[RASMB] another vbar question

[Rocco Mattia]

"it's" = "its".... :-( sorry about that...

________________________________

From: RASMB on behalf of Rocco Mattia
Sent: Thu 9/28/2017 5:52 PM
To: Rufer, Arne; HGSR (Holger Martin Strauss)
Cc: rasmb at list.rasmb.org
Subject: Re: [RASMB] another vbar question



Hi Arne,

I don't have any particular comment on it. To me, it's more of the same, interactions between solvent, ions, etc. with the solute will define it's partial molar volume. The example in the Wikipedia page I mentioned, regarding the pmv of water in water and in ethanol, I find it very illuminating...

Mattia

________________________________

From: RASMB on behalf of Rufer, Arne
Sent: Thu 9/28/2017 5:46 PM
To: HGSR (Holger Martin Strauss)
Cc: rasmb at list.rasmb.org
Subject: Re: [RASMB] another vbar question


Hi Holger,

would preferential hydration play a role at the very high NaCl concentrations you are using? Regarding anecdotes on vbar, I can add that when we worked with acylated peptides the vbar measured by densitometry turned out to be much smaller than vbar calculated from the aa sequence + modification. We had congruent AUC and SEC-MALLS data showing that certain acylations led to oligomerisation, presumably due to an hydrophobic interaction that became stronger with higher salt concentration. At that time we argued the effect on vbar could be due to a solvent envelope for packed acyl-moieties that is smaller than that of the separated acyl-moieties. Makes sense? I am curious to read Mattia's comment on this, too.

Best,

Arne





On Thu, Sep 28, 2017 at 3:48 PM, HGSR (Holger Martin Strauss) <hgsr at novonordisk.com> wrote:


       
        Hello yall,
        
        Wow, vbar trending?!
        
        I actually have a question regarding the salt-dependency of the vbar. We are working with peptides modified with some organic linkers and a diacid (between C4-C50, to give a range). We measure the droh/dc (DMA5000) at different concentrations and calculate the vbar. Controls OK, concentration accurate and measurements reproducible, buffer dialysed. Salt-concentration is varied (NaCl, 5-1500 mM-ish). Turns out the vbar is considerably different at high salt. (And so is the self-association, btw.) No detergents or denaturants, just some additional phosphate for buffering, besides the NaCl.
        

               
        *       How can this be rationalised structurally?
        *       Any tests when droh/dc is more appropriate for Mw /sigma than vbar?
        *       Other examples in the literature for peptides?
        *       Any general comments/anectodes/remarks?

        
        Cheers,
       
        
        Holger
        

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