I have extracted a metal-peptide conjugate in precipitate form by methanol extraction. However, to continue further experiments on it, the precipitates must be dissolved in a solvent.
Unfortunately, after dissolving in water, the hydroxyl ions of water compete with the peptide and binds to the metal, making the conjugate unstable.
I have tried various aprotic and organic solvents such as:Acetonitrile, DMSO, Acetone, DMF, ethanol, iso octane,pentane, hexane and cyclohexane but the precipitates are not soluble in them. Although precipitates are soluble in acidic conditions such as in formic acid but can any one suggest a solvent other than this such that hydroxyl ions are not there.
Thank You
best wishes
Hi Rajbinder,
So your compound precipitates in methanol, which is convenient for collecting your product, but not so convenient for running reactions, am I understanding correctly? One resource that I really like using when I'm in a problem like this is this polarity chart. You've probably already seen this, so I apologize if I'm just stating the obvious to you. Since you're dealing with a peptide, I would assume you would have to deal with solvents that can dissolve amides. It's unfortunate that DMF didn't work, that's the first solvent I would have recommended. Would it be safe to heat your compound in DMF to induce solubility? Or is your metal conjugate too unstable to withstand that kind of energy? In other words, does it need to be kept at a low temperature? When nothing seems to work, and it's safe to do so, heating helps. And in fact, a lot of the reactions I am running depend on the temperature of my solvent. It is convenient, because your starting material will precipitate out when you cool down again, making work up a little easier. A little more information about your reaction conditions would help me answer more helpfully.
Hope this helps.
Good luck!
Diana
Hello Muhammad Adil S. Aslam
I am thankful for your reply, as you advised, I tried to dissolve the conjugate in dioxane but unfortunately it is not soluble in it either. At the moment THF is not available in our lab.
Thank you for your help
Hello Diana M. Cedillo
I am very thankful for your reply. The metal is binding to the peptide and making a complex of stoichiometry : metal(peptide)3. The binding is taking place via the sulphydryl group of the peptide. Thus, at higher temperature the peptide is prone to be converted into an oxidized form having disulphide linkages. In this condition, due to the absence free sulphydryls metal peptide conjugate do not form.
Earlier we prepared precipitates at pH ~2, now we have prepared the precipitates at pH 7.4 still they are not getting dissolved in solvents other than water.
Hope I was able to convey my problem.
Thank you in advance :)
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