= Marguerite Rinaudo
{c}
\b[Marguerite Rinaudo] investigated <polysaccharides> and the interactions governing their behavior in solution and assembled materials. Her 2006 paper discusses how ionic interactions, <hydrogen bonds> and other non-covalent interactions affect chain conformation, solubility and gel formation. Its primary byline identifies her CERMAV-CNRS affiliation.<Non-covalent interactions in polysaccharide systems by Marguerite Rinaudo>[full byline, affiliation and Abstract]{ref}
This connects chemical composition to behavior without requiring a new covalent bond for every structural change. Changing <pH> can change the charge state of an ionizable chain, and changing <ionic strength> can alter interactions between charged segments. Measuring only the <polymer repeat unit> therefore need not predict the chain's shape or interactions in a particular solution.
For an original independent-site model of protonatable amine groups, suppose the conjugate acid has $\mathrm{p}K_a=6.5$. The protonated fraction is
$$
\alpha=\frac1{1+10^{\mathrm{pH}-\mathrm{p}K_a}}.
$$
At pH 5.5 it is $10/11\approx0.909$; at pH 7.5 it is $1/11\approx0.091$. A chain with 100 equivalent sites would therefore have mean charges about $+91$ and $+9$ in this stipulated model. The backbone need not be cleaved for its electrostatic behavior to change.
Real chains can couple neighboring sites and change their effective acid-base behavior with salt concentration and conformation. The simple calculation is not a fitted result from Rinaudo's paper. It illustrates why controlled solution conditions and measurements of charge, size or viscosity complement a structural formula.
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