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We'd been studying chromatography in our instrumental analysis course and I was wondering if chromatography could induce a conformational change.

For example, you have a straight chain with a hydrophobic side and hydrophilic side; when relaxed, its conformation is such that it has a hydrophilic outer surface and a hydrophobic core.

If you run it through a normal phase column, could the stationary phase cause a change in conformation to, let's say, a hydrophilic core and hydrophobic outer surface?

Also, if this could happen, then it would initially go through the column at a rate similar to the mobile phase and then slow way down, yes? If so, what would be the implication? Would the peaks be broadened?

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  • $\begingroup$ Compounds react and break down in the column (especially in GC). Such reactions take more energy. Thus, it doesn't seem unlikely that conformational changes couldn't be induced by the higher temperatures of a GC oven. If you are talking about HPLC: I am not sure if this can be done with only with the stationary phase. If I recall correctly, there was a study done in which scientists tried to switch the hydrophobic core with the hydrophilic surface by using different solvents. It didn't work. $\endgroup$
    – CoffeeIsLife
    Commented May 11, 2017 at 7:56
  • $\begingroup$ There is a technique called 'molecular combing' that is used to straighten DNA's and AFM's are used to stretch proteins so it is possible that forcing molecules down columns could effect a conformational change. However, it may be that the forces applied are too small, you would have to compare with what is used in these other techniques. In particular how swiftly these forces are applied is important. The faster they are applied the stiffer molecules become. $\endgroup$
    – porphyrin
    Commented May 11, 2017 at 20:55

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While I do not have numbers at hand to support it, I think it is possible, chromatography on silica indeed may influence, may restrain the conformational flexibilty of molecules in the mobile phase.

Normal phase chromatography depends on adsorption. A complete rotation around a $\sigma$-bond, even in absence of other molecules around, needs some energy to pass from one stagggered to an other staggered conformtion.

enter image description here

(figure source)

If there were now -- instead of methyl groups separated by three bonds, as depicted in the diagram -- two groups with a high affinity to the stationary phase, this said energetical barrier would increase. Assuming lowered temperature and affinity of these groups "just intense enough" (e.g., deportontated sulfonic acids, not per-alkylated ammonium groups), the propability to find one molecule in such $\ce{s-cis}$ conformation will increase. I just see a potentially relevent publication Langmuir, 2004, 20, 10639–10647 about proteins decoiling on silica. I imagine, amphiphlic structures like reverse micelles may be equally influenced and will "swap their inner to the outer" as if they were (again) exposed to aqueous systems when facing silica.

Yet I am still hesitant to state if this may by become a constraint, leading to a situation where once conformation is looked, as in the instance of atropisomers.

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