Fascinating organic molecules from nature (original) (raw)
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Structural Chemistry, 2017
Quantitative HPLC and colorimetry are used to study color variations in dyeings with indigo, 6-bromoindigo, and 6,6′-dibromoindigo, the main components of the historic dye Tyrian purple. For the first time, visible light is identified conclusively as a cause of debromination of the leuco form of 6-bromoindigo. A dyeing run using 6-bromoindigo alone is found to yield a dyed fabric containing large amounts of indigo, when the vat is exposed to visible light. The extent of debromination is dependent upon the pH of the dye bath and also the source of the visible light. This information allowed development of a dyeing procedure which is demonstrated to give consistent colors through two passes. Quantitative HPLC analysis of extracts from the dyed fabrics indicates that the leuco form of 6-bromoindigo vs. the leuco forms of indigo and 6,6′-dibromoindigo has the strongest affinity for wool fabric. This is postulated to be due to attractive electrostatic interactions between the leuco form of 6-bromoindigo and wool.
Dyes and Pigments, 2015
Thirteen fabrics are each dyed with either indigo, or 6-bromoindigo, or 6,6 0 -dibromoindigo. When the dyed fabrics, which had not undergone any finishing procedures, are boiled in water for 10 min, color changes are observed: many indigo-and 6-bromoindigo-dyed fabrics turn more blue, while many 6,6 0dibromoindigo-dyed fabrics turn more red. These color changes are characterized by reflectance spectra and colorimetry data. Evidence is presented that the color changes are related to particle sizes of the dyes: 6,6 0 -dibromoindigo-dyed carbon nanotubes, used as a fabric surrogate, show an increase in dyeparticle size upon heating, as judged by electron microscopy. Because we have shown previously that 6-bromoindigo-dyed carbon nanotubes give decreased dye-particle size when heated, we infer that, no matter the indigoid or fabric, smaller particles tend to cause a bluer fabric shade, while larger particles cause a redder shade.
Dyes and Pigments, 2015
Thirteen fabrics are each dyed with either indigo, or 6-bromoindigo, or 6,60-dibromoindigo. When the dyed fabrics, which had not undergone any finishing procedures, are boiled in water for 10 min, color changes are observed: many indigo- and 6-bromoindigo-dyed fabrics turn more blue, while many 6,60-dibromoindigo-dyed fabrics turn more red. These color changes are characterized by reflectance spectra and colorimetry data. Evidence is presented that the color changes are related to particle sizes of the dyes: 6,60-dibromoindigo-dyed carbon nanotubes, used as a fabric surrogate, show an increase in dyeparticle size upon heating, as judged by electron microscopy. Because we have shown previously that 6-bromoindigo-dyed carbon nanotubes give decreased dye-particle size when heated, we infer that, no matter the indigoid or fabric, smaller particles tend to cause a bluer fabric shade, while larger particles cause a redder shade.
Authors: M. Aceto, E. Calà, A. Agostino, G. Fenoglio, M. Gulmini, A. Idone, C. Porter, C. Hofmann, C. Rabitsch, C. Denoël, Christian Förstel, A. Quandt. The traditional knowledge concerning the use of Tyrian purple in Late Antique and Medieval purple codices-those precious biblical texts written with noble metal inks on parchment dyed or painted with purple colourants-is here updated in view of new analytical evidence. Recent literature reports the analysis carried out on some purple codices, suggesting that Tyrian purple has not, if ever, been used in their making. A large number of purple codices has been considered in this work to elucidate the nature of the purple colour. Results have been discussed within the frame of previous information, thus covering a vast majority of the purple codices presently identified. In most of the instances the use of less expensive dyes such as folium or orchil is suggested. Moreover, analytical results from a non-invasive spectroscopic approach have been definitely confirmed by micro-invasive surface-enhanced Raman analysis performed on micro samples of purple parchment taken from two 6th century codices.
Detection of Natural Dyes: Historical Importance of Indigo
Journal of emerging technologies and innovative research, 2019
Many raw materials like fibres, employs either natural or chemical dyes for dyeing. Synthetic dyes are famous for their features like adhesion & resistance towards washing & chemicals but are marred by its mutagenic property on the environment. Natural dyes obtained from the natural world are not only quite tolerant to washing, having shown good adhesion and longevity is also environment friendly. In order to obtain information about the history and methods with types of natural dyes used, many analytical methods have been utilized. One of the natural dyes of historical importance is Indigo which is found in 3 forms, Indigo, Indirubin & the leuco or colourless form. The aim of this review paper is to have a brief understanding of the various detection methods for natural dyes in historical textiles and to understand how these techniques can be used for detection of the various forms and isomers of natural Indigo.
Preparation of Tyrian Purple (6,6′-Dibromoindigo): Past and Present
Molecules, 2010
Over the past century, various synthetic approaches have been suggested to the most famous dye of antiquity, Tyrian purple (6,6′-dibromoindigo). These synthetic routes have been exhaustively surveyed and critically evaluated from the perspective of convenience, cost, safety and yield.
Tyrian purple: an ancient natural dye for cross-conjugated n-type charge transport
Journal of Materials Chemistry C, 2021
Herein, we present two novel organic semiconducting polymers synthesised from an ancient dye. By employing cross-conjugation within the polymer backbone as a synthetic strategy, we are able to engineer optical gaps such that the novel materials absorb over the entire visible spectrum. The cross-conjugated polymers exhibited relatively high n-type charge transport performance in organic field-effect transistors, a rare characteristic for this type of polymer. Quantum chemical calculations provide insight into this behaviour, suggesting that, whilst conjugation along the HOMO is indeed inhibited via molecular design, these materials possess highly delocalized LUMOs, facilitating high n-type charge transport.
Indigo chromophores and pigments: Structure and dynamics
Dyes and Pigments, 2020
In this study, we explore the molecular mechanisms of the stability of indigo chromophores and pigments. Assisted with density functional theory, we compare visible, infrared and Raman spectral properties of model molecules, chromophores and pigments derived from living organisms. Using indigo carmine as a representative model system, we characterize the structure and dynamics of the chromophore in the first electronic excited state using femtosecond visible pump-infrared probe spectroscopy. Results of experiments and theoretical studies indicate that, while the trans geometry is strongly dominant in the electronic ground state, upon photoexcitation, in the Franck-Condon region, some molecules may experience isomerization and proton transfer dynamics. If this happens, however, the normal modes of the trans geometry of the electronic excited state are reconfirmed within several hundred femtoseconds. Supported by quantum theory, first, we ascribe stabilization of the trans geometry in the Franck-Condon region to the reactive character of the potential energy surface for the indigo chromophore when under the cis geometry in the electronic excited state. Second, we suggest that a conical intersection crossing, due to the high barrier along the isomerization pathway in the ground state, would provide for the effective relaxation and observed dominance of the trans geometry of the chromophore in the ground state. Planarity of the chromophore under the trans geometry assists effective dissipation of energy via a cascade of in-plane CC , C-O•••H-N stretchings and CC -C bending modes delocalized over the molecular mainframe. The described mechanisms help to explain the remarkable photo-stability of indigo chromophores.