00:43
赤色にも色々あるんです🐞【科学系ポッドキャストの日】
赤色にも色々あるんです🐞【科学系ポッドキャストの日】
赤色にも色々あるんです🐞【科学系ポッドキャストの日】
赤色にも色々あるんです🐞【科学系ポッドキャストの日】
I immediately had to think of five different possible episodes that are all rooted in chemistry.
I actually did have to pare down the episode ideas for once because usually we struggle
to come up with what is going to fit the theme. But this time I'm like wow I can come up with
so many different ways. But I have come down to just two. And I guess it depends on how well the
first one is received. We may or may not make the second episode because colors, as far as people
who are interested in colors in sort of molecular way, or like, you know, in terms of light matter
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interaction, like, you know, it's not like I got a PhD in that, right? But for those of us in like
a more molecular minded people, I guess color comes from chemistry, like chemical colors.
And then there's structural colors. Both are coming from very small structures, I guess
chemical structures are smaller than structural colors that we're talking about. But yes, very
small unit of things that causes color perception in humans. And so I may or may not want to do a
structural color episode in future. Because it's also a fascinating topic. And also an interesting
problem that I encountered in the museum recently. So structural colors interesting, but for now,
let's focus on chemical colors. Now we've got chemical colors, structural is a future thing.
I think for anyone who's having a hard time maybe grasping that chemical colors, yes, you might
think of many types of dyes, you might think of like, you know, the maybe old pigment stories
and where they come from and stuff, which we'll talk about today. structural colors that I have
in mind are like bird feathers, butterfly wings, things like that, where sort of like a
each individual structure, typically in like a nanoscale size in order to exhibit like a
perceivable color to human eyes. And, you know, the changes in that structure,
the unit structures, causes the color perceptions. And those are different from chemical
structures, because chemical structures originate from the molecular structures. So like,
different chemical bond combinations, and what part of chemical bond absorbs what part of the
visible wavelength spectrum. So if, you know, particular combinations of C's and H's and O's
result in absorbing a lot of green light, then you will get a red color perception,
that sort of thing. Which, let me forcibly segue into our topic today, because we're going to talk
about red chemicals that are responsible for chemical colors. Okay, nice. So we're going to
focus on red in particular. That's, that's something we're not only going to focus on red,
we're going to focus on one particular type of chemical compound that exhibits red. Got it. Okay.
All right. Well, I'm ready to dive in. I'm ready to soak myself in this dye or something. I'll come
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up with something more clever. So that's, that's, that's not terrible. That's not terrible.
Okay, so our main character today is called carminic acid.
And I know the name alone doesn't say much to anybody, really. It makes me think of like,
where in the world is Carmen Sandiego, which no listener might know, but that's fine. So
I don't even know what you're talking about. So I'll explain it later. But if you if you look,
Len, at my extremely detailed notes for this episode, I am looking blown away by the detail.
The first figure is the molecular structure of carminic acid.
First figure. Yes. Okay. Ah, yep. I see it.
So it's a fairly chunky molecule. I mean, that being chunky being relative term, I guess,
because for me, more than 12 atom molecules are big. But you know, for protein people,
that's like nothing. Yeah.
I mean, for you're looking at the scale between what you know, chemists usually consider and
biologists usually consider, right? I mean, this is a chunky molecule. So exactly. Do you want to
describe it a little bit in more detail for those listening or, you know, I feel like this is a
limitation of podcast being audio media, which makes it incredibly difficult to describe something
precisely in a visual form. So what I'm going to do instead of making listeners
suffer through my verbal explanation of what a carminic acid looks like,
I'm going to slap this picture onto an artwork of this episode.
Oh, nice. Okay. All right.
You should be able to see what it looks like. Okay.
Okay. Insert picture into audio here. Insert image here. So let's just start.
But first of all, maybe before we go into the details of carminic acid
specifically, so carminic acid is a type of dyes. And I don't know about you,
Len, but have you thought about what is the definition of dyes?
I probably thought about it about five years ago when I taught my little
summer course, but recently, no.
It's just like, I think most people's understanding of dyes is like, it's a colorful stuff.
Sure. That's probably fair, right? A baseline, this stuff is colorful, and maybe I would say
the color sticks to things might be the minimum description.
That's a good point. And I think we're going to get to it soon.
Awesome. Okay.
So sort of like the generic definition of dyes is that they are organic compounds that
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selectively absorbs light in a visible range. So in order for us to see color, it needs to
absorb somewhere in between 350 to 750-ish nanometers in wavelength, because otherwise
we cannot see. And if we cannot see, humans don't consider them as colorful. So that's a
problem for another day. But so if we can see colors that are responsible by organic compounds,
we tend to call them dyes. And this absorption in visible range that happens that we can see
colors, this is specifically due to the conjugated pi system. So most of these dyes comes in different
shapes, but they have fused ring structures, typically, that enables the conjugation of
pi system. We call it generally chromophores, like, you know, center of chromo, the color.
So that's what is responsible for this very distinct colors. And they need to absorb
physically onto a substrate or chemically bond to a substrate in order to be classified as dyes.
Okay.
As opposed to pigments, which is another colorful thing.
So pigments, by definition, they don't bind directly to the substrate, they need to bind
in a medium called binding medium. So this might be your oils in oil painting or acrylics in acrylic
paintings. And they are essentially just coating on top of the substrate. And the binding happens
between binding medium and the substrate rather than substrate and the pigments.
Okay, can I can I recap it so that I understand?
Please, yes.
All right. So I liked the oil painting analogy, because what I'm hearing is that a pigment,
right, you have essentially bound it to the medium, the oil. So those things are attached already.
But the pigment by itself would not necessarily bind to like your canvas.
Yeah, exactly.
It needs to be on that medium, then the medium and the pigment can sort of cover whatever the
surface is. But even that isn't binding. It's just physically kind of drying out or resting on.
Yeah, yeah, yeah. The binding happens really in the binding between the binding medium and
the substrate and the binding medium and the pigments. So pigment is only attached to binding
medium, whereas dyes, they are either physically adsorbed onto the substrate or chemically bonded
onto the surface of the substrate. And that's the biggest differences. I've seen other definitions
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like dyes are soluble in water and pigments are not. I find it to be somewhat misleading because
that's not always the case. So I tend to sort of avoid that descriptors. But it's true that
because of this, you know, different nature of how they stick to surface,
dyes tend to be water soluble and pigments tend to be not soluble in water.
Okay, interesting.
But yeah, yeah. So now you know the differences between dyes and pigments.
And we're specifically today talking about dyes today.
Got it.
All right. So our main character dye, carbonic acid, is a red anthraquinone dyes. And anthraquinone
is just like a fancy name for two benzenes being sandwiched by dicarbonyl type of structures.
Like that's the sort of the backbone structure and there's all sort of fancy dressings around it.
But that's the chromophore. Anthraquinone is a type of chromophore.
So this with the visual that the audience here will have, right, the sort of benzenes
sandwiching a dicarbonyl. Those are the two sort of hexagonal structures with another one in the
middle. It's a three hexagonal structure, which turns out to be, you know, relatively flat
that you will see in the image, right? Okay.
Yeah, yeah, yeah. So that's the part. And on its own, it's yellow and not very soluble in water,
the anthraquinone part itself. But when it's dressed with enough H's and OH's and other
R groups that you can see in the figure that I am not verbally describing,
you, this then becomes soluble in water, which is essential for the dye to be dye, basically.
That makes sense. And these are, so, so carminic acid is a natural product of
scaly insects, especially cochineal, cochineal insects. Apologies.
I, look, nobody's going to complain about that pronunciation. I'm still not convinced that it's
the way we looked it up. So like, it's fine. Wikipedia told me it's cochineal. So it is
cochineal, I want to say. But there's two pronunciations on the Cambridge British
English Dictionary. So like, and they're both kind of that. So like, yeah, it's fine.
The interesting thing, maybe more than a pronunciation of these insects is that they
are like the insects that reside in cactus in places like Peru and Mexico. Yes. And
they're like white little insects. But when you crush them, you get this like,
fluid that is like red and kind of blood like it's kind of creepy.
Very, very horror-esque. We probably should have tried to wait for this until like, you know,
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October, but it's fine.
But yeah, so these are the natural product that carminic acids are extracted from. And the exact
extraction method also changes the final hues that you get in the end when you're using it in a
product. So it's interesting. It's not just that the raw material has all these interesting
properties, but the extraction method also changes the optical properties of these molecules.
Got it. Okay.
And just because I think it's always fun to think about the history of carminic acid.
Carminic acid is actually more prevalent than you think it is. You might just not know
that they are there. They were first used in a sort of recorded case is as early as 700 BC,
which is like Yayoi period in Japan. Wow. Okay.
Yeah. Which is quite far back in the history. Like I said, they were first found in Peru and
Mexico. And when the Spanish colonized the Aztec empire, the Spain began importing this red colors
that were previously unknown to the European populations. And they loved this so much that
they protected this extraction method and recipe of Morden chemistry, which I'm going to talk about
later for like 300 years, basically until the empire died. And they still remain highly prized
pigment in Renaissance and Baroque Europe until the synthetic alternative emerged in the 19th
century. So if you see like these like old masters painting, like Vermeer, Tichon, Raphael,
like all these, like, you know, what you think to be like the classic old school painting, like
Western painting, more likely than not, their reds are these carminic acid reds or carminic acid
derived pigments. Red. Okay. And for those of us who are less fond of oil painting, you can think
the other use of this particular red hues are Catholic Cardinals red robe, like this really
striking red robes that they wear. And also the British military uniforms, you know, those like
ones with a fluffy head, they're wearing the red jacket. Right. And that red also comes from
carminic acid red. Whoa. All right. Yeah. This stuff is everywhere. This stuff is everywhere. Yeah. And
not only used in these kind of like, you know, paintings and fabrics, they're used as food dyes.
They're safe to consume. They have been US FDA approved. And, you know, I'm sure in a lot of
other places, they're usually labeled as E120 in food products. And they are favorite, you know,
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of reds in the food dye reds, because they're shelf stable, they're light stable, they're heat
stable, so you can cook it and they're safe to consume. You may also have seen red 40 in your
ingredients list. This is a synthetic alternative of carminic acid. Okay, these are sort of our
history, you know, how we have known carminic acid to exist in our lives. But even more recently,
people have realized that this very convenient and very safe molecule can be used for
electrochemical modifiers and photosynthesizers. So like your solar cells and stuff like that,
or like for research purposes, off, you know, these like solar cells and other things that
anything that interacts with light, and by basically attaching these carminic acids to
whatever molecules that you want to absorb more of, of specific wavelength, you can either
shift the absorption yield so that you absorb more of what you want. And which is typically the goal
for solar cells, right? So yeah, that's something you can do in research. So very versatile molecule.
Yeah, I mean, it seems to, there's definitely a relationship, right? All of this is still
visual, essentially, even down to the electrochemical, well, maybe the photosynthesizers
more so, but it still has to do right with that bit of sort of control or modification to light.
So yeah, so being able to control light at a molecular level like you can with these carminic
acid is really important for us. So if we take a further sort of zoom into the, you know,
what is responsible for the colors of carminic acid. So again, I would like the listeners to
look back at the profile picture of this main character today, carminic acid, you will realize
that you have that three fused hexagonal shape, and around it is lots of, you know, sticks that
are sticking out with letters like OHS and O's. Yep, I see, I see a whole bunch of them, a bunch
of O8, I see a bunch of hydroxides floating all over the place. So we've got a lot of bonds out
there that might be susceptible. Yeah, exactly. So what happens when you put this kind of molecule
into something like water is that it's going to deprotonate, meaning it's going to lose
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one of the H's around the OHS into the solvent. And then since you did acid chemistry
course, you would know that that changes what in the water?
The pH, well, the pOH, if you prefer the other way around.
Yes, but it changes the acidity of the solvent. And so now I would like you
listeners to see the second picture that I'm going to put into this episode.
It's all the slew of colors from orange to red to deep purple to like pink,
with a label 1, 2, 3, 4, 5, all the way to 14. And that's the value of 1 to 14 is a pH scale.
So depending on the solvent environment, you can force these guys to protonate or deprotonate from
different sites in different amounts, causing it to change the local environment around
the chromophore, the three fused ring part. And that causes it to change the absorption,
which causes the change in the colors that we perceive.
Right. Yep.
So far, so good.
Yep. I'm still with you, I guess, as there may be a need to capture this. So basically,
the molecule at its form that we see on the image, for instance, right, has a particular structure,
both electrically speaking, right, and physically speaking. At this stage, it will absorb and,
you know, reflect certain levels of light. If you start popping off hydrogens, right,
into solution, right, increasing pH, if you do it the other way, decreasing pH,
then what happens is that the electronics within that now start absorbing or, you know,
rejecting differently things of light. I think when I think about this, for anybody who does
some little bit of chemistry, right, I usually point them to the particle in a box model.
So this is just pretend that your, you know, system is in a box, and you have a certain number
of electrons, and those electrons can only make, you know, so many shapes based off of our
understanding of quantum chemistry, right? And so you get energy levels, turns out those energy
level gaps are color, right? Usually visible spectrum, if you have a dot in this case.
Yep.
Yeah.
Yeah, that makes sense to me.
And that sort of gap can change in sort of scale. So the gap size changes, changing the color
perception that we see. So I think carminic acid is just like one of those flukes in nature that
worked in such advantage for humanity, because just by changing the acidic environment that
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these dyes are in, we are able to get all these different hues of colors. However, I think the
most sort of stable format that it likes to be in is the red, the around pH of like 7 point
something that we usually see, which makes sense, water at pH around 7 point something. So, you
know, we most frequently recognize this color at the red hue, but depending on the extraction
method of these colors, as I said previously, very briefly, you can get a different kind of
hues of red from the same molecule, which I think is pretty cool.
It's certainly very cool. I mean, you've sort of shared almost an overabundance of ways in which
this can be used on top of how it can be tuned, right? To sort of adapt itself color, not to
adapt itself, but to be adapted, right? To particular situations.
Yep. So just to like give you one more information on already an information-dense
episode, these types of dyes are called polyacidic dyes. So it's not just carmonic
acid that is polyacidic. It just means different acidity is possible from this one molecule,
depending on the solvent environment. Yeah, you can think about it as being,
it is stable across like a wide pH range, and at each of those pH ranges, it just changes it
enough that you shift this energy level. Yeah, exactly. So that's sort of what carmonic acid
is on its own. However, when we use it for, you know, British military jackets or our food
colorings, it's almost never in the carmonic acid state. It is actually in a complexed state. And
this is where I point you to the third figure, where it's an example of a complexation. So
complexation in chemistry means that, you know, there's usually some sort of chelation agent
that's like, you know, becomes the center of the complexation. And then the surrounding
molecules or ligands, we call it, they will specifically sort of arrange themselves around
that metal, the center, in this case, it's an aluminum metal, and then forms a salt. And that's
sort of like an extra stable format of this molecule rather than floating in an acid.
And now we can precipitate it out as like powder, or things like that. Right. Yeah. For our use.
So this type of complexation, specifically in like a dye chemistry, it's called mordant.
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And mordant, yes, I know, it's like a little funny word. Mordant, the word mordant comes from
the Latin mordere, which means to bite. Okay, bite into, like, I don't know, you, you bite
into your burger or something like you bite. Okay. With your teeth. Yeah, yeah. And that's kind of
fitting, because that's, that implies that it forms a strong bond between biter and a bitey,
I guess, and informs a strong bond. And that's what exactly the mordant does. So
in mordant chemistry, like when you're trying to use dyes as a stable color source,
what you would typically do is to have what you want to put the color on. So, you know,
this might be cotton or like wool, silk, or some kind of cellulose, which, you know,
it's like a cloth, right, or some kind of polymer, dimer that you want to put colors on.
And carminic acid or other type of polyacidic dyes can be thrown in the mix with this metal dye,
complexes, okay, and then they would adhere, now form the complex with the surface of these
fabrics, which will then chemically bind these colors onto the fabric. So like, if you if your
colored sweater washes out, every time you put it into a laundry, you're not going to want that
sweater. But because of these mordant chemistry that people figured out, we now have a red sweater
that can stay red for quite some time. So so that's what mordant does, like by putting in
this salt complexes. And that's what makes carminic acid useful, because it also forms
a nice stable complex with many of the salts that are very available to us. Fascinating.
This, it's, it's fascinating to see just how I guess useful this final part is. Because,
say earlier on, right, when you're talking about all of say, its uses are in particular in, you
know, coloring things. Yeah. You know, I wasn't even thinking that it would struggle, right,
to sort of bind. But, but this sort of salt form, it's just a whole lot more able to latch
onto the clothing, or onto the things that you want. Is it, is this mainly for fabrics? Yes,
this isn't like... Yeah, it's mainly for fabrics, but you know, like anything fibrous, like paper,
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it works the same way as well. Anything, anything fibrous in that sense is able to,
right, sort of get netted in there. Because, you know, you're usually putting colors onto
fabric or cellulose of some kind. Right, right, right. Okay. Wow. Yeah. And the cool thing about
carminic acid, or other sort of polyacidic dyes, is that if you throw in a different metal to
complex, it can form a slightly different complexation. Because now we see in a structure,
there are multiple possible ways it can complex. And depending on the exact complex that you create,
it shifts the absorption. And then when the absorption is shifted, you can have a different
color effect. And so now you can really fine tune, do you want this like particular shade of red?
Or do you want this other shade of red? And you can fix that based on the metal ions you throw in.
It also depends on a stoichiometry of the metal ions that you throw in. So the amount in which
you put in also lets you fine tune the colors. Right. It's a very sort of trade secret. And,
you know, companies and stuff, they wanted to keep it a secret recipe. So I bet all of these
have like a very specific recipe to get a very specific red. Sure. Yeah. Yeah. Yeah, you have
so many. I'm just sort of rolling over the variation, right? And this idea of, you know,
not only can you adapt the, say, polyacidic dye that you chose, right? Carminic acid is popular.
Yeah. But as you mentioned, you know, swapping in and out, right, the types of metal, right,
that you that you want in metal complexation will be different. Anybody who loves inorganic chemistry,
I mean, like, I had memories flooding back when you described this. Yeah. Right. You know, this
is, you know, ligand binding strengths and saturations and like. Exactly. Exactly. So
specifically for carminic acid, it enables a two plus type of complex as well as three plus. Okay.
So that already makes a huge difference. And within the same oxidation state of the complex,
you can have different carbonyl and different hydroxyl group get involved in the complexation,
causing different 3D structures and also different conjugation. Yeah. Therefore. Yeah. So
all of this results into color. And I kind of find it fascinating that like we figured this out,
you know, as chemists, we figured that this tiny changes at a molecular scale can have a huge
impact in how we perceive colors. And another sort of as a final remark, like the fun sort of thing
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I always think about when I think about color is that we have such limited range of what we think
of color as. We can only see optically between 350-ish to 750-ish nanometers. That's a small,
small range of the entire electromagnetic spectrum. And yet we make such a big deal about it.
Like if you lose sight, I feel like your world is a very different place. And, you know, so many of
us rely so heavily on sight as a way to interact with the world. And the fact that what we think
of world is already so limited and within it, there's so much richness to it. It's just kind of
like a fun sort of like a meditation prompt to think about if you want to remind yourself how
small your world is, but at the same time, so big. Even in this small speck of dirt in which you
consider your world to be, there is a large ecosystem hiding within it. Right. So this is...
Yeah. You know, in terms of human history, we only very recently realized that we can only see so much
and we can only hear so much. Right. Up until that point, we thought that was the entire world.
Like that's bonkers to me. Yeah. Yeah. Yeah. To put oneself in the shoes of like before,
right. It it feels wild and strange because you have to remove a lot of the assumptions or the
knowledge that you consider common. Right. And you don't have to go too far back to lose some
of that. I mean, you still have, I think, people pondering and considering like those things that
cannot be understood way back. But the ability to both think about them and investigate them
with the tools and technology we have. Right. Yeah. Sort of continued thinking that that that
came along with that, you know, pretty big realizations. So it's a big realization. We
like only recently managed to augment sort of like the detectors that we have beyond our physically
possible detectors, which are our eyes and nose and, you know, things like that. And.
Yeah, it's just like such a wild concept for me. But with that sort of meta thinking,
I guess I'll leave this episode of Colors by Kawakukei Podcast. Yeah. Yeah. That's it. And
depending on how well this episode is perceived and how well it's made known to us, we may or
may not make the structural colors as a part two of this. Yeah. You you heard us on me. Everyone
make posts, share, you know, tweet, retweet, kill the dead bird again, like whatever it takes.
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Yeah. Let us know if you thought it was a shit episode. Also, let us know. But, you know,
like, let us know. Well, let us let us know what you wish we had talked about. Like, you know,
amidst this, because there's a lot here. Right. Maybe maybe you're annoyed we didn't spend more
time on pH sensitivity. Right. Or maybe you wanted to hear more about, like, the the idea
of going to box. Yeah. Particle. I don't want to talk about that. I just wanted to mention it
in case it was useful. You know, but maybe there's there's something in here for that. I think I
think there's a lot more to say. I think if, you know, if people want to hear more, then that'd be
great. And honestly, yeah, if if you want to talk about it, I think there's plenty to talk about
there at some point in the future. So. Oh, yeah. No, every every like in each part of the this
episode, I think we can spend a solid half an hour on it. And but yeah, thank you to FA Radio
Sun for prompting us to talk about color because we haven't done that apparently. Nope. And thank
you. Yeah. And thanks for listening. Why? I don't know.
That's it for the show today. Thanks for listening and find us on X at
Ego de Science. That is E-I-G-O-D-E-S-C-I-E-N-C. See you next time.
