Maya Blue Research Articles

Anthocyanins stabilization of Hibiscus sabdariffa extract with sepiolite: Analytical and reactive force fields approaches

Anthocyanins are natural pigments responsible for color in fruits and flowers. They are unstable to diverse ambient conditions like pH, light, or the presence of ions. Thus, in industry, several techniques are employed to protect and use anthocyanins. Likewise, ancient Mayas used clay and indigo extract to prepare a pigment known as Maya Blue, resistant to time and chemicals. For this reason, this work aims to characterize the hibiscus extract and sepiolite bio-hybrids created according to Maya methodology and observe the stability of anthocyanins, which are color-responsible in flowers and fruits. Spectral analysis shows that anthocyanins and color were more stable than controls. Powder bio-hybrids show less color change under UV radiation and allochroic behavior in acid or alkaline atmospheres. At the same time, spectroscopy analyses and X-ray diffraction show no chemical interaction between sepiolite and hibiscus compounds. Our molecular dynamics with Reactive Force Fields (ReaxFF) studies reveal a similar behavior. Thus, our method protected the color of anthocyanins, in the temperature range from 15 to 35 °C. The interaction of hibiscus compounds with clay is due to van der Waals forces.

A Mayan-inspired DAPI fluorophore stabilized and enhanced through sorption on palygorskite

DAPI (4′,6-diamidino-2-phenylindole, di-hydrochloride) is a photoactive dye used as a fluorescent marker for nucleic acids, due to its high affinity for the major groove in the DNA double helix. By following a Mayan-inspired recipe (namely grinding, heating and washing in H2O), the DAPI molecule was fastened to the microporous framework of palygorskite – a clay mineral used to produce the famed Maya Blue pigment, whose fibrous crystals are carved by surface grooves similar in size to those of DNA – in order to obtain a newly designed fluorescent material. This hybrid composite was investigated with a multi-analytical approach, which includes FE-SEM-EDS, BET-specific surface area (SSA)/micropore volume measurements, thermogravimetry, UV–vis, fluorescence and FT-IR spectroscopies. Supramolecular interactions form between the clay and the dye already after grinding, apparently involving a two-step binding process. Evidence is found of an incipient, electrostatic interaction between cationic DAPI and the negatively charged surface of the palygorskite fibrils, which then evolves in H-bonding interaction between the dye amine groups and the zeolitic and/or structural water in the clay surface grooves. Heating and washing in H2O seemingly deteriorate the composite morphology and stability, jeopardizing – rather than strengthening – the previously formed host/guest interactions. This hybrid composite, with remarkable stability and appreciable quantum yield, is potentially fit to be used as a low-cost, fluorescent material for applications such as spectrum manipulation technologies, sensors, optical devices, imaging and design-targeted drug-delivery systems.

Influence of indigo-hydroxyl interactions on the properties of sepiolite-based Maya blue pigment

Maya blue is a greenish-blue and stable pigment composed of indigo and palygorskite or sepiolite. Previous studies implied that the properties of Maya blue were influenced by different hydroxyl groups in the clay structure, e.g., zeolitic water, coordinated water, and structural hydroxyls. Therefore, an in-depth investigation was planned to analyze the structures and properties of indigo-sepiolite hybrid pigments in this work. Sepiolite materials were heated at 160, 360, 610, and 880 °C to remove zeolitic water, the first coordinated water, the second coordinated water, and structural hydroxyls. A series of Maya blue simulants were prepared by heating the mixture of indigo and sepiolite materials at 180 °C. Reflectance spectroscopy and CIE 1976 color space were employed to characterize color properties and color differences of hybrid pigments. Chemical resistance to concentrated HNO3 and dimethyl sulfoxide (DMSO), and photostability under visible light were evaluated. Microporous analysis and Fourier transform infrared spectroscopy were applied to study the indigo-sepiolite interaction. Coordinated water was essential for the greenish-blue color and outstanding stability of Maya blue, while zeolitic water and structural hydroxyls did not affect pigments’ properties. Indigo molecules were confirmed to be inserted into sepiolite channels and formed hydrogen bonds with coordinated water at one side. Structural hydroxyls were insignificant for the formation of Maya blue. This work provides a guideline for preparing stable clay-dye hybrid pigments.

Influences of micropores and water molecules in the palygorskite structure on the color and stability of Maya blue pigment

Maya blue is an ancient hybrid pigment composed of indigo and microporous palygorskite, with a fantastic hue and outstanding stability. Its color-causing and stabilization mechanism are unsolved problems. In this work, different palygorskite materials were obtained by heating at 180, 300 and 570 °C, with raw palygorskite as a reference. Maya blue-like pigments were prepared from these palygorskite materials and solid indigo. The microporous structure of palygorskite and the status of inside water molecules were investigated by thermal analysis, X-ray diffraction, Fourier transform infrared and microporous analysis. The color properties, chemical resistance and photostability of pigments were characterized by reflectance spectra, CIE color parameters and color differences after the attack of concentrated nitric acid, dimethyl sulfoxide, and visible light exposure equaling to about 100 years. It was confirmed that the greenish-blue and stable hybrid pigment could only be prepared when indigo molecules were inserted into the micropores of palygorskite. Zeolitic water molecules inside the micropores should be removed because they hindered the insertion of indigo molecules. The key to immobilizing indigo molecules inside micropores was hydrogen bonds between indigo and coordinated water (CO … …H–OH). This study emphasized the important role of micropores and hydrogen bonds in the synthesis of organic-inorganic hybrid pigments.

Isomerization and Redox Tuning: Reorganizing the Maya Blue Puzzle from Synthetic, Spectral, and Electrochemical Issues

A new approach to describe the composition of Maya blue (MB), an ancient organic–inorganic hybrid material, is presented. It is based on the analysis of attenuated total reflection-Fourier transform infrared (ATR-FTIR), Raman spectroscopy, UV–visible (vis) spectroscopic, and electrochemical data for indigo and dehydroindigo plus palygorskite hybrids, including a novel methodology using electrocatalytic effects on the oxygen reduction reaction. As a result, it is concluded that MB results from the tautomerization of indigo-to-indigo hemienol and the subsequent oxidation of these isomeric forms to dehydroindigo, all associated with the palygorskite clay framework, at temperatures above 100 °C. This model is also consistent with 13C NMR data on indigo plus sepiolite hybrids. A consistent set of thermochemical parameters is obtained from ATR-FTIR, solid-state electrochemistry, and UV–vis diffuse reflectance spectra for the successive isomerization and redox tuning processes experienced by palygorskite-associated indigo.

The chemistry of making color in art

In this review, the main technological processes involved in the production of color in glasses, ceramics and pigments are reported. Iron (as oxides or dispersed ion) is the main responsible of the color in archeological and historical ceramics and glasses, but other d-metals can be also found (Cu, Ag, Co, Cr, Ni) as nano-particles or dispersed ions. The final coloration is usually a result of the sapient choice of raw materials and firing conditions (temperature, atmosphere). Some pigments are chosen to represent the different, often sophisticated, chemical processes that have been used during the history to produce them: solid state reaction (Egyptian and Chinese Blue, Naples Yellow, Ultramarine Blue), host-guest complexation (Maya Blue), corrosion/redox processes (Lead White, Verdigris), wet/solution synthesis (Prussian Blue, Cadmium Yellow). In addition, a brief overview on the vast production of modern compounds (inorganic and mostly organic) is given. This review shows how behind the artistic choice and way of expression lies a high level of technological skill and chemical knowledge achieved/reached by (ancient) craftsmen to obtain the desired colors.

The Survival of Maya Blue in Sixteenth-Century Mexican Colonial Mural Paintings

ABSTRACT The famous Maya blue, a nanostructured hybrid organic–inorganic material, has been the subject of numerous studies since its discovery in 1931. These mainly focused on mural paintings, manuscripts, cultural artifacts from ancient Mesoamerica, and notable examples of syncretic art produced in early colonial times in New Spain as a result of the convergence of Mesoamerican and European traditions. This article reports on the identification of Maya blue in the wall painting programs of four mendicant monasteries founded in Southern and Central Mexico during the sixteenth century. It discusses the pictorial effects, painting mixtures, and artistic inventiveness of indigenous artists who expressed themselves through the quality of color and the meanings of materials by using Maya blue in Christian images. This article proposes that Maya blue reappeared in the palette of local artists in the second half of the sixteenth century, as a traditional technology that integrated the complex worldview of Mesoamerican cultures and their knowledge of its extraction, production, and use in the art of painting.

The Hunt for Maya Purple: Revisiting Ancient Pigments Syntheses and Properties

Syntheses of analogues of historical indigo and Maya blue pigments using an inquiry-based approach are presented. Derivatives of indigo were synthesized (in particular Tyrian purple) and used as vat dyes for dyeing cotton or wool fabrics or mixed with a sepiolite clay to create new hues or colors of Maya blues using a green chemistry hydrothermal microwave synthesis. The hydrothermal approach allows a very quick preparation of Maya analogue pigments (typically 1 h) while illustrating a green chemistry approach. The obtained Maya pigments can have very different colors (or not) from their initial indigo derivative and furthermore undergo color change under annealing (thermochromism) or mechanical grinding (tribochromism). In particular, the Tyrian purple/sepiolite chromism allows a direct visual illustration for students of the structural changes in sepiolite host-matrix associated with its pores closure and water loss.

Maya Blue Used in Wall Paintings in Mexican Colonial Convents of the XVI Century

Maya blue is a well-known pre-Hispanic pigment, composed of palygorskite or sepiolite and indigo blue, which was used by various Mesoamerican cultures for centuries. There has been limited research about its continued use during the Viceroyalty period; therefore, the sixteenth century is the perfect period through which to study the continuity of pre-Hispanic traditions. The fact that the indigenous people were active participants in the construction and decoration of convents makes their wall paintings a good sampling material. X-ray fluorescence (XRF), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were performed in samples of blue found in convents across Puebla, Tlaxcala and Morelos in order to identify whether the numerous hues of blue were achieved with Maya blue or with other pigments. We found no copper (Cu) or cobalt (Co) with the XRF, so several pigments, such as azurite, smalt or verdigris, were discarded. With SEM, we discovered that the micromorphology of certain blues was clearly needle-shaped, suggesting the presence of palygorskite or sepiolite. In addition, we found silicon (Si), magnesium (Mg) and aluminum (Al) by using energy-dispersive X-ray spectroscopy (EDS) in all blue samples, which also suggests the presence of these magnesium-rich clay minerals. With the XRD samples, we verified that the blues were produced with these two clay minerals, thus confirming that several wall paintings were manufactured with Maya blue. These findings confirm that this particular manmade pre-Hispanic pigment, Maya blue, was an important pigment prior to the Viceroyal period.

Crystal–chemical and diffraction analyses of Maya blue suggesting a different provenance of the palygorskite found in Aztec pigments*

Maya blue is a pigment found in different archaeological sites of different cultures from Mesoamerica, and also in colonial buildings in Mexico and Cuba. The pigment is made from a thermally treated mixture of indigo and palygorskite. Pigment samples from Aztec and non‐Aztec archaeological sites as well as reference Yucatecan palygorskites were studied in this paper to assess their differences. The characterization of the samples was carried out by a combination of a crystal–chemical‐point analyses using electron microscopy to obtain the structural formulae of the palygorskite crystals, and studied using high‐resolution X‐ray diffraction. The data show evidence that the palygorskite used by non‐Aztec cultures, such as the Maya, is compatible with palygorskite from known sources in the Yucatan Peninsula, while the palygorskite used by the Aztec culture is different in its structure and has an origin that is still unknown.

Kinetic analysis of the multistep thermal decomposition of Maya Blue-type pigments to evaluate thermal stability

This study aimed to evaluate the practical usefulness of kinetic deconvolution analysis (kDa) as a means to obtain the kinetic information on specific reaction steps that characterize the thermal properties of materials for various purposes. The partially overlapping multistep thermal decomposition of Maya Blue (MB)-type pigments was used as an example reaction. Red and yellow MB-type pigment materials, composed of a fibrous clay mineral and an organic dye, were synthesized using palygorskite and sepiolite as the clay minerals and Methyl Red and Alizarin as red and yellow dyes, respectively. The multistep thermal decompositions of the MB-type pigments were investigated using thermogravimetry. The thermoanalytical data were deconvoluted into individual component reaction steps using an empirical kDa technique based on a cumulative kinetic equation that considers the contribution of each reaction step to the overall thermal decomposition. By comparing the kDa results for the thermal decomposition of the composites with those for the decomposition of pure palygorskite and sepiolite, the thermal decomposition steps for the incorporated organic dyes were extracted from the multistep thermal decompositions of the MB-type pigments. Finally, the thermal stabilities of MB-type pigments comprising different clay minerals and organic dyes were compared using the kinetic results extracted for the reaction step associated with the decomposition of the organic dyes.

Shades of blue: non-invasive spectroscopic investigations of Maya blue pigments. From laboratory mock-ups to Mesoamerican codices

Maya blue is a hybrid pigment where an organic component, indigo, is incorporated in a porous clay. Despite its widespread use in the Mesoamerican artistic production and numerous studies devoted to understand the type of interactions between indigo and the host framework, its technology has not been completely unravelled yet. In this study portable non-invasive UV–vis reflection spectroscopy is proposed as a robust method for in situ investigation of Maya blue pigments. Laboratory mock-ups of powder Maya blue have been prepared employing different synthesis procedures (varying the nature of: clays, indigo–clay ratios, heating temperatures and time). The goodness of the prepared Maya blue samples—namely the occurrence of indigo–clay interactions—have been probed by micro-Raman spectroscopy and related UV–vis spectral markers have been identified. DFT calculations as well have been performed to deeply explain UV–vis profiles. The set of spectral markers have been finally exploited to interpret spectra recorded on Mesoamerican pictorial codices, through a multi-technique approach based on exploring the UV–Vis properties of the blue paint supported by the FT-IR vibrational study of the inorganic clays. The characterization of blue colours on pre-Hispanic and colonial Mesoamerican codices contribute to a better understanding of the compositional variability of these painting materials and to point out the existence of different technological traditions of colour preparation in ancient Mesoamerica.

New Hints on the Maya Blue Formation Process by PCA-Assisted In Situ XRPD/PDF and Optical Spectroscopy.

The exact recipe to prepare the ancient Maya Blue (MB), an incredibly resistant and brilliant pigment prepared from indigo (dye) and Palygorskite (clay), is lost to the ages. To unravel the key features of the MB formation process, several inorganic-dye couples were heated to 200 °C and cooled to RT, to investigate their reactivity and the diffusion and degree of sequestration of the dye into the inorganic host. In situ XRPD/PDF and fiber optic reflectance spectroscopy (FORS) data, along with TGA, provided a comprehensive overview on MB formation mechanism. XRPD/PDF gave information on long/short range behaviors of water desorption/adsorption and indigo sequestration, while TGA and in situ FORS gave information on mass and optical changes within temperature. Ex situ dye removal was used to understand the sample stability after the thermal treatment. A statistical approach based on principal component analysis was exploited to efficiently and jointly analyze the ≈3000 collected patterns. MB formation starts below 110 °C with disordered distribution of indigo within the channels, reaching maximum reaction speed and higher ordering at 150 °C. Above 175 °C, color changes and a stronger sequestration of indigo into framework channels are observed, whereas the affinity for water is dramatically reduced. The origin of different colors, hues, and stability in historical MB samples can then be explained in terms of different thermal histories of the starting mechanical indigo/palygorskite mixtures.

Composition and Color of Maya Blue: Reexamination of Literature Data Based On the Dehydroindigo Model

An analysis of literature data studying the composition and color of Maya blue (MB) type materials prepared from indigo, dehydroindigo, and different aluminosilicates, accompanied by new spectral data, is presented. After thermal treatment at above 100 °C, indigo-based specimens displayed Raman and UV–vis spectroscopic features common to those of equivalent dehydroindigo-based replicants, thus supporting the so-called dehydroindigo model (J. Phys. Chem. B 2006, 110, 6027–6039) in which the dehydroindigo/indigo ratio, increasing with temperature, is crucial to determine the color of MB and its variability. The current analysis supports the view of MB as a polyfunctional hybrid material just characterized by the presence of different organic components, each one distributed in topological isomers differently attached to the clay support. On the basis of the comparison of spectral data for different channeled silicates (among others, palygorskite, sepiolite, and montmorillonite clays, and different zeolites), we proposed a view on the color characteristics of Maya blue-type specimens as defined by the compromise between trapping ability for indigo molecules and facility to promote the oxidation of indigo to dehydroindigo.

Probing the Indigo Molecule in Maya Blue Simulants with Resonance Raman Spectroscopy

Maya blue (MB) simulants were prepared from mixtures of indigo and palygorskite (ind–paly) and investigated by resonance Raman and UV–vis absorption spectroscopies together with thermogravimetric analysis, aiming to enlarge the understanding of the dye–clay interaction, the relationship between color and chemical stability, and the alleged formation of dehydroindigo (DHI); for comparative purposes, other simulants were prepared using sepiolite, laponite, and montmorillonite. The results obtained here suggest that the greenish hue that develops when the ind–paly is heated seems to be linked with a decrease in the indigo molecular symmetry, which causes an increase in the oscillator strength of an absorption band at 500 nm (forbidden under the C2h symmetry) and a bathochromic shift and narrowing of the intense electronic transition at 657 nm (indigo). The DHI characteristic features are not observed in the resonance Raman spectrum (457.9 nm) of the ind–paly system, contrary to what happens with sepiolite, L...

A ratiometric nanosensor based on lanthanide-functionalized attapulgite nanoparticle for rapid and sensitive detection of bacterial spore biomarker

Since the 2001 anthrax attacks, researchers have focused on the development of a bacterial spore biomarker detector with rapid response time and high sensitivity and selectivity. Hence, a ratiometric fluorescent nanosensor based on lanthanide-functionalized attapulgite (Atta) was designed and prepared using dye-doped Atta as an internal reference. Atta, which is famous because of Maya Blue, is a hydrated magnesium aluminum silicate present in nature, with pronounced adsorption and a large specific surface area rich in silicon hydroxyl. The adsorption of dye molecules benefits the formation of an internal reference with orange fluorescence. Meanwhile, silicon hydroxyl would be available for terbium (Tb3+) complex grafting, which favors the sensitization of the bacterial spore biomarker. With increasing dipicolinic acid (DPA) concentrations, energy transfer from DPA to Tb3+ gradually enhanced, thereby resulting in strong and predominant green fluorescence. The ratiometric fluorescence intensity is highly sensitive. It has a limit of detection of 9.8 nM, which is much lower than the infectious dosage of Bacillus anthracis spores (60 μM) for humans. The rapid response time (10s), high selectivity, and reliable and practical performances in actual applications make this ratiometric fluorescent nanosensor useful in the detection of biomarkers for various bacterial spores. Moreover, the reported construction of visual ratiometric detection system follows the sustainable development idea of ‘‘from nature, for nature, into the nature’’ and promotes the use of naturally renewable resources to produce promising and eco-friendly functional materials for various applications.

Trapping and diffusion of organic dyes inside of palygorskite clay: The ancient Maya Blue pigment

The Maya Blue is an artificial colorant with a remarkable stability to chemical attacks and a characteristic pale blue color, with tonalities going from greenish to turquoise. A systematic study of the energetics, structural, bonding and electronic properties of the unusual stable pigment known as Maya Blue is presented. Total energy calculations based on density functional theory are used. Particular attention is paid to the high stability of the Maya blue pigment. We present a comparative study of the energetic barriers for indigo and dehydroindigo in the tunnels taking into account the presence of aluminum in the palygorskite. A clay-framework dependence for the indigo diffusion and a blocking due to dehydroindigo is shown by the binding energy as the molecules take several positions into the tunnels. In the hybrid dye-clay system, the high binding energy is due to the strong hydrogen bonds of carbonyl and amine functional groups of the dyes with the structural water molecules at the edge of the dioctahedral layer in the clay. The electronic and optical properties near the Fermi level in the nanostructured Maya blue are exclusively due to the slightly modified electronic states from the molecules with no contribution from the clay. Indigo and dehydroindigo show a red- and blue-shifted, respectively.

Colorful Superamphiphobic Coatings with Low Sliding Angles and High Durability Based on Natural Nanorods.

Superamphiphobic coatings with low sliding angles (SAs) and high durability are very attractive in academic and industrial areas but are very challenging to invent. Here, inspired by Maya Blue, we report for the first time colorful superamphiphobic coatings with low SAs and high durability by the combination of natural palygorskite (PAL) nanorods and organosilanes. The coatings were characterized using a wide range of electron microscopy and other analytical techniques. Different from the previously reported methods, the micro/nanostructure of the superamphiphobic coatings were constructed by using the abundant natural PAL nanorods as the building blocks. Superamphiphobicity of the coatings depends on surface morphology and chemical composition of the coatings, which can be regulated by the concentrations of PAL and organosilanes. The colorful superamphiphobic coatings feature high contact angles and low SAs for various liquids, including water and n-decane. The coatings also showed high mechanical, environmental, chemical, and thermal durability even under harsh conditions. Moreover, the coatings in different colors with comparable superamphiphobicity and durability can be prepared using different cationic dyes applied onto various substrates via the same approach. The colorful superamphiphobic coatings with low SAs and high durability may be useful in various fields, e.g., anticreeping of oils and restoration of cultural relics.

Time-Resolved Spectroscopy of Indigo and of a Maya Blue Simulant

Maya Blue is a puzzling pigment found in objects produced by the ancient Maya civilization. It is a combination of indigo and palygorskite, and it is well-known for the high chemical and photochemical stability of the dye promoted by the clay confined environment. This pigment has survived over 1500 years, and it was first thought to be purely inorganic. The reasons for such stability have been investigated over the past years, and it may involve hydrogen bonds, complexation, and oxidation to dehydroindigo. However, these theories are not completely understood, and more evidence about indigo/palygorskite interactions must be obtained. In this study indigo and a Maya Blue simulant pigment were, for the first time, studied by transient absorption (TA) and time-resolved infrared (TRIR) spectroscopy. From such analysis it was possible to investigate the electronic excited states of indigo and the photochemistry behavior of the dye when interacting with the palygorskite. Concerning the TRIR measurements, the s...

Nanocompósitos de poli(álcool vinílico) contendo materiais híbridos mimetizando o pigmento Azul Maya

Resumo De forma a mimetizar o pigmento Azul Maya, dois corantes azo (alaranjado de metila - AM e vermelho congo - VC) foram inseridos na estrutura porosa da paligorsquita. Os materiais híbridos foram caracterizados por difração de raios X, espectroscopia de energia dispersiva, microscopia eletrônica de varredura, espectroscopia na região do ultravioleta-visível e análise superficial (área superficial por BET, tamanho e volume de poros por BJH). Após dispersar os materiais híbridos no poli(álcool vinílico), filmes coloridos e transparentes foram obtidos por casting úmido. Após acondicionamento em uma dessecador por uma semana a uma umidade controlada de 43 ± 2% os filmes foram avaliados em relação as suas propriedades mecânicas. De modo geral, o material PVA-PGS/AM teve um aumento no módulo de Young, tensão de ruptura e redução do alongamento enquanto que a paligorsquita bruta e PVA-PGS/VC apresentaram um comportamento oposto.