# Drawing cellulose

Recently two questions on TeX.sx popped up about a way to draw cellulose. The first one was about getting the glucose molecules connected to get a glucose strand. It already started with the right idea: use a submol for a glucose and then draw cellulose by using multiple instances of that submol. However, the trick is to get the submol starting and ending with the right bond and, as cellulose alternatively has glucoses rotated by 180 degrees, I suggested to define two submols.

\definesubmol{glucoBeta}{
-[:10,.7]4
(
-[:-10](-[:150,0.7]-[2,0.7]OH)
-[:10]{\color{red}{O}}-[:-50,.75]
)
-[:-50](-[:170]HO)
-[:10](-[:-55,0.7]OH)
-[:-10]1(-[6,0.7]H)
-[:10,.7]O
}

\definesubmol{turned-glucoBeta}{
-[:-10,.7]4
(
-[:10](-[:-150,0.7]-[6,0.7]OH)
-[:-10]{\color{red}{O}}-[:50,.75]
)
-[:50](-[:-170]HO)
-[:-10](-[:55,0.7]OH)
-[:10]1(-[2,0.7]H)
-[:-10,.7]O
}
\chemfig{O!{glucoBeta}!{turned-glucoBeta}!{glucoBeta}!{turned-glucoBeta}
}

One might, however, argue that one could (should?) define a single submol instead containing the two glucose molecules to get something that in a chemical sense better reflects the monomer character of those two connected ones in a cellulose strand.

The second question was about how to align two strands of cellulose and connect them with hydrogen bonds. The main idea is the same: define a submol and use it to create the polymer. But in this case it is better to define a submol containing the whole part that is repeated, i.e. parts of both strands, containing of four beta-glucose molecules on the whole. I offered the following solution re-using one of the submols defined for the previous question (be soft on me — I haven’t paid attention to chemical details too much):

\tikzset{
bridge/.style={dotted,blue} ,
glycosid/.style={glyc}
}
\colorlet{glyc}{green}

\definesubmol{turned-glucoBeta}{
-[:-10,.7,,,glycosid]4
(
-[:10](-[:-150,0.7]-[6,0.7]OH)
-[:-10]{\color{red}{O}}-[:50,.75]
)
-[:50](-[:-170]HO)
-[:-10](-[:55,0.7]OH)
-[:10]1(-[2,0.7]H)
-[:-10,.7,,,glycosid]{\color{glyc}{O}}
}
\definesubmol{bridged}{
-[:10,.7,,,glycosid]4
(
-[:-10](-[:150,0.7]-[2,0.7]OH)
-[:10]{\color{red}{O}}(-[:-8,1.2,,,bridge])
-[:-50,.75]
)
-[:-50]
(
-[:170]HO
-[6,,2,2,bridge]
OH
-[6,.7]
-[:-30]
-[:170]4(-[:-170,.475,,,glycosid])
-[:-50](-[:170]HO)
-[:10](-[:-50,.7]OH)
-[:-10]1(-[6]H)(-[:10,.7,,,glycosid]{\color{glyc}O}!{turned-glucoBeta})
-[:130]{\color{red}O}(-[:-8,1.2,,,bridge])
-[:-170]
)
-[:10](-[:-55,0.7]OH)
-[:-10]1(-[6,0.7]H)
-[:10,.7,,,glycosid]{\color{glyc}O}
!{turned-glucoBeta}
}

\chemfig{!{bridged}!{bridged}!{bridged}
}

This post has not included any pictures but uses the awesome QuickLaTeX plugin for WordPress.