[dmtr19]

Is it possible that flavonoid molecules aggregate in anhydrous organic solvents (DMF, DCM) or not if concentration is about 10mkM?

[wildfyr]

Can only be determined experimentally... UV-Vis should be able to give hints.

[Babcock_Hall]

NMR is sometimes used to study aggregates.

[dmtr19]

Can only be determined experimentally... UV-Vis should be able to give hints.

NMR is sometimes used to study aggregates.

Thank you for the answers!

But is it possible theoretically that polar molecules agregate in aprotic polar solvent (without water) if concentration is about 10-20mkM?

[Babcock_Hall]

I don't know enough to say specifically in this case.

[wildfyr]

It is SUCH a case by case scenario.

[rolnor]

It sounds strange in a polar solvent like DMF that can form hydrogen bonds, if you have some kind of problem I would look elsewhere to explain this.

[dmtr19]

It sounds strange in a polar solvent like DMF that can form hydrogen bonds, if you have some kind of problem I would look elsewhere to explain this.

I observe some changes in UV-Vis absorption spectrum and violation of the Beer–Lambert law (which is very similar to case when aggregation is observe), but it looks unlikely that there is aggregation of polar molecules in DMF. So can I exclude aggregation theoretically in this case?

[wildfyr]

Take uv vis at even lower and even higher concentrations and see what beer lambert deviations and changes in lambda max are. If they are significant, then no, you can’t ignore aggregation, because that is what is happening.

Aggregation changes uv vis spectra due to the occurrence of excimers or other charge transfer phenomena

[dmtr19]

Take uv vis at even lower and even higher concentrations and see what beer lambert deviations and changes in lambda max are. If they are significant, then no, you can’t ignore aggregation, because that is what is happening.

Aggregation changes uv vis spectra due to the occurrence of excimers or other charge transfer phenomena

Changes are significant but it also can be caused by tautomerization and ionization processes, but not aggregation. Or aggregation is more likely?

[wildfyr]

Those two phenomena aren't very concentration dependent though. They can be solvent dependent but you aren't varying that.