A bit of Chem: Flavonoids and Anthraquinones

So, someone asked a question while I was away. It was a good question.

It had to do with natural dyes and flavonoids, and how they compare to anthraquinones.

“What?” some of you are no doubt querying.

The Difference Between Dyes

Fiber Chemistry

Anthraquinones are a common structure for acid dyes to be based off. Flavonoids are a common structure for some natural dyes.

So here’s the most basic structure of an anthraquinone:

Anthraquinone

And here’s the most basic structure of a flavenoid:
Flavone

You can see, they’re pretty similar. Big difference is that the phenol rings (the hexagons) have a linker in flavenoid, and not in the anthraquinone. As you get more complicated, that starts to seem a little less important.

One important thing to note here is that these basic structures make the chemical colored, that’s actually the most defining feature of a dye chemical. The “dye” aspect is usually added on after the fact, or if it’s a natural dye, is a lucky chance addition for the dyer.

Here are some simple-ish anthraquinone dyes:

dyes

Acid Blue, Vat Violet, the dye that makes your gas blue, and Disperse Red

These are dyes made synthetically, but the colors from lichen, fungi, rhubarb, buckthorn, and senna are all anthraquinone colors as well.

Here’s an example of a far more complex flavenoid dye. This is marigold dye, “patulitin.”

marigold

And here’s a few flavenoid colors…

Luteolin, the yellow from weld:

Luteolin

Quercitin, the yellow from onions (and part of the color from oak and tea):

Quercitin

Which is all a very long, roundabout way to say that structurally they are very similar. Most of the natural dye flavenoids are in the yellow/orange range (but not universally so), while the anthraquinones are mostly in the blue range (but not universally so). The main difference between them as DYES, is that with most flavenoids you need a mordant in order to serve as a linker to bind it to the fiber, while most anthraquinone dyes are synthesized with an acid moiety like a sulfate or the like. But the natural ones (aforementioned lichen, etc) will need a mordant, just like the flavenoids.

Hope that answers your question!

That’s all for now!
~The Gnome

Fae

2 thoughts on “A bit of Chem: Flavonoids and Anthraquinones

  1. Is there something about the molecular bonds in these guys that makes colors? I’m pretty sure you can put hexagons like those in molecules without making dye.

  2. Yes… and no.

    The double rings are key, but not sufficient. Things with a couple/bunch of those in close proximity tend to be colored, but not always. And modifying things that are colored to make other colors is a very hit-and-miss process. Sometimes you’ll get something logical, like a lighter/darker version of the same color. Sometimes it will suddenly change to a whole new color, or lose color entirely.

    What exactly makes a molecule interact with light in just the right way to make color is still very poorly understood.

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