[RASMB] non-ideality in velocity [was: interference optics]

[Borries Demeler]

> 
> John -
> 
> Yes, I take your point. I think we both know the 'biotech crowd', and the
> desire which they can often have for results obtained under 'formulation
> conditions'. But of course there may be a real problem involved in
> correcting for Johnston-Ogston effects.

John and Arthur,

Aside from the points about J-O effect and other non-ideality effects, I
think that the premise of the 'biotech crowd' of evaluating formulations
exclusively at high concentration should be re-evaluated. Formulation
conditions often require high concentrations of the solute, and drug
companies are interested in the percentage of undesirable aggregate. 

I think it is not unreasonable to separate the "aggregates" into
2 kinds: reversible oligomerization (not necessarily undesirable)
and irreversible aggregation. The amount of reversible aggregate is
clearly related to concentration, the higher the concentration, the
more you have.  Once the formulation is injected, the solute is diluted
in the blood stream and presumably at a concentration resembling a low
concentration AUC experiment (or lower), so why worry about it? If one
really were interested in the Kd, and if it were high, an SE experiment
at higher concentration may be more appropriate to determine the amount
of reversible oligomerization, without having to worry about pitfalls
of SV at high concentration.

This leaves the irreversible aggregates, which really are undesirable.
Even upon dilution, the percent of irreversible aggregation will not
change, because, by definition, those aggregates are irreversible, and
therefore any method measuring the formulation at low concentration should
provide the correct percentage, with the added benefit of not having to
worry about J-O effects, boundary sharpening, and Weiner skewing etc.

So my question is: Why are drug companies interested in the reversible
kind, or is there another reason to measure at high concentration?

Incidentally, it has been my experience that SEC-MALS is not so great
at detecting large irreversible aggregates, because they can get stuck in
the SEC column and you never see them in the MALS detector. However,
the reversible oligomerization may be detected fine by MALS .

Comments?

-Borries