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Research Team Uses Coal-Tar Dyes to Analyze Biomolecules

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A woman and a man with lab coats and safety goggles standing in a chemistry lab. © Martina Hengesbach​/​TU Dortmund
The group led by Dr. Irene Regeni and Prof. Guido Clever has managed to integrate multiple colors into self-assembled nanocages for the first time.

A research team led by Prof. Guido Clever from the Faculty of Chemistry and Chemical Biology at TU Dortmund University has discovered new, promising ways of using well-known coal-tar dyes to analyze biomolecules. The results were recently published in the renowned journal Angewandte Chemie International Edition. The journal selected the article as a “Hot Paper,” thus emphasizing the method’s future potential.

The family of dyes that Clever’s team works with has a long tradition along the rivers Rhine, Ruhr and Wupper. These are artificial dyes that were traditionally obtained from coal – more precisely, from coal tar. The early German chemical industry, which evolved into one of the major branches of the economy, particularly in North Rhine-Westphalia, began as early as the 19th century with the production of synthetic, coal-based dyes used for coloring textiles, paper and cosmetics, as well as in coatings and inks. In more advanced applications, these artificial dyes are used as pH indicators and photosensitizers, for example.

Dr. Irene Regeni, a young chemist in the faculty and lead author of the publication, explains that the team works with several colors, also known as chromophores, covering the entire color spectrum of the rainbow with Michler’s ketone (yellow), rhodamine B (pink), malachite green, methylene blue and crystal violet. How does this new “color theory” work in the faculty? Prof. Clever and his team use the synthetic dyes to develop three-dimensional objects that are mere nanometers in size. These objects bind to biomolecules such as DNA or proteins. This makes it easier to analyze certain properties of the molecules.

The intense color of the coal-tar dye is retained

What makes this discovery so innovative is that Guido Clever’s group managed to integrate the chromophores into self-assembled nanocages for the first time, while also retaining their most important property – their intense color. These colors make it easier than usual to measure a crucial property of biomolecules: chirality. A molecule or an object in general is considered chiral if it cannot be superimposed onto its mirror image – like our hands. Chirality is an important factor, for example, when it comes to how drugs interact with biological structures.

The chiral signatures of molecules are difficult to tell apart, particularly in complex mixtures. “This is where our probes come in,” says Dr. Irene Regeni. “They are mixed with the biomolecules, such as DNA. These biomolecules then transfer their chiral properties to the synthetic nano-objects. Because of their intense color, the properties can then be read out with light.” This is done using a device that can measure the rotation of polarized light. 3D glasses at the movies work in a similar way.

“We can now produce a whole color palette of these nanocages,” explains Prof. Clever. “We can then use that palette as a basis for developing selective analytical methods for DNA or other biological samples, for instance.” It remains to be seen whether this basic research can help revive coal-tar dyes in terms of both economics and production, and in what way. These fundamental developments are already showing promising potential for applications in the areas of sustainable synthesis methods, new materials, biodiagnostics and even DNA-sensing active ingredients.

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