# Upper size limit for a molecule? **URL:** \ **Category:** Factual Questions\ **Created:** [February 18, 2004, 7:26am UTC](https://boards.straightdope.com/t/upper-size-limit-for-a-molecule/229761 "2004-02-18T07:26:54Z")\ **Posts on this page:** 4\ **Page:** 2
**Author:** ![Fish\_Cheer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fish_cheer/32/17179_2.png) [@Fish\_Cheer](https://boards.straightdope.com/u/Fish_Cheer)\ **Post date:** [February 19, 2004, 11:45am UTC](https://boards.straightdope.com/t/upper-size-limit-for-a-molecule/229761/21 "2004-02-19T11:45:44Z")
> [@brainfizz](#): > > Astronomers have just identified an enormous diamond (which they’re calling “Lucy”) somewhere in the night sky. It’s about 1/10 the size of the earth. This sounds interesting. Do you have a cite for that? Possible including driving directions? :calls trailer rental: ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [February 19, 2004, 11:48am UTC](https://boards.straightdope.com/t/upper-size-limit-for-a-molecule/229761/22 "2004-02-19T11:48:15Z")
> [@Mycroft Holmes](#): > > And here is the official last word from the IUPAC (International Union of Pure and Applied Chemistry): > > [Definition of “molecule”:](http://www.chemsoc.org/chembytes/goldbook/M04002.PDF) > [Definition of “molecular entity”:](http://www.chemsoc.org/chembytes/goldbook/M03986.PDF) > [Definition of “macromolecule”:](http://www.chemsoc.org/chembytes/goldbook/M03667.PDF) > > So, in other words, we are looking for something that has a well defined molecular weight, so we can say that we have one mole of whatever molecule we are using. … > Now name a molecule larger than that using the official IUPAC definition. Where in the IUPAC definition does it say anything about a well defined molecular weight? Indeed, it specifically talks about polymer molecules. An individual polymer molecule has a well defined molecular weight (eg. 20,234 or 10,345,333). Samples of a polymer of course have a mixture of molecules with a wide range of individual molecular weights. Unless a polymer is soluble then it becomes hard to tell if it is completely one molecule, or just several entangled together. Polymers are routinely measured up to 10 million molecular weightby chromatography, and light scattering will measure weights higher than this. Whether your cross-linked chair or diamond crystal actually has a complete covalent network throughout, or there are grain boundaries where noncovalent linkages exist is tricky and may not be known for sure. So my guess is that we are completely sure that soluble molecules exist with molecular weights of 50 million or so. Almost certainly there are diamonds and polymers much much bigger, but it is probably almost impossible to prove. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [February 19, 2004, 11:52am UTC](https://boards.straightdope.com/t/upper-size-limit-for-a-molecule/229761/23 "2004-02-19T11:52:07Z")
> [@Mycroft Holmes](#): > > Now name a molecule larger than that using the official IUPAC definition. My pleasure. I give you [titin](http://www.leeds.ac.uk/bms/research/muscle/titin.htm). Beta-galactosidase weighs in at a puny 116.4kDa. The best estimate for titin is a whopping 3.5 **MDa** , and contains 26-27,000 amino acid residues, as compared with “over 1,000” for beta-galactosidase. It is still only 1 micron long though. ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [February 19, 2004, 12:45pm UTC](https://boards.straightdope.com/t/upper-size-limit-for-a-molecule/229761/24 "2004-02-19T12:45:11Z")
> [@fishcheer15](#): > > This sounds interesting. Do you have a cite for that? Possible including driving directions? > > :calls trailer rental: [Bling bling, girlfriend.](http://news.bbc.co.uk/1/hi/sci/tech/3492919.stm) A _molecule_ of carbon? Dunno. [Previous page](https://boards.straightdope.com/t/upper-size-limit-for-a-molecule/229761.md?page=1)