Insoluble ligand?

From: Chaudhary, Ritcha
Date: 16 September 2011 17:04
Hi All

I have a ligand that is dissolved in 100% DMSO. The ligand crashes out even when diluted to 20% final DMSO concentration in the protein buffer. I have heard of people using detergents such as n octyl Beta D glucoside to keep the ligand solubilized at lower DMSO concentrations. Can someone give me pointers in this direction? Any suggestions, references etc.....

Thanks much
Ritcha
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From: Smita Mohanty
Hi Ritcha,

Did you try Methanol or Ethanol to see if your ligand dissolve in these
solvents? You should try these solvents first before adding any
detergents.

Good luck.

Smita Mohanty

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From: Roger Rowlett

Keep in mind it may also be possible to soak in ligand from the solid if the binding constant is tight enough. Le Chatelier's principle will drag it from the undissolved solid into the complex. This process will be improved if you can increase solubility in solution, e.g. by incuding 20% DMSO or some other cosolvent in your drop. If you crystals will tolerate some cosolvent without cracking or dissolving, the equilibrium concentration of ligand in solution may still be high enough to populate your protein. This won't work for a loose-binding ligand.

Cheers,
_______________________________________
Roger S. Rowlett
Gordon & Dorothy Kline Professor
Department of Chemistry
Colgate University
13 Oak Drive
Hamilton, NY 1334
6

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From: <Herman.Schreuder
Dear Ritcha,

You could also try low molecular weight PEG's, e.g. PEG400 in fairly
high concentrations. They often do a good job in solubilizing ligands
and are usually much more crystal-friendly than e.g. DMSO.

Best,
Herman