New Units - Molecular Mass (Dalton)

[rogerfydp]

Is your feature request related to a problem? Please describe.
Within existing quantity Mass there is no units often used for "Molecular mass"

Describe the solution you'd like
Molecular mass (m) is the mass of a given molecule. The unit dalton (Da) is often used.

Will be nice to extend the quantity mass (if it's the proper one) to include Dalton (unit) such as,

• Daltons (Da) - Used for individual molecules or small biomolecules.
• Kilodaltons (kDa) - Used for larger molecules, such as proteins.
• Megadaltons (MDa) - Used for very large molecular complexes, such as viruses and large protein assemblies.
• Gigadaltons (GDa) - Used for extremely large molecular structures.

Describe alternatives you've considered
None. Using other mass units for 'molecular mass' is not common.

[angularsen]

Hi, sure this sounds reasonable to add.
Would you be interested in attempting a pull request? I'm happy to assist.

Detailed steps here:
https://github.com/angularsen/UnitsNet/wiki/Adding-a-New-Unit

[rogerfydp]

Hi, thanks for accepting it!

I can do a pull request, no problem.

I was adding the quantity mass.json in the following way,

{
  "SingularName": "Dalton",
  "PluralName": "Daltons",
  "BaseUnits": {
    "M": "Dalton"
  },
  "FromUnitToBaseFunc": "{x} * 1.66053906660e-27",
  "FromBaseToUnitFunc": "{x} / 1.66053906660e-27",
  "Prefixes": ["Kilo", "Mega", "Giga"],
  "Localization": [
    {
      "Culture": "en-US",
      "Abbreviations": ["Da"]
    }
  ],
  "XmlDocSummary": "A Dalton, also known as the unified atomic mass unit, is a unit of mass commonly used to express the mass of atoms and molecules. It is defined as one twelfth of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state.",
  "XmlDocRemarks": "https://en.wikipedia.org/wiki/Dalton_(unit)"
}

Taking initially the value from Wikipedia. But when double checking with other sources I see variations, here some examples.

Source	Value
Wikipedia	1.66053906892(52)×10−27 kg
CODATA (2018) (page 50)	1.66053906660(50)x10−27
UCLA	1.660538921x10−27 kg
chemeurope.com	1.660538782(83)×10−27 kg

On the other hand, on Wikipedia's article, in the references we can find

• Bureau International des Poids et Mesures (2019): [The International System of Units (SI)] 9th edition, English version, page 145 which value is 1 Da = 1.66053906660(50)×10−27 kg which matches with CODATA 2018.

Therefor I would like your opinion on the value to take, to comply with your project. Do you have any other reference or source?

Thanks!

[angularsen]

@rogerfydp Sorry for the late reply.
I don't have any domain knowledge here, but generally I would follow SI definitions.

The wiki article seems quite thorough, but I'm confused why the wiki constant differs from CODATA/SI and I can't see any reference to where they got their value.

Until we learn otherwise, I'd say use CODATA/SI. They seem fairly up to date at least.

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