Hyaluronic acid does not hold a thousand times its weight in water | Hacker News Reader

Hyaluronic acid does not hold a thousand times its weight in water

oumere.com

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This is on the commercial website of a company that wants me to buy their non-HA containing $150/bottle eye serum.

Not only that, but the assumptions are poor to begin with. Most skincare products containing sodium hyaluronate are either micronized or in a crosspolymer so that it can penetrate the skin, not HA on its own (something I'd expect a chemist/dermatologist to know). Cursory googling it seems the writer/owner was attaching her name to reddit submissions of scientific articles unrelated to her to game SEO and give her credibility that it it's painfully obvious she doesn't have.

“Daltons are used to measure something very low in mass”

Why not just use nanograms or picograms?

A dalton has two nice properties.

One is that a hydrogen atom weighs one dalton, and a carbon atom twelve etc, so a mass in daltons immediately tells you roughly how big a molecule is in atomic terms. 100 Da is a small molecule, 1 kDa would be a peptide or macrolide or something, 10 kDa is a small protein, 100 kDa is a big protein, etc.

The other is that a dalton is a gram per mole, so if you know the mass of a molecule in daltons, you can easily convert between mass and concentration at macroscopic scale. So, glucose is 180 Da, you can dissolve 180 g of it in 1 litre of water to make 1 molar solution.

These properties are really the same property, because of how the mole is defined, but that property is useful in two quite different ways.

Thanks, that was a really clear explanation!

Apparently picograms are still orders of magnitude bigger and thus not useful for this type of measurement. Science!

Looking further into it, yoctagrams or zetograms would be small enough to express the measurement. I suspect daltons are used because they’re pegged to a 1/12 of a carbon atom and that makes the math easier to reason about or something like that.

Yeah, one Dalton = one neutron or one proton [0], so it's a convenient unit if you're literally adding up atomic weights to find the weight of a single molecule.

[0] This is true for chemists, but not for physicists, who pay more attention to the mass defect rounding error.

To expand on that, for physicists Carbon-12 is exactly 12 daltons also denoted 12 Da or 12 u. All other isotopes deviate slightly from a whole number of daltons. If I recall correctly the number of nucleons minus the daltons continues to decrease until you get to iron, which has the lowest nuclear binding energy, after which it continues to increase again (although there's some variation between isotopes so this is more of a general trend).

And that's why you can have nuclear power either from combining really small atoms (fusion) or splitting big ones (fission) but nobody would propose a nuclear reactor that runs on iron?

1 Da = 1.66 yg (yoctograms), approximately. So that kinda works out.

Another unit that is occasionally used for atomic scale masses is eV, as in electronvolt. 1 Da = 0.93 GeV

zeptograms

I skimmed the article and I think the author should have used CaCl2 to improve the gelling strenght. Ca-alginate which is comparable in structure forms gels in very low concentrations when Ca ions are present.

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