratory experimental reproduction of the Sevillian painting technique was made using three different lakes (cochineal, madder lake and brazilwood) mixed with four varieties of glass to explore the optical properties and the influence of the transparent and translucent aggregates into the oil paint layers. The experimental reproductions were analyzed using ultraviolet-visible spectroscopy, optical and fluorescence microscopy and scanning electron microscopy (SEM-EDX). A comparison between the originals and the reproduced red lakes layers was carried out to understand the artistic process of Murillo’s color application. Preliminary results suggest that glass was not used as a siccative agent as the historical treatises mentioned but mainly as an additive to increase brightness, thickness and color saturation of the red lake layers related to the artist’s intention.

Natural dyes have been extracted from both plants and animal to give color to textiles and handicrafts. This is the case of purple dye extracted from Justicia spicigera Schldt, an acanthaceae used as a color source since pre-Hispanic period in the Mayan area of Mexico and Central America. Spectroscopic (UV-Vis and FT-IR) and chromatographic (PY-GC/MS) techniques were employed in order to characterize some of their chemical properties. UV-VIS absorption spectra indicates a λmaxpeak at 581 nm, value associated to anthocyanins group under bathochromic effect. On the other hand, a structural characterization realized by FT-IR and Py-GC/MS indicated the presence of polar hydroxibenzoic acids and phenolic compounds which are characteristics of the molecular structure of anthocyanins.

Textile research has become an important field of archaeology. Although the established analytical methods are often viewed as specialized, their integration with other interdisciplinary approaches allows us to deal with broader archaeological issues and provides the interpretational base for a much more comprehensive investigation of textiles in ancient times. Analyses of fibres, dyes, archaeobotanical and archaeozoological remains, as well as palaeoenvironmental and geochemical investigations, provide information about available resources, while tool studies, experimental testing, and visual grouping are approaches that explore the technology and techniques. Together, these approaches can provide new knowledge about textile production and consumption and, thereby, about people and society in ancient times.