[RASMB] another vbar question

[John Sumida]

Hi Borries,

Thank you for pointing me at the manuscript.

What would boundary data stemming from the MWL detector look like?  I am
fascinated that the spectral shifts shown in the paper can be observed in
real time at each radial position - if my reading is accurate?

Also in applying the 2DSA analysis wouldn't one still need to know what
v-bar was for the CdSe/ZnS qdots in order to calculate the equivalent
radius, MW etc. of the particles?  I am, perhaps, making the erroneous
assumption that "equivalent radius" is related to the core shell diameter in
your manuscript. 

Also, by "leveraging error" you are referring to the very real situation
where the density of the q-dot is such that it would require too great a
proportion of the density matching solvent component?

Best regards,
John Sumida
Molecular Analysis Facility
University of Washington

-----Original Message-----
From: Borries Demeler [mailto:demeler at biochem.uthscsa.edu] 
Sent: Thursday, September 28, 2017 11:59 AM
To: John Sumida <jpsumida at uw.edu>
Cc: 'Rocco Mattia' <mattia.rocco at hsanmartino.it>; 'HGSR (Holger Martin
Strauss)' <hgsr at novonordisk.com>; rasmb at list.rasmb.org
Subject: Re: [RASMB] another vbar question

On Thu, Sep 28, 2017 at 11:42:44AM -0700, John Sumida wrote:
> Hi Everyone,
> 
> Nice discussion on v-bar, thank you for asking the question!
> 
> I am wondering about the overall utility of the density contrast approach.
> For unknown materials such as CdSe/ZnS qdots or block-polymer micelles 
> which can be highly heterogeneous and for which a calculation of v-bar 
> may not be facile, the density contrast approach would seem to have 
> great utility.  In these cases a densitometric measurement of the 
> density increment can be severely sample limited.
> 
> However, how would the sample heterogeneity in this case affect the 
> v-bar measurement?  Seems that the best possible outcome here would be 
> some weight averaged quantity, which, while not precise, may have some 
> utility nonetheless?
> 

For CdSe, CdTe, etc. qdots the method is likely not useful, because the
density of the qdots is too high, your extrapolation to zero s is going to
be subject to considerable "leverage" error. Depending on your
functionalization it may be possible to come up with a density model that
works quite well, see the SI from this article:

	https://www.ncbi.nlm.nih.gov/pubmed/27461742

For block-polymer micelles the extrapolation problem should be far less
significant, since their densities are much closer to that regime which can
be modulated with D2O or H2O18, though how much success you'll have may
depend on the precise nature of the polymer and the degree of heterogeneity.

Regards, -b.
---
Borries Demeler, Ph.D.
Professor
The University of Texas Health Science Center at San Antonio Dept. of
Biochemistry and Structural Biology, MC 7760
7703 Floyd Curl Drive, San Antonio, Texas 78229-3901
Voice: 210-767-3332, Email: demeler at biochem.uthscsa.edu