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X-ray tomography has become an indispensable tool for studying complex 3D interior structures with high spatial resolution. Three-dimensional imaging using soft X-rays offers powerful contrast mechanisms but has seen limited success with tomography due to the restrictions imposed by the much lower energy of the probe beam. The generalized geometry of laminography, characterized by a tilted axis of rotation, provides nm-scale 3D resolution for the investigation of extended (mm range) but thin (µm to nm) samples that are well suited to soft X-ray studies. This work reports on the implementation of soft X-ray laminography (SoXL) at the scanning transmission X-ray spectromicroscope of the PolLux beamline at the Swiss Light Source, Paul Scherrer Institut, which enables 3D imaging of extended specimens from 270 to 1500 eV. Soft X-ray imaging provides contrast mechanisms for both chemical sensitivity to molecular bonds and oxidation states and magnetic dichroism due to the much stronger attenuation of X-rays in this energy range. The presented examples of applications range from functionalized nanomaterials to biological photonic crystals and sophisticated nanoscaled magnetic domain patterns, thus illustrating the wide fields of research that can benefit from SoXL.
Assuntos
Meios de Contraste/química , Imageamento Tridimensional/métodos , Nanoestruturas/química , Tomografia por Raios X/métodos , Meios de Contraste/uso terapêutico , Humanos , Magnetismo , Microscopia Eletrônica de Varredura , Nanoestruturas/uso terapêutico , Fótons , Radiografia , Raios XRESUMO
Focal stack (FS) is an effective technique for fast 3D imaging in high-resolution scanning transmission X-ray microscopy. Its crucial issue is to assign each object within the sample to the correct position along the optical axis according to a proper focus measure. There is probably information loss with previous algorithms for FS reconstruction because the old algorithms can only detect one focused object along each optical-axial pixel line (OAPL). In this study, we present an improved FS algorithm, which utilizes an elaborately calculated threshold for normalized local variances to extract multiple focused objects in each OAPL. Simulation and experimental results show its feasibility and high efficiency for 3D imaging of high contrast, sparse samples. It is expected that our advanced approach has potential applications in 3D X-ray microscopy for more complex samples.
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Light-mediated killing of pathogens by cationic photosensitizers (PS) is a promising antimicrobial approach avoiding resistance as being present upon the use of antibiotics. In this study we focused on the impact of the substituents in phenalen-1-one PS. Photodynamic efficacy depending on positively charged moieties including a primary aliphatic, quaternary aliphatic, aromatic ammonium and a guanidinium cation was investigated against Gram-positive and Gram-negative pathogens. Considering the altered steric demand and lipophilicity of these functional groups we deduced a structure-activity relationship. SAGUA was the most potent PS in this series reaching a maximum efficacy of ≥6log10 steps of bacteria killing at a concentration of 10 µM upon irradiation with blue light (20 mW cm(-2)) for 60 s (1.2 J cm(-2)) without exhibiting inherent dark toxicity. Its guanidinium moiety may be able to form strong bidentate and directional hydrogen bonds to carboxylate groups of bacterial surfaces in addition to ionic charge attraction. This may supplement fast and effective antimicrobial activity.
Assuntos
Antibacterianos/química , Antibacterianos/farmacologia , Fenalenos/química , Fotoquimioterapia , Fármacos Fotossensibilizantes/química , Fármacos Fotossensibilizantes/farmacologia , Actinomyces/efeitos dos fármacos , Antibacterianos/síntese química , Cátions/química , Relação Dose-Resposta a Droga , Enterococcus faecalis/efeitos dos fármacos , Escherichia coli/efeitos dos fármacos , Testes de Sensibilidade Microbiana , Estrutura Molecular , Fármacos Fotossensibilizantes/síntese química , Staphylococcus aureus/efeitos dos fármacos , Streptococcus mutans/efeitos dos fármacos , Relação Estrutura-AtividadeRESUMO
Zone-plate-based scanning transmission soft X-ray microspectroscopy (STXM) is a well established technique for high-contrast imaging of sufficiently transparent specimens (e.g. ultrathin biological tissues, polymer materials, archaeometric specimens or magnetic thin films) with spatial resolutions in the regime of 20 nm and high spectroscopic or chemical sensitivity. However, due to the relatively large depth of focus of zone plates, the resolution of STXM along the optical axis so far stays unambiguously behind for thicker X-ray transparent specimens. This challenge can be addressed by the implementation of a second zone plate in the detection pathway of the beam, resulting in a confocal arrangement. Within this paper a first proof-of-principle study for a confocal STXM (cSTXM) and an elaborate alignment procedure in transmission and fluorescence geometry are presented. Based on first confocal soft X-ray micrographs of well known specimens, the advantage and limitation of cSTXM as well as further development potentials for future applications are discussed.
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This study focuses on the structure-response relationship of symmetrically substituted phenothiazinium dyes. Four hydrophilic derivatives with the ability of additional hydrogen bonding (, ) or additional electrostatic interaction (, ) were synthesized, photophysically characterized and compared to the parent compound methylene blue (MB, ) and a lipophilic derivative () without additional coordination sites. Derivative was most effective against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli reaching a maximum photodynamic efficacy of >5log10 steps (≥99.999%) of bacteria killing in 10 minutes (5 µM, 30 J cm(-2)) without inherent dark toxicity after one single treatment with the incoherent light source PDT1200 (λmax = 660 nm, 50 mW cm(-2)). Interestingly, one derivative with two additional primary positive charges () showed selective killing of Escherichia coli (5 µM, 30 J cm(-2), 4log10 steps inactivation (≥99.99%)) and no antimicrobial effect on Staphylococcus aureus. This might allow the development of a new generation of photosensitizers with higher antimicrobial efficacy and selectivity for future applications.
Assuntos
Anti-Infecciosos/farmacologia , Azul de Metileno/análogos & derivados , Fármacos Fotossensibilizantes/farmacologia , Anti-Infecciosos/síntese química , Anti-Infecciosos/química , Relação Dose-Resposta a Droga , Escherichia coli/efeitos dos fármacos , Escherichia coli/efeitos da radiação , Ligação de Hidrogênio , Interações Hidrofóbicas e Hidrofílicas , Luz , Azul de Metileno/química , Azul de Metileno/farmacologia , Estrutura Molecular , Processos Fotoquímicos , Fármacos Fotossensibilizantes/síntese química , Fármacos Fotossensibilizantes/química , Oxigênio Singlete/química , Análise Espectral , Staphylococcus aureus/efeitos dos fármacos , Staphylococcus aureus/efeitos da radiação , Eletricidade EstáticaRESUMO
Highly resistant endospores may cause severe problems in medicine as well as in the food and packaging industries. We found that bacterial endospores can be inactivated quickly with reactive oxygen species (ROS) that were generated by a new generation of flavin photosensitizers. Flavins like the natural compound vitamin B2 are already known to produce ROS but they show a poor antimicrobial photodynamic killing efficacy due to the lack of positive charges. Therefore we synthesized new flavin photosensitizers that have one (FLASH-01a) or eight (FLASH-07a) positive charges and can hence attach to the negatively charged surface of endospores. In this study we used standardized Bacillus atrophaeus endospores (ATCC 9372) as a biological surrogate model for a proof-of-concept study of photodynamic inactivation experiments using FLASH-01a and FLASH-07a. After incubation of spores with different flavin concentrations, the flavin derivatives were excited with blue light at a light dose of 70 J cm(-2). The inactivation of spores was investigated either in suspension or after attachment to polyethylene terephthalate (PET) surfaces. Incubation of spores suspended in Millipore water with 4 mM FLASH-01a for 10 seconds and irradiation with blue light for 10 seconds caused a biologically relevant decrease of spore survival of 3.5 log10 orders. Using FLASH-07a under the same conditions we achieved a decrease of 4.4 log10 orders. Immobilized spores on PET surfaces were efficiently killed with 7.0 log10 orders using 8 mM FLASH-07a. The total treatment time (incubation + irradiation) was as short as 20 seconds. The results of this study show evidence that endospores can be fastly and effectively inactivated with new generations of flavin photosensitizers that may be useful for industrial or medical applications in the future.
Assuntos
Bacillus/efeitos dos fármacos , Bacillus/fisiologia , Flavinas/farmacologia , Luz , Fármacos Fotossensibilizantes/farmacologia , Riboflavina/análogos & derivados , Anti-Infecciosos/síntese química , Anti-Infecciosos/química , Anti-Infecciosos/farmacologia , Bacillus/efeitos da radiação , Bacillus/ultraestrutura , Linhagem Celular , Sobrevivência Celular/efeitos dos fármacos , Sobrevivência Celular/efeitos da radiação , Relação Dose-Resposta a Droga , Flavinas/síntese química , Flavinas/química , Humanos , Microscopia Eletrônica de Transmissão , Fármacos Fotossensibilizantes/síntese química , Fármacos Fotossensibilizantes/química , Polietilenotereftalatos/química , Oxigênio Singlete/química , Esporos Bacterianos/efeitos dos fármacos , Esporos Bacterianos/efeitos da radiação , Esporos Bacterianos/ultraestrutura , Água/químicaRESUMO
Quantitative studies of soft X-ray induced radiation damage in zone-plate-based X-ray microspectroscopy have so far concentrated on investigations of homogeneous specimens. However, more complex materials can show unexpected radiation-induced behaviour. Here a quantitative radiochemical analysis of biological tissue from Xantophan morganii praedicta eyes is presented. Contrast enhancement due to tissue selective mass loss leading to a significant improvement of imaging quality is reported. Since conventional quantitative analysis of the absorbed dose cannot conclusively explain the experimental observations on photon-energy-dependent radiation damage, a significant contribution of photo- and secondary electrons to soft matter damage for photon energies above the investigated absorption edge is proposed.
Assuntos
Olho Composto de Artrópodes/efeitos da radiação , Traumatismos Oculares/etiologia , Mariposas , Microtomografia por Raio-X/métodos , Animais , Olho Composto de Artrópodes/ultraestrutura , Meios de Contraste/farmacologia , Aumento da Imagem/instrumentação , Aumento da Imagem/métodos , Microscopia Eletrônica de Transmissão , Doses de Radiação , Razão Sinal-Ruído , Coloração e Rotulagem , Microtomografia por Raio-X/instrumentaçãoRESUMO
Surfaces can be coated with photosensitizer molecules, which generate singlet oxygen ((1)O2) when the surface is exposed to light. (1)O2 may diffuse from the coating and has the potential to kill microorganisms present on the surface. In the present study a derivative of the meso-tetraphenylporphyrin (TPP) was immobilized onto polyurethane (PU) after being sprayed and polymerized as a thin layer onto poly-methylmethacrylate (PMMA). PU is gas permeable and thus a sufficient amount of oxygen reaches the photosensitizer in this coating. The surface generation of (1)O2 and its diffusion were investigated by detecting its luminescence at 1270 nm and a tri-iodide assay. Antimicrobial photodynamic surface effects were tested on Staphylococcus aureus. The spectrally resolved detection of (1)O2 luminescence yielded a clear peak at 1275 nm. The time-resolved luminescence showed multi-exponential decay, revealing rise and decay times in the range of 5-2 × 10(2)µs. The photodynamic inactivation of S. aureus was monitored at different photosensitizer concentrations and radiant exposures of light. A photodynamic killing of >99.9% (>3log10-steps) was achieved within an irradiation time of 30 min. The photodynamic killing on the bioactive surface confirmed the antimicrobial effect of (1)O2 that was generated in the PU-coating and reached the bacteria by diffusion.
Assuntos
Materiais Revestidos Biocompatíveis/química , Materiais Revestidos Biocompatíveis/farmacologia , Fármacos Fotossensibilizantes/farmacologia , Poliuretanos/química , Porfirinas/química , Oxigênio Singlete/farmacologia , Staphylococcus aureus/fisiologia , Adsorção , Anti-Infecciosos/síntese química , Anti-Infecciosos/farmacologia , Apoptose/efeitos dos fármacos , Luz , Teste de Materiais , Fármacos Fotossensibilizantes/química , Porfirinas/efeitos da radiação , Oxigênio Singlete/química , Staphylococcus aureus/efeitos dos fármacosRESUMO
OBJECTIVES: The aim of this study was to demonstrate that the periodontal pathogen Aggregatibacter actinomycetemcomitans (AA) can be killed by irradiation with blue light derived from a LED light-curing unit due to its endogenous photosensitizers. MATERIALS AND METHODS: Planktonic cultures of AA and Escherichia coli were irradiated with blue light from a bluephase® C8 light-curing unit with an emission peak at 460 nm, which is usually applied for polymerization of dental resins. A CFU-assay was performed for the analysis of viable bacteria after treatment. Moreover, bacterial cells were lysed and the lysed AA and E. coli were investigated for generation of singlet oxygen. Spectroscopic measurements of lysed AA and E. coli were performed and analyzed for characteristic absorption and emission peaks. RESULTS: A light dose of 150 J/cm(2) induced a reduction of ≥5 log10 steps of viable AA, whereas no effect of blue light was found against E. coli. Spectrally resolved measurements of singlet oxygen luminescence showed clearly that a singlet oxygen signal is generated from lysed AA upon excitation at 460 nm. Spectroscopic measurements of lysed AA exhibited characteristic absorption and emission peaks similar to those of known porphyrins and flavins. CONCLUSIONS: AA can be inactivated by irradiation with blue light only, without application of an exogenous photosensitizer. CLINICAL RELEVANCE: These results encourage further studies on the potential use of these blue light-mediated auto-photosensitization processes in the treatment of periodontitis for the successful inactivation of Aggregatibacter actinomycetemcomitans.
Assuntos
Aggregatibacter actinomycetemcomitans/efeitos da radiação , Lâmpadas de Polimerização Dentária , Luz , Escherichia coli/efeitos da radiação , Humanos , Doenças Periodontais/microbiologia , Oxigênio Singlete , Espectrometria de FluorescênciaRESUMO
We have prepared a series of new and some literature-reported GABA-amides and determined their effect on the activation of GABAA-receptors expressed in CHO cells. Special attention was paid to the purification of the target compounds to remove even traces of GABA contaminations, which may arise from deprotection steps in the synthesis. GABA-amides were previously reported to be partial, full or superagonists. In our hands these compounds were not able to activate GABAA-receptor channels in whole-cell patch-clamp recordings. New GABA-amides, however, gave moderate activation responses with a clear structure-activity relationship suggesting some of these compounds as promising molecular tools for the functional analysis of GABAA-receptors.
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Crystalline organic semiconducting thin films from the benchmark molecule C8-BTBT-C8 were obtained using physical vapor deposition and various solution-based methods. Utilizing atomic force microscopy and X-ray spectromicroscopy, we illustrate the influence of the underlying growth mechanism and determine the highly preparation-dependent orientation of the thiophene backbone. We observe a continuous trend for crystalline C8-BTBT-C8 thin film domains to extend into the square millimeter-range under near-equilibrium growth conditions. For such well-defined systems, electron diffraction tomography allows us to precisely determine the unit cell directly after film deposition and to reveal an 8° molecular tilt angle with respect to the surface normal. This finding is in almost perfect accordance with the values derived from near-edge X-ray absorption fine structure linear dichroism. Within this work, we shine a light on both the successes and challenges connected to the realization of potent, thiophene-based semiconducting films, paving the way toward square centimeter-sized ultrathin organic crystals and their application in organic circuitry.
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Many European sculptures and altarpieces from the Middle Ages were decorated with Zwischgold, a bilayer metal leaf with an ultra-thin gold face backed by silver. Zwischgold corrodes quickly when exposed to air, causing the surface of the artefact to darken and lose gloss. The conservation of such Zwischgold applied artefacts has been an obstinate problem. We have acquired quantitative, 3D nanoscale images of Zwischgold samples from 15th century artefacts and modern materials using ptychographic X-ray computed tomography (PXCT), a recently developed coherent diffractive imaging technique, to investigate the leaf structure and chemical state of Zwischgold. The measurements clearly demonstrate decreasing density (increasing porosity) of the leaf materials and their corrosion products, as well as delamination of the leaves from their substrate. Each of these effects speak to typically observed issues in the conservation of such Zwischgold applied artefacts. Further, a rare variant of Zwischgold that contains extremely thin multiple gold layers and an overlapping phenomenon of Zwischgold with other metal leaves are observed through PXCT. As supportive data, scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray analysis (EDX) were performed on the medieval samples.
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Photodynamic inactivation (PDI) of pathogenic bacteria is a promising technology in different applications. Thereby, a photosensitizer (PS) absorbs visible light and transfers the energy to oxygen yielding reactive oxygen species (ROS). The produced ROS are then capable of killing microorganisms via oxidative damage of cellular constituents. Among other PS, some flavins are capable of producing ROS and cationic flavins are already successfully applied in PDI. When PDI is used for example on tap water, PS like flavins will encounter various ions and other small organic molecules which might hamper the efficacy of PDI. Thus, the impact of carbonate and phosphate ions on PDI using two different cationic flavins (FLASH-02a, FLASH-06a) was investigated using Staphylococcus aureus and Pseudomonas aeruginosa as model organisms. Both were inactivated in vitro at a low light exposure of 0.72 J cm-2. Upon irradiation, FLASH-02a reacts to single substances in the presence of carbonate or phosphate, whereas the photochemical reaction for FLASH-06a was more unspecific. DPBF-assays indicated that carbonate and phosphate ions decreased the generation of singlet oxygen of both flavins. Both microorganisms could be easily inactivated by at least one PS with up to 6 log10 steps of cell counts in low ion concentrations. Using the constant radiation exposure of 0.72 J cm-2, the inactivation efficacy decreased somewhat at medium ion concentrations but reached almost zero for high ion concentrations. Depending on the application of PDI, the presence of carbonate and phosphate ions is unavoidable. Only upon light irradiation such ions may attack the PS molecule and reduce the efficacy of PDI. Our results indicate concentrations for carbonate and phosphate, in which PDI can still lead to efficient reduction of bacterial cells when using flavin based PS.
Assuntos
Carbonatos/metabolismo , Flavinas/uso terapêutico , Fosfatos/metabolismo , Fotoquimioterapia/métodos , Fármacos Fotossensibilizantes/uso terapêutico , Infecções por Pseudomonas/tratamento farmacológico , Staphylococcus aureus/efeitos dos fármacos , Flavinas/química , Humanos , Espécies Reativas de Oxigênio/metabolismo , Análise EspectralRESUMO
The excellent craftsmanship of ancient Oriental and Central Asian textile dyers is already demonstrated in the remarkable brilliance and fastness of the colours of the so-called Pazyryk carpet, the by far oldest pile carpet found to date. This specimen resembles the advanced craftsmanship of Iron Age Central Asian textile production. We have employed synchrotron-based µ-XRF imaging to detect the distribution of metal organic pigments within individual fibres of the Pazyryk carpet (about 2500 years old) and compare the results to wool fibres, which we prepared according to traditional Anatolian dyeing recipes. We observe congruent pigment distribution within specimens from the Pazyryk carpet and natural wool fibres that we have fermented prior to dyeing. Therefore, we conclude that the superior fermentation technique has been utilized about 2000 years earlier than known so far.
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Ammonium ions are ubiquitous in chemistry and molecular biology. Considerable efforts have been undertaken to develop synthetic receptors for their selective molecular recognition. The type of host compounds for organic ammonium ion binding span a wide range from crown ethers to calixarenes to metal complexes. Typical intermolecular interactions are hydrogen bonds, electrostatic and cation-π interactions, hydrophobic interactions or reversible covalent bond formation. In this review we discuss the different classes of synthetic receptors for organic ammonium ion recognition and illustrate the scope and limitations of each class with selected examples from the recent literature. The molecular recognition of ammonium ions in amino acids is included and the enantioselective binding of chiral ammonium ions by synthetic receptors is also covered. In our conclusion we compare the strengths and weaknesses of the different types of ammonium ion receptors which may help to select the best approach for specific applications.
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Focused soft X-ray beam induced deposition (FXBID) is a novel technique for direct-write nanofabrication of metallic nanostructures from metal organic precursor gases. It combines the established concepts of focused electron beam induced processing (FEBIP) and X-ray lithography (XRL). The present setup is based on a scanning transmission X-ray microscope (STXM) equipped with a gas flow cell to provide metal organic precursor molecules towards the intended deposition zone. Fundamentals of X-ray microscopy instrumentation and X-ray radiation chemistry relevant for FXBID development are presented in a comprehensive form. Recently published proof-of-concept studies on initial experiments on FXBID nanolithography are reviewed for an overview on current progress and proposed advances of nanofabrication performance. Potential applications and advantages of FXBID are discussed with respect to competing electron/ion based techniques.
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Development of high-quality organic nanoparticle inks is a significant scientific challenge for the industrial production of solution-processed organic photovoltaics (OPVs) with eco-friendly processing methods. In this work, we demonstrate a novel, robot-based, high-throughput procedure performing automatic poly(3-hexylthio-phene-2,5-diyl) and indene-C60 bisadduct nanoparticle ink synthesis in nontoxic alcohols. A novel methodology to prepare particle dispersions for fully functional OPVs by manipulating the particle size and solvent system was studied in detail. The ethanol dispersion with a particle diameter of around 80-100 nm exhibits reduced degradation, yielding a power conversion efficiency of 4.52%, which is the highest performance reported so far for water/alcohol-processed OPV devices. By successfully deploying the high-throughput robot-based approach for an organic nanoparticle ink preparation, we believe that the findings demonstrated in this work will trigger more research interest and effort on eco-friendly industrial production of OPVs.
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There is a strong market driven need for processing organic photovoltaics from eco-friendly solvents. Water-dispersed organic semiconducting nanoparticles (NPs) satisfy these premises convincingly. However, the necessity of surfactants, which are inevitable for stabilizing NPs, is a major obstacle towards realizing competitive power conversion efficiencies for water-processed devices. Here, we report on a concept for minimizing the adverse impact of surfactants on solar cell performance. A poloxamer facilitates the purification of organic semiconducting NPs through stripping excess surfactants from aqueous dispersion. The use of surfactant-stripped NPs based on poly(3-hexylthiophene) / non-fullerene acceptor leads to a device efficiency and stability comparable to the one from devices processed by halogenated solvents. A record efficiency of 7.5% is achieved for NP devices based on a low-band gap polymer system. This elegant approach opens an avenue that future organic photovoltaics processing may be indeed based on non-toxic water-based nanoparticle inks.
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AIM: Five photoactive compounds with variable elongated alkyl-substituents in a phenalen-1-one structure were examined in view of structural similarity to the antimicrobial agent benzalkonium chloride (BAC). METHODS: All phenalen-1-ones and BAC were evaluated for their antimicrobial properties against Staphylococcus aureus, methicillin-resistant S. aureus, Escherichia coli, Pseudomonas aeruginosa and for their eukaryotic toxicity against normal human epidermal keratinocyte (NHEK) cells to narrow down the BAC-like effect and the photodynamic effect depending on the chemical structure. All compounds were investigated for effective concentration ranges, where a bacterial reduction of 5 log10 is achieved, while an NHEK survival of 80% is ensured. RESULTS: Effective concentration ranges were found for four out of five photoactive compounds, but not for BAC and the compound with BAC-like alkyl chain length. CONCLUSION: Chain length size and polar area of the respective head-groups of phenalen-1-one compounds or BAC showed an influence on the incorporation inside lipid membranes and thus, head-groups may have an impact on the toxicity of antimicrobials.
Assuntos
Antibacterianos/farmacologia , Anti-Infecciosos Locais/farmacologia , Bactérias/efeitos dos fármacos , Compostos de Benzalcônio/farmacologia , Fenalenos/farmacologia , Antibacterianos/química , Antibacterianos/efeitos da radiação , Anti-Infecciosos Locais/química , Anti-Infecciosos Locais/efeitos da radiação , Compostos de Benzalcônio/química , Linhagem Celular , Membrana Celular/química , Escherichia coli/efeitos dos fármacos , Humanos , Queratinócitos/efeitos dos fármacos , Luz , Lipídeos de Membrana/química , Staphylococcus aureus Resistente à Meticilina/efeitos dos fármacos , Fenalenos/química , Fenalenos/efeitos da radiação , Pseudomonas aeruginosa/efeitos dos fármacos , Oxigênio Singlete/química , Staphylococcus aureus/efeitos dos fármacosRESUMO
Many handmade ancient and recent oriental wool carpets show outstanding brilliance and persistence of colour that is not achieved by common industrial dyeing procedures. Anthropologists have suggested the influence of wool fermentation prior to dyeing as key technique to achieve the high dyeing quality. By means of µ-XRF elemental mapping of mordant metals we corroborate this view and show a deep and homogenous penetration of colourants into fermented wool fibres. Furthermore we are able to apply this technique and prove that the fermentation process for ancient specimens cannot be investigated by standard methods due to the lack of intact cuticle layers. This finding suggests a broad range of further investigations that will contribute to a deeper understanding of the development of traditional dyeing techniques. Spectroscopic studies add information on the oxidation states of the metal ions within the respective mordant-dye-complexes and suggest a partial charge transfer as basis for a significant colour change when Fe mordants are used.